[PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

set gpg.format = ssh and user.signingkey to a ssh public key string (like from an
authorized_keys file) and commits/tags can be signed using the private
key from your ssh-agent.

Verification uses a allowed_signers_file (see ssh-keygen(1)) which
defaults to .gitsigners but can be set via gpg.ssh.allowedsigners
A possible gpg.ssh.revocationfile is also passed to ssh-keygen on
verification.

needs openssh>8.2p1

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
    RFC: Add commit & tag signing/verification via SSH keys using ssh-keygen
    
    Support for using private keyfiles directly is still missing and i'm
    unsure on how to configure it or if the pubkey in the signingkey field
    is such a good idea. A SSH Fingerprint as signingkey would be nicer, but
    key lookup would be quite cumbersome. Maybe storing the fingerprint in
    signingkey and then have a gpg.ssh.$FINGERPRINT.publickey/privatekeyfile
    setting? As a default we could get the first ssh key from ssh-add and
    store it in the config to avoid unintentional changes of the used
    signing key. I've started with some tests for SSH Signing but having
    static private keyfiles would make this a lot easier. So still on my
    TODO.
    
    This feature makes git signing much more accessible to the average user.
    Usually they have a SSH Key for pushing code already. Using it for
    signing commits allows us to verify not only the transport but the
    pushed code as well. The allowed_signers file could be kept in the
    repository if all receives are verified (allowing only useris with valid
    signatures to add/change them) or outside if generated/managed
    differently. Tools like gitolite could optionally generate and enforce
    them from the already existing user ssh keys for example.
    
    In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
    signing/encryption and ssh keys which i think is quite common (at least
    for the email part). This way we can establish the correct trust for the
    SSH Keys without setting up a separate GPG Infrastructure (which is
    still quite painful for users) or implementing x509 signing support for
    git (which lacks good forwarding mechanisms). Using ssh agent forwarding
    makes this feature easily usable in todays development environments
    where code is often checked out in remote VMs / containers.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1041%2FFStelzer%2Fsshsign-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1041/FStelzer/sshsign-v1
Pull-Request: https://github.com/git/git/pull/1041

 Documentation/config/gpg.txt  |  13 ++-
 Documentation/config/user.txt |   4 +
 gpg-interface.c               | 212 ++++++++++++++++++++++++++++++----
 gpg-interface.h               |   3 +
 4 files changed, 205 insertions(+), 27 deletions(-)

diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
index d94025cb368..fd71bd782ec 100644
--- a/Documentation/config/gpg.txt
+++ b/Documentation/config/gpg.txt
@@ -11,13 +11,13 @@ gpg.program::
 
 gpg.format::
 	Specifies which key format to use when signing with `--gpg-sign`.
-	Default is "openpgp" and another possible value is "x509".
+	Default is "openpgp". Other possible values are "x509", "ssh".
 
 gpg.<format>.program::
 	Use this to customize the program used for the signing format you
 	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
 	be used as a legacy synonym for `gpg.openpgp.program`. The default
-	value for `gpg.x509.program` is "gpgsm".
+	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
 
 gpg.minTrustLevel::
 	Specifies a minimum trust level for signature verification.  If
@@ -27,6 +27,15 @@ gpg.minTrustLevel::
 	with at least `undefined` trust.  Setting this option overrides
 	the required trust-level for all operations.  Supported values,
 	in increasing order of significance:
+
+gpg.ssh.allowedSigners::
+	A file containing all valid SSH signing principals. 
+	Similar to an .ssh/authorized_keys file. See ssh-keygen(1) for details.
+	Defaults to .gitsigners
+
+gpg.ssh.revocationFile::
+	Either a SSH KRL or a list of revoked public keys.
+	See ssh-keygen(1) for details.
 +
 * `undefined`
 * `never`
diff --git a/Documentation/config/user.txt b/Documentation/config/user.txt
index 59aec7c3aed..1632e7b320f 100644
--- a/Documentation/config/user.txt
+++ b/Documentation/config/user.txt
@@ -36,3 +36,7 @@ user.signingKey::
 	commit, you can override the default selection with this variable.
 	This option is passed unchanged to gpg's --local-user parameter,
 	so you may specify a key using any method that gpg supports.
+	If gpg.format is set to "ssh" this needs to contain the valid
+	ssh public key (e.g.: "ssh-rsa XXXXXX identifier") which corresponds
+	to the private key used for signing. The private key needs to be available
+	via ssh-agent. Direct private key files are not supported yet.
diff --git a/gpg-interface.c b/gpg-interface.c
index 127aecfc2b0..53504f64410 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -8,6 +8,7 @@
 #include "tempfile.h"
 
 static char *configured_signing_key;
+const char *ssh_allowed_signers, *ssh_revocation_file;
 static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
 
 struct gpg_format {
@@ -35,6 +36,14 @@ static const char *x509_sigs[] = {
 	NULL
 };
 
+static const char *ssh_verify_args[] = {
+	NULL
+};
+static const char *ssh_sigs[] = {
+	"-----BEGIN SSH SIGNATURE-----",
+	NULL
+};
+
 static struct gpg_format gpg_format[] = {
 	{ .name = "openpgp", .program = "gpg",
 	  .verify_args = openpgp_verify_args,
@@ -44,6 +53,9 @@ static struct gpg_format gpg_format[] = {
 	  .verify_args = x509_verify_args,
 	  .sigs = x509_sigs
 	},
+	{ .name = "ssh", .program = "ssh-keygen",
+	  .verify_args = ssh_verify_args,
+	  .sigs = ssh_sigs },
 };
 
 static struct gpg_format *use_format = &gpg_format[0];
@@ -144,6 +156,38 @@ static int parse_gpg_trust_level(const char *level,
 	return 1;
 }
 
+static void parse_ssh_output(struct signature_check *sigc)
+{
+	const char *output = NULL;
+	char *next = NULL;
+
+	// ssh-keysign output should be:
+	// Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
+
+	output = xmemdupz(sigc->gpg_status, strcspn(sigc->gpg_status, " \n"));
+	if (skip_prefix(sigc->gpg_status, "Good \"git\" signature for ", &output)) {
+		sigc->result = 'G';
+
+		next = strchrnul(output, ' ');
+		replace_cstring(&sigc->signer, output, next);
+		output = next + 1;
+		next = strchrnul(output, ' '); // 'with'
+		output = next + 1;
+		next = strchrnul(output, ' '); // KEY Type
+		output = next + 1;
+		next = strchrnul(output, ' '); // 'key'
+		output = next + 1;
+		next = strchrnul(output, ' '); // key
+		replace_cstring(&sigc->fingerprint, output, next);
+	} else {
+		sigc->result = 'B';
+	}
+
+	// SSH-Keygen prints onto stdout instead of stderr like the output code expects - so we just copy it over
+	free(sigc->gpg_output);
+	sigc->gpg_output = xmemdupz(sigc->gpg_status, strlen(sigc->gpg_status));
+}
+
 static void parse_gpg_output(struct signature_check *sigc)
 {
 	const char *buf = sigc->gpg_status;
@@ -262,11 +306,17 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 				struct strbuf *gpg_output,
 				struct strbuf *gpg_status)
 {
-	struct child_process gpg = CHILD_PROCESS_INIT;
+	struct child_process gpg = CHILD_PROCESS_INIT,
+			     ssh_keygen = CHILD_PROCESS_INIT;
 	struct gpg_format *fmt;
 	struct tempfile *temp;
 	int ret;
-	struct strbuf buf = STRBUF_INIT;
+	const char *line;
+	size_t trust_size;
+	char *principal;
+	struct strbuf buf = STRBUF_INIT,
+		      principal_out = STRBUF_INIT,
+		      principal_err = STRBUF_INIT;
 
 	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
 	if (!temp)
@@ -283,24 +333,77 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 	if (!fmt)
 		BUG("bad signature '%s'", signature);
 
-	strvec_push(&gpg.args, fmt->program);
-	strvec_pushv(&gpg.args, fmt->verify_args);
-	strvec_pushl(&gpg.args,
-		     "--status-fd=1",
-		     "--verify", temp->filename.buf, "-",
-		     NULL);
+	if (!strcmp(use_format->name, "ssh")) {
+		// Find the principal from the  signers
+		strvec_push(&ssh_keygen.args, fmt->program);
+		strvec_pushl(&ssh_keygen.args,  "-Y", "find-principals",
+						"-f", get_ssh_allowed_signers(),
+						"-s", temp->filename.buf,
+						NULL);
+		ret = pipe_command(&ssh_keygen, NULL, 0, &principal_out, 0, &principal_err, 0);
+		if (strstr(principal_err.buf, "unknown option")) {
+			error(_("openssh version > 8.2p1 is needed for ssh signature verification (ssh-keygen needs -Y find-principals/verify option)"));
+		}
+		if (ret || !principal_out.len)
+			goto out;
+
+		/* Iterate over all lines */
+		for (line = principal_out.buf; *line; line = strchrnul(line + 1, '\n')) {
+			while (*line == '\n')
+				line++;
+			if (!*line)
+				break;
 
-	if (!gpg_status)
-		gpg_status = &buf;
+			trust_size = strcspn(line, " \n");
+			principal = xmemdupz(line, trust_size);
 
-	sigchain_push(SIGPIPE, SIG_IGN);
-	ret = pipe_command(&gpg, payload, payload_size,
-			   gpg_status, 0, gpg_output, 0);
-	sigchain_pop(SIGPIPE);
+			strvec_push(&gpg.args,fmt->program);
+			// We found principals - Try with each until we find a match
+			strvec_pushl(&gpg.args, "-Y", "verify",
+						"-n", "git",
+						"-f", get_ssh_allowed_signers(),
+						"-I", principal,
+						"-s", temp->filename.buf,
+						 NULL);
 
-	delete_tempfile(&temp);
+			if (ssh_revocation_file) {
+				strvec_pushl(&gpg.args, "-r", ssh_revocation_file, NULL);
+			}
+
+			if (!gpg_status)
+				gpg_status = &buf;
+
+			sigchain_push(SIGPIPE, SIG_IGN);
+			ret = pipe_command(&gpg, payload, payload_size,
+					   gpg_status, 0, gpg_output, 0);
+			sigchain_pop(SIGPIPE);
 
-	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
+			ret |= !strstr(gpg_status->buf, "Good");
+			if (ret == 0)
+				break;
+		}
+	} else {
+		strvec_push(&gpg.args, fmt->program);
+		strvec_pushv(&gpg.args, fmt->verify_args);
+		strvec_pushl(&gpg.args,
+				"--status-fd=1",
+				"--verify", temp->filename.buf, "-",
+				NULL);
+
+		if (!gpg_status)
+			gpg_status = &buf;
+
+		sigchain_push(SIGPIPE, SIG_IGN);
+		ret = pipe_command(&gpg, payload, payload_size, gpg_status, 0,
+				   gpg_output, 0);
+		sigchain_pop(SIGPIPE);
+		ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
+	}
+
+out:
+	delete_tempfile(&temp);
+	strbuf_release(&principal_out);
+	strbuf_release(&principal_err);
 	strbuf_release(&buf); /* no matter it was used or not */
 
 	return ret;
@@ -323,7 +426,11 @@ int check_signature(const char *payload, size_t plen, const char *signature,
 	sigc->payload = xmemdupz(payload, plen);
 	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
 	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
-	parse_gpg_output(sigc);
+	if (!strcmp(use_format->name, "ssh")) {
+		parse_ssh_output(sigc);
+	} else {
+		parse_gpg_output(sigc);
+	}
 	status |= sigc->result != 'G';
 	status |= sigc->trust_level < configured_min_trust_level;
 
@@ -394,6 +501,14 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(var, "gpg.ssh.allowedsigners")) {
+		return git_config_string(&ssh_allowed_signers, var, value);
+	}
+
+	if (!strcmp(var, "gpg.ssh.revocationfile")) {
+		return git_config_string(&ssh_revocation_file, var, value);
+	}
+
 	if (!strcmp(var, "gpg.format")) {
 		if (!value)
 			return config_error_nonbool(var);
@@ -425,6 +540,9 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	if (!strcmp(var, "gpg.x509.program"))
 		fmtname = "x509";
 
+	if (!strcmp(var, "gpg.ssh.program"))
+		fmtname = "ssh";
+
 	if (fmtname) {
 		fmt = get_format_by_name(fmtname);
 		return git_config_string(&fmt->program, var, value);
@@ -437,7 +555,19 @@ const char *get_signing_key(void)
 {
 	if (configured_signing_key)
 		return configured_signing_key;
-	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
+	if (!strcmp(use_format->name, "ssh")) {
+		// We could simply use the first key listed by ssh-add -L and risk signing with the wrong key
+		return "";
+	} else {
+		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
+	}
+}
+
+const char *get_ssh_allowed_signers(void)
+{
+	if (ssh_allowed_signers)
+		return ssh_allowed_signers;
+	return GPG_SSH_ALLOWED_SIGNERS;
 }
 
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
@@ -446,12 +576,35 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
 	int ret;
 	size_t i, j, bottom;
 	struct strbuf gpg_status = STRBUF_INIT;
-
-	strvec_pushl(&gpg.args,
-		     use_format->program,
-		     "--status-fd=2",
-		     "-bsau", signing_key,
-		     NULL);
+	struct tempfile *temp = NULL;
+
+	if (!strcmp(use_format->name, "ssh")) {
+		if (!signing_key)
+			return error(_("user.signingkey needs to be set to a ssh public key for ssh signing"));
+
+		// signing_key is a public ssh key
+		// FIXME: Allow specifying a key file so we can use private keyfiles instead of ssh-agent
+		temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
+		if (!temp)
+			return error_errno(_("could not create temporary file"));
+		if (write_in_full(temp->fd, signing_key,
+					strlen(signing_key)) < 0 ||
+			close_tempfile_gently(temp) < 0) {
+			error_errno(_("failed writing ssh signing key to '%s'"), temp->filename.buf);
+			delete_tempfile(&temp);
+			return -1;
+		}
+		strvec_pushl(&gpg.args, use_format->program ,
+					"-Y", "sign",
+					"-n", "git",
+					"-f", temp->filename.buf,
+					NULL);
+	} else {
+		strvec_pushl(&gpg.args, use_format->program ,
+					"--status-fd=2",
+					"-bsau", signing_key,
+					NULL);
+	}
 
 	bottom = signature->len;
 
@@ -464,7 +617,16 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
 			   signature, 1024, &gpg_status, 0);
 	sigchain_pop(SIGPIPE);
 
-	ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
+	if (temp)
+		delete_tempfile(&temp);
+
+	if (!strcmp(use_format->name, "ssh")) {
+		if (strstr(gpg_status.buf, "unknown option")) {
+			error(_("openssh version > 8.2p1 is needed for ssh signing (ssh-keygen needs -Y sign option)"));
+		}
+	} else {
+		ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
+	}
 	strbuf_release(&gpg_status);
 	if (ret)
 		return error(_("gpg failed to sign the data"));
diff --git a/gpg-interface.h b/gpg-interface.h
index 80567e48948..286c1b4167a 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -7,6 +7,8 @@ struct strbuf;
 #define GPG_VERIFY_RAW			2
 #define GPG_VERIFY_OMIT_STATUS	4
 
+#define GPG_SSH_ALLOWED_SIGNERS ".gitsigners"
+
 enum signature_trust_level {
 	TRUST_UNDEFINED,
 	TRUST_NEVER,
@@ -64,6 +66,7 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
 int git_gpg_config(const char *, const char *, void *);
 void set_signing_key(const char *);
 const char *get_signing_key(void);
+const char *get_ssh_allowed_signers(void);
 int check_signature(const char *payload, size_t plen,
 		    const char *signature, size_t slen,
 		    struct signature_check *sigc);

base-commit: 670b81a890388c60b7032a4f5b879f2ece8c4558
-- 
gitgitgadget

Re: [PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[Han-Wen Nienhuys]

On Tue, Jul 6, 2021 at 10:20 AM Fabian Stelzer via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: Fabian Stelzer <fs@gigacodes.de>
>
> set gpg.format = ssh and user.signingkey to a ssh public key string (like from an
> authorized_keys file) and commits/tags can be signed using the private
> key from your ssh-agent.
>
> Verification uses a allowed_signers_file (see ssh-keygen(1)) which
> defaults to .gitsigners but can be set via gpg.ssh.allowedsigners
> A possible gpg.ssh.revocationfile is also passed to ssh-keygen on
> verification.
>
...
>     In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
>     signing/encryption and ssh keys which i think is quite common (at least
>     for the email part). This way we can establish the correct trust for the
>     SSH Keys without setting up a separate GPG Infrastructure (which is
>     still quite painful for users) or implementing x509 signing support for
>     git (which lacks good forwarding mechanisms). Using ssh agent forwarding
>     makes this feature easily usable in todays development environments
>     where code is often checked out in remote VMs / containers.

Thanks for working on this, and I support this initiative. I
coincidentally have started proselytizing something similar just weeks
ago.

My interest is in signing pushes rather than commits/tags, as that (in
combination with SSH U2F support) provides a simple mechanism to
require (forwardable!) 2-factor authentication on pushes over HTTP. I
haven't looked at the signing code in detail, but I had the impression
that adding SSH signatures would automatically also add support for
signed pushes? (aka. push-certs) Do you know?

-- 
Han-Wen Nienhuys - Google Munich
I work 80%. Don't expect answers from me on Fridays.
--

Google Germany GmbH, Erika-Mann-Strasse 33, 80636 Munich

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Sitz der Gesellschaft: Hamburg

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Re: [PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer]

[-- Attachment #1: Type: text/plain, Size: 2112 bytes --]

>> From: Fabian Stelzer <fs@gigacodes.de>
>>
>> set gpg.format = ssh and user.signingkey to a ssh public key string (like from an
>> authorized_keys file) and commits/tags can be signed using the private
>> key from your ssh-agent.
>>
>> Verification uses a allowed_signers_file (see ssh-keygen(1)) which
>> defaults to .gitsigners but can be set via gpg.ssh.allowedsigners
>> A possible gpg.ssh.revocationfile is also passed to ssh-keygen on
>> verification.
>>
> ...
>>      In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
>>      signing/encryption and ssh keys which i think is quite common (at least
>>      for the email part). This way we can establish the correct trust for the
>>      SSH Keys without setting up a separate GPG Infrastructure (which is
>>      still quite painful for users) or implementing x509 signing support for
>>      git (which lacks good forwarding mechanisms). Using ssh agent forwarding
>>      makes this feature easily usable in todays development environments
>>      where code is often checked out in remote VMs / containers.
> Thanks for working on this, and I support this initiative. I
> coincidentally have started proselytizing something similar just weeks
> ago.
>
> My interest is in signing pushes rather than commits/tags, as that (in
> combination with SSH U2F support) provides a simple mechanism to
> require (forwardable!) 2-factor authentication on pushes over HTTP. I
> haven't looked at the signing code in detail, but I had the impression
> that adding SSH signatures would automatically also add support for
> signed pushes? (aka. push-certs) Do you know?
>
Up until now i was not actually aware of the "push signing" 
functionality in git.
I can see that the send/receive-pack use the same api function calls as 
commit/tag signing.
So this should work just as well. Especially if using an ssh agent the whole
process is identical to git. I still need to try private key files 
directly to see
how user interaction (like entering a passphrase or touching the U2F 
Token) would work.



[-- Attachment #2: S/MIME Cryptographic Signature --]
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Re: [PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[brian m. carlson]

[-- Attachment #1: Type: text/plain, Size: 5468 bytes --]

On 2021-07-06 at 08:19:53, Fabian Stelzer via GitGitGadget wrote:
> From: Fabian Stelzer <fs@gigacodes.de>
> 
> set gpg.format = ssh and user.signingkey to a ssh public key string (like from an
> authorized_keys file) and commits/tags can be signed using the private
> key from your ssh-agent.
> 
> Verification uses a allowed_signers_file (see ssh-keygen(1)) which
> defaults to .gitsigners but can be set via gpg.ssh.allowedsigners
> A possible gpg.ssh.revocationfile is also passed to ssh-keygen on
> verification.
> 
> needs openssh>8.2p1

Usually we'll want to write the explanation here in full sentences with
typical capitalization.

> Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
> ---
>     RFC: Add commit & tag signing/verification via SSH keys using ssh-keygen
>     
>     Support for using private keyfiles directly is still missing and i'm
>     unsure on how to configure it or if the pubkey in the signingkey field
>     is such a good idea. A SSH Fingerprint as signingkey would be nicer, but
>     key lookup would be quite cumbersome. Maybe storing the fingerprint in
>     signingkey and then have a gpg.ssh.$FINGERPRINT.publickey/privatekeyfile
>     setting? As a default we could get the first ssh key from ssh-add and
>     store it in the config to avoid unintentional changes of the used
>     signing key. I've started with some tests for SSH Signing but having
>     static private keyfiles would make this a lot easier. So still on my
>     TODO.

I think user.signingKey could be helpful for signing here.  That could
be a file name, not just a fingerprint, although we'd probably want to
have support for tilde expansion.  You could add an additional option,
gpg.ssh.keyring, that specifies the signatures to verify.  That would be
named the same thing as a potential option of gpg.openpgp.keyring,
which would be convenient.  Also, gpg.ssh.revokedKeyring could maybe be
the name for revoked keys?

>     This feature makes git signing much more accessible to the average user.
>     Usually they have a SSH Key for pushing code already. Using it for
>     signing commits allows us to verify not only the transport but the
>     pushed code as well. The allowed_signers file could be kept in the
>     repository if all receives are verified (allowing only useris with valid
>     signatures to add/change them) or outside if generated/managed
>     differently. Tools like gitolite could optionally generate and enforce
>     them from the already existing user ssh keys for example.
>     
>     In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
>     signing/encryption and ssh keys which i think is quite common (at least
>     for the email part). This way we can establish the correct trust for the
>     SSH Keys without setting up a separate GPG Infrastructure (which is
>     still quite painful for users) or implementing x509 signing support for
>     git (which lacks good forwarding mechanisms). Using ssh agent forwarding
>     makes this feature easily usable in todays development environments
>     where code is often checked out in remote VMs / containers.

I think some of this rationale would work well in the commit message,
especially the part about the fact that using an SSH key may be easier
for users and the fact that it can be well supported by smart cards.
Those are compelling arguments about why this is a desirable change, and
should be in the commit message.

I haven't looked too deeply at the intricacies of the change, but I'm in
favor of it.  I would, however, like to see some tests here, including
for commits, tags, and push certificates.  Note that you'll probably
need to run the testsuite both with and without
GIT_TEST_DEFAULT_HASH=sha256 to verify everything works.

> diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
> index d94025cb368..fd71bd782ec 100644
> --- a/Documentation/config/gpg.txt
> +++ b/Documentation/config/gpg.txt
> @@ -11,13 +11,13 @@ gpg.program::
>  
>  gpg.format::
>  	Specifies which key format to use when signing with `--gpg-sign`.
> -	Default is "openpgp" and another possible value is "x509".
> +	Default is "openpgp". Other possible values are "x509", "ssh".
>  
>  gpg.<format>.program::
>  	Use this to customize the program used for the signing format you
>  	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
>  	be used as a legacy synonym for `gpg.openpgp.program`. The default
> -	value for `gpg.x509.program` is "gpgsm".
> +	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
>  
>  gpg.minTrustLevel::
>  	Specifies a minimum trust level for signature verification.  If
> @@ -27,6 +27,15 @@ gpg.minTrustLevel::
>  	with at least `undefined` trust.  Setting this option overrides
>  	the required trust-level for all operations.  Supported values,
>  	in increasing order of significance:
> +
> +gpg.ssh.allowedSigners::
> +	A file containing all valid SSH signing principals. 
> +	Similar to an .ssh/authorized_keys file. See ssh-keygen(1) for details.
> +	Defaults to .gitsigners

We probably don't want to store this in the repository.  If OpenSSH has
a standard location for this, then we can default to that; otherwise, we
should pick something in .ssh or in $XDG_CONFIG_HOME/git.
-- 
brian m. carlson (he/him or they/them)
Toronto, Ontario, CA

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 262 bytes --]

Re: [PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Fabian Stelzer <fs@gigacodes.de>
>
> set gpg.format = ssh and user.signingkey to a ssh public key string (like from an
> authorized_keys file) and commits/tags can be signed using the private
> key from your ssh-agent.
>
> Verification uses a allowed_signers_file (see ssh-keygen(1)) which
> defaults to .gitsigners but can be set via gpg.ssh.allowedsigners
> A possible gpg.ssh.revocationfile is also passed to ssh-keygen on
> verification.

There are probably style and coding-guideline nit people will pick
in the patch, but first of all I have to say that I am uncomfortably
excited to see this addition.

One thing that is unclear is how the 'allowed-signers' is expected
to be maintained in the larger picture.  Who decides which keys
(belong to whom) are trustworthy?  Does a contributor has to agree
with the decision that certain keys are trustworthy made by somebody
else in the project and use the same 'allowed-signers' collection of
keys to effectively participate in the project?  How do revoking and
rotating keys work?

It was a deliberate design decision to let PGP infrastructure that
is used to sign and verify signatures when we use PGP for signing
without tying any of these decisions to the tracked contents, as
that would reduce the attack surface for a malicious tree contents
to affect the signing and verification (in other words, "we punted"
;-).  Even though I am not sure exactly what you meant by "defaults
to .gitsigners", I am assuming that you meant a file with the name
at the top-level of the working tree, which makes me worried, as it
opens us to the risk of reading from and blindly trusting whatever
somebody else placed in the tree contents immediately after we "git
pull" (or "git clone").

Thanks for working on it.

Re: [PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer]

From: Fabian Stelzer <fs@gigacodes.de>
>> set gpg.format = ssh and user.signingkey to a ssh public key string (like from an
>> authorized_keys file) and commits/tags can be signed using the private
>> key from your ssh-agent.
>>
>> Verification uses a allowed_signers_file (see ssh-keygen(1)) which
>> defaults to .gitsigners but can be set via gpg.ssh.allowedsigners
>> A possible gpg.ssh.revocationfile is also passed to ssh-keygen on
>> verification.
>>
>> needs openssh>8.2p1
> Usually we'll want to write the explanation here in full sentences with
> typical capitalization.
Thanks, i was unsure about what to put in the commit and what into the 
cover letter.
I'll fix this with the next patch update and move some of it into the 
commit message.
In our env the commit messages are usually kept quite short.
>
>> Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
>> ---
>>      RFC: Add commit & tag signing/verification via SSH keys using ssh-keygen
>>      
>>      Support for using private keyfiles directly is still missing and i'm
>>      unsure on how to configure it or if the pubkey in the signingkey field
>>      is such a good idea. A SSH Fingerprint as signingkey would be nicer, but
>>      key lookup would be quite cumbersome. Maybe storing the fingerprint in
>>      signingkey and then have a gpg.ssh.$FINGERPRINT.publickey/privatekeyfile
>>      setting? As a default we could get the first ssh key from ssh-add and
>>      store it in the config to avoid unintentional changes of the used
>>      signing key. I've started with some tests for SSH Signing but having
>>      static private keyfiles would make this a lot easier. So still on my
>>      TODO.
> I think user.signingKey could be helpful for signing here.  That could
> be a file name, not just a fingerprint, although we'd probably want to
> have support for tilde expansion.  You could add an additional option,
> gpg.ssh.keyring, that specifies the signatures to verify.  That would be
> named the same thing as a potential option of gpg.openpgp.keyring,
> which would be convenient.  Also, gpg.ssh.revokedKeyring could maybe be
> the name for revoked keys?
The problem ist that looking up a key by fingerprint alone is not really 
possible with ssh :/
A referenced file (which could contain a public or private key) would be 
fine and i could return the fingerprint in the get_signing_key api which 
the pushcerts code uses as "pusher" info in the cert.
I'll change the keyring naming to what you suggested. Makes sense to 
have this option for gpg as well.

>
>>      This feature makes git signing much more accessible to the average user.
>>      Usually they have a SSH Key for pushing code already. Using it for
>>      signing commits allows us to verify not only the transport but the
>>      pushed code as well. The allowed_signers file could be kept in the
>>      repository if all receives are verified (allowing only useris with valid
>>      signatures to add/change them) or outside if generated/managed
>>      differently. Tools like gitolite could optionally generate and enforce
>>      them from the already existing user ssh keys for example.
>>      
>>      In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
>>      signing/encryption and ssh keys which i think is quite common (at least
>>      for the email part). This way we can establish the correct trust for the
>>      SSH Keys without setting up a separate GPG Infrastructure (which is
>>      still quite painful for users) or implementing x509 signing support for
>>      git (which lacks good forwarding mechanisms). Using ssh agent forwarding
>>      makes this feature easily usable in todays development environments
>>      where code is often checked out in remote VMs / containers.
> I think some of this rationale would work well in the commit message,
> especially the part about the fact that using an SSH key may be easier
> for users and the fact that it can be well supported by smart cards.
> Those are compelling arguments about why this is a desirable change, and
> should be in the commit message.
>
> I haven't looked too deeply at the intricacies of the change, but I'm in
> favor of it.  I would, however, like to see some tests here, including
> for commits, tags, and push certificates.  Note that you'll probably
> need to run the testsuite both with and without
> GIT_TEST_DEFAULT_HASH=sha256 to verify everything works.
I'm working on some tests but there are lots of GPG / GPGSM tests in the 
suite and i'm unsure of how many i should duplicate.
Thanks for the info with the hash setting.
>
>> diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
>> index d94025cb368..fd71bd782ec 100644
>> --- a/Documentation/config/gpg.txt
>> +++ b/Documentation/config/gpg.txt
>> @@ -11,13 +11,13 @@ gpg.program::
>>   
>>   gpg.format::
>>   	Specifies which key format to use when signing with `--gpg-sign`.
>> -	Default is "openpgp" and another possible value is "x509".
>> +	Default is "openpgp". Other possible values are "x509", "ssh".
>>   
>>   gpg.<format>.program::
>>   	Use this to customize the program used for the signing format you
>>   	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
>>   	be used as a legacy synonym for `gpg.openpgp.program`. The default
>> -	value for `gpg.x509.program` is "gpgsm".
>> +	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
>>   
>>   gpg.minTrustLevel::
>>   	Specifies a minimum trust level for signature verification.  If
>> @@ -27,6 +27,15 @@ gpg.minTrustLevel::
>>   	with at least `undefined` trust.  Setting this option overrides
>>   	the required trust-level for all operations.  Supported values,
>>   	in increasing order of significance:
>> +
>> +gpg.ssh.allowedSigners::
>> +	A file containing all valid SSH signing principals.
>> +	Similar to an .ssh/authorized_keys file. See ssh-keygen(1) for details.
>> +	Defaults to .gitsigners
> We probably don't want to store this in the repository.  If OpenSSH has
> a standard location for this, then we can default to that; otherwise, we
> should pick something in .ssh or in $XDG_CONFIG_HOME/git.
I'm not aware of a standard location. I think there are use cases to 
store this in the repo, but i'm of course fine not defaulting to it.

Re: [PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer]

> "Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>> From: Fabian Stelzer <fs@gigacodes.de>
>>
>> set gpg.format = ssh and user.signingkey to a ssh public key string (like from an
>> authorized_keys file) and commits/tags can be signed using the private
>> key from your ssh-agent.
>>
>> Verification uses a allowed_signers_file (see ssh-keygen(1)) which
>> defaults to .gitsigners but can be set via gpg.ssh.allowedsigners
>> A possible gpg.ssh.revocationfile is also passed to ssh-keygen on
>> verification.
> There are probably style and coding-guideline nit people will pick
> in the patch, but first of all I have to say that I am uncomfortably
> excited to see this addition.
>
> One thing that is unclear is how the 'allowed-signers' is expected
> to be maintained in the larger picture.  Who decides which keys
> (belong to whom) are trustworthy?  Does a contributor has to agree
> with the decision that certain keys are trustworthy made by somebody
> else in the project and use the same 'allowed-signers' collection of
> keys to effectively participate in the project?  How do revoking and
> rotating keys work?
>
> It was a deliberate design decision to let PGP infrastructure that
> is used to sign and verify signatures when we use PGP for signing
> without tying any of these decisions to the tracked contents, as
> that would reduce the attack surface for a malicious tree contents
> to affect the signing and verification (in other words, "we punted"
> ;-).  Even though I am not sure exactly what you meant by "defaults
> to .gitsigners", I am assuming that you meant a file with the name
> at the top-level of the working tree, which makes me worried, as it
> opens us to the risk of reading from and blindly trusting whatever
> somebody else placed in the tree contents immediately after we "git
> pull" (or "git clone").
>
> Thanks for working on it.
Glad to hear that :)
I tried to keep the style with the existing code but the IDE sometimes 
has its own idea.

I think there are two basic options for maintaining the allowed signers 
file:
1. Every developer has their own stored outside of the repo and 
adds/revokes trust manually like with gpg.
     A central repo would probably verify against a list managed by the 
tool (e.g. gitolite)
2. Store it in a .gitsigners file in the repo. This would only work if 
you only allow signed commits/pushes from this point onwards. But this 
way a shared understading of trusted users can be maintained easily.
     Only already trusted committers can add new users or change their 
own keys. The signers file is basically a ssh_authorized_keys file with 
an additional principal identifier added at the front like:
     fs@gigacodes.de ssh-rsa XXXKEYXXX Comment
     a@b.com ssh-ed25519 XXXKEYXXX Comment

Where are commits usually verified at the moment? On every devs checkout 
or only centrally on pushes?

The signers file also supports SSH CA keys and wildcard identifiers. At 
the moment i look up the principal dynamically via the public key so 
it's just a text info of who's key is it at the moment.
The SSH CA Stuff is probably a niche use case but could be cool in a 
corporate setting. Thats also what the revocation file is used for. The 
SSH CA can generate a KRL (like crl) which you put into it or you can 
specify explicit public keys in it to deny them.

Re: [PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[Junio C Hamano]

Fabian Stelzer <fs@gigacodes.de> writes:

>> One thing that is unclear is how the 'allowed-signers' is expected
>> to be maintained in the larger picture.  Who decides which keys
>> ...
>> Thanks for working on it.
> Glad to hear that :)

Thanks for explaining your thoughts (omitted).  When I say "this is
unclear" in my response to a patch, I expect that unclear-ness will
be shared by other readers of the code, the doc and/or the log
message, so please make sure an updated patch will reduce the need
to ask the same question by future readers.

> I tried to keep the style with the existing code but the IDE sometimes
> has its own idea.

Documentation/CodingGuidelines and Documentation/SubmittingPatches
would hopefully help (if not, please ask and/or suggest clarification
on these documents).

Thanks.

RE: [PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[Randall S. Becker]

On July 6, 2021 11:46 AM, Fabian Stelzer wrote:
>> "Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:
>>
>>> From: Fabian Stelzer <fs@gigacodes.de>
>>>
>>> set gpg.format = ssh and user.signingkey to a ssh public key string
>>> (like from an authorized_keys file) and commits/tags can be signed
>>> using the private key from your ssh-agent.
>>>
>>> Verification uses a allowed_signers_file (see ssh-keygen(1)) which
>>> defaults to .gitsigners but can be set via gpg.ssh.allowedsigners A
>>> possible gpg.ssh.revocationfile is also passed to ssh-keygen on
>>> verification.
>> There are probably style and coding-guideline nit people will pick in
>> the patch, but first of all I have to say that I am uncomfortably
>> excited to see this addition.
>>
>> One thing that is unclear is how the 'allowed-signers' is expected to
>> be maintained in the larger picture.  Who decides which keys (belong
>> to whom) are trustworthy?  Does a contributor has to agree with the
>> decision that certain keys are trustworthy made by somebody else in
>> the project and use the same 'allowed-signers' collection of keys to
>> effectively participate in the project?  How do revoking and rotating
>> keys work?
>>
>> It was a deliberate design decision to let PGP infrastructure that is
>> used to sign and verify signatures when we use PGP for signing without
>> tying any of these decisions to the tracked contents, as that would
>> reduce the attack surface for a malicious tree contents to affect the
>> signing and verification (in other words, "we punted"
>> ;-).  Even though I am not sure exactly what you meant by "defaults to
>> .gitsigners", I am assuming that you meant a file with the name at the
>> top-level of the working tree, which makes me worried, as it opens us
>> to the risk of reading from and blindly trusting whatever somebody
>> else placed in the tree contents immediately after we "git pull" (or
>> "git clone").
>>
>> Thanks for working on it.
>Glad to hear that :)
>I tried to keep the style with the existing code but the IDE sometimes has its own idea.
>
>I think there are two basic options for maintaining the allowed signers
>file:
>1. Every developer has their own stored outside of the repo and adds/revokes trust manually like with gpg.
>     A central repo would probably verify against a list managed by the tool (e.g. gitolite) 2. Store it in a .gitsigners file in the repo. This
>would only work if you only allow signed commits/pushes from this point onwards. But this way a shared understading of trusted users can
>be maintained easily.
>     Only already trusted committers can add new users or change their own keys. The signers file is basically a ssh_authorized_keys file
>with an additional principal identifier added at the front like:
>     fs@gigacodes.de ssh-rsa XXXKEYXXX Comment
>     a@b.com ssh-ed25519 XXXKEYXXX Comment
>
>Where are commits usually verified at the moment? On every devs checkout or only centrally on pushes?
>
>The signers file also supports SSH CA keys and wildcard identifiers. At the moment i look up the principal dynamically via the public key so
>it's just a text info of who's key is it at the moment.
>The SSH CA Stuff is probably a niche use case but could be cool in a corporate setting. Thats also what the revocation file is used for. The
>SSH CA can generate a KRL (like crl) which you put into it or you can specify explicit public keys in it to deny them.

Just musing here... If adding SSH CA, would not adding support for a self-signed SSL CA make sense? In such a situation, a self-signed certificate can be created at an organizational level, or even from an official root CA. Per-user self-signed certificates, or organizationally defined CAs and certificates, could be created that are more stable than SSH CAs. Then something like OpenSSL (via libcurl) could handle the signature and validation management. Signed content could propagate to Cloud-based git servers and retain their ability to be property verified. Although I can see a drawback here, which relates to expiring certificates - although the concept of an expired signed content is somewhat compelling. Imaging the use case where a company has an employee who signs a tag/commit. The employee departs/retires/terminated/etc., and with it the published certificate is also revoked - an extreme case perhaps, but if the code can no longer be trusted by virtue of the termination, maybe this is semantically interesting. This could be a core git function with no additional dependencies.

Regards,
Randall

Re: [PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[Bagas Sanjaya]

On 06/07/21 15.19, Fabian Stelzer via GitGitGadget wrote:
> From: Fabian Stelzer <fs@gigacodes.de>
> 
> set gpg.format = ssh and user.signingkey to a ssh public key string (like from an
> authorized_keys file) and commits/tags can be signed using the private
> key from your ssh-agent.
> 
> Verification uses a allowed_signers_file (see ssh-keygen(1)) which
> defaults to .gitsigners but can be set via gpg.ssh.allowedsigners
> A possible gpg.ssh.revocationfile is also passed to ssh-keygen on
> verification.
> 
> needs openssh>8.2p1
> 

Why did you choose to implement SSH-based signing as GPG interface? Why 
not create similar one?

If at later times we need to implement other signing methods (besides 
GPG and SSH), we can refactor gpg-interface into generic signing 
interface (say `signing.h`) and let each signing methods implement from it.

-- 
An old man doll... just what I always wanted! - Clara

Re: [PATCH] Add commit & tag signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer]

On 07.07.21 08:26, Bagas Sanjaya wrote:
> On 06/07/21 15.19, Fabian Stelzer via GitGitGadget wrote:
>> From: Fabian Stelzer <fs@gigacodes.de>
>>
>> set gpg.format = ssh and user.signingkey to a ssh public key string 
>> (like from an
>> authorized_keys file) and commits/tags can be signed using the private
>> key from your ssh-agent.
>>
>> Verification uses a allowed_signers_file (see ssh-keygen(1)) which
>> defaults to .gitsigners but can be set via gpg.ssh.allowedsigners
>> A possible gpg.ssh.revocationfile is also passed to ssh-keygen on
>> verification.
>>
>> needs openssh>8.2p1
>>
>
> Why did you choose to implement SSH-based signing as GPG interface? 
> Why not create similar one?
>
> If at later times we need to implement other signing methods (besides 
> GPG and SSH), we can refactor gpg-interface into generic signing 
> interface (say `signing.h`) and let each signing methods implement 
> from it. 
I agree that a general purpose "signing" would be cleaner. The GPG 
kewords are scattered all over the codebase but all the paths i found 
just call the generic sign_buffer / verify_signed_buffer from 
gpg-interface.c in the end whose api works quite well for other signing 
mechanisms as well. I will rename some struct fields to be more generic 
and adjust a few messages printed to the user which currently say things 
like "gpg failed to sign the data" or "has a gpg signature" to be 
generic. Do we just want to call this "signature" and remove the gpg 
prefix or would that be too generic?

Refactoring the whole gpg part to a generic "signing" would be quite 
involved and should probably be a different patch even though its mostly 
renaming stuff.
If we want to go into that direction i could add the new config keys 
under signing.* (signing.format = ssh|gpg, ...) and keep the 
compatibility for the older gpg.* keys.

[PATCH v2] Add commit, tag & push signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Openssh v8.2p1 added some new options to ssh-keygen for signature
creation and verification. These allow us to use ssh keys for git
signatures easily.

Set gpg.format = ssh and user.signingkey to either a ssh public key
string (like from an authorized_keys file), or a ssh key file.
If the key file or the config value itself contains only a public key
then the private key needs to be available via ssh-agent.
If no signingkey is set then git will call 'ssh-add -L' to check for
available agent keys and use the first one for signing.

Verification uses the gpg.ssh.keyring file (see ssh-keygen(1) "ALLOWED
SIGNERS") which contains valid public keys and an principal (usually
user@domain). Depending on the environment this file can be managed by
the individual developer or for example generated by the central
repository server from known ssh keys with push access. If the
repository only allows signed commits / pushes then the file can even be
stored inside it.

To revoke a key put the public key without the principal prefix into
gpg.ssh.revocationKeyring or generate a KRL (see ssh-keygen(1)
"KEY REVOCATION LISTS"). The same considerations about who to trust for
verification as with the keyring file apply.

This feature makes git signing much more accessible to the average user.
Usually they have a SSH Key for pushing code already. Using it
for signing commits allows us to verify not only the transport but the
pushed code as well.

In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
signing/encryption and ssh keys which i think is quite common
(at least for the email part). This way we can establish the correct
trust for the SSH Keys without setting up a separate GPG Infrastructure
(which is still quite painful for users) or implementing x509 signing
support for git (which lacks good forwarding mechanisms).
Using ssh agent forwarding makes this feature easily usable in todays
development environments where code is often checked out in remote VMs / containers.
In such a setup the keyring & revocationKeyring can be centrally
generated from the x509 CA information and distributed to the users.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
    RFC: Add commit & tag signing/verification via SSH keys using ssh-keygen
    
    I have added support for using keyfiles directly, lots of tests and
    generally cleaned up the signing & verification code a lot.
    
    I can still rename things from being gpg specific to a more general
    "signing" but thats rather cosmetic. Also i'm not sure if i named the
    new test files correctly.
    
    There is a patch in the pipeline for openssh by Damien Miller that will
    add valid-after, valid-before options to the allowed keys keyring. This
    allows us to pass the commit timestamp to the verification call and make
    key rollover possible and still be able to verify older commits. Set
    valid-after=NOW when adding your key to the keyring and set valid-before
    to make it fail if used after a certain date. Software like
    gitolite/github or corporate automation can do this automatically when
    ssh push keys are addded / removed

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1041%2FFStelzer%2Fsshsign-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1041/FStelzer/sshsign-v2
Pull-Request: https://github.com/git/git/pull/1041

Range-diff vs v1:

 1:  f238392bfa8 ! 1:  b8b16f8e6ec Add commit & tag signing/verification via SSH keys using ssh-keygen
     @@ Metadata
      Author: Fabian Stelzer <fs@gigacodes.de>
      
       ## Commit message ##
     -    Add commit & tag signing/verification via SSH keys using ssh-keygen
     +    Add commit, tag & push signing/verification via SSH keys using ssh-keygen
      
     -    set gpg.format = ssh and user.signingkey to a ssh public key string (like from an
     -    authorized_keys file) and commits/tags can be signed using the private
     -    key from your ssh-agent.
     +    Openssh v8.2p1 added some new options to ssh-keygen for signature
     +    creation and verification. These allow us to use ssh keys for git
     +    signatures easily.
      
     -    Verification uses a allowed_signers_file (see ssh-keygen(1)) which
     -    defaults to .gitsigners but can be set via gpg.ssh.allowedsigners
     -    A possible gpg.ssh.revocationfile is also passed to ssh-keygen on
     -    verification.
     +    Set gpg.format = ssh and user.signingkey to either a ssh public key
     +    string (like from an authorized_keys file), or a ssh key file.
     +    If the key file or the config value itself contains only a public key
     +    then the private key needs to be available via ssh-agent.
     +    If no signingkey is set then git will call 'ssh-add -L' to check for
     +    available agent keys and use the first one for signing.
      
     -    needs openssh>8.2p1
     +    Verification uses the gpg.ssh.keyring file (see ssh-keygen(1) "ALLOWED
     +    SIGNERS") which contains valid public keys and an principal (usually
     +    user@domain). Depending on the environment this file can be managed by
     +    the individual developer or for example generated by the central
     +    repository server from known ssh keys with push access. If the
     +    repository only allows signed commits / pushes then the file can even be
     +    stored inside it.
     +
     +    To revoke a key put the public key without the principal prefix into
     +    gpg.ssh.revocationKeyring or generate a KRL (see ssh-keygen(1)
     +    "KEY REVOCATION LISTS"). The same considerations about who to trust for
     +    verification as with the keyring file apply.
     +
     +    This feature makes git signing much more accessible to the average user.
     +    Usually they have a SSH Key for pushing code already. Using it
     +    for signing commits allows us to verify not only the transport but the
     +    pushed code as well.
     +
     +    In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
     +    signing/encryption and ssh keys which i think is quite common
     +    (at least for the email part). This way we can establish the correct
     +    trust for the SSH Keys without setting up a separate GPG Infrastructure
     +    (which is still quite painful for users) or implementing x509 signing
     +    support for git (which lacks good forwarding mechanisms).
     +    Using ssh agent forwarding makes this feature easily usable in todays
     +    development environments where code is often checked out in remote VMs / containers.
     +    In such a setup the keyring & revocationKeyring can be centrally
     +    generated from the x509 CA information and distributed to the users.
      
          Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
      
     @@ Documentation/config/gpg.txt: gpg.program::
       gpg.minTrustLevel::
       	Specifies a minimum trust level for signature verification.  If
      @@ Documentation/config/gpg.txt: gpg.minTrustLevel::
     - 	with at least `undefined` trust.  Setting this option overrides
     - 	the required trust-level for all operations.  Supported values,
     - 	in increasing order of significance:
     + * `marginal`
     + * `fully`
     + * `ultimate`
     ++
     ++gpg.ssh.keyring::
     ++	A file containing all valid SSH public signing keys. 
     ++	Similar to an .ssh/authorized_keys file.
     ++	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
     ++	If a signing key is found in this file then the trust level will
     ++	be set to "fully". Otherwise if the key is not present
     ++	but the signature is still valid then the trust level will be "undefined".
     ++
     ++	This file can be set to a location outside of the repository
     ++	and every developer maintains their own trust store.
     ++	A central repository server could generate this file automatically
     ++	from ssh keys with push	access to verify the code against.
     ++	In a corporate setting this file is probably generated at a global location
     ++	from some automation that already handles developer ssh keys. 
     ++	
     ++	A repository that is only allowing signed commits can store the file 
     ++	in the repository itself using a relative path. This way only committers
     ++	with an already valid key can add or change keys in the keyring.
      +
     -+gpg.ssh.allowedSigners::
     -+	A file containing all valid SSH signing principals. 
     -+	Similar to an .ssh/authorized_keys file. See ssh-keygen(1) for details.
     -+	Defaults to .gitsigners
     ++	Using a SSH CA key with the cert-authority option 
     ++	(see ssh-keygen(1) "CERTIFICATES") is also valid.
      +
     -+gpg.ssh.revocationFile::
     -+	Either a SSH KRL or a list of revoked public keys.
     ++	To revoke a key place the public key without the principal into the 
     ++	revocationKeyring.
     ++
     ++gpg.ssh.revocationKeyring::
     ++	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
      +	See ssh-keygen(1) for details.
     - +
     - * `undefined`
     - * `never`
     ++	If a public key is found in this file then it will always be treated
     ++	as having trust level "never" and signatures will show as invalid.
      
       ## Documentation/config/user.txt ##
      @@ Documentation/config/user.txt: user.signingKey::
       	commit, you can override the default selection with this variable.
       	This option is passed unchanged to gpg's --local-user parameter,
       	so you may specify a key using any method that gpg supports.
     -+	If gpg.format is set to "ssh" this needs to contain the valid
     -+	ssh public key (e.g.: "ssh-rsa XXXXXX identifier") which corresponds
     -+	to the private key used for signing. The private key needs to be available
     -+	via ssh-agent. Direct private key files are not supported yet.
     ++	If gpg.format is set to "ssh" this can contain the literal ssh public
     ++	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and 
     ++	corresponds to the private key used for signing. The private key 
     ++	needs to be available via ssh-agent. Alternatively it can be set to
     ++	a file containing a private key directly. If not set git will call 
     ++	"ssh-add -L" and try to use the first key available.
     +
     + ## builtin/receive-pack.c ##
     +@@ builtin/receive-pack.c: static int receive_pack_config(const char *var, const char *value, void *cb)
     + {
     + 	int status = parse_hide_refs_config(var, value, "receive");
     + 
     ++	git_gpg_config(var, value, NULL);
     ++
     + 	if (status)
     + 		return status;
     + 
     +@@ builtin/receive-pack.c: static void prepare_push_cert_sha1(struct child_process *proc)
     + 		bogs = parse_signed_buffer(push_cert.buf, push_cert.len);
     + 		check_signature(push_cert.buf, bogs, push_cert.buf + bogs,
     + 				push_cert.len - bogs, &sigcheck);
     +-
     ++		
     + 		nonce_status = check_nonce(push_cert.buf, bogs);
     + 	}
     + 	if (!is_null_oid(&push_cert_oid)) {
     +
     + ## fmt-merge-msg.c ##
     +@@ fmt-merge-msg.c: static void fmt_merge_msg_sigs(struct strbuf *out)
     + 			len = payload.len;
     + 			if (check_signature(payload.buf, payload.len, sig.buf,
     + 					 sig.len, &sigc) &&
     +-				!sigc.gpg_output)
     ++				!sigc.output)
     + 				strbuf_addstr(&sig, "gpg verification failed.\n");
     + 			else
     +-				strbuf_addstr(&sig, sigc.gpg_output);
     ++				strbuf_addstr(&sig, sigc.output);
     + 		}
     + 		signature_check_clear(&sigc);
     + 
      
       ## gpg-interface.c ##
      @@
     + #include "config.h"
     + #include "run-command.h"
     + #include "strbuf.h"
     ++#include "dir.h"
     + #include "gpg-interface.h"
     + #include "sigchain.h"
       #include "tempfile.h"
       
       static char *configured_signing_key;
     @@ gpg-interface.c: static struct gpg_format gpg_format[] = {
       };
       
       static struct gpg_format *use_format = &gpg_format[0];
     +@@ gpg-interface.c: static struct gpg_format *get_format_by_sig(const char *sig)
     + void signature_check_clear(struct signature_check *sigc)
     + {
     + 	FREE_AND_NULL(sigc->payload);
     ++	FREE_AND_NULL(sigc->output);
     + 	FREE_AND_NULL(sigc->gpg_output);
     + 	FREE_AND_NULL(sigc->gpg_status);
     + 	FREE_AND_NULL(sigc->signer);
      @@ gpg-interface.c: static int parse_gpg_trust_level(const char *level,
       	return 1;
       }
     @@ gpg-interface.c: static int parse_gpg_trust_level(const char *level,
      +	const char *output = NULL;
      +	char *next = NULL;
      +
     -+	// ssh-keysign output should be:
     -+	// Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
     ++	/* ssh-keysign output should be:
     ++	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
     ++	 * or for valid but unknown keys:
     ++	 * Good "git" signature with RSA key SHA256:FINGERPRINT
     ++	 */
      +
     -+	output = xmemdupz(sigc->gpg_status, strcspn(sigc->gpg_status, " \n"));
     -+	if (skip_prefix(sigc->gpg_status, "Good \"git\" signature for ", &output)) {
     ++	output = xmemdupz(sigc->output, strcspn(sigc->output, " \n"));
     ++	if (skip_prefix(sigc->output, "Good \"git\" signature for ", &output)) {
     ++		// Valid signature for a trusted signer
      +		sigc->result = 'G';
     ++		sigc->trust_level = TRUST_FULLY;
      +
     -+		next = strchrnul(output, ' ');
     ++		next = strchrnul(output, ' '); // 'principal'
      +		replace_cstring(&sigc->signer, output, next);
      +		output = next + 1;
      +		next = strchrnul(output, ' '); // 'with'
     @@ gpg-interface.c: static int parse_gpg_trust_level(const char *level,
      +		output = next + 1;
      +		next = strchrnul(output, ' '); // 'key'
      +		output = next + 1;
     -+		next = strchrnul(output, ' '); // key
     ++		next = strchrnul(output, '\n'); // key
      +		replace_cstring(&sigc->fingerprint, output, next);
     ++		replace_cstring(&sigc->key, output, next);
     ++	} else if (skip_prefix(sigc->output, "Good \"git\" signature with ", &output)) {
     ++		// Valid signature, but key unknown
     ++		sigc->result = 'G';
     ++		sigc->trust_level = TRUST_UNDEFINED;
     ++
     ++		next = strchrnul(output, ' '); // KEY Type
     ++		output = next + 1;
     ++		next = strchrnul(output, ' '); // 'key'
     ++		output = next + 1;
     ++		next = strchrnul(output, '\n'); // key
     ++		replace_cstring(&sigc->fingerprint, output, next);
     ++		replace_cstring(&sigc->key, output, next);
      +	} else {
      +		sigc->result = 'B';
     ++		sigc->trust_level = TRUST_NEVER;
      +	}
     -+
     -+	// SSH-Keygen prints onto stdout instead of stderr like the output code expects - so we just copy it over
     -+	free(sigc->gpg_output);
     -+	sigc->gpg_output = xmemdupz(sigc->gpg_status, strlen(sigc->gpg_status));
      +}
      +
       static void parse_gpg_output(struct signature_check *sigc)
       {
       	const char *buf = sigc->gpg_status;
     -@@ gpg-interface.c: static int verify_signed_buffer(const char *payload, size_t payload_size,
     - 				struct strbuf *gpg_output,
     - 				struct strbuf *gpg_status)
     +@@ gpg-interface.c: error:
     + 	FREE_AND_NULL(sigc->key);
     + }
     + 
     +-static int verify_signed_buffer(const char *payload, size_t payload_size,
     +-				const char *signature, size_t signature_size,
     +-				struct strbuf *gpg_output,
     +-				struct strbuf *gpg_status)
     ++static int verify_ssh_signature(struct signature_check *sigc, struct gpg_format *fmt,
     ++	const char *payload, size_t payload_size,
     ++	const char *signature, size_t signature_size)
       {
      -	struct child_process gpg = CHILD_PROCESS_INIT;
     -+	struct child_process gpg = CHILD_PROCESS_INIT,
     -+			     ssh_keygen = CHILD_PROCESS_INIT;
     - 	struct gpg_format *fmt;
     +-	struct gpg_format *fmt;
     ++	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
       	struct tempfile *temp;
       	int ret;
      -	struct strbuf buf = STRBUF_INIT;
      +	const char *line;
      +	size_t trust_size;
      +	char *principal;
     -+	struct strbuf buf = STRBUF_INIT,
     -+		      principal_out = STRBUF_INIT,
     -+		      principal_err = STRBUF_INIT;
     ++	struct strbuf ssh_keygen_out = STRBUF_INIT;
     ++	struct strbuf ssh_keygen_err = STRBUF_INIT;
       
       	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
       	if (!temp)
      @@ gpg-interface.c: static int verify_signed_buffer(const char *payload, size_t payload_size,
     - 	if (!fmt)
     - 		BUG("bad signature '%s'", signature);
     + 		return -1;
     + 	}
       
     --	strvec_push(&gpg.args, fmt->program);
     --	strvec_pushv(&gpg.args, fmt->verify_args);
     --	strvec_pushl(&gpg.args,
     --		     "--status-fd=1",
     --		     "--verify", temp->filename.buf, "-",
     --		     NULL);
     -+	if (!strcmp(use_format->name, "ssh")) {
     -+		// Find the principal from the  signers
     -+		strvec_push(&ssh_keygen.args, fmt->program);
     -+		strvec_pushl(&ssh_keygen.args,  "-Y", "find-principals",
     -+						"-f", get_ssh_allowed_signers(),
     +-	fmt = get_format_by_sig(signature);
     +-	if (!fmt)
     +-		BUG("bad signature '%s'", signature);
     ++	// Find the principal from the  signers
     ++	strvec_pushl(&ssh_keygen.args,  fmt->program,
     ++					"-Y", "find-principals",
     ++					"-f", get_ssh_allowed_signers(),
     ++					"-s", temp->filename.buf,
     ++					NULL);
     ++	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
     ++	if (strstr(ssh_keygen_err.buf, "unknown option")) {
     ++		error(_("openssh version > 8.2p1 is needed for ssh signature verification (ssh-keygen needs -Y find-principals/verify option)"));
     ++	}
     ++	if (ret || !ssh_keygen_out.len) {
     ++		// We did not find a matching principal in the keyring - Check without validation
     ++		child_process_init(&ssh_keygen);
     ++		strvec_pushl(&ssh_keygen.args,  fmt->program,
     ++						"-Y", "check-novalidate",
     ++						"-n", "git",
      +						"-s", temp->filename.buf,
      +						NULL);
     -+		ret = pipe_command(&ssh_keygen, NULL, 0, &principal_out, 0, &principal_err, 0);
     -+		if (strstr(principal_err.buf, "unknown option")) {
     -+			error(_("openssh version > 8.2p1 is needed for ssh signature verification (ssh-keygen needs -Y find-principals/verify option)"));
     -+		}
     -+		if (ret || !principal_out.len)
     -+			goto out;
     -+
     -+		/* Iterate over all lines */
     -+		for (line = principal_out.buf; *line; line = strchrnul(line + 1, '\n')) {
     ++		ret = pipe_command(&ssh_keygen, payload, payload_size, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
     ++	} else {
     ++		// Check every principal we found (one per line)
     ++		for (line = ssh_keygen_out.buf; *line; line = strchrnul(line + 1, '\n')) {
      +			while (*line == '\n')
      +				line++;
      +			if (!*line)
      +				break;
     - 
     --	if (!gpg_status)
     --		gpg_status = &buf;
     ++
      +			trust_size = strcspn(line, " \n");
      +			principal = xmemdupz(line, trust_size);
     - 
     --	sigchain_push(SIGPIPE, SIG_IGN);
     --	ret = pipe_command(&gpg, payload, payload_size,
     --			   gpg_status, 0, gpg_output, 0);
     --	sigchain_pop(SIGPIPE);
     -+			strvec_push(&gpg.args,fmt->program);
     ++
     ++			child_process_init(&ssh_keygen);
     ++			strbuf_release(&ssh_keygen_out);
     ++			strbuf_release(&ssh_keygen_err);
     ++			strvec_push(&ssh_keygen.args,fmt->program);
      +			// We found principals - Try with each until we find a match
     -+			strvec_pushl(&gpg.args, "-Y", "verify",
     -+						"-n", "git",
     -+						"-f", get_ssh_allowed_signers(),
     -+						"-I", principal,
     -+						"-s", temp->filename.buf,
     -+						 NULL);
     - 
     --	delete_tempfile(&temp);
     -+			if (ssh_revocation_file) {
     -+				strvec_pushl(&gpg.args, "-r", ssh_revocation_file, NULL);
     -+			}
     ++			strvec_pushl(&ssh_keygen.args,  "-Y", "verify",
     ++							//TODO: sprintf("-Overify-time=%s", commit->date...),
     ++							"-n", "git",
     ++							"-f", get_ssh_allowed_signers(),
     ++							"-I", principal,
     ++							"-s", temp->filename.buf,
     ++							NULL);
      +
     -+			if (!gpg_status)
     -+				gpg_status = &buf;
     ++			if (ssh_revocation_file && file_exists(ssh_revocation_file)) {
     ++				strvec_pushl(&ssh_keygen.args, "-r", ssh_revocation_file, NULL);
     ++			}
      +
      +			sigchain_push(SIGPIPE, SIG_IGN);
     -+			ret = pipe_command(&gpg, payload, payload_size,
     -+					   gpg_status, 0, gpg_output, 0);
     ++			ret = pipe_command(&ssh_keygen, payload, payload_size,
     ++					&ssh_keygen_out, 0, &ssh_keygen_err, 0);
      +			sigchain_pop(SIGPIPE);
     - 
     --	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
     -+			ret |= !strstr(gpg_status->buf, "Good");
     ++
     ++			ret &= starts_with(ssh_keygen_out.buf, "Good");
      +			if (ret == 0)
      +				break;
      +		}
     -+	} else {
     -+		strvec_push(&gpg.args, fmt->program);
     -+		strvec_pushv(&gpg.args, fmt->verify_args);
     -+		strvec_pushl(&gpg.args,
     -+				"--status-fd=1",
     -+				"--verify", temp->filename.buf, "-",
     -+				NULL);
     ++	}
      +
     -+		if (!gpg_status)
     -+			gpg_status = &buf;
     ++	sigc->payload = xmemdupz(payload, payload_size);
     ++	strbuf_stripspace(&ssh_keygen_out, 0);
     ++	strbuf_stripspace(&ssh_keygen_err, 0);
     ++	strbuf_add(&ssh_keygen_out, ssh_keygen_err.buf, ssh_keygen_err.len);
     ++	sigc->output = strbuf_detach(&ssh_keygen_out, NULL);
      +
     -+		sigchain_push(SIGPIPE, SIG_IGN);
     -+		ret = pipe_command(&gpg, payload, payload_size, gpg_status, 0,
     -+				   gpg_output, 0);
     -+		sigchain_pop(SIGPIPE);
     -+		ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
     ++	//sigc->gpg_output = strbuf_detach(&ssh_keygen_err, NULL); // This flip around is broken...
     ++	sigc->gpg_status = strbuf_detach(&ssh_keygen_out, NULL);
     ++
     ++	parse_ssh_output(sigc);
     ++
     ++	delete_tempfile(&temp);
     ++	strbuf_release(&ssh_keygen_out);
     ++	strbuf_release(&ssh_keygen_err);
     ++
     ++	return ret;
     ++}
     ++
     ++static int verify_gpg_signature(struct signature_check *sigc, struct gpg_format *fmt, 
     ++	const char *payload, size_t payload_size,
     ++	const char *signature, size_t signature_size)
     ++{
     ++	struct child_process gpg = CHILD_PROCESS_INIT;
     ++	struct tempfile *temp;
     ++	int ret;
     ++	struct strbuf gpg_out = STRBUF_INIT;
     ++	struct strbuf gpg_err = STRBUF_INIT;
     ++
     ++	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
     ++	if (!temp)
     ++		return error_errno(_("could not create temporary file"));
     ++	if (write_in_full(temp->fd, signature, signature_size) < 0 ||
     ++	    close_tempfile_gently(temp) < 0) {
     ++		error_errno(_("failed writing detached signature to '%s'"),
     ++			    temp->filename.buf);
     ++		delete_tempfile(&temp);
     ++		return -1;
      +	}
     + 
     + 	strvec_push(&gpg.args, fmt->program);
     + 	strvec_pushv(&gpg.args, fmt->verify_args);
     + 	strvec_pushl(&gpg.args,
     +-		     "--status-fd=1",
     +-		     "--verify", temp->filename.buf, "-",
     +-		     NULL);
     +-
     +-	if (!gpg_status)
     +-		gpg_status = &buf;
     ++			"--status-fd=1",
     ++			"--verify", temp->filename.buf, "-",
     ++			NULL);
     + 
     + 	sigchain_push(SIGPIPE, SIG_IGN);
     +-	ret = pipe_command(&gpg, payload, payload_size,
     +-			   gpg_status, 0, gpg_output, 0);
     ++	ret = pipe_command(&gpg, payload, payload_size, &gpg_out, 0,
     ++				&gpg_err, 0);
     + 	sigchain_pop(SIGPIPE);
     ++	ret |= !strstr(gpg_out.buf, "\n[GNUPG:] GOODSIG ");
     + 
     +-	delete_tempfile(&temp);
     ++	sigc->payload = xmemdupz(payload, payload_size);
     ++	sigc->output = strbuf_detach(&gpg_err, NULL);
     ++	sigc->gpg_status = strbuf_detach(&gpg_out, NULL);
     + 
     +-	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
     +-	strbuf_release(&buf); /* no matter it was used or not */
     ++	parse_gpg_output(sigc);
      +
     -+out:
      +	delete_tempfile(&temp);
     -+	strbuf_release(&principal_out);
     -+	strbuf_release(&principal_err);
     - 	strbuf_release(&buf); /* no matter it was used or not */
     ++	strbuf_release(&gpg_out);
     ++	strbuf_release(&gpg_err);
       
       	return ret;
     -@@ gpg-interface.c: int check_signature(const char *payload, size_t plen, const char *signature,
     - 	sigc->payload = xmemdupz(payload, plen);
     - 	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
     - 	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
     + }
     +@@ gpg-interface.c: static int verify_signed_buffer(const char *payload, size_t payload_size,
     + int check_signature(const char *payload, size_t plen, const char *signature,
     + 	size_t slen, struct signature_check *sigc)
     + {
     +-	struct strbuf gpg_output = STRBUF_INIT;
     +-	struct strbuf gpg_status = STRBUF_INIT;
     ++	struct gpg_format *fmt;
     + 	int status;
     + 
     + 	sigc->result = 'N';
     + 	sigc->trust_level = -1;
     + 
     +-	status = verify_signed_buffer(payload, plen, signature, slen,
     +-				      &gpg_output, &gpg_status);
     +-	if (status && !gpg_output.len)
     +-		goto out;
     +-	sigc->payload = xmemdupz(payload, plen);
     +-	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
     +-	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
      -	parse_gpg_output(sigc);
     -+	if (!strcmp(use_format->name, "ssh")) {
     -+		parse_ssh_output(sigc);
     ++	fmt = get_format_by_sig(signature);
     ++	if (!fmt)
     ++		BUG("bad signature '%s'", signature);
     ++
     ++	if (!strcmp(fmt->name, "ssh")) {
     ++		status = verify_ssh_signature(sigc, fmt, payload, plen, signature, slen);
      +	} else {
     -+		parse_gpg_output(sigc);
     ++		status = verify_gpg_signature(sigc, fmt, payload, plen, signature, slen);
      +	}
     ++	if (status && !sigc->gpg_output)
     ++		return !!status;
     ++
       	status |= sigc->result != 'G';
       	status |= sigc->trust_level < configured_min_trust_level;
       
     +- out:
     +-	strbuf_release(&gpg_status);
     +-	strbuf_release(&gpg_output);
     +-
     + 	return !!status;
     + }
     + 
     + void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
     + {
     + 	const char *output = flags & GPG_VERIFY_RAW ?
     +-		sigc->gpg_status : sigc->gpg_output;
     ++		sigc->gpg_status : sigc->output;
     + 
     + 	if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
     + 		fputs(sigc->payload, stdout);
      @@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb)
     + 	int ret;
     + 
     + 	if (!strcmp(var, "user.signingkey")) {
     ++		/* user.signingkey can contain one of the following
     ++		 * when format = openpgp/x509
     ++		 *   - GPG KeyID
     ++		 * when format = ssh
     ++		 *   - literal ssh public key (e.g. ssh-rsa XXXKEYXXX comment)
     ++		 *   - path to a file containing a public or a private ssh key
     ++		 */
     + 		if (!value)
     + 			return config_error_nonbool(var);
     + 		set_signing_key(value);
       		return 0;
       	}
       
     -+	if (!strcmp(var, "gpg.ssh.allowedsigners")) {
     ++	if (!strcmp(var, "gpg.ssh.keyring")) {
     ++		if (!value)
     ++			return config_error_nonbool(var);
      +		return git_config_string(&ssh_allowed_signers, var, value);
      +	}
      +
     -+	if (!strcmp(var, "gpg.ssh.revocationfile")) {
     ++	if (!strcmp(var, "gpg.ssh.revocationkeyring")) {
     ++		if (!value)
     ++			return config_error_nonbool(var);
      +		return git_config_string(&ssh_revocation_file, var, value);
      +	}
      +
     @@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb
       	if (fmtname) {
       		fmt = get_format_by_name(fmtname);
       		return git_config_string(&fmt->program, var, value);
     -@@ gpg-interface.c: const char *get_signing_key(void)
     +@@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb)
     + 	return 0;
     + }
     + 
     ++static char *get_ssh_key_fingerprint(const char *signing_key) {
     ++	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
     ++	int ret = -1;
     ++	struct strbuf fingerprint_stdout = STRBUF_INIT;
     ++	struct strbuf **fingerprint;
     ++
     ++	/* For SSH Signing this can contain a filename or a public key
     ++	* For textual representation we usually want a fingerprint
     ++	*/
     ++	if (istarts_with(signing_key, "ssh-")) {
     ++		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
     ++					"-lf", "-",
     ++					NULL);
     ++		ret = pipe_command(&ssh_keygen, signing_key, strlen(signing_key), &fingerprint_stdout, 0,  NULL, 0);
     ++	} else {
     ++		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
     ++					"-lf", configured_signing_key,
     ++					NULL);
     ++		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0, NULL, 0);
     ++		if (!!ret)
     ++			die_errno(_("failed to get the ssh fingerprint for key '%s'"), signing_key);
     ++		fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
     ++		if (fingerprint[1]) {
     ++			return strbuf_detach(fingerprint[1], NULL);
     ++		}
     ++	}
     ++	die_errno(_("failed to get the ssh fingerprint for key '%s'"), signing_key);
     ++}
     ++
     ++// Returns the first public key from an ssh-agent to use for signing
     ++static char *get_default_ssh_signing_key(void) {
     ++	struct child_process ssh_add = CHILD_PROCESS_INIT;
     ++	int ret = -1;
     ++	struct strbuf key_stdout = STRBUF_INIT;
     ++	struct strbuf **keys;
     ++
     ++	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
     ++	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
     ++	if (!ret) { 
     ++		keys = strbuf_split_max(&key_stdout, '\n', 2);
     ++		if (keys[0])
     ++			return strbuf_detach(keys[0], NULL);
     ++	}
     ++
     ++	return "";
     ++}
     ++
     ++// Returns a textual but unique representation ot the signing key
     ++const char *get_signing_key_id(void) {
     ++	if (!strcmp(use_format->name, "ssh")) {
     ++		return get_ssh_key_fingerprint(get_signing_key());
     ++	} else {
     ++		// GPG/GPGSM only store a key id on this variable
     ++		return get_signing_key();
     ++	}
     ++}
     ++
     + const char *get_signing_key(void)
       {
       	if (configured_signing_key)
       		return configured_signing_key;
      -	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
      +	if (!strcmp(use_format->name, "ssh")) {
     -+		// We could simply use the first key listed by ssh-add -L and risk signing with the wrong key
     -+		return "";
     ++		return get_default_ssh_signing_key();
      +	} else {
      +		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
      +	}
     @@ gpg-interface.c: const char *get_signing_key(void)
      +{
      +	if (ssh_allowed_signers)
      +		return ssh_allowed_signers;
     -+	return GPG_SSH_ALLOWED_SIGNERS;
     ++
     ++	die("A Path to an allowed signers ssh keyring is needed for validation");
       }
       
       int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
     @@ gpg-interface.c: int sign_buffer(struct strbuf *buffer, struct strbuf *signature
       	int ret;
       	size_t i, j, bottom;
       	struct strbuf gpg_status = STRBUF_INIT;
     --
     ++	struct tempfile *temp = NULL, *buffer_file = NULL;
     ++	char *ssh_signing_key_file = NULL;
     ++	struct strbuf ssh_signature_filename = STRBUF_INIT;
     ++
     ++	if (!strcmp(use_format->name, "ssh")) {
     ++		if (!signing_key || signing_key[0] == '\0')
     ++			return error(_("user.signingkey needs to be set for ssh signing"));
     ++
     ++
     ++		if (istarts_with(signing_key, "ssh-")) {
     ++			// A literal ssh key
     ++			temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
     ++			if (!temp)
     ++				return error_errno(_("could not create temporary file"));
     ++			if (write_in_full(temp->fd, signing_key, strlen(signing_key)) < 0 ||
     ++				close_tempfile_gently(temp) < 0) {
     ++				error_errno(_("failed writing ssh signing key to '%s'"), temp->filename.buf);
     ++				delete_tempfile(&temp);
     ++				return -1;
     ++			}
     ++			ssh_signing_key_file= temp->filename.buf;
     ++		} else {
     ++			// We assume a file
     ++			ssh_signing_key_file = expand_user_path(signing_key, 1);
     ++		}
     + 
      -	strvec_pushl(&gpg.args,
      -		     use_format->program,
      -		     "--status-fd=2",
      -		     "-bsau", signing_key,
      -		     NULL);
     -+	struct tempfile *temp = NULL;
     -+
     -+	if (!strcmp(use_format->name, "ssh")) {
     -+		if (!signing_key)
     -+			return error(_("user.signingkey needs to be set to a ssh public key for ssh signing"));
     -+
     -+		// signing_key is a public ssh key
     -+		// FIXME: Allow specifying a key file so we can use private keyfiles instead of ssh-agent
     -+		temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
     -+		if (!temp)
     ++		buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
     ++		if (!buffer_file)
      +			return error_errno(_("could not create temporary file"));
     -+		if (write_in_full(temp->fd, signing_key,
     -+					strlen(signing_key)) < 0 ||
     -+			close_tempfile_gently(temp) < 0) {
     -+			error_errno(_("failed writing ssh signing key to '%s'"), temp->filename.buf);
     -+			delete_tempfile(&temp);
     ++		if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
     ++			close_tempfile_gently(buffer_file) < 0) {
     ++			error_errno(_("failed writing ssh signing key buffer to '%s'"), buffer_file->filename.buf);
     ++			delete_tempfile(&buffer_file);
      +			return -1;
      +		}
     ++
      +		strvec_pushl(&gpg.args, use_format->program ,
      +					"-Y", "sign",
      +					"-n", "git",
     -+					"-f", temp->filename.buf,
     ++					"-f", ssh_signing_key_file,
     ++					buffer_file->filename.buf,
      +					NULL);
     ++
     ++		sigchain_push(SIGPIPE, SIG_IGN);
     ++		ret = pipe_command(&gpg, NULL, 0, NULL, 0, &gpg_status, 0);
     ++		sigchain_pop(SIGPIPE);
     ++
     ++		strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
     ++		strbuf_addstr(&ssh_signature_filename, ".sig");
     ++		if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {
     ++			error_errno(_("failed reading ssh signing data buffer from '%s'"), ssh_signature_filename.buf);
     ++		}
     ++		unlink_or_warn(ssh_signature_filename.buf);
     ++		strbuf_release(&ssh_signature_filename);
     ++		delete_tempfile(&buffer_file);
      +	} else {
      +		strvec_pushl(&gpg.args, use_format->program ,
      +					"--status-fd=2",
      +					"-bsau", signing_key,
      +					NULL);
     ++
     ++		/*
     ++		* When the username signingkey is bad, program could be terminated
     ++		* because gpg exits without reading and then write gets SIGPIPE.
     ++		*/
     ++		sigchain_push(SIGPIPE, SIG_IGN);
     ++		ret = pipe_command(&gpg, buffer->buf, buffer->len, signature, 1024, &gpg_status, 0);
     ++		sigchain_pop(SIGPIPE);
      +	}
       
       	bottom = signature->len;
       
     -@@ gpg-interface.c: int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
     - 			   signature, 1024, &gpg_status, 0);
     - 	sigchain_pop(SIGPIPE);
     - 
     --	ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
     +-	/*
     +-	 * When the username signingkey is bad, program could be terminated
     +-	 * because gpg exits without reading and then write gets SIGPIPE.
     +-	 */
     +-	sigchain_push(SIGPIPE, SIG_IGN);
     +-	ret = pipe_command(&gpg, buffer->buf, buffer->len,
     +-			   signature, 1024, &gpg_status, 0);
     +-	sigchain_pop(SIGPIPE);
      +	if (temp)
      +		delete_tempfile(&temp);
     -+
     + 
     +-	ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
      +	if (!strcmp(use_format->name, "ssh")) {
      +		if (strstr(gpg_status.buf, "unknown option")) {
      +			error(_("openssh version > 8.2p1 is needed for ssh signing (ssh-keygen needs -Y sign option)"));
     @@ gpg-interface.c: int sign_buffer(struct strbuf *buffer, struct strbuf *signature
       		return error(_("gpg failed to sign the data"));
      
       ## gpg-interface.h ##
     -@@ gpg-interface.h: struct strbuf;
     - #define GPG_VERIFY_RAW			2
     - #define GPG_VERIFY_OMIT_STATUS	4
     +@@ gpg-interface.h: enum signature_trust_level {
       
     -+#define GPG_SSH_ALLOWED_SIGNERS ".gitsigners"
     -+
     - enum signature_trust_level {
     - 	TRUST_UNDEFINED,
     - 	TRUST_NEVER,
     + struct signature_check {
     + 	char *payload;
     +-	char *gpg_output;
     +-	char *gpg_status;
     ++	char *output;
     ++	char *gpg_output; // This will be printed in commit logs
     ++	char *gpg_status; // Only used internally -> remove
     + 
     + 	/*
     + 	 * possible "result":
      @@ gpg-interface.h: int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
       int git_gpg_config(const char *, const char *, void *);
       void set_signing_key(const char *);
       const char *get_signing_key(void);
     ++
     ++/* Returns a textual unique representation of the signing key in use
     ++ * Either a GPG KeyID or a SSH Key Fingerprint
     ++ */
     ++const char *get_signing_key_id(void);
     ++
      +const char *get_ssh_allowed_signers(void);
       int check_signature(const char *payload, size_t plen,
       		    const char *signature, size_t slen,
       		    struct signature_check *sigc);
     +
     + ## log-tree.c ##
     +@@ log-tree.c: static void show_signature(struct rev_info *opt, struct commit *commit)
     + 
     + 	status = check_signature(payload.buf, payload.len, signature.buf,
     + 				 signature.len, &sigc);
     +-	if (status && !sigc.gpg_output)
     ++	if (status && !sigc.output)
     + 		show_sig_lines(opt, status, "No signature\n");
     + 	else
     +-		show_sig_lines(opt, status, sigc.gpg_output);
     ++		show_sig_lines(opt, status, sigc.output);
     + 	signature_check_clear(&sigc);
     + 
     +  out:
     +@@ log-tree.c: static int show_one_mergetag(struct commit *commit,
     + 		/* could have a good signature */
     + 		status = check_signature(payload.buf, payload.len,
     + 					 signature.buf, signature.len, &sigc);
     +-		if (sigc.gpg_output)
     +-			strbuf_addstr(&verify_message, sigc.gpg_output);
     ++		if (sigc.output)
     ++			strbuf_addstr(&verify_message, sigc.output);
     + 		else
     + 			strbuf_addstr(&verify_message, "No signature\n");
     + 		signature_check_clear(&sigc);
     +
     + ## pretty.c ##
     +@@ pretty.c: static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
     + 			check_commit_signature(c->commit, &(c->signature_check));
     + 		switch (placeholder[1]) {
     + 		case 'G':
     +-			if (c->signature_check.gpg_output)
     +-				strbuf_addstr(sb, c->signature_check.gpg_output);
     ++			if (c->signature_check.output)
     ++				strbuf_addstr(sb, c->signature_check.output);
     + 			break;
     + 		case '?':
     + 			switch (c->signature_check.result) {
     +
     + ## send-pack.c ##
     +@@ send-pack.c: static int generate_push_cert(struct strbuf *req_buf,
     + 	const struct ref *ref;
     + 	struct string_list_item *item;
     + 	char *signing_key = xstrdup(get_signing_key());
     ++	char *signing_key_id = xstrdup(get_signing_key_id());
     + 	const char *cp, *np;
     + 	struct strbuf cert = STRBUF_INIT;
     + 	int update_seen = 0;
     +-
     ++	
     + 	strbuf_addstr(&cert, "certificate version 0.1\n");
     +-	strbuf_addf(&cert, "pusher %s ", signing_key);
     ++	strbuf_addf(&cert, "pusher %s ", signing_key_id);
     + 	datestamp(&cert);
     + 	strbuf_addch(&cert, '\n');
     + 	if (args->url && *args->url) {
     +@@ send-pack.c: static int generate_push_cert(struct strbuf *req_buf,
     + 
     + free_return:
     + 	free(signing_key);
     ++	free(signing_key_id);
     + 	strbuf_release(&cert);
     + 	return update_seen;
     + }
     +
     + ## t/lib-gpg.sh ##
     +@@ t/lib-gpg.sh: test_lazy_prereq RFC1991 '
     + 	echo | gpg --homedir "${GNUPGHOME}" -b --rfc1991 >/dev/null
     + '
     + 
     ++test_lazy_prereq GPGSSH '
     ++	ssh_version=$(ssh-keygen -Y find-principals -n "git" 2>&1)
     ++	test $? != 127 || exit 1
     ++	echo $ssh_version | grep -q "find-principals:missing signature file"
     ++	test $? = 0 || exit 1; 
     ++	mkdir -p "${GNUPGHOME}" &&
     ++	chmod 0700 "${GNUPGHOME}" &&
     ++	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/ed25519_ssh_signing_key" >/dev/null &&
     ++	ssh-keygen -t rsa -b 2048 -N "" -f "${GNUPGHOME}/rsa_2048_ssh_signing_key" >/dev/null &&
     ++	ssh-keygen -t ed25519 -N "super_secret" -f "${GNUPGHOME}/protected_ssh_signing_key" >/dev/null &&
     ++	find "${GNUPGHOME}" -name *ssh_signing_key.pub -exec cat {} \; | awk "{print \"principal_\" NR \" \" \$0}" > "${GNUPGHOME}/ssh.all_valid.keyring" &&
     ++	cat "${GNUPGHOME}/ssh.all_valid.keyring" &&
     ++	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/untrusted_ssh_signing_key" >/dev/null
     ++'
     ++
     ++SIGNING_KEY_PRIMARY="${GNUPGHOME}/ed25519_ssh_signing_key"
     ++SIGNING_KEY_SECONDARY="${GNUPGHOME}/rsa_2048_ssh_signing_key"
     ++SIGNING_KEY_UNTRUSTED="${GNUPGHOME}/untrusted_ssh_signing_key"
     ++SIGNING_KEY_WITH_PASSPHRASE="${GNUPGHOME}/protected_ssh_signing_key"
     ++SIGNING_KEY_PASSPHRASE="super_secret"
     ++SIGNING_KEYRING="${GNUPGHOME}/ssh.all_valid.keyring"
     ++
     ++GOOD_SIGNATURE_TRUSTED='Good "git" signature for'
     ++GOOD_SIGNATURE_UNTRUSTED='Good "git" signature with'
     ++KEY_NOT_TRUSTED="No principal matched"
     ++BAD_SIGNATURE="Signature verification failed"
     ++
     + sanitize_pgp() {
     + 	perl -ne '
     + 		/^-----END PGP/ and $in_pgp = 0;
     +
     + ## t/t4202-log.sh ##
     +@@ t/t4202-log.sh: test_expect_success GPGSM 'setup signed branch x509' '
     + 	git commit -S -m signed_commit
     + '
     + 
     ++test_expect_success GPGSSH 'setup sshkey signed branch' '
     ++	test_config gpg.format ssh &&
     ++	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     ++	test_when_finished "git reset --hard && git checkout main" &&
     ++	git checkout -b signed-ssh main &&
     ++	echo foo >foo &&
     ++	git add foo &&
     ++	git commit -S -m signed_commit
     ++'
     ++
     + test_expect_success GPGSM 'log x509 fingerprint' '
     + 	echo "F8BF62E0693D0694816377099909C779FA23FD65 | " >expect &&
     + 	git log -n1 --format="%GF | %GP" signed-x509 >actual &&
     +@@ t/t4202-log.sh: test_expect_success GPGSM 'log --graph --show-signature x509' '
     + 	grep "^| gpgsm: Good signature" actual
     + '
     + 
     ++test_expect_success GPGSSH 'log ssh key fingerprint' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	ssh-keygen -lf  "${SIGNING_KEY_PRIMARY}" | awk "{print \$2\" | \"}" >expect &&
     ++	git log -n1 --format="%GF | %GP" signed-ssh >actual &&
     ++	test_cmp expect actual
     ++'
     ++
     + test_expect_success GPG 'log --graph --show-signature for merged tag' '
     + 	test_when_finished "git reset --hard && git checkout main" &&
     + 	git checkout -b plain main &&
     +
     + ## t/t5534-push-signed.sh ##
     +@@ t/t5534-push-signed.sh: test_expect_success GPG 'signed push sends push certificate' '
     + 	test_cmp expect dst/push-cert-status
     + '
     + 
     ++test_expect_success GPGSSH 'ssh signed push sends push certificate' '
     ++	prepare_dst &&
     ++	mkdir -p dst/.git/hooks &&
     ++	git -C dst config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	git -C dst config receive.certnonceseed sekrit &&
     ++	write_script dst/.git/hooks/post-receive <<-\EOF &&
     ++	# discard the update list
     ++	cat >/dev/null
     ++	# record the push certificate
     ++	if test -n "${GIT_PUSH_CERT-}"
     ++	then
     ++		git cat-file blob $GIT_PUSH_CERT >../push-cert
     ++	fi &&
     ++
     ++	cat >../push-cert-status <<E_O_F
     ++	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
     ++	KEY=${GIT_PUSH_CERT_KEY-nokey}
     ++	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
     ++	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
     ++	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
     ++	E_O_F
     ++
     ++	EOF
     ++
     ++	test_config gpg.format ssh &&
     ++	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     ++	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
     ++	git push --signed dst noop ff +noff &&
     ++
     ++	(
     ++		cat <<-\EOF &&
     ++		SIGNER=principal_1
     ++		KEY=FINGERPRINT
     ++		STATUS=G
     ++		NONCE_STATUS=OK
     ++		EOF
     ++		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
     ++	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
     ++
     ++	noop=$(git rev-parse noop) &&
     ++	ff=$(git rev-parse ff) &&
     ++	noff=$(git rev-parse noff) &&
     ++	grep "$noop $ff refs/heads/ff" dst/push-cert &&
     ++	grep "$noop $noff refs/heads/noff" dst/push-cert &&
     ++	test_cmp expect dst/push-cert-status
     ++'
     ++
     + test_expect_success GPG 'inconsistent push options in signed push not allowed' '
     + 	# First, invoke receive-pack with dummy input to obtain its preamble.
     + 	prepare_dst &&
     +@@ t/t5534-push-signed.sh: test_expect_success GPGSM 'fail without key and heed user.signingkey x509' '
     + 	test_cmp expect dst/push-cert-status
     + '
     + 
     ++test_expect_success GPGSSH 'fail without key and heed user.signingkey ssh' '
     ++	test_config gpg.format ssh &&
     ++	prepare_dst &&
     ++	mkdir -p dst/.git/hooks &&
     ++	git -C dst config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	git -C dst config receive.certnonceseed sekrit &&
     ++	write_script dst/.git/hooks/post-receive <<-\EOF &&
     ++	# discard the update list
     ++	cat >/dev/null
     ++	# record the push certificate
     ++	if test -n "${GIT_PUSH_CERT-}"
     ++	then
     ++		git cat-file blob $GIT_PUSH_CERT >../push-cert
     ++	fi &&
     ++
     ++	cat >../push-cert-status <<E_O_F
     ++	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
     ++	KEY=${GIT_PUSH_CERT_KEY-nokey}
     ++	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
     ++	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
     ++	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
     ++	E_O_F
     ++
     ++	EOF
     ++
     ++	test_config user.email hasnokey@nowhere.com &&
     ++	test_config gpg.format ssh &&
     ++	
     ++	test_config user.signingkey "" &&
     ++	(
     ++		sane_unset GIT_COMMITTER_EMAIL &&
     ++		test_must_fail git push --signed dst noop ff +noff
     ++	) &&
     ++	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     ++	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
     ++	git push --signed dst noop ff +noff &&
     ++
     ++	(
     ++		cat <<-\EOF &&
     ++		SIGNER=principal_1
     ++		KEY=FINGERPRINT
     ++		STATUS=G
     ++		NONCE_STATUS=OK
     ++		EOF
     ++		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
     ++	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
     ++
     ++	noop=$(git rev-parse noop) &&
     ++	ff=$(git rev-parse ff) &&
     ++	noff=$(git rev-parse noff) &&
     ++	grep "$noop $ff refs/heads/ff" dst/push-cert &&
     ++	grep "$noop $noff refs/heads/noff" dst/push-cert &&
     ++	test_cmp expect dst/push-cert-status
     ++'
     ++
     + test_expect_success GPG 'failed atomic push does not execute GPG' '
     + 	prepare_dst &&
     + 	git -C dst config receive.certnonceseed sekrit &&
     +
     + ## t/t7031-verify-tag-signed-ssh.sh (new) ##
     +@@
     ++#!/bin/sh
     ++
     ++test_description='signed tag tests'
     ++GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
     ++export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
     ++
     ++. ./test-lib.sh
     ++. "$TEST_DIRECTORY/lib-gpg.sh"
     ++
     ++test_expect_success GPGSSH 'create signed tags ssh' '
     ++	test_when_finished "test_unconfig commit.gpgsign" &&
     ++	test_config gpg.format ssh &&
     ++	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     ++
     ++	echo 1 >file && git add file &&
     ++	test_tick && git commit -m initial &&
     ++	git tag -s -m initial initial &&
     ++	git branch side &&
     ++
     ++	echo 2 >file && test_tick && git commit -a -m second &&
     ++	git tag -s -m second second &&
     ++
     ++	git checkout side &&
     ++	echo 3 >elif && git add elif &&
     ++	test_tick && git commit -m "third on side" &&
     ++
     ++	git checkout main &&
     ++	test_tick && git merge -S side &&
     ++	git tag -s -m merge merge &&
     ++
     ++	echo 4 >file && test_tick && git commit -a -S -m "fourth unsigned" &&
     ++	git tag -a -m fourth-unsigned fourth-unsigned &&
     ++
     ++	test_tick && git commit --amend -S -m "fourth signed" &&
     ++	git tag -s -m fourth fourth-signed &&
     ++
     ++	echo 5 >file && test_tick && git commit -a -m "fifth" &&
     ++	git tag fifth-unsigned &&
     ++
     ++	git config commit.gpgsign true &&
     ++	echo 6 >file && test_tick && git commit -a -m "sixth" &&
     ++	git tag -a -m sixth sixth-unsigned &&
     ++
     ++	test_tick && git rebase -f HEAD^^ && git tag -s -m 6th sixth-signed HEAD^ &&
     ++	git tag -m seventh -s seventh-signed &&
     ++
     ++	echo 8 >file && test_tick && git commit -a -m eighth &&
     ++	git tag -u"${SIGNING_KEY_UNTRUSTED}" -m eighth eighth-signed-alt
     ++'
     ++
     ++test_expect_success GPGSSH 'verify and show ssh signatures' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.mintrustlevel UNDEFINED &&
     ++	(
     ++		for tag in initial second merge fourth-signed sixth-signed seventh-signed
     ++		do
     ++			git verify-tag $tag 2>actual &&
     ++			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
     ++			! grep "${BAD_SIGNATURE}" actual &&
     ++			echo $tag OK || exit 1
     ++		done
     ++	) &&
     ++	(
     ++		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
     ++		do
     ++			test_must_fail git verify-tag $tag 2>actual &&
     ++			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
     ++			! grep "${BAD_SIGNATURE}" actual &&
     ++			echo $tag OK || exit 1
     ++		done
     ++	) &&
     ++	(
     ++		for tag in eighth-signed-alt
     ++		do
     ++			git verify-tag $tag 2>actual &&
     ++			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
     ++			! grep "${BAD_SIGNATURE}" actual &&
     ++			grep "${KEY_NOT_TRUSTED}" actual &&
     ++			echo $tag OK || exit 1
     ++		done
     ++	)
     ++'
     ++
     ++test_expect_success GPGSSH 'detect fudged ssh signature' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	git cat-file tag seventh-signed >raw &&
     ++	sed -e "/^tag / s/seventh/7th forged/" raw >forged1 &&
     ++	git hash-object -w -t tag forged1 >forged1.tag &&
     ++	test_must_fail git verify-tag $(cat forged1.tag) 2>actual1 &&
     ++	grep "${BAD_SIGNATURE}" actual1 &&
     ++	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
     ++	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
     ++'
     ++
     ++# test_expect_success GPGSSH 'verify ssh signatures with --raw' '
     ++# 	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++# 	(
     ++# 		for tag in initial second merge fourth-signed sixth-signed seventh-signed
     ++# 		do
     ++# 			git verify-tag --raw $tag 2>actual &&
     ++# 			grep "GOODSIG" actual &&
     ++# 			! grep "BADSIG" actual &&
     ++# 			echo $tag OK || exit 1
     ++# 		done
     ++# 	) &&
     ++# 	(
     ++# 		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
     ++# 		do
     ++# 			test_must_fail git verify-tag --raw $tag 2>actual &&
     ++# 			! grep "GOODSIG" actual &&
     ++# 			! grep "BADSIG" actual &&
     ++# 			echo $tag OK || exit 1
     ++# 		done
     ++# 	) &&
     ++# 	(
     ++# 		for tag in eighth-signed-alt
     ++# 		do
     ++# 			git verify-tag --raw $tag 2>actual &&
     ++# 			grep "GOODSIG" actual &&
     ++# 			! grep "BADSIG" actual &&
     ++# 			grep "TRUST_UNDEFINED" actual &&
     ++# 			echo $tag OK || exit 1
     ++# 		done
     ++# 	)
     ++# '
     ++
     ++# test_expect_success GPGSM 'verify signatures with --raw x509' '
     ++# 	git verify-tag --raw ninth-signed-x509 2>actual &&
     ++# 	grep "GOODSIG" actual &&
     ++# 	! grep "BADSIG" actual &&
     ++# 	echo ninth-signed-x509 OK
     ++# '
     ++
     ++# test_expect_success GPGSSH 'verify multiple tags' '
     ++# 	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++# 	tags="fourth-signed sixth-signed seventh-signed" &&
     ++# 	for i in $tags
     ++# 	do
     ++# 		git verify-tag -v --raw $i || return 1
     ++# 	done >expect.stdout 2>expect.stderr.1 &&
     ++# 	grep "^.GNUPG:." <expect.stderr.1 >expect.stderr &&
     ++# 	git verify-tag -v --raw $tags >actual.stdout 2>actual.stderr.1 &&
     ++# 	grep "^.GNUPG:." <actual.stderr.1 >actual.stderr &&
     ++# 	test_cmp expect.stdout actual.stdout &&
     ++# 	test_cmp expect.stderr actual.stderr
     ++# '
     ++
     ++# test_expect_success GPGSM 'verify multiple tags x509' '
     ++#	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++# 	tags="seventh-signed ninth-signed-x509" &&
     ++# 	for i in $tags
     ++# 	do
     ++# 		git verify-tag -v --raw $i || return 1
     ++# 	done >expect.stdout 2>expect.stderr.1 &&
     ++# 	grep "^.GNUPG:." <expect.stderr.1 >expect.stderr &&
     ++# 	git verify-tag -v --raw $tags >actual.stdout 2>actual.stderr.1 &&
     ++# 	grep "^.GNUPG:." <actual.stderr.1 >actual.stderr &&
     ++# 	test_cmp expect.stdout actual.stdout &&
     ++# 	test_cmp expect.stderr actual.stderr
     ++# '
     ++
     ++test_expect_success GPGSSH 'verifying tag with --format' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	cat >expect <<-\EOF &&
     ++	tagname : fourth-signed
     ++	EOF
     ++	git verify-tag --format="tagname : %(tag)" "fourth-signed" >actual &&
     ++	test_cmp expect actual
     ++'
     ++
     ++test_expect_success GPGSSH 'verifying a forged tag with --format should fail silently' '
     ++	test_must_fail git verify-tag --format="tagname : %(tag)" $(cat forged1.tag) >actual-forged &&
     ++	test_must_be_empty actual-forged
     ++'
     ++
     ++test_done
     +
     + ## t/t7527-signed-commit-ssh.sh (new) ##
     +@@
     ++#!/bin/sh
     ++
     ++test_description='ssh signed commit tests'
     ++GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
     ++export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
     ++
     ++. ./test-lib.sh
     ++GNUPGHOME_NOT_USED=$GNUPGHOME
     ++. "$TEST_DIRECTORY/lib-gpg.sh"
     ++
     ++test_expect_success GPGSSH 'create signed commits' '
     ++	test_oid_cache <<-\EOF &&
     ++	header sha1:gpgsig
     ++	header sha256:gpgsig-sha256
     ++	EOF
     ++
     ++	test_when_finished "test_unconfig commit.gpgsign" &&
     ++	test_config gpg.format ssh &&
     ++	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     ++
     ++	echo 1 >file && git add file &&
     ++	test_tick && git commit -S -m initial &&
     ++	git tag initial &&
     ++	git branch side &&
     ++
     ++	echo 2 >file && test_tick && git commit -a -S -m second &&
     ++	git tag second &&
     ++
     ++	git checkout side &&
     ++	echo 3 >elif && git add elif &&
     ++	test_tick && git commit -m "third on side" &&
     ++
     ++	git checkout main &&
     ++	test_tick && git merge -S side &&
     ++	git tag merge &&
     ++
     ++	echo 4 >file && test_tick && git commit -a -m "fourth unsigned" &&
     ++	git tag fourth-unsigned &&
     ++
     ++	test_tick && git commit --amend -S -m "fourth signed" &&
     ++	git tag fourth-signed &&
     ++
     ++	git config commit.gpgsign true &&
     ++	echo 5 >file && test_tick && git commit -a -m "fifth signed" &&
     ++	git tag fifth-signed &&
     ++
     ++	git config commit.gpgsign false &&
     ++	echo 6 >file && test_tick && git commit -a -m "sixth" &&
     ++	git tag sixth-unsigned &&
     ++
     ++	git config commit.gpgsign true &&
     ++	echo 7 >file && test_tick && git commit -a -m "seventh" --no-gpg-sign &&
     ++	git tag seventh-unsigned &&
     ++
     ++	test_tick && git rebase -f HEAD^^ && git tag sixth-signed HEAD^ &&
     ++	git tag seventh-signed &&
     ++
     ++	echo 8 >file && test_tick && git commit -a -m eighth -S"${SIGNING_KEY_UNTRUSTED}" &&
     ++	git tag eighth-signed-alt &&
     ++
     ++	# commit.gpgsign is still on but this must not be signed
     ++	echo 9 | git commit-tree HEAD^{tree} >oid &&
     ++	test_line_count = 1 oid &&
     ++	git tag ninth-unsigned $(cat oid) &&
     ++	# explicit -S of course must sign.
     ++	echo 10 | git commit-tree -S HEAD^{tree} >oid &&
     ++	test_line_count = 1 oid &&
     ++	git tag tenth-signed $(cat oid) &&
     ++
     ++	# --gpg-sign[=<key-id>] must sign.
     ++	echo 11 | git commit-tree --gpg-sign HEAD^{tree} >oid &&
     ++	test_line_count = 1 oid &&
     ++	git tag eleventh-signed $(cat oid) &&
     ++	echo 12 | git commit-tree --gpg-sign="${SIGNING_KEY_UNTRUSTED}" HEAD^{tree} >oid &&
     ++	test_line_count = 1 oid &&
     ++	git tag twelfth-signed-alt $(cat oid)
     ++'
     ++
     ++test_expect_success GPGSSH 'verify and show signatures' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.mintrustlevel UNDEFINED &&
     ++	(
     ++		for commit in initial second merge fourth-signed \
     ++			fifth-signed sixth-signed seventh-signed tenth-signed \
     ++			eleventh-signed
     ++		do
     ++			git verify-commit $commit &&
     ++			git show --pretty=short --show-signature $commit >actual &&
     ++			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
     ++			! grep "${BAD_SIGNATURE}" actual &&
     ++			echo $commit OK || exit 1
     ++		done
     ++	) &&
     ++	(
     ++		for commit in merge^2 fourth-unsigned sixth-unsigned \
     ++			seventh-unsigned ninth-unsigned
     ++		do
     ++			test_must_fail git verify-commit $commit &&
     ++			git show --pretty=short --show-signature $commit >actual &&
     ++			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
     ++			! grep "${BAD_SIGNATURE}" actual &&
     ++			echo $commit OK || exit 1
     ++		done
     ++	) &&
     ++	(
     ++		for commit in eighth-signed-alt twelfth-signed-alt
     ++		do
     ++			git show --pretty=short --show-signature $commit >actual &&
     ++			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
     ++			! grep "${BAD_SIGNATURE}" actual &&
     ++			grep "${KEY_NOT_TRUSTED}" actual &&
     ++			echo $commit OK || exit 1
     ++		done
     ++	)
     ++'
     ++
     ++test_expect_success GPGSSH 'verify-commit exits success on untrusted signature' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	git verify-commit eighth-signed-alt 2>actual &&
     ++	grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
     ++	! grep "${BAD_SIGNATURE}" actual &&
     ++	grep "${KEY_NOT_TRUSTED}" actual
     ++'
     ++
     ++test_expect_success GPGSSH 'verify-commit exits success with matching minTrustLevel' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.minTrustLevel fully &&
     ++	git verify-commit sixth-signed
     ++'
     ++
     ++test_expect_success GPGSSH 'verify-commit exits success with low minTrustLevel' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.minTrustLevel marginal &&
     ++	git verify-commit sixth-signed
     ++'
     ++
     ++test_expect_success GPGSSH 'verify-commit exits failure with high minTrustLevel' '
     ++	test_config gpg.minTrustLevel ultimate &&
     ++	test_must_fail git verify-commit eighth-signed-alt
     ++'
     ++
     ++# test_expect_success GPGSSH 'verify signatures with --raw' '
     ++# 	(
     ++# 		for commit in initial second merge fourth-signed fifth-signed sixth-signed seventh-signed
     ++# 		do
     ++# 			git verify-commit --raw $commit 2>actual &&
     ++# 			grep "GOODSIG" actual &&
     ++# 			! grep "BADSIG" actual &&
     ++# 			echo $commit OK || exit 1
     ++# 		done
     ++# 	) &&
     ++# 	(
     ++# 		for commit in merge^2 fourth-unsigned sixth-unsigned seventh-unsigned
     ++# 		do
     ++# 			test_must_fail git verify-commit --raw $commit 2>actual &&
     ++# 			! grep "GOODSIG" actual &&
     ++# 			! grep "BADSIG" actual &&
     ++# 			echo $commit OK || exit 1
     ++# 		done
     ++# 	) &&
     ++# 	(
     ++# 		for commit in eighth-signed-alt
     ++# 		do
     ++# 			git verify-commit --raw $commit 2>actual &&
     ++# 			grep "GOODSIG" actual &&
     ++# 			! grep "BADSIG" actual &&
     ++# 			grep "TRUST_UNDEFINED" actual &&
     ++# 			echo $commit OK || exit 1
     ++# 		done
     ++# 	)
     ++# '
     ++
     ++test_expect_success GPGSSH 'proper header is used for hash algorithm' '
     ++	git cat-file commit fourth-signed >output &&
     ++	grep "^$(test_oid header) -----BEGIN SSH SIGNATURE-----" output
     ++'
     ++
     ++test_expect_success GPGSSH 'show signed commit with signature' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	git show -s initial >commit &&
     ++	git show -s --show-signature initial >show &&
     ++	git verify-commit -v initial >verify.1 2>verify.2 &&
     ++	git cat-file commit initial >cat &&
     ++	grep -v -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.commit &&
     ++	grep -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.gpg &&
     ++	grep -v "^ " cat | grep -v "^gpgsig.* " >cat.commit &&
     ++	test_cmp show.commit commit &&
     ++	test_cmp show.gpg verify.2 &&
     ++	test_cmp cat.commit verify.1
     ++'
     ++
     ++test_expect_success GPGSSH 'detect fudged signature' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	git cat-file commit seventh-signed >raw &&
     ++	sed -e "s/^seventh/7th forged/" raw >forged1 &&
     ++	git hash-object -w -t commit forged1 >forged1.commit &&
     ++	test_must_fail git verify-commit $(cat forged1.commit) &&
     ++	git show --pretty=short --show-signature $(cat forged1.commit) >actual1 &&
     ++	grep "${BAD_SIGNATURE}" actual1 &&
     ++	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
     ++	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
     ++'
     ++
     ++test_expect_success GPGSSH 'detect fudged signature with NUL' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	git cat-file commit seventh-signed >raw &&
     ++	cat raw >forged2 &&
     ++	echo Qwik | tr "Q" "\000" >>forged2 &&
     ++	git hash-object -w -t commit forged2 >forged2.commit &&
     ++	test_must_fail git verify-commit $(cat forged2.commit) &&
     ++	git show --pretty=short --show-signature $(cat forged2.commit) >actual2 &&
     ++	grep "${BAD_SIGNATURE}" actual2 &&
     ++	! grep "${GOOD_SIGNATURE_TRUSTED}" actual2
     ++'
     ++
     ++test_expect_success GPGSSH 'amending already signed commit' '
     ++	test_config gpg.format ssh &&
     ++	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	git checkout fourth-signed^0 &&
     ++	git commit --amend -S --no-edit &&
     ++	git verify-commit HEAD &&
     ++	git show -s --show-signature HEAD >actual &&
     ++	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
     ++	! grep "${BAD_SIGNATURE}" actual
     ++'
     ++
     ++test_expect_success GPGSSH 'show good signature with custom format' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
     ++	cat >expect.tmpl <<-\EOF &&
     ++	G
     ++	FINGERPRINT
     ++	principal_1
     ++	FINGERPRINT
     ++	
     ++	EOF
     ++	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
     ++	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
     ++	test_cmp expect actual
     ++'
     ++
     ++test_expect_success GPGSSH 'show bad signature with custom format' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	cat >expect <<-\EOF &&
     ++	B
     ++
     ++
     ++
     ++
     ++	EOF
     ++	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat forged1.commit) >actual &&
     ++	test_cmp expect actual
     ++'
     ++
     ++test_expect_success GPGSSH 'show untrusted signature with custom format' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	cat >expect.tmpl <<-\EOF &&
     ++	U
     ++	FINGERPRINT
     ++
     ++	FINGERPRINT
     ++	
     ++	EOF
     ++	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
     ++	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
     ++	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
     ++	test_cmp expect actual
     ++'
     ++
     ++test_expect_success GPGSSH 'show untrusted signature with undefined trust level' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	cat >expect.tmpl <<-\EOF &&
     ++	undefined
     ++	FINGERPRINT
     ++
     ++	FINGERPRINT
     ++
     ++	EOF
     ++	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
     ++	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
     ++	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
     ++	test_cmp expect actual
     ++'
     ++
     ++test_expect_success GPGSSH 'show untrusted signature with ultimate trust level' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	cat >expect.tmpl <<-\EOF &&
     ++	fully
     ++	FINGERPRINT
     ++	principal_1
     ++	FINGERPRINT
     ++
     ++	EOF
     ++	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
     ++	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
     ++	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
     ++	test_cmp expect actual
     ++'
     ++
     ++test_expect_success GPGSSH 'show lack of signature with custom format' '
     ++	cat >expect <<-\EOF &&
     ++	N
     ++
     ++
     ++
     ++
     ++	EOF
     ++	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" seventh-unsigned >actual &&
     ++	test_cmp expect actual
     ++'
     ++
     ++test_expect_success GPGSSH 'log.showsignature behaves like --show-signature' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config log.showsignature true &&
     ++	git show initial >actual &&
     ++	grep "${GOOD_SIGNATURE_TRUSTED}" actual
     ++'
     ++
     ++test_expect_success GPGSSH 'check config gpg.format values' '
     ++	test_config gpg.format ssh &&
     ++	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     ++	test_config gpg.format ssh &&
     ++	git commit -S --amend -m "success" &&
     ++	test_config gpg.format OpEnPgP &&
     ++	test_must_fail git commit -S --amend -m "fail"
     ++'
     ++
     ++# test_expect_success GPGSSH 'detect fudged commit with double signature' '
     ++# 	sed -e "/gpgsig/,/END PGP/d" forged1 >double-base &&
     ++# 	sed -n -e "/gpgsig/,/END PGP/p" forged1 | \
     ++# 		sed -e "s/^$(test_oid header)//;s/^ //" | gpg --dearmor >double-sig1.sig &&
     ++# 	gpg -o double-sig2.sig -u 29472784 --detach-sign double-base &&
     ++# 	cat double-sig1.sig double-sig2.sig | gpg --enarmor >double-combined.asc &&
     ++# 	sed -e "s/^\(-.*\)ARMORED FILE/\1SIGNATURE/;1s/^/$(test_oid header) /;2,\$s/^/ /" \
     ++# 		double-combined.asc > double-gpgsig &&
     ++# 	sed -e "/committer/r double-gpgsig" double-base >double-commit &&
     ++# 	git hash-object -w -t commit double-commit >double-commit.commit &&
     ++# 	test_must_fail git verify-commit $(cat double-commit.commit) &&
     ++# 	git show --pretty=short --show-signature $(cat double-commit.commit) >double-actual &&
     ++# 	grep "BAD signature from" double-actual &&
     ++# 	grep "Good signature from" double-actual
     ++# '
     ++
     ++# test_expect_success GPGSSH 'show double signature with custom format' '
     ++# 	cat >expect <<-\EOF &&
     ++# 	E
     ++
     ++
     ++
     ++
     ++# 	EOF
     ++# 	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat double-commit.commit) >actual &&
     ++# 	test_cmp expect actual
     ++# '
     ++
     ++
     ++# test_expect_success GPGSSH 'verify-commit verifies multiply signed commits' '
     ++# 	git init multiply-signed &&
     ++# 	cd multiply-signed &&
     ++# 	test_commit first &&
     ++# 	echo 1 >second &&
     ++# 	git add second &&
     ++# 	tree=$(git write-tree) &&
     ++# 	parent=$(git rev-parse HEAD^{commit}) &&
     ++# 	git commit --gpg-sign -m second &&
     ++# 	git cat-file commit HEAD &&
     ++# 	# Avoid trailing whitespace.
     ++# 	sed -e "s/^Q//" -e "s/^Z/ /" >commit <<-EOF &&
     ++# 	Qtree $tree
     ++# 	Qparent $parent
     ++# 	Qauthor A U Thor <author@example.com> 1112912653 -0700
     ++# 	Qcommitter C O Mitter <committer@example.com> 1112912653 -0700
     ++# 	Qgpgsig -----BEGIN PGP SIGNATURE-----
     ++# 	QZ
     ++# 	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBDRYcY29tbWl0dGVy
     ++# 	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMNd+8AoK1I8mhLHviPH+q2I5fIVgPsEtYC
     ++# 	Q AKCTqBh+VabJceXcGIZuF0Ry+udbBQ==
     ++# 	Q =tQ0N
     ++# 	Q -----END PGP SIGNATURE-----
     ++# 	Qgpgsig-sha256 -----BEGIN PGP SIGNATURE-----
     ++# 	QZ
     ++# 	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBIBYcY29tbWl0dGVy
     ++# 	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMN/NEAn0XO9RYSBj2dFyozi0JKSbssYMtO
     ++# 	Q AJwKCQ1BQOtuwz//IjU8TiS+6S4iUw==
     ++# 	Q =pIwP
     ++# 	Q -----END PGP SIGNATURE-----
     ++# 	Q
     ++# 	Qsecond
     ++# 	EOF
     ++# 	head=$(git hash-object -t commit -w commit) &&
     ++# 	git reset --hard $head &&
     ++# 	git verify-commit $head 2>actual &&
     ++# 	grep "Good signature from" actual &&
     ++# 	! grep "BAD signature from" actual
     ++# '
     ++
     ++test_done


 Documentation/config/gpg.txt     |  35 ++-
 Documentation/config/user.txt    |   6 +
 builtin/receive-pack.c           |   4 +-
 fmt-merge-msg.c                  |   4 +-
 gpg-interface.c                  | 414 +++++++++++++++++++++++++++----
 gpg-interface.h                  |  12 +-
 log-tree.c                       |   8 +-
 pretty.c                         |   4 +-
 send-pack.c                      |   6 +-
 t/lib-gpg.sh                     |  27 ++
 t/t4202-log.sh                   |  17 ++
 t/t5534-push-signed.sh           | 102 ++++++++
 t/t7031-verify-tag-signed-ssh.sh | 176 +++++++++++++
 t/t7527-signed-commit-ssh.sh     | 398 +++++++++++++++++++++++++++++
 14 files changed, 1147 insertions(+), 66 deletions(-)
 create mode 100755 t/t7031-verify-tag-signed-ssh.sh
 create mode 100755 t/t7527-signed-commit-ssh.sh

diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
index d94025cb368..c2bc4d06a66 100644
--- a/Documentation/config/gpg.txt
+++ b/Documentation/config/gpg.txt
@@ -11,13 +11,13 @@ gpg.program::
 
 gpg.format::
 	Specifies which key format to use when signing with `--gpg-sign`.
-	Default is "openpgp" and another possible value is "x509".
+	Default is "openpgp". Other possible values are "x509", "ssh".
 
 gpg.<format>.program::
 	Use this to customize the program used for the signing format you
 	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
 	be used as a legacy synonym for `gpg.openpgp.program`. The default
-	value for `gpg.x509.program` is "gpgsm".
+	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
 
 gpg.minTrustLevel::
 	Specifies a minimum trust level for signature verification.  If
@@ -33,3 +33,34 @@ gpg.minTrustLevel::
 * `marginal`
 * `fully`
 * `ultimate`
+
+gpg.ssh.keyring::
+	A file containing all valid SSH public signing keys. 
+	Similar to an .ssh/authorized_keys file.
+	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
+	If a signing key is found in this file then the trust level will
+	be set to "fully". Otherwise if the key is not present
+	but the signature is still valid then the trust level will be "undefined".
+
+	This file can be set to a location outside of the repository
+	and every developer maintains their own trust store.
+	A central repository server could generate this file automatically
+	from ssh keys with push	access to verify the code against.
+	In a corporate setting this file is probably generated at a global location
+	from some automation that already handles developer ssh keys. 
+	
+	A repository that is only allowing signed commits can store the file 
+	in the repository itself using a relative path. This way only committers
+	with an already valid key can add or change keys in the keyring.
+
+	Using a SSH CA key with the cert-authority option 
+	(see ssh-keygen(1) "CERTIFICATES") is also valid.
+
+	To revoke a key place the public key without the principal into the 
+	revocationKeyring.
+
+gpg.ssh.revocationKeyring::
+	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
+	See ssh-keygen(1) for details.
+	If a public key is found in this file then it will always be treated
+	as having trust level "never" and signatures will show as invalid.
diff --git a/Documentation/config/user.txt b/Documentation/config/user.txt
index 59aec7c3aed..e71a099b8b8 100644
--- a/Documentation/config/user.txt
+++ b/Documentation/config/user.txt
@@ -36,3 +36,9 @@ user.signingKey::
 	commit, you can override the default selection with this variable.
 	This option is passed unchanged to gpg's --local-user parameter,
 	so you may specify a key using any method that gpg supports.
+	If gpg.format is set to "ssh" this can contain the literal ssh public
+	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and 
+	corresponds to the private key used for signing. The private key 
+	needs to be available via ssh-agent. Alternatively it can be set to
+	a file containing a private key directly. If not set git will call 
+	"ssh-add -L" and try to use the first key available.
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index a34742513ac..fd790f7fd72 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -131,6 +131,8 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 {
 	int status = parse_hide_refs_config(var, value, "receive");
 
+	git_gpg_config(var, value, NULL);
+
 	if (status)
 		return status;
 
@@ -767,7 +769,7 @@ static void prepare_push_cert_sha1(struct child_process *proc)
 		bogs = parse_signed_buffer(push_cert.buf, push_cert.len);
 		check_signature(push_cert.buf, bogs, push_cert.buf + bogs,
 				push_cert.len - bogs, &sigcheck);
-
+		
 		nonce_status = check_nonce(push_cert.buf, bogs);
 	}
 	if (!is_null_oid(&push_cert_oid)) {
diff --git a/fmt-merge-msg.c b/fmt-merge-msg.c
index 0f66818e0f8..1d7b64fa021 100644
--- a/fmt-merge-msg.c
+++ b/fmt-merge-msg.c
@@ -527,10 +527,10 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 			len = payload.len;
 			if (check_signature(payload.buf, payload.len, sig.buf,
 					 sig.len, &sigc) &&
-				!sigc.gpg_output)
+				!sigc.output)
 				strbuf_addstr(&sig, "gpg verification failed.\n");
 			else
-				strbuf_addstr(&sig, sigc.gpg_output);
+				strbuf_addstr(&sig, sigc.output);
 		}
 		signature_check_clear(&sigc);
 
diff --git a/gpg-interface.c b/gpg-interface.c
index 127aecfc2b0..3b1a350bcfd 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -3,11 +3,13 @@
 #include "config.h"
 #include "run-command.h"
 #include "strbuf.h"
+#include "dir.h"
 #include "gpg-interface.h"
 #include "sigchain.h"
 #include "tempfile.h"
 
 static char *configured_signing_key;
+const char *ssh_allowed_signers, *ssh_revocation_file;
 static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
 
 struct gpg_format {
@@ -35,6 +37,14 @@ static const char *x509_sigs[] = {
 	NULL
 };
 
+static const char *ssh_verify_args[] = {
+	NULL
+};
+static const char *ssh_sigs[] = {
+	"-----BEGIN SSH SIGNATURE-----",
+	NULL
+};
+
 static struct gpg_format gpg_format[] = {
 	{ .name = "openpgp", .program = "gpg",
 	  .verify_args = openpgp_verify_args,
@@ -44,6 +54,9 @@ static struct gpg_format gpg_format[] = {
 	  .verify_args = x509_verify_args,
 	  .sigs = x509_sigs
 	},
+	{ .name = "ssh", .program = "ssh-keygen",
+	  .verify_args = ssh_verify_args,
+	  .sigs = ssh_sigs },
 };
 
 static struct gpg_format *use_format = &gpg_format[0];
@@ -72,6 +85,7 @@ static struct gpg_format *get_format_by_sig(const char *sig)
 void signature_check_clear(struct signature_check *sigc)
 {
 	FREE_AND_NULL(sigc->payload);
+	FREE_AND_NULL(sigc->output);
 	FREE_AND_NULL(sigc->gpg_output);
 	FREE_AND_NULL(sigc->gpg_status);
 	FREE_AND_NULL(sigc->signer);
@@ -144,6 +158,53 @@ static int parse_gpg_trust_level(const char *level,
 	return 1;
 }
 
+static void parse_ssh_output(struct signature_check *sigc)
+{
+	const char *output = NULL;
+	char *next = NULL;
+
+	/* ssh-keysign output should be:
+	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
+	 * or for valid but unknown keys:
+	 * Good "git" signature with RSA key SHA256:FINGERPRINT
+	 */
+
+	output = xmemdupz(sigc->output, strcspn(sigc->output, " \n"));
+	if (skip_prefix(sigc->output, "Good \"git\" signature for ", &output)) {
+		// Valid signature for a trusted signer
+		sigc->result = 'G';
+		sigc->trust_level = TRUST_FULLY;
+
+		next = strchrnul(output, ' '); // 'principal'
+		replace_cstring(&sigc->signer, output, next);
+		output = next + 1;
+		next = strchrnul(output, ' '); // 'with'
+		output = next + 1;
+		next = strchrnul(output, ' '); // KEY Type
+		output = next + 1;
+		next = strchrnul(output, ' '); // 'key'
+		output = next + 1;
+		next = strchrnul(output, '\n'); // key
+		replace_cstring(&sigc->fingerprint, output, next);
+		replace_cstring(&sigc->key, output, next);
+	} else if (skip_prefix(sigc->output, "Good \"git\" signature with ", &output)) {
+		// Valid signature, but key unknown
+		sigc->result = 'G';
+		sigc->trust_level = TRUST_UNDEFINED;
+
+		next = strchrnul(output, ' '); // KEY Type
+		output = next + 1;
+		next = strchrnul(output, ' '); // 'key'
+		output = next + 1;
+		next = strchrnul(output, '\n'); // key
+		replace_cstring(&sigc->fingerprint, output, next);
+		replace_cstring(&sigc->key, output, next);
+	} else {
+		sigc->result = 'B';
+		sigc->trust_level = TRUST_NEVER;
+	}
+}
+
 static void parse_gpg_output(struct signature_check *sigc)
 {
 	const char *buf = sigc->gpg_status;
@@ -257,16 +318,18 @@ error:
 	FREE_AND_NULL(sigc->key);
 }
 
-static int verify_signed_buffer(const char *payload, size_t payload_size,
-				const char *signature, size_t signature_size,
-				struct strbuf *gpg_output,
-				struct strbuf *gpg_status)
+static int verify_ssh_signature(struct signature_check *sigc, struct gpg_format *fmt,
+	const char *payload, size_t payload_size,
+	const char *signature, size_t signature_size)
 {
-	struct child_process gpg = CHILD_PROCESS_INIT;
-	struct gpg_format *fmt;
+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
 	struct tempfile *temp;
 	int ret;
-	struct strbuf buf = STRBUF_INIT;
+	const char *line;
+	size_t trust_size;
+	char *principal;
+	struct strbuf ssh_keygen_out = STRBUF_INIT;
+	struct strbuf ssh_keygen_err = STRBUF_INIT;
 
 	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
 	if (!temp)
@@ -279,29 +342,125 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 		return -1;
 	}
 
-	fmt = get_format_by_sig(signature);
-	if (!fmt)
-		BUG("bad signature '%s'", signature);
+	// Find the principal from the  signers
+	strvec_pushl(&ssh_keygen.args,  fmt->program,
+					"-Y", "find-principals",
+					"-f", get_ssh_allowed_signers(),
+					"-s", temp->filename.buf,
+					NULL);
+	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
+	if (strstr(ssh_keygen_err.buf, "unknown option")) {
+		error(_("openssh version > 8.2p1 is needed for ssh signature verification (ssh-keygen needs -Y find-principals/verify option)"));
+	}
+	if (ret || !ssh_keygen_out.len) {
+		// We did not find a matching principal in the keyring - Check without validation
+		child_process_init(&ssh_keygen);
+		strvec_pushl(&ssh_keygen.args,  fmt->program,
+						"-Y", "check-novalidate",
+						"-n", "git",
+						"-s", temp->filename.buf,
+						NULL);
+		ret = pipe_command(&ssh_keygen, payload, payload_size, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
+	} else {
+		// Check every principal we found (one per line)
+		for (line = ssh_keygen_out.buf; *line; line = strchrnul(line + 1, '\n')) {
+			while (*line == '\n')
+				line++;
+			if (!*line)
+				break;
+
+			trust_size = strcspn(line, " \n");
+			principal = xmemdupz(line, trust_size);
+
+			child_process_init(&ssh_keygen);
+			strbuf_release(&ssh_keygen_out);
+			strbuf_release(&ssh_keygen_err);
+			strvec_push(&ssh_keygen.args,fmt->program);
+			// We found principals - Try with each until we find a match
+			strvec_pushl(&ssh_keygen.args,  "-Y", "verify",
+							//TODO: sprintf("-Overify-time=%s", commit->date...),
+							"-n", "git",
+							"-f", get_ssh_allowed_signers(),
+							"-I", principal,
+							"-s", temp->filename.buf,
+							NULL);
+
+			if (ssh_revocation_file && file_exists(ssh_revocation_file)) {
+				strvec_pushl(&ssh_keygen.args, "-r", ssh_revocation_file, NULL);
+			}
+
+			sigchain_push(SIGPIPE, SIG_IGN);
+			ret = pipe_command(&ssh_keygen, payload, payload_size,
+					&ssh_keygen_out, 0, &ssh_keygen_err, 0);
+			sigchain_pop(SIGPIPE);
+
+			ret &= starts_with(ssh_keygen_out.buf, "Good");
+			if (ret == 0)
+				break;
+		}
+	}
+
+	sigc->payload = xmemdupz(payload, payload_size);
+	strbuf_stripspace(&ssh_keygen_out, 0);
+	strbuf_stripspace(&ssh_keygen_err, 0);
+	strbuf_add(&ssh_keygen_out, ssh_keygen_err.buf, ssh_keygen_err.len);
+	sigc->output = strbuf_detach(&ssh_keygen_out, NULL);
+
+	//sigc->gpg_output = strbuf_detach(&ssh_keygen_err, NULL); // This flip around is broken...
+	sigc->gpg_status = strbuf_detach(&ssh_keygen_out, NULL);
+
+	parse_ssh_output(sigc);
+
+	delete_tempfile(&temp);
+	strbuf_release(&ssh_keygen_out);
+	strbuf_release(&ssh_keygen_err);
+
+	return ret;
+}
+
+static int verify_gpg_signature(struct signature_check *sigc, struct gpg_format *fmt, 
+	const char *payload, size_t payload_size,
+	const char *signature, size_t signature_size)
+{
+	struct child_process gpg = CHILD_PROCESS_INIT;
+	struct tempfile *temp;
+	int ret;
+	struct strbuf gpg_out = STRBUF_INIT;
+	struct strbuf gpg_err = STRBUF_INIT;
+
+	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
+	if (!temp)
+		return error_errno(_("could not create temporary file"));
+	if (write_in_full(temp->fd, signature, signature_size) < 0 ||
+	    close_tempfile_gently(temp) < 0) {
+		error_errno(_("failed writing detached signature to '%s'"),
+			    temp->filename.buf);
+		delete_tempfile(&temp);
+		return -1;
+	}
 
 	strvec_push(&gpg.args, fmt->program);
 	strvec_pushv(&gpg.args, fmt->verify_args);
 	strvec_pushl(&gpg.args,
-		     "--status-fd=1",
-		     "--verify", temp->filename.buf, "-",
-		     NULL);
-
-	if (!gpg_status)
-		gpg_status = &buf;
+			"--status-fd=1",
+			"--verify", temp->filename.buf, "-",
+			NULL);
 
 	sigchain_push(SIGPIPE, SIG_IGN);
-	ret = pipe_command(&gpg, payload, payload_size,
-			   gpg_status, 0, gpg_output, 0);
+	ret = pipe_command(&gpg, payload, payload_size, &gpg_out, 0,
+				&gpg_err, 0);
 	sigchain_pop(SIGPIPE);
+	ret |= !strstr(gpg_out.buf, "\n[GNUPG:] GOODSIG ");
 
-	delete_tempfile(&temp);
+	sigc->payload = xmemdupz(payload, payload_size);
+	sigc->output = strbuf_detach(&gpg_err, NULL);
+	sigc->gpg_status = strbuf_detach(&gpg_out, NULL);
 
-	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
-	strbuf_release(&buf); /* no matter it was used or not */
+	parse_gpg_output(sigc);
+
+	delete_tempfile(&temp);
+	strbuf_release(&gpg_out);
+	strbuf_release(&gpg_err);
 
 	return ret;
 }
@@ -309,35 +468,34 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 int check_signature(const char *payload, size_t plen, const char *signature,
 	size_t slen, struct signature_check *sigc)
 {
-	struct strbuf gpg_output = STRBUF_INIT;
-	struct strbuf gpg_status = STRBUF_INIT;
+	struct gpg_format *fmt;
 	int status;
 
 	sigc->result = 'N';
 	sigc->trust_level = -1;
 
-	status = verify_signed_buffer(payload, plen, signature, slen,
-				      &gpg_output, &gpg_status);
-	if (status && !gpg_output.len)
-		goto out;
-	sigc->payload = xmemdupz(payload, plen);
-	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
-	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
-	parse_gpg_output(sigc);
+	fmt = get_format_by_sig(signature);
+	if (!fmt)
+		BUG("bad signature '%s'", signature);
+
+	if (!strcmp(fmt->name, "ssh")) {
+		status = verify_ssh_signature(sigc, fmt, payload, plen, signature, slen);
+	} else {
+		status = verify_gpg_signature(sigc, fmt, payload, plen, signature, slen);
+	}
+	if (status && !sigc->gpg_output)
+		return !!status;
+
 	status |= sigc->result != 'G';
 	status |= sigc->trust_level < configured_min_trust_level;
 
- out:
-	strbuf_release(&gpg_status);
-	strbuf_release(&gpg_output);
-
 	return !!status;
 }
 
 void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
 {
 	const char *output = flags & GPG_VERIFY_RAW ?
-		sigc->gpg_status : sigc->gpg_output;
+		sigc->gpg_status : sigc->output;
 
 	if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
 		fputs(sigc->payload, stdout);
@@ -388,12 +546,31 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	int ret;
 
 	if (!strcmp(var, "user.signingkey")) {
+		/* user.signingkey can contain one of the following
+		 * when format = openpgp/x509
+		 *   - GPG KeyID
+		 * when format = ssh
+		 *   - literal ssh public key (e.g. ssh-rsa XXXKEYXXX comment)
+		 *   - path to a file containing a public or a private ssh key
+		 */
 		if (!value)
 			return config_error_nonbool(var);
 		set_signing_key(value);
 		return 0;
 	}
 
+	if (!strcmp(var, "gpg.ssh.keyring")) {
+		if (!value)
+			return config_error_nonbool(var);
+		return git_config_string(&ssh_allowed_signers, var, value);
+	}
+
+	if (!strcmp(var, "gpg.ssh.revocationkeyring")) {
+		if (!value)
+			return config_error_nonbool(var);
+		return git_config_string(&ssh_revocation_file, var, value);
+	}
+
 	if (!strcmp(var, "gpg.format")) {
 		if (!value)
 			return config_error_nonbool(var);
@@ -425,6 +602,9 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	if (!strcmp(var, "gpg.x509.program"))
 		fmtname = "x509";
 
+	if (!strcmp(var, "gpg.ssh.program"))
+		fmtname = "ssh";
+
 	if (fmtname) {
 		fmt = get_format_by_name(fmtname);
 		return git_config_string(&fmt->program, var, value);
@@ -433,11 +613,80 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	return 0;
 }
 
+static char *get_ssh_key_fingerprint(const char *signing_key) {
+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf fingerprint_stdout = STRBUF_INIT;
+	struct strbuf **fingerprint;
+
+	/* For SSH Signing this can contain a filename or a public key
+	* For textual representation we usually want a fingerprint
+	*/
+	if (istarts_with(signing_key, "ssh-")) {
+		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
+					"-lf", "-",
+					NULL);
+		ret = pipe_command(&ssh_keygen, signing_key, strlen(signing_key), &fingerprint_stdout, 0,  NULL, 0);
+	} else {
+		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
+					"-lf", configured_signing_key,
+					NULL);
+		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0, NULL, 0);
+		if (!!ret)
+			die_errno(_("failed to get the ssh fingerprint for key '%s'"), signing_key);
+		fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
+		if (fingerprint[1]) {
+			return strbuf_detach(fingerprint[1], NULL);
+		}
+	}
+	die_errno(_("failed to get the ssh fingerprint for key '%s'"), signing_key);
+}
+
+// Returns the first public key from an ssh-agent to use for signing
+static char *get_default_ssh_signing_key(void) {
+	struct child_process ssh_add = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf key_stdout = STRBUF_INIT;
+	struct strbuf **keys;
+
+	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
+	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
+	if (!ret) { 
+		keys = strbuf_split_max(&key_stdout, '\n', 2);
+		if (keys[0])
+			return strbuf_detach(keys[0], NULL);
+	}
+
+	return "";
+}
+
+// Returns a textual but unique representation ot the signing key
+const char *get_signing_key_id(void) {
+	if (!strcmp(use_format->name, "ssh")) {
+		return get_ssh_key_fingerprint(get_signing_key());
+	} else {
+		// GPG/GPGSM only store a key id on this variable
+		return get_signing_key();
+	}
+}
+
 const char *get_signing_key(void)
 {
 	if (configured_signing_key)
 		return configured_signing_key;
-	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
+	if (!strcmp(use_format->name, "ssh")) {
+		return get_default_ssh_signing_key();
+	} else {
+		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
+	}
+}
+
+const char *get_ssh_allowed_signers(void)
+{
+	if (ssh_allowed_signers)
+		return ssh_allowed_signers;
+
+	die("A Path to an allowed signers ssh keyring is needed for validation");
 }
 
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
@@ -446,25 +695,88 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
 	int ret;
 	size_t i, j, bottom;
 	struct strbuf gpg_status = STRBUF_INIT;
+	struct tempfile *temp = NULL, *buffer_file = NULL;
+	char *ssh_signing_key_file = NULL;
+	struct strbuf ssh_signature_filename = STRBUF_INIT;
+
+	if (!strcmp(use_format->name, "ssh")) {
+		if (!signing_key || signing_key[0] == '\0')
+			return error(_("user.signingkey needs to be set for ssh signing"));
+
+
+		if (istarts_with(signing_key, "ssh-")) {
+			// A literal ssh key
+			temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
+			if (!temp)
+				return error_errno(_("could not create temporary file"));
+			if (write_in_full(temp->fd, signing_key, strlen(signing_key)) < 0 ||
+				close_tempfile_gently(temp) < 0) {
+				error_errno(_("failed writing ssh signing key to '%s'"), temp->filename.buf);
+				delete_tempfile(&temp);
+				return -1;
+			}
+			ssh_signing_key_file= temp->filename.buf;
+		} else {
+			// We assume a file
+			ssh_signing_key_file = expand_user_path(signing_key, 1);
+		}
 
-	strvec_pushl(&gpg.args,
-		     use_format->program,
-		     "--status-fd=2",
-		     "-bsau", signing_key,
-		     NULL);
+		buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
+		if (!buffer_file)
+			return error_errno(_("could not create temporary file"));
+		if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
+			close_tempfile_gently(buffer_file) < 0) {
+			error_errno(_("failed writing ssh signing key buffer to '%s'"), buffer_file->filename.buf);
+			delete_tempfile(&buffer_file);
+			return -1;
+		}
+
+		strvec_pushl(&gpg.args, use_format->program ,
+					"-Y", "sign",
+					"-n", "git",
+					"-f", ssh_signing_key_file,
+					buffer_file->filename.buf,
+					NULL);
+
+		sigchain_push(SIGPIPE, SIG_IGN);
+		ret = pipe_command(&gpg, NULL, 0, NULL, 0, &gpg_status, 0);
+		sigchain_pop(SIGPIPE);
+
+		strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
+		strbuf_addstr(&ssh_signature_filename, ".sig");
+		if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {
+			error_errno(_("failed reading ssh signing data buffer from '%s'"), ssh_signature_filename.buf);
+		}
+		unlink_or_warn(ssh_signature_filename.buf);
+		strbuf_release(&ssh_signature_filename);
+		delete_tempfile(&buffer_file);
+	} else {
+		strvec_pushl(&gpg.args, use_format->program ,
+					"--status-fd=2",
+					"-bsau", signing_key,
+					NULL);
+
+		/*
+		* When the username signingkey is bad, program could be terminated
+		* because gpg exits without reading and then write gets SIGPIPE.
+		*/
+		sigchain_push(SIGPIPE, SIG_IGN);
+		ret = pipe_command(&gpg, buffer->buf, buffer->len, signature, 1024, &gpg_status, 0);
+		sigchain_pop(SIGPIPE);
+	}
 
 	bottom = signature->len;
 
-	/*
-	 * When the username signingkey is bad, program could be terminated
-	 * because gpg exits without reading and then write gets SIGPIPE.
-	 */
-	sigchain_push(SIGPIPE, SIG_IGN);
-	ret = pipe_command(&gpg, buffer->buf, buffer->len,
-			   signature, 1024, &gpg_status, 0);
-	sigchain_pop(SIGPIPE);
+	if (temp)
+		delete_tempfile(&temp);
 
-	ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
+	if (!strcmp(use_format->name, "ssh")) {
+		if (strstr(gpg_status.buf, "unknown option")) {
+			error(_("openssh version > 8.2p1 is needed for ssh signing (ssh-keygen needs -Y sign option)"));
+		}
+	} else {
+		ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
+	}
 	strbuf_release(&gpg_status);
 	if (ret)
 		return error(_("gpg failed to sign the data"));
diff --git a/gpg-interface.h b/gpg-interface.h
index 80567e48948..03d56475b56 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -17,8 +17,9 @@ enum signature_trust_level {
 
 struct signature_check {
 	char *payload;
-	char *gpg_output;
-	char *gpg_status;
+	char *output;
+	char *gpg_output; // This will be printed in commit logs
+	char *gpg_status; // Only used internally -> remove
 
 	/*
 	 * possible "result":
@@ -64,6 +65,13 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
 int git_gpg_config(const char *, const char *, void *);
 void set_signing_key(const char *);
 const char *get_signing_key(void);
+
+/* Returns a textual unique representation of the signing key in use
+ * Either a GPG KeyID or a SSH Key Fingerprint
+ */
+const char *get_signing_key_id(void);
+
+const char *get_ssh_allowed_signers(void);
 int check_signature(const char *payload, size_t plen,
 		    const char *signature, size_t slen,
 		    struct signature_check *sigc);
diff --git a/log-tree.c b/log-tree.c
index 7b823786c2c..20af9bd1c82 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -513,10 +513,10 @@ static void show_signature(struct rev_info *opt, struct commit *commit)
 
 	status = check_signature(payload.buf, payload.len, signature.buf,
 				 signature.len, &sigc);
-	if (status && !sigc.gpg_output)
+	if (status && !sigc.output)
 		show_sig_lines(opt, status, "No signature\n");
 	else
-		show_sig_lines(opt, status, sigc.gpg_output);
+		show_sig_lines(opt, status, sigc.output);
 	signature_check_clear(&sigc);
 
  out:
@@ -583,8 +583,8 @@ static int show_one_mergetag(struct commit *commit,
 		/* could have a good signature */
 		status = check_signature(payload.buf, payload.len,
 					 signature.buf, signature.len, &sigc);
-		if (sigc.gpg_output)
-			strbuf_addstr(&verify_message, sigc.gpg_output);
+		if (sigc.output)
+			strbuf_addstr(&verify_message, sigc.output);
 		else
 			strbuf_addstr(&verify_message, "No signature\n");
 		signature_check_clear(&sigc);
diff --git a/pretty.c b/pretty.c
index b1ecd039cef..daa71394efd 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1432,8 +1432,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 			check_commit_signature(c->commit, &(c->signature_check));
 		switch (placeholder[1]) {
 		case 'G':
-			if (c->signature_check.gpg_output)
-				strbuf_addstr(sb, c->signature_check.gpg_output);
+			if (c->signature_check.output)
+				strbuf_addstr(sb, c->signature_check.output);
 			break;
 		case '?':
 			switch (c->signature_check.result) {
diff --git a/send-pack.c b/send-pack.c
index 9cb9f716509..c8fb0c30f87 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -342,12 +342,13 @@ static int generate_push_cert(struct strbuf *req_buf,
 	const struct ref *ref;
 	struct string_list_item *item;
 	char *signing_key = xstrdup(get_signing_key());
+	char *signing_key_id = xstrdup(get_signing_key_id());
 	const char *cp, *np;
 	struct strbuf cert = STRBUF_INIT;
 	int update_seen = 0;
-
+	
 	strbuf_addstr(&cert, "certificate version 0.1\n");
-	strbuf_addf(&cert, "pusher %s ", signing_key);
+	strbuf_addf(&cert, "pusher %s ", signing_key_id);
 	datestamp(&cert);
 	strbuf_addch(&cert, '\n');
 	if (args->url && *args->url) {
@@ -387,6 +388,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 
 free_return:
 	free(signing_key);
+	free(signing_key_id);
 	strbuf_release(&cert);
 	return update_seen;
 }
diff --git a/t/lib-gpg.sh b/t/lib-gpg.sh
index 9fc5241228e..96935582262 100644
--- a/t/lib-gpg.sh
+++ b/t/lib-gpg.sh
@@ -87,6 +87,33 @@ test_lazy_prereq RFC1991 '
 	echo | gpg --homedir "${GNUPGHOME}" -b --rfc1991 >/dev/null
 '
 
+test_lazy_prereq GPGSSH '
+	ssh_version=$(ssh-keygen -Y find-principals -n "git" 2>&1)
+	test $? != 127 || exit 1
+	echo $ssh_version | grep -q "find-principals:missing signature file"
+	test $? = 0 || exit 1; 
+	mkdir -p "${GNUPGHOME}" &&
+	chmod 0700 "${GNUPGHOME}" &&
+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/ed25519_ssh_signing_key" >/dev/null &&
+	ssh-keygen -t rsa -b 2048 -N "" -f "${GNUPGHOME}/rsa_2048_ssh_signing_key" >/dev/null &&
+	ssh-keygen -t ed25519 -N "super_secret" -f "${GNUPGHOME}/protected_ssh_signing_key" >/dev/null &&
+	find "${GNUPGHOME}" -name *ssh_signing_key.pub -exec cat {} \; | awk "{print \"principal_\" NR \" \" \$0}" > "${GNUPGHOME}/ssh.all_valid.keyring" &&
+	cat "${GNUPGHOME}/ssh.all_valid.keyring" &&
+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/untrusted_ssh_signing_key" >/dev/null
+'
+
+SIGNING_KEY_PRIMARY="${GNUPGHOME}/ed25519_ssh_signing_key"
+SIGNING_KEY_SECONDARY="${GNUPGHOME}/rsa_2048_ssh_signing_key"
+SIGNING_KEY_UNTRUSTED="${GNUPGHOME}/untrusted_ssh_signing_key"
+SIGNING_KEY_WITH_PASSPHRASE="${GNUPGHOME}/protected_ssh_signing_key"
+SIGNING_KEY_PASSPHRASE="super_secret"
+SIGNING_KEYRING="${GNUPGHOME}/ssh.all_valid.keyring"
+
+GOOD_SIGNATURE_TRUSTED='Good "git" signature for'
+GOOD_SIGNATURE_UNTRUSTED='Good "git" signature with'
+KEY_NOT_TRUSTED="No principal matched"
+BAD_SIGNATURE="Signature verification failed"
+
 sanitize_pgp() {
 	perl -ne '
 		/^-----END PGP/ and $in_pgp = 0;
diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index 350cfa35936..84227066685 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -1616,6 +1616,16 @@ test_expect_success GPGSM 'setup signed branch x509' '
 	git commit -S -m signed_commit
 '
 
+test_expect_success GPGSSH 'setup sshkey signed branch' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_when_finished "git reset --hard && git checkout main" &&
+	git checkout -b signed-ssh main &&
+	echo foo >foo &&
+	git add foo &&
+	git commit -S -m signed_commit
+'
+
 test_expect_success GPGSM 'log x509 fingerprint' '
 	echo "F8BF62E0693D0694816377099909C779FA23FD65 | " >expect &&
 	git log -n1 --format="%GF | %GP" signed-x509 >actual &&
@@ -1640,6 +1650,13 @@ test_expect_success GPGSM 'log --graph --show-signature x509' '
 	grep "^| gpgsm: Good signature" actual
 '
 
+test_expect_success GPGSSH 'log ssh key fingerprint' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	ssh-keygen -lf  "${SIGNING_KEY_PRIMARY}" | awk "{print \$2\" | \"}" >expect &&
+	git log -n1 --format="%GF | %GP" signed-ssh >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success GPG 'log --graph --show-signature for merged tag' '
 	test_when_finished "git reset --hard && git checkout main" &&
 	git checkout -b plain main &&
diff --git a/t/t5534-push-signed.sh b/t/t5534-push-signed.sh
index bba768f5ded..19b37e999b4 100755
--- a/t/t5534-push-signed.sh
+++ b/t/t5534-push-signed.sh
@@ -137,6 +137,53 @@ test_expect_success GPG 'signed push sends push certificate' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPGSSH 'ssh signed push sends push certificate' '
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=principal_1
+		KEY=FINGERPRINT
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
+
+	noop=$(git rev-parse noop) &&
+	ff=$(git rev-parse ff) &&
+	noff=$(git rev-parse noff) &&
+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_expect_success GPG 'inconsistent push options in signed push not allowed' '
 	# First, invoke receive-pack with dummy input to obtain its preamble.
 	prepare_dst &&
@@ -276,6 +323,61 @@ test_expect_success GPGSM 'fail without key and heed user.signingkey x509' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPGSSH 'fail without key and heed user.signingkey ssh' '
+	test_config gpg.format ssh &&
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	test_config user.email hasnokey@nowhere.com &&
+	test_config gpg.format ssh &&
+	
+	test_config user.signingkey "" &&
+	(
+		sane_unset GIT_COMMITTER_EMAIL &&
+		test_must_fail git push --signed dst noop ff +noff
+	) &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=principal_1
+		KEY=FINGERPRINT
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
+
+	noop=$(git rev-parse noop) &&
+	ff=$(git rev-parse ff) &&
+	noff=$(git rev-parse noff) &&
+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_expect_success GPG 'failed atomic push does not execute GPG' '
 	prepare_dst &&
 	git -C dst config receive.certnonceseed sekrit &&
diff --git a/t/t7031-verify-tag-signed-ssh.sh b/t/t7031-verify-tag-signed-ssh.sh
new file mode 100755
index 00000000000..d2b7a525584
--- /dev/null
+++ b/t/t7031-verify-tag-signed-ssh.sh
@@ -0,0 +1,176 @@
+#!/bin/sh
+
+test_description='signed tag tests'
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPGSSH 'create signed tags ssh' '
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+
+	echo 1 >file && git add file &&
+	test_tick && git commit -m initial &&
+	git tag -s -m initial initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -m second &&
+	git tag -s -m second second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout main &&
+	test_tick && git merge -S side &&
+	git tag -s -m merge merge &&
+
+	echo 4 >file && test_tick && git commit -a -S -m "fourth unsigned" &&
+	git tag -a -m fourth-unsigned fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag -s -m fourth fourth-signed &&
+
+	echo 5 >file && test_tick && git commit -a -m "fifth" &&
+	git tag fifth-unsigned &&
+
+	git config commit.gpgsign true &&
+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
+	git tag -a -m sixth sixth-unsigned &&
+
+	test_tick && git rebase -f HEAD^^ && git tag -s -m 6th sixth-signed HEAD^ &&
+	git tag -m seventh -s seventh-signed &&
+
+	echo 8 >file && test_tick && git commit -a -m eighth &&
+	git tag -u"${SIGNING_KEY_UNTRUSTED}" -m eighth eighth-signed-alt
+'
+
+test_expect_success GPGSSH 'verify and show ssh signatures' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	test_config gpg.mintrustlevel UNDEFINED &&
+	(
+		for tag in initial second merge fourth-signed sixth-signed seventh-signed
+		do
+			git verify-tag $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
+		do
+			test_must_fail git verify-tag $tag 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in eighth-signed-alt
+		do
+			git verify-tag $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			grep "${KEY_NOT_TRUSTED}" actual &&
+			echo $tag OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'detect fudged ssh signature' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git cat-file tag seventh-signed >raw &&
+	sed -e "/^tag / s/seventh/7th forged/" raw >forged1 &&
+	git hash-object -w -t tag forged1 >forged1.tag &&
+	test_must_fail git verify-tag $(cat forged1.tag) 2>actual1 &&
+	grep "${BAD_SIGNATURE}" actual1 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
+'
+
+# test_expect_success GPGSSH 'verify ssh signatures with --raw' '
+# 	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+# 	(
+# 		for tag in initial second merge fourth-signed sixth-signed seventh-signed
+# 		do
+# 			git verify-tag --raw $tag 2>actual &&
+# 			grep "GOODSIG" actual &&
+# 			! grep "BADSIG" actual &&
+# 			echo $tag OK || exit 1
+# 		done
+# 	) &&
+# 	(
+# 		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
+# 		do
+# 			test_must_fail git verify-tag --raw $tag 2>actual &&
+# 			! grep "GOODSIG" actual &&
+# 			! grep "BADSIG" actual &&
+# 			echo $tag OK || exit 1
+# 		done
+# 	) &&
+# 	(
+# 		for tag in eighth-signed-alt
+# 		do
+# 			git verify-tag --raw $tag 2>actual &&
+# 			grep "GOODSIG" actual &&
+# 			! grep "BADSIG" actual &&
+# 			grep "TRUST_UNDEFINED" actual &&
+# 			echo $tag OK || exit 1
+# 		done
+# 	)
+# '
+
+# test_expect_success GPGSM 'verify signatures with --raw x509' '
+# 	git verify-tag --raw ninth-signed-x509 2>actual &&
+# 	grep "GOODSIG" actual &&
+# 	! grep "BADSIG" actual &&
+# 	echo ninth-signed-x509 OK
+# '
+
+# test_expect_success GPGSSH 'verify multiple tags' '
+# 	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+# 	tags="fourth-signed sixth-signed seventh-signed" &&
+# 	for i in $tags
+# 	do
+# 		git verify-tag -v --raw $i || return 1
+# 	done >expect.stdout 2>expect.stderr.1 &&
+# 	grep "^.GNUPG:." <expect.stderr.1 >expect.stderr &&
+# 	git verify-tag -v --raw $tags >actual.stdout 2>actual.stderr.1 &&
+# 	grep "^.GNUPG:." <actual.stderr.1 >actual.stderr &&
+# 	test_cmp expect.stdout actual.stdout &&
+# 	test_cmp expect.stderr actual.stderr
+# '
+
+# test_expect_success GPGSM 'verify multiple tags x509' '
+#	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+# 	tags="seventh-signed ninth-signed-x509" &&
+# 	for i in $tags
+# 	do
+# 		git verify-tag -v --raw $i || return 1
+# 	done >expect.stdout 2>expect.stderr.1 &&
+# 	grep "^.GNUPG:." <expect.stderr.1 >expect.stderr &&
+# 	git verify-tag -v --raw $tags >actual.stdout 2>actual.stderr.1 &&
+# 	grep "^.GNUPG:." <actual.stderr.1 >actual.stderr &&
+# 	test_cmp expect.stdout actual.stdout &&
+# 	test_cmp expect.stderr actual.stderr
+# '
+
+test_expect_success GPGSSH 'verifying tag with --format' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	cat >expect <<-\EOF &&
+	tagname : fourth-signed
+	EOF
+	git verify-tag --format="tagname : %(tag)" "fourth-signed" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'verifying a forged tag with --format should fail silently' '
+	test_must_fail git verify-tag --format="tagname : %(tag)" $(cat forged1.tag) >actual-forged &&
+	test_must_be_empty actual-forged
+'
+
+test_done
diff --git a/t/t7527-signed-commit-ssh.sh b/t/t7527-signed-commit-ssh.sh
new file mode 100755
index 00000000000..f397a6dd327
--- /dev/null
+++ b/t/t7527-signed-commit-ssh.sh
@@ -0,0 +1,398 @@
+#!/bin/sh
+
+test_description='ssh signed commit tests'
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+GNUPGHOME_NOT_USED=$GNUPGHOME
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPGSSH 'create signed commits' '
+	test_oid_cache <<-\EOF &&
+	header sha1:gpgsig
+	header sha256:gpgsig-sha256
+	EOF
+
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+
+	echo 1 >file && git add file &&
+	test_tick && git commit -S -m initial &&
+	git tag initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -S -m second &&
+	git tag second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout main &&
+	test_tick && git merge -S side &&
+	git tag merge &&
+
+	echo 4 >file && test_tick && git commit -a -m "fourth unsigned" &&
+	git tag fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag fourth-signed &&
+
+	git config commit.gpgsign true &&
+	echo 5 >file && test_tick && git commit -a -m "fifth signed" &&
+	git tag fifth-signed &&
+
+	git config commit.gpgsign false &&
+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
+	git tag sixth-unsigned &&
+
+	git config commit.gpgsign true &&
+	echo 7 >file && test_tick && git commit -a -m "seventh" --no-gpg-sign &&
+	git tag seventh-unsigned &&
+
+	test_tick && git rebase -f HEAD^^ && git tag sixth-signed HEAD^ &&
+	git tag seventh-signed &&
+
+	echo 8 >file && test_tick && git commit -a -m eighth -S"${SIGNING_KEY_UNTRUSTED}" &&
+	git tag eighth-signed-alt &&
+
+	# commit.gpgsign is still on but this must not be signed
+	echo 9 | git commit-tree HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag ninth-unsigned $(cat oid) &&
+	# explicit -S of course must sign.
+	echo 10 | git commit-tree -S HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag tenth-signed $(cat oid) &&
+
+	# --gpg-sign[=<key-id>] must sign.
+	echo 11 | git commit-tree --gpg-sign HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag eleventh-signed $(cat oid) &&
+	echo 12 | git commit-tree --gpg-sign="${SIGNING_KEY_UNTRUSTED}" HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag twelfth-signed-alt $(cat oid)
+'
+
+test_expect_success GPGSSH 'verify and show signatures' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	test_config gpg.mintrustlevel UNDEFINED &&
+	(
+		for commit in initial second merge fourth-signed \
+			fifth-signed sixth-signed seventh-signed tenth-signed \
+			eleventh-signed
+		do
+			git verify-commit $commit &&
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in merge^2 fourth-unsigned sixth-unsigned \
+			seventh-unsigned ninth-unsigned
+		do
+			test_must_fail git verify-commit $commit &&
+			git show --pretty=short --show-signature $commit >actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in eighth-signed-alt twelfth-signed-alt
+		do
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			grep "${KEY_NOT_TRUSTED}" actual &&
+			echo $commit OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'verify-commit exits success on untrusted signature' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git verify-commit eighth-signed-alt 2>actual &&
+	grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual &&
+	grep "${KEY_NOT_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH 'verify-commit exits success with matching minTrustLevel' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	test_config gpg.minTrustLevel fully &&
+	git verify-commit sixth-signed
+'
+
+test_expect_success GPGSSH 'verify-commit exits success with low minTrustLevel' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	test_config gpg.minTrustLevel marginal &&
+	git verify-commit sixth-signed
+'
+
+test_expect_success GPGSSH 'verify-commit exits failure with high minTrustLevel' '
+	test_config gpg.minTrustLevel ultimate &&
+	test_must_fail git verify-commit eighth-signed-alt
+'
+
+# test_expect_success GPGSSH 'verify signatures with --raw' '
+# 	(
+# 		for commit in initial second merge fourth-signed fifth-signed sixth-signed seventh-signed
+# 		do
+# 			git verify-commit --raw $commit 2>actual &&
+# 			grep "GOODSIG" actual &&
+# 			! grep "BADSIG" actual &&
+# 			echo $commit OK || exit 1
+# 		done
+# 	) &&
+# 	(
+# 		for commit in merge^2 fourth-unsigned sixth-unsigned seventh-unsigned
+# 		do
+# 			test_must_fail git verify-commit --raw $commit 2>actual &&
+# 			! grep "GOODSIG" actual &&
+# 			! grep "BADSIG" actual &&
+# 			echo $commit OK || exit 1
+# 		done
+# 	) &&
+# 	(
+# 		for commit in eighth-signed-alt
+# 		do
+# 			git verify-commit --raw $commit 2>actual &&
+# 			grep "GOODSIG" actual &&
+# 			! grep "BADSIG" actual &&
+# 			grep "TRUST_UNDEFINED" actual &&
+# 			echo $commit OK || exit 1
+# 		done
+# 	)
+# '
+
+test_expect_success GPGSSH 'proper header is used for hash algorithm' '
+	git cat-file commit fourth-signed >output &&
+	grep "^$(test_oid header) -----BEGIN SSH SIGNATURE-----" output
+'
+
+test_expect_success GPGSSH 'show signed commit with signature' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git show -s initial >commit &&
+	git show -s --show-signature initial >show &&
+	git verify-commit -v initial >verify.1 2>verify.2 &&
+	git cat-file commit initial >cat &&
+	grep -v -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.commit &&
+	grep -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.gpg &&
+	grep -v "^ " cat | grep -v "^gpgsig.* " >cat.commit &&
+	test_cmp show.commit commit &&
+	test_cmp show.gpg verify.2 &&
+	test_cmp cat.commit verify.1
+'
+
+test_expect_success GPGSSH 'detect fudged signature' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git cat-file commit seventh-signed >raw &&
+	sed -e "s/^seventh/7th forged/" raw >forged1 &&
+	git hash-object -w -t commit forged1 >forged1.commit &&
+	test_must_fail git verify-commit $(cat forged1.commit) &&
+	git show --pretty=short --show-signature $(cat forged1.commit) >actual1 &&
+	grep "${BAD_SIGNATURE}" actual1 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
+'
+
+test_expect_success GPGSSH 'detect fudged signature with NUL' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git cat-file commit seventh-signed >raw &&
+	cat raw >forged2 &&
+	echo Qwik | tr "Q" "\000" >>forged2 &&
+	git hash-object -w -t commit forged2 >forged2.commit &&
+	test_must_fail git verify-commit $(cat forged2.commit) &&
+	git show --pretty=short --show-signature $(cat forged2.commit) >actual2 &&
+	grep "${BAD_SIGNATURE}" actual2 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual2
+'
+
+test_expect_success GPGSSH 'amending already signed commit' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git checkout fourth-signed^0 &&
+	git commit --amend -S --no-edit &&
+	git verify-commit HEAD &&
+	git show -s --show-signature HEAD >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual
+'
+
+test_expect_success GPGSSH 'show good signature with custom format' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	cat >expect.tmpl <<-\EOF &&
+	G
+	FINGERPRINT
+	principal_1
+	FINGERPRINT
+	
+	EOF
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show bad signature with custom format' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	cat >expect <<-\EOF &&
+	B
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat forged1.commit) >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with custom format' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	cat >expect.tmpl <<-\EOF &&
+	U
+	FINGERPRINT
+
+	FINGERPRINT
+	
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with undefined trust level' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	cat >expect.tmpl <<-\EOF &&
+	undefined
+	FINGERPRINT
+
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with ultimate trust level' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	cat >expect.tmpl <<-\EOF &&
+	fully
+	FINGERPRINT
+	principal_1
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show lack of signature with custom format' '
+	cat >expect <<-\EOF &&
+	N
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" seventh-unsigned >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'log.showsignature behaves like --show-signature' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	test_config log.showsignature true &&
+	git show initial >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH 'check config gpg.format values' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_config gpg.format ssh &&
+	git commit -S --amend -m "success" &&
+	test_config gpg.format OpEnPgP &&
+	test_must_fail git commit -S --amend -m "fail"
+'
+
+# test_expect_success GPGSSH 'detect fudged commit with double signature' '
+# 	sed -e "/gpgsig/,/END PGP/d" forged1 >double-base &&
+# 	sed -n -e "/gpgsig/,/END PGP/p" forged1 | \
+# 		sed -e "s/^$(test_oid header)//;s/^ //" | gpg --dearmor >double-sig1.sig &&
+# 	gpg -o double-sig2.sig -u 29472784 --detach-sign double-base &&
+# 	cat double-sig1.sig double-sig2.sig | gpg --enarmor >double-combined.asc &&
+# 	sed -e "s/^\(-.*\)ARMORED FILE/\1SIGNATURE/;1s/^/$(test_oid header) /;2,\$s/^/ /" \
+# 		double-combined.asc > double-gpgsig &&
+# 	sed -e "/committer/r double-gpgsig" double-base >double-commit &&
+# 	git hash-object -w -t commit double-commit >double-commit.commit &&
+# 	test_must_fail git verify-commit $(cat double-commit.commit) &&
+# 	git show --pretty=short --show-signature $(cat double-commit.commit) >double-actual &&
+# 	grep "BAD signature from" double-actual &&
+# 	grep "Good signature from" double-actual
+# '
+
+# test_expect_success GPGSSH 'show double signature with custom format' '
+# 	cat >expect <<-\EOF &&
+# 	E
+
+
+
+
+# 	EOF
+# 	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat double-commit.commit) >actual &&
+# 	test_cmp expect actual
+# '
+
+
+# test_expect_success GPGSSH 'verify-commit verifies multiply signed commits' '
+# 	git init multiply-signed &&
+# 	cd multiply-signed &&
+# 	test_commit first &&
+# 	echo 1 >second &&
+# 	git add second &&
+# 	tree=$(git write-tree) &&
+# 	parent=$(git rev-parse HEAD^{commit}) &&
+# 	git commit --gpg-sign -m second &&
+# 	git cat-file commit HEAD &&
+# 	# Avoid trailing whitespace.
+# 	sed -e "s/^Q//" -e "s/^Z/ /" >commit <<-EOF &&
+# 	Qtree $tree
+# 	Qparent $parent
+# 	Qauthor A U Thor <author@example.com> 1112912653 -0700
+# 	Qcommitter C O Mitter <committer@example.com> 1112912653 -0700
+# 	Qgpgsig -----BEGIN PGP SIGNATURE-----
+# 	QZ
+# 	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBDRYcY29tbWl0dGVy
+# 	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMNd+8AoK1I8mhLHviPH+q2I5fIVgPsEtYC
+# 	Q AKCTqBh+VabJceXcGIZuF0Ry+udbBQ==
+# 	Q =tQ0N
+# 	Q -----END PGP SIGNATURE-----
+# 	Qgpgsig-sha256 -----BEGIN PGP SIGNATURE-----
+# 	QZ
+# 	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBIBYcY29tbWl0dGVy
+# 	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMN/NEAn0XO9RYSBj2dFyozi0JKSbssYMtO
+# 	Q AJwKCQ1BQOtuwz//IjU8TiS+6S4iUw==
+# 	Q =pIwP
+# 	Q -----END PGP SIGNATURE-----
+# 	Q
+# 	Qsecond
+# 	EOF
+# 	head=$(git hash-object -t commit -w commit) &&
+# 	git reset --hard $head &&
+# 	git verify-commit $head 2>actual &&
+# 	grep "Good signature from" actual &&
+# 	! grep "BAD signature from" actual
+# '
+
+test_done

base-commit: d486ca60a51c9cb1fe068803c3f540724e95e83a
-- 
gitgitgadget

Re: [PATCH v2] Add commit, tag & push signing/verification via SSH keys using ssh-keygen

[Ævar Arnfjörð Bjarmason]

On Mon, Jul 12 2021, Fabian Stelzer via GitGitGadget wrote:

>  gpg.format::
>  	Specifies which key format to use when signing with `--gpg-sign`.
> -	Default is "openpgp" and another possible value is "x509".
> +	Default is "openpgp". Other possible values are "x509", "ssh".
>  
>  gpg.<format>.program::
>  	Use this to customize the program used for the signing format you
>  	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
>  	be used as a legacy synonym for `gpg.openpgp.program`. The default
> -	value for `gpg.x509.program` is "gpgsm".
> +	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
>  
>  gpg.minTrustLevel::
>  	Specifies a minimum trust level for signature verification.  If
> @@ -33,3 +33,34 @@ gpg.minTrustLevel::
>  * `marginal`
>  * `fully`
>  * `ultimate`
> +
> +gpg.ssh.keyring::
> +	A file containing all valid SSH public signing keys. 
> +	Similar to an .ssh/authorized_keys file.
> +	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
> +	If a signing key is found in this file then the trust level will
> +	be set to "fully". Otherwise if the key is not present
> +	but the signature is still valid then the trust level will be "undefined".
> +
> +	This file can be set to a location outside of the repository
> +	and every developer maintains their own trust store.
> +	A central repository server could generate this file automatically
> +	from ssh keys with push	access to verify the code against.
> +	In a corporate setting this file is probably generated at a global location
> +	from some automation that already handles developer ssh keys. 
> +	
> +	A repository that is only allowing signed commits can store the file 
> +	in the repository itself using a relative path. This way only committers
> +	with an already valid key can add or change keys in the keyring.
> +
> +	Using a SSH CA key with the cert-authority option 
> +	(see ssh-keygen(1) "CERTIFICATES") is also valid.
> +
> +	To revoke a key place the public key without the principal into the 
> +	revocationKeyring.
> +
> +gpg.ssh.revocationKeyring::
> +	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
> +	See ssh-keygen(1) for details.
> +	If a public key is found in this file then it will always be treated
> +	as having trust level "never" and signatures will show as invalid.
> diff --git a/Documentation/config/user.txt b/Documentation/config/user.txt
> index 59aec7c3aed..e71a099b8b8 100644
> --- a/Documentation/config/user.txt
> +++ b/Documentation/config/user.txt
> @@ -36,3 +36,9 @@ user.signingKey::
>  	commit, you can override the default selection with this variable.
>  	This option is passed unchanged to gpg's --local-user parameter,
>  	so you may specify a key using any method that gpg supports.
> +	If gpg.format is set to "ssh" this can contain the literal ssh public
> +	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and 
> +	corresponds to the private key used for signing. The private key 
> +	needs to be available via ssh-agent. Alternatively it can be set to
> +	a file containing a private key directly. If not set git will call 
> +	"ssh-add -L" and try to use the first key available.
> diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
> index a34742513ac..fd790f7fd72 100644
> --- a/builtin/receive-pack.c
> +++ b/builtin/receive-pack.c
> @@ -131,6 +131,8 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
>  {
>  	int status = parse_hide_refs_config(var, value, "receive");
>  
> +	git_gpg_config(var, value, NULL);
> +
>  	if (status)
>  		return status;
>  
> @@ -767,7 +769,7 @@ static void prepare_push_cert_sha1(struct child_process *proc)
>  		bogs = parse_signed_buffer(push_cert.buf, push_cert.len);
>  		check_signature(push_cert.buf, bogs, push_cert.buf + bogs,
>  				push_cert.len - bogs, &sigcheck);
> -
> +		

Stray whitespace change.

> +static void parse_ssh_output(struct signature_check *sigc)
> +{
> +	const char *output = NULL;
> +	char *next = NULL;
> +
> +	/* ssh-keysign output should be:
> +	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
> +	 * or for valid but unknown keys:
> +	 * Good "git" signature with RSA key SHA256:FINGERPRINT
> +	 */

Style:

 /*
  * Comments like this
  */

Not /* Comments [...]

> +
> +	output = xmemdupz(sigc->output, strcspn(sigc->output, " \n"));
> +	if (skip_prefix(sigc->output, "Good \"git\" signature for ", &output)) {
> +		// Valid signature for a trusted signer

We don't use C99 comments, so /* ... */ (but perhaps we should nowadays,
but that's another topic...).

> +		sigc->result = 'G';
> +		sigc->trust_level = TRUST_FULLY;
> +
> +		next = strchrnul(output, ' '); // 'principal'
> +		replace_cstring(&sigc->signer, output, next);
> +		output = next + 1;
> +		next = strchrnul(output, ' '); // 'with'
> +		output = next + 1;
> +		next = strchrnul(output, ' '); // KEY Type
> +		output = next + 1;
> +		next = strchrnul(output, ' '); // 'key'
> +		output = next + 1;

FWIW for new code we'd probably use string_list_split() or
string_list_split_in_place() or strbuf_split_buf() or something, but I
see this is following the existing pattern in the file...

> +		next = strchrnul(output, '\n'); // key
>
> +		replace_cstring(&sigc->fingerprint, output, next);
> +		replace_cstring(&sigc->key, output, next);
> +	} else if (skip_prefix(sigc->output, "Good \"git\" signature with ", &output)) {
> +		// Valid signature, but key unknown
> +		sigc->result = 'G';
> +		sigc->trust_level = TRUST_UNDEFINED;
> +
> +		next = strchrnul(output, ' '); // KEY Type
> +		output = next + 1;
> +		next = strchrnul(output, ' '); // 'key'
> +		output = next + 1;
> +		next = strchrnul(output, '\n'); // key
> +		replace_cstring(&sigc->fingerprint, output, next);
> +		replace_cstring(&sigc->key, output, next);
> +	} else {
> +		sigc->result = 'B';
> +		sigc->trust_level = TRUST_NEVER;
> +	}
> +}
> +
>  static void parse_gpg_output(struct signature_check *sigc)
>  {
>  	const char *buf = sigc->gpg_status;
> @@ -257,16 +318,18 @@ error:
>  	FREE_AND_NULL(sigc->key);
>  }
>  
> -static int verify_signed_buffer(const char *payload, size_t payload_size,
> -				const char *signature, size_t signature_size,
> -				struct strbuf *gpg_output,
> -				struct strbuf *gpg_status)
> +static int verify_ssh_signature(struct signature_check *sigc, struct gpg_format *fmt,

We usually wrap at 80 characters, so since you're wrapping anyway...

> +	const char *payload, size_t payload_size,
> +	const char *signature, size_t signature_size)
>  {
> -	struct child_process gpg = CHILD_PROCESS_INIT;
> -	struct gpg_format *fmt;
> +	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
>  	struct tempfile *temp;
>  	int ret;
> -	struct strbuf buf = STRBUF_INIT;
> +	const char *line;
> +	size_t trust_size;
> +	char *principal;
> +	struct strbuf ssh_keygen_out = STRBUF_INIT;
> +	struct strbuf ssh_keygen_err = STRBUF_INIT;
>  
>  	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
>  	if (!temp)
> @@ -279,29 +342,125 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
>  		return -1;
>  	}
>  
> -	fmt = get_format_by_sig(signature);
> -	if (!fmt)
> -		BUG("bad signature '%s'", signature);
> +	// Find the principal from the  signers
> +	strvec_pushl(&ssh_keygen.args,  fmt->program,
> +					"-Y", "find-principals",
> +					"-f", get_ssh_allowed_signers(),
> +					"-s", temp->filename.buf,
> +					NULL);
> +	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
> +	if (strstr(ssh_keygen_err.buf, "unknown option")) {
> +		error(_("openssh version > 8.2p1 is needed for ssh signature verification (ssh-keygen needs -Y find-principals/verify option)"));
> +	}
> +	if (ret || !ssh_keygen_out.len) {
> +		// We did not find a matching principal in the keyring - Check without validation
> +		child_process_init(&ssh_keygen);
> +		strvec_pushl(&ssh_keygen.args,  fmt->program,
> +						"-Y", "check-novalidate",
> +						"-n", "git",
> +						"-s", temp->filename.buf,
> +						NULL);
> +		ret = pipe_command(&ssh_keygen, payload, payload_size, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
> +	} else {
> +		// Check every principal we found (one per line)
> +		for (line = ssh_keygen_out.buf; *line; line = strchrnul(line + 1, '\n')) {

Hrm, can't we use strbuf_getline() here with the underlying io_pump API
that pipe_command() uses, instead of slurping it all up, and then
splitting on '\n' ourselves? (I'm not sure)

> +			while (*line == '\n')
> +				line++;
> +			if (!*line)
> +				break;
> +
> +			trust_size = strcspn(line, " \n");
> +			principal = xmemdupz(line, trust_size);
> +
> +			child_process_init(&ssh_keygen);
> +			strbuf_release(&ssh_keygen_out);
> +			strbuf_release(&ssh_keygen_err);
> +			strvec_push(&ssh_keygen.args,fmt->program);
> +			// We found principals - Try with each until we find a match
> +			strvec_pushl(&ssh_keygen.args,  "-Y", "verify",
> +							//TODO: sprintf("-Overify-time=%s", commit->date...),
> +							"-n", "git",
> +							"-f", get_ssh_allowed_signers(),
> +							"-I", principal,
> +							"-s", temp->filename.buf,
> +							NULL);
> +
> +			if (ssh_revocation_file && file_exists(ssh_revocation_file)) {
> +				strvec_pushl(&ssh_keygen.args, "-r", ssh_revocation_file, NULL);

Do we want to silently ignore missing but configured revocation files?

> +			}
> +
> +			sigchain_push(SIGPIPE, SIG_IGN);
> +			ret = pipe_command(&ssh_keygen, payload, payload_size,
> +					&ssh_keygen_out, 0, &ssh_keygen_err, 0);
> +			sigchain_pop(SIGPIPE);
> +
> +			ret &= starts_with(ssh_keygen_out.buf, "Good");
> +			if (ret == 0)
> +				break;
> +		}
> +	}
> +
> +	sigc->payload = xmemdupz(payload, payload_size);
> +	strbuf_stripspace(&ssh_keygen_out, 0);
> +	strbuf_stripspace(&ssh_keygen_err, 0);
> +	strbuf_add(&ssh_keygen_out, ssh_keygen_err.buf, ssh_keygen_err.len);
> +	sigc->output = strbuf_detach(&ssh_keygen_out, NULL);
> +
> +	//sigc->gpg_output = strbuf_detach(&ssh_keygen_err, NULL); // This flip around is broken...

Broken how? And why the commented-out code as part of the patch?

> -	status = verify_signed_buffer(payload, plen, signature, slen,
> -				      &gpg_output, &gpg_status);
> -	if (status && !gpg_output.len)
> -		goto out;
> -	sigc->payload = xmemdupz(payload, plen);
> -	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
> -	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
> -	parse_gpg_output(sigc);
> +	fmt = get_format_by_sig(signature);
> +	if (!fmt)
> +		BUG("bad signature '%s'", signature);

So if we run this from receive-pack or whatever we'll BUG() out? I.e. I
think this should be an fsck check or something, but not a BUG(), or
does this not rely on potentially bad object-store state?

> +static char *get_ssh_key_fingerprint(const char *signing_key) {
> +	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
> +	int ret = -1;
> +	struct strbuf fingerprint_stdout = STRBUF_INIT;
> +	struct strbuf **fingerprint;
> +
> +	/* For SSH Signing this can contain a filename or a public key
> +	* For textual representation we usually want a fingerprint
> +	*/
> +	if (istarts_with(signing_key, "ssh-")) {
> +		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
> +					"-lf", "-",
> +					NULL);
> +		ret = pipe_command(&ssh_keygen, signing_key, strlen(signing_key), &fingerprint_stdout, 0,  NULL, 0);
> +	} else {
> +		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
> +					"-lf", configured_signing_key,
> +					NULL);
> +		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0, NULL, 0);
> +		if (!!ret)
> +			die_errno(_("failed to get the ssh fingerprint for key '%s'"), signing_key);
> +		fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
> +		if (fingerprint[1]) {
> +			return strbuf_detach(fingerprint[1], NULL);
> +		}
> +	}
> +	die_errno(_("failed to get the ssh fingerprint for key '%s'"), signing_key);
> +}

Her you declare a ret that's not used at all in the "istarts_with"
branch, and we fall through to die_errno()?

[I stopped reading mostly at this point]

> [...]
> +# test_expect_success GPGSSH 'detect fudged commit with double signature' '
> +# 	sed -e "/gpgsig/,/END PGP/d" forged1 >double-base &&
> +# 	sed -n -e "/gpgsig/,/END PGP/p" forged1 | \
> +# 		sed -e "s/^$(test_oid header)//;s/^ //" | gpg --dearmor >double-sig1.sig &&
> +# 	gpg -o double-sig2.sig -u 29472784 --detach-sign double-base &&
> +# 	cat double-sig1.sig double-sig2.sig | gpg --enarmor >double-combined.asc &&
> +# 	sed -e "s/^\(-.*\)ARMORED FILE/\1SIGNATURE/;1s/^/$(test_oid header) /;2,\$s/^/ /" \
> +# 		double-combined.asc > double-gpgsig &&
> +# 	sed -e "/committer/r double-gpgsig" double-base >double-commit &&
> +# 	git hash-object -w -t commit double-commit >double-commit.commit &&
> +# 	test_must_fail git verify-commit $(cat double-commit.commit) &&
> +# 	git show --pretty=short --show-signature $(cat double-commit.commit) >double-actual &&
> +# 	grep "BAD signature from" double-actual &&
> +# 	grep "Good signature from" double-actual
> +# '
> +
> +# test_expect_success GPGSSH 'show double signature with custom format' '
> +# 	cat >expect <<-\EOF &&
> +# 	E
> +
> +
> +
> +
> +# 	EOF
> +# 	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat double-commit.commit) >actual &&
> +# 	test_cmp expect actual
> +# '

Perhaps you're looking for test_expect_failure for TODO tests?

I think this patch is *way* past the point of benefitting from being
split into a patch series. It grew from ~200 lines added to ~1k.

Re: [PATCH v2] Add commit, tag & push signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer]

On 12.07.21 18:55, Ævar Arnfjörð Bjarmason wrote:

I'll change all the whitespace / comments / style issues with the next 
commit. Thanks
>> +		sigc->result = 'G';
>> +		sigc->trust_level = TRUST_FULLY;
>> +
>> +		next = strchrnul(output, ' '); // 'principal'
>> +		replace_cstring(&sigc->signer, output, next);
>> +		output = next + 1;
>> +		next = strchrnul(output, ' '); // 'with'
>> +		output = next + 1;
>> +		next = strchrnul(output, ' '); // KEY Type
>> +		output = next + 1;
>> +		next = strchrnul(output, ' '); // 'key'
>> +		output = next + 1;
> FWIW for new code we'd probably use string_list_split() or
> string_list_split_in_place() or strbuf_split_buf() or something, but I
> see this is following the existing pattern in the file...
I agree. This is my first patch in the git codebase so it takes a bit 
getting used to all the available utilities.
>> +	const char *payload, size_t payload_size,
>> +	const char *signature, size_t signature_size)
>>   {
>> -	struct child_process gpg = CHILD_PROCESS_INIT;
>> -	struct gpg_format *fmt;
>> +	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
>>   	struct tempfile *temp;
>>   	int ret;
>> -	struct strbuf buf = STRBUF_INIT;
>> +	const char *line;
>> +	size_t trust_size;
>> +	char *principal;
>> +	struct strbuf ssh_keygen_out = STRBUF_INIT;
>> +	struct strbuf ssh_keygen_err = STRBUF_INIT;
>>   
>>   	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
>>   	if (!temp)
>> @@ -279,29 +342,125 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
>>   		return -1;
>>   	}
>>   
>> -	fmt = get_format_by_sig(signature);
>> -	if (!fmt)
>> -		BUG("bad signature '%s'", signature);
>> +	// Find the principal from the  signers
>> +	strvec_pushl(&ssh_keygen.args,  fmt->program,
>> +					"-Y", "find-principals",
>> +					"-f", get_ssh_allowed_signers(),
>> +					"-s", temp->filename.buf,
>> +					NULL);
>> +	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
>> +	if (strstr(ssh_keygen_err.buf, "unknown option")) {
>> +		error(_("openssh version > 8.2p1 is needed for ssh signature verification (ssh-keygen needs -Y find-principals/verify option)"));
>> +	}
>> +	if (ret || !ssh_keygen_out.len) {
>> +		// We did not find a matching principal in the keyring - Check without validation
>> +		child_process_init(&ssh_keygen);
>> +		strvec_pushl(&ssh_keygen.args,  fmt->program,
>> +						"-Y", "check-novalidate",
>> +						"-n", "git",
>> +						"-s", temp->filename.buf,
>> +						NULL);
>> +		ret = pipe_command(&ssh_keygen, payload, payload_size, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
>> +	} else {
>> +		// Check every principal we found (one per line)
>> +		for (line = ssh_keygen_out.buf; *line; line = strchrnul(line + 1, '\n')) {
> Hrm, can't we use strbuf_getline() here with the underlying io_pump API
> that pipe_command() uses, instead of slurping it all up, and then
> splitting on '\n' ourselves? (I'm not sure)
Sounds good. I'll give it a try.
>> +			while (*line == '\n')
>> +				line++;
>> +			if (!*line)
>> +				break;
>> +
>> +			trust_size = strcspn(line, " \n");
>> +			principal = xmemdupz(line, trust_size);
>> +
>> +			child_process_init(&ssh_keygen);
>> +			strbuf_release(&ssh_keygen_out);
>> +			strbuf_release(&ssh_keygen_err);
>> +			strvec_push(&ssh_keygen.args,fmt->program);
>> +			// We found principals - Try with each until we find a match
>> +			strvec_pushl(&ssh_keygen.args,  "-Y", "verify",
>> +							//TODO: sprintf("-Overify-time=%s", commit->date...),
>> +							"-n", "git",
>> +							"-f", get_ssh_allowed_signers(),
>> +							"-I", principal,
>> +							"-s", temp->filename.buf,
>> +							NULL);
>> +
>> +			if (ssh_revocation_file && file_exists(ssh_revocation_file)) {
>> +				strvec_pushl(&ssh_keygen.args, "-r", ssh_revocation_file, NULL);
> Do we want to silently ignore missing but configured revocation files?
I'll add a warning
>
>> +			}
>> +
>> +			sigchain_push(SIGPIPE, SIG_IGN);
>> +			ret = pipe_command(&ssh_keygen, payload, payload_size,
>> +					&ssh_keygen_out, 0, &ssh_keygen_err, 0);
>> +			sigchain_pop(SIGPIPE);
>> +
>> +			ret &= starts_with(ssh_keygen_out.buf, "Good");
>> +			if (ret == 0)
>> +				break;
>> +		}
>> +	}
>> +
>> +	sigc->payload = xmemdupz(payload, payload_size);
>> +	strbuf_stripspace(&ssh_keygen_out, 0);
>> +	strbuf_stripspace(&ssh_keygen_err, 0);
>> +	strbuf_add(&ssh_keygen_out, ssh_keygen_err.buf, ssh_keygen_err.len);
>> +	sigc->output = strbuf_detach(&ssh_keygen_out, NULL);
>> +
>> +	//sigc->gpg_output = strbuf_detach(&ssh_keygen_err, NULL); // This flip around is broken...
> Broken how? And why the commented-out code as part of the patch?
Sorry, i should have removed it. The original code assigned gpg's stdout 
to gpg_status and stdout to gpg_output which can be a bit confusing.
>
>> -	status = verify_signed_buffer(payload, plen, signature, slen,
>> -				      &gpg_output, &gpg_status);
>> -	if (status && !gpg_output.len)
>> -		goto out;
>> -	sigc->payload = xmemdupz(payload, plen);
>> -	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
>> -	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
>> -	parse_gpg_output(sigc);
>> +	fmt = get_format_by_sig(signature);
>> +	if (!fmt)
>> +		BUG("bad signature '%s'", signature);
> So if we run this from receive-pack or whatever we'll BUG() out? I.e. I
> think this should be an fsck check or something, but not a BUG(), or
> does this not rely on potentially bad object-store state?
The BUG() call is also from the original code. I agree that it should be 
handled differently.
Unfortunately this call is also the reason that when trying to verify a 
new SSH signature with a current git version you'll get a segfault from 
this BUG() :/
I'm not sure if i can do anything about this other than adding a 
completely new tag in the commit itself instead of "gpgsig" which might 
be quite involved. I haven't looked into that too much yet.
>
>> +static char *get_ssh_key_fingerprint(const char *signing_key) {
>> +	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
>> +	int ret = -1;
>> +	struct strbuf fingerprint_stdout = STRBUF_INIT;
>> +	struct strbuf **fingerprint;
>> +
>> +	/* For SSH Signing this can contain a filename or a public key
>> +	* For textual representation we usually want a fingerprint
>> +	*/
>> +	if (istarts_with(signing_key, "ssh-")) {
>> +		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
>> +					"-lf", "-",
>> +					NULL);
>> +		ret = pipe_command(&ssh_keygen, signing_key, strlen(signing_key), &fingerprint_stdout, 0,  NULL, 0);
>> +	} else {
>> +		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
>> +					"-lf", configured_signing_key,
>> +					NULL);
>> +		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0, NULL, 0);
>> +		if (!!ret)
>> +			die_errno(_("failed to get the ssh fingerprint for key '%s'"), signing_key);
>> +		fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
>> +		if (fingerprint[1]) {
>> +			return strbuf_detach(fingerprint[1], NULL);
>> +		}
>> +	}
>> +	die_errno(_("failed to get the ssh fingerprint for key '%s'"), signing_key);
>> +}
> Her you declare a ret that's not used at all in the "istarts_with"
> branch, and we fall through to die_errno()?
I'll clean up the logic. Thanks
>
> [I stopped reading mostly at this point]
>
>> [...]
>> +# test_expect_success GPGSSH 'detect fudged commit with double signature' '
>> +# 	sed -e "/gpgsig/,/END PGP/d" forged1 >double-base &&
>> +# 	sed -n -e "/gpgsig/,/END PGP/p" forged1 | \
>> +# 		sed -e "s/^$(test_oid header)//;s/^ //" | gpg --dearmor >double-sig1.sig &&
>> +# 	gpg -o double-sig2.sig -u 29472784 --detach-sign double-base &&
>> +# 	cat double-sig1.sig double-sig2.sig | gpg --enarmor >double-combined.asc &&
>> +# 	sed -e "s/^\(-.*\)ARMORED FILE/\1SIGNATURE/;1s/^/$(test_oid header) /;2,\$s/^/ /" \
>> +# 		double-combined.asc > double-gpgsig &&
>> +# 	sed -e "/committer/r double-gpgsig" double-base >double-commit &&
>> +# 	git hash-object -w -t commit double-commit >double-commit.commit &&
>> +# 	test_must_fail git verify-commit $(cat double-commit.commit) &&
>> +# 	git show --pretty=short --show-signature $(cat double-commit.commit) >double-actual &&
>> +# 	grep "BAD signature from" double-actual &&
>> +# 	grep "Good signature from" double-actual
>> +# '
>> +
>> +# test_expect_success GPGSSH 'show double signature with custom format' '
>> +# 	cat >expect <<-\EOF &&
>> +# 	E
>> +
>> +
>> +
>> +
>> +# 	EOF
>> +# 	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat double-commit.commit) >actual &&
>> +# 	test_cmp expect actual
>> +# '
> Perhaps you're looking for test_expect_failure for TODO tests?
Yes. Although this test explicitly i'm having a hard time to duplicate 
for ssh. I'm still trying to find out if the duplicate signature thing 
is actually an issue with ssh.
>
> I think this patch is *way* past the point of benefitting from being
> split into a patch series. It grew from ~200 lines added to ~1k.
Sure, I can easily split the patch into seperate commits. But do i 
create a v3 patch from this or issue a new pull request?
The diff between v2 & v3 would be quite useless otherwise wouldn't it?

And maybe another beginner contribution question:

When i make changes to a patchset do i put new changes from the review 
on top as new commits or do i edit the existing commits?
If so what is the workflow you normally use for this? fixup commits? I 
know about those but haven't worked with them before.

Thanks for your help!

Re: [PATCH v2] Add commit, tag & push signing/verification via SSH keys using ssh-keygen

[Felipe Contreras]

Fabian Stelzer wrote:
> On 12.07.21 18:55, Ævar Arnfjörð Bjarmason wrote:

> > I think this patch is *way* past the point of benefitting from being
> > split into a patch series. It grew from ~200 lines added to ~1k.
> Sure, I can easily split the patch into seperate commits. But do i 
> create a v3 patch from this or issue a new pull request?
> The diff between v2 & v3 would be quite useless otherwise wouldn't it?

The interdiff might be quite useless, but not the rangediff. Either way
both of those are merely tools to visualize changes between versions,
ultimately what really matters is the final commits themselves.

Moreover, not all reviewers have seen every version, so for example if
you properly split this patch, I might join the review process at v3,
and I don't really care what was in v2, therefore I wouldn't look at the
rangediff.

> And maybe another beginner contribution question:
> 
> When i make changes to a patchset do i put new changes from the review 
> on top as new commits or do i edit the existing commits?

Edit existing commits.

> If so what is the workflow you normally use for this? fixup commits? I 
> know about those but haven't worked with them before.

`git rebase --interactive` is what I use, and I think that's what most
people use.

This allows you to easily edit commits and add specific changes to
specific commits.

Once you are familiar with this process it's easier to understand fixup
commits, but I'd say rebasing comes first.

Cheers.

-- 
Felipe Contreras

[PATCH v3 0/9] RFC: Add commit & tag signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer via GitGitGadget]

I have added support for using keyfiles directly, lots of tests and
generally cleaned up the signing & verification code a lot.

I can still rename things from being gpg specific to a more general
"signing" but thats rather cosmetic. Also i'm not sure if i named the new
test files correctly.

There is a patch in the pipeline for openssh by Damien Miller that will add
valid-after, valid-before options to the allowed keys keyring. This allows
us to pass the commit timestamp to the verification call and make key
rollover possible and still be able to verify older commits. Set
valid-after=NOW when adding your key to the keyring and set valid-before to
make it fail if used after a certain date. Software like gitolite/github or
corporate automation can do this automatically when ssh push keys are addded
/ removed

v3 addresses some issues & refactoring and splits the large commit into
several smaller ones.

Fabian Stelzer (9):
  Add commit, tag & push signing via SSH keys
  ssh signing: add documentation
  ssh signing: retrieve a default key from ssh-agent
  ssh signing: sign using either gpg or ssh keys
  ssh signing: provide a textual representation of the signing key
  ssh signing: parse ssh-keygen output and verify signatures
  ssh signing: add test prereqs
  ssh signing: duplicate t7510 tests for commits
  ssh signing: add more tests for logs, tags & push certs

 Documentation/config/gpg.txt     |  35 ++-
 Documentation/config/user.txt    |   6 +
 builtin/receive-pack.c           |   2 +
 fmt-merge-msg.c                  |   4 +-
 gpg-interface.c                  | 411 +++++++++++++++++++++++++++----
 gpg-interface.h                  |  12 +-
 log-tree.c                       |   8 +-
 pretty.c                         |   4 +-
 send-pack.c                      |   8 +-
 t/lib-gpg.sh                     |  27 ++
 t/t4202-log.sh                   |  23 ++
 t/t5534-push-signed.sh           | 101 ++++++++
 t/t7031-verify-tag-signed-ssh.sh | 161 ++++++++++++
 t/t7527-signed-commit-ssh.sh     | 398 ++++++++++++++++++++++++++++++
 14 files changed, 1136 insertions(+), 64 deletions(-)
 create mode 100755 t/t7031-verify-tag-signed-ssh.sh
 create mode 100755 t/t7527-signed-commit-ssh.sh


base-commit: d486ca60a51c9cb1fe068803c3f540724e95e83a
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1041%2FFStelzer%2Fsshsign-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1041/FStelzer/sshsign-v3
Pull-Request: https://github.com/git/git/pull/1041

Range-diff vs v2:

  -:  ----------- >  1:  390a8f816cd Add commit, tag & push signing via SSH keys
  -:  ----------- >  2:  2f8452f6570 ssh signing: add documentation
  -:  ----------- >  3:  b84b2812470 ssh signing: retrieve a default key from ssh-agent
  -:  ----------- >  4:  df55b9e1d59 ssh signing: sign using either gpg or ssh keys
  -:  ----------- >  5:  0581c72634c ssh signing: provide a textual representation of the signing key
  -:  ----------- >  6:  381a950a6e1 ssh signing: parse ssh-keygen output and verify signatures
  -:  ----------- >  7:  1d292a8d7a2 ssh signing: add test prereqs
  1:  b8b16f8e6ec !  8:  338d1b976e9 Add commit, tag & push signing/verification via SSH keys using ssh-keygen
     @@ Metadata
      Author: Fabian Stelzer <fs@gigacodes.de>
      
       ## Commit message ##
     -    Add commit, tag & push signing/verification via SSH keys using ssh-keygen
     -
     -    Openssh v8.2p1 added some new options to ssh-keygen for signature
     -    creation and verification. These allow us to use ssh keys for git
     -    signatures easily.
     -
     -    Set gpg.format = ssh and user.signingkey to either a ssh public key
     -    string (like from an authorized_keys file), or a ssh key file.
     -    If the key file or the config value itself contains only a public key
     -    then the private key needs to be available via ssh-agent.
     -    If no signingkey is set then git will call 'ssh-add -L' to check for
     -    available agent keys and use the first one for signing.
     -
     -    Verification uses the gpg.ssh.keyring file (see ssh-keygen(1) "ALLOWED
     -    SIGNERS") which contains valid public keys and an principal (usually
     -    user@domain). Depending on the environment this file can be managed by
     -    the individual developer or for example generated by the central
     -    repository server from known ssh keys with push access. If the
     -    repository only allows signed commits / pushes then the file can even be
     -    stored inside it.
     -
     -    To revoke a key put the public key without the principal prefix into
     -    gpg.ssh.revocationKeyring or generate a KRL (see ssh-keygen(1)
     -    "KEY REVOCATION LISTS"). The same considerations about who to trust for
     -    verification as with the keyring file apply.
     -
     -    This feature makes git signing much more accessible to the average user.
     -    Usually they have a SSH Key for pushing code already. Using it
     -    for signing commits allows us to verify not only the transport but the
     -    pushed code as well.
     -
     -    In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
     -    signing/encryption and ssh keys which i think is quite common
     -    (at least for the email part). This way we can establish the correct
     -    trust for the SSH Keys without setting up a separate GPG Infrastructure
     -    (which is still quite painful for users) or implementing x509 signing
     -    support for git (which lacks good forwarding mechanisms).
     -    Using ssh agent forwarding makes this feature easily usable in todays
     -    development environments where code is often checked out in remote VMs / containers.
     -    In such a setup the keyring & revocationKeyring can be centrally
     -    generated from the x509 CA information and distributed to the users.
     +    ssh signing: duplicate t7510 tests for commits
      
          Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
      
     - ## Documentation/config/gpg.txt ##
     -@@ Documentation/config/gpg.txt: gpg.program::
     - 
     - gpg.format::
     - 	Specifies which key format to use when signing with `--gpg-sign`.
     --	Default is "openpgp" and another possible value is "x509".
     -+	Default is "openpgp". Other possible values are "x509", "ssh".
     - 
     - gpg.<format>.program::
     - 	Use this to customize the program used for the signing format you
     - 	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
     - 	be used as a legacy synonym for `gpg.openpgp.program`. The default
     --	value for `gpg.x509.program` is "gpgsm".
     -+	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
     - 
     - gpg.minTrustLevel::
     - 	Specifies a minimum trust level for signature verification.  If
     -@@ Documentation/config/gpg.txt: gpg.minTrustLevel::
     - * `marginal`
     - * `fully`
     - * `ultimate`
     -+
     -+gpg.ssh.keyring::
     -+	A file containing all valid SSH public signing keys. 
     -+	Similar to an .ssh/authorized_keys file.
     -+	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
     -+	If a signing key is found in this file then the trust level will
     -+	be set to "fully". Otherwise if the key is not present
     -+	but the signature is still valid then the trust level will be "undefined".
     -+
     -+	This file can be set to a location outside of the repository
     -+	and every developer maintains their own trust store.
     -+	A central repository server could generate this file automatically
     -+	from ssh keys with push	access to verify the code against.
     -+	In a corporate setting this file is probably generated at a global location
     -+	from some automation that already handles developer ssh keys. 
     -+	
     -+	A repository that is only allowing signed commits can store the file 
     -+	in the repository itself using a relative path. This way only committers
     -+	with an already valid key can add or change keys in the keyring.
     -+
     -+	Using a SSH CA key with the cert-authority option 
     -+	(see ssh-keygen(1) "CERTIFICATES") is also valid.
     -+
     -+	To revoke a key place the public key without the principal into the 
     -+	revocationKeyring.
     -+
     -+gpg.ssh.revocationKeyring::
     -+	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
     -+	See ssh-keygen(1) for details.
     -+	If a public key is found in this file then it will always be treated
     -+	as having trust level "never" and signatures will show as invalid.
     -
     - ## Documentation/config/user.txt ##
     -@@ Documentation/config/user.txt: user.signingKey::
     - 	commit, you can override the default selection with this variable.
     - 	This option is passed unchanged to gpg's --local-user parameter,
     - 	so you may specify a key using any method that gpg supports.
     -+	If gpg.format is set to "ssh" this can contain the literal ssh public
     -+	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and 
     -+	corresponds to the private key used for signing. The private key 
     -+	needs to be available via ssh-agent. Alternatively it can be set to
     -+	a file containing a private key directly. If not set git will call 
     -+	"ssh-add -L" and try to use the first key available.
     -
     - ## builtin/receive-pack.c ##
     -@@ builtin/receive-pack.c: static int receive_pack_config(const char *var, const char *value, void *cb)
     - {
     - 	int status = parse_hide_refs_config(var, value, "receive");
     - 
     -+	git_gpg_config(var, value, NULL);
     -+
     - 	if (status)
     - 		return status;
     - 
     -@@ builtin/receive-pack.c: static void prepare_push_cert_sha1(struct child_process *proc)
     - 		bogs = parse_signed_buffer(push_cert.buf, push_cert.len);
     - 		check_signature(push_cert.buf, bogs, push_cert.buf + bogs,
     - 				push_cert.len - bogs, &sigcheck);
     --
     -+		
     - 		nonce_status = check_nonce(push_cert.buf, bogs);
     - 	}
     - 	if (!is_null_oid(&push_cert_oid)) {
     -
     - ## fmt-merge-msg.c ##
     -@@ fmt-merge-msg.c: static void fmt_merge_msg_sigs(struct strbuf *out)
     - 			len = payload.len;
     - 			if (check_signature(payload.buf, payload.len, sig.buf,
     - 					 sig.len, &sigc) &&
     --				!sigc.gpg_output)
     -+				!sigc.output)
     - 				strbuf_addstr(&sig, "gpg verification failed.\n");
     - 			else
     --				strbuf_addstr(&sig, sigc.gpg_output);
     -+				strbuf_addstr(&sig, sigc.output);
     - 		}
     - 		signature_check_clear(&sigc);
     - 
     -
     - ## gpg-interface.c ##
     -@@
     - #include "config.h"
     - #include "run-command.h"
     - #include "strbuf.h"
     -+#include "dir.h"
     - #include "gpg-interface.h"
     - #include "sigchain.h"
     - #include "tempfile.h"
     - 
     - static char *configured_signing_key;
     -+const char *ssh_allowed_signers, *ssh_revocation_file;
     - static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
     - 
     - struct gpg_format {
     -@@ gpg-interface.c: static const char *x509_sigs[] = {
     - 	NULL
     - };
     - 
     -+static const char *ssh_verify_args[] = {
     -+	NULL
     -+};
     -+static const char *ssh_sigs[] = {
     -+	"-----BEGIN SSH SIGNATURE-----",
     -+	NULL
     -+};
     -+
     - static struct gpg_format gpg_format[] = {
     - 	{ .name = "openpgp", .program = "gpg",
     - 	  .verify_args = openpgp_verify_args,
     -@@ gpg-interface.c: static struct gpg_format gpg_format[] = {
     - 	  .verify_args = x509_verify_args,
     - 	  .sigs = x509_sigs
     - 	},
     -+	{ .name = "ssh", .program = "ssh-keygen",
     -+	  .verify_args = ssh_verify_args,
     -+	  .sigs = ssh_sigs },
     - };
     - 
     - static struct gpg_format *use_format = &gpg_format[0];
     -@@ gpg-interface.c: static struct gpg_format *get_format_by_sig(const char *sig)
     - void signature_check_clear(struct signature_check *sigc)
     - {
     - 	FREE_AND_NULL(sigc->payload);
     -+	FREE_AND_NULL(sigc->output);
     - 	FREE_AND_NULL(sigc->gpg_output);
     - 	FREE_AND_NULL(sigc->gpg_status);
     - 	FREE_AND_NULL(sigc->signer);
     -@@ gpg-interface.c: static int parse_gpg_trust_level(const char *level,
     - 	return 1;
     - }
     - 
     -+static void parse_ssh_output(struct signature_check *sigc)
     -+{
     -+	const char *output = NULL;
     -+	char *next = NULL;
     -+
     -+	/* ssh-keysign output should be:
     -+	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
     -+	 * or for valid but unknown keys:
     -+	 * Good "git" signature with RSA key SHA256:FINGERPRINT
     -+	 */
     -+
     -+	output = xmemdupz(sigc->output, strcspn(sigc->output, " \n"));
     -+	if (skip_prefix(sigc->output, "Good \"git\" signature for ", &output)) {
     -+		// Valid signature for a trusted signer
     -+		sigc->result = 'G';
     -+		sigc->trust_level = TRUST_FULLY;
     -+
     -+		next = strchrnul(output, ' '); // 'principal'
     -+		replace_cstring(&sigc->signer, output, next);
     -+		output = next + 1;
     -+		next = strchrnul(output, ' '); // 'with'
     -+		output = next + 1;
     -+		next = strchrnul(output, ' '); // KEY Type
     -+		output = next + 1;
     -+		next = strchrnul(output, ' '); // 'key'
     -+		output = next + 1;
     -+		next = strchrnul(output, '\n'); // key
     -+		replace_cstring(&sigc->fingerprint, output, next);
     -+		replace_cstring(&sigc->key, output, next);
     -+	} else if (skip_prefix(sigc->output, "Good \"git\" signature with ", &output)) {
     -+		// Valid signature, but key unknown
     -+		sigc->result = 'G';
     -+		sigc->trust_level = TRUST_UNDEFINED;
     -+
     -+		next = strchrnul(output, ' '); // KEY Type
     -+		output = next + 1;
     -+		next = strchrnul(output, ' '); // 'key'
     -+		output = next + 1;
     -+		next = strchrnul(output, '\n'); // key
     -+		replace_cstring(&sigc->fingerprint, output, next);
     -+		replace_cstring(&sigc->key, output, next);
     -+	} else {
     -+		sigc->result = 'B';
     -+		sigc->trust_level = TRUST_NEVER;
     -+	}
     -+}
     -+
     - static void parse_gpg_output(struct signature_check *sigc)
     - {
     - 	const char *buf = sigc->gpg_status;
     -@@ gpg-interface.c: error:
     - 	FREE_AND_NULL(sigc->key);
     - }
     - 
     --static int verify_signed_buffer(const char *payload, size_t payload_size,
     --				const char *signature, size_t signature_size,
     --				struct strbuf *gpg_output,
     --				struct strbuf *gpg_status)
     -+static int verify_ssh_signature(struct signature_check *sigc, struct gpg_format *fmt,
     -+	const char *payload, size_t payload_size,
     -+	const char *signature, size_t signature_size)
     - {
     --	struct child_process gpg = CHILD_PROCESS_INIT;
     --	struct gpg_format *fmt;
     -+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
     - 	struct tempfile *temp;
     - 	int ret;
     --	struct strbuf buf = STRBUF_INIT;
     -+	const char *line;
     -+	size_t trust_size;
     -+	char *principal;
     -+	struct strbuf ssh_keygen_out = STRBUF_INIT;
     -+	struct strbuf ssh_keygen_err = STRBUF_INIT;
     - 
     - 	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
     - 	if (!temp)
     -@@ gpg-interface.c: static int verify_signed_buffer(const char *payload, size_t payload_size,
     - 		return -1;
     - 	}
     - 
     --	fmt = get_format_by_sig(signature);
     --	if (!fmt)
     --		BUG("bad signature '%s'", signature);
     -+	// Find the principal from the  signers
     -+	strvec_pushl(&ssh_keygen.args,  fmt->program,
     -+					"-Y", "find-principals",
     -+					"-f", get_ssh_allowed_signers(),
     -+					"-s", temp->filename.buf,
     -+					NULL);
     -+	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
     -+	if (strstr(ssh_keygen_err.buf, "unknown option")) {
     -+		error(_("openssh version > 8.2p1 is needed for ssh signature verification (ssh-keygen needs -Y find-principals/verify option)"));
     -+	}
     -+	if (ret || !ssh_keygen_out.len) {
     -+		// We did not find a matching principal in the keyring - Check without validation
     -+		child_process_init(&ssh_keygen);
     -+		strvec_pushl(&ssh_keygen.args,  fmt->program,
     -+						"-Y", "check-novalidate",
     -+						"-n", "git",
     -+						"-s", temp->filename.buf,
     -+						NULL);
     -+		ret = pipe_command(&ssh_keygen, payload, payload_size, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
     -+	} else {
     -+		// Check every principal we found (one per line)
     -+		for (line = ssh_keygen_out.buf; *line; line = strchrnul(line + 1, '\n')) {
     -+			while (*line == '\n')
     -+				line++;
     -+			if (!*line)
     -+				break;
     -+
     -+			trust_size = strcspn(line, " \n");
     -+			principal = xmemdupz(line, trust_size);
     -+
     -+			child_process_init(&ssh_keygen);
     -+			strbuf_release(&ssh_keygen_out);
     -+			strbuf_release(&ssh_keygen_err);
     -+			strvec_push(&ssh_keygen.args,fmt->program);
     -+			// We found principals - Try with each until we find a match
     -+			strvec_pushl(&ssh_keygen.args,  "-Y", "verify",
     -+							//TODO: sprintf("-Overify-time=%s", commit->date...),
     -+							"-n", "git",
     -+							"-f", get_ssh_allowed_signers(),
     -+							"-I", principal,
     -+							"-s", temp->filename.buf,
     -+							NULL);
     -+
     -+			if (ssh_revocation_file && file_exists(ssh_revocation_file)) {
     -+				strvec_pushl(&ssh_keygen.args, "-r", ssh_revocation_file, NULL);
     -+			}
     -+
     -+			sigchain_push(SIGPIPE, SIG_IGN);
     -+			ret = pipe_command(&ssh_keygen, payload, payload_size,
     -+					&ssh_keygen_out, 0, &ssh_keygen_err, 0);
     -+			sigchain_pop(SIGPIPE);
     -+
     -+			ret &= starts_with(ssh_keygen_out.buf, "Good");
     -+			if (ret == 0)
     -+				break;
     -+		}
     -+	}
     -+
     -+	sigc->payload = xmemdupz(payload, payload_size);
     -+	strbuf_stripspace(&ssh_keygen_out, 0);
     -+	strbuf_stripspace(&ssh_keygen_err, 0);
     -+	strbuf_add(&ssh_keygen_out, ssh_keygen_err.buf, ssh_keygen_err.len);
     -+	sigc->output = strbuf_detach(&ssh_keygen_out, NULL);
     -+
     -+	//sigc->gpg_output = strbuf_detach(&ssh_keygen_err, NULL); // This flip around is broken...
     -+	sigc->gpg_status = strbuf_detach(&ssh_keygen_out, NULL);
     -+
     -+	parse_ssh_output(sigc);
     -+
     -+	delete_tempfile(&temp);
     -+	strbuf_release(&ssh_keygen_out);
     -+	strbuf_release(&ssh_keygen_err);
     -+
     -+	return ret;
     -+}
     -+
     -+static int verify_gpg_signature(struct signature_check *sigc, struct gpg_format *fmt, 
     -+	const char *payload, size_t payload_size,
     -+	const char *signature, size_t signature_size)
     -+{
     -+	struct child_process gpg = CHILD_PROCESS_INIT;
     -+	struct tempfile *temp;
     -+	int ret;
     -+	struct strbuf gpg_out = STRBUF_INIT;
     -+	struct strbuf gpg_err = STRBUF_INIT;
     -+
     -+	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
     -+	if (!temp)
     -+		return error_errno(_("could not create temporary file"));
     -+	if (write_in_full(temp->fd, signature, signature_size) < 0 ||
     -+	    close_tempfile_gently(temp) < 0) {
     -+		error_errno(_("failed writing detached signature to '%s'"),
     -+			    temp->filename.buf);
     -+		delete_tempfile(&temp);
     -+		return -1;
     -+	}
     - 
     - 	strvec_push(&gpg.args, fmt->program);
     - 	strvec_pushv(&gpg.args, fmt->verify_args);
     - 	strvec_pushl(&gpg.args,
     --		     "--status-fd=1",
     --		     "--verify", temp->filename.buf, "-",
     --		     NULL);
     --
     --	if (!gpg_status)
     --		gpg_status = &buf;
     -+			"--status-fd=1",
     -+			"--verify", temp->filename.buf, "-",
     -+			NULL);
     - 
     - 	sigchain_push(SIGPIPE, SIG_IGN);
     --	ret = pipe_command(&gpg, payload, payload_size,
     --			   gpg_status, 0, gpg_output, 0);
     -+	ret = pipe_command(&gpg, payload, payload_size, &gpg_out, 0,
     -+				&gpg_err, 0);
     - 	sigchain_pop(SIGPIPE);
     -+	ret |= !strstr(gpg_out.buf, "\n[GNUPG:] GOODSIG ");
     - 
     --	delete_tempfile(&temp);
     -+	sigc->payload = xmemdupz(payload, payload_size);
     -+	sigc->output = strbuf_detach(&gpg_err, NULL);
     -+	sigc->gpg_status = strbuf_detach(&gpg_out, NULL);
     - 
     --	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
     --	strbuf_release(&buf); /* no matter it was used or not */
     -+	parse_gpg_output(sigc);
     -+
     -+	delete_tempfile(&temp);
     -+	strbuf_release(&gpg_out);
     -+	strbuf_release(&gpg_err);
     - 
     - 	return ret;
     - }
     -@@ gpg-interface.c: static int verify_signed_buffer(const char *payload, size_t payload_size,
     - int check_signature(const char *payload, size_t plen, const char *signature,
     - 	size_t slen, struct signature_check *sigc)
     - {
     --	struct strbuf gpg_output = STRBUF_INIT;
     --	struct strbuf gpg_status = STRBUF_INIT;
     -+	struct gpg_format *fmt;
     - 	int status;
     - 
     - 	sigc->result = 'N';
     - 	sigc->trust_level = -1;
     - 
     --	status = verify_signed_buffer(payload, plen, signature, slen,
     --				      &gpg_output, &gpg_status);
     --	if (status && !gpg_output.len)
     --		goto out;
     --	sigc->payload = xmemdupz(payload, plen);
     --	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
     --	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
     --	parse_gpg_output(sigc);
     -+	fmt = get_format_by_sig(signature);
     -+	if (!fmt)
     -+		BUG("bad signature '%s'", signature);
     -+
     -+	if (!strcmp(fmt->name, "ssh")) {
     -+		status = verify_ssh_signature(sigc, fmt, payload, plen, signature, slen);
     -+	} else {
     -+		status = verify_gpg_signature(sigc, fmt, payload, plen, signature, slen);
     -+	}
     -+	if (status && !sigc->gpg_output)
     -+		return !!status;
     -+
     - 	status |= sigc->result != 'G';
     - 	status |= sigc->trust_level < configured_min_trust_level;
     - 
     -- out:
     --	strbuf_release(&gpg_status);
     --	strbuf_release(&gpg_output);
     --
     - 	return !!status;
     - }
     - 
     - void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
     - {
     - 	const char *output = flags & GPG_VERIFY_RAW ?
     --		sigc->gpg_status : sigc->gpg_output;
     -+		sigc->gpg_status : sigc->output;
     - 
     - 	if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
     - 		fputs(sigc->payload, stdout);
     -@@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb)
     - 	int ret;
     - 
     - 	if (!strcmp(var, "user.signingkey")) {
     -+		/* user.signingkey can contain one of the following
     -+		 * when format = openpgp/x509
     -+		 *   - GPG KeyID
     -+		 * when format = ssh
     -+		 *   - literal ssh public key (e.g. ssh-rsa XXXKEYXXX comment)
     -+		 *   - path to a file containing a public or a private ssh key
     -+		 */
     - 		if (!value)
     - 			return config_error_nonbool(var);
     - 		set_signing_key(value);
     - 		return 0;
     - 	}
     - 
     -+	if (!strcmp(var, "gpg.ssh.keyring")) {
     -+		if (!value)
     -+			return config_error_nonbool(var);
     -+		return git_config_string(&ssh_allowed_signers, var, value);
     -+	}
     -+
     -+	if (!strcmp(var, "gpg.ssh.revocationkeyring")) {
     -+		if (!value)
     -+			return config_error_nonbool(var);
     -+		return git_config_string(&ssh_revocation_file, var, value);
     -+	}
     -+
     - 	if (!strcmp(var, "gpg.format")) {
     - 		if (!value)
     - 			return config_error_nonbool(var);
     -@@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb)
     - 	if (!strcmp(var, "gpg.x509.program"))
     - 		fmtname = "x509";
     - 
     -+	if (!strcmp(var, "gpg.ssh.program"))
     -+		fmtname = "ssh";
     -+
     - 	if (fmtname) {
     - 		fmt = get_format_by_name(fmtname);
     - 		return git_config_string(&fmt->program, var, value);
     -@@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb)
     - 	return 0;
     - }
     - 
     -+static char *get_ssh_key_fingerprint(const char *signing_key) {
     -+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
     -+	int ret = -1;
     -+	struct strbuf fingerprint_stdout = STRBUF_INIT;
     -+	struct strbuf **fingerprint;
     -+
     -+	/* For SSH Signing this can contain a filename or a public key
     -+	* For textual representation we usually want a fingerprint
     -+	*/
     -+	if (istarts_with(signing_key, "ssh-")) {
     -+		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
     -+					"-lf", "-",
     -+					NULL);
     -+		ret = pipe_command(&ssh_keygen, signing_key, strlen(signing_key), &fingerprint_stdout, 0,  NULL, 0);
     -+	} else {
     -+		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
     -+					"-lf", configured_signing_key,
     -+					NULL);
     -+		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0, NULL, 0);
     -+		if (!!ret)
     -+			die_errno(_("failed to get the ssh fingerprint for key '%s'"), signing_key);
     -+		fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
     -+		if (fingerprint[1]) {
     -+			return strbuf_detach(fingerprint[1], NULL);
     -+		}
     -+	}
     -+	die_errno(_("failed to get the ssh fingerprint for key '%s'"), signing_key);
     -+}
     -+
     -+// Returns the first public key from an ssh-agent to use for signing
     -+static char *get_default_ssh_signing_key(void) {
     -+	struct child_process ssh_add = CHILD_PROCESS_INIT;
     -+	int ret = -1;
     -+	struct strbuf key_stdout = STRBUF_INIT;
     -+	struct strbuf **keys;
     -+
     -+	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
     -+	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
     -+	if (!ret) { 
     -+		keys = strbuf_split_max(&key_stdout, '\n', 2);
     -+		if (keys[0])
     -+			return strbuf_detach(keys[0], NULL);
     -+	}
     -+
     -+	return "";
     -+}
     -+
     -+// Returns a textual but unique representation ot the signing key
     -+const char *get_signing_key_id(void) {
     -+	if (!strcmp(use_format->name, "ssh")) {
     -+		return get_ssh_key_fingerprint(get_signing_key());
     -+	} else {
     -+		// GPG/GPGSM only store a key id on this variable
     -+		return get_signing_key();
     -+	}
     -+}
     -+
     - const char *get_signing_key(void)
     - {
     - 	if (configured_signing_key)
     - 		return configured_signing_key;
     --	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
     -+	if (!strcmp(use_format->name, "ssh")) {
     -+		return get_default_ssh_signing_key();
     -+	} else {
     -+		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
     -+	}
     -+}
     -+
     -+const char *get_ssh_allowed_signers(void)
     -+{
     -+	if (ssh_allowed_signers)
     -+		return ssh_allowed_signers;
     -+
     -+	die("A Path to an allowed signers ssh keyring is needed for validation");
     - }
     - 
     - int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
     -@@ gpg-interface.c: int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
     - 	int ret;
     - 	size_t i, j, bottom;
     - 	struct strbuf gpg_status = STRBUF_INIT;
     -+	struct tempfile *temp = NULL, *buffer_file = NULL;
     -+	char *ssh_signing_key_file = NULL;
     -+	struct strbuf ssh_signature_filename = STRBUF_INIT;
     -+
     -+	if (!strcmp(use_format->name, "ssh")) {
     -+		if (!signing_key || signing_key[0] == '\0')
     -+			return error(_("user.signingkey needs to be set for ssh signing"));
     -+
     -+
     -+		if (istarts_with(signing_key, "ssh-")) {
     -+			// A literal ssh key
     -+			temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
     -+			if (!temp)
     -+				return error_errno(_("could not create temporary file"));
     -+			if (write_in_full(temp->fd, signing_key, strlen(signing_key)) < 0 ||
     -+				close_tempfile_gently(temp) < 0) {
     -+				error_errno(_("failed writing ssh signing key to '%s'"), temp->filename.buf);
     -+				delete_tempfile(&temp);
     -+				return -1;
     -+			}
     -+			ssh_signing_key_file= temp->filename.buf;
     -+		} else {
     -+			// We assume a file
     -+			ssh_signing_key_file = expand_user_path(signing_key, 1);
     -+		}
     - 
     --	strvec_pushl(&gpg.args,
     --		     use_format->program,
     --		     "--status-fd=2",
     --		     "-bsau", signing_key,
     --		     NULL);
     -+		buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
     -+		if (!buffer_file)
     -+			return error_errno(_("could not create temporary file"));
     -+		if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
     -+			close_tempfile_gently(buffer_file) < 0) {
     -+			error_errno(_("failed writing ssh signing key buffer to '%s'"), buffer_file->filename.buf);
     -+			delete_tempfile(&buffer_file);
     -+			return -1;
     -+		}
     -+
     -+		strvec_pushl(&gpg.args, use_format->program ,
     -+					"-Y", "sign",
     -+					"-n", "git",
     -+					"-f", ssh_signing_key_file,
     -+					buffer_file->filename.buf,
     -+					NULL);
     -+
     -+		sigchain_push(SIGPIPE, SIG_IGN);
     -+		ret = pipe_command(&gpg, NULL, 0, NULL, 0, &gpg_status, 0);
     -+		sigchain_pop(SIGPIPE);
     -+
     -+		strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
     -+		strbuf_addstr(&ssh_signature_filename, ".sig");
     -+		if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {
     -+			error_errno(_("failed reading ssh signing data buffer from '%s'"), ssh_signature_filename.buf);
     -+		}
     -+		unlink_or_warn(ssh_signature_filename.buf);
     -+		strbuf_release(&ssh_signature_filename);
     -+		delete_tempfile(&buffer_file);
     -+	} else {
     -+		strvec_pushl(&gpg.args, use_format->program ,
     -+					"--status-fd=2",
     -+					"-bsau", signing_key,
     -+					NULL);
     -+
     -+		/*
     -+		* When the username signingkey is bad, program could be terminated
     -+		* because gpg exits without reading and then write gets SIGPIPE.
     -+		*/
     -+		sigchain_push(SIGPIPE, SIG_IGN);
     -+		ret = pipe_command(&gpg, buffer->buf, buffer->len, signature, 1024, &gpg_status, 0);
     -+		sigchain_pop(SIGPIPE);
     -+	}
     - 
     - 	bottom = signature->len;
     - 
     --	/*
     --	 * When the username signingkey is bad, program could be terminated
     --	 * because gpg exits without reading and then write gets SIGPIPE.
     --	 */
     --	sigchain_push(SIGPIPE, SIG_IGN);
     --	ret = pipe_command(&gpg, buffer->buf, buffer->len,
     --			   signature, 1024, &gpg_status, 0);
     --	sigchain_pop(SIGPIPE);
     -+	if (temp)
     -+		delete_tempfile(&temp);
     - 
     --	ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
     -+	if (!strcmp(use_format->name, "ssh")) {
     -+		if (strstr(gpg_status.buf, "unknown option")) {
     -+			error(_("openssh version > 8.2p1 is needed for ssh signing (ssh-keygen needs -Y sign option)"));
     -+		}
     -+	} else {
     -+		ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
     -+	}
     - 	strbuf_release(&gpg_status);
     - 	if (ret)
     - 		return error(_("gpg failed to sign the data"));
     -
     - ## gpg-interface.h ##
     -@@ gpg-interface.h: enum signature_trust_level {
     - 
     - struct signature_check {
     - 	char *payload;
     --	char *gpg_output;
     --	char *gpg_status;
     -+	char *output;
     -+	char *gpg_output; // This will be printed in commit logs
     -+	char *gpg_status; // Only used internally -> remove
     - 
     - 	/*
     - 	 * possible "result":
     -@@ gpg-interface.h: int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
     - int git_gpg_config(const char *, const char *, void *);
     - void set_signing_key(const char *);
     - const char *get_signing_key(void);
     -+
     -+/* Returns a textual unique representation of the signing key in use
     -+ * Either a GPG KeyID or a SSH Key Fingerprint
     -+ */
     -+const char *get_signing_key_id(void);
     -+
     -+const char *get_ssh_allowed_signers(void);
     - int check_signature(const char *payload, size_t plen,
     - 		    const char *signature, size_t slen,
     - 		    struct signature_check *sigc);
     -
     - ## log-tree.c ##
     -@@ log-tree.c: static void show_signature(struct rev_info *opt, struct commit *commit)
     - 
     - 	status = check_signature(payload.buf, payload.len, signature.buf,
     - 				 signature.len, &sigc);
     --	if (status && !sigc.gpg_output)
     -+	if (status && !sigc.output)
     - 		show_sig_lines(opt, status, "No signature\n");
     - 	else
     --		show_sig_lines(opt, status, sigc.gpg_output);
     -+		show_sig_lines(opt, status, sigc.output);
     - 	signature_check_clear(&sigc);
     - 
     -  out:
     -@@ log-tree.c: static int show_one_mergetag(struct commit *commit,
     - 		/* could have a good signature */
     - 		status = check_signature(payload.buf, payload.len,
     - 					 signature.buf, signature.len, &sigc);
     --		if (sigc.gpg_output)
     --			strbuf_addstr(&verify_message, sigc.gpg_output);
     -+		if (sigc.output)
     -+			strbuf_addstr(&verify_message, sigc.output);
     - 		else
     - 			strbuf_addstr(&verify_message, "No signature\n");
     - 		signature_check_clear(&sigc);
     -
     - ## pretty.c ##
     -@@ pretty.c: static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
     - 			check_commit_signature(c->commit, &(c->signature_check));
     - 		switch (placeholder[1]) {
     - 		case 'G':
     --			if (c->signature_check.gpg_output)
     --				strbuf_addstr(sb, c->signature_check.gpg_output);
     -+			if (c->signature_check.output)
     -+				strbuf_addstr(sb, c->signature_check.output);
     - 			break;
     - 		case '?':
     - 			switch (c->signature_check.result) {
     -
     - ## send-pack.c ##
     -@@ send-pack.c: static int generate_push_cert(struct strbuf *req_buf,
     - 	const struct ref *ref;
     - 	struct string_list_item *item;
     - 	char *signing_key = xstrdup(get_signing_key());
     -+	char *signing_key_id = xstrdup(get_signing_key_id());
     - 	const char *cp, *np;
     - 	struct strbuf cert = STRBUF_INIT;
     - 	int update_seen = 0;
     --
     -+	
     - 	strbuf_addstr(&cert, "certificate version 0.1\n");
     --	strbuf_addf(&cert, "pusher %s ", signing_key);
     -+	strbuf_addf(&cert, "pusher %s ", signing_key_id);
     - 	datestamp(&cert);
     - 	strbuf_addch(&cert, '\n');
     - 	if (args->url && *args->url) {
     -@@ send-pack.c: static int generate_push_cert(struct strbuf *req_buf,
     - 
     - free_return:
     - 	free(signing_key);
     -+	free(signing_key_id);
     - 	strbuf_release(&cert);
     - 	return update_seen;
     - }
     -
     - ## t/lib-gpg.sh ##
     -@@ t/lib-gpg.sh: test_lazy_prereq RFC1991 '
     - 	echo | gpg --homedir "${GNUPGHOME}" -b --rfc1991 >/dev/null
     - '
     - 
     -+test_lazy_prereq GPGSSH '
     -+	ssh_version=$(ssh-keygen -Y find-principals -n "git" 2>&1)
     -+	test $? != 127 || exit 1
     -+	echo $ssh_version | grep -q "find-principals:missing signature file"
     -+	test $? = 0 || exit 1; 
     -+	mkdir -p "${GNUPGHOME}" &&
     -+	chmod 0700 "${GNUPGHOME}" &&
     -+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/ed25519_ssh_signing_key" >/dev/null &&
     -+	ssh-keygen -t rsa -b 2048 -N "" -f "${GNUPGHOME}/rsa_2048_ssh_signing_key" >/dev/null &&
     -+	ssh-keygen -t ed25519 -N "super_secret" -f "${GNUPGHOME}/protected_ssh_signing_key" >/dev/null &&
     -+	find "${GNUPGHOME}" -name *ssh_signing_key.pub -exec cat {} \; | awk "{print \"principal_\" NR \" \" \$0}" > "${GNUPGHOME}/ssh.all_valid.keyring" &&
     -+	cat "${GNUPGHOME}/ssh.all_valid.keyring" &&
     -+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/untrusted_ssh_signing_key" >/dev/null
     -+'
     -+
     -+SIGNING_KEY_PRIMARY="${GNUPGHOME}/ed25519_ssh_signing_key"
     -+SIGNING_KEY_SECONDARY="${GNUPGHOME}/rsa_2048_ssh_signing_key"
     -+SIGNING_KEY_UNTRUSTED="${GNUPGHOME}/untrusted_ssh_signing_key"
     -+SIGNING_KEY_WITH_PASSPHRASE="${GNUPGHOME}/protected_ssh_signing_key"
     -+SIGNING_KEY_PASSPHRASE="super_secret"
     -+SIGNING_KEYRING="${GNUPGHOME}/ssh.all_valid.keyring"
     -+
     -+GOOD_SIGNATURE_TRUSTED='Good "git" signature for'
     -+GOOD_SIGNATURE_UNTRUSTED='Good "git" signature with'
     -+KEY_NOT_TRUSTED="No principal matched"
     -+BAD_SIGNATURE="Signature verification failed"
     -+
     - sanitize_pgp() {
     - 	perl -ne '
     - 		/^-----END PGP/ and $in_pgp = 0;
     -
     - ## t/t4202-log.sh ##
     -@@ t/t4202-log.sh: test_expect_success GPGSM 'setup signed branch x509' '
     - 	git commit -S -m signed_commit
     - '
     - 
     -+test_expect_success GPGSSH 'setup sshkey signed branch' '
     -+	test_config gpg.format ssh &&
     -+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     -+	test_when_finished "git reset --hard && git checkout main" &&
     -+	git checkout -b signed-ssh main &&
     -+	echo foo >foo &&
     -+	git add foo &&
     -+	git commit -S -m signed_commit
     -+'
     -+
     - test_expect_success GPGSM 'log x509 fingerprint' '
     - 	echo "F8BF62E0693D0694816377099909C779FA23FD65 | " >expect &&
     - 	git log -n1 --format="%GF | %GP" signed-x509 >actual &&
     -@@ t/t4202-log.sh: test_expect_success GPGSM 'log --graph --show-signature x509' '
     - 	grep "^| gpgsm: Good signature" actual
     - '
     - 
     -+test_expect_success GPGSSH 'log ssh key fingerprint' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     -+	ssh-keygen -lf  "${SIGNING_KEY_PRIMARY}" | awk "{print \$2\" | \"}" >expect &&
     -+	git log -n1 --format="%GF | %GP" signed-ssh >actual &&
     -+	test_cmp expect actual
     -+'
     -+
     - test_expect_success GPG 'log --graph --show-signature for merged tag' '
     - 	test_when_finished "git reset --hard && git checkout main" &&
     - 	git checkout -b plain main &&
     -
     - ## t/t5534-push-signed.sh ##
     -@@ t/t5534-push-signed.sh: test_expect_success GPG 'signed push sends push certificate' '
     - 	test_cmp expect dst/push-cert-status
     - '
     - 
     -+test_expect_success GPGSSH 'ssh signed push sends push certificate' '
     -+	prepare_dst &&
     -+	mkdir -p dst/.git/hooks &&
     -+	git -C dst config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     -+	git -C dst config receive.certnonceseed sekrit &&
     -+	write_script dst/.git/hooks/post-receive <<-\EOF &&
     -+	# discard the update list
     -+	cat >/dev/null
     -+	# record the push certificate
     -+	if test -n "${GIT_PUSH_CERT-}"
     -+	then
     -+		git cat-file blob $GIT_PUSH_CERT >../push-cert
     -+	fi &&
     -+
     -+	cat >../push-cert-status <<E_O_F
     -+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
     -+	KEY=${GIT_PUSH_CERT_KEY-nokey}
     -+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
     -+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
     -+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
     -+	E_O_F
     -+
     -+	EOF
     -+
     -+	test_config gpg.format ssh &&
     -+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     -+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
     -+	git push --signed dst noop ff +noff &&
     -+
     -+	(
     -+		cat <<-\EOF &&
     -+		SIGNER=principal_1
     -+		KEY=FINGERPRINT
     -+		STATUS=G
     -+		NONCE_STATUS=OK
     -+		EOF
     -+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
     -+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
     -+
     -+	noop=$(git rev-parse noop) &&
     -+	ff=$(git rev-parse ff) &&
     -+	noff=$(git rev-parse noff) &&
     -+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
     -+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
     -+	test_cmp expect dst/push-cert-status
     -+'
     -+
     - test_expect_success GPG 'inconsistent push options in signed push not allowed' '
     - 	# First, invoke receive-pack with dummy input to obtain its preamble.
     - 	prepare_dst &&
     -@@ t/t5534-push-signed.sh: test_expect_success GPGSM 'fail without key and heed user.signingkey x509' '
     - 	test_cmp expect dst/push-cert-status
     - '
     - 
     -+test_expect_success GPGSSH 'fail without key and heed user.signingkey ssh' '
     -+	test_config gpg.format ssh &&
     -+	prepare_dst &&
     -+	mkdir -p dst/.git/hooks &&
     -+	git -C dst config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     -+	git -C dst config receive.certnonceseed sekrit &&
     -+	write_script dst/.git/hooks/post-receive <<-\EOF &&
     -+	# discard the update list
     -+	cat >/dev/null
     -+	# record the push certificate
     -+	if test -n "${GIT_PUSH_CERT-}"
     -+	then
     -+		git cat-file blob $GIT_PUSH_CERT >../push-cert
     -+	fi &&
     -+
     -+	cat >../push-cert-status <<E_O_F
     -+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
     -+	KEY=${GIT_PUSH_CERT_KEY-nokey}
     -+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
     -+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
     -+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
     -+	E_O_F
     -+
     -+	EOF
     -+
     -+	test_config user.email hasnokey@nowhere.com &&
     -+	test_config gpg.format ssh &&
     -+	
     -+	test_config user.signingkey "" &&
     -+	(
     -+		sane_unset GIT_COMMITTER_EMAIL &&
     -+		test_must_fail git push --signed dst noop ff +noff
     -+	) &&
     -+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     -+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
     -+	git push --signed dst noop ff +noff &&
     -+
     -+	(
     -+		cat <<-\EOF &&
     -+		SIGNER=principal_1
     -+		KEY=FINGERPRINT
     -+		STATUS=G
     -+		NONCE_STATUS=OK
     -+		EOF
     -+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
     -+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
     -+
     -+	noop=$(git rev-parse noop) &&
     -+	ff=$(git rev-parse ff) &&
     -+	noff=$(git rev-parse noff) &&
     -+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
     -+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
     -+	test_cmp expect dst/push-cert-status
     -+'
     -+
     - test_expect_success GPG 'failed atomic push does not execute GPG' '
     - 	prepare_dst &&
     - 	git -C dst config receive.certnonceseed sekrit &&
     -
     - ## t/t7031-verify-tag-signed-ssh.sh (new) ##
     -@@
     -+#!/bin/sh
     -+
     -+test_description='signed tag tests'
     -+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
     -+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
     -+
     -+. ./test-lib.sh
     -+. "$TEST_DIRECTORY/lib-gpg.sh"
     -+
     -+test_expect_success GPGSSH 'create signed tags ssh' '
     -+	test_when_finished "test_unconfig commit.gpgsign" &&
     -+	test_config gpg.format ssh &&
     -+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     -+
     -+	echo 1 >file && git add file &&
     -+	test_tick && git commit -m initial &&
     -+	git tag -s -m initial initial &&
     -+	git branch side &&
     -+
     -+	echo 2 >file && test_tick && git commit -a -m second &&
     -+	git tag -s -m second second &&
     -+
     -+	git checkout side &&
     -+	echo 3 >elif && git add elif &&
     -+	test_tick && git commit -m "third on side" &&
     -+
     -+	git checkout main &&
     -+	test_tick && git merge -S side &&
     -+	git tag -s -m merge merge &&
     -+
     -+	echo 4 >file && test_tick && git commit -a -S -m "fourth unsigned" &&
     -+	git tag -a -m fourth-unsigned fourth-unsigned &&
     -+
     -+	test_tick && git commit --amend -S -m "fourth signed" &&
     -+	git tag -s -m fourth fourth-signed &&
     -+
     -+	echo 5 >file && test_tick && git commit -a -m "fifth" &&
     -+	git tag fifth-unsigned &&
     -+
     -+	git config commit.gpgsign true &&
     -+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
     -+	git tag -a -m sixth sixth-unsigned &&
     -+
     -+	test_tick && git rebase -f HEAD^^ && git tag -s -m 6th sixth-signed HEAD^ &&
     -+	git tag -m seventh -s seventh-signed &&
     -+
     -+	echo 8 >file && test_tick && git commit -a -m eighth &&
     -+	git tag -u"${SIGNING_KEY_UNTRUSTED}" -m eighth eighth-signed-alt
     -+'
     -+
     -+test_expect_success GPGSSH 'verify and show ssh signatures' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     -+	test_config gpg.mintrustlevel UNDEFINED &&
     -+	(
     -+		for tag in initial second merge fourth-signed sixth-signed seventh-signed
     -+		do
     -+			git verify-tag $tag 2>actual &&
     -+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
     -+			! grep "${BAD_SIGNATURE}" actual &&
     -+			echo $tag OK || exit 1
     -+		done
     -+	) &&
     -+	(
     -+		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
     -+		do
     -+			test_must_fail git verify-tag $tag 2>actual &&
     -+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
     -+			! grep "${BAD_SIGNATURE}" actual &&
     -+			echo $tag OK || exit 1
     -+		done
     -+	) &&
     -+	(
     -+		for tag in eighth-signed-alt
     -+		do
     -+			git verify-tag $tag 2>actual &&
     -+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
     -+			! grep "${BAD_SIGNATURE}" actual &&
     -+			grep "${KEY_NOT_TRUSTED}" actual &&
     -+			echo $tag OK || exit 1
     -+		done
     -+	)
     -+'
     -+
     -+test_expect_success GPGSSH 'detect fudged ssh signature' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     -+	git cat-file tag seventh-signed >raw &&
     -+	sed -e "/^tag / s/seventh/7th forged/" raw >forged1 &&
     -+	git hash-object -w -t tag forged1 >forged1.tag &&
     -+	test_must_fail git verify-tag $(cat forged1.tag) 2>actual1 &&
     -+	grep "${BAD_SIGNATURE}" actual1 &&
     -+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
     -+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
     -+'
     -+
     -+# test_expect_success GPGSSH 'verify ssh signatures with --raw' '
     -+# 	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     -+# 	(
     -+# 		for tag in initial second merge fourth-signed sixth-signed seventh-signed
     -+# 		do
     -+# 			git verify-tag --raw $tag 2>actual &&
     -+# 			grep "GOODSIG" actual &&
     -+# 			! grep "BADSIG" actual &&
     -+# 			echo $tag OK || exit 1
     -+# 		done
     -+# 	) &&
     -+# 	(
     -+# 		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
     -+# 		do
     -+# 			test_must_fail git verify-tag --raw $tag 2>actual &&
     -+# 			! grep "GOODSIG" actual &&
     -+# 			! grep "BADSIG" actual &&
     -+# 			echo $tag OK || exit 1
     -+# 		done
     -+# 	) &&
     -+# 	(
     -+# 		for tag in eighth-signed-alt
     -+# 		do
     -+# 			git verify-tag --raw $tag 2>actual &&
     -+# 			grep "GOODSIG" actual &&
     -+# 			! grep "BADSIG" actual &&
     -+# 			grep "TRUST_UNDEFINED" actual &&
     -+# 			echo $tag OK || exit 1
     -+# 		done
     -+# 	)
     -+# '
     -+
     -+# test_expect_success GPGSM 'verify signatures with --raw x509' '
     -+# 	git verify-tag --raw ninth-signed-x509 2>actual &&
     -+# 	grep "GOODSIG" actual &&
     -+# 	! grep "BADSIG" actual &&
     -+# 	echo ninth-signed-x509 OK
     -+# '
     -+
     -+# test_expect_success GPGSSH 'verify multiple tags' '
     -+# 	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     -+# 	tags="fourth-signed sixth-signed seventh-signed" &&
     -+# 	for i in $tags
     -+# 	do
     -+# 		git verify-tag -v --raw $i || return 1
     -+# 	done >expect.stdout 2>expect.stderr.1 &&
     -+# 	grep "^.GNUPG:." <expect.stderr.1 >expect.stderr &&
     -+# 	git verify-tag -v --raw $tags >actual.stdout 2>actual.stderr.1 &&
     -+# 	grep "^.GNUPG:." <actual.stderr.1 >actual.stderr &&
     -+# 	test_cmp expect.stdout actual.stdout &&
     -+# 	test_cmp expect.stderr actual.stderr
     -+# '
     -+
     -+# test_expect_success GPGSM 'verify multiple tags x509' '
     -+#	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     -+# 	tags="seventh-signed ninth-signed-x509" &&
     -+# 	for i in $tags
     -+# 	do
     -+# 		git verify-tag -v --raw $i || return 1
     -+# 	done >expect.stdout 2>expect.stderr.1 &&
     -+# 	grep "^.GNUPG:." <expect.stderr.1 >expect.stderr &&
     -+# 	git verify-tag -v --raw $tags >actual.stdout 2>actual.stderr.1 &&
     -+# 	grep "^.GNUPG:." <actual.stderr.1 >actual.stderr &&
     -+# 	test_cmp expect.stdout actual.stdout &&
     -+# 	test_cmp expect.stderr actual.stderr
     -+# '
     -+
     -+test_expect_success GPGSSH 'verifying tag with --format' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     -+	cat >expect <<-\EOF &&
     -+	tagname : fourth-signed
     -+	EOF
     -+	git verify-tag --format="tagname : %(tag)" "fourth-signed" >actual &&
     -+	test_cmp expect actual
     -+'
     -+
     -+test_expect_success GPGSSH 'verifying a forged tag with --format should fail silently' '
     -+	test_must_fail git verify-tag --format="tagname : %(tag)" $(cat forged1.tag) >actual-forged &&
     -+	test_must_be_empty actual-forged
     -+'
     -+
     -+test_done
     -
       ## t/t7527-signed-commit-ssh.sh (new) ##
      @@
      +#!/bin/sh
     @@ t/t7527-signed-commit-ssh.sh (new)
      +	test_must_fail git verify-commit eighth-signed-alt
      +'
      +
     -+# test_expect_success GPGSSH 'verify signatures with --raw' '
     -+# 	(
     -+# 		for commit in initial second merge fourth-signed fifth-signed sixth-signed seventh-signed
     -+# 		do
     -+# 			git verify-commit --raw $commit 2>actual &&
     -+# 			grep "GOODSIG" actual &&
     -+# 			! grep "BADSIG" actual &&
     -+# 			echo $commit OK || exit 1
     -+# 		done
     -+# 	) &&
     -+# 	(
     -+# 		for commit in merge^2 fourth-unsigned sixth-unsigned seventh-unsigned
     -+# 		do
     -+# 			test_must_fail git verify-commit --raw $commit 2>actual &&
     -+# 			! grep "GOODSIG" actual &&
     -+# 			! grep "BADSIG" actual &&
     -+# 			echo $commit OK || exit 1
     -+# 		done
     -+# 	) &&
     -+# 	(
     -+# 		for commit in eighth-signed-alt
     -+# 		do
     -+# 			git verify-commit --raw $commit 2>actual &&
     -+# 			grep "GOODSIG" actual &&
     -+# 			! grep "BADSIG" actual &&
     -+# 			grep "TRUST_UNDEFINED" actual &&
     -+# 			echo $commit OK || exit 1
     -+# 		done
     -+# 	)
     -+# '
     ++test_expect_success GPGSSH 'verify signatures with --raw' '
     ++	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	(
     ++		for commit in initial second merge fourth-signed fifth-signed sixth-signed seventh-signed
     ++		do
     ++			git verify-commit --raw $commit 2>actual &&
     ++			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
     ++			! grep "${BAD_SIGNATURE}" actual &&
     ++			echo $commit OK || exit 1
     ++		done
     ++	) &&
     ++	(
     ++		for commit in merge^2 fourth-unsigned sixth-unsigned seventh-unsigned
     ++		do
     ++			test_must_fail git verify-commit --raw $commit 2>actual &&
     ++			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
     ++			! grep "${BAD_SIGNATURE}" actual &&
     ++			echo $commit OK || exit 1
     ++		done
     ++	) &&
     ++	(
     ++		for commit in eighth-signed-alt
     ++		do
     ++			git verify-commit --raw $commit 2>actual &&
     ++			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
     ++			! grep "${BAD_SIGNATURE}" actual &&
     ++			echo $commit OK || exit 1
     ++		done
     ++	)
     ++'
      +
      +test_expect_success GPGSSH 'proper header is used for hash algorithm' '
      +	git cat-file commit fourth-signed >output &&
     @@ t/t7527-signed-commit-ssh.sh (new)
      +	FINGERPRINT
      +	principal_1
      +	FINGERPRINT
     -+	
     ++
      +	EOF
      +	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
      +	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
     @@ t/t7527-signed-commit-ssh.sh (new)
      +	FINGERPRINT
      +
      +	FINGERPRINT
     -+	
     ++
      +	EOF
      +	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
      +	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
     @@ t/t7527-signed-commit-ssh.sh (new)
      +	test_must_fail git commit -S --amend -m "fail"
      +'
      +
     -+# test_expect_success GPGSSH 'detect fudged commit with double signature' '
     -+# 	sed -e "/gpgsig/,/END PGP/d" forged1 >double-base &&
     -+# 	sed -n -e "/gpgsig/,/END PGP/p" forged1 | \
     -+# 		sed -e "s/^$(test_oid header)//;s/^ //" | gpg --dearmor >double-sig1.sig &&
     -+# 	gpg -o double-sig2.sig -u 29472784 --detach-sign double-base &&
     -+# 	cat double-sig1.sig double-sig2.sig | gpg --enarmor >double-combined.asc &&
     -+# 	sed -e "s/^\(-.*\)ARMORED FILE/\1SIGNATURE/;1s/^/$(test_oid header) /;2,\$s/^/ /" \
     -+# 		double-combined.asc > double-gpgsig &&
     -+# 	sed -e "/committer/r double-gpgsig" double-base >double-commit &&
     -+# 	git hash-object -w -t commit double-commit >double-commit.commit &&
     -+# 	test_must_fail git verify-commit $(cat double-commit.commit) &&
     -+# 	git show --pretty=short --show-signature $(cat double-commit.commit) >double-actual &&
     -+# 	grep "BAD signature from" double-actual &&
     -+# 	grep "Good signature from" double-actual
     -+# '
     ++test_expect_failure GPGSSH 'detect fudged commit with double signature (TODO)' '
     ++	sed -e "/gpgsig/,/END PGP/d" forged1 >double-base &&
     ++	sed -n -e "/gpgsig/,/END PGP/p" forged1 | \
     ++		sed -e "s/^$(test_oid header)//;s/^ //" | gpg --dearmor >double-sig1.sig &&
     ++	gpg -o double-sig2.sig -u 29472784 --detach-sign double-base &&
     ++	cat double-sig1.sig double-sig2.sig | gpg --enarmor >double-combined.asc &&
     ++	sed -e "s/^\(-.*\)ARMORED FILE/\1SIGNATURE/;1s/^/$(test_oid header) /;2,\$s/^/ /" \
     ++		double-combined.asc > double-gpgsig &&
     ++	sed -e "/committer/r double-gpgsig" double-base >double-commit &&
     ++	git hash-object -w -t commit double-commit >double-commit.commit &&
     ++	test_must_fail git verify-commit $(cat double-commit.commit) &&
     ++	git show --pretty=short --show-signature $(cat double-commit.commit) >double-actual &&
     ++	grep "BAD signature from" double-actual &&
     ++	grep "Good signature from" double-actual
     ++'
      +
     -+# test_expect_success GPGSSH 'show double signature with custom format' '
     -+# 	cat >expect <<-\EOF &&
     -+# 	E
     ++test_expect_failure GPGSSH 'show double signature with custom format (TODO)' '
     ++	cat >expect <<-\EOF &&
     ++	E
      +
      +
      +
      +
     -+# 	EOF
     -+# 	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat double-commit.commit) >actual &&
     -+# 	test_cmp expect actual
     -+# '
     ++	EOF
     ++	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat double-commit.commit) >actual &&
     ++	test_cmp expect actual
     ++'
      +
      +
     -+# test_expect_success GPGSSH 'verify-commit verifies multiply signed commits' '
     -+# 	git init multiply-signed &&
     -+# 	cd multiply-signed &&
     -+# 	test_commit first &&
     -+# 	echo 1 >second &&
     -+# 	git add second &&
     -+# 	tree=$(git write-tree) &&
     -+# 	parent=$(git rev-parse HEAD^{commit}) &&
     -+# 	git commit --gpg-sign -m second &&
     -+# 	git cat-file commit HEAD &&
     -+# 	# Avoid trailing whitespace.
     -+# 	sed -e "s/^Q//" -e "s/^Z/ /" >commit <<-EOF &&
     -+# 	Qtree $tree
     -+# 	Qparent $parent
     -+# 	Qauthor A U Thor <author@example.com> 1112912653 -0700
     -+# 	Qcommitter C O Mitter <committer@example.com> 1112912653 -0700
     -+# 	Qgpgsig -----BEGIN PGP SIGNATURE-----
     -+# 	QZ
     -+# 	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBDRYcY29tbWl0dGVy
     -+# 	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMNd+8AoK1I8mhLHviPH+q2I5fIVgPsEtYC
     -+# 	Q AKCTqBh+VabJceXcGIZuF0Ry+udbBQ==
     -+# 	Q =tQ0N
     -+# 	Q -----END PGP SIGNATURE-----
     -+# 	Qgpgsig-sha256 -----BEGIN PGP SIGNATURE-----
     -+# 	QZ
     -+# 	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBIBYcY29tbWl0dGVy
     -+# 	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMN/NEAn0XO9RYSBj2dFyozi0JKSbssYMtO
     -+# 	Q AJwKCQ1BQOtuwz//IjU8TiS+6S4iUw==
     -+# 	Q =pIwP
     -+# 	Q -----END PGP SIGNATURE-----
     -+# 	Q
     -+# 	Qsecond
     -+# 	EOF
     -+# 	head=$(git hash-object -t commit -w commit) &&
     -+# 	git reset --hard $head &&
     -+# 	git verify-commit $head 2>actual &&
     -+# 	grep "Good signature from" actual &&
     -+# 	! grep "BAD signature from" actual
     -+# '
     ++test_expect_failure GPGSSH 'verify-commit verifies multiply signed commits (TODO)' '
     ++	git init multiply-signed &&
     ++	cd multiply-signed &&
     ++	test_commit first &&
     ++	echo 1 >second &&
     ++	git add second &&
     ++	tree=$(git write-tree) &&
     ++	parent=$(git rev-parse HEAD^{commit}) &&
     ++	git commit --gpg-sign -m second &&
     ++	git cat-file commit HEAD &&
     ++	# Avoid trailing whitespace.
     ++	sed -e "s/^Q//" -e "s/^Z/ /" >commit <<-EOF &&
     ++	Qtree $tree
     ++	Qparent $parent
     ++	Qauthor A U Thor <author@example.com> 1112912653 -0700
     ++	Qcommitter C O Mitter <committer@example.com> 1112912653 -0700
     ++	Qgpgsig -----BEGIN PGP SIGNATURE-----
     ++	QZ
     ++	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBDRYcY29tbWl0dGVy
     ++	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMNd+8AoK1I8mhLHviPH+q2I5fIVgPsEtYC
     ++	Q AKCTqBh+VabJceXcGIZuF0Ry+udbBQ==
     ++	Q =tQ0N
     ++	Q -----END PGP SIGNATURE-----
     ++	Qgpgsig-sha256 -----BEGIN PGP SIGNATURE-----
     ++	QZ
     ++	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBIBYcY29tbWl0dGVy
     ++	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMN/NEAn0XO9RYSBj2dFyozi0JKSbssYMtO
     ++	Q AJwKCQ1BQOtuwz//IjU8TiS+6S4iUw==
     ++	Q =pIwP
     ++	Q -----END PGP SIGNATURE-----
     ++	Q
     ++	Qsecond
     ++	EOF
     ++	head=$(git hash-object -t commit -w commit) &&
     ++	git reset --hard $head &&
     ++	git verify-commit $head 2>actual &&
     ++	grep "Good signature from" actual &&
     ++	! grep "BAD signature from" actual
     ++'
      +
      +test_done
  -:  ----------- >  9:  33330fda441 ssh signing: add more tests for logs, tags & push certs

-- 
gitgitgadget

[PATCH v3 1/9] Add commit, tag & push signing via SSH keys

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Openssh v8.2p1 added some new options to ssh-keygen for signature
creation and verification. These allow us to use ssh keys for git
signatures easily.

Start with adding the new signature format, new config options and
rename some fields for consistency.

This feature makes git signing much more accessible to the average user.
Usually they have a SSH Key for pushing code already. Using it
for signing commits allows us to verify not only the transport but the
pushed code as well.

In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
signing/encryption and ssh keys which i think is quite common
(at least for the email part). This way we can establish the correct
trust for the SSH Keys without setting up a separate GPG Infrastructure
(which is still quite painful for users) or implementing x509 signing
support for git (which lacks good forwarding mechanisms).
Using ssh agent forwarding makes this feature easily usable in todays
development environments where code is often checked out in remote VMs / containers.
In such a setup the keyring & revocationKeyring can be centrally
generated from the x509 CA information and distributed to the users.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 fmt-merge-msg.c |   4 +-
 gpg-interface.c | 122 +++++++++++++++++++++++++++++++++---------------
 gpg-interface.h |   5 +-
 log-tree.c      |   8 ++--
 pretty.c        |   4 +-
 5 files changed, 95 insertions(+), 48 deletions(-)

diff --git a/fmt-merge-msg.c b/fmt-merge-msg.c
index 0f66818e0f8..1d7b64fa021 100644
--- a/fmt-merge-msg.c
+++ b/fmt-merge-msg.c
@@ -527,10 +527,10 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 			len = payload.len;
 			if (check_signature(payload.buf, payload.len, sig.buf,
 					 sig.len, &sigc) &&
-				!sigc.gpg_output)
+				!sigc.output)
 				strbuf_addstr(&sig, "gpg verification failed.\n");
 			else
-				strbuf_addstr(&sig, sigc.gpg_output);
+				strbuf_addstr(&sig, sigc.output);
 		}
 		signature_check_clear(&sigc);
 
diff --git a/gpg-interface.c b/gpg-interface.c
index 127aecfc2b0..3c9a48c8e7e 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -8,6 +8,7 @@
 #include "tempfile.h"
 
 static char *configured_signing_key;
+const char *ssh_allowed_signers, *ssh_revocation_file;
 static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
 
 struct gpg_format {
@@ -35,6 +36,14 @@ static const char *x509_sigs[] = {
 	NULL
 };
 
+static const char *ssh_verify_args[] = {
+	NULL
+};
+static const char *ssh_sigs[] = {
+	"-----BEGIN SSH SIGNATURE-----",
+	NULL
+};
+
 static struct gpg_format gpg_format[] = {
 	{ .name = "openpgp", .program = "gpg",
 	  .verify_args = openpgp_verify_args,
@@ -44,6 +53,9 @@ static struct gpg_format gpg_format[] = {
 	  .verify_args = x509_verify_args,
 	  .sigs = x509_sigs
 	},
+	{ .name = "ssh", .program = "ssh-keygen",
+	  .verify_args = ssh_verify_args,
+	  .sigs = ssh_sigs },
 };
 
 static struct gpg_format *use_format = &gpg_format[0];
@@ -72,7 +84,7 @@ static struct gpg_format *get_format_by_sig(const char *sig)
 void signature_check_clear(struct signature_check *sigc)
 {
 	FREE_AND_NULL(sigc->payload);
-	FREE_AND_NULL(sigc->gpg_output);
+	FREE_AND_NULL(sigc->output);
 	FREE_AND_NULL(sigc->gpg_status);
 	FREE_AND_NULL(sigc->signer);
 	FREE_AND_NULL(sigc->key);
@@ -257,16 +269,15 @@ error:
 	FREE_AND_NULL(sigc->key);
 }
 
-static int verify_signed_buffer(const char *payload, size_t payload_size,
-				const char *signature, size_t signature_size,
-				struct strbuf *gpg_output,
-				struct strbuf *gpg_status)
+static int verify_gpg_signature(struct signature_check *sigc, struct gpg_format *fmt,
+	const char *payload, size_t payload_size,
+	const char *signature, size_t signature_size)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
-	struct gpg_format *fmt;
 	struct tempfile *temp;
 	int ret;
-	struct strbuf buf = STRBUF_INIT;
+	struct strbuf gpg_out = STRBUF_INIT;
+	struct strbuf gpg_err = STRBUF_INIT;
 
 	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
 	if (!temp)
@@ -279,29 +290,28 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 		return -1;
 	}
 
-	fmt = get_format_by_sig(signature);
-	if (!fmt)
-		BUG("bad signature '%s'", signature);
-
 	strvec_push(&gpg.args, fmt->program);
 	strvec_pushv(&gpg.args, fmt->verify_args);
 	strvec_pushl(&gpg.args,
-		     "--status-fd=1",
-		     "--verify", temp->filename.buf, "-",
-		     NULL);
-
-	if (!gpg_status)
-		gpg_status = &buf;
+			"--status-fd=1",
+			"--verify", temp->filename.buf, "-",
+			NULL);
 
 	sigchain_push(SIGPIPE, SIG_IGN);
-	ret = pipe_command(&gpg, payload, payload_size,
-			   gpg_status, 0, gpg_output, 0);
+	ret = pipe_command(&gpg, payload, payload_size, &gpg_out, 0,
+				&gpg_err, 0);
 	sigchain_pop(SIGPIPE);
+	ret |= !strstr(gpg_out.buf, "\n[GNUPG:] GOODSIG ");
 
-	delete_tempfile(&temp);
+	sigc->payload = xmemdupz(payload, payload_size);
+	sigc->output = strbuf_detach(&gpg_err, NULL);
+	sigc->gpg_status = strbuf_detach(&gpg_out, NULL);
 
-	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
-	strbuf_release(&buf); /* no matter it was used or not */
+	parse_gpg_output(sigc);
+
+	delete_tempfile(&temp);
+	strbuf_release(&gpg_out);
+	strbuf_release(&gpg_err);
 
 	return ret;
 }
@@ -309,35 +319,36 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 int check_signature(const char *payload, size_t plen, const char *signature,
 	size_t slen, struct signature_check *sigc)
 {
-	struct strbuf gpg_output = STRBUF_INIT;
-	struct strbuf gpg_status = STRBUF_INIT;
+	struct gpg_format *fmt;
 	int status;
 
 	sigc->result = 'N';
 	sigc->trust_level = -1;
 
-	status = verify_signed_buffer(payload, plen, signature, slen,
-				      &gpg_output, &gpg_status);
-	if (status && !gpg_output.len)
-		goto out;
-	sigc->payload = xmemdupz(payload, plen);
-	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
-	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
-	parse_gpg_output(sigc);
+	fmt = get_format_by_sig(signature);
+	if (!fmt) {
+		error(_("bad/incompatible signature '%s'"), signature);
+		return -1;
+	}
+
+	if (!strcmp(fmt->name, "ssh")) {
+		status = verify_ssh_signature(sigc, fmt, payload, plen, signature, slen);
+	} else {
+		status = verify_gpg_signature(sigc, fmt, payload, plen, signature, slen);
+	}
+	if (status && !sigc->output)
+		return !!status;
+
 	status |= sigc->result != 'G';
 	status |= sigc->trust_level < configured_min_trust_level;
 
- out:
-	strbuf_release(&gpg_status);
-	strbuf_release(&gpg_output);
-
 	return !!status;
 }
 
 void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
 {
 	const char *output = flags & GPG_VERIFY_RAW ?
-		sigc->gpg_status : sigc->gpg_output;
+		sigc->gpg_status : sigc->output;
 
 	if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
 		fputs(sigc->payload, stdout);
@@ -388,12 +399,32 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	int ret;
 
 	if (!strcmp(var, "user.signingkey")) {
+		/*
+		 * user.signingkey can contain one of the following
+		 * when format = openpgp/x509
+		 *   - GPG KeyID
+		 * when format = ssh
+		 *   - literal ssh public key (e.g. ssh-rsa XXXKEYXXX comment)
+		 *   - path to a file containing a public or a private ssh key
+		 */
 		if (!value)
 			return config_error_nonbool(var);
 		set_signing_key(value);
 		return 0;
 	}
 
+	if (!strcmp(var, "gpg.ssh.keyring")) {
+		if (!value)
+			return config_error_nonbool(var);
+		return git_config_string(&ssh_allowed_signers, var, value);
+	}
+
+	if (!strcmp(var, "gpg.ssh.revocationkeyring")) {
+		if (!value)
+			return config_error_nonbool(var);
+		return git_config_string(&ssh_revocation_file, var, value);
+	}
+
 	if (!strcmp(var, "gpg.format")) {
 		if (!value)
 			return config_error_nonbool(var);
@@ -425,6 +456,9 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	if (!strcmp(var, "gpg.x509.program"))
 		fmtname = "x509";
 
+	if (!strcmp(var, "gpg.ssh.program"))
+		fmtname = "ssh";
+
 	if (fmtname) {
 		fmt = get_format_by_name(fmtname);
 		return git_config_string(&fmt->program, var, value);
@@ -437,7 +471,19 @@ const char *get_signing_key(void)
 {
 	if (configured_signing_key)
 		return configured_signing_key;
-	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
+	if (!strcmp(use_format->name, "ssh")) {
+		return get_default_ssh_signing_key();
+	} else {
+		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
+	}
+}
+
+const char *get_ssh_allowed_signers(void)
+{
+	if (ssh_allowed_signers)
+		return ssh_allowed_signers;
+
+	die("A Path to an allowed signers ssh keyring is needed for validation");
 }
 
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
diff --git a/gpg-interface.h b/gpg-interface.h
index 80567e48948..5dfd92b81f6 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -17,8 +17,8 @@ enum signature_trust_level {
 
 struct signature_check {
 	char *payload;
-	char *gpg_output;
-	char *gpg_status;
+	char *output;
+	char *gpg_status; /* Only used internally -> remove from this public api */
 
 	/*
 	 * possible "result":
@@ -64,6 +64,7 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
 int git_gpg_config(const char *, const char *, void *);
 void set_signing_key(const char *);
 const char *get_signing_key(void);
+const char *get_ssh_allowed_signers(void);
 int check_signature(const char *payload, size_t plen,
 		    const char *signature, size_t slen,
 		    struct signature_check *sigc);
diff --git a/log-tree.c b/log-tree.c
index 7b823786c2c..20af9bd1c82 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -513,10 +513,10 @@ static void show_signature(struct rev_info *opt, struct commit *commit)
 
 	status = check_signature(payload.buf, payload.len, signature.buf,
 				 signature.len, &sigc);
-	if (status && !sigc.gpg_output)
+	if (status && !sigc.output)
 		show_sig_lines(opt, status, "No signature\n");
 	else
-		show_sig_lines(opt, status, sigc.gpg_output);
+		show_sig_lines(opt, status, sigc.output);
 	signature_check_clear(&sigc);
 
  out:
@@ -583,8 +583,8 @@ static int show_one_mergetag(struct commit *commit,
 		/* could have a good signature */
 		status = check_signature(payload.buf, payload.len,
 					 signature.buf, signature.len, &sigc);
-		if (sigc.gpg_output)
-			strbuf_addstr(&verify_message, sigc.gpg_output);
+		if (sigc.output)
+			strbuf_addstr(&verify_message, sigc.output);
 		else
 			strbuf_addstr(&verify_message, "No signature\n");
 		signature_check_clear(&sigc);
diff --git a/pretty.c b/pretty.c
index b1ecd039cef..daa71394efd 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1432,8 +1432,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 			check_commit_signature(c->commit, &(c->signature_check));
 		switch (placeholder[1]) {
 		case 'G':
-			if (c->signature_check.gpg_output)
-				strbuf_addstr(sb, c->signature_check.gpg_output);
+			if (c->signature_check.output)
+				strbuf_addstr(sb, c->signature_check.output);
 			break;
 		case '?':
 			switch (c->signature_check.result) {
-- 
gitgitgadget

[PATCH v3 2/9] ssh signing: add documentation

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 Documentation/config/gpg.txt  | 35 +++++++++++++++++++++++++++++++++--
 Documentation/config/user.txt |  6 ++++++
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
index d94025cb368..16af0b0ada8 100644
--- a/Documentation/config/gpg.txt
+++ b/Documentation/config/gpg.txt
@@ -11,13 +11,13 @@ gpg.program::
 
 gpg.format::
 	Specifies which key format to use when signing with `--gpg-sign`.
-	Default is "openpgp" and another possible value is "x509".
+	Default is "openpgp". Other possible values are "x509", "ssh".
 
 gpg.<format>.program::
 	Use this to customize the program used for the signing format you
 	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
 	be used as a legacy synonym for `gpg.openpgp.program`. The default
-	value for `gpg.x509.program` is "gpgsm".
+	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
 
 gpg.minTrustLevel::
 	Specifies a minimum trust level for signature verification.  If
@@ -33,3 +33,34 @@ gpg.minTrustLevel::
 * `marginal`
 * `fully`
 * `ultimate`
+
+gpg.ssh.keyring::
+	A file containing all valid SSH public signing keys.
+	Similar to an .ssh/authorized_keys file.
+	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
+	If a signing key is found in this file then the trust level will
+	be set to "fully". Otherwise if the key is not present
+	but the signature is still valid then the trust level will be "undefined".
+
+	This file can be set to a location outside of the repository
+	and every developer maintains their own trust store.
+	A central repository server could generate this file automatically
+	from ssh keys with push	access to verify the code against.
+	In a corporate setting this file is probably generated at a global location
+	from some automation that already handles developer ssh keys.
+
+	A repository that is only allowing signed commits can store the file
+	in the repository itself using a relative path. This way only committers
+	with an already valid key can add or change keys in the keyring.
+
+	Using a SSH CA key with the cert-authority option
+	(see ssh-keygen(1) "CERTIFICATES") is also valid.
+
+	To revoke a key place the public key without the principal into the
+	revocationKeyring.
+
+gpg.ssh.revocationKeyring::
+	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
+	See ssh-keygen(1) for details.
+	If a public key is found in this file then it will always be treated
+	as having trust level "never" and signatures will show as invalid.
diff --git a/Documentation/config/user.txt b/Documentation/config/user.txt
index 59aec7c3aed..b3c2f2c541e 100644
--- a/Documentation/config/user.txt
+++ b/Documentation/config/user.txt
@@ -36,3 +36,9 @@ user.signingKey::
 	commit, you can override the default selection with this variable.
 	This option is passed unchanged to gpg's --local-user parameter,
 	so you may specify a key using any method that gpg supports.
+	If gpg.format is set to "ssh" this can contain the literal ssh public
+	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and
+	corresponds to the private key used for signing. The private key
+	needs to be available via ssh-agent. Alternatively it can be set to
+	a file containing a private key directly. If not set git will call
+	"ssh-add -L" and try to use the first key available.
-- 
gitgitgadget

[PATCH v3 3/9] ssh signing: retrieve a default key from ssh-agent

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

calls ssh-add -L and uses the first key

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/gpg-interface.c b/gpg-interface.c
index 3c9a48c8e7e..c956ed87475 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -467,6 +467,23 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	return 0;
 }
 
+/* Returns the first public key from an ssh-agent to use for signing */
+static char *get_default_ssh_signing_key(void) {
+	struct child_process ssh_add = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf key_stdout = STRBUF_INIT;
+	struct strbuf **keys;
+
+	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
+	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
+	if (!ret) {
+		keys = strbuf_split_max(&key_stdout, '\n', 2);
+		if (keys[0])
+			return strbuf_detach(keys[0], NULL);
+	}
+
+	return "";
+}
 const char *get_signing_key(void)
 {
 	if (configured_signing_key)
-- 
gitgitgadget

[PATCH v3 4/9] ssh signing: sign using either gpg or ssh keys

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

implements the actual ssh-keygen -Y sign operation

Set gpg.format = ssh and user.signingkey to either a ssh public key
string (like from an authorized_keys file), or a ssh key file.
If the key file or the config value itself contains only a public key
then the private key needs to be available via ssh-agent.
If no signingkey is set then git will call 'ssh-add -L' to check for
available agent keys and use the first one for signing.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 86 +++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 76 insertions(+), 10 deletions(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index c956ed87475..fa32a57d372 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -505,30 +505,96 @@ const char *get_ssh_allowed_signers(void)
 
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
 {
-	struct child_process gpg = CHILD_PROCESS_INIT;
+	struct child_process signer = CHILD_PROCESS_INIT;
 	int ret;
 	size_t i, j, bottom;
-	struct strbuf gpg_status = STRBUF_INIT;
+	struct strbuf signer_stderr = STRBUF_INIT;
+	struct tempfile *temp = NULL, *buffer_file = NULL;
+	char *ssh_signing_key_file = NULL;
+	struct strbuf ssh_signature_filename = STRBUF_INIT;
 
-	strvec_pushl(&gpg.args,
-		     use_format->program,
+	if (!strcmp(use_format->name, "ssh")) {
+		if (!signing_key || signing_key[0] == '\0')
+			return error(_("user.signingkey needs to be set for ssh signing"));
+
+
+		if (istarts_with(signing_key, "ssh-")) {
+			/* A literal ssh key */
+			temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
+			if (!temp)
+				return error_errno(_("could not create temporary file"));
+			if (write_in_full(temp->fd, signing_key, strlen(signing_key)) < 0 ||
+				close_tempfile_gently(temp) < 0) {
+				error_errno(_("failed writing ssh signing key to '%s'"),
+					temp->filename.buf);
+				delete_tempfile(&temp);
+				return -1;
+			}
+			ssh_signing_key_file= temp->filename.buf;
+		} else {
+			/* We assume a file */
+			ssh_signing_key_file = expand_user_path(signing_key, 1);
+		}
+
+		buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
+		if (!buffer_file)
+			return error_errno(_("could not create temporary file"));
+		if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
+			close_tempfile_gently(buffer_file) < 0) {
+			error_errno(_("failed writing ssh signing key buffer to '%s'"),
+				buffer_file->filename.buf);
+			delete_tempfile(&buffer_file);
+			return -1;
+		}
+
+		strvec_pushl(&signer.args, use_format->program ,
+					"-Y", "sign",
+					"-n", "git",
+					"-f", ssh_signing_key_file,
+					buffer_file->filename.buf,
+					NULL);
+
+		sigchain_push(SIGPIPE, SIG_IGN);
+		ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
+		sigchain_pop(SIGPIPE);
+
+		strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
+		strbuf_addstr(&ssh_signature_filename, ".sig");
+		if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {
+			error_errno(_("failed reading ssh signing data buffer from '%s'"),
+				ssh_signature_filename.buf);
+		}
+		unlink_or_warn(ssh_signature_filename.buf);
+		strbuf_release(&ssh_signature_filename);
+		delete_tempfile(&buffer_file);
+	} else {
+		strvec_pushl(&signer.args, use_format->program ,
 		     "--status-fd=2",
 		     "-bsau", signing_key,
 		     NULL);
 
-	bottom = signature->len;
-
 	/*
 	 * When the username signingkey is bad, program could be terminated
 	 * because gpg exits without reading and then write gets SIGPIPE.
 	 */
 	sigchain_push(SIGPIPE, SIG_IGN);
-	ret = pipe_command(&gpg, buffer->buf, buffer->len,
-			   signature, 1024, &gpg_status, 0);
+		ret = pipe_command(&signer, buffer->buf, buffer->len, signature, 1024, &signer_stderr, 0);
 	sigchain_pop(SIGPIPE);
+	}
+
+	bottom = signature->len;
+
+	if (temp)
+		delete_tempfile(&temp);
 
-	ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
-	strbuf_release(&gpg_status);
+	if (!strcmp(use_format->name, "ssh")) {
+		if (strstr(signer_stderr.buf, "usage:")) {
+			error(_("openssh version > 8.2p1 is needed for ssh signing (ssh-keygen needs -Y sign option)"));
+		}
+	} else {
+		ret |= !strstr(signer_stderr.buf, "\n[GNUPG:] SIG_CREATED ");
+	}
+	strbuf_release(&signer_stderr);
 	if (ret)
 		return error(_("gpg failed to sign the data"));
 
-- 
gitgitgadget

[PATCH v3 5/9] ssh signing: provide a textual representation of the signing key

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

for ssh the key can be a filename/path or even a literal ssh pubkey
in push certs and textual output we prefer the ssh fingerprint instead

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 gpg-interface.h |  7 +++++++
 send-pack.c     |  8 ++++----
 3 files changed, 58 insertions(+), 4 deletions(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index fa32a57d372..328af86c272 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -467,6 +467,42 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	return 0;
 }
 
+static char *get_ssh_key_fingerprint(const char *signing_key) {
+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf fingerprint_stdout = STRBUF_INIT;
+	struct strbuf **fingerprint;
+
+	/*
+	 * With SSH Signing this can contain a filename or a public key
+	 * For textual representation we usually want a fingerprint
+	 */
+	if (istarts_with(signing_key, "ssh-")) {
+		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
+					"-lf", "-",
+					NULL);
+		ret = pipe_command(&ssh_keygen, signing_key, strlen(signing_key),
+			&fingerprint_stdout, 0,  NULL, 0);
+	} else {
+		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
+					"-lf", configured_signing_key,
+					NULL);
+		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0,
+			NULL, 0);
+	}
+
+	if (!!ret)
+		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
+			signing_key);
+
+	fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
+	if (!fingerprint[1])
+		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
+			signing_key);
+
+	return strbuf_detach(fingerprint[1], NULL);
+}
+
 /* Returns the first public key from an ssh-agent to use for signing */
 static char *get_default_ssh_signing_key(void) {
 	struct child_process ssh_add = CHILD_PROCESS_INIT;
@@ -484,6 +520,17 @@ static char *get_default_ssh_signing_key(void) {
 
 	return "";
 }
+
+/* Returns a textual but unique representation ot the signing key */
+const char *get_signing_key_id(void) {
+	if (!strcmp(use_format->name, "ssh")) {
+		return get_ssh_key_fingerprint(get_signing_key());
+	} else {
+		/* GPG/GPGSM only store a key id on this variable */
+		return get_signing_key();
+	}
+}
+
 const char *get_signing_key(void)
 {
 	if (configured_signing_key)
diff --git a/gpg-interface.h b/gpg-interface.h
index 5dfd92b81f6..1e842188c26 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -64,6 +64,13 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
 int git_gpg_config(const char *, const char *, void *);
 void set_signing_key(const char *);
 const char *get_signing_key(void);
+
+/*
+ * Returns a textual unique representation of the signing key in use
+ * Either a GPG KeyID or a SSH Key Fingerprint
+ */
+const char *get_signing_key_id(void);
+
 const char *get_ssh_allowed_signers(void);
 int check_signature(const char *payload, size_t plen,
 		    const char *signature, size_t slen,
diff --git a/send-pack.c b/send-pack.c
index 9cb9f716509..191fc6da544 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -341,13 +341,13 @@ static int generate_push_cert(struct strbuf *req_buf,
 {
 	const struct ref *ref;
 	struct string_list_item *item;
-	char *signing_key = xstrdup(get_signing_key());
+	char *signing_key_id = xstrdup(get_signing_key_id());
 	const char *cp, *np;
 	struct strbuf cert = STRBUF_INIT;
 	int update_seen = 0;
 
 	strbuf_addstr(&cert, "certificate version 0.1\n");
-	strbuf_addf(&cert, "pusher %s ", signing_key);
+	strbuf_addf(&cert, "pusher %s ", signing_key_id);
 	datestamp(&cert);
 	strbuf_addch(&cert, '\n');
 	if (args->url && *args->url) {
@@ -374,7 +374,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 	if (!update_seen)
 		goto free_return;
 
-	if (sign_buffer(&cert, &cert, signing_key))
+	if (sign_buffer(&cert, &cert, get_signing_key()))
 		die(_("failed to sign the push certificate"));
 
 	packet_buf_write(req_buf, "push-cert%c%s", 0, cap_string);
@@ -386,7 +386,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 	packet_buf_write(req_buf, "push-cert-end\n");
 
 free_return:
-	free(signing_key);
+	free(signing_key_id);
 	strbuf_release(&cert);
 	return update_seen;
 }
-- 
gitgitgadget

[PATCH v3 6/9] ssh signing: parse ssh-keygen output and verify signatures

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Verification uses the gpg.ssh.keyring file (see ssh-keygen(1) "ALLOWED
SIGNERS") which contains valid public keys and a principal (usually
user@domain). Depending on the environment this file can be managed by
the individual developer or for example generated by the central
repository server from known ssh keys with push access. If the
repository only allows signed commits / pushes then the file can even be
stored inside it.

To revoke a key put the public key without the principal prefix into
gpg.ssh.revocationKeyring or generate a KRL (see ssh-keygen(1)
"KEY REVOCATION LISTS"). The same considerations about who to trust for
verification as with the keyring file apply.

Using SSH CA Keys with these files is also possible. Add
"cert-authority" as key option between the principal and the key to mark
it as a CA and all keys signed by it as valid for this CA.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 builtin/receive-pack.c |   2 +
 gpg-interface.c        | 139 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 141 insertions(+)

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index a34742513ac..62b11c5f3a4 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -131,6 +131,8 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 {
 	int status = parse_hide_refs_config(var, value, "receive");
 
+	git_gpg_config(var, value, NULL);
+
 	if (status)
 		return status;
 
diff --git a/gpg-interface.c b/gpg-interface.c
index 328af86c272..1be88b87d96 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -3,6 +3,7 @@
 #include "config.h"
 #include "run-command.h"
 #include "strbuf.h"
+#include "dir.h"
 #include "gpg-interface.h"
 #include "sigchain.h"
 #include "tempfile.h"
@@ -156,6 +157,42 @@ static int parse_gpg_trust_level(const char *level,
 	return 1;
 }
 
+static void parse_ssh_output(struct signature_check *sigc)
+{
+	struct string_list parts = STRING_LIST_INIT_DUP;
+	char *line = NULL;
+
+	/*
+	 * ssh-keysign output should be:
+	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
+	 * or for valid but unknown keys:
+	 * Good "git" signature with RSA key SHA256:FINGERPRINT
+	 */
+	sigc->result = 'B';
+	sigc->trust_level = TRUST_NEVER;
+
+	line = xmemdupz(sigc->output, strcspn(sigc->output, "\n"));
+	string_list_split(&parts, line, ' ', 8);
+	if (parts.nr >= 9 && starts_with(line, "Good \"git\" signature for ")) {
+		/* Valid signature for a trusted signer */
+		sigc->result = 'G';
+		sigc->trust_level = TRUST_FULLY;
+		sigc->signer = xstrdup(parts.items[4].string);
+		sigc->fingerprint = xstrdup(parts.items[8].string);
+		sigc->key = xstrdup(sigc->fingerprint);
+	} else if (parts.nr >= 7 && starts_with(line, "Good \"git\" signature with ")) {
+		/* Valid signature, but key unknown */
+		sigc->result = 'G';
+		sigc->trust_level = TRUST_UNDEFINED;
+		sigc->fingerprint = xstrdup(parts.items[6].string);
+		sigc->key = xstrdup(sigc->fingerprint);
+	}
+	trace_printf("trace: sigc result %c/%d - %s %s %s", sigc->result, sigc->trust_level, sigc->signer, sigc->fingerprint, sigc->key);
+
+	string_list_clear(&parts, 0);
+	FREE_AND_NULL(line);
+}
+
 static void parse_gpg_output(struct signature_check *sigc)
 {
 	const char *buf = sigc->gpg_status;
@@ -269,6 +306,108 @@ error:
 	FREE_AND_NULL(sigc->key);
 }
 
+static int verify_ssh_signature(struct signature_check *sigc,
+	struct gpg_format *fmt,
+	const char *payload, size_t payload_size,
+	const char *signature, size_t signature_size)
+{
+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
+	struct tempfile *temp;
+	int ret;
+	const char *line;
+	size_t trust_size;
+	char *principal;
+	struct strbuf ssh_keygen_out = STRBUF_INIT;
+	struct strbuf ssh_keygen_err = STRBUF_INIT;
+
+	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
+	if (!temp)
+		return error_errno(_("could not create temporary file"));
+	if (write_in_full(temp->fd, signature, signature_size) < 0 ||
+	    close_tempfile_gently(temp) < 0) {
+		error_errno(_("failed writing detached signature to '%s'"),
+			    temp->filename.buf);
+		delete_tempfile(&temp);
+		return -1;
+	}
+
+	/* Find the principal from the signers */
+	strvec_pushl(&ssh_keygen.args,  fmt->program,
+					"-Y", "find-principals",
+					"-f", get_ssh_allowed_signers(),
+					"-s", temp->filename.buf,
+					NULL);
+	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
+	if (strstr(ssh_keygen_err.buf, "usage:")) {
+		error(_("openssh version > 8.2p1 is needed for ssh signature verification (ssh-keygen needs -Y find-principals/verify option)"));
+	}
+	if (ret || !ssh_keygen_out.len) {
+		/* We did not find a matching principal in the keyring - Check without validation */
+		child_process_init(&ssh_keygen);
+		strvec_pushl(&ssh_keygen.args,  fmt->program,
+						"-Y", "check-novalidate",
+						"-n", "git",
+						"-s", temp->filename.buf,
+						NULL);
+		ret = pipe_command(&ssh_keygen, payload, payload_size, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
+	} else {
+		/* Check every principal we found (one per line) */
+		for (line = ssh_keygen_out.buf; *line; line = strchrnul(line + 1, '\n')) {
+			while (*line == '\n')
+				line++;
+			if (!*line)
+				break;
+
+			trust_size = strcspn(line, " \n");
+			principal = xmemdupz(line, trust_size);
+
+			child_process_init(&ssh_keygen);
+			strbuf_release(&ssh_keygen_out);
+			strbuf_release(&ssh_keygen_err);
+			strvec_push(&ssh_keygen.args,fmt->program);
+			/* We found principals - Try with each until we find a match */
+			strvec_pushl(&ssh_keygen.args,  "-Y", "verify",
+							"-n", "git",
+							"-f", get_ssh_allowed_signers(),
+							"-I", principal,
+							"-s", temp->filename.buf,
+							NULL);
+
+			if (ssh_revocation_file) {
+				if (file_exists(ssh_revocation_file)) {
+					strvec_pushl(&ssh_keygen.args, "-r", ssh_revocation_file, NULL);
+				} else {
+					warning(_("ssh signing revocation file configured but not found: %s"), ssh_revocation_file);
+				}
+			}
+
+			sigchain_push(SIGPIPE, SIG_IGN);
+			ret = pipe_command(&ssh_keygen, payload, payload_size,
+					&ssh_keygen_out, 0, &ssh_keygen_err, 0);
+			sigchain_pop(SIGPIPE);
+
+			ret &= starts_with(ssh_keygen_out.buf, "Good");
+			if (ret == 0)
+				break;
+		}
+	}
+
+	sigc->payload = xmemdupz(payload, payload_size);
+	strbuf_stripspace(&ssh_keygen_out, 0);
+	strbuf_stripspace(&ssh_keygen_err, 0);
+	strbuf_add(&ssh_keygen_out, ssh_keygen_err.buf, ssh_keygen_err.len);
+	sigc->output = strbuf_detach(&ssh_keygen_out, NULL);
+	sigc->gpg_status = xstrdup(sigc->output);
+
+	parse_ssh_output(sigc);
+
+	delete_tempfile(&temp);
+	strbuf_release(&ssh_keygen_out);
+	strbuf_release(&ssh_keygen_err);
+
+	return ret;
+}
+
 static int verify_gpg_signature(struct signature_check *sigc, struct gpg_format *fmt,
 	const char *payload, size_t payload_size,
 	const char *signature, size_t signature_size)
-- 
gitgitgadget

[PATCH v3 7/9] ssh signing: add test prereqs

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

generate some ssh keys and a allowed keys keyring for testing

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/lib-gpg.sh | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/t/lib-gpg.sh b/t/lib-gpg.sh
index 9fc5241228e..c65cdde9e5f 100644
--- a/t/lib-gpg.sh
+++ b/t/lib-gpg.sh
@@ -87,6 +87,33 @@ test_lazy_prereq RFC1991 '
 	echo | gpg --homedir "${GNUPGHOME}" -b --rfc1991 >/dev/null
 '
 
+test_lazy_prereq GPGSSH '
+	ssh_version=$(ssh-keygen -Y find-principals -n "git" 2>&1)
+	test $? != 127 || exit 1
+	echo $ssh_version | grep -q "find-principals:missing signature file"
+	test $? = 0 || exit 1;
+	mkdir -p "${GNUPGHOME}" &&
+	chmod 0700 "${GNUPGHOME}" &&
+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/ed25519_ssh_signing_key" >/dev/null &&
+	ssh-keygen -t rsa -b 2048 -N "" -f "${GNUPGHOME}/rsa_2048_ssh_signing_key" >/dev/null &&
+	ssh-keygen -t ed25519 -N "super_secret" -f "${GNUPGHOME}/protected_ssh_signing_key" >/dev/null &&
+	find "${GNUPGHOME}" -name *ssh_signing_key.pub -exec cat {} \; | awk "{print \"principal_\" NR \" \" \$0}" > "${GNUPGHOME}/ssh.all_valid.keyring" &&
+	cat "${GNUPGHOME}/ssh.all_valid.keyring" &&
+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/untrusted_ssh_signing_key" >/dev/null
+'
+
+SIGNING_KEY_PRIMARY="${GNUPGHOME}/ed25519_ssh_signing_key"
+SIGNING_KEY_SECONDARY="${GNUPGHOME}/rsa_2048_ssh_signing_key"
+SIGNING_KEY_UNTRUSTED="${GNUPGHOME}/untrusted_ssh_signing_key"
+SIGNING_KEY_WITH_PASSPHRASE="${GNUPGHOME}/protected_ssh_signing_key"
+SIGNING_KEY_PASSPHRASE="super_secret"
+SIGNING_KEYRING="${GNUPGHOME}/ssh.all_valid.keyring"
+
+GOOD_SIGNATURE_TRUSTED='Good "git" signature for'
+GOOD_SIGNATURE_UNTRUSTED='Good "git" signature with'
+KEY_NOT_TRUSTED="No principal matched"
+BAD_SIGNATURE="Signature verification failed"
+
 sanitize_pgp() {
 	perl -ne '
 		/^-----END PGP/ and $in_pgp = 0;
-- 
gitgitgadget

[PATCH v3 8/9] ssh signing: duplicate t7510 tests for commits

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/t7527-signed-commit-ssh.sh | 398 +++++++++++++++++++++++++++++++++++
 1 file changed, 398 insertions(+)
 create mode 100755 t/t7527-signed-commit-ssh.sh

diff --git a/t/t7527-signed-commit-ssh.sh b/t/t7527-signed-commit-ssh.sh
new file mode 100755
index 00000000000..305b3b9160b
--- /dev/null
+++ b/t/t7527-signed-commit-ssh.sh
@@ -0,0 +1,398 @@
+#!/bin/sh
+
+test_description='ssh signed commit tests'
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+GNUPGHOME_NOT_USED=$GNUPGHOME
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPGSSH 'create signed commits' '
+	test_oid_cache <<-\EOF &&
+	header sha1:gpgsig
+	header sha256:gpgsig-sha256
+	EOF
+
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+
+	echo 1 >file && git add file &&
+	test_tick && git commit -S -m initial &&
+	git tag initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -S -m second &&
+	git tag second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout main &&
+	test_tick && git merge -S side &&
+	git tag merge &&
+
+	echo 4 >file && test_tick && git commit -a -m "fourth unsigned" &&
+	git tag fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag fourth-signed &&
+
+	git config commit.gpgsign true &&
+	echo 5 >file && test_tick && git commit -a -m "fifth signed" &&
+	git tag fifth-signed &&
+
+	git config commit.gpgsign false &&
+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
+	git tag sixth-unsigned &&
+
+	git config commit.gpgsign true &&
+	echo 7 >file && test_tick && git commit -a -m "seventh" --no-gpg-sign &&
+	git tag seventh-unsigned &&
+
+	test_tick && git rebase -f HEAD^^ && git tag sixth-signed HEAD^ &&
+	git tag seventh-signed &&
+
+	echo 8 >file && test_tick && git commit -a -m eighth -S"${SIGNING_KEY_UNTRUSTED}" &&
+	git tag eighth-signed-alt &&
+
+	# commit.gpgsign is still on but this must not be signed
+	echo 9 | git commit-tree HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag ninth-unsigned $(cat oid) &&
+	# explicit -S of course must sign.
+	echo 10 | git commit-tree -S HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag tenth-signed $(cat oid) &&
+
+	# --gpg-sign[=<key-id>] must sign.
+	echo 11 | git commit-tree --gpg-sign HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag eleventh-signed $(cat oid) &&
+	echo 12 | git commit-tree --gpg-sign="${SIGNING_KEY_UNTRUSTED}" HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag twelfth-signed-alt $(cat oid)
+'
+
+test_expect_success GPGSSH 'verify and show signatures' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	test_config gpg.mintrustlevel UNDEFINED &&
+	(
+		for commit in initial second merge fourth-signed \
+			fifth-signed sixth-signed seventh-signed tenth-signed \
+			eleventh-signed
+		do
+			git verify-commit $commit &&
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in merge^2 fourth-unsigned sixth-unsigned \
+			seventh-unsigned ninth-unsigned
+		do
+			test_must_fail git verify-commit $commit &&
+			git show --pretty=short --show-signature $commit >actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in eighth-signed-alt twelfth-signed-alt
+		do
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			grep "${KEY_NOT_TRUSTED}" actual &&
+			echo $commit OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'verify-commit exits success on untrusted signature' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git verify-commit eighth-signed-alt 2>actual &&
+	grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual &&
+	grep "${KEY_NOT_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH 'verify-commit exits success with matching minTrustLevel' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	test_config gpg.minTrustLevel fully &&
+	git verify-commit sixth-signed
+'
+
+test_expect_success GPGSSH 'verify-commit exits success with low minTrustLevel' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	test_config gpg.minTrustLevel marginal &&
+	git verify-commit sixth-signed
+'
+
+test_expect_success GPGSSH 'verify-commit exits failure with high minTrustLevel' '
+	test_config gpg.minTrustLevel ultimate &&
+	test_must_fail git verify-commit eighth-signed-alt
+'
+
+test_expect_success GPGSSH 'verify signatures with --raw' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	(
+		for commit in initial second merge fourth-signed fifth-signed sixth-signed seventh-signed
+		do
+			git verify-commit --raw $commit 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in merge^2 fourth-unsigned sixth-unsigned seventh-unsigned
+		do
+			test_must_fail git verify-commit --raw $commit 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in eighth-signed-alt
+		do
+			git verify-commit --raw $commit 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'proper header is used for hash algorithm' '
+	git cat-file commit fourth-signed >output &&
+	grep "^$(test_oid header) -----BEGIN SSH SIGNATURE-----" output
+'
+
+test_expect_success GPGSSH 'show signed commit with signature' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git show -s initial >commit &&
+	git show -s --show-signature initial >show &&
+	git verify-commit -v initial >verify.1 2>verify.2 &&
+	git cat-file commit initial >cat &&
+	grep -v -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.commit &&
+	grep -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.gpg &&
+	grep -v "^ " cat | grep -v "^gpgsig.* " >cat.commit &&
+	test_cmp show.commit commit &&
+	test_cmp show.gpg verify.2 &&
+	test_cmp cat.commit verify.1
+'
+
+test_expect_success GPGSSH 'detect fudged signature' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git cat-file commit seventh-signed >raw &&
+	sed -e "s/^seventh/7th forged/" raw >forged1 &&
+	git hash-object -w -t commit forged1 >forged1.commit &&
+	test_must_fail git verify-commit $(cat forged1.commit) &&
+	git show --pretty=short --show-signature $(cat forged1.commit) >actual1 &&
+	grep "${BAD_SIGNATURE}" actual1 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
+'
+
+test_expect_success GPGSSH 'detect fudged signature with NUL' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git cat-file commit seventh-signed >raw &&
+	cat raw >forged2 &&
+	echo Qwik | tr "Q" "\000" >>forged2 &&
+	git hash-object -w -t commit forged2 >forged2.commit &&
+	test_must_fail git verify-commit $(cat forged2.commit) &&
+	git show --pretty=short --show-signature $(cat forged2.commit) >actual2 &&
+	grep "${BAD_SIGNATURE}" actual2 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual2
+'
+
+test_expect_success GPGSSH 'amending already signed commit' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git checkout fourth-signed^0 &&
+	git commit --amend -S --no-edit &&
+	git verify-commit HEAD &&
+	git show -s --show-signature HEAD >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual
+'
+
+test_expect_success GPGSSH 'show good signature with custom format' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	cat >expect.tmpl <<-\EOF &&
+	G
+	FINGERPRINT
+	principal_1
+	FINGERPRINT
+
+	EOF
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show bad signature with custom format' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	cat >expect <<-\EOF &&
+	B
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat forged1.commit) >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with custom format' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	cat >expect.tmpl <<-\EOF &&
+	U
+	FINGERPRINT
+
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with undefined trust level' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	cat >expect.tmpl <<-\EOF &&
+	undefined
+	FINGERPRINT
+
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with ultimate trust level' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	cat >expect.tmpl <<-\EOF &&
+	fully
+	FINGERPRINT
+	principal_1
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show lack of signature with custom format' '
+	cat >expect <<-\EOF &&
+	N
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" seventh-unsigned >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'log.showsignature behaves like --show-signature' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	test_config log.showsignature true &&
+	git show initial >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH 'check config gpg.format values' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_config gpg.format ssh &&
+	git commit -S --amend -m "success" &&
+	test_config gpg.format OpEnPgP &&
+	test_must_fail git commit -S --amend -m "fail"
+'
+
+test_expect_failure GPGSSH 'detect fudged commit with double signature (TODO)' '
+	sed -e "/gpgsig/,/END PGP/d" forged1 >double-base &&
+	sed -n -e "/gpgsig/,/END PGP/p" forged1 | \
+		sed -e "s/^$(test_oid header)//;s/^ //" | gpg --dearmor >double-sig1.sig &&
+	gpg -o double-sig2.sig -u 29472784 --detach-sign double-base &&
+	cat double-sig1.sig double-sig2.sig | gpg --enarmor >double-combined.asc &&
+	sed -e "s/^\(-.*\)ARMORED FILE/\1SIGNATURE/;1s/^/$(test_oid header) /;2,\$s/^/ /" \
+		double-combined.asc > double-gpgsig &&
+	sed -e "/committer/r double-gpgsig" double-base >double-commit &&
+	git hash-object -w -t commit double-commit >double-commit.commit &&
+	test_must_fail git verify-commit $(cat double-commit.commit) &&
+	git show --pretty=short --show-signature $(cat double-commit.commit) >double-actual &&
+	grep "BAD signature from" double-actual &&
+	grep "Good signature from" double-actual
+'
+
+test_expect_failure GPGSSH 'show double signature with custom format (TODO)' '
+	cat >expect <<-\EOF &&
+	E
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat double-commit.commit) >actual &&
+	test_cmp expect actual
+'
+
+
+test_expect_failure GPGSSH 'verify-commit verifies multiply signed commits (TODO)' '
+	git init multiply-signed &&
+	cd multiply-signed &&
+	test_commit first &&
+	echo 1 >second &&
+	git add second &&
+	tree=$(git write-tree) &&
+	parent=$(git rev-parse HEAD^{commit}) &&
+	git commit --gpg-sign -m second &&
+	git cat-file commit HEAD &&
+	# Avoid trailing whitespace.
+	sed -e "s/^Q//" -e "s/^Z/ /" >commit <<-EOF &&
+	Qtree $tree
+	Qparent $parent
+	Qauthor A U Thor <author@example.com> 1112912653 -0700
+	Qcommitter C O Mitter <committer@example.com> 1112912653 -0700
+	Qgpgsig -----BEGIN PGP SIGNATURE-----
+	QZ
+	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBDRYcY29tbWl0dGVy
+	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMNd+8AoK1I8mhLHviPH+q2I5fIVgPsEtYC
+	Q AKCTqBh+VabJceXcGIZuF0Ry+udbBQ==
+	Q =tQ0N
+	Q -----END PGP SIGNATURE-----
+	Qgpgsig-sha256 -----BEGIN PGP SIGNATURE-----
+	QZ
+	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBIBYcY29tbWl0dGVy
+	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMN/NEAn0XO9RYSBj2dFyozi0JKSbssYMtO
+	Q AJwKCQ1BQOtuwz//IjU8TiS+6S4iUw==
+	Q =pIwP
+	Q -----END PGP SIGNATURE-----
+	Q
+	Qsecond
+	EOF
+	head=$(git hash-object -t commit -w commit) &&
+	git reset --hard $head &&
+	git verify-commit $head 2>actual &&
+	grep "Good signature from" actual &&
+	! grep "BAD signature from" actual
+'
+
+test_done
-- 
gitgitgadget

[PATCH v3 9/9] ssh signing: add more tests for logs, tags & push certs

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/t4202-log.sh                   |  23 +++++
 t/t5534-push-signed.sh           | 101 +++++++++++++++++++
 t/t7031-verify-tag-signed-ssh.sh | 161 +++++++++++++++++++++++++++++++
 3 files changed, 285 insertions(+)
 create mode 100755 t/t7031-verify-tag-signed-ssh.sh

diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index 350cfa35936..41767627ad0 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -1616,6 +1616,16 @@ test_expect_success GPGSM 'setup signed branch x509' '
 	git commit -S -m signed_commit
 '
 
+test_expect_success GPGSSH 'setup sshkey signed branch' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_when_finished "git reset --hard && git checkout main" &&
+	git checkout -b signed-ssh main &&
+	echo foo >foo &&
+	git add foo &&
+	git commit -S -m signed_commit
+'
+
 test_expect_success GPGSM 'log x509 fingerprint' '
 	echo "F8BF62E0693D0694816377099909C779FA23FD65 | " >expect &&
 	git log -n1 --format="%GF | %GP" signed-x509 >actual &&
@@ -1628,6 +1638,13 @@ test_expect_success GPGSM 'log OpenPGP fingerprint' '
 	test_cmp expect actual
 '
 
+test_expect_success GPGSSH 'log ssh key fingerprint' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	ssh-keygen -lf  "${SIGNING_KEY_PRIMARY}" | awk "{print \$2\" | \"}" >expect &&
+	git log -n1 --format="%GF | %GP" signed-ssh >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success GPG 'log --graph --show-signature' '
 	git log --graph --show-signature -n1 signed >actual &&
 	grep "^| gpg: Signature made" actual &&
@@ -1640,6 +1657,12 @@ test_expect_success GPGSM 'log --graph --show-signature x509' '
 	grep "^| gpgsm: Good signature" actual
 '
 
+test_expect_success GPGSSH 'log --graph --show-signature ssh' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git log --graph --show-signature -n1 signed-ssh >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual
+'
+
 test_expect_success GPG 'log --graph --show-signature for merged tag' '
 	test_when_finished "git reset --hard && git checkout main" &&
 	git checkout -b plain main &&
diff --git a/t/t5534-push-signed.sh b/t/t5534-push-signed.sh
index bba768f5ded..37c97756032 100755
--- a/t/t5534-push-signed.sh
+++ b/t/t5534-push-signed.sh
@@ -137,6 +137,53 @@ test_expect_success GPG 'signed push sends push certificate' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPGSSH 'ssh signed push sends push certificate' '
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=principal_1
+		KEY=FINGERPRINT
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
+
+	noop=$(git rev-parse noop) &&
+	ff=$(git rev-parse ff) &&
+	noff=$(git rev-parse noff) &&
+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_expect_success GPG 'inconsistent push options in signed push not allowed' '
 	# First, invoke receive-pack with dummy input to obtain its preamble.
 	prepare_dst &&
@@ -276,6 +323,60 @@ test_expect_success GPGSM 'fail without key and heed user.signingkey x509' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPGSSH 'fail without key and heed user.signingkey ssh' '
+	test_config gpg.format ssh &&
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	test_config user.email hasnokey@nowhere.com &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "" &&
+	(
+		sane_unset GIT_COMMITTER_EMAIL &&
+		test_must_fail git push --signed dst noop ff +noff
+	) &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=principal_1
+		KEY=FINGERPRINT
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
+
+	noop=$(git rev-parse noop) &&
+	ff=$(git rev-parse ff) &&
+	noff=$(git rev-parse noff) &&
+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_expect_success GPG 'failed atomic push does not execute GPG' '
 	prepare_dst &&
 	git -C dst config receive.certnonceseed sekrit &&
diff --git a/t/t7031-verify-tag-signed-ssh.sh b/t/t7031-verify-tag-signed-ssh.sh
new file mode 100755
index 00000000000..2148a246385
--- /dev/null
+++ b/t/t7031-verify-tag-signed-ssh.sh
@@ -0,0 +1,161 @@
+#!/bin/sh
+
+test_description='signed tag tests'
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPGSSH 'create signed tags ssh' '
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+
+	echo 1 >file && git add file &&
+	test_tick && git commit -m initial &&
+	git tag -s -m initial initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -m second &&
+	git tag -s -m second second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout main &&
+	test_tick && git merge -S side &&
+	git tag -s -m merge merge &&
+
+	echo 4 >file && test_tick && git commit -a -S -m "fourth unsigned" &&
+	git tag -a -m fourth-unsigned fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag -s -m fourth fourth-signed &&
+
+	echo 5 >file && test_tick && git commit -a -m "fifth" &&
+	git tag fifth-unsigned &&
+
+	git config commit.gpgsign true &&
+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
+	git tag -a -m sixth sixth-unsigned &&
+
+	test_tick && git rebase -f HEAD^^ && git tag -s -m 6th sixth-signed HEAD^ &&
+	git tag -m seventh -s seventh-signed &&
+
+	echo 8 >file && test_tick && git commit -a -m eighth &&
+	git tag -u"${SIGNING_KEY_UNTRUSTED}" -m eighth eighth-signed-alt
+'
+
+test_expect_success GPGSSH 'verify and show ssh signatures' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	(
+		for tag in initial second merge fourth-signed sixth-signed seventh-signed
+		do
+			git verify-tag $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
+		do
+			test_must_fail git verify-tag $tag 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in eighth-signed-alt
+		do
+			git verify-tag $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			grep "${KEY_NOT_TRUSTED}" actual &&
+			echo $tag OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'detect fudged ssh signature' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git cat-file tag seventh-signed >raw &&
+	sed -e "/^tag / s/seventh/7th forged/" raw >forged1 &&
+	git hash-object -w -t tag forged1 >forged1.tag &&
+	test_must_fail git verify-tag $(cat forged1.tag) 2>actual1 &&
+	grep "${BAD_SIGNATURE}" actual1 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
+'
+
+test_expect_success GPGSSH 'verify ssh signatures with --raw' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	(
+		for tag in initial second merge fourth-signed sixth-signed seventh-signed
+		do
+			git verify-tag --raw $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
+		do
+			test_must_fail git verify-tag --raw $tag 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in eighth-signed-alt
+		do
+			git verify-tag --raw $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'verify signatures with --raw ssh' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	git verify-tag --raw sixth-signed 2>actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual &&
+	echo sixth-signed OK
+'
+
+test_expect_success GPGSSH 'verify multiple tags ssh' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	tags="seventh-signed sixth-signed" &&
+	for i in $tags
+	do
+		git verify-tag -v --raw $i || return 1
+	done >expect.stdout 2>expect.stderr.1 &&
+	grep "^${GOOD_SIGNATURE_TRUSTED}" <expect.stderr.1 >expect.stderr &&
+	git verify-tag -v --raw $tags >actual.stdout 2>actual.stderr.1 &&
+	grep "^${GOOD_SIGNATURE_TRUSTED}" <actual.stderr.1 >actual.stderr &&
+	test_cmp expect.stdout actual.stdout &&
+	test_cmp expect.stderr actual.stderr
+'
+
+test_expect_success GPGSSH 'verifying tag with --format - ssh' '
+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
+	cat >expect <<-\EOF &&
+	tagname : fourth-signed
+	EOF
+	git verify-tag --format="tagname : %(tag)" "fourth-signed" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'verifying a forged tag with --format should fail silently - ssh' '
+	test_must_fail git verify-tag --format="tagname : %(tag)" $(cat forged1.tag) >actual-forged &&
+	test_must_be_empty actual-forged
+'
+
+test_done
-- 
gitgitgadget

Re: [PATCH v3 1/9] Add commit, tag & push signing via SSH keys

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Fabian Stelzer <fs@gigacodes.de>
> Subject: [PATCH v3 1/9] Add commit, tag & push signing via SSH keys

If you chose "ssh signing:" as the common prefix for the series, use
it consistently with this step, too.

> Openssh v8.2p1 added some new options to ssh-keygen for signature
> creation and verification. These allow us to use ssh keys for git
> signatures easily.
>
> Start with adding the new signature format, new config options and
> rename some fields for consistency.

OK.

> This feature makes git signing much more accessible to the average user.
> Usually they have a SSH Key for pushing code already. Using it
> for signing commits allows us to verify not only the transport but the
> pushed code as well.

Drop this paragraph or at least tone it down.  It may hold true only
around your immediate circle but it is far from clear and obvious.
I'd expect more people push over https:// than ssh://.

We do not really require a new feature to make much more accessible
for wide average user---making it just a bit more accessible to
folks in your immediate circle is perfectly fine, as long as you are
not harming other people ;-)

> In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
> signing/encryption and ssh keys which i think is quite common

Upcase "I".

> (at least for the email part). This way we can establish the correct
> trust for the SSH Keys without setting up a separate GPG Infrastructure
> (which is still quite painful for users) or implementing x509 signing
> support for git (which lacks good forwarding mechanisms).
> Using ssh agent forwarding makes this feature easily usable in todays
> development environments where code is often checked out in remote VMs / containers.
> In such a setup the keyring & revocationKeyring can be centrally
> generated from the x509 CA information and distributed to the users.

All of the above promises a wonderful new world, but what is left
unclear is with this step alone how much of the new world we already
gain.  When you ask others to read and understand your code, please
give them a bit more hint to guide them what to expect and where you
are taking them next. 

> diff --git a/fmt-merge-msg.c b/fmt-merge-msg.c
> index 0f66818e0f8..1d7b64fa021 100644
> --- a/fmt-merge-msg.c
> +++ b/fmt-merge-msg.c
> @@ -527,10 +527,10 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
>  			len = payload.len;
>  			if (check_signature(payload.buf, payload.len, sig.buf,
>  					 sig.len, &sigc) &&
> -				!sigc.gpg_output)
> +				!sigc.output)
>  				strbuf_addstr(&sig, "gpg verification failed.\n");
>  			else
> -				strbuf_addstr(&sig, sigc.gpg_output);
> +				strbuf_addstr(&sig, sigc.output);

These are "rename some fields for consistency" the proposed log
message promised.  Makes sense, as you are taking the sigc structure
away from pgp/gpg dependency.

> diff --git a/gpg-interface.c b/gpg-interface.c
> index 127aecfc2b0..3c9a48c8e7e 100644
> --- a/gpg-interface.c
> +++ b/gpg-interface.c
> @@ -8,6 +8,7 @@
>  #include "tempfile.h"
>  
>  static char *configured_signing_key;
> +const char *ssh_allowed_signers, *ssh_revocation_file;

Very likely these want to be file-scope statics?

>  static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
>  
>  struct gpg_format {
> @@ -35,6 +36,14 @@ static const char *x509_sigs[] = {
>  	NULL
>  };
>  
> +static const char *ssh_verify_args[] = {
> +	NULL
> +};

A blank line is missing from here.

> +static const char *ssh_sigs[] = {
> +	"-----BEGIN SSH SIGNATURE-----",
> +	NULL
> +};
> +
>  static struct gpg_format gpg_format[] = {
>  	{ .name = "openpgp", .program = "gpg",
>  	  .verify_args = openpgp_verify_args,
> @@ -44,6 +53,9 @@ static struct gpg_format gpg_format[] = {
>  	  .verify_args = x509_verify_args,
>  	  .sigs = x509_sigs
>  	},
> +	{ .name = "ssh", .program = "ssh-keygen",
> +	  .verify_args = ssh_verify_args,
> +	  .sigs = ssh_sigs },
>  };
>  
>  static struct gpg_format *use_format = &gpg_format[0];
> @@ -72,7 +84,7 @@ static struct gpg_format *get_format_by_sig(const char *sig)
>  void signature_check_clear(struct signature_check *sigc)
>  {
>  	FREE_AND_NULL(sigc->payload);
> -	FREE_AND_NULL(sigc->gpg_output);
> +	FREE_AND_NULL(sigc->output);
>  	FREE_AND_NULL(sigc->gpg_status);
>  	FREE_AND_NULL(sigc->signer);
>  	FREE_AND_NULL(sigc->key);
> @@ -257,16 +269,15 @@ error:
>  	FREE_AND_NULL(sigc->key);
>  }
>  
> -static int verify_signed_buffer(const char *payload, size_t payload_size,
> -				const char *signature, size_t signature_size,
> -				struct strbuf *gpg_output,
> -				struct strbuf *gpg_status)
> +static int verify_gpg_signature(struct signature_check *sigc, struct gpg_format *fmt,
> +	const char *payload, size_t payload_size,
> +	const char *signature, size_t signature_size)
>  {

What is this hunk about?  The more generic name "verify-signed-buffer"
is rescinded and gets replaced by a more GPG/PGP specific helper?

You'd need to help readers a bit more by explaining in the proposed
log message that you shifted the boundary of responsibility between
check_signature() and verify_signed_buffer()---it used to be that
the latter inspected the signed payload to see if it a valid GPG/PGP
signature before doing GPG specific validation, but you want to make
the former responsible for calling get_format_by_sig(), so that you
can dispatch a totally new backend that sits next to this GPG
specific one.

>  	struct child_process gpg = CHILD_PROCESS_INIT;
> -	struct gpg_format *fmt;
>  	struct tempfile *temp;
>  	int ret;
> -	struct strbuf buf = STRBUF_INIT;
> +	struct strbuf gpg_out = STRBUF_INIT;
> +	struct strbuf gpg_err = STRBUF_INIT;
>  
>  	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
>  	if (!temp)
> @@ -279,29 +290,28 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
>  		return -1;
>  	}
>  
> -	fmt = get_format_by_sig(signature);
> -	if (!fmt)
> -		BUG("bad signature '%s'", signature);
> -
>  	strvec_push(&gpg.args, fmt->program);
>  	strvec_pushv(&gpg.args, fmt->verify_args);
>  	strvec_pushl(&gpg.args,
> -		     "--status-fd=1",
> -		     "--verify", temp->filename.buf, "-",
> -		     NULL);
> -
> -	if (!gpg_status)
> -		gpg_status = &buf;
> +			"--status-fd=1",
> +			"--verify", temp->filename.buf, "-",
> +			NULL);

What is going on around here?  Ahh, an unnecessary indentation
change is fooling the diff and made the patch unreadable.  Sigh...

>  	sigchain_push(SIGPIPE, SIG_IGN);
> -	ret = pipe_command(&gpg, payload, payload_size,
> -			   gpg_status, 0, gpg_output, 0);
> +	ret = pipe_command(&gpg, payload, payload_size, &gpg_out, 0,
> +				&gpg_err, 0);

What is this change about?  Is it another unnecessary indentation
change?  Please make sure you keep distraction to your readers to
the minimum.

> @@ -309,35 +319,36 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
>  int check_signature(const char *payload, size_t plen, const char *signature,
>  	size_t slen, struct signature_check *sigc)
>  {
> -	struct strbuf gpg_output = STRBUF_INIT;
> -	struct strbuf gpg_status = STRBUF_INIT;
> +	struct gpg_format *fmt;
>  	int status;
>  
>  	sigc->result = 'N';
>  	sigc->trust_level = -1;
>  
> -	status = verify_signed_buffer(payload, plen, signature, slen,
> -				      &gpg_output, &gpg_status);
> -	if (status && !gpg_output.len)
> -		goto out;
> -	sigc->payload = xmemdupz(payload, plen);
> -	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
> -	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
> -	parse_gpg_output(sigc);
> +	fmt = get_format_by_sig(signature);
> +	if (!fmt) {
> +		error(_("bad/incompatible signature '%s'"), signature);
> +		return -1;
> +	}
> +
> +	if (!strcmp(fmt->name, "ssh")) {
> +		status = verify_ssh_signature(sigc, fmt, payload, plen, signature, slen);
> +	} else {
> +		status = verify_gpg_signature(sigc, fmt, payload, plen, signature, slen);
> +	}

OK, so get_format_by_sig() now is used to dispatch to the right
backend.  Which sort of makes sense, but ...

 * "ssh" is the newcomer; it has no right to come before the
   battle-tested existing one.

 * If we are dispatching via "fmt" variable, we should add
   fmt->verify() method to each of these formats, so that we don't
   have to switch based on the name.

IOW, this part should just be

	fmt = get_format_by_sig(signature);
	if (!fmt)
		return error(_("...bad signature..."));
	fmt->verify_signature(sigc, fmt, payload, plen, signature, slen);

> +	if (status && !sigc->output)
> +		return !!status;
> +
>  	status |= sigc->result != 'G';
>  	status |= sigc->trust_level < configured_min_trust_level;

By the way, there is no verify_ssh_signature() function defined at
this step [1/9], so this won't compile from the source at all.
Please make sure that each step builds and passes tests.

If I were doing this patch, I probably would NOT do anything related
to "ssh" in this step.  Probably just doing

 - rename gpg_* variables to generic names in codepaths that _will_
   become generic in future steps (like "check_signature()"
   function);

 - introduce verify_signature member to the fmt struct;

 - hoist get_format_by_sig()'s callsite to check_signature() from
   its callee.

would be sufficient amount of work for the first step.  Call that a
preliminary refactoring and clean-up.

And then in the second and subsequent steps, you may start adding
additional code to support ssh signing, including the new instance
of fmt that has verify_ssh_signature() as its verify_signature
method, etc.

Introducing ssh_allowed_signers and ssh_revocation_file at this step
is way premature.  Nobody uses them in this step, the code that uses
them is already referenced but missing (hence the code does not
build), so they are only there to frustrate readers wondering what
they are for and how they will be used.

Thanks.

Re: [PATCH v3 2/9] ssh signing: add documentation

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Fabian Stelzer <fs@gigacodes.de>
>
> Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
> ---
>  Documentation/config/gpg.txt  | 35 +++++++++++++++++++++++++++++++++--
>  Documentation/config/user.txt |  6 ++++++
>  2 files changed, 39 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
> index d94025cb368..16af0b0ada8 100644
> --- a/Documentation/config/gpg.txt
> +++ b/Documentation/config/gpg.txt
> @@ -11,13 +11,13 @@ gpg.program::
>  
>  gpg.format::
>  	Specifies which key format to use when signing with `--gpg-sign`.
> -	Default is "openpgp" and another possible value is "x509".
> +	Default is "openpgp". Other possible values are "x509", "ssh".

Makes sense.

>  gpg.<format>.program::
>  	Use this to customize the program used for the signing format you
>  	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
>  	be used as a legacy synonym for `gpg.openpgp.program`. The default
> -	value for `gpg.x509.program` is "gpgsm".
> +	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".

Again, makes sense.

Once the dust settles, we might want to move the hierarchy from
gpg.* to a more neutral name, with proper backward compatibility
migration plan, but there is no need to do so right away.

Below, I'll ask many questions.  They are mostly not rhetorical and
questions that you should anticipate readers of the documentation
will ask (hence, you would want to update your documentation in such
a way that future readers will not have to ask for clarification).

> @@ -33,3 +33,34 @@ gpg.minTrustLevel::
>  * `marginal`
>  * `fully`
>  * `ultimate`
> +
> +gpg.ssh.keyring::
> +	A file containing all valid SSH public signing keys.

Is "SSH public signing key" the phrase we want to use here?  At
first glance I mistakenly thought that I maintain a bag of my keys I
will use for signing, but from the mention of "authorized keys", it
apparently is the other way around, i.e. I have a bag of public keys
that I can use to _verify_ signatures other people made.

What do we exactly want to convey with the phrase "all valid" to our
readers?  Even if I have a valid SSH key that I could sign with, if
you and your project do not trust me enough, such a valid key of
mine would not be in your keyring, so the phrase "all valid keys" is
not all that meaningful without further qualification in the context
of this sentence.  A file containing ssh public keys, signatures
made with which you are willing to accept, or something?

> +	Similar to an .ssh/authorized_keys file.

It is unclear what "similarity" is of interest here.  Similar to
authorized keys file, meaning that presense of this file allows
holders of the listed ssh keys to remotely log-in to the repository?
I somehow doubt that it is what you meant, but then ...?  Did you
mean "Uses the same format as .ssh/authorized_keys file" or
something like that?

> +	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
> +	If a signing key is found in this file then the trust level will
> +	be set to "fully". Otherwise if the key is not present
> +	but the signature is still valid then the trust level will be "undefined".

I tried to look up the "ALLOWED SIGNERS" section for details, but
failed to find what "trust level" is and how trusted "fully" level
is (is there higher or lower trust levels than that???).  Or is the
notion of "trust level" foreign to ssh signing world and the readers
are expected to read this description as "listed ones are treated as
having the same trust level as 'fully' trusted keys in the GPG/PGP
world"?

I suspect that the section is only useful to learn the details of
what the file looks like?  If so, perhaps instead of saying that the
keyring file looks similar to authorized-keys, be more direct and
say that the keyring file uses the "ALLOWED SIGNERS" file format
described in that manual page (i.e. bypassing the redirection of
authorized-keys)?

> +	This file can be set to a location outside of the repository
> +	and every developer maintains their own trust store.
> +	A central repository server could generate this file automatically
> +	from ssh keys with push	access to verify the code against.
> +	In a corporate setting this file is probably generated at a global location
> +	from some automation that already handles developer ssh keys.

OK.

> +	A repository that is only allowing signed commits can store the file

"is only allowing" -> "only allows".

> +	in the repository itself using a relative path.

It is unclear relative to what.  Relative to the top-level of the
working tree?

> +	This way only committers
> +	with an already valid key can add or change keys in the keyring.

OK.

> +	Using a SSH CA key with the cert-authority option
> +	(see ssh-keygen(1) "CERTIFICATES") is also valid.
> +
> +	To revoke a key place the public key without the principal into the
> +	revocationKeyring.

All of the above unfortunately would not format correctly with
multiple paragraphs.  The second and subsequent paragraphs are
preceded by a line with single '+' on it (instead of a blank line)
and not indented.

Mimick the way the entry for "ssh.variant" uses multiple paragraphs.

> +gpg.ssh.revocationKeyring::
> +	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
> +	See ssh-keygen(1) for details.
> +	If a public key is found in this file then it will always be treated
> +	as having trust level "never" and signatures will show as invalid.
> diff --git a/Documentation/config/user.txt b/Documentation/config/user.txt
> index 59aec7c3aed..b3c2f2c541e 100644
> --- a/Documentation/config/user.txt
> +++ b/Documentation/config/user.txt
> @@ -36,3 +36,9 @@ user.signingKey::
>  	commit, you can override the default selection with this variable.
>  	This option is passed unchanged to gpg's --local-user parameter,
>  	so you may specify a key using any method that gpg supports.
> +	If gpg.format is set to "ssh" this can contain the literal ssh public
> +	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and
> +	corresponds to the private key used for signing. The private key
> +	needs to be available via ssh-agent. Alternatively it can be set to
> +	a file containing a private key directly. If not set git will call
> +	"ssh-add -L" and try to use the first key available.

Thanks.

Re: [PATCH v3 3/9] ssh signing: retrieve a default key from ssh-agent

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Fabian Stelzer <fs@gigacodes.de>
>
> calls ssh-add -L and uses the first key

Documentation/SubmittingPatches::[[describe-changes]].

> Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
> ---
>  gpg-interface.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/gpg-interface.c b/gpg-interface.c
> index 3c9a48c8e7e..c956ed87475 100644
> --- a/gpg-interface.c
> +++ b/gpg-interface.c
> @@ -467,6 +467,23 @@ int git_gpg_config(const char *var, const char *value, void *cb)
>  	return 0;
>  }
>  
> +/* Returns the first public key from an ssh-agent to use for signing */
> +static char *get_default_ssh_signing_key(void) {

Style.  Open and close braces around a function sit on their own
lines by themselves.

> +	struct child_process ssh_add = CHILD_PROCESS_INIT;
> +	int ret = -1;
> +	struct strbuf key_stdout = STRBUF_INIT;
> +	struct strbuf **keys;

Whose releasing the resource held by "keys" when we return?

> +	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
> +	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);

I often load about half a dozen keys to my ssh-agent so "ssh-add -L"
will give me multi-line output.  I know you wrote "the first public
key" above, but that does not mean users who needs to have multiple
keys can be limited to use only the first key for signing.  There
should be a way to say "I may have many keys for other reasons, but
for signing I want to use this key, not the other ones".

> +	if (!ret) {
> +		keys = strbuf_split_max(&key_stdout, '\n', 2);

Let's not use strbuf_split_*() that is a horribly wrong interface.
You do not want a set of elastic buffer after splitting.  You only
are peeking the first line, no?  You are leaking keys[] array and
probably keys[1], too.

	eol = strchrnul(key_stdout.buf, '\n');
	strbuf_setlen(&key_stdout, eol - key_stdout.buf);

or something along that line, perhaps?

> +		if (keys[0])
> +			return strbuf_detach(keys[0], NULL);
> +	}
> +
> +	return "";
> +}
>  const char *get_signing_key(void)

Missing blank line after the function body.

>  {
>  	if (configured_signing_key)

Re: [PATCH v3 4/9] ssh signing: sign using either gpg or ssh keys

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

>  int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
>  {
> -	struct child_process gpg = CHILD_PROCESS_INIT;
> +	struct child_process signer = CHILD_PROCESS_INIT;
>  	int ret;
>  	size_t i, j, bottom;
> -	struct strbuf gpg_status = STRBUF_INIT;
> +	struct strbuf signer_stderr = STRBUF_INIT;
> +	struct tempfile *temp = NULL, *buffer_file = NULL;
> +	char *ssh_signing_key_file = NULL;
> +	struct strbuf ssh_signature_filename = STRBUF_INIT;
>  
> -	strvec_pushl(&gpg.args,
> -		     use_format->program,
> +	if (!strcmp(use_format->name, "ssh")) {

I wonder if we can split the body of these if/else clauses into
separate helper functions, point them with fmt structure and
dispatch via use_format->sign_buffer pointer, just like I suggested
how to do the same on the signature validation side.

> +		if (!signing_key || signing_key[0] == '\0')
> +			return error(_("user.signingkey needs to be set for ssh signing"));
> +
> +
> +		if (istarts_with(signing_key, "ssh-")) {
> +			/* A literal ssh key */
> +			temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
> +			if (!temp)
> +				return error_errno(_("could not create temporary file"));
> +			if (write_in_full(temp->fd, signing_key, strlen(signing_key)) < 0 ||
> +				close_tempfile_gently(temp) < 0) {
> +				error_errno(_("failed writing ssh signing key to '%s'"),
> +					temp->filename.buf);
> +				delete_tempfile(&temp);
> +				return -1;
> +			}
> +			ssh_signing_key_file= temp->filename.buf;
> +		} else {
> +			/* We assume a file */
> +			ssh_signing_key_file = expand_user_path(signing_key, 1);
> +		}
> +
> +		buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
> +		if (!buffer_file)
> +			return error_errno(_("could not create temporary file"));
> +		if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
> +			close_tempfile_gently(buffer_file) < 0) {
> +			error_errno(_("failed writing ssh signing key buffer to '%s'"),
> +				buffer_file->filename.buf);
> +			delete_tempfile(&buffer_file);
> +			return -1;
> +		}
> +
> +		strvec_pushl(&signer.args, use_format->program ,
> +					"-Y", "sign",
> +					"-n", "git",
> +					"-f", ssh_signing_key_file,
> +					buffer_file->filename.buf,
> +					NULL);
> +
> +		sigchain_push(SIGPIPE, SIG_IGN);
> +		ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
> +		sigchain_pop(SIGPIPE);
> +
> +		strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
> +		strbuf_addstr(&ssh_signature_filename, ".sig");
> +		if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {
> +			error_errno(_("failed reading ssh signing data buffer from '%s'"),
> +				ssh_signature_filename.buf);
> +		}
> +		unlink_or_warn(ssh_signature_filename.buf);
> +		strbuf_release(&ssh_signature_filename);
> +		delete_tempfile(&buffer_file);
> +	} else {
> +		strvec_pushl(&signer.args, use_format->program ,
>  		     "--status-fd=2",
>  		     "-bsau", signing_key,
>  		     NULL);
>  
> -	bottom = signature->len;
> -
>  	/*
>  	 * When the username signingkey is bad, program could be terminated
>  	 * because gpg exits without reading and then write gets SIGPIPE.
>  	 */
>  	sigchain_push(SIGPIPE, SIG_IGN);
> -	ret = pipe_command(&gpg, buffer->buf, buffer->len,
> -			   signature, 1024, &gpg_status, 0);
> +		ret = pipe_command(&signer, buffer->buf, buffer->len, signature, 1024, &signer_stderr, 0);
>  	sigchain_pop(SIGPIPE);
> +	}
> +
> +	bottom = signature->len;
> +
> +	if (temp)
> +		delete_tempfile(&temp);
>  
> -	ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
> -	strbuf_release(&gpg_status);
> +	if (!strcmp(use_format->name, "ssh")) {
> +		if (strstr(signer_stderr.buf, "usage:")) {
> +			error(_("openssh version > 8.2p1 is needed for ssh signing (ssh-keygen needs -Y sign option)"));

This looks iffy.  You do call error() to show the error message, but
you do not set "ret", which affects how the return value from the
function is computed at the end of the function.

> +		}
> +	} else {
> +		ret |= !strstr(signer_stderr.buf, "\n[GNUPG:] SIG_CREATED ");
> +	}
> +	strbuf_release(&signer_stderr);

>  	if (ret)
>  		return error(_("gpg failed to sign the data"));

And this error message belongs to the GPG half of the logic, not
ssh (you are allowed to have a separate "ssh failed to sign"
message, of course, but the point is that the error message emission
should happen in the codepath dispatched for each crypto backend.

And of course, again the "if (ssh) {do this shiny new ssh thing}
else {do gpg thing}" structure is questionable.  We should be
dispatching with use_format->fn (whatever the method name is), no?

THanks.

Re: [PATCH v3 1/9] Add commit, tag & push signing via SSH keys

[Eric Sunshine]

On Wed, Jul 14, 2021 at 2:19 PM Junio C Hamano <gitster@pobox.com> wrote:
> "Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:
> > In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
> > signing/encryption and ssh keys which i think is quite common
>
> Upcase "I".

Also: s/environemnt/environment/

Re: [PATCH v3 3/9] ssh signing: retrieve a default key from ssh-agent

[Han-Wen Nienhuys]

On Wed, Jul 14, 2021 at 10:20 PM Junio C Hamano <gitster@pobox.com> wrote:
> > calls ssh-add -L and uses the first key
>
> > +/* Returns the first public key from an ssh-agent to use for signing */
> > +static char *get_default_ssh_signing_key(void) {
>
> Style.  Open and close braces around a function sit on their own
> lines by themselves.

I recommend using clang-format (there is a config file checked into
the tree) which handles most formatting conventions automatically.

-- 
Han-Wen Nienhuys - Google Munich
I work 80%. Don't expect answers from me on Fridays.
--

Google Germany GmbH, Erika-Mann-Strasse 33, 80636 Munich

Registergericht und -nummer: Hamburg, HRB 86891

Sitz der Gesellschaft: Hamburg

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado

Re: [PATCH v3 3/9] ssh signing: retrieve a default key from ssh-agent

[Fabian Stelzer]

On 15.07.21 09:49, Han-Wen Nienhuys wrote:
> On Wed, Jul 14, 2021 at 10:20 PM Junio C Hamano <gitster@pobox.com> wrote:
>>> calls ssh-add -L and uses the first key
>>> +/* Returns the first public key from an ssh-agent to use for signing */
>>> +static char *get_default_ssh_signing_key(void) {
>> Style.  Open and close braces around a function sit on their own
>> lines by themselves.
> I recommend using clang-format (there is a config file checked into
> the tree) which handles most formatting conventions automatically.
Thanks a lot.
This should really be in the in the CodingGuidelines and the 
MyFirstContribution docs.

Especially the clang-format-diff line from its help
"git diff -U0 --no-color --relative HEAD^ | clang-format-diff -p1 -i"
is incredibly useful. Otherwise people will reformat all the things ^^

Re: [PATCH v3 3/9] ssh signing: retrieve a default key from ssh-agent

[Fabian Stelzer]

On 14.07.21 22:20, Junio C Hamano wrote:

> "Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>> From: Fabian Stelzer <fs@gigacodes.de>
>>
>> calls ssh-add -L and uses the first key
> Documentation/SubmittingPatches::[[describe-changes]].
>
>> Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
>> ---
>>   gpg-interface.c | 17 +++++++++++++++++
>>   1 file changed, 17 insertions(+)
>>
>> diff --git a/gpg-interface.c b/gpg-interface.c
>> index 3c9a48c8e7e..c956ed87475 100644
>> --- a/gpg-interface.c
>> +++ b/gpg-interface.c
>> @@ -467,6 +467,23 @@ int git_gpg_config(const char *var, const char *value, void *cb)
>>   	return 0;
>>   }
>>   
>> +/* Returns the first public key from an ssh-agent to use for signing */
>> +static char *get_default_ssh_signing_key(void) {
> Style.  Open and close braces around a function sit on their own
> lines by themselves.
>> +	struct child_process ssh_add = CHILD_PROCESS_INIT;
>> +	int ret = -1;
>> +	struct strbuf key_stdout = STRBUF_INIT;
>> +	struct strbuf **keys;
> Whose releasing the resource held by "keys" when we return?
>
>> +	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
>> +	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
> I often load about half a dozen keys to my ssh-agent so "ssh-add -L"
> will give me multi-line output.  I know you wrote "the first public
> key" above, but that does not mean users who needs to have multiple
> keys can be limited to use only the first key for signing.  There
> should be a way to say "I may have many keys for other reasons, but
> for signing I want to use this key, not the other ones".
I will make the commit message clearer. This function only provides a 
default key in case no key is configured in user.signingkey.
If you set user.signingkey to a public key the correct private key from 
your agent will be used for signing.
>
>> +	if (!ret) {
>> +		keys = strbuf_split_max(&key_stdout, '\n', 2);
> Let's not use strbuf_split_*() that is a horribly wrong interface.
> You do not want a set of elastic buffer after splitting.  You only
> are peeking the first line, no?  You are leaking keys[] array and
> probably keys[1], too.
>
> 	eol = strchrnul(key_stdout.buf, '\n');
> 	strbuf_setlen(&key_stdout, eol - key_stdout.buf);
>
> or something along that line, perhaps?
I have changed it to what you suggested. I'm always a bit hesitant to 
use arithmetic with string pointers.
I know its simple and efficient, but IMHO can be hard to read.
>
>> +		if (keys[0])
>> +			return strbuf_detach(keys[0], NULL);
>> +	}
>> +
>> +	return "";
>> +}
>>   const char *get_signing_key(void)
> Missing blank line after the function body.
>
>>   {
>>   	if (configured_signing_key)

-- 
GIGACODES GmbH | Dr. Hermann-Neubauer-Ring 32 | D-63500 Seligenstadt
www.gigacodes.de | fs@gigacodes.de
Phone +49 6182 8955-114 | Fax +49 6182 8955-299 |
HRB 40711 AG Offenbach a. Main
Geschäftsführer: Fabian Stelzer | Umsatzsteuer-ID DE219379936

Re: [PATCH v3 1/9] Add commit, tag & push signing via SSH keys

[Fabian Stelzer]

On 14.07.21 20:19, Junio C Hamano wrote:
> "Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>> From: Fabian Stelzer <fs@gigacodes.de>
>> Subject: [PATCH v3 1/9] Add commit, tag & push signing via SSH keys
> If you chose "ssh signing:" as the common prefix for the series, use
> it consistently with this step, too.
done
>
>> Openssh v8.2p1 added some new options to ssh-keygen for signature
>> creation and verification. These allow us to use ssh keys for git
>> signatures easily.
>>
>> Start with adding the new signature format, new config options and
>> rename some fields for consistency.
> OK.
>
>> This feature makes git signing much more accessible to the average user.
>> Usually they have a SSH Key for pushing code already. Using it
>> for signing commits allows us to verify not only the transport but the
>> pushed code as well.
> Drop this paragraph or at least tone it down.  It may hold true only
> around your immediate circle but it is far from clear and obvious.
> I'd expect more people push over https:// than ssh://.
>
> We do not really require a new feature to make much more accessible
> for wide average user---making it just a bit more accessible to
> folks in your immediate circle is perfectly fine, as long as you are
> not harming other people ;-)
i will redo the first commit with your suggestions from below only doing 
preperation for the upcoming change and then rewrite the commit message 
to reflect this as well.
>
>> In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
>> signing/encryption and ssh keys which i think is quite common
> Upcase "I".
>
>> (at least for the email part). This way we can establish the correct
>> trust for the SSH Keys without setting up a separate GPG Infrastructure
>> (which is still quite painful for users) or implementing x509 signing
>> support for git (which lacks good forwarding mechanisms).
>> Using ssh agent forwarding makes this feature easily usable in todays
>> development environments where code is often checked out in remote VMs / containers.
>> In such a setup the keyring & revocationKeyring can be centrally
>> generated from the x509 CA information and distributed to the users.
> All of the above promises a wonderful new world, but what is left
> unclear is with this step alone how much of the new world we already
> gain.  When you ask others to read and understand your code, please
> give them a bit more hint to guide them what to expect and where you
> are taking them next.
>
>> diff --git a/fmt-merge-msg.c b/fmt-merge-msg.c
>> index 0f66818e0f8..1d7b64fa021 100644
>> --- a/fmt-merge-msg.c
>> +++ b/fmt-merge-msg.c
>> @@ -527,10 +527,10 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
>>   			len = payload.len;
>>   			if (check_signature(payload.buf, payload.len, sig.buf,
>>   					 sig.len, &sigc) &&
>> -				!sigc.gpg_output)
>> +				!sigc.output)
>>   				strbuf_addstr(&sig, "gpg verification failed.\n");
>>   			else
>> -				strbuf_addstr(&sig, sigc.gpg_output);
>> +				strbuf_addstr(&sig, sigc.output);
> These are "rename some fields for consistency" the proposed log
> message promised.  Makes sense, as you are taking the sigc structure
> away from pgp/gpg dependency.
>
>> diff --git a/gpg-interface.c b/gpg-interface.c
>> index 127aecfc2b0..3c9a48c8e7e 100644
>> --- a/gpg-interface.c
>> +++ b/gpg-interface.c
>> @@ -8,6 +8,7 @@
>>   #include "tempfile.h"
>>   
>>   static char *configured_signing_key;
>> +const char *ssh_allowed_signers, *ssh_revocation_file;
> Very likely these want to be file-scope statics?
true
>
>>   static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
>>   
>>   struct gpg_format {
>> @@ -35,6 +36,14 @@ static const char *x509_sigs[] = {
>>   	NULL
>>   };
>>   
>> +static const char *ssh_verify_args[] = {
>> +	NULL
>> +};
> A blank line is missing from here.
>
>> +static const char *ssh_sigs[] = {
>> +	"-----BEGIN SSH SIGNATURE-----",
>> +	NULL
>> +};
>> +
>>   static struct gpg_format gpg_format[] = {
>>   	{ .name = "openpgp", .program = "gpg",
>>   	  .verify_args = openpgp_verify_args,
>> @@ -44,6 +53,9 @@ static struct gpg_format gpg_format[] = {
>>   	  .verify_args = x509_verify_args,
>>   	  .sigs = x509_sigs
>>   	},
>> +	{ .name = "ssh", .program = "ssh-keygen",
>> +	  .verify_args = ssh_verify_args,
>> +	  .sigs = ssh_sigs },
>>   };
>>   
>>   static struct gpg_format *use_format = &gpg_format[0];
>> @@ -72,7 +84,7 @@ static struct gpg_format *get_format_by_sig(const char *sig)
>>   void signature_check_clear(struct signature_check *sigc)
>>   {
>>   	FREE_AND_NULL(sigc->payload);
>> -	FREE_AND_NULL(sigc->gpg_output);
>> +	FREE_AND_NULL(sigc->output);
>>   	FREE_AND_NULL(sigc->gpg_status);
>>   	FREE_AND_NULL(sigc->signer);
>>   	FREE_AND_NULL(sigc->key);
>> @@ -257,16 +269,15 @@ error:
>>   	FREE_AND_NULL(sigc->key);
>>   }
>>   
>> -static int verify_signed_buffer(const char *payload, size_t payload_size,
>> -				const char *signature, size_t signature_size,
>> -				struct strbuf *gpg_output,
>> -				struct strbuf *gpg_status)
>> +static int verify_gpg_signature(struct signature_check *sigc, struct gpg_format *fmt,
>> +	const char *payload, size_t payload_size,
>> +	const char *signature, size_t signature_size)
>>   {
> What is this hunk about?  The more generic name "verify-signed-buffer"
> is rescinded and gets replaced by a more GPG/PGP specific helper?
>
> You'd need to help readers a bit more by explaining in the proposed
> log message that you shifted the boundary of responsibility between
> check_signature() and verify_signed_buffer()---it used to be that
> the latter inspected the signed payload to see if it a valid GPG/PGP
> signature before doing GPG specific validation, but you want to make
> the former responsible for calling get_format_by_sig(), so that you
> can dispatch a totally new backend that sits next to this GPG
> specific one.
>
>>   	struct child_process gpg = CHILD_PROCESS_INIT;
>> -	struct gpg_format *fmt;
>>   	struct tempfile *temp;
>>   	int ret;
>> -	struct strbuf buf = STRBUF_INIT;
>> +	struct strbuf gpg_out = STRBUF_INIT;
>> +	struct strbuf gpg_err = STRBUF_INIT;
>>   
>>   	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
>>   	if (!temp)
>> @@ -279,29 +290,28 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
>>   		return -1;
>>   	}
>>   
>> -	fmt = get_format_by_sig(signature);
>> -	if (!fmt)
>> -		BUG("bad signature '%s'", signature);
>> -
>>   	strvec_push(&gpg.args, fmt->program);
>>   	strvec_pushv(&gpg.args, fmt->verify_args);
>>   	strvec_pushl(&gpg.args,
>> -		     "--status-fd=1",
>> -		     "--verify", temp->filename.buf, "-",
>> -		     NULL);
>> -
>> -	if (!gpg_status)
>> -		gpg_status = &buf;
>> +			"--status-fd=1",
>> +			"--verify", temp->filename.buf, "-",
>> +			NULL);
> What is going on around here?  Ahh, an unnecessary indentation
> change is fooling the diff and made the patch unreadable.  Sigh...
>
>>   	sigchain_push(SIGPIPE, SIG_IGN);
>> -	ret = pipe_command(&gpg, payload, payload_size,
>> -			   gpg_status, 0, gpg_output, 0);
>> +	ret = pipe_command(&gpg, payload, payload_size, &gpg_out, 0,
>> +				&gpg_err, 0);
> What is this change about?  Is it another unnecessary indentation
> change?  Please make sure you keep distraction to your readers to
> the minimum.
>
>> @@ -309,35 +319,36 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
>>   int check_signature(const char *payload, size_t plen, const char *signature,
>>   	size_t slen, struct signature_check *sigc)
>>   {
>> -	struct strbuf gpg_output = STRBUF_INIT;
>> -	struct strbuf gpg_status = STRBUF_INIT;
>> +	struct gpg_format *fmt;
>>   	int status;
>>   
>>   	sigc->result = 'N';
>>   	sigc->trust_level = -1;
>>   
>> -	status = verify_signed_buffer(payload, plen, signature, slen,
>> -				      &gpg_output, &gpg_status);
>> -	if (status && !gpg_output.len)
>> -		goto out;
>> -	sigc->payload = xmemdupz(payload, plen);
>> -	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
>> -	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
>> -	parse_gpg_output(sigc);
>> +	fmt = get_format_by_sig(signature);
>> +	if (!fmt) {
>> +		error(_("bad/incompatible signature '%s'"), signature);
>> +		return -1;
>> +	}
>> +
>> +	if (!strcmp(fmt->name, "ssh")) {
>> +		status = verify_ssh_signature(sigc, fmt, payload, plen, signature, slen);
>> +	} else {
>> +		status = verify_gpg_signature(sigc, fmt, payload, plen, signature, slen);
>> +	}
> OK, so get_format_by_sig() now is used to dispatch to the right
> backend.  Which sort of makes sense, but ...
>
>   * "ssh" is the newcomer; it has no right to come before the
>     battle-tested existing one.
>
>   * If we are dispatching via "fmt" variable, we should add
>     fmt->verify() method to each of these formats, so that we don't
>     have to switch based on the name.
>
> IOW, this part should just be
>
> 	fmt = get_format_by_sig(signature);
> 	if (!fmt)
> 		return error(_("...bad signature..."));
> 	fmt->verify_signature(sigc, fmt, payload, plen, signature, slen);
i did put ssh first to keep the default with gpg and only needing to 
match the new format. But the fmt->fn variant is much better. For 
signing as well.
>   
>> +	if (status && !sigc->output)
>> +		return !!status;
>> +
>>   	status |= sigc->result != 'G';
>>   	status |= sigc->trust_level < configured_min_trust_level;
> By the way, there is no verify_ssh_signature() function defined at
> this step [1/9], so this won't compile from the source at all.
> Please make sure that each step builds and passes tests.
I was thinking about this one when i split up the patch. I was not sure 
if that was required and didn't want to add synthetic changes (that 
would only appear between the diffs) just for the split.
>
> If I were doing this patch, I probably would NOT do anything related
> to "ssh" in this step.  Probably just doing
>
>   - rename gpg_* variables to generic names in codepaths that _will_
>     become generic in future steps (like "check_signature()"
>     function);
>
>   - introduce verify_signature member to the fmt struct;
>
>   - hoist get_format_by_sig()'s callsite to check_signature() from
>     its callee.
>
> would be sufficient amount of work for the first step.  Call that a
> preliminary refactoring and clean-up.
>
> And then in the second and subsequent steps, you may start adding
> additional code to support ssh signing, including the new instance
> of fmt that has verify_ssh_signature() as its verify_signature
> method, etc.
>
> Introducing ssh_allowed_signers and ssh_revocation_file at this step
> is way premature.  Nobody uses them in this step, the code that uses
> them is already referenced but missing (hence the code does not
> build), so they are only there to frustrate readers wondering what
> they are for and how they will be used.
>
> Thanks.

Re: [PATCH v3 4/9] ssh signing: sign using either gpg or ssh keys

[Fabian Stelzer]

On 14.07.21 22:32, Junio C Hamano wrote:
> "Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>>   int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
>>   {
>> -	struct child_process gpg = CHILD_PROCESS_INIT;
>> +	struct child_process signer = CHILD_PROCESS_INIT;
>>   	int ret;
>>   	size_t i, j, bottom;
>> -	struct strbuf gpg_status = STRBUF_INIT;
>> +	struct strbuf signer_stderr = STRBUF_INIT;
>> +	struct tempfile *temp = NULL, *buffer_file = NULL;
>> +	char *ssh_signing_key_file = NULL;
>> +	struct strbuf ssh_signature_filename = STRBUF_INIT;
>>   
>> -	strvec_pushl(&gpg.args,
>> -		     use_format->program,
>> +	if (!strcmp(use_format->name, "ssh")) {
> I wonder if we can split the body of these if/else clauses into
> separate helper functions, point them with fmt structure and
> dispatch via use_format->sign_buffer pointer, just like I suggested
> how to do the same on the signature validation side.
yes, i like the idea and will do that.
>
>> +		if (!signing_key || signing_key[0] == '\0')
>> +			return error(_("user.signingkey needs to be set for ssh signing"));
>> +
>> +
>> +		if (istarts_with(signing_key, "ssh-")) {
>> +			/* A literal ssh key */
>> +			temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
>> +			if (!temp)
>> +				return error_errno(_("could not create temporary file"));
>> +			if (write_in_full(temp->fd, signing_key, strlen(signing_key)) < 0 ||
>> +				close_tempfile_gently(temp) < 0) {
>> +				error_errno(_("failed writing ssh signing key to '%s'"),
>> +					temp->filename.buf);
>> +				delete_tempfile(&temp);
>> +				return -1;
>> +			}
>> +			ssh_signing_key_file= temp->filename.buf;
>> +		} else {
>> +			/* We assume a file */
>> +			ssh_signing_key_file = expand_user_path(signing_key, 1);
>> +		}
>> +
>> +		buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
>> +		if (!buffer_file)
>> +			return error_errno(_("could not create temporary file"));
>> +		if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
>> +			close_tempfile_gently(buffer_file) < 0) {
>> +			error_errno(_("failed writing ssh signing key buffer to '%s'"),
>> +				buffer_file->filename.buf);
>> +			delete_tempfile(&buffer_file);
>> +			return -1;
>> +		}
>> +
>> +		strvec_pushl(&signer.args, use_format->program ,
>> +					"-Y", "sign",
>> +					"-n", "git",
>> +					"-f", ssh_signing_key_file,
>> +					buffer_file->filename.buf,
>> +					NULL);
>> +
>> +		sigchain_push(SIGPIPE, SIG_IGN);
>> +		ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
>> +		sigchain_pop(SIGPIPE);
>> +
>> +		strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
>> +		strbuf_addstr(&ssh_signature_filename, ".sig");
>> +		if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {
>> +			error_errno(_("failed reading ssh signing data buffer from '%s'"),
>> +				ssh_signature_filename.buf);
>> +		}
>> +		unlink_or_warn(ssh_signature_filename.buf);
>> +		strbuf_release(&ssh_signature_filename);
>> +		delete_tempfile(&buffer_file);
>> +	} else {
>> +		strvec_pushl(&signer.args, use_format->program ,
>>   		     "--status-fd=2",
>>   		     "-bsau", signing_key,
>>   		     NULL);
>>   
>> -	bottom = signature->len;
>> -
>>   	/*
>>   	 * When the username signingkey is bad, program could be terminated
>>   	 * because gpg exits without reading and then write gets SIGPIPE.
>>   	 */
>>   	sigchain_push(SIGPIPE, SIG_IGN);
>> -	ret = pipe_command(&gpg, buffer->buf, buffer->len,
>> -			   signature, 1024, &gpg_status, 0);
>> +		ret = pipe_command(&signer, buffer->buf, buffer->len, signature, 1024, &signer_stderr, 0);
>>   	sigchain_pop(SIGPIPE);
>> +	}
>> +
>> +	bottom = signature->len;
>> +
>> +	if (temp)
>> +		delete_tempfile(&temp);
>>   
>> -	ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
>> -	strbuf_release(&gpg_status);
>> +	if (!strcmp(use_format->name, "ssh")) {
>> +		if (strstr(signer_stderr.buf, "usage:")) {
>> +			error(_("openssh version > 8.2p1 is needed for ssh signing (ssh-keygen needs -Y sign option)"));
> This looks iffy.  You do call error() to show the error message, but
> you do not set "ret", which affects how the return value from the
> function is computed at the end of the function.
I can of course fix the ret logic, but i'm not happy with this check in 
general either :/
The problem is that ssh-keygen seems to give different error messages 
especially in between the versions when the command was added (8.1 -> 
8.2) and mac os x has one of those by default. The check in the 
t/lib-gpg.sh is much safer, but requires an additional call to 
ssh-keygen which i wanted to avoid here.
>
>> +		}
>> +	} else {
>> +		ret |= !strstr(signer_stderr.buf, "\n[GNUPG:] SIG_CREATED ");
>> +	}
>> +	strbuf_release(&signer_stderr);
>>   	if (ret)
>>   		return error(_("gpg failed to sign the data"));
> And this error message belongs to the GPG half of the logic, not
> ssh (you are allowed to have a separate "ssh failed to sign"
> message, of course, but the point is that the error message emission
> should happen in the codepath dispatched for each crypto backend.
>
> And of course, again the "if (ssh) {do this shiny new ssh thing}
> else {do gpg thing}" structure is questionable.  We should be
> dispatching with use_format->fn (whatever the method name is), no?
  I will rewrite this with the fmt->fn logic.
>
> THanks.
>
-- 
GIGACODES GmbH | Dr. Hermann-Neubauer-Ring 32 | D-63500 Seligenstadt
www.gigacodes.de | fs@gigacodes.de
Phone +49 6182 8955-114 | Fax +49 6182 8955-299 |
HRB 40711 AG Offenbach a. Main
Geschäftsführer: Fabian Stelzer | Umsatzsteuer-ID DE219379936

Re: [PATCH v3 2/9] ssh signing: add documentation

[Fabian Stelzer]

On 14.07.21 22:07, Junio C Hamano wrote:
> "Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>> From: Fabian Stelzer <fs@gigacodes.de>
>>
>> Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
>> ---
>>   Documentation/config/gpg.txt  | 35 +++++++++++++++++++++++++++++++++--
>>   Documentation/config/user.txt |  6 ++++++
>>   2 files changed, 39 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
>> index d94025cb368..16af0b0ada8 100644
>> --- a/Documentation/config/gpg.txt
>> +++ b/Documentation/config/gpg.txt
>> @@ -11,13 +11,13 @@ gpg.program::
>>   
>>   gpg.format::
>>   	Specifies which key format to use when signing with `--gpg-sign`.
>> -	Default is "openpgp" and another possible value is "x509".
>> +	Default is "openpgp". Other possible values are "x509", "ssh".
> Makes sense.
>
>>   gpg.<format>.program::
>>   	Use this to customize the program used for the signing format you
>>   	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
>>   	be used as a legacy synonym for `gpg.openpgp.program`. The default
>> -	value for `gpg.x509.program` is "gpgsm".
>> +	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
> Again, makes sense.
>
> Once the dust settles, we might want to move the hierarchy from
> gpg.* to a more neutral name, with proper backward compatibility
> migration plan, but there is no need to do so right away.
>
> Below, I'll ask many questions.  They are mostly not rhetorical and
> questions that you should anticipate readers of the documentation
> will ask (hence, you would want to update your documentation in such
> a way that future readers will not have to ask for clarification).
>
>> @@ -33,3 +33,34 @@ gpg.minTrustLevel::
>>   * `marginal`
>>   * `fully`
>>   * `ultimate`
>> +
>> +gpg.ssh.keyring::
>> +	A file containing all valid SSH public signing keys.
> Is "SSH public signing key" the phrase we want to use here?  At
> first glance I mistakenly thought that I maintain a bag of my keys I
> will use for signing, but from the mention of "authorized keys", it
> apparently is the other way around, i.e. I have a bag of public keys
> that I can use to _verify_ signatures other people made.
>
> What do we exactly want to convey with the phrase "all valid" to our
> readers?  Even if I have a valid SSH key that I could sign with, if
> you and your project do not trust me enough, such a valid key of
> mine would not be in your keyring, so the phrase "all valid keys" is
> not all that meaningful without further qualification in the context
> of this sentence.  A file containing ssh public keys, signatures
> made with which you are willing to accept, or something?
maybe keeeping the name "allowedSignersFile" like its called in the ssh 
manpage will make this clearer without needing a lot of extra explanation?
The keyring name was suggested earlier to make this consistent with gpg. 
But it really is something different from a gpg keyring.
>
>> +	Similar to an .ssh/authorized_keys file.
> It is unclear what "similarity" is of interest here.  Similar to
> authorized keys file, meaning that presense of this file allows
> holders of the listed ssh keys to remotely log-in to the repository?
> I somehow doubt that it is what you meant, but then ...?  Did you
> mean "Uses the same format as .ssh/authorized_keys file" or
> something like that?
I meant that the format is really similar but i see the problem. I 
wanted to explain the format (which pretty much is just one ssh pubkey 
per line with a name prefixed to identify the key with) so that users 
don't have to look into the ssh manpage for a basic example. Maybe just 
provide a short example of the file contents?
>
>> +	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
>> +	If a signing key is found in this file then the trust level will
>> +	be set to "fully". Otherwise if the key is not present
>> +	but the signature is still valid then the trust level will be "undefined".
> I tried to look up the "ALLOWED SIGNERS" section for details, but
> failed to find what "trust level" is and how trusted "fully" level
> is (is there higher or lower trust levels than that???).  Or is the
> notion of "trust level" foreign to ssh signing world and the readers
> are expected to read this description as "listed ones are treated as
> having the same trust level as 'fully' trusted keys in the GPG/PGP
> world"?
SSH has nothing compared to the gpg trust levels. Your key is either in 
the allowed signers file or it is not. However even if it is not in the 
file then the signature might still be "Good" but has no matching 
principal to it. To be able to differentiate the two "Good" cases i used 
the existing gpg trust levels. This way if you set gpg.mintrustlevel = 
fully then the signatures with no matching key in the allowed signers 
file will fail to verify. Otherwise they will verify but show a message 
that no principal matched with this key.
>
> I suspect that the section is only useful to learn the details of
> what the file looks like?  If so, perhaps instead of saying that the
> keyring file looks similar to authorized-keys, be more direct and
> say that the keyring file uses the "ALLOWED SIGNERS" file format
> described in that manual page (i.e. bypassing the redirection of
> authorized-keys)?
>
>> +	This file can be set to a location outside of the repository
>> +	and every developer maintains their own trust store.
>> +	A central repository server could generate this file automatically
>> +	from ssh keys with push	access to verify the code against.
>> +	In a corporate setting this file is probably generated at a global location
>> +	from some automation that already handles developer ssh keys.
> OK.
>
>> +	A repository that is only allowing signed commits can store the file
> "is only allowing" -> "only allows".
>
>> +	in the repository itself using a relative path.
> It is unclear relative to what.  Relative to the top-level of the
> working tree?
>
>> +	This way only committers
>> +	with an already valid key can add or change keys in the keyring.
> OK.
>
>> +	Using a SSH CA key with the cert-authority option
>> +	(see ssh-keygen(1) "CERTIFICATES") is also valid.
>> +
>> +	To revoke a key place the public key without the principal into the
>> +	revocationKeyring.
> All of the above unfortunately would not format correctly with
> multiple paragraphs.  The second and subsequent paragraphs are
> preceded by a line with single '+' on it (instead of a blank line)
> and not indented.
>
> Mimick the way the entry for "ssh.variant" uses multiple paragraphs.
I'll take a look, thanks.
>
>> +gpg.ssh.revocationKeyring::
>> +	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
>> +	See ssh-keygen(1) for details.
>> +	If a public key is found in this file then it will always be treated
>> +	as having trust level "never" and signatures will show as invalid.
>> diff --git a/Documentation/config/user.txt b/Documentation/config/user.txt
>> index 59aec7c3aed..b3c2f2c541e 100644
>> --- a/Documentation/config/user.txt
>> +++ b/Documentation/config/user.txt
>> @@ -36,3 +36,9 @@ user.signingKey::
>>   	commit, you can override the default selection with this variable.
>>   	This option is passed unchanged to gpg's --local-user parameter,
>>   	so you may specify a key using any method that gpg supports.
>> +	If gpg.format is set to "ssh" this can contain the literal ssh public
>> +	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and
>> +	corresponds to the private key used for signing. The private key
>> +	needs to be available via ssh-agent. Alternatively it can be set to
>> +	a file containing a private key directly. If not set git will call
>> +	"ssh-add -L" and try to use the first key available.
> Thanks.

-- 
GIGACODES GmbH | Dr. Hermann-Neubauer-Ring 32 | D-63500 Seligenstadt
www.gigacodes.de | fs@gigacodes.de
Phone +49 6182 8955-114 | Fax +49 6182 8955-299 |
HRB 40711 AG Offenbach a. Main
Geschäftsführer: Fabian Stelzer | Umsatzsteuer-ID DE219379936

Re: [PATCH v3 2/9] ssh signing: add documentation

[Bagas Sanjaya]

On 15/07/21 15.48, Fabian Stelzer wrote:
> I meant that the format is really similar but i see the problem. I 
> wanted to explain the format (which pretty much is just one ssh pubkey 
> per line with a name prefixed to identify the key with) so that users 
> don't have to look into the ssh manpage for a basic example. Maybe just 
> provide a short example of the file contents?

You can write full format description in git-allowedsigners(5) manpage, 
along with examples of course.

-- 
An old man doll... just what I always wanted! - Clara

Re: [PATCH v3 2/9] ssh signing: add documentation

[Junio C Hamano]

Fabian Stelzer <fs@gigacodes.de> writes:

>>> +gpg.ssh.keyring::
>>> ...
> maybe keeeping the name "allowedSignersFile" like its called in the
> ssh manpage will make this clearer without needing a lot of extra
> explanation?

Yup, that sounds like an excellent way to present this to our users.

> SSH has nothing compared to the gpg trust levels. Your key is either
> in the allowed signers file or it is not. However even if it is not in
> the file then the signature might still be "Good" but has no matching 
> principal to it. To be able to differentiate the two "Good" cases i
> used the existing gpg trust levels. This way if you set
> gpg.mintrustlevel = fully then the signatures with no matching key in
> the allowed signers file will fail to verify. Otherwise they will
> verify but show a message that no principal matched with this key.

Sounds sensible.  Our task is to make sure that readers (not me, who
have already been spoon-fed the answer by you just now) would reach
the above understanding by just reading what we put in the
documentation.

Thanks.

Re: [PATCH v3 6/9] ssh signing: parse ssh-keygen output and verify signatures

[Gwyneth Morgan]

On 2021-07-14 12:10:10+0000, Fabian Stelzer via GitGitGadget wrote:
> +		for (line = ssh_keygen_out.buf; *line; line = strchrnul(line + 1, '\n')) {
> +			while (*line == '\n')
> +				line++;
> +			if (!*line)
> +				break;
> +
> +			trust_size = strcspn(line, " \n");
> +			principal = xmemdupz(line, trust_size);

This breaks on principals with spaces in them (principals in the allowed
signers file can have spaces if surrounded by quotes). Looks like
strcspn should reject "\n" instead of " \n".

BTW, thanks for working on this feature. It seems much more convenient
than GPG in my testing.

Re: [PATCH v3 6/9] ssh signing: parse ssh-keygen output and verify signatures

[Fabian Stelzer]

On 16.07.21 02:07, Gwyneth Morgan wrote:
> On 2021-07-14 12:10:10+0000, Fabian Stelzer via GitGitGadget wrote:
>> +		for (line = ssh_keygen_out.buf; *line; line = strchrnul(line + 1, '\n')) {
>> +			while (*line == '\n')
>> +				line++;
>> +			if (!*line)
>> +				break;
>> +
>> +			trust_size = strcspn(line, " \n");
>> +			principal = xmemdupz(line, trust_size);
> This breaks on principals with spaces in them (principals in the allowed
> signers file can have spaces if surrounded by quotes). Looks like
> strcspn should reject "\n" instead of " \n".
>
> BTW, thanks for working on this feature. It seems much more convenient
> than GPG in my testing.
Oh thanks. Very nice catch. Easily fixed here but i'll have to rewrite 
the verification output parsing to account for this as well.
I will add a testcase too.

[PATCH v4 0/9] ssh signing: Add commit & tag signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer via GitGitGadget]

I have added support for using keyfiles directly, lots of tests and
generally cleaned up the signing & verification code a lot.

I can still rename things from being gpg specific to a more general
"signing" but thats rather cosmetic. Also i'm not sure if i named the new
test files correctly.

There is a patch in the pipeline for openssh by Damien Miller that will add
valid-after, valid-before options to the allowed keys keyring. This allows
us to pass the commit timestamp to the verification call and make key
rollover possible and still be able to verify older commits. Set
valid-after=NOW when adding your key to the keyring and set valid-before to
make it fail if used after a certain date. Software like gitolite/github or
corporate automation can do this automatically when ssh push keys are addded
/ removed

v3 addresses some issues & refactoring and splits the large commit into
several smaller ones.

v4:

 * restructures and cleans up the whole patch set - patches build on its own
   now and commit messages try to explain whats going on
 * got rid of the if branches and used callback functions in the format
   struct
 * fixed a bug with whitespace in principal identifiers that required a
   rewrite of the parse_ssh_output function
 * rewrote documentation to be more clear - also renamed keyring back to
   allowedSignersFile

another thing we could add later (via a config switch) is to use the
committer email as principal, instead of looking it up with the key that was
used to sign, to allow only specific trusted keys per committer.

Fabian Stelzer (9):
  ssh signing: preliminary refactoring and clean-up
  ssh signing: add ssh signature format and signing using ssh keys
  ssh signing: retrieve a default key from ssh-agent
  ssh signing: provide a textual representation of the signing key
  ssh signing: parse ssh-keygen output and verify signatures
  ssh signing: add test prereqs
  ssh signing: duplicate t7510 tests for commits
  ssh signing: add more tests for logs, tags & push certs
  ssh signing: add documentation

 Documentation/config/gpg.txt     |  39 ++-
 Documentation/config/user.txt    |   6 +
 builtin/receive-pack.c           |   2 +
 fmt-merge-msg.c                  |   6 +-
 gpg-interface.c                  | 485 +++++++++++++++++++++++++++----
 gpg-interface.h                  |   8 +-
 log-tree.c                       |   8 +-
 pretty.c                         |   4 +-
 send-pack.c                      |   8 +-
 t/lib-gpg.sh                     |  27 ++
 t/t4202-log.sh                   |  23 ++
 t/t5534-push-signed.sh           | 101 +++++++
 t/t7031-verify-tag-signed-ssh.sh | 161 ++++++++++
 t/t7527-signed-commit-ssh.sh     | 398 +++++++++++++++++++++++++
 14 files changed, 1211 insertions(+), 65 deletions(-)
 create mode 100755 t/t7031-verify-tag-signed-ssh.sh
 create mode 100755 t/t7527-signed-commit-ssh.sh


base-commit: 75ae10bc75336db031ee58d13c5037b929235912
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1041%2FFStelzer%2Fsshsign-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1041/FStelzer/sshsign-v4
Pull-Request: https://github.com/git/git/pull/1041

Range-diff vs v3:

  1:  390a8f816cd !  1:  b4b0e2bac1c Add commit, tag & push signing via SSH keys
     @@ Metadata
      Author: Fabian Stelzer <fs@gigacodes.de>
      
       ## Commit message ##
     -    Add commit, tag & push signing via SSH keys
     +    ssh signing: preliminary refactoring and clean-up
      
          Openssh v8.2p1 added some new options to ssh-keygen for signature
          creation and verification. These allow us to use ssh keys for git
          signatures easily.
      
     -    Start with adding the new signature format, new config options and
     -    rename some fields for consistency.
     -
     -    This feature makes git signing much more accessible to the average user.
     -    Usually they have a SSH Key for pushing code already. Using it
     -    for signing commits allows us to verify not only the transport but the
     -    pushed code as well.
     -
     -    In our corporate environemnt we use PIV x509 Certs on Yubikeys for email
     -    signing/encryption and ssh keys which i think is quite common
     +    In our corporate environment we use PIV x509 Certs on Yubikeys for email
     +    signing/encryption and ssh keys which I think is quite common
          (at least for the email part). This way we can establish the correct
          trust for the SSH Keys without setting up a separate GPG Infrastructure
          (which is still quite painful for users) or implementing x509 signing
     @@ Commit message
          In such a setup the keyring & revocationKeyring can be centrally
          generated from the x509 CA information and distributed to the users.
      
     +    To be able to implement new signing formats this commit:
     +     - makes the sigc structure more generic by renaming "gpg_output" to
     +       "output"
     +     - introduces function pointers in the gpg_format structure to call
     +       format specific signing and verification functions
     +     - moves format detection from verify_signed_buffer into the check_signature
     +       api function and calls the format specific verify
     +     - renames and wraps sign_buffer to handle format specific signing logic
     +       as well
     +
          Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
      
       ## fmt-merge-msg.c ##
      @@ fmt-merge-msg.c: static void fmt_merge_msg_sigs(struct strbuf *out)
     + 			buf = payload.buf;
       			len = payload.len;
       			if (check_signature(payload.buf, payload.len, sig.buf,
     - 					 sig.len, &sigc) &&
     +-					 sig.len, &sigc) &&
      -				!sigc.gpg_output)
     -+				!sigc.output)
     ++					    sig.len, &sigc) &&
     ++			    !sigc.output)
       				strbuf_addstr(&sig, "gpg verification failed.\n");
       			else
      -				strbuf_addstr(&sig, sigc.gpg_output);
     @@ fmt-merge-msg.c: static void fmt_merge_msg_sigs(struct strbuf *out)
       
      
       ## gpg-interface.c ##
     -@@
     - #include "tempfile.h"
     - 
     - static char *configured_signing_key;
     -+const char *ssh_allowed_signers, *ssh_revocation_file;
     - static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
     +@@ gpg-interface.c: struct gpg_format {
     + 	const char *program;
     + 	const char **verify_args;
     + 	const char **sigs;
     ++	int (*verify_signed_buffer)(struct signature_check *sigc,
     ++				    struct gpg_format *fmt, const char *payload,
     ++				    size_t payload_size, const char *signature,
     ++				    size_t signature_size);
     ++	int (*sign_buffer)(struct strbuf *buffer, struct strbuf *signature,
     ++			   const char *signing_key);
     + };
       
     - struct gpg_format {
     + static const char *openpgp_verify_args[] = {
      @@ gpg-interface.c: static const char *x509_sigs[] = {
       	NULL
       };
       
     -+static const char *ssh_verify_args[] = {
     -+	NULL
     -+};
     -+static const char *ssh_sigs[] = {
     -+	"-----BEGIN SSH SIGNATURE-----",
     -+	NULL
     -+};
     ++static int verify_gpg_signed_buffer(struct signature_check *sigc,
     ++				    struct gpg_format *fmt, const char *payload,
     ++				    size_t payload_size, const char *signature,
     ++				    size_t signature_size);
     ++static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
     ++			   const char *signing_key);
      +
       static struct gpg_format gpg_format[] = {
     - 	{ .name = "openpgp", .program = "gpg",
     - 	  .verify_args = openpgp_verify_args,
     -@@ gpg-interface.c: static struct gpg_format gpg_format[] = {
     - 	  .verify_args = x509_verify_args,
     - 	  .sigs = x509_sigs
     +-	{ .name = "openpgp", .program = "gpg",
     +-	  .verify_args = openpgp_verify_args,
     +-	  .sigs = openpgp_sigs
     ++	{
     ++		.name = "openpgp",
     ++		.program = "gpg",
     ++		.verify_args = openpgp_verify_args,
     ++		.sigs = openpgp_sigs,
     ++		.verify_signed_buffer = verify_gpg_signed_buffer,
     ++		.sign_buffer = sign_buffer_gpg,
     + 	},
     +-	{ .name = "x509", .program = "gpgsm",
     +-	  .verify_args = x509_verify_args,
     +-	  .sigs = x509_sigs
     ++	{
     ++		.name = "x509",
     ++		.program = "gpgsm",
     ++		.verify_args = x509_verify_args,
     ++		.sigs = x509_sigs,
     ++		.verify_signed_buffer = verify_gpg_signed_buffer,
     ++		.sign_buffer = sign_buffer_gpg,
       	},
     -+	{ .name = "ssh", .program = "ssh-keygen",
     -+	  .verify_args = ssh_verify_args,
     -+	  .sigs = ssh_sigs },
       };
       
     - static struct gpg_format *use_format = &gpg_format[0];
      @@ gpg-interface.c: static struct gpg_format *get_format_by_sig(const char *sig)
       void signature_check_clear(struct signature_check *sigc)
       {
     @@ gpg-interface.c: error:
      -				const char *signature, size_t signature_size,
      -				struct strbuf *gpg_output,
      -				struct strbuf *gpg_status)
     -+static int verify_gpg_signature(struct signature_check *sigc, struct gpg_format *fmt,
     -+	const char *payload, size_t payload_size,
     -+	const char *signature, size_t signature_size)
     ++static int verify_gpg_signed_buffer(struct signature_check *sigc,
     ++				    struct gpg_format *fmt, const char *payload,
     ++				    size_t payload_size, const char *signature,
     ++				    size_t signature_size)
       {
       	struct child_process gpg = CHILD_PROCESS_INIT;
      -	struct gpg_format *fmt;
       	struct tempfile *temp;
       	int ret;
      -	struct strbuf buf = STRBUF_INIT;
     -+	struct strbuf gpg_out = STRBUF_INIT;
     -+	struct strbuf gpg_err = STRBUF_INIT;
     ++	struct strbuf gpg_stdout = STRBUF_INIT;
     ++	struct strbuf gpg_stderr = STRBUF_INIT;
       
       	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
       	if (!temp)
     @@ gpg-interface.c: static int verify_signed_buffer(const char *payload, size_t pay
       	strvec_push(&gpg.args, fmt->program);
       	strvec_pushv(&gpg.args, fmt->verify_args);
       	strvec_pushl(&gpg.args,
     --		     "--status-fd=1",
     --		     "--verify", temp->filename.buf, "-",
     --		     NULL);
     --
     +@@ gpg-interface.c: static int verify_signed_buffer(const char *payload, size_t payload_size,
     + 		     "--verify", temp->filename.buf, "-",
     + 		     NULL);
     + 
      -	if (!gpg_status)
      -		gpg_status = &buf;
     -+			"--status-fd=1",
     -+			"--verify", temp->filename.buf, "-",
     -+			NULL);
     - 
     +-
       	sigchain_push(SIGPIPE, SIG_IGN);
      -	ret = pipe_command(&gpg, payload, payload_size,
      -			   gpg_status, 0, gpg_output, 0);
     -+	ret = pipe_command(&gpg, payload, payload_size, &gpg_out, 0,
     -+				&gpg_err, 0);
     ++	ret = pipe_command(&gpg, payload, payload_size, &gpg_stdout, 0,
     ++			   &gpg_stderr, 0);
       	sigchain_pop(SIGPIPE);
     -+	ret |= !strstr(gpg_out.buf, "\n[GNUPG:] GOODSIG ");
       
     --	delete_tempfile(&temp);
     -+	sigc->payload = xmemdupz(payload, payload_size);
     -+	sigc->output = strbuf_detach(&gpg_err, NULL);
     -+	sigc->gpg_status = strbuf_detach(&gpg_out, NULL);
     + 	delete_tempfile(&temp);
       
      -	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
      -	strbuf_release(&buf); /* no matter it was used or not */
     ++	ret |= !strstr(gpg_stdout.buf, "\n[GNUPG:] GOODSIG ");
     ++	sigc->payload = xmemdupz(payload, payload_size);
     ++	sigc->output = strbuf_detach(&gpg_stderr, NULL);
     ++	sigc->gpg_status = strbuf_detach(&gpg_stdout, NULL);
     ++
      +	parse_gpg_output(sigc);
      +
     -+	delete_tempfile(&temp);
     -+	strbuf_release(&gpg_out);
     -+	strbuf_release(&gpg_err);
     ++	strbuf_release(&gpg_stdout);
     ++	strbuf_release(&gpg_stderr);
       
       	return ret;
       }
     @@ gpg-interface.c: static int verify_signed_buffer(const char *payload, size_t pay
      -	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
      -	parse_gpg_output(sigc);
      +	fmt = get_format_by_sig(signature);
     -+	if (!fmt) {
     -+		error(_("bad/incompatible signature '%s'"), signature);
     -+		return -1;
     -+	}
     ++	if (!fmt)
     ++		return error(_("bad/incompatible signature '%s'"), signature);
     ++
     ++	status = fmt->verify_signed_buffer(sigc, fmt, payload, plen, signature,
     ++					   slen);
      +
     -+	if (!strcmp(fmt->name, "ssh")) {
     -+		status = verify_ssh_signature(sigc, fmt, payload, plen, signature, slen);
     -+	} else {
     -+		status = verify_gpg_signature(sigc, fmt, payload, plen, signature, slen);
     -+	}
      +	if (status && !sigc->output)
      +		return !!status;
      +
     @@ gpg-interface.c: static int verify_signed_buffer(const char *payload, size_t pay
       
       void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
       {
     - 	const char *output = flags & GPG_VERIFY_RAW ?
     +-	const char *output = flags & GPG_VERIFY_RAW ?
      -		sigc->gpg_status : sigc->gpg_output;
     -+		sigc->gpg_status : sigc->output;
     ++	const char *output = flags & GPG_VERIFY_RAW ? sigc->gpg_status :
     ++							    sigc->output;
       
       	if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
       		fputs(sigc->payload, stdout);
     -@@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb)
     - 	int ret;
     - 
     - 	if (!strcmp(var, "user.signingkey")) {
     -+		/*
     -+		 * user.signingkey can contain one of the following
     -+		 * when format = openpgp/x509
     -+		 *   - GPG KeyID
     -+		 * when format = ssh
     -+		 *   - literal ssh public key (e.g. ssh-rsa XXXKEYXXX comment)
     -+		 *   - path to a file containing a public or a private ssh key
     -+		 */
     - 		if (!value)
     - 			return config_error_nonbool(var);
     - 		set_signing_key(value);
     - 		return 0;
     - 	}
     - 
     -+	if (!strcmp(var, "gpg.ssh.keyring")) {
     -+		if (!value)
     -+			return config_error_nonbool(var);
     -+		return git_config_string(&ssh_allowed_signers, var, value);
     -+	}
     -+
     -+	if (!strcmp(var, "gpg.ssh.revocationkeyring")) {
     -+		if (!value)
     -+			return config_error_nonbool(var);
     -+		return git_config_string(&ssh_revocation_file, var, value);
     -+	}
     -+
     - 	if (!strcmp(var, "gpg.format")) {
     - 		if (!value)
     - 			return config_error_nonbool(var);
     -@@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb)
     - 	if (!strcmp(var, "gpg.x509.program"))
     - 		fmtname = "x509";
     - 
     -+	if (!strcmp(var, "gpg.ssh.program"))
     -+		fmtname = "ssh";
     -+
     - 	if (fmtname) {
     - 		fmt = get_format_by_name(fmtname);
     - 		return git_config_string(&fmt->program, var, value);
      @@ gpg-interface.c: const char *get_signing_key(void)
     - {
     - 	if (configured_signing_key)
     - 		return configured_signing_key;
     --	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
     -+	if (!strcmp(use_format->name, "ssh")) {
     -+		return get_default_ssh_signing_key();
     -+	} else {
     -+		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
     -+	}
     -+}
     -+
     -+const char *get_ssh_allowed_signers(void)
     -+{
     -+	if (ssh_allowed_signers)
     -+		return ssh_allowed_signers;
     -+
     -+	die("A Path to an allowed signers ssh keyring is needed for validation");
       }
       
       int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
     ++{
     ++	return use_format->sign_buffer(buffer, signature, signing_key);
     ++}
     ++
     ++static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
     ++		    const char *signing_key)
     + {
     + 	struct child_process gpg = CHILD_PROCESS_INIT;
     + 	int ret;
      
       ## gpg-interface.h ##
      @@ gpg-interface.h: enum signature_trust_level {
     @@ gpg-interface.h: enum signature_trust_level {
       struct signature_check {
       	char *payload;
      -	char *gpg_output;
     --	char *gpg_status;
      +	char *output;
     -+	char *gpg_status; /* Only used internally -> remove from this public api */
     + 	char *gpg_status;
       
       	/*
     - 	 * possible "result":
     -@@ gpg-interface.h: int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
     - int git_gpg_config(const char *, const char *, void *);
     - void set_signing_key(const char *);
     - const char *get_signing_key(void);
     -+const char *get_ssh_allowed_signers(void);
     - int check_signature(const char *payload, size_t plen,
     - 		    const char *signature, size_t slen,
     - 		    struct signature_check *sigc);
      
       ## log-tree.c ##
      @@ log-tree.c: static void show_signature(struct rev_info *opt, struct commit *commit)
  4:  df55b9e1d59 !  2:  2c75adee8e1 ssh signing: sign using either gpg or ssh keys
     @@ Metadata
      Author: Fabian Stelzer <fs@gigacodes.de>
      
       ## Commit message ##
     -    ssh signing: sign using either gpg or ssh keys
     +    ssh signing: add ssh signature format and signing using ssh keys
      
     -    implements the actual ssh-keygen -Y sign operation
     +    implements the actual sign_buffer_ssh operation and move some shared
     +    cleanup code into a strbuf function
      
          Set gpg.format = ssh and user.signingkey to either a ssh public key
          string (like from an authorized_keys file), or a ssh key file.
          If the key file or the config value itself contains only a public key
          then the private key needs to be available via ssh-agent.
     -    If no signingkey is set then git will call 'ssh-add -L' to check for
     -    available agent keys and use the first one for signing.
     +
     +    gpg.ssh.program can be set to an alternative location of ssh-keygen.
     +    A somewhat recent openssh version (8.2p1+) of ssh-keygen is needed for
     +    this feature. Since only ssh-keygen is needed it can this way be
     +    installed seperately without upgrading your system openssh packages.
      
          Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
      
       ## gpg-interface.c ##
     -@@ gpg-interface.c: const char *get_ssh_allowed_signers(void)
     +@@ gpg-interface.c: static const char *x509_sigs[] = {
     + 	NULL
     + };
     + 
     ++static const char *ssh_verify_args[] = { NULL };
     ++static const char *ssh_sigs[] = {
     ++	"-----BEGIN SSH SIGNATURE-----",
     ++	NULL
     ++};
     ++
     + static int verify_gpg_signed_buffer(struct signature_check *sigc,
     + 				    struct gpg_format *fmt, const char *payload,
     + 				    size_t payload_size, const char *signature,
     + 				    size_t signature_size);
     + static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
     + 			   const char *signing_key);
     ++static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
     ++			   const char *signing_key);
     + 
     + static struct gpg_format gpg_format[] = {
     + 	{
     +@@ gpg-interface.c: static struct gpg_format gpg_format[] = {
     + 		.verify_signed_buffer = verify_gpg_signed_buffer,
     + 		.sign_buffer = sign_buffer_gpg,
     + 	},
     ++	{
     ++		.name = "ssh",
     ++		.program = "ssh-keygen",
     ++		.verify_args = ssh_verify_args,
     ++		.sigs = ssh_sigs,
     ++		.verify_signed_buffer = NULL, /* TODO */
     ++		.sign_buffer = sign_buffer_ssh
     ++	},
     + };
     + 
     + static struct gpg_format *use_format = &gpg_format[0];
     +@@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb)
     + 	if (!strcmp(var, "gpg.x509.program"))
     + 		fmtname = "x509";
     + 
     ++	if (!strcmp(var, "gpg.ssh.program"))
     ++		fmtname = "ssh";
     ++
     + 	if (fmtname) {
     + 		fmt = get_format_by_name(fmtname);
     + 		return git_config_string(&fmt->program, var, value);
     +@@ gpg-interface.c: int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
     + 	return use_format->sign_buffer(buffer, signature, signing_key);
     + }
       
     - int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
     ++static void strbuf_trim_trailing_cr(struct strbuf *buffer, int offset)
     ++{
     ++	size_t i, j;
     ++
     ++	for (i = j = offset; i < buffer->len; i++) {
     ++		if (buffer->buf[i] != '\r') {
     ++			if (i != j)
     ++				buffer->buf[j] = buffer->buf[i];
     ++			j++;
     ++		}
     ++	}
     ++	strbuf_setlen(buffer, j);
     ++}
     ++
     + static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
     + 		    const char *signing_key)
       {
     --	struct child_process gpg = CHILD_PROCESS_INIT;
     -+	struct child_process signer = CHILD_PROCESS_INIT;
     + 	struct child_process gpg = CHILD_PROCESS_INIT;
       	int ret;
     - 	size_t i, j, bottom;
     --	struct strbuf gpg_status = STRBUF_INIT;
     +-	size_t i, j, bottom;
     ++	size_t bottom;
     + 	struct strbuf gpg_status = STRBUF_INIT;
     + 
     + 	strvec_pushl(&gpg.args,
     +@@ gpg-interface.c: static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
     + 		return error(_("gpg failed to sign the data"));
     + 
     + 	/* Strip CR from the line endings, in case we are on Windows. */
     +-	for (i = j = bottom; i < signature->len; i++)
     +-		if (signature->buf[i] != '\r') {
     +-			if (i != j)
     +-				signature->buf[j] = signature->buf[i];
     +-			j++;
     +-		}
     +-	strbuf_setlen(signature, j);
     ++	strbuf_trim_trailing_cr(signature, bottom);
     + 
     + 	return 0;
     + }
     ++
     ++static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
     ++			   const char *signing_key)
     ++{
     ++	struct child_process signer = CHILD_PROCESS_INIT;
     ++	int ret = -1;
     ++	size_t bottom;
      +	struct strbuf signer_stderr = STRBUF_INIT;
      +	struct tempfile *temp = NULL, *buffer_file = NULL;
      +	char *ssh_signing_key_file = NULL;
      +	struct strbuf ssh_signature_filename = STRBUF_INIT;
     - 
     --	strvec_pushl(&gpg.args,
     --		     use_format->program,
     -+	if (!strcmp(use_format->name, "ssh")) {
     -+		if (!signing_key || signing_key[0] == '\0')
     -+			return error(_("user.signingkey needs to be set for ssh signing"));
     -+
     -+
     -+		if (istarts_with(signing_key, "ssh-")) {
     -+			/* A literal ssh key */
     -+			temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
     -+			if (!temp)
     -+				return error_errno(_("could not create temporary file"));
     -+			if (write_in_full(temp->fd, signing_key, strlen(signing_key)) < 0 ||
     -+				close_tempfile_gently(temp) < 0) {
     -+				error_errno(_("failed writing ssh signing key to '%s'"),
     -+					temp->filename.buf);
     -+				delete_tempfile(&temp);
     -+				return -1;
     -+			}
     -+			ssh_signing_key_file= temp->filename.buf;
     -+		} else {
     -+			/* We assume a file */
     -+			ssh_signing_key_file = expand_user_path(signing_key, 1);
     -+		}
      +
     -+		buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
     -+		if (!buffer_file)
     -+			return error_errno(_("could not create temporary file"));
     -+		if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
     -+			close_tempfile_gently(buffer_file) < 0) {
     -+			error_errno(_("failed writing ssh signing key buffer to '%s'"),
     -+				buffer_file->filename.buf);
     -+			delete_tempfile(&buffer_file);
     -+			return -1;
     -+		}
     ++	if (!signing_key || signing_key[0] == '\0')
     ++		return error(
     ++			_("user.signingkey needs to be set for ssh signing"));
      +
     -+		strvec_pushl(&signer.args, use_format->program ,
     -+					"-Y", "sign",
     -+					"-n", "git",
     -+					"-f", ssh_signing_key_file,
     -+					buffer_file->filename.buf,
     -+					NULL);
     -+
     -+		sigchain_push(SIGPIPE, SIG_IGN);
     -+		ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
     -+		sigchain_pop(SIGPIPE);
     -+
     -+		strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
     -+		strbuf_addstr(&ssh_signature_filename, ".sig");
     -+		if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {
     -+			error_errno(_("failed reading ssh signing data buffer from '%s'"),
     -+				ssh_signature_filename.buf);
     ++	if (istarts_with(signing_key, "ssh-")) {
     ++		/* A literal ssh key */
     ++		temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
     ++		if (!temp)
     ++			return error_errno(
     ++				_("could not create temporary file"));
     ++		if (write_in_full(temp->fd, signing_key, strlen(signing_key)) <
     ++			    0 ||
     ++		    close_tempfile_gently(temp) < 0) {
     ++			error_errno(_("failed writing ssh signing key to '%s'"),
     ++				    temp->filename.buf);
     ++			goto out;
      +		}
     -+		unlink_or_warn(ssh_signature_filename.buf);
     -+		strbuf_release(&ssh_signature_filename);
     -+		delete_tempfile(&buffer_file);
     ++		ssh_signing_key_file = temp->filename.buf;
      +	} else {
     -+		strvec_pushl(&signer.args, use_format->program ,
     - 		     "--status-fd=2",
     - 		     "-bsau", signing_key,
     - 		     NULL);
     - 
     --	bottom = signature->len;
     --
     - 	/*
     - 	 * When the username signingkey is bad, program could be terminated
     - 	 * because gpg exits without reading and then write gets SIGPIPE.
     - 	 */
     - 	sigchain_push(SIGPIPE, SIG_IGN);
     --	ret = pipe_command(&gpg, buffer->buf, buffer->len,
     --			   signature, 1024, &gpg_status, 0);
     -+		ret = pipe_command(&signer, buffer->buf, buffer->len, signature, 1024, &signer_stderr, 0);
     - 	sigchain_pop(SIGPIPE);
     ++		/* We assume a file */
     ++		ssh_signing_key_file = expand_user_path(signing_key, 1);
     ++	}
     ++
     ++	buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
     ++	if (!buffer_file) {
     ++		error_errno(_("could not create temporary file"));
     ++		goto out;
     ++	}
     ++
     ++	if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
     ++	    close_tempfile_gently(buffer_file) < 0) {
     ++		error_errno(_("failed writing ssh signing key buffer to '%s'"),
     ++			    buffer_file->filename.buf);
     ++		goto out;
     ++	}
     ++
     ++	strvec_pushl(&signer.args, use_format->program, "-Y", "sign", "-n",
     ++		     "git", "-f", ssh_signing_key_file,
     ++		     buffer_file->filename.buf, NULL);
     ++
     ++	sigchain_push(SIGPIPE, SIG_IGN);
     ++	ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
     ++	sigchain_pop(SIGPIPE);
     ++
     ++	if (ret && strstr(signer_stderr.buf, "usage:")) {
     ++		error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
     ++		goto out;
     ++	}
     ++
     ++	if (ret) {
     ++		error("%s", signer_stderr.buf);
     ++		goto out;
      +	}
      +
      +	bottom = signature->len;
      +
     ++	strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
     ++	strbuf_addstr(&ssh_signature_filename, ".sig");
     ++	if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {
     ++		error_errno(
     ++			_("failed reading ssh signing data buffer from '%s'"),
     ++			ssh_signature_filename.buf);
     ++	}
     ++	unlink_or_warn(ssh_signature_filename.buf);
     ++
     ++	if (ret) {
     ++		error(_("ssh failed to sign the data"));
     ++		goto out;
     ++	}
     ++
     ++	/* Strip CR from the line endings, in case we are on Windows. */
     ++	strbuf_trim_trailing_cr(signature, bottom);
     ++
     ++out:
      +	if (temp)
      +		delete_tempfile(&temp);
     - 
     --	ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
     --	strbuf_release(&gpg_status);
     -+	if (!strcmp(use_format->name, "ssh")) {
     -+		if (strstr(signer_stderr.buf, "usage:")) {
     -+			error(_("openssh version > 8.2p1 is needed for ssh signing (ssh-keygen needs -Y sign option)"));
     -+		}
     -+	} else {
     -+		ret |= !strstr(signer_stderr.buf, "\n[GNUPG:] SIG_CREATED ");
     -+	}
     ++	if (buffer_file)
     ++		delete_tempfile(&buffer_file);
      +	strbuf_release(&signer_stderr);
     - 	if (ret)
     - 		return error(_("gpg failed to sign the data"));
     - 
     ++	strbuf_release(&ssh_signature_filename);
     ++	return ret;
     ++}
  3:  b84b2812470 !  3:  1ec5c06cbe9 ssh signing: retrieve a default key from ssh-agent
     @@ Metadata
       ## Commit message ##
          ssh signing: retrieve a default key from ssh-agent
      
     -    calls ssh-add -L and uses the first key
     +    if user.signingkey is not set and a ssh signature is requested we call
     +    ssh-add -L and use the first key we get
      
          Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
      
     @@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb
       }
       
      +/* Returns the first public key from an ssh-agent to use for signing */
     -+static char *get_default_ssh_signing_key(void) {
     ++static char *get_default_ssh_signing_key(void)
     ++{
      +	struct child_process ssh_add = CHILD_PROCESS_INIT;
      +	int ret = -1;
      +	struct strbuf key_stdout = STRBUF_INIT;
     @@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb
      +			return strbuf_detach(keys[0], NULL);
      +	}
      +
     ++	strbuf_release(&key_stdout);
      +	return "";
      +}
     ++
       const char *get_signing_key(void)
       {
       	if (configured_signing_key)
     + 		return configured_signing_key;
     +-	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
     ++	if (!strcmp(use_format->name, "ssh")) {
     ++		return get_default_ssh_signing_key();
     ++	} else {
     ++		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
     ++	}
     + }
     + 
     + int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
  5:  0581c72634c !  4:  ec6931082ee ssh signing: provide a textual representation of the signing key
     @@ Metadata
       ## Commit message ##
          ssh signing: provide a textual representation of the signing key
      
     -    for ssh the key can be a filename/path or even a literal ssh pubkey
     -    in push certs and textual output we prefer the ssh fingerprint instead
     +    for ssh the user.signingkey can be a filename/path or even a literal ssh pubkey.
     +    in push certs and textual output we prefer the ssh fingerprint instead.
      
          Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
      
     @@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb
       	return 0;
       }
       
     -+static char *get_ssh_key_fingerprint(const char *signing_key) {
     ++static char *get_ssh_key_fingerprint(const char *signing_key)
     ++{
      +	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
      +	int ret = -1;
      +	struct strbuf fingerprint_stdout = STRBUF_INIT;
     @@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb
      +	 * For textual representation we usually want a fingerprint
      +	 */
      +	if (istarts_with(signing_key, "ssh-")) {
     -+		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
     -+					"-lf", "-",
     -+					NULL);
     -+		ret = pipe_command(&ssh_keygen, signing_key, strlen(signing_key),
     -+			&fingerprint_stdout, 0,  NULL, 0);
     ++		strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf", "-", NULL);
     ++		ret = pipe_command(&ssh_keygen, signing_key,
     ++				   strlen(signing_key), &fingerprint_stdout, 0,
     ++				   NULL, 0);
      +	} else {
     -+		strvec_pushl(&ssh_keygen.args, "ssh-keygen",
     -+					"-lf", configured_signing_key,
     -+					NULL);
     ++		strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf",
     ++			     configured_signing_key, NULL);
      +		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0,
     -+			NULL, 0);
     ++				   NULL, 0);
      +	}
      +
      +	if (!!ret)
      +		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
     -+			signing_key);
     ++			  signing_key);
      +
      +	fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
      +	if (!fingerprint[1])
      +		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
     -+			signing_key);
     ++			  signing_key);
      +
      +	return strbuf_detach(fingerprint[1], NULL);
      +}
      +
       /* Returns the first public key from an ssh-agent to use for signing */
     - static char *get_default_ssh_signing_key(void) {
     - 	struct child_process ssh_add = CHILD_PROCESS_INIT;
     -@@ gpg-interface.c: static char *get_default_ssh_signing_key(void) {
     - 
     + static char *get_default_ssh_signing_key(void)
     + {
     +@@ gpg-interface.c: static char *get_default_ssh_signing_key(void)
       	return "";
       }
     -+
     + 
      +/* Returns a textual but unique representation ot the signing key */
     -+const char *get_signing_key_id(void) {
     ++const char *get_signing_key_id(void)
     ++{
      +	if (!strcmp(use_format->name, "ssh")) {
      +		return get_ssh_key_fingerprint(get_signing_key());
      +	} else {
     @@ gpg-interface.h: int sign_buffer(struct strbuf *buffer, struct strbuf *signature
      + * Either a GPG KeyID or a SSH Key Fingerprint
      + */
      +const char *get_signing_key_id(void);
     -+
     - const char *get_ssh_allowed_signers(void);
       int check_signature(const char *payload, size_t plen,
       		    const char *signature, size_t slen,
     + 		    struct signature_check *sigc);
      
       ## send-pack.c ##
      @@ send-pack.c: static int generate_push_cert(struct strbuf *req_buf,
  6:  381a950a6e1 !  5:  4436cb3a122 ssh signing: parse ssh-keygen output and verify signatures
     @@ Metadata
       ## Commit message ##
          ssh signing: parse ssh-keygen output and verify signatures
      
     -    Verification uses the gpg.ssh.keyring file (see ssh-keygen(1) "ALLOWED
     +    to verify a ssh signature we first call ssh-keygen -Y find-principal to
     +    look up the signing principal by their public key from the
     +    allowedSignersFile. If the key is found then we do a verify. Otherwise
     +    we only validate the signature but can not verify the signers identity.
     +
     +    Verification uses the gpg.ssh.allowedSignersFile (see ssh-keygen(1) "ALLOWED
          SIGNERS") which contains valid public keys and a principal (usually
          user@domain). Depending on the environment this file can be managed by
          the individual developer or for example generated by the central
     @@ Commit message
          To revoke a key put the public key without the principal prefix into
          gpg.ssh.revocationKeyring or generate a KRL (see ssh-keygen(1)
          "KEY REVOCATION LISTS"). The same considerations about who to trust for
     -    verification as with the keyring file apply.
     +    verification as with the allowedSignersFile apply.
      
          Using SSH CA Keys with these files is also possible. Add
          "cert-authority" as key option between the principal and the key to mark
     @@ gpg-interface.c
       #include "gpg-interface.h"
       #include "sigchain.h"
       #include "tempfile.h"
     -@@ gpg-interface.c: static int parse_gpg_trust_level(const char *level,
     - 	return 1;
     + 
     + static char *configured_signing_key;
     ++static const char *ssh_allowed_signers, *ssh_revocation_file;
     + static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
     + 
     + struct gpg_format {
     +@@ gpg-interface.c: static int verify_gpg_signed_buffer(struct signature_check *sigc,
     + 				    struct gpg_format *fmt, const char *payload,
     + 				    size_t payload_size, const char *signature,
     + 				    size_t signature_size);
     ++static int verify_ssh_signed_buffer(struct signature_check *sigc,
     ++				    struct gpg_format *fmt, const char *payload,
     ++				    size_t payload_size, const char *signature,
     ++				    size_t signature_size);
     + static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
     + 			   const char *signing_key);
     + static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
     +@@ gpg-interface.c: static struct gpg_format gpg_format[] = {
     + 		.program = "ssh-keygen",
     + 		.verify_args = ssh_verify_args,
     + 		.sigs = ssh_sigs,
     +-		.verify_signed_buffer = NULL, /* TODO */
     ++		.verify_signed_buffer = verify_ssh_signed_buffer,
     + 		.sign_buffer = sign_buffer_ssh
     + 	},
     + };
     +@@ gpg-interface.c: static int verify_gpg_signed_buffer(struct signature_check *sigc,
     + 	return ret;
       }
       
      +static void parse_ssh_output(struct signature_check *sigc)
      +{
     -+	struct string_list parts = STRING_LIST_INIT_DUP;
     -+	char *line = NULL;
     ++	const char *line, *principal, *search;
      +
      +	/*
      +	 * ssh-keysign output should be:
      +	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
     ++	 * Good "git" signature for PRINCIPAL WITH WHITESPACE with RSA key SHA256:FINGERPRINT
      +	 * or for valid but unknown keys:
      +	 * Good "git" signature with RSA key SHA256:FINGERPRINT
      +	 */
     @@ gpg-interface.c: static int parse_gpg_trust_level(const char *level,
      +	sigc->trust_level = TRUST_NEVER;
      +
      +	line = xmemdupz(sigc->output, strcspn(sigc->output, "\n"));
     -+	string_list_split(&parts, line, ' ', 8);
     -+	if (parts.nr >= 9 && starts_with(line, "Good \"git\" signature for ")) {
     -+		/* Valid signature for a trusted signer */
     ++
     ++	if (skip_prefix(line, "Good \"git\" signature for ", &line)) {
     ++		/* Valid signature and known principal */
      +		sigc->result = 'G';
      +		sigc->trust_level = TRUST_FULLY;
     -+		sigc->signer = xstrdup(parts.items[4].string);
     -+		sigc->fingerprint = xstrdup(parts.items[8].string);
     ++
     ++		/* Search for the last "with" to get the full principal */
     ++		principal = line;
     ++		do {
     ++			search = strstr(line, " with ");
     ++			if (search)
     ++				line = search + 1;
     ++		} while (search != NULL);
     ++		sigc->signer = xmemdupz(principal, line - principal - 1);
     ++		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);
      +		sigc->key = xstrdup(sigc->fingerprint);
     -+	} else if (parts.nr >= 7 && starts_with(line, "Good \"git\" signature with ")) {
     ++	} else if (skip_prefix(line, "Good \"git\" signature with ", &line)) {
      +		/* Valid signature, but key unknown */
      +		sigc->result = 'G';
      +		sigc->trust_level = TRUST_UNDEFINED;
     -+		sigc->fingerprint = xstrdup(parts.items[6].string);
     ++		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);
      +		sigc->key = xstrdup(sigc->fingerprint);
      +	}
     -+	trace_printf("trace: sigc result %c/%d - %s %s %s", sigc->result, sigc->trust_level, sigc->signer, sigc->fingerprint, sigc->key);
     ++}
     ++
     ++static const char *get_ssh_allowed_signers(void)
     ++{
     ++	if (ssh_allowed_signers)
     ++		return ssh_allowed_signers;
      +
     -+	string_list_clear(&parts, 0);
     -+	FREE_AND_NULL(line);
     ++	die("gpg.ssh.allowedSignersFile needs to be configured and exist for validation");
      +}
      +
     - static void parse_gpg_output(struct signature_check *sigc)
     - {
     - 	const char *buf = sigc->gpg_status;
     -@@ gpg-interface.c: error:
     - 	FREE_AND_NULL(sigc->key);
     - }
     - 
     -+static int verify_ssh_signature(struct signature_check *sigc,
     -+	struct gpg_format *fmt,
     -+	const char *payload, size_t payload_size,
     -+	const char *signature, size_t signature_size)
     ++static int verify_ssh_signed_buffer(struct signature_check *sigc,
     ++				    struct gpg_format *fmt, const char *payload,
     ++				    size_t payload_size, const char *signature,
     ++				    size_t signature_size)
      +{
      +	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
      +	struct tempfile *temp;
     @@ gpg-interface.c: error:
      +	}
      +
      +	/* Find the principal from the signers */
     -+	strvec_pushl(&ssh_keygen.args,  fmt->program,
     -+					"-Y", "find-principals",
     -+					"-f", get_ssh_allowed_signers(),
     -+					"-s", temp->filename.buf,
     -+					NULL);
     -+	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
     -+	if (strstr(ssh_keygen_err.buf, "usage:")) {
     -+		error(_("openssh version > 8.2p1 is needed for ssh signature verification (ssh-keygen needs -Y find-principals/verify option)"));
     ++	strvec_pushl(&ssh_keygen.args, fmt->program, "-Y", "find-principals",
     ++		     "-f", get_ssh_allowed_signers(), "-s", temp->filename.buf,
     ++		     NULL);
     ++	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0,
     ++			   &ssh_keygen_err, 0);
     ++	if (ret && strstr(ssh_keygen_err.buf, "usage:")) {
     ++		error(_("ssh-keygen -Y find-principals/verify is needed for ssh signature verification (available in openssh version 8.2p1+)"));
     ++		return ret;
      +	}
      +	if (ret || !ssh_keygen_out.len) {
     -+		/* We did not find a matching principal in the keyring - Check without validation */
     ++		/* We did not find a matching principal in the allowedSigners - Check
     ++		 * without validation */
      +		child_process_init(&ssh_keygen);
     -+		strvec_pushl(&ssh_keygen.args,  fmt->program,
     -+						"-Y", "check-novalidate",
     -+						"-n", "git",
     -+						"-s", temp->filename.buf,
     -+						NULL);
     -+		ret = pipe_command(&ssh_keygen, payload, payload_size, &ssh_keygen_out, 0, &ssh_keygen_err, 0);
     ++		strvec_pushl(&ssh_keygen.args, fmt->program, "-Y",
     ++			     "check-novalidate", "-n", "git", "-s",
     ++			     temp->filename.buf, NULL);
     ++		ret = pipe_command(&ssh_keygen, payload, payload_size,
     ++				   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
      +	} else {
      +		/* Check every principal we found (one per line) */
     -+		for (line = ssh_keygen_out.buf; *line; line = strchrnul(line + 1, '\n')) {
     ++		for (line = ssh_keygen_out.buf; *line;
     ++		     line = strchrnul(line + 1, '\n')) {
      +			while (*line == '\n')
      +				line++;
      +			if (!*line)
      +				break;
      +
     -+			trust_size = strcspn(line, " \n");
     ++			trust_size = strcspn(line, "\n");
      +			principal = xmemdupz(line, trust_size);
      +
      +			child_process_init(&ssh_keygen);
      +			strbuf_release(&ssh_keygen_out);
      +			strbuf_release(&ssh_keygen_err);
     -+			strvec_push(&ssh_keygen.args,fmt->program);
     -+			/* We found principals - Try with each until we find a match */
     -+			strvec_pushl(&ssh_keygen.args,  "-Y", "verify",
     -+							"-n", "git",
     -+							"-f", get_ssh_allowed_signers(),
     -+							"-I", principal,
     -+							"-s", temp->filename.buf,
     -+							NULL);
     ++			strvec_push(&ssh_keygen.args, fmt->program);
     ++			/* We found principals - Try with each until we find a
     ++			 * match */
     ++			strvec_pushl(&ssh_keygen.args, "-Y", "verify", "-n",
     ++				     "git", "-f", get_ssh_allowed_signers(),
     ++				     "-I", principal, "-s", temp->filename.buf,
     ++				     NULL);
      +
      +			if (ssh_revocation_file) {
      +				if (file_exists(ssh_revocation_file)) {
     -+					strvec_pushl(&ssh_keygen.args, "-r", ssh_revocation_file, NULL);
     ++					strvec_pushl(&ssh_keygen.args, "-r",
     ++						     ssh_revocation_file, NULL);
      +				} else {
     -+					warning(_("ssh signing revocation file configured but not found: %s"), ssh_revocation_file);
     ++					warning(_("ssh signing revocation file configured but not found: %s"),
     ++						ssh_revocation_file);
      +				}
      +			}
      +
      +			sigchain_push(SIGPIPE, SIG_IGN);
      +			ret = pipe_command(&ssh_keygen, payload, payload_size,
     -+					&ssh_keygen_out, 0, &ssh_keygen_err, 0);
     ++					   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
      +			sigchain_pop(SIGPIPE);
      +
     ++			FREE_AND_NULL(principal);
     ++
      +			ret &= starts_with(ssh_keygen_out.buf, "Good");
      +			if (ret == 0)
      +				break;
     @@ gpg-interface.c: error:
      +	return ret;
      +}
      +
     - static int verify_gpg_signature(struct signature_check *sigc, struct gpg_format *fmt,
     - 	const char *payload, size_t payload_size,
     - 	const char *signature, size_t signature_size)
     + int check_signature(const char *payload, size_t plen, const char *signature,
     + 	size_t slen, struct signature_check *sigc)
     + {
     +@@ gpg-interface.c: int git_gpg_config(const char *var, const char *value, void *cb)
     + 		return 0;
     + 	}
     + 
     ++	if (!strcmp(var, "gpg.ssh.allowedsignersfile")) {
     ++		if (!value)
     ++			return config_error_nonbool(var);
     ++		return git_config_string(&ssh_allowed_signers, var, value);
     ++	}
     ++
     ++	if (!strcmp(var, "gpg.ssh.revocationFile")) {
     ++		if (!value)
     ++			return config_error_nonbool(var);
     ++		return git_config_string(&ssh_revocation_file, var, value);
     ++	}
     ++
     + 	if (!strcmp(var, "gpg.program") || !strcmp(var, "gpg.openpgp.program"))
     + 		fmtname = "openpgp";
     + 
  7:  1d292a8d7a2 !  6:  06a76e64b35 ssh signing: add test prereqs
     @@ Metadata
       ## Commit message ##
          ssh signing: add test prereqs
      
     -    generate some ssh keys and a allowed keys keyring for testing
     +    generate some ssh keys and a allowedSignersFile for testing
      
          Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
      
     @@ t/lib-gpg.sh: test_lazy_prereq RFC1991 '
      +	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/ed25519_ssh_signing_key" >/dev/null &&
      +	ssh-keygen -t rsa -b 2048 -N "" -f "${GNUPGHOME}/rsa_2048_ssh_signing_key" >/dev/null &&
      +	ssh-keygen -t ed25519 -N "super_secret" -f "${GNUPGHOME}/protected_ssh_signing_key" >/dev/null &&
     -+	find "${GNUPGHOME}" -name *ssh_signing_key.pub -exec cat {} \; | awk "{print \"principal_\" NR \" \" \$0}" > "${GNUPGHOME}/ssh.all_valid.keyring" &&
     -+	cat "${GNUPGHOME}/ssh.all_valid.keyring" &&
     ++	find "${GNUPGHOME}" -name *ssh_signing_key.pub -exec cat {} \; | awk "{print \"\\\"principal with number \" NR \"\\\" \" \$0}" > "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
     ++	cat "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
      +	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/untrusted_ssh_signing_key" >/dev/null
      +'
      +
     @@ t/lib-gpg.sh: test_lazy_prereq RFC1991 '
      +SIGNING_KEY_UNTRUSTED="${GNUPGHOME}/untrusted_ssh_signing_key"
      +SIGNING_KEY_WITH_PASSPHRASE="${GNUPGHOME}/protected_ssh_signing_key"
      +SIGNING_KEY_PASSPHRASE="super_secret"
     -+SIGNING_KEYRING="${GNUPGHOME}/ssh.all_valid.keyring"
     ++SIGNING_ALLOWED_SIGNERS="${GNUPGHOME}/ssh.all_valid.allowedSignersFile"
      +
      +GOOD_SIGNATURE_TRUSTED='Good "git" signature for'
      +GOOD_SIGNATURE_UNTRUSTED='Good "git" signature with'
  8:  338d1b976e9 !  7:  4dc5572083b ssh signing: duplicate t7510 tests for commits
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'verify and show signatures' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	test_config gpg.mintrustlevel UNDEFINED &&
      +	(
      +		for commit in initial second merge fourth-signed \
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'verify-commit exits success on untrusted signature' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	git verify-commit eighth-signed-alt 2>actual &&
      +	grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
      +	! grep "${BAD_SIGNATURE}" actual &&
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'verify-commit exits success with matching minTrustLevel' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	test_config gpg.minTrustLevel fully &&
      +	git verify-commit sixth-signed
      +'
      +
      +test_expect_success GPGSSH 'verify-commit exits success with low minTrustLevel' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	test_config gpg.minTrustLevel marginal &&
      +	git verify-commit sixth-signed
      +'
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'verify signatures with --raw' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	(
      +		for commit in initial second merge fourth-signed fifth-signed sixth-signed seventh-signed
      +		do
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'show signed commit with signature' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	git show -s initial >commit &&
      +	git show -s --show-signature initial >show &&
      +	git verify-commit -v initial >verify.1 2>verify.2 &&
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'detect fudged signature' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	git cat-file commit seventh-signed >raw &&
      +	sed -e "s/^seventh/7th forged/" raw >forged1 &&
      +	git hash-object -w -t commit forged1 >forged1.commit &&
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'detect fudged signature with NUL' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	git cat-file commit seventh-signed >raw &&
      +	cat raw >forged2 &&
      +	echo Qwik | tr "Q" "\000" >>forged2 &&
     @@ t/t7527-signed-commit-ssh.sh (new)
      +test_expect_success GPGSSH 'amending already signed commit' '
      +	test_config gpg.format ssh &&
      +	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	git checkout fourth-signed^0 &&
      +	git commit --amend -S --no-edit &&
      +	git verify-commit HEAD &&
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'show good signature with custom format' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
      +	cat >expect.tmpl <<-\EOF &&
      +	G
      +	FINGERPRINT
     -+	principal_1
     ++	principal with number 1
      +	FINGERPRINT
      +
      +	EOF
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'show bad signature with custom format' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	cat >expect <<-\EOF &&
      +	B
      +
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'show untrusted signature with custom format' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	cat >expect.tmpl <<-\EOF &&
      +	U
      +	FINGERPRINT
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'show untrusted signature with undefined trust level' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	cat >expect.tmpl <<-\EOF &&
      +	undefined
      +	FINGERPRINT
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'show untrusted signature with ultimate trust level' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	cat >expect.tmpl <<-\EOF &&
      +	fully
      +	FINGERPRINT
     -+	principal_1
     ++	principal with number 1
      +	FINGERPRINT
      +
      +	EOF
     @@ t/t7527-signed-commit-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'log.showsignature behaves like --show-signature' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	test_config log.showsignature true &&
      +	git show initial >actual &&
      +	grep "${GOOD_SIGNATURE_TRUSTED}" actual
  9:  33330fda441 !  8:  275dd8a1013 ssh signing: add more tests for logs, tags & push certs
     @@ t/t4202-log.sh: test_expect_success GPGSM 'log OpenPGP fingerprint' '
       '
       
      +test_expect_success GPGSSH 'log ssh key fingerprint' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	ssh-keygen -lf  "${SIGNING_KEY_PRIMARY}" | awk "{print \$2\" | \"}" >expect &&
      +	git log -n1 --format="%GF | %GP" signed-ssh >actual &&
      +	test_cmp expect actual
     @@ t/t4202-log.sh: test_expect_success GPGSM 'log --graph --show-signature x509' '
       '
       
      +test_expect_success GPGSSH 'log --graph --show-signature ssh' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	git log --graph --show-signature -n1 signed-ssh >actual &&
      +	grep "${GOOD_SIGNATURE_TRUSTED}" actual
      +'
     @@ t/t5534-push-signed.sh: test_expect_success GPG 'signed push sends push certific
      +test_expect_success GPGSSH 'ssh signed push sends push certificate' '
      +	prepare_dst &&
      +	mkdir -p dst/.git/hooks &&
     -+	git -C dst config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	git -C dst config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	git -C dst config receive.certnonceseed sekrit &&
      +	write_script dst/.git/hooks/post-receive <<-\EOF &&
      +	# discard the update list
     @@ t/t5534-push-signed.sh: test_expect_success GPG 'signed push sends push certific
      +
      +	(
      +		cat <<-\EOF &&
     -+		SIGNER=principal_1
     ++		SIGNER=principal with number 1
      +		KEY=FINGERPRINT
      +		STATUS=G
      +		NONCE_STATUS=OK
     @@ t/t5534-push-signed.sh: test_expect_success GPGSM 'fail without key and heed use
      +	test_config gpg.format ssh &&
      +	prepare_dst &&
      +	mkdir -p dst/.git/hooks &&
     -+	git -C dst config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	git -C dst config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	git -C dst config receive.certnonceseed sekrit &&
      +	write_script dst/.git/hooks/post-receive <<-\EOF &&
      +	# discard the update list
     @@ t/t5534-push-signed.sh: test_expect_success GPGSM 'fail without key and heed use
      +
      +	(
      +		cat <<-\EOF &&
     -+		SIGNER=principal_1
     ++		SIGNER=principal with number 1
      +		KEY=FINGERPRINT
      +		STATUS=G
      +		NONCE_STATUS=OK
     @@ t/t7031-verify-tag-signed-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'verify and show ssh signatures' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	(
      +		for tag in initial second merge fourth-signed sixth-signed seventh-signed
      +		do
     @@ t/t7031-verify-tag-signed-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'detect fudged ssh signature' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	git cat-file tag seventh-signed >raw &&
      +	sed -e "/^tag / s/seventh/7th forged/" raw >forged1 &&
      +	git hash-object -w -t tag forged1 >forged1.tag &&
     @@ t/t7031-verify-tag-signed-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'verify ssh signatures with --raw' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	(
      +		for tag in initial second merge fourth-signed sixth-signed seventh-signed
      +		do
     @@ t/t7031-verify-tag-signed-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'verify signatures with --raw ssh' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	git verify-tag --raw sixth-signed 2>actual &&
      +	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
      +	! grep "${BAD_SIGNATURE}" actual &&
     @@ t/t7031-verify-tag-signed-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'verify multiple tags ssh' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	tags="seventh-signed sixth-signed" &&
      +	for i in $tags
      +	do
     @@ t/t7031-verify-tag-signed-ssh.sh (new)
      +'
      +
      +test_expect_success GPGSSH 'verifying tag with --format - ssh' '
     -+	test_config gpg.ssh.keyring "${SIGNING_KEYRING}" &&
     ++	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
      +	cat >expect <<-\EOF &&
      +	tagname : fourth-signed
      +	EOF
  2:  2f8452f6570 !  9:  13f6c229bd1 ssh signing: add documentation
     @@ Documentation/config/gpg.txt: gpg.minTrustLevel::
       * `fully`
       * `ultimate`
      +
     -+gpg.ssh.keyring::
     -+	A file containing all valid SSH public signing keys.
     -+	Similar to an .ssh/authorized_keys file.
     ++gpg.ssh.allowedSignersFile::
     ++	A file containing ssh public keys which you are willing to trust.
     ++	The file consists of one or more lines of principals followed by an ssh
     ++	public key.
     ++	e.g.: user1@example.com,user2@example.com ssh-rsa AAAAX1...
      +	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
     -+	If a signing key is found in this file then the trust level will
     -+	be set to "fully". Otherwise if the key is not present
     -+	but the signature is still valid then the trust level will be "undefined".
     ++	The principal is only used to identify the key and is available when
     ++	verifying a signature.
     +++
     ++SSH has no concept of trust levels like gpg does. To be able to differentiate
     ++between valid signatures and trusted signatures the trust level of a signature
     ++verification is set to `fully` when the public key is present in the allowedSignersFile.
     ++Therefore to only mark fully trusted keys as verified set gpg.minTrustLevel to `fully`.
     ++Otherwise valid but untrusted signatures will still verify but show no principal
     ++name of the signer.
     +++
     ++This file can be set to a location outside of the repository and every developer
     ++maintains their own trust store. A central repository server could generate this
     ++file automatically from ssh keys with push access to verify the code against.
     ++In a corporate setting this file is probably generated at a global location
     ++from automation that already handles developer ssh keys.
     +++
     ++A repository that only allows signed commits can store the file
     ++in the repository itself using a path relative to the top-level of the working tree.
     ++This way only committers with an already valid key can add or change keys in the keyring.
     +++
     ++Using a SSH CA key with the cert-authority option
     ++(see ssh-keygen(1) "CERTIFICATES") is also valid.
      +
     -+	This file can be set to a location outside of the repository
     -+	and every developer maintains their own trust store.
     -+	A central repository server could generate this file automatically
     -+	from ssh keys with push	access to verify the code against.
     -+	In a corporate setting this file is probably generated at a global location
     -+	from some automation that already handles developer ssh keys.
     -+
     -+	A repository that is only allowing signed commits can store the file
     -+	in the repository itself using a relative path. This way only committers
     -+	with an already valid key can add or change keys in the keyring.
     -+
     -+	Using a SSH CA key with the cert-authority option
     -+	(see ssh-keygen(1) "CERTIFICATES") is also valid.
     -+
     -+	To revoke a key place the public key without the principal into the
     -+	revocationKeyring.
     -+
     -+gpg.ssh.revocationKeyring::
     ++gpg.ssh.revocationFile::
      +	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
      +	See ssh-keygen(1) for details.
      +	If a public key is found in this file then it will always be treated

-- 
gitgitgadget

[PATCH v4 1/9] ssh signing: preliminary refactoring and clean-up

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Openssh v8.2p1 added some new options to ssh-keygen for signature
creation and verification. These allow us to use ssh keys for git
signatures easily.

In our corporate environment we use PIV x509 Certs on Yubikeys for email
signing/encryption and ssh keys which I think is quite common
(at least for the email part). This way we can establish the correct
trust for the SSH Keys without setting up a separate GPG Infrastructure
(which is still quite painful for users) or implementing x509 signing
support for git (which lacks good forwarding mechanisms).
Using ssh agent forwarding makes this feature easily usable in todays
development environments where code is often checked out in remote VMs / containers.
In such a setup the keyring & revocationKeyring can be centrally
generated from the x509 CA information and distributed to the users.

To be able to implement new signing formats this commit:
 - makes the sigc structure more generic by renaming "gpg_output" to
   "output"
 - introduces function pointers in the gpg_format structure to call
   format specific signing and verification functions
 - moves format detection from verify_signed_buffer into the check_signature
   api function and calls the format specific verify
 - renames and wraps sign_buffer to handle format specific signing logic
   as well

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 fmt-merge-msg.c |   6 +--
 gpg-interface.c | 104 +++++++++++++++++++++++++++++-------------------
 gpg-interface.h |   2 +-
 log-tree.c      |   8 ++--
 pretty.c        |   4 +-
 5 files changed, 74 insertions(+), 50 deletions(-)

diff --git a/fmt-merge-msg.c b/fmt-merge-msg.c
index 0f66818e0f8..fb300bb4b67 100644
--- a/fmt-merge-msg.c
+++ b/fmt-merge-msg.c
@@ -526,11 +526,11 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 			buf = payload.buf;
 			len = payload.len;
 			if (check_signature(payload.buf, payload.len, sig.buf,
-					 sig.len, &sigc) &&
-				!sigc.gpg_output)
+					    sig.len, &sigc) &&
+			    !sigc.output)
 				strbuf_addstr(&sig, "gpg verification failed.\n");
 			else
-				strbuf_addstr(&sig, sigc.gpg_output);
+				strbuf_addstr(&sig, sigc.output);
 		}
 		signature_check_clear(&sigc);
 
diff --git a/gpg-interface.c b/gpg-interface.c
index 127aecfc2b0..31cf4ba3938 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -15,6 +15,12 @@ struct gpg_format {
 	const char *program;
 	const char **verify_args;
 	const char **sigs;
+	int (*verify_signed_buffer)(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size);
+	int (*sign_buffer)(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key);
 };
 
 static const char *openpgp_verify_args[] = {
@@ -35,14 +41,29 @@ static const char *x509_sigs[] = {
 	NULL
 };
 
+static int verify_gpg_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size);
+static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key);
+
 static struct gpg_format gpg_format[] = {
-	{ .name = "openpgp", .program = "gpg",
-	  .verify_args = openpgp_verify_args,
-	  .sigs = openpgp_sigs
+	{
+		.name = "openpgp",
+		.program = "gpg",
+		.verify_args = openpgp_verify_args,
+		.sigs = openpgp_sigs,
+		.verify_signed_buffer = verify_gpg_signed_buffer,
+		.sign_buffer = sign_buffer_gpg,
 	},
-	{ .name = "x509", .program = "gpgsm",
-	  .verify_args = x509_verify_args,
-	  .sigs = x509_sigs
+	{
+		.name = "x509",
+		.program = "gpgsm",
+		.verify_args = x509_verify_args,
+		.sigs = x509_sigs,
+		.verify_signed_buffer = verify_gpg_signed_buffer,
+		.sign_buffer = sign_buffer_gpg,
 	},
 };
 
@@ -72,7 +93,7 @@ static struct gpg_format *get_format_by_sig(const char *sig)
 void signature_check_clear(struct signature_check *sigc)
 {
 	FREE_AND_NULL(sigc->payload);
-	FREE_AND_NULL(sigc->gpg_output);
+	FREE_AND_NULL(sigc->output);
 	FREE_AND_NULL(sigc->gpg_status);
 	FREE_AND_NULL(sigc->signer);
 	FREE_AND_NULL(sigc->key);
@@ -257,16 +278,16 @@ error:
 	FREE_AND_NULL(sigc->key);
 }
 
-static int verify_signed_buffer(const char *payload, size_t payload_size,
-				const char *signature, size_t signature_size,
-				struct strbuf *gpg_output,
-				struct strbuf *gpg_status)
+static int verify_gpg_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
-	struct gpg_format *fmt;
 	struct tempfile *temp;
 	int ret;
-	struct strbuf buf = STRBUF_INIT;
+	struct strbuf gpg_stdout = STRBUF_INIT;
+	struct strbuf gpg_stderr = STRBUF_INIT;
 
 	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
 	if (!temp)
@@ -279,10 +300,6 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 		return -1;
 	}
 
-	fmt = get_format_by_sig(signature);
-	if (!fmt)
-		BUG("bad signature '%s'", signature);
-
 	strvec_push(&gpg.args, fmt->program);
 	strvec_pushv(&gpg.args, fmt->verify_args);
 	strvec_pushl(&gpg.args,
@@ -290,18 +307,22 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 		     "--verify", temp->filename.buf, "-",
 		     NULL);
 
-	if (!gpg_status)
-		gpg_status = &buf;
-
 	sigchain_push(SIGPIPE, SIG_IGN);
-	ret = pipe_command(&gpg, payload, payload_size,
-			   gpg_status, 0, gpg_output, 0);
+	ret = pipe_command(&gpg, payload, payload_size, &gpg_stdout, 0,
+			   &gpg_stderr, 0);
 	sigchain_pop(SIGPIPE);
 
 	delete_tempfile(&temp);
 
-	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
-	strbuf_release(&buf); /* no matter it was used or not */
+	ret |= !strstr(gpg_stdout.buf, "\n[GNUPG:] GOODSIG ");
+	sigc->payload = xmemdupz(payload, payload_size);
+	sigc->output = strbuf_detach(&gpg_stderr, NULL);
+	sigc->gpg_status = strbuf_detach(&gpg_stdout, NULL);
+
+	parse_gpg_output(sigc);
+
+	strbuf_release(&gpg_stdout);
+	strbuf_release(&gpg_stderr);
 
 	return ret;
 }
@@ -309,35 +330,32 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 int check_signature(const char *payload, size_t plen, const char *signature,
 	size_t slen, struct signature_check *sigc)
 {
-	struct strbuf gpg_output = STRBUF_INIT;
-	struct strbuf gpg_status = STRBUF_INIT;
+	struct gpg_format *fmt;
 	int status;
 
 	sigc->result = 'N';
 	sigc->trust_level = -1;
 
-	status = verify_signed_buffer(payload, plen, signature, slen,
-				      &gpg_output, &gpg_status);
-	if (status && !gpg_output.len)
-		goto out;
-	sigc->payload = xmemdupz(payload, plen);
-	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
-	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
-	parse_gpg_output(sigc);
+	fmt = get_format_by_sig(signature);
+	if (!fmt)
+		return error(_("bad/incompatible signature '%s'"), signature);
+
+	status = fmt->verify_signed_buffer(sigc, fmt, payload, plen, signature,
+					   slen);
+
+	if (status && !sigc->output)
+		return !!status;
+
 	status |= sigc->result != 'G';
 	status |= sigc->trust_level < configured_min_trust_level;
 
- out:
-	strbuf_release(&gpg_status);
-	strbuf_release(&gpg_output);
-
 	return !!status;
 }
 
 void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
 {
-	const char *output = flags & GPG_VERIFY_RAW ?
-		sigc->gpg_status : sigc->gpg_output;
+	const char *output = flags & GPG_VERIFY_RAW ? sigc->gpg_status :
+							    sigc->output;
 
 	if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
 		fputs(sigc->payload, stdout);
@@ -441,6 +459,12 @@ const char *get_signing_key(void)
 }
 
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
+{
+	return use_format->sign_buffer(buffer, signature, signing_key);
+}
+
+static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
+		    const char *signing_key)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
 	int ret;
diff --git a/gpg-interface.h b/gpg-interface.h
index 80567e48948..feac4decf8b 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -17,7 +17,7 @@ enum signature_trust_level {
 
 struct signature_check {
 	char *payload;
-	char *gpg_output;
+	char *output;
 	char *gpg_status;
 
 	/*
diff --git a/log-tree.c b/log-tree.c
index 7b823786c2c..20af9bd1c82 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -513,10 +513,10 @@ static void show_signature(struct rev_info *opt, struct commit *commit)
 
 	status = check_signature(payload.buf, payload.len, signature.buf,
 				 signature.len, &sigc);
-	if (status && !sigc.gpg_output)
+	if (status && !sigc.output)
 		show_sig_lines(opt, status, "No signature\n");
 	else
-		show_sig_lines(opt, status, sigc.gpg_output);
+		show_sig_lines(opt, status, sigc.output);
 	signature_check_clear(&sigc);
 
  out:
@@ -583,8 +583,8 @@ static int show_one_mergetag(struct commit *commit,
 		/* could have a good signature */
 		status = check_signature(payload.buf, payload.len,
 					 signature.buf, signature.len, &sigc);
-		if (sigc.gpg_output)
-			strbuf_addstr(&verify_message, sigc.gpg_output);
+		if (sigc.output)
+			strbuf_addstr(&verify_message, sigc.output);
 		else
 			strbuf_addstr(&verify_message, "No signature\n");
 		signature_check_clear(&sigc);
diff --git a/pretty.c b/pretty.c
index b1ecd039cef..daa71394efd 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1432,8 +1432,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 			check_commit_signature(c->commit, &(c->signature_check));
 		switch (placeholder[1]) {
 		case 'G':
-			if (c->signature_check.gpg_output)
-				strbuf_addstr(sb, c->signature_check.gpg_output);
+			if (c->signature_check.output)
+				strbuf_addstr(sb, c->signature_check.output);
 			break;
 		case '?':
 			switch (c->signature_check.result) {
-- 
gitgitgadget

[PATCH v4 2/9] ssh signing: add ssh signature format and signing using ssh keys

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

implements the actual sign_buffer_ssh operation and move some shared
cleanup code into a strbuf function

Set gpg.format = ssh and user.signingkey to either a ssh public key
string (like from an authorized_keys file), or a ssh key file.
If the key file or the config value itself contains only a public key
then the private key needs to be available via ssh-agent.

gpg.ssh.program can be set to an alternative location of ssh-keygen.
A somewhat recent openssh version (8.2p1+) of ssh-keygen is needed for
this feature. Since only ssh-keygen is needed it can this way be
installed seperately without upgrading your system openssh packages.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 137 +++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 129 insertions(+), 8 deletions(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index 31cf4ba3938..a086123754d 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -41,12 +41,20 @@ static const char *x509_sigs[] = {
 	NULL
 };
 
+static const char *ssh_verify_args[] = { NULL };
+static const char *ssh_sigs[] = {
+	"-----BEGIN SSH SIGNATURE-----",
+	NULL
+};
+
 static int verify_gpg_signed_buffer(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
 				    size_t payload_size, const char *signature,
 				    size_t signature_size);
 static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 			   const char *signing_key);
+static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key);
 
 static struct gpg_format gpg_format[] = {
 	{
@@ -65,6 +73,14 @@ static struct gpg_format gpg_format[] = {
 		.verify_signed_buffer = verify_gpg_signed_buffer,
 		.sign_buffer = sign_buffer_gpg,
 	},
+	{
+		.name = "ssh",
+		.program = "ssh-keygen",
+		.verify_args = ssh_verify_args,
+		.sigs = ssh_sigs,
+		.verify_signed_buffer = NULL, /* TODO */
+		.sign_buffer = sign_buffer_ssh
+	},
 };
 
 static struct gpg_format *use_format = &gpg_format[0];
@@ -443,6 +459,9 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	if (!strcmp(var, "gpg.x509.program"))
 		fmtname = "x509";
 
+	if (!strcmp(var, "gpg.ssh.program"))
+		fmtname = "ssh";
+
 	if (fmtname) {
 		fmt = get_format_by_name(fmtname);
 		return git_config_string(&fmt->program, var, value);
@@ -463,12 +482,26 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
 	return use_format->sign_buffer(buffer, signature, signing_key);
 }
 
+static void strbuf_trim_trailing_cr(struct strbuf *buffer, int offset)
+{
+	size_t i, j;
+
+	for (i = j = offset; i < buffer->len; i++) {
+		if (buffer->buf[i] != '\r') {
+			if (i != j)
+				buffer->buf[j] = buffer->buf[i];
+			j++;
+		}
+	}
+	strbuf_setlen(buffer, j);
+}
+
 static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 		    const char *signing_key)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
 	int ret;
-	size_t i, j, bottom;
+	size_t bottom;
 	struct strbuf gpg_status = STRBUF_INIT;
 
 	strvec_pushl(&gpg.args,
@@ -494,13 +527,101 @@ static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 		return error(_("gpg failed to sign the data"));
 
 	/* Strip CR from the line endings, in case we are on Windows. */
-	for (i = j = bottom; i < signature->len; i++)
-		if (signature->buf[i] != '\r') {
-			if (i != j)
-				signature->buf[j] = signature->buf[i];
-			j++;
-		}
-	strbuf_setlen(signature, j);
+	strbuf_trim_trailing_cr(signature, bottom);
 
 	return 0;
 }
+
+static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key)
+{
+	struct child_process signer = CHILD_PROCESS_INIT;
+	int ret = -1;
+	size_t bottom;
+	struct strbuf signer_stderr = STRBUF_INIT;
+	struct tempfile *temp = NULL, *buffer_file = NULL;
+	char *ssh_signing_key_file = NULL;
+	struct strbuf ssh_signature_filename = STRBUF_INIT;
+
+	if (!signing_key || signing_key[0] == '\0')
+		return error(
+			_("user.signingkey needs to be set for ssh signing"));
+
+	if (istarts_with(signing_key, "ssh-")) {
+		/* A literal ssh key */
+		temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
+		if (!temp)
+			return error_errno(
+				_("could not create temporary file"));
+		if (write_in_full(temp->fd, signing_key, strlen(signing_key)) <
+			    0 ||
+		    close_tempfile_gently(temp) < 0) {
+			error_errno(_("failed writing ssh signing key to '%s'"),
+				    temp->filename.buf);
+			goto out;
+		}
+		ssh_signing_key_file = temp->filename.buf;
+	} else {
+		/* We assume a file */
+		ssh_signing_key_file = expand_user_path(signing_key, 1);
+	}
+
+	buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
+	if (!buffer_file) {
+		error_errno(_("could not create temporary file"));
+		goto out;
+	}
+
+	if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
+	    close_tempfile_gently(buffer_file) < 0) {
+		error_errno(_("failed writing ssh signing key buffer to '%s'"),
+			    buffer_file->filename.buf);
+		goto out;
+	}
+
+	strvec_pushl(&signer.args, use_format->program, "-Y", "sign", "-n",
+		     "git", "-f", ssh_signing_key_file,
+		     buffer_file->filename.buf, NULL);
+
+	sigchain_push(SIGPIPE, SIG_IGN);
+	ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
+	sigchain_pop(SIGPIPE);
+
+	if (ret && strstr(signer_stderr.buf, "usage:")) {
+		error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
+		goto out;
+	}
+
+	if (ret) {
+		error("%s", signer_stderr.buf);
+		goto out;
+	}
+
+	bottom = signature->len;
+
+	strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
+	strbuf_addstr(&ssh_signature_filename, ".sig");
+	if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {
+		error_errno(
+			_("failed reading ssh signing data buffer from '%s'"),
+			ssh_signature_filename.buf);
+	}
+	unlink_or_warn(ssh_signature_filename.buf);
+
+	if (ret) {
+		error(_("ssh failed to sign the data"));
+		goto out;
+	}
+
+	/* Strip CR from the line endings, in case we are on Windows. */
+	strbuf_trim_trailing_cr(signature, bottom);
+
+out:
+	if (temp)
+		delete_tempfile(&temp);
+	if (buffer_file)
+		delete_tempfile(&buffer_file);
+	strbuf_release(&signer_stderr);
+	strbuf_release(&ssh_signature_filename);
+	return ret;
+}
-- 
gitgitgadget

[PATCH v4 3/9] ssh signing: retrieve a default key from ssh-agent

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

if user.signingkey is not set and a ssh signature is requested we call
ssh-add -L and use the first key we get

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index a086123754d..35e584b94ef 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -470,11 +470,35 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	return 0;
 }
 
+/* Returns the first public key from an ssh-agent to use for signing */
+static char *get_default_ssh_signing_key(void)
+{
+	struct child_process ssh_add = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf key_stdout = STRBUF_INIT;
+	struct strbuf **keys;
+
+	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
+	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
+	if (!ret) {
+		keys = strbuf_split_max(&key_stdout, '\n', 2);
+		if (keys[0])
+			return strbuf_detach(keys[0], NULL);
+	}
+
+	strbuf_release(&key_stdout);
+	return "";
+}
+
 const char *get_signing_key(void)
 {
 	if (configured_signing_key)
 		return configured_signing_key;
-	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
+	if (!strcmp(use_format->name, "ssh")) {
+		return get_default_ssh_signing_key();
+	} else {
+		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
+	}
 }
 
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
-- 
gitgitgadget

[PATCH v4 4/9] ssh signing: provide a textual representation of the signing key

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

for ssh the user.signingkey can be a filename/path or even a literal ssh pubkey.
in push certs and textual output we prefer the ssh fingerprint instead.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 gpg-interface.h |  6 ++++++
 send-pack.c     |  8 ++++----
 3 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index 35e584b94ef..2c6eaf47d0f 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -470,6 +470,41 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	return 0;
 }
 
+static char *get_ssh_key_fingerprint(const char *signing_key)
+{
+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf fingerprint_stdout = STRBUF_INIT;
+	struct strbuf **fingerprint;
+
+	/*
+	 * With SSH Signing this can contain a filename or a public key
+	 * For textual representation we usually want a fingerprint
+	 */
+	if (istarts_with(signing_key, "ssh-")) {
+		strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf", "-", NULL);
+		ret = pipe_command(&ssh_keygen, signing_key,
+				   strlen(signing_key), &fingerprint_stdout, 0,
+				   NULL, 0);
+	} else {
+		strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf",
+			     configured_signing_key, NULL);
+		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0,
+				   NULL, 0);
+	}
+
+	if (!!ret)
+		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
+			  signing_key);
+
+	fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
+	if (!fingerprint[1])
+		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
+			  signing_key);
+
+	return strbuf_detach(fingerprint[1], NULL);
+}
+
 /* Returns the first public key from an ssh-agent to use for signing */
 static char *get_default_ssh_signing_key(void)
 {
@@ -490,6 +525,17 @@ static char *get_default_ssh_signing_key(void)
 	return "";
 }
 
+/* Returns a textual but unique representation ot the signing key */
+const char *get_signing_key_id(void)
+{
+	if (!strcmp(use_format->name, "ssh")) {
+		return get_ssh_key_fingerprint(get_signing_key());
+	} else {
+		/* GPG/GPGSM only store a key id on this variable */
+		return get_signing_key();
+	}
+}
+
 const char *get_signing_key(void)
 {
 	if (configured_signing_key)
diff --git a/gpg-interface.h b/gpg-interface.h
index feac4decf8b..beefacbb1e9 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -64,6 +64,12 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
 int git_gpg_config(const char *, const char *, void *);
 void set_signing_key(const char *);
 const char *get_signing_key(void);
+
+/*
+ * Returns a textual unique representation of the signing key in use
+ * Either a GPG KeyID or a SSH Key Fingerprint
+ */
+const char *get_signing_key_id(void);
 int check_signature(const char *payload, size_t plen,
 		    const char *signature, size_t slen,
 		    struct signature_check *sigc);
diff --git a/send-pack.c b/send-pack.c
index 9cb9f716509..191fc6da544 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -341,13 +341,13 @@ static int generate_push_cert(struct strbuf *req_buf,
 {
 	const struct ref *ref;
 	struct string_list_item *item;
-	char *signing_key = xstrdup(get_signing_key());
+	char *signing_key_id = xstrdup(get_signing_key_id());
 	const char *cp, *np;
 	struct strbuf cert = STRBUF_INIT;
 	int update_seen = 0;
 
 	strbuf_addstr(&cert, "certificate version 0.1\n");
-	strbuf_addf(&cert, "pusher %s ", signing_key);
+	strbuf_addf(&cert, "pusher %s ", signing_key_id);
 	datestamp(&cert);
 	strbuf_addch(&cert, '\n');
 	if (args->url && *args->url) {
@@ -374,7 +374,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 	if (!update_seen)
 		goto free_return;
 
-	if (sign_buffer(&cert, &cert, signing_key))
+	if (sign_buffer(&cert, &cert, get_signing_key()))
 		die(_("failed to sign the push certificate"));
 
 	packet_buf_write(req_buf, "push-cert%c%s", 0, cap_string);
@@ -386,7 +386,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 	packet_buf_write(req_buf, "push-cert-end\n");
 
 free_return:
-	free(signing_key);
+	free(signing_key_id);
 	strbuf_release(&cert);
 	return update_seen;
 }
-- 
gitgitgadget

[PATCH v4 5/9] ssh signing: parse ssh-keygen output and verify signatures

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

to verify a ssh signature we first call ssh-keygen -Y find-principal to
look up the signing principal by their public key from the
allowedSignersFile. If the key is found then we do a verify. Otherwise
we only validate the signature but can not verify the signers identity.

Verification uses the gpg.ssh.allowedSignersFile (see ssh-keygen(1) "ALLOWED
SIGNERS") which contains valid public keys and a principal (usually
user@domain). Depending on the environment this file can be managed by
the individual developer or for example generated by the central
repository server from known ssh keys with push access. If the
repository only allows signed commits / pushes then the file can even be
stored inside it.

To revoke a key put the public key without the principal prefix into
gpg.ssh.revocationKeyring or generate a KRL (see ssh-keygen(1)
"KEY REVOCATION LISTS"). The same considerations about who to trust for
verification as with the allowedSignersFile apply.

Using SSH CA Keys with these files is also possible. Add
"cert-authority" as key option between the principal and the key to mark
it as a CA and all keys signed by it as valid for this CA.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 builtin/receive-pack.c |   2 +
 gpg-interface.c        | 174 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 175 insertions(+), 1 deletion(-)

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index a34742513ac..62b11c5f3a4 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -131,6 +131,8 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 {
 	int status = parse_hide_refs_config(var, value, "receive");
 
+	git_gpg_config(var, value, NULL);
+
 	if (status)
 		return status;
 
diff --git a/gpg-interface.c b/gpg-interface.c
index 2c6eaf47d0f..761aa91d648 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -3,11 +3,13 @@
 #include "config.h"
 #include "run-command.h"
 #include "strbuf.h"
+#include "dir.h"
 #include "gpg-interface.h"
 #include "sigchain.h"
 #include "tempfile.h"
 
 static char *configured_signing_key;
+static const char *ssh_allowed_signers, *ssh_revocation_file;
 static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
 
 struct gpg_format {
@@ -51,6 +53,10 @@ static int verify_gpg_signed_buffer(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
 				    size_t payload_size, const char *signature,
 				    size_t signature_size);
+static int verify_ssh_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size);
 static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 			   const char *signing_key);
 static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
@@ -78,7 +84,7 @@ static struct gpg_format gpg_format[] = {
 		.program = "ssh-keygen",
 		.verify_args = ssh_verify_args,
 		.sigs = ssh_sigs,
-		.verify_signed_buffer = NULL, /* TODO */
+		.verify_signed_buffer = verify_ssh_signed_buffer,
 		.sign_buffer = sign_buffer_ssh
 	},
 };
@@ -343,6 +349,160 @@ static int verify_gpg_signed_buffer(struct signature_check *sigc,
 	return ret;
 }
 
+static void parse_ssh_output(struct signature_check *sigc)
+{
+	const char *line, *principal, *search;
+
+	/*
+	 * ssh-keysign output should be:
+	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
+	 * Good "git" signature for PRINCIPAL WITH WHITESPACE with RSA key SHA256:FINGERPRINT
+	 * or for valid but unknown keys:
+	 * Good "git" signature with RSA key SHA256:FINGERPRINT
+	 */
+	sigc->result = 'B';
+	sigc->trust_level = TRUST_NEVER;
+
+	line = xmemdupz(sigc->output, strcspn(sigc->output, "\n"));
+
+	if (skip_prefix(line, "Good \"git\" signature for ", &line)) {
+		/* Valid signature and known principal */
+		sigc->result = 'G';
+		sigc->trust_level = TRUST_FULLY;
+
+		/* Search for the last "with" to get the full principal */
+		principal = line;
+		do {
+			search = strstr(line, " with ");
+			if (search)
+				line = search + 1;
+		} while (search != NULL);
+		sigc->signer = xmemdupz(principal, line - principal - 1);
+		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);
+		sigc->key = xstrdup(sigc->fingerprint);
+	} else if (skip_prefix(line, "Good \"git\" signature with ", &line)) {
+		/* Valid signature, but key unknown */
+		sigc->result = 'G';
+		sigc->trust_level = TRUST_UNDEFINED;
+		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);
+		sigc->key = xstrdup(sigc->fingerprint);
+	}
+}
+
+static const char *get_ssh_allowed_signers(void)
+{
+	if (ssh_allowed_signers)
+		return ssh_allowed_signers;
+
+	die("gpg.ssh.allowedSignersFile needs to be configured and exist for validation");
+}
+
+static int verify_ssh_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size)
+{
+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
+	struct tempfile *temp;
+	int ret;
+	const char *line;
+	size_t trust_size;
+	char *principal;
+	struct strbuf ssh_keygen_out = STRBUF_INIT;
+	struct strbuf ssh_keygen_err = STRBUF_INIT;
+
+	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
+	if (!temp)
+		return error_errno(_("could not create temporary file"));
+	if (write_in_full(temp->fd, signature, signature_size) < 0 ||
+	    close_tempfile_gently(temp) < 0) {
+		error_errno(_("failed writing detached signature to '%s'"),
+			    temp->filename.buf);
+		delete_tempfile(&temp);
+		return -1;
+	}
+
+	/* Find the principal from the signers */
+	strvec_pushl(&ssh_keygen.args, fmt->program, "-Y", "find-principals",
+		     "-f", get_ssh_allowed_signers(), "-s", temp->filename.buf,
+		     NULL);
+	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0,
+			   &ssh_keygen_err, 0);
+	if (ret && strstr(ssh_keygen_err.buf, "usage:")) {
+		error(_("ssh-keygen -Y find-principals/verify is needed for ssh signature verification (available in openssh version 8.2p1+)"));
+		return ret;
+	}
+	if (ret || !ssh_keygen_out.len) {
+		/* We did not find a matching principal in the allowedSigners - Check
+		 * without validation */
+		child_process_init(&ssh_keygen);
+		strvec_pushl(&ssh_keygen.args, fmt->program, "-Y",
+			     "check-novalidate", "-n", "git", "-s",
+			     temp->filename.buf, NULL);
+		ret = pipe_command(&ssh_keygen, payload, payload_size,
+				   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
+	} else {
+		/* Check every principal we found (one per line) */
+		for (line = ssh_keygen_out.buf; *line;
+		     line = strchrnul(line + 1, '\n')) {
+			while (*line == '\n')
+				line++;
+			if (!*line)
+				break;
+
+			trust_size = strcspn(line, "\n");
+			principal = xmemdupz(line, trust_size);
+
+			child_process_init(&ssh_keygen);
+			strbuf_release(&ssh_keygen_out);
+			strbuf_release(&ssh_keygen_err);
+			strvec_push(&ssh_keygen.args, fmt->program);
+			/* We found principals - Try with each until we find a
+			 * match */
+			strvec_pushl(&ssh_keygen.args, "-Y", "verify", "-n",
+				     "git", "-f", get_ssh_allowed_signers(),
+				     "-I", principal, "-s", temp->filename.buf,
+				     NULL);
+
+			if (ssh_revocation_file) {
+				if (file_exists(ssh_revocation_file)) {
+					strvec_pushl(&ssh_keygen.args, "-r",
+						     ssh_revocation_file, NULL);
+				} else {
+					warning(_("ssh signing revocation file configured but not found: %s"),
+						ssh_revocation_file);
+				}
+			}
+
+			sigchain_push(SIGPIPE, SIG_IGN);
+			ret = pipe_command(&ssh_keygen, payload, payload_size,
+					   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
+			sigchain_pop(SIGPIPE);
+
+			FREE_AND_NULL(principal);
+
+			ret &= starts_with(ssh_keygen_out.buf, "Good");
+			if (ret == 0)
+				break;
+		}
+	}
+
+	sigc->payload = xmemdupz(payload, payload_size);
+	strbuf_stripspace(&ssh_keygen_out, 0);
+	strbuf_stripspace(&ssh_keygen_err, 0);
+	strbuf_add(&ssh_keygen_out, ssh_keygen_err.buf, ssh_keygen_err.len);
+	sigc->output = strbuf_detach(&ssh_keygen_out, NULL);
+	sigc->gpg_status = xstrdup(sigc->output);
+
+	parse_ssh_output(sigc);
+
+	delete_tempfile(&temp);
+	strbuf_release(&ssh_keygen_out);
+	strbuf_release(&ssh_keygen_err);
+
+	return ret;
+}
+
 int check_signature(const char *payload, size_t plen, const char *signature,
 	size_t slen, struct signature_check *sigc)
 {
@@ -453,6 +613,18 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(var, "gpg.ssh.allowedsignersfile")) {
+		if (!value)
+			return config_error_nonbool(var);
+		return git_config_string(&ssh_allowed_signers, var, value);
+	}
+
+	if (!strcmp(var, "gpg.ssh.revocationFile")) {
+		if (!value)
+			return config_error_nonbool(var);
+		return git_config_string(&ssh_revocation_file, var, value);
+	}
+
 	if (!strcmp(var, "gpg.program") || !strcmp(var, "gpg.openpgp.program"))
 		fmtname = "openpgp";
 
-- 
gitgitgadget

[PATCH v4 6/9] ssh signing: add test prereqs

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

generate some ssh keys and a allowedSignersFile for testing

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/lib-gpg.sh | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/t/lib-gpg.sh b/t/lib-gpg.sh
index 9fc5241228e..b4fbcad4bf3 100644
--- a/t/lib-gpg.sh
+++ b/t/lib-gpg.sh
@@ -87,6 +87,33 @@ test_lazy_prereq RFC1991 '
 	echo | gpg --homedir "${GNUPGHOME}" -b --rfc1991 >/dev/null
 '
 
+test_lazy_prereq GPGSSH '
+	ssh_version=$(ssh-keygen -Y find-principals -n "git" 2>&1)
+	test $? != 127 || exit 1
+	echo $ssh_version | grep -q "find-principals:missing signature file"
+	test $? = 0 || exit 1;
+	mkdir -p "${GNUPGHOME}" &&
+	chmod 0700 "${GNUPGHOME}" &&
+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/ed25519_ssh_signing_key" >/dev/null &&
+	ssh-keygen -t rsa -b 2048 -N "" -f "${GNUPGHOME}/rsa_2048_ssh_signing_key" >/dev/null &&
+	ssh-keygen -t ed25519 -N "super_secret" -f "${GNUPGHOME}/protected_ssh_signing_key" >/dev/null &&
+	find "${GNUPGHOME}" -name *ssh_signing_key.pub -exec cat {} \; | awk "{print \"\\\"principal with number \" NR \"\\\" \" \$0}" > "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
+	cat "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/untrusted_ssh_signing_key" >/dev/null
+'
+
+SIGNING_KEY_PRIMARY="${GNUPGHOME}/ed25519_ssh_signing_key"
+SIGNING_KEY_SECONDARY="${GNUPGHOME}/rsa_2048_ssh_signing_key"
+SIGNING_KEY_UNTRUSTED="${GNUPGHOME}/untrusted_ssh_signing_key"
+SIGNING_KEY_WITH_PASSPHRASE="${GNUPGHOME}/protected_ssh_signing_key"
+SIGNING_KEY_PASSPHRASE="super_secret"
+SIGNING_ALLOWED_SIGNERS="${GNUPGHOME}/ssh.all_valid.allowedSignersFile"
+
+GOOD_SIGNATURE_TRUSTED='Good "git" signature for'
+GOOD_SIGNATURE_UNTRUSTED='Good "git" signature with'
+KEY_NOT_TRUSTED="No principal matched"
+BAD_SIGNATURE="Signature verification failed"
+
 sanitize_pgp() {
 	perl -ne '
 		/^-----END PGP/ and $in_pgp = 0;
-- 
gitgitgadget

[PATCH v4 7/9] ssh signing: duplicate t7510 tests for commits

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/t7527-signed-commit-ssh.sh | 398 +++++++++++++++++++++++++++++++++++
 1 file changed, 398 insertions(+)
 create mode 100755 t/t7527-signed-commit-ssh.sh

diff --git a/t/t7527-signed-commit-ssh.sh b/t/t7527-signed-commit-ssh.sh
new file mode 100755
index 00000000000..e2c48f69e6d
--- /dev/null
+++ b/t/t7527-signed-commit-ssh.sh
@@ -0,0 +1,398 @@
+#!/bin/sh
+
+test_description='ssh signed commit tests'
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+GNUPGHOME_NOT_USED=$GNUPGHOME
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPGSSH 'create signed commits' '
+	test_oid_cache <<-\EOF &&
+	header sha1:gpgsig
+	header sha256:gpgsig-sha256
+	EOF
+
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+
+	echo 1 >file && git add file &&
+	test_tick && git commit -S -m initial &&
+	git tag initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -S -m second &&
+	git tag second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout main &&
+	test_tick && git merge -S side &&
+	git tag merge &&
+
+	echo 4 >file && test_tick && git commit -a -m "fourth unsigned" &&
+	git tag fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag fourth-signed &&
+
+	git config commit.gpgsign true &&
+	echo 5 >file && test_tick && git commit -a -m "fifth signed" &&
+	git tag fifth-signed &&
+
+	git config commit.gpgsign false &&
+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
+	git tag sixth-unsigned &&
+
+	git config commit.gpgsign true &&
+	echo 7 >file && test_tick && git commit -a -m "seventh" --no-gpg-sign &&
+	git tag seventh-unsigned &&
+
+	test_tick && git rebase -f HEAD^^ && git tag sixth-signed HEAD^ &&
+	git tag seventh-signed &&
+
+	echo 8 >file && test_tick && git commit -a -m eighth -S"${SIGNING_KEY_UNTRUSTED}" &&
+	git tag eighth-signed-alt &&
+
+	# commit.gpgsign is still on but this must not be signed
+	echo 9 | git commit-tree HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag ninth-unsigned $(cat oid) &&
+	# explicit -S of course must sign.
+	echo 10 | git commit-tree -S HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag tenth-signed $(cat oid) &&
+
+	# --gpg-sign[=<key-id>] must sign.
+	echo 11 | git commit-tree --gpg-sign HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag eleventh-signed $(cat oid) &&
+	echo 12 | git commit-tree --gpg-sign="${SIGNING_KEY_UNTRUSTED}" HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag twelfth-signed-alt $(cat oid)
+'
+
+test_expect_success GPGSSH 'verify and show signatures' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config gpg.mintrustlevel UNDEFINED &&
+	(
+		for commit in initial second merge fourth-signed \
+			fifth-signed sixth-signed seventh-signed tenth-signed \
+			eleventh-signed
+		do
+			git verify-commit $commit &&
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in merge^2 fourth-unsigned sixth-unsigned \
+			seventh-unsigned ninth-unsigned
+		do
+			test_must_fail git verify-commit $commit &&
+			git show --pretty=short --show-signature $commit >actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in eighth-signed-alt twelfth-signed-alt
+		do
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			grep "${KEY_NOT_TRUSTED}" actual &&
+			echo $commit OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'verify-commit exits success on untrusted signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git verify-commit eighth-signed-alt 2>actual &&
+	grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual &&
+	grep "${KEY_NOT_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH 'verify-commit exits success with matching minTrustLevel' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config gpg.minTrustLevel fully &&
+	git verify-commit sixth-signed
+'
+
+test_expect_success GPGSSH 'verify-commit exits success with low minTrustLevel' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config gpg.minTrustLevel marginal &&
+	git verify-commit sixth-signed
+'
+
+test_expect_success GPGSSH 'verify-commit exits failure with high minTrustLevel' '
+	test_config gpg.minTrustLevel ultimate &&
+	test_must_fail git verify-commit eighth-signed-alt
+'
+
+test_expect_success GPGSSH 'verify signatures with --raw' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	(
+		for commit in initial second merge fourth-signed fifth-signed sixth-signed seventh-signed
+		do
+			git verify-commit --raw $commit 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in merge^2 fourth-unsigned sixth-unsigned seventh-unsigned
+		do
+			test_must_fail git verify-commit --raw $commit 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in eighth-signed-alt
+		do
+			git verify-commit --raw $commit 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'proper header is used for hash algorithm' '
+	git cat-file commit fourth-signed >output &&
+	grep "^$(test_oid header) -----BEGIN SSH SIGNATURE-----" output
+'
+
+test_expect_success GPGSSH 'show signed commit with signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git show -s initial >commit &&
+	git show -s --show-signature initial >show &&
+	git verify-commit -v initial >verify.1 2>verify.2 &&
+	git cat-file commit initial >cat &&
+	grep -v -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.commit &&
+	grep -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.gpg &&
+	grep -v "^ " cat | grep -v "^gpgsig.* " >cat.commit &&
+	test_cmp show.commit commit &&
+	test_cmp show.gpg verify.2 &&
+	test_cmp cat.commit verify.1
+'
+
+test_expect_success GPGSSH 'detect fudged signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git cat-file commit seventh-signed >raw &&
+	sed -e "s/^seventh/7th forged/" raw >forged1 &&
+	git hash-object -w -t commit forged1 >forged1.commit &&
+	test_must_fail git verify-commit $(cat forged1.commit) &&
+	git show --pretty=short --show-signature $(cat forged1.commit) >actual1 &&
+	grep "${BAD_SIGNATURE}" actual1 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
+'
+
+test_expect_success GPGSSH 'detect fudged signature with NUL' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git cat-file commit seventh-signed >raw &&
+	cat raw >forged2 &&
+	echo Qwik | tr "Q" "\000" >>forged2 &&
+	git hash-object -w -t commit forged2 >forged2.commit &&
+	test_must_fail git verify-commit $(cat forged2.commit) &&
+	git show --pretty=short --show-signature $(cat forged2.commit) >actual2 &&
+	grep "${BAD_SIGNATURE}" actual2 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual2
+'
+
+test_expect_success GPGSSH 'amending already signed commit' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git checkout fourth-signed^0 &&
+	git commit --amend -S --no-edit &&
+	git verify-commit HEAD &&
+	git show -s --show-signature HEAD >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual
+'
+
+test_expect_success GPGSSH 'show good signature with custom format' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	cat >expect.tmpl <<-\EOF &&
+	G
+	FINGERPRINT
+	principal with number 1
+	FINGERPRINT
+
+	EOF
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show bad signature with custom format' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect <<-\EOF &&
+	B
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat forged1.commit) >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with custom format' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect.tmpl <<-\EOF &&
+	U
+	FINGERPRINT
+
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with undefined trust level' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect.tmpl <<-\EOF &&
+	undefined
+	FINGERPRINT
+
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with ultimate trust level' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect.tmpl <<-\EOF &&
+	fully
+	FINGERPRINT
+	principal with number 1
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show lack of signature with custom format' '
+	cat >expect <<-\EOF &&
+	N
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" seventh-unsigned >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'log.showsignature behaves like --show-signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config log.showsignature true &&
+	git show initial >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH 'check config gpg.format values' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_config gpg.format ssh &&
+	git commit -S --amend -m "success" &&
+	test_config gpg.format OpEnPgP &&
+	test_must_fail git commit -S --amend -m "fail"
+'
+
+test_expect_failure GPGSSH 'detect fudged commit with double signature (TODO)' '
+	sed -e "/gpgsig/,/END PGP/d" forged1 >double-base &&
+	sed -n -e "/gpgsig/,/END PGP/p" forged1 | \
+		sed -e "s/^$(test_oid header)//;s/^ //" | gpg --dearmor >double-sig1.sig &&
+	gpg -o double-sig2.sig -u 29472784 --detach-sign double-base &&
+	cat double-sig1.sig double-sig2.sig | gpg --enarmor >double-combined.asc &&
+	sed -e "s/^\(-.*\)ARMORED FILE/\1SIGNATURE/;1s/^/$(test_oid header) /;2,\$s/^/ /" \
+		double-combined.asc > double-gpgsig &&
+	sed -e "/committer/r double-gpgsig" double-base >double-commit &&
+	git hash-object -w -t commit double-commit >double-commit.commit &&
+	test_must_fail git verify-commit $(cat double-commit.commit) &&
+	git show --pretty=short --show-signature $(cat double-commit.commit) >double-actual &&
+	grep "BAD signature from" double-actual &&
+	grep "Good signature from" double-actual
+'
+
+test_expect_failure GPGSSH 'show double signature with custom format (TODO)' '
+	cat >expect <<-\EOF &&
+	E
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat double-commit.commit) >actual &&
+	test_cmp expect actual
+'
+
+
+test_expect_failure GPGSSH 'verify-commit verifies multiply signed commits (TODO)' '
+	git init multiply-signed &&
+	cd multiply-signed &&
+	test_commit first &&
+	echo 1 >second &&
+	git add second &&
+	tree=$(git write-tree) &&
+	parent=$(git rev-parse HEAD^{commit}) &&
+	git commit --gpg-sign -m second &&
+	git cat-file commit HEAD &&
+	# Avoid trailing whitespace.
+	sed -e "s/^Q//" -e "s/^Z/ /" >commit <<-EOF &&
+	Qtree $tree
+	Qparent $parent
+	Qauthor A U Thor <author@example.com> 1112912653 -0700
+	Qcommitter C O Mitter <committer@example.com> 1112912653 -0700
+	Qgpgsig -----BEGIN PGP SIGNATURE-----
+	QZ
+	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBDRYcY29tbWl0dGVy
+	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMNd+8AoK1I8mhLHviPH+q2I5fIVgPsEtYC
+	Q AKCTqBh+VabJceXcGIZuF0Ry+udbBQ==
+	Q =tQ0N
+	Q -----END PGP SIGNATURE-----
+	Qgpgsig-sha256 -----BEGIN PGP SIGNATURE-----
+	QZ
+	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBIBYcY29tbWl0dGVy
+	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMN/NEAn0XO9RYSBj2dFyozi0JKSbssYMtO
+	Q AJwKCQ1BQOtuwz//IjU8TiS+6S4iUw==
+	Q =pIwP
+	Q -----END PGP SIGNATURE-----
+	Q
+	Qsecond
+	EOF
+	head=$(git hash-object -t commit -w commit) &&
+	git reset --hard $head &&
+	git verify-commit $head 2>actual &&
+	grep "Good signature from" actual &&
+	! grep "BAD signature from" actual
+'
+
+test_done
-- 
gitgitgadget

[PATCH v4 8/9] ssh signing: add more tests for logs, tags & push certs

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/t4202-log.sh                   |  23 +++++
 t/t5534-push-signed.sh           | 101 +++++++++++++++++++
 t/t7031-verify-tag-signed-ssh.sh | 161 +++++++++++++++++++++++++++++++
 3 files changed, 285 insertions(+)
 create mode 100755 t/t7031-verify-tag-signed-ssh.sh

diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index 39e746fbcbe..afd7f2516ee 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -1616,6 +1616,16 @@ test_expect_success GPGSM 'setup signed branch x509' '
 	git commit -S -m signed_commit
 '
 
+test_expect_success GPGSSH 'setup sshkey signed branch' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_when_finished "git reset --hard && git checkout main" &&
+	git checkout -b signed-ssh main &&
+	echo foo >foo &&
+	git add foo &&
+	git commit -S -m signed_commit
+'
+
 test_expect_success GPGSM 'log x509 fingerprint' '
 	echo "F8BF62E0693D0694816377099909C779FA23FD65 | " >expect &&
 	git log -n1 --format="%GF | %GP" signed-x509 >actual &&
@@ -1628,6 +1638,13 @@ test_expect_success GPGSM 'log OpenPGP fingerprint' '
 	test_cmp expect actual
 '
 
+test_expect_success GPGSSH 'log ssh key fingerprint' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	ssh-keygen -lf  "${SIGNING_KEY_PRIMARY}" | awk "{print \$2\" | \"}" >expect &&
+	git log -n1 --format="%GF | %GP" signed-ssh >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success GPG 'log --graph --show-signature' '
 	git log --graph --show-signature -n1 signed >actual &&
 	grep "^| gpg: Signature made" actual &&
@@ -1640,6 +1657,12 @@ test_expect_success GPGSM 'log --graph --show-signature x509' '
 	grep "^| gpgsm: Good signature" actual
 '
 
+test_expect_success GPGSSH 'log --graph --show-signature ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git log --graph --show-signature -n1 signed-ssh >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual
+'
+
 test_expect_success GPG 'log --graph --show-signature for merged tag' '
 	test_when_finished "git reset --hard && git checkout main" &&
 	git checkout -b plain main &&
diff --git a/t/t5534-push-signed.sh b/t/t5534-push-signed.sh
index bba768f5ded..d590249b995 100755
--- a/t/t5534-push-signed.sh
+++ b/t/t5534-push-signed.sh
@@ -137,6 +137,53 @@ test_expect_success GPG 'signed push sends push certificate' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPGSSH 'ssh signed push sends push certificate' '
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=principal with number 1
+		KEY=FINGERPRINT
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
+
+	noop=$(git rev-parse noop) &&
+	ff=$(git rev-parse ff) &&
+	noff=$(git rev-parse noff) &&
+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_expect_success GPG 'inconsistent push options in signed push not allowed' '
 	# First, invoke receive-pack with dummy input to obtain its preamble.
 	prepare_dst &&
@@ -276,6 +323,60 @@ test_expect_success GPGSM 'fail without key and heed user.signingkey x509' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPGSSH 'fail without key and heed user.signingkey ssh' '
+	test_config gpg.format ssh &&
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	test_config user.email hasnokey@nowhere.com &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "" &&
+	(
+		sane_unset GIT_COMMITTER_EMAIL &&
+		test_must_fail git push --signed dst noop ff +noff
+	) &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=principal with number 1
+		KEY=FINGERPRINT
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
+
+	noop=$(git rev-parse noop) &&
+	ff=$(git rev-parse ff) &&
+	noff=$(git rev-parse noff) &&
+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_expect_success GPG 'failed atomic push does not execute GPG' '
 	prepare_dst &&
 	git -C dst config receive.certnonceseed sekrit &&
diff --git a/t/t7031-verify-tag-signed-ssh.sh b/t/t7031-verify-tag-signed-ssh.sh
new file mode 100755
index 00000000000..05bf520a332
--- /dev/null
+++ b/t/t7031-verify-tag-signed-ssh.sh
@@ -0,0 +1,161 @@
+#!/bin/sh
+
+test_description='signed tag tests'
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPGSSH 'create signed tags ssh' '
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+
+	echo 1 >file && git add file &&
+	test_tick && git commit -m initial &&
+	git tag -s -m initial initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -m second &&
+	git tag -s -m second second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout main &&
+	test_tick && git merge -S side &&
+	git tag -s -m merge merge &&
+
+	echo 4 >file && test_tick && git commit -a -S -m "fourth unsigned" &&
+	git tag -a -m fourth-unsigned fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag -s -m fourth fourth-signed &&
+
+	echo 5 >file && test_tick && git commit -a -m "fifth" &&
+	git tag fifth-unsigned &&
+
+	git config commit.gpgsign true &&
+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
+	git tag -a -m sixth sixth-unsigned &&
+
+	test_tick && git rebase -f HEAD^^ && git tag -s -m 6th sixth-signed HEAD^ &&
+	git tag -m seventh -s seventh-signed &&
+
+	echo 8 >file && test_tick && git commit -a -m eighth &&
+	git tag -u"${SIGNING_KEY_UNTRUSTED}" -m eighth eighth-signed-alt
+'
+
+test_expect_success GPGSSH 'verify and show ssh signatures' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	(
+		for tag in initial second merge fourth-signed sixth-signed seventh-signed
+		do
+			git verify-tag $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
+		do
+			test_must_fail git verify-tag $tag 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in eighth-signed-alt
+		do
+			git verify-tag $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			grep "${KEY_NOT_TRUSTED}" actual &&
+			echo $tag OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'detect fudged ssh signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git cat-file tag seventh-signed >raw &&
+	sed -e "/^tag / s/seventh/7th forged/" raw >forged1 &&
+	git hash-object -w -t tag forged1 >forged1.tag &&
+	test_must_fail git verify-tag $(cat forged1.tag) 2>actual1 &&
+	grep "${BAD_SIGNATURE}" actual1 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
+'
+
+test_expect_success GPGSSH 'verify ssh signatures with --raw' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	(
+		for tag in initial second merge fourth-signed sixth-signed seventh-signed
+		do
+			git verify-tag --raw $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
+		do
+			test_must_fail git verify-tag --raw $tag 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in eighth-signed-alt
+		do
+			git verify-tag --raw $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'verify signatures with --raw ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git verify-tag --raw sixth-signed 2>actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual &&
+	echo sixth-signed OK
+'
+
+test_expect_success GPGSSH 'verify multiple tags ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	tags="seventh-signed sixth-signed" &&
+	for i in $tags
+	do
+		git verify-tag -v --raw $i || return 1
+	done >expect.stdout 2>expect.stderr.1 &&
+	grep "^${GOOD_SIGNATURE_TRUSTED}" <expect.stderr.1 >expect.stderr &&
+	git verify-tag -v --raw $tags >actual.stdout 2>actual.stderr.1 &&
+	grep "^${GOOD_SIGNATURE_TRUSTED}" <actual.stderr.1 >actual.stderr &&
+	test_cmp expect.stdout actual.stdout &&
+	test_cmp expect.stderr actual.stderr
+'
+
+test_expect_success GPGSSH 'verifying tag with --format - ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect <<-\EOF &&
+	tagname : fourth-signed
+	EOF
+	git verify-tag --format="tagname : %(tag)" "fourth-signed" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'verifying a forged tag with --format should fail silently - ssh' '
+	test_must_fail git verify-tag --format="tagname : %(tag)" $(cat forged1.tag) >actual-forged &&
+	test_must_be_empty actual-forged
+'
+
+test_done
-- 
gitgitgadget

[PATCH v4 9/9] ssh signing: add documentation

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 Documentation/config/gpg.txt  | 39 +++++++++++++++++++++++++++++++++--
 Documentation/config/user.txt |  6 ++++++
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
index d94025cb368..dc790512e86 100644
--- a/Documentation/config/gpg.txt
+++ b/Documentation/config/gpg.txt
@@ -11,13 +11,13 @@ gpg.program::
 
 gpg.format::
 	Specifies which key format to use when signing with `--gpg-sign`.
-	Default is "openpgp" and another possible value is "x509".
+	Default is "openpgp". Other possible values are "x509", "ssh".
 
 gpg.<format>.program::
 	Use this to customize the program used for the signing format you
 	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
 	be used as a legacy synonym for `gpg.openpgp.program`. The default
-	value for `gpg.x509.program` is "gpgsm".
+	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
 
 gpg.minTrustLevel::
 	Specifies a minimum trust level for signature verification.  If
@@ -33,3 +33,38 @@ gpg.minTrustLevel::
 * `marginal`
 * `fully`
 * `ultimate`
+
+gpg.ssh.allowedSignersFile::
+	A file containing ssh public keys which you are willing to trust.
+	The file consists of one or more lines of principals followed by an ssh
+	public key.
+	e.g.: user1@example.com,user2@example.com ssh-rsa AAAAX1...
+	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
+	The principal is only used to identify the key and is available when
+	verifying a signature.
++
+SSH has no concept of trust levels like gpg does. To be able to differentiate
+between valid signatures and trusted signatures the trust level of a signature
+verification is set to `fully` when the public key is present in the allowedSignersFile.
+Therefore to only mark fully trusted keys as verified set gpg.minTrustLevel to `fully`.
+Otherwise valid but untrusted signatures will still verify but show no principal
+name of the signer.
++
+This file can be set to a location outside of the repository and every developer
+maintains their own trust store. A central repository server could generate this
+file automatically from ssh keys with push access to verify the code against.
+In a corporate setting this file is probably generated at a global location
+from automation that already handles developer ssh keys.
++
+A repository that only allows signed commits can store the file
+in the repository itself using a path relative to the top-level of the working tree.
+This way only committers with an already valid key can add or change keys in the keyring.
++
+Using a SSH CA key with the cert-authority option
+(see ssh-keygen(1) "CERTIFICATES") is also valid.
+
+gpg.ssh.revocationFile::
+	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
+	See ssh-keygen(1) for details.
+	If a public key is found in this file then it will always be treated
+	as having trust level "never" and signatures will show as invalid.
diff --git a/Documentation/config/user.txt b/Documentation/config/user.txt
index 59aec7c3aed..b3c2f2c541e 100644
--- a/Documentation/config/user.txt
+++ b/Documentation/config/user.txt
@@ -36,3 +36,9 @@ user.signingKey::
 	commit, you can override the default selection with this variable.
 	This option is passed unchanged to gpg's --local-user parameter,
 	so you may specify a key using any method that gpg supports.
+	If gpg.format is set to "ssh" this can contain the literal ssh public
+	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and
+	corresponds to the private key used for signing. The private key
+	needs to be available via ssh-agent. Alternatively it can be set to
+	a file containing a private key directly. If not set git will call
+	"ssh-add -L" and try to use the first key available.
-- 
gitgitgadget

Re: [PATCH v4 1/9] ssh signing: preliminary refactoring and clean-up

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

> diff --git a/gpg-interface.c b/gpg-interface.c
> index 127aecfc2b0..31cf4ba3938 100644
> --- a/gpg-interface.c
> +++ b/gpg-interface.c
> @@ -15,6 +15,12 @@ struct gpg_format {
>  	const char *program;
>  	const char **verify_args;
>  	const char **sigs;
> +	int (*verify_signed_buffer)(struct signature_check *sigc,
> +				    struct gpg_format *fmt, const char *payload,
> +				    size_t payload_size, const char *signature,
> +				    size_t signature_size);
> +	int (*sign_buffer)(struct strbuf *buffer, struct strbuf *signature,
> +			   const char *signing_key);
>  };

Thanks for a pleasant read.  Looking good.

Re: [PATCH v4 2/9] ssh signing: add ssh signature format and signing using ssh keys

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

> @@ -65,6 +73,14 @@ static struct gpg_format gpg_format[] = {
>  		.verify_signed_buffer = verify_gpg_signed_buffer,
>  		.sign_buffer = sign_buffer_gpg,
>  	},
> +	{
> +		.name = "ssh",
> +		.program = "ssh-keygen",
> +		.verify_args = ssh_verify_args,
> +		.sigs = ssh_sigs,
> +		.verify_signed_buffer = NULL, /* TODO */
> +		.sign_buffer = sign_buffer_ssh
> +	},
>  };

A payload a malicious person may feed this version of Git can have a
pattern that happens to match the ssh_sigs[] string, and the code
will blindly try to call .verify_signed_buffer==NULL and die, no?

That is not the end of the world; as long as we know that with the
above "TODO" comment it is probably OK.

> @@ -463,12 +482,26 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
>  	return use_format->sign_buffer(buffer, signature, signing_key);
>  }
>  
> +static void strbuf_trim_trailing_cr(struct strbuf *buffer, int offset)
> +{

This removes any and all CR, not just trimming the trailing ones, so
the function is misnamed. Call it remove_cr_after() perhaps?

Alternatively we could tighten the implementation and strip only the
CR that come immediately before a LF.  That would be a better longer
term thing to do, but because you are lifting an existing code from
the end of the gpg side of the thing, it may make sense to keep the
implementation as-is, but give it a name that is more faithful to
what it actually does.  When the dust settles, we may want to
revisit and fix this helper function to actually trim CRLF into LF
(and leave CR in the middle of lines intact), but I do not think it
is urgent.  Just leaving "NEEDSWORK: make it trim only CRs before LFs
and rename" comment would be OK.

Shouldn't the offset (aka bottom) be of type size_t?

I do not recommend giving the function a name that begins with
"strbuf_", as it would tempt unthinking person to suggest moving it
to strbuf.c, but the presense of the "offset" thing means it will be
klunky to reuse in other more generic contexts as a part of the
strbuf API.

> +	size_t i, j;
> +
> +	for (i = j = offset; i < buffer->len; i++) {
> +		if (buffer->buf[i] != '\r') {
> ...

Now it gets interesting ;-)

> +static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
> +			   const char *signing_key)
> +{
> +	struct child_process signer = CHILD_PROCESS_INIT;
> +	int ret = -1;
> +	size_t bottom;
> +	struct strbuf signer_stderr = STRBUF_INIT;
> +	struct tempfile *temp = NULL, *buffer_file = NULL;
> +	char *ssh_signing_key_file = NULL;
> +	struct strbuf ssh_signature_filename = STRBUF_INIT;
> +
> +	if (!signing_key || signing_key[0] == '\0')
> +		return error(
> +			_("user.signingkey needs to be set for ssh signing"));
> +
> +	if (istarts_with(signing_key, "ssh-")) {

Is it common in the ssh world to treat ssh- prefix as case
insensitive?  Not a strong objection but I tend to prefer to start
strict unless there is a good reason to be loose when we do not have
to, as loosening after the fact is much easier than tightening after
starting with a loose definition.

> +		/* A literal ssh key */
> +		temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
> +		if (!temp)
> +			return error_errno(
> +				_("could not create temporary file"));
> +		if (write_in_full(temp->fd, signing_key, strlen(signing_key)) <
> +			    0 ||

"keylen = strlen(signing_key)" before that line, for example, could
have easily avoided the line-wrapping at such a place.  Wrapping at
places like after ||, i.e. after an operator with a low precedence,
would make the code easier to follow.

> +		    close_tempfile_gently(temp) < 0) {
> +			error_errno(_("failed writing ssh signing key to '%s'"),
> +				    temp->filename.buf);
> +			goto out;
> +		}
> +		ssh_signing_key_file = temp->filename.buf;

It is kind'a sad that we need a fresh temporary file every time, but
we can easily tell the user in the documentation that they can use a
file with a key in it to avoid it, so it's OK (actually, better than
OK, as without this, we may not consume temporary files but we won't
offer an ability to take a literal key string).

Is ".git_whatever file in the current directory" a good place to
have this temporary file?  I would have expected that we would use
either $GIT_DIR, $HOME, or $TMPDIR for a thing like this (with
different pros-and-cons discussion).  At least it is consistent with
how a temporary file for the payload to be sign-verified is created,
so let's leave it as-is.

> +	} else {
> +		/* We assume a file */
> +		ssh_signing_key_file = expand_user_path(signing_key, 1);
> +	}
> +
> +	buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
> +	if (!buffer_file) {
> +		error_errno(_("could not create temporary file"));
> +		goto out;
> +	}
> +
> +	if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
> +	    close_tempfile_gently(buffer_file) < 0) {
> +		error_errno(_("failed writing ssh signing key buffer to '%s'"),
> +			    buffer_file->filename.buf);
> +		goto out;
> +	}
> +
> +	strvec_pushl(&signer.args, use_format->program, "-Y", "sign", "-n",
> +		     "git", "-f", ssh_signing_key_file,

Wrap the line before "-n" to keep "-n" and "git" together, if "git"
is meant as an argument to the "-n" option.

> +		     buffer_file->filename.buf, NULL);
> +
> +	sigchain_push(SIGPIPE, SIG_IGN);
> +	ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
> +	sigchain_pop(SIGPIPE);
> +
> +	if (ret && strstr(signer_stderr.buf, "usage:")) {
> +		error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
> +		goto out;

This error message is important to give to the end users, but is it
enough?  That is, unless "usage:" does not appear, we show the whole
raw error message and that would help end users and those helping
them to diagnose the issue, but once the underlying program says
"usage:", no matter what else it says, it is hidden by this code,
since we assume it is a wrong version of openssh.

> +	}
> +
> +	if (ret) {
> +		error("%s", signer_stderr.buf);
> +		goto out;
> +	}

Also, prehaps

	if (ret) {
		if (strstr(..., "usage"))
			error(_("ssh-keygen -Y sign is needed..."));
		else
                        error("%s", signer_stderr.buf);
		goto out;
	}

would be easier to follow.

> +	bottom = signature->len;
> +
> +	strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
> +	strbuf_addstr(&ssh_signature_filename, ".sig");
> +	if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {

Is it likely that signature file is smaller than 2kB?  I am just
wondering how much we care to pick the default that is specific to
this codepath vs passing 0 to ask the strbuf API to use whatever
default it wants to.

> +		error_errno(
> +			_("failed reading ssh signing data buffer from '%s'"),
> +			ssh_signature_filename.buf);
> +	}
> +	unlink_or_warn(ssh_signature_filename.buf);

Wait a bit.  Even when pipe_command() tells us that we failed, we
read from ssh_signature_filename anyway?  What is going on?  And ...

> +	if (ret) {

... does this ever trigger?  I thought we would have hit one of the
two "goto out" when ret signals an error by being non-zero earlier,
and since then nobody touched the variable so far.

> +		error(_("ssh failed to sign the data"));
> +		goto out;
> +	}
> +
> +	/* Strip CR from the line endings, in case we are on Windows. */
> +	strbuf_trim_trailing_cr(signature, bottom);
> +
> +out:
> +	if (temp)
> +		delete_tempfile(&temp);
> +	if (buffer_file)
> +		delete_tempfile(&buffer_file);

It is clear that the latter one was holding the contents of the
buffer to be signed, but reminding the readers what "temp" was about
would be a good move.  Perhaps renaming the variable to "key_file"
or something may help?

> +	strbuf_release(&signer_stderr);
> +	strbuf_release(&ssh_signature_filename);
> +	return ret;
> +}

Looking good, except for the "when does 'ret' get updated?
shouldn't we refrain from reading the resulting buffer when it is
set?" question.

Thanks for a pleasant read.

Re: [PATCH v4 0/9] ssh signing: Add commit & tag signing/verification via SSH keys using ssh-keygen

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

>  create mode 100755 t/t7031-verify-tag-signed-ssh.sh
>  create mode 100755 t/t7527-signed-commit-ssh.sh

As the number 7527 is already in use by another topic in 'seen',
this new one must be relocated to coexist with them.

Re: [PATCH v4 2/9] ssh signing: add ssh signature format and signing using ssh keys

[Fabian Stelzer]

On 20.07.21 01:53, Junio C Hamano wrote:
> "Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>> @@ -65,6 +73,14 @@ static struct gpg_format gpg_format[] = {
>>   		.verify_signed_buffer = verify_gpg_signed_buffer,
>>   		.sign_buffer = sign_buffer_gpg,
>>   	},
>> +	{
>> +		.name = "ssh",
>> +		.program = "ssh-keygen",
>> +		.verify_args = ssh_verify_args,
>> +		.sigs = ssh_sigs,
>> +		.verify_signed_buffer = NULL, /* TODO */
>> +		.sign_buffer = sign_buffer_ssh
>> +	},
>>   };
> A payload a malicious person may feed this version of Git can have a
> pattern that happens to match the ssh_sigs[] string, and the code
> will blindly try to call .verify_signed_buffer==NULL and die, no?
>
> That is not the end of the world; as long as we know that with the
> above "TODO" comment it is probably OK.
I thought about adding an if(!fmt->sign) BUG() but since these callbacks 
are static it shoud really only be an issue between patches of the set.
>
>> @@ -463,12 +482,26 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
>>   	return use_format->sign_buffer(buffer, signature, signing_key);
>>   }
>>   
>> +static void strbuf_trim_trailing_cr(struct strbuf *buffer, int offset)
>> +{
> This removes any and all CR, not just trimming the trailing ones, so
> the function is misnamed. Call it remove_cr_after() perhaps?
>
> Alternatively we could tighten the implementation and strip only the
> CR that come immediately before a LF.  That would be a better longer
> term thing to do, but because you are lifting an existing code from
> the end of the gpg side of the thing, it may make sense to keep the
> implementation as-is, but give it a name that is more faithful to
> what it actually does.  When the dust settles, we may want to
> revisit and fix this helper function to actually trim CRLF into LF
> (and leave CR in the middle of lines intact), but I do not think it
> is urgent.  Just leaving "NEEDSWORK: make it trim only CRs before LFs
> and rename" comment would be OK.
Agreed. I've renamed it and added the comment.
>
> Shouldn't the offset (aka bottom) be of type size_t?
fixed
>> +static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
>> +			   const char *signing_key)
>> +{
>> +	struct child_process signer = CHILD_PROCESS_INIT;
>> +	int ret = -1;
>> +	size_t bottom;
>> +	struct strbuf signer_stderr = STRBUF_INIT;
>> +	struct tempfile *temp = NULL, *buffer_file = NULL;
>> +	char *ssh_signing_key_file = NULL;
>> +	struct strbuf ssh_signature_filename = STRBUF_INIT;
>> +
>> +	if (!signing_key || signing_key[0] == '\0')
>> +		return error(
>> +			_("user.signingkey needs to be set for ssh signing"));
>> +
>> +	if (istarts_with(signing_key, "ssh-")) {
> Is it common in the ssh world to treat ssh- prefix as case
> insensitive?  Not a strong objection but I tend to prefer to start
> strict unless there is a good reason to be loose when we do not have
> to, as loosening after the fact is much easier than tightening after
> starting with a loose definition.
I don't think so. I will make it case sensitive.
>
>> +		/* A literal ssh key */
>> +		temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
>> +		if (!temp)
>> +			return error_errno(
>> +				_("could not create temporary file"));
>> +		if (write_in_full(temp->fd, signing_key, strlen(signing_key)) <
>> +			    0 ||
> "keylen = strlen(signing_key)" before that line, for example, could
> have easily avoided the line-wrapping at such a place.  Wrapping at
> places like after ||, i.e. after an operator with a low precedence,
> would make the code easier to follow.
agreed.
>
>> +		    close_tempfile_gently(temp) < 0) {
>> +			error_errno(_("failed writing ssh signing key to '%s'"),
>> +				    temp->filename.buf);
>> +			goto out;
>> +		}
>> +		ssh_signing_key_file = temp->filename.buf;
> It is kind'a sad that we need a fresh temporary file every time, but
> we can easily tell the user in the documentation that they can use a
> file with a key in it to avoid it, so it's OK (actually, better than
> OK, as without this, we may not consume temporary files but we won't
> offer an ability to take a literal key string).
>
> Is ".git_whatever file in the current directory" a good place to
> have this temporary file?  I would have expected that we would use
> either $GIT_DIR, $HOME, or $TMPDIR for a thing like this (with
> different pros-and-cons discussion).  At least it is consistent with
> how a temporary file for the payload to be sign-verified is created,
> so let's leave it as-is.
Intuitively i thought just using mks_tempfile_t() would choose a good 
dir for such files.
>
>> +	} else {
>> +		/* We assume a file */
>> +		ssh_signing_key_file = expand_user_path(signing_key, 1);
>> +	}
>> +
>> +	buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
>> +	if (!buffer_file) {
>> +		error_errno(_("could not create temporary file"));
>> +		goto out;
>> +	}
>> +
>> +	if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
>> +	    close_tempfile_gently(buffer_file) < 0) {
>> +		error_errno(_("failed writing ssh signing key buffer to '%s'"),
>> +			    buffer_file->filename.buf);
>> +		goto out;
>> +	}
>> +
>> +	strvec_pushl(&signer.args, use_format->program, "-Y", "sign", "-n",
>> +		     "git", "-f", ssh_signing_key_file,
> Wrap the line before "-n" to keep "-n" and "git" together, if "git"
> is meant as an argument to the "-n" option.
done. some things clang-format can't really understand. overall it is 
quite helpful but a few things i still had to reformat.
>
>> +		     buffer_file->filename.buf, NULL);
>> +
>> +	sigchain_push(SIGPIPE, SIG_IGN);
>> +	ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
>> +	sigchain_pop(SIGPIPE);
>> +
>> +	if (ret && strstr(signer_stderr.buf, "usage:")) {
>> +		error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
>> +		goto out;
> This error message is important to give to the end users, but is it
> enough?  That is, unless "usage:" does not appear, we show the whole
> raw error message and that would help end users and those helping
> them to diagnose the issue, but once the underlying program says
> "usage:", no matter what else it says, it is hidden by this code,
> since we assume it is a wrong version of openssh.
>
>> +	}
>> +
>> +	if (ret) {
>> +		error("%s", signer_stderr.buf);
>> +		goto out;
>> +	}
> Also, prehaps
>
> 	if (ret) {
> 		if (strstr(..., "usage"))
> 			error(_("ssh-keygen -Y sign is needed..."));
> 		else
>                          error("%s", signer_stderr.buf);
> 		goto out;
> 	}
>
> would be easier to follow.

I have changed this to:
if (ret) {
     if (strstr(..., "usage"))
         error(_("ssh-keygen -Y sign is needed..."));

     error("%s", signer_stderr.buf);
     goto out;
}
and removed the if (ret) further down in the function that had no effect.

I had removed the raw stderr output from verify & sign because it 
becomes quite unreadable when doing a "git log --show-signature" with 
ssh signatures present and not support in ssh for it.
I think in case of signing the full output is good. The user is taking 
an active action (wanting to sign something) so we should give them all 
the help we can when things go wrong.
The output for verification is debatable. The config might have a 
"log.showSignature" for verifying gpg signatures and when ssh signatures 
show up we should tell them it's not supported on their setup but 
probably not showing endless lines of errors when they do a "git log". A 
"git verify-commit" might be a different case. But code-path-wise this 
is the same thing at the moment.

>> +		error(_("ssh failed to sign the data"));
>> +		goto out;
>> +	}
>> +
>> +	/* Strip CR from the line endings, in case we are on Windows. */
>> +	strbuf_trim_trailing_cr(signature, bottom);
>> +
>> +out:
>> +	if (temp)
>> +		delete_tempfile(&temp);
>> +	if (buffer_file)
>> +		delete_tempfile(&buffer_file);
> It is clear that the latter one was holding the contents of the
> buffer to be signed, but reminding the readers what "temp" was about
> would be a good move.  Perhaps renaming the variable to "key_file"
> or something may help?
renamed to "key_file"
>
>> +	strbuf_release(&signer_stderr);
>> +	strbuf_release(&ssh_signature_filename);
>> +	return ret;
>> +}
> Looking good, except for the "when does 'ret' get updated?
> shouldn't we refrain from reading the resulting buffer when it is
> set?" question.
>
> Thanks for a pleasant read.
Thanks a lot for your support with this!
>

[PATCH v5 0/9] ssh signing: Add commit & tag signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer via GitGitGadget]

I have added support for using keyfiles directly, lots of tests and
generally cleaned up the signing & verification code a lot.

I can still rename things from being gpg specific to a more general
"signing" but thats rather cosmetic. Also i'm not sure if i named the new
test files correctly.

openssh 8.7 will add valid-after, valid-before options to the allowed keys
keyring. This allows us to pass the commit timestamp to the verification
call and make key rollover possible and still be able to verify older
commits. Set valid-after=NOW when adding your key to the keyring and set
valid-before to make it fail if used after a certain date. Software like
gitolite/github or corporate automation can do this automatically when ssh
push keys are addded / removed I will add this feature in a follow up patch
afterwards.

v3 addresses some issues & refactoring and splits the large commit into
several smaller ones.

v4:

 * restructures and cleans up the whole patch set - patches build on its own
   now and commit messages try to explain whats going on
 * got rid of the if branches and used callback functions in the format
   struct
 * fixed a bug with whitespace in principal identifiers that required a
   rewrite of the parse_ssh_output function
 * rewrote documentation to be more clear - also renamed keyring back to
   allowedSignersFile

v5:

 * moved t7527 to t7528 to not collide with another patch in "seen"
 * clean up return logic for failed signing & verification
 * some minor renames / reformatting to make things clearer

Fabian Stelzer (9):
  ssh signing: preliminary refactoring and clean-up
  ssh signing: add ssh signature format and signing using ssh keys
  ssh signing: retrieve a default key from ssh-agent
  ssh signing: provide a textual representation of the signing key
  ssh signing: parse ssh-keygen output and verify signatures
  ssh signing: add test prereqs
  ssh signing: duplicate t7510 tests for commits
  ssh signing: add more tests for logs, tags & push certs
  ssh signing: add documentation

 Documentation/config/gpg.txt     |  39 ++-
 Documentation/config/user.txt    |   6 +
 builtin/receive-pack.c           |   2 +
 fmt-merge-msg.c                  |   6 +-
 gpg-interface.c                  | 490 +++++++++++++++++++++++++++----
 gpg-interface.h                  |   8 +-
 log-tree.c                       |   8 +-
 pretty.c                         |   4 +-
 send-pack.c                      |   8 +-
 t/lib-gpg.sh                     |  27 ++
 t/t4202-log.sh                   |  23 ++
 t/t5534-push-signed.sh           | 101 +++++++
 t/t7031-verify-tag-signed-ssh.sh | 161 ++++++++++
 t/t7528-signed-commit-ssh.sh     | 398 +++++++++++++++++++++++++
 14 files changed, 1216 insertions(+), 65 deletions(-)
 create mode 100755 t/t7031-verify-tag-signed-ssh.sh
 create mode 100755 t/t7528-signed-commit-ssh.sh


base-commit: eb27b338a3e71c7c4079fbac8aeae3f8fbb5c687
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1041%2FFStelzer%2Fsshsign-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1041/FStelzer/sshsign-v5
Pull-Request: https://github.com/git/git/pull/1041

Range-diff vs v4:

  1:  b4b0e2bac1c =  1:  7c8502c65b8 ssh signing: preliminary refactoring and clean-up
  2:  2c75adee8e1 !  2:  f05bab16096 ssh signing: add ssh signature format and signing using ssh keys
     @@ gpg-interface.c: int sign_buffer(struct strbuf *buffer, struct strbuf *signature
       	return use_format->sign_buffer(buffer, signature, signing_key);
       }
       
     -+static void strbuf_trim_trailing_cr(struct strbuf *buffer, int offset)
     ++/*
     ++ * Strip CR from the line endings, in case we are on Windows.
     ++ * NEEDSWORK: make it trim only CRs before LFs and rename
     ++ */
     ++static void remove_cr_after(struct strbuf *buffer, size_t offset)
      +{
      +	size_t i, j;
      +
     @@ gpg-interface.c: static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf
      -			j++;
      -		}
      -	strbuf_setlen(signature, j);
     -+	strbuf_trim_trailing_cr(signature, bottom);
     ++	remove_cr_after(signature, bottom);
       
       	return 0;
       }
     @@ gpg-interface.c: static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf
      +{
      +	struct child_process signer = CHILD_PROCESS_INIT;
      +	int ret = -1;
     -+	size_t bottom;
     ++	size_t bottom, keylen;
      +	struct strbuf signer_stderr = STRBUF_INIT;
     -+	struct tempfile *temp = NULL, *buffer_file = NULL;
     ++	struct tempfile *key_file = NULL, *buffer_file = NULL;
      +	char *ssh_signing_key_file = NULL;
      +	struct strbuf ssh_signature_filename = STRBUF_INIT;
      +
     @@ gpg-interface.c: static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf
      +		return error(
      +			_("user.signingkey needs to be set for ssh signing"));
      +
     -+	if (istarts_with(signing_key, "ssh-")) {
     ++	if (starts_with(signing_key, "ssh-")) {
      +		/* A literal ssh key */
     -+		temp = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
     -+		if (!temp)
     ++		key_file = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
     ++		if (!key_file)
      +			return error_errno(
      +				_("could not create temporary file"));
     -+		if (write_in_full(temp->fd, signing_key, strlen(signing_key)) <
     -+			    0 ||
     -+		    close_tempfile_gently(temp) < 0) {
     ++		keylen = strlen(signing_key);
     ++		if (write_in_full(key_file->fd, signing_key, keylen) < 0 ||
     ++		    close_tempfile_gently(key_file) < 0) {
      +			error_errno(_("failed writing ssh signing key to '%s'"),
     -+				    temp->filename.buf);
     ++				    key_file->filename.buf);
      +			goto out;
      +		}
     -+		ssh_signing_key_file = temp->filename.buf;
     ++		ssh_signing_key_file = key_file->filename.buf;
      +	} else {
      +		/* We assume a file */
      +		ssh_signing_key_file = expand_user_path(signing_key, 1);
     @@ gpg-interface.c: static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf
      +		goto out;
      +	}
      +
     -+	strvec_pushl(&signer.args, use_format->program, "-Y", "sign", "-n",
     -+		     "git", "-f", ssh_signing_key_file,
     -+		     buffer_file->filename.buf, NULL);
     ++	strvec_pushl(&signer.args, use_format->program,
     ++		     "-Y", "sign",
     ++		     "-n", "git",
     ++		     "-f", ssh_signing_key_file,
     ++		     buffer_file->filename.buf,
     ++		     NULL);
      +
      +	sigchain_push(SIGPIPE, SIG_IGN);
      +	ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
      +	sigchain_pop(SIGPIPE);
      +
     -+	if (ret && strstr(signer_stderr.buf, "usage:")) {
     -+		error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
     -+		goto out;
     -+	}
     -+
      +	if (ret) {
     ++		if (strstr(signer_stderr.buf, "usage:"))
     ++			error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
     ++
      +		error("%s", signer_stderr.buf);
      +		goto out;
      +	}
     @@ gpg-interface.c: static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf
      +
      +	strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
      +	strbuf_addstr(&ssh_signature_filename, ".sig");
     -+	if (strbuf_read_file(signature, ssh_signature_filename.buf, 2048) < 0) {
     ++	if (strbuf_read_file(signature, ssh_signature_filename.buf, 0) < 0) {
      +		error_errno(
      +			_("failed reading ssh signing data buffer from '%s'"),
      +			ssh_signature_filename.buf);
      +	}
      +	unlink_or_warn(ssh_signature_filename.buf);
      +
     -+	if (ret) {
     -+		error(_("ssh failed to sign the data"));
     -+		goto out;
     -+	}
     -+
      +	/* Strip CR from the line endings, in case we are on Windows. */
     -+	strbuf_trim_trailing_cr(signature, bottom);
     ++	remove_cr_after(signature, bottom);
      +
      +out:
     -+	if (temp)
     -+		delete_tempfile(&temp);
     ++	if (key_file)
     ++		delete_tempfile(&key_file);
      +	if (buffer_file)
      +		delete_tempfile(&buffer_file);
      +	strbuf_release(&signer_stderr);
  3:  1ec5c06cbe9 =  3:  071e6173d8e ssh signing: retrieve a default key from ssh-agent
  4:  ec6931082ee =  4:  7d1d131ff5b ssh signing: provide a textual representation of the signing key
  5:  4436cb3a122 !  5:  725764018ce ssh signing: parse ssh-keygen output and verify signatures
     @@ gpg-interface.c: static int verify_gpg_signed_buffer(struct signature_check *sig
      +	}
      +}
      +
     -+static const char *get_ssh_allowed_signers(void)
     -+{
     -+	if (ssh_allowed_signers)
     -+		return ssh_allowed_signers;
     -+
     -+	die("gpg.ssh.allowedSignersFile needs to be configured and exist for validation");
     -+}
     -+
      +static int verify_ssh_signed_buffer(struct signature_check *sigc,
      +				    struct gpg_format *fmt, const char *payload,
      +				    size_t payload_size, const char *signature,
      +				    size_t signature_size)
      +{
      +	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
     -+	struct tempfile *temp;
     -+	int ret;
     ++	struct tempfile *buffer_file;
     ++	int ret = -1;
      +	const char *line;
      +	size_t trust_size;
      +	char *principal;
      +	struct strbuf ssh_keygen_out = STRBUF_INIT;
      +	struct strbuf ssh_keygen_err = STRBUF_INIT;
      +
     -+	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
     -+	if (!temp)
     ++	if (!ssh_allowed_signers) {
     ++		error(_("gpg.ssh.allowedSignersFile needs to be configured and exist for ssh signature verification"));
     ++		return -1;
     ++	}
     ++
     ++	buffer_file = mks_tempfile_t(".git_vtag_tmpXXXXXX");
     ++	if (!buffer_file)
      +		return error_errno(_("could not create temporary file"));
     -+	if (write_in_full(temp->fd, signature, signature_size) < 0 ||
     -+	    close_tempfile_gently(temp) < 0) {
     ++	if (write_in_full(buffer_file->fd, signature, signature_size) < 0 ||
     ++	    close_tempfile_gently(buffer_file) < 0) {
      +		error_errno(_("failed writing detached signature to '%s'"),
     -+			    temp->filename.buf);
     -+		delete_tempfile(&temp);
     ++			    buffer_file->filename.buf);
     ++		delete_tempfile(&buffer_file);
      +		return -1;
      +	}
      +
      +	/* Find the principal from the signers */
     -+	strvec_pushl(&ssh_keygen.args, fmt->program, "-Y", "find-principals",
     -+		     "-f", get_ssh_allowed_signers(), "-s", temp->filename.buf,
     ++	strvec_pushl(&ssh_keygen.args, fmt->program,
     ++		     "-Y", "find-principals",
     ++		     "-f", ssh_allowed_signers,
     ++		     "-s", buffer_file->filename.buf,
      +		     NULL);
      +	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0,
      +			   &ssh_keygen_err, 0);
      +	if (ret && strstr(ssh_keygen_err.buf, "usage:")) {
      +		error(_("ssh-keygen -Y find-principals/verify is needed for ssh signature verification (available in openssh version 8.2p1+)"));
     -+		return ret;
     ++		goto out;
      +	}
      +	if (ret || !ssh_keygen_out.len) {
      +		/* We did not find a matching principal in the allowedSigners - Check
      +		 * without validation */
      +		child_process_init(&ssh_keygen);
     -+		strvec_pushl(&ssh_keygen.args, fmt->program, "-Y",
     -+			     "check-novalidate", "-n", "git", "-s",
     -+			     temp->filename.buf, NULL);
     ++		strvec_pushl(&ssh_keygen.args, fmt->program,
     ++			     "-Y", "check-novalidate",
     ++			     "-n", "git",
     ++			     "-s", buffer_file->filename.buf,
     ++			     NULL);
      +		ret = pipe_command(&ssh_keygen, payload, payload_size,
      +				   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
      +	} else {
     @@ gpg-interface.c: static int verify_gpg_signed_buffer(struct signature_check *sig
      +			strvec_push(&ssh_keygen.args, fmt->program);
      +			/* We found principals - Try with each until we find a
      +			 * match */
     -+			strvec_pushl(&ssh_keygen.args, "-Y", "verify", "-n",
     -+				     "git", "-f", get_ssh_allowed_signers(),
     -+				     "-I", principal, "-s", temp->filename.buf,
     ++			strvec_pushl(&ssh_keygen.args, "-Y", "verify",
     ++				     "-n", "git",
     ++				     "-f", ssh_allowed_signers,
     ++				     "-I", principal,
     ++				     "-s", buffer_file->filename.buf,
      +				     NULL);
      +
      +			if (ssh_revocation_file) {
     @@ gpg-interface.c: static int verify_gpg_signed_buffer(struct signature_check *sig
      +
      +	parse_ssh_output(sigc);
      +
     -+	delete_tempfile(&temp);
     ++out:
     ++	if (buffer_file)
     ++		delete_tempfile(&buffer_file);
      +	strbuf_release(&ssh_keygen_out);
      +	strbuf_release(&ssh_keygen_err);
      +
  6:  06a76e64b35 =  6:  eb677b1b6a8 ssh signing: add test prereqs
  7:  4dc5572083b !  7:  c877951df23 ssh signing: duplicate t7510 tests for commits
     @@ Commit message
      
          Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
      
     - ## t/t7527-signed-commit-ssh.sh (new) ##
     + ## t/t7528-signed-commit-ssh.sh (new) ##
      @@
      +#!/bin/sh
      +
  8:  275dd8a1013 =  8:  60265e8c399 ssh signing: add more tests for logs, tags & push certs
  9:  13f6c229bd1 =  9:  f758ce0ade4 ssh signing: add documentation

-- 
gitgitgadget

[PATCH v5 1/9] ssh signing: preliminary refactoring and clean-up

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Openssh v8.2p1 added some new options to ssh-keygen for signature
creation and verification. These allow us to use ssh keys for git
signatures easily.

In our corporate environment we use PIV x509 Certs on Yubikeys for email
signing/encryption and ssh keys which I think is quite common
(at least for the email part). This way we can establish the correct
trust for the SSH Keys without setting up a separate GPG Infrastructure
(which is still quite painful for users) or implementing x509 signing
support for git (which lacks good forwarding mechanisms).
Using ssh agent forwarding makes this feature easily usable in todays
development environments where code is often checked out in remote VMs / containers.
In such a setup the keyring & revocationKeyring can be centrally
generated from the x509 CA information and distributed to the users.

To be able to implement new signing formats this commit:
 - makes the sigc structure more generic by renaming "gpg_output" to
   "output"
 - introduces function pointers in the gpg_format structure to call
   format specific signing and verification functions
 - moves format detection from verify_signed_buffer into the check_signature
   api function and calls the format specific verify
 - renames and wraps sign_buffer to handle format specific signing logic
   as well

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 fmt-merge-msg.c |   6 +--
 gpg-interface.c | 104 +++++++++++++++++++++++++++++-------------------
 gpg-interface.h |   2 +-
 log-tree.c      |   8 ++--
 pretty.c        |   4 +-
 5 files changed, 74 insertions(+), 50 deletions(-)

diff --git a/fmt-merge-msg.c b/fmt-merge-msg.c
index 0f66818e0f8..fb300bb4b67 100644
--- a/fmt-merge-msg.c
+++ b/fmt-merge-msg.c
@@ -526,11 +526,11 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 			buf = payload.buf;
 			len = payload.len;
 			if (check_signature(payload.buf, payload.len, sig.buf,
-					 sig.len, &sigc) &&
-				!sigc.gpg_output)
+					    sig.len, &sigc) &&
+			    !sigc.output)
 				strbuf_addstr(&sig, "gpg verification failed.\n");
 			else
-				strbuf_addstr(&sig, sigc.gpg_output);
+				strbuf_addstr(&sig, sigc.output);
 		}
 		signature_check_clear(&sigc);
 
diff --git a/gpg-interface.c b/gpg-interface.c
index 127aecfc2b0..31cf4ba3938 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -15,6 +15,12 @@ struct gpg_format {
 	const char *program;
 	const char **verify_args;
 	const char **sigs;
+	int (*verify_signed_buffer)(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size);
+	int (*sign_buffer)(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key);
 };
 
 static const char *openpgp_verify_args[] = {
@@ -35,14 +41,29 @@ static const char *x509_sigs[] = {
 	NULL
 };
 
+static int verify_gpg_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size);
+static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key);
+
 static struct gpg_format gpg_format[] = {
-	{ .name = "openpgp", .program = "gpg",
-	  .verify_args = openpgp_verify_args,
-	  .sigs = openpgp_sigs
+	{
+		.name = "openpgp",
+		.program = "gpg",
+		.verify_args = openpgp_verify_args,
+		.sigs = openpgp_sigs,
+		.verify_signed_buffer = verify_gpg_signed_buffer,
+		.sign_buffer = sign_buffer_gpg,
 	},
-	{ .name = "x509", .program = "gpgsm",
-	  .verify_args = x509_verify_args,
-	  .sigs = x509_sigs
+	{
+		.name = "x509",
+		.program = "gpgsm",
+		.verify_args = x509_verify_args,
+		.sigs = x509_sigs,
+		.verify_signed_buffer = verify_gpg_signed_buffer,
+		.sign_buffer = sign_buffer_gpg,
 	},
 };
 
@@ -72,7 +93,7 @@ static struct gpg_format *get_format_by_sig(const char *sig)
 void signature_check_clear(struct signature_check *sigc)
 {
 	FREE_AND_NULL(sigc->payload);
-	FREE_AND_NULL(sigc->gpg_output);
+	FREE_AND_NULL(sigc->output);
 	FREE_AND_NULL(sigc->gpg_status);
 	FREE_AND_NULL(sigc->signer);
 	FREE_AND_NULL(sigc->key);
@@ -257,16 +278,16 @@ error:
 	FREE_AND_NULL(sigc->key);
 }
 
-static int verify_signed_buffer(const char *payload, size_t payload_size,
-				const char *signature, size_t signature_size,
-				struct strbuf *gpg_output,
-				struct strbuf *gpg_status)
+static int verify_gpg_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
-	struct gpg_format *fmt;
 	struct tempfile *temp;
 	int ret;
-	struct strbuf buf = STRBUF_INIT;
+	struct strbuf gpg_stdout = STRBUF_INIT;
+	struct strbuf gpg_stderr = STRBUF_INIT;
 
 	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
 	if (!temp)
@@ -279,10 +300,6 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 		return -1;
 	}
 
-	fmt = get_format_by_sig(signature);
-	if (!fmt)
-		BUG("bad signature '%s'", signature);
-
 	strvec_push(&gpg.args, fmt->program);
 	strvec_pushv(&gpg.args, fmt->verify_args);
 	strvec_pushl(&gpg.args,
@@ -290,18 +307,22 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 		     "--verify", temp->filename.buf, "-",
 		     NULL);
 
-	if (!gpg_status)
-		gpg_status = &buf;
-
 	sigchain_push(SIGPIPE, SIG_IGN);
-	ret = pipe_command(&gpg, payload, payload_size,
-			   gpg_status, 0, gpg_output, 0);
+	ret = pipe_command(&gpg, payload, payload_size, &gpg_stdout, 0,
+			   &gpg_stderr, 0);
 	sigchain_pop(SIGPIPE);
 
 	delete_tempfile(&temp);
 
-	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
-	strbuf_release(&buf); /* no matter it was used or not */
+	ret |= !strstr(gpg_stdout.buf, "\n[GNUPG:] GOODSIG ");
+	sigc->payload = xmemdupz(payload, payload_size);
+	sigc->output = strbuf_detach(&gpg_stderr, NULL);
+	sigc->gpg_status = strbuf_detach(&gpg_stdout, NULL);
+
+	parse_gpg_output(sigc);
+
+	strbuf_release(&gpg_stdout);
+	strbuf_release(&gpg_stderr);
 
 	return ret;
 }
@@ -309,35 +330,32 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 int check_signature(const char *payload, size_t plen, const char *signature,
 	size_t slen, struct signature_check *sigc)
 {
-	struct strbuf gpg_output = STRBUF_INIT;
-	struct strbuf gpg_status = STRBUF_INIT;
+	struct gpg_format *fmt;
 	int status;
 
 	sigc->result = 'N';
 	sigc->trust_level = -1;
 
-	status = verify_signed_buffer(payload, plen, signature, slen,
-				      &gpg_output, &gpg_status);
-	if (status && !gpg_output.len)
-		goto out;
-	sigc->payload = xmemdupz(payload, plen);
-	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
-	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
-	parse_gpg_output(sigc);
+	fmt = get_format_by_sig(signature);
+	if (!fmt)
+		return error(_("bad/incompatible signature '%s'"), signature);
+
+	status = fmt->verify_signed_buffer(sigc, fmt, payload, plen, signature,
+					   slen);
+
+	if (status && !sigc->output)
+		return !!status;
+
 	status |= sigc->result != 'G';
 	status |= sigc->trust_level < configured_min_trust_level;
 
- out:
-	strbuf_release(&gpg_status);
-	strbuf_release(&gpg_output);
-
 	return !!status;
 }
 
 void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
 {
-	const char *output = flags & GPG_VERIFY_RAW ?
-		sigc->gpg_status : sigc->gpg_output;
+	const char *output = flags & GPG_VERIFY_RAW ? sigc->gpg_status :
+							    sigc->output;
 
 	if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
 		fputs(sigc->payload, stdout);
@@ -441,6 +459,12 @@ const char *get_signing_key(void)
 }
 
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
+{
+	return use_format->sign_buffer(buffer, signature, signing_key);
+}
+
+static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
+		    const char *signing_key)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
 	int ret;
diff --git a/gpg-interface.h b/gpg-interface.h
index 80567e48948..feac4decf8b 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -17,7 +17,7 @@ enum signature_trust_level {
 
 struct signature_check {
 	char *payload;
-	char *gpg_output;
+	char *output;
 	char *gpg_status;
 
 	/*
diff --git a/log-tree.c b/log-tree.c
index 7b823786c2c..20af9bd1c82 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -513,10 +513,10 @@ static void show_signature(struct rev_info *opt, struct commit *commit)
 
 	status = check_signature(payload.buf, payload.len, signature.buf,
 				 signature.len, &sigc);
-	if (status && !sigc.gpg_output)
+	if (status && !sigc.output)
 		show_sig_lines(opt, status, "No signature\n");
 	else
-		show_sig_lines(opt, status, sigc.gpg_output);
+		show_sig_lines(opt, status, sigc.output);
 	signature_check_clear(&sigc);
 
  out:
@@ -583,8 +583,8 @@ static int show_one_mergetag(struct commit *commit,
 		/* could have a good signature */
 		status = check_signature(payload.buf, payload.len,
 					 signature.buf, signature.len, &sigc);
-		if (sigc.gpg_output)
-			strbuf_addstr(&verify_message, sigc.gpg_output);
+		if (sigc.output)
+			strbuf_addstr(&verify_message, sigc.output);
 		else
 			strbuf_addstr(&verify_message, "No signature\n");
 		signature_check_clear(&sigc);
diff --git a/pretty.c b/pretty.c
index b1ecd039cef..daa71394efd 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1432,8 +1432,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 			check_commit_signature(c->commit, &(c->signature_check));
 		switch (placeholder[1]) {
 		case 'G':
-			if (c->signature_check.gpg_output)
-				strbuf_addstr(sb, c->signature_check.gpg_output);
+			if (c->signature_check.output)
+				strbuf_addstr(sb, c->signature_check.output);
 			break;
 		case '?':
 			switch (c->signature_check.result) {
-- 
gitgitgadget

[PATCH v5 2/9] ssh signing: add ssh signature format and signing using ssh keys

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

implements the actual sign_buffer_ssh operation and move some shared
cleanup code into a strbuf function

Set gpg.format = ssh and user.signingkey to either a ssh public key
string (like from an authorized_keys file), or a ssh key file.
If the key file or the config value itself contains only a public key
then the private key needs to be available via ssh-agent.

gpg.ssh.program can be set to an alternative location of ssh-keygen.
A somewhat recent openssh version (8.2p1+) of ssh-keygen is needed for
this feature. Since only ssh-keygen is needed it can this way be
installed seperately without upgrading your system openssh packages.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 137 +++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 129 insertions(+), 8 deletions(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index 31cf4ba3938..c131977b347 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -41,12 +41,20 @@ static const char *x509_sigs[] = {
 	NULL
 };
 
+static const char *ssh_verify_args[] = { NULL };
+static const char *ssh_sigs[] = {
+	"-----BEGIN SSH SIGNATURE-----",
+	NULL
+};
+
 static int verify_gpg_signed_buffer(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
 				    size_t payload_size, const char *signature,
 				    size_t signature_size);
 static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 			   const char *signing_key);
+static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key);
 
 static struct gpg_format gpg_format[] = {
 	{
@@ -65,6 +73,14 @@ static struct gpg_format gpg_format[] = {
 		.verify_signed_buffer = verify_gpg_signed_buffer,
 		.sign_buffer = sign_buffer_gpg,
 	},
+	{
+		.name = "ssh",
+		.program = "ssh-keygen",
+		.verify_args = ssh_verify_args,
+		.sigs = ssh_sigs,
+		.verify_signed_buffer = NULL, /* TODO */
+		.sign_buffer = sign_buffer_ssh
+	},
 };
 
 static struct gpg_format *use_format = &gpg_format[0];
@@ -443,6 +459,9 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	if (!strcmp(var, "gpg.x509.program"))
 		fmtname = "x509";
 
+	if (!strcmp(var, "gpg.ssh.program"))
+		fmtname = "ssh";
+
 	if (fmtname) {
 		fmt = get_format_by_name(fmtname);
 		return git_config_string(&fmt->program, var, value);
@@ -463,12 +482,30 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
 	return use_format->sign_buffer(buffer, signature, signing_key);
 }
 
+/*
+ * Strip CR from the line endings, in case we are on Windows.
+ * NEEDSWORK: make it trim only CRs before LFs and rename
+ */
+static void remove_cr_after(struct strbuf *buffer, size_t offset)
+{
+	size_t i, j;
+
+	for (i = j = offset; i < buffer->len; i++) {
+		if (buffer->buf[i] != '\r') {
+			if (i != j)
+				buffer->buf[j] = buffer->buf[i];
+			j++;
+		}
+	}
+	strbuf_setlen(buffer, j);
+}
+
 static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 		    const char *signing_key)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
 	int ret;
-	size_t i, j, bottom;
+	size_t bottom;
 	struct strbuf gpg_status = STRBUF_INIT;
 
 	strvec_pushl(&gpg.args,
@@ -494,13 +531,97 @@ static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 		return error(_("gpg failed to sign the data"));
 
 	/* Strip CR from the line endings, in case we are on Windows. */
-	for (i = j = bottom; i < signature->len; i++)
-		if (signature->buf[i] != '\r') {
-			if (i != j)
-				signature->buf[j] = signature->buf[i];
-			j++;
-		}
-	strbuf_setlen(signature, j);
+	remove_cr_after(signature, bottom);
 
 	return 0;
 }
+
+static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key)
+{
+	struct child_process signer = CHILD_PROCESS_INIT;
+	int ret = -1;
+	size_t bottom, keylen;
+	struct strbuf signer_stderr = STRBUF_INIT;
+	struct tempfile *key_file = NULL, *buffer_file = NULL;
+	char *ssh_signing_key_file = NULL;
+	struct strbuf ssh_signature_filename = STRBUF_INIT;
+
+	if (!signing_key || signing_key[0] == '\0')
+		return error(
+			_("user.signingkey needs to be set for ssh signing"));
+
+	if (starts_with(signing_key, "ssh-")) {
+		/* A literal ssh key */
+		key_file = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
+		if (!key_file)
+			return error_errno(
+				_("could not create temporary file"));
+		keylen = strlen(signing_key);
+		if (write_in_full(key_file->fd, signing_key, keylen) < 0 ||
+		    close_tempfile_gently(key_file) < 0) {
+			error_errno(_("failed writing ssh signing key to '%s'"),
+				    key_file->filename.buf);
+			goto out;
+		}
+		ssh_signing_key_file = key_file->filename.buf;
+	} else {
+		/* We assume a file */
+		ssh_signing_key_file = expand_user_path(signing_key, 1);
+	}
+
+	buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
+	if (!buffer_file) {
+		error_errno(_("could not create temporary file"));
+		goto out;
+	}
+
+	if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
+	    close_tempfile_gently(buffer_file) < 0) {
+		error_errno(_("failed writing ssh signing key buffer to '%s'"),
+			    buffer_file->filename.buf);
+		goto out;
+	}
+
+	strvec_pushl(&signer.args, use_format->program,
+		     "-Y", "sign",
+		     "-n", "git",
+		     "-f", ssh_signing_key_file,
+		     buffer_file->filename.buf,
+		     NULL);
+
+	sigchain_push(SIGPIPE, SIG_IGN);
+	ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
+	sigchain_pop(SIGPIPE);
+
+	if (ret) {
+		if (strstr(signer_stderr.buf, "usage:"))
+			error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
+
+		error("%s", signer_stderr.buf);
+		goto out;
+	}
+
+	bottom = signature->len;
+
+	strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
+	strbuf_addstr(&ssh_signature_filename, ".sig");
+	if (strbuf_read_file(signature, ssh_signature_filename.buf, 0) < 0) {
+		error_errno(
+			_("failed reading ssh signing data buffer from '%s'"),
+			ssh_signature_filename.buf);
+	}
+	unlink_or_warn(ssh_signature_filename.buf);
+
+	/* Strip CR from the line endings, in case we are on Windows. */
+	remove_cr_after(signature, bottom);
+
+out:
+	if (key_file)
+		delete_tempfile(&key_file);
+	if (buffer_file)
+		delete_tempfile(&buffer_file);
+	strbuf_release(&signer_stderr);
+	strbuf_release(&ssh_signature_filename);
+	return ret;
+}
-- 
gitgitgadget

[PATCH v5 3/9] ssh signing: retrieve a default key from ssh-agent

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

if user.signingkey is not set and a ssh signature is requested we call
ssh-add -L and use the first key we get

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index c131977b347..3afacb48900 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -470,11 +470,35 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	return 0;
 }
 
+/* Returns the first public key from an ssh-agent to use for signing */
+static char *get_default_ssh_signing_key(void)
+{
+	struct child_process ssh_add = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf key_stdout = STRBUF_INIT;
+	struct strbuf **keys;
+
+	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
+	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
+	if (!ret) {
+		keys = strbuf_split_max(&key_stdout, '\n', 2);
+		if (keys[0])
+			return strbuf_detach(keys[0], NULL);
+	}
+
+	strbuf_release(&key_stdout);
+	return "";
+}
+
 const char *get_signing_key(void)
 {
 	if (configured_signing_key)
 		return configured_signing_key;
-	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
+	if (!strcmp(use_format->name, "ssh")) {
+		return get_default_ssh_signing_key();
+	} else {
+		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
+	}
 }
 
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
-- 
gitgitgadget

[PATCH v5 4/9] ssh signing: provide a textual representation of the signing key

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

for ssh the user.signingkey can be a filename/path or even a literal ssh pubkey.
in push certs and textual output we prefer the ssh fingerprint instead.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 gpg-interface.h |  6 ++++++
 send-pack.c     |  8 ++++----
 3 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index 3afacb48900..ec48a37b6cc 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -470,6 +470,41 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	return 0;
 }
 
+static char *get_ssh_key_fingerprint(const char *signing_key)
+{
+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf fingerprint_stdout = STRBUF_INIT;
+	struct strbuf **fingerprint;
+
+	/*
+	 * With SSH Signing this can contain a filename or a public key
+	 * For textual representation we usually want a fingerprint
+	 */
+	if (istarts_with(signing_key, "ssh-")) {
+		strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf", "-", NULL);
+		ret = pipe_command(&ssh_keygen, signing_key,
+				   strlen(signing_key), &fingerprint_stdout, 0,
+				   NULL, 0);
+	} else {
+		strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf",
+			     configured_signing_key, NULL);
+		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0,
+				   NULL, 0);
+	}
+
+	if (!!ret)
+		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
+			  signing_key);
+
+	fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
+	if (!fingerprint[1])
+		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
+			  signing_key);
+
+	return strbuf_detach(fingerprint[1], NULL);
+}
+
 /* Returns the first public key from an ssh-agent to use for signing */
 static char *get_default_ssh_signing_key(void)
 {
@@ -490,6 +525,17 @@ static char *get_default_ssh_signing_key(void)
 	return "";
 }
 
+/* Returns a textual but unique representation ot the signing key */
+const char *get_signing_key_id(void)
+{
+	if (!strcmp(use_format->name, "ssh")) {
+		return get_ssh_key_fingerprint(get_signing_key());
+	} else {
+		/* GPG/GPGSM only store a key id on this variable */
+		return get_signing_key();
+	}
+}
+
 const char *get_signing_key(void)
 {
 	if (configured_signing_key)
diff --git a/gpg-interface.h b/gpg-interface.h
index feac4decf8b..beefacbb1e9 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -64,6 +64,12 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
 int git_gpg_config(const char *, const char *, void *);
 void set_signing_key(const char *);
 const char *get_signing_key(void);
+
+/*
+ * Returns a textual unique representation of the signing key in use
+ * Either a GPG KeyID or a SSH Key Fingerprint
+ */
+const char *get_signing_key_id(void);
 int check_signature(const char *payload, size_t plen,
 		    const char *signature, size_t slen,
 		    struct signature_check *sigc);
diff --git a/send-pack.c b/send-pack.c
index 5a79e0e7110..50cca7e439b 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -341,13 +341,13 @@ static int generate_push_cert(struct strbuf *req_buf,
 {
 	const struct ref *ref;
 	struct string_list_item *item;
-	char *signing_key = xstrdup(get_signing_key());
+	char *signing_key_id = xstrdup(get_signing_key_id());
 	const char *cp, *np;
 	struct strbuf cert = STRBUF_INIT;
 	int update_seen = 0;
 
 	strbuf_addstr(&cert, "certificate version 0.1\n");
-	strbuf_addf(&cert, "pusher %s ", signing_key);
+	strbuf_addf(&cert, "pusher %s ", signing_key_id);
 	datestamp(&cert);
 	strbuf_addch(&cert, '\n');
 	if (args->url && *args->url) {
@@ -374,7 +374,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 	if (!update_seen)
 		goto free_return;
 
-	if (sign_buffer(&cert, &cert, signing_key))
+	if (sign_buffer(&cert, &cert, get_signing_key()))
 		die(_("failed to sign the push certificate"));
 
 	packet_buf_write(req_buf, "push-cert%c%s", 0, cap_string);
@@ -386,7 +386,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 	packet_buf_write(req_buf, "push-cert-end\n");
 
 free_return:
-	free(signing_key);
+	free(signing_key_id);
 	strbuf_release(&cert);
 	return update_seen;
 }
-- 
gitgitgadget

[PATCH v5 5/9] ssh signing: parse ssh-keygen output and verify signatures

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

to verify a ssh signature we first call ssh-keygen -Y find-principal to
look up the signing principal by their public key from the
allowedSignersFile. If the key is found then we do a verify. Otherwise
we only validate the signature but can not verify the signers identity.

Verification uses the gpg.ssh.allowedSignersFile (see ssh-keygen(1) "ALLOWED
SIGNERS") which contains valid public keys and a principal (usually
user@domain). Depending on the environment this file can be managed by
the individual developer or for example generated by the central
repository server from known ssh keys with push access. If the
repository only allows signed commits / pushes then the file can even be
stored inside it.

To revoke a key put the public key without the principal prefix into
gpg.ssh.revocationKeyring or generate a KRL (see ssh-keygen(1)
"KEY REVOCATION LISTS"). The same considerations about who to trust for
verification as with the allowedSignersFile apply.

Using SSH CA Keys with these files is also possible. Add
"cert-authority" as key option between the principal and the key to mark
it as a CA and all keys signed by it as valid for this CA.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 builtin/receive-pack.c |   2 +
 gpg-interface.c        | 179 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 180 insertions(+), 1 deletion(-)

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index a34742513ac..62b11c5f3a4 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -131,6 +131,8 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 {
 	int status = parse_hide_refs_config(var, value, "receive");
 
+	git_gpg_config(var, value, NULL);
+
 	if (status)
 		return status;
 
diff --git a/gpg-interface.c b/gpg-interface.c
index ec48a37b6cc..703225c3cd3 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -3,11 +3,13 @@
 #include "config.h"
 #include "run-command.h"
 #include "strbuf.h"
+#include "dir.h"
 #include "gpg-interface.h"
 #include "sigchain.h"
 #include "tempfile.h"
 
 static char *configured_signing_key;
+static const char *ssh_allowed_signers, *ssh_revocation_file;
 static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
 
 struct gpg_format {
@@ -51,6 +53,10 @@ static int verify_gpg_signed_buffer(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
 				    size_t payload_size, const char *signature,
 				    size_t signature_size);
+static int verify_ssh_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size);
 static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 			   const char *signing_key);
 static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
@@ -78,7 +84,7 @@ static struct gpg_format gpg_format[] = {
 		.program = "ssh-keygen",
 		.verify_args = ssh_verify_args,
 		.sigs = ssh_sigs,
-		.verify_signed_buffer = NULL, /* TODO */
+		.verify_signed_buffer = verify_ssh_signed_buffer,
 		.sign_buffer = sign_buffer_ssh
 	},
 };
@@ -343,6 +349,165 @@ static int verify_gpg_signed_buffer(struct signature_check *sigc,
 	return ret;
 }
 
+static void parse_ssh_output(struct signature_check *sigc)
+{
+	const char *line, *principal, *search;
+
+	/*
+	 * ssh-keysign output should be:
+	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
+	 * Good "git" signature for PRINCIPAL WITH WHITESPACE with RSA key SHA256:FINGERPRINT
+	 * or for valid but unknown keys:
+	 * Good "git" signature with RSA key SHA256:FINGERPRINT
+	 */
+	sigc->result = 'B';
+	sigc->trust_level = TRUST_NEVER;
+
+	line = xmemdupz(sigc->output, strcspn(sigc->output, "\n"));
+
+	if (skip_prefix(line, "Good \"git\" signature for ", &line)) {
+		/* Valid signature and known principal */
+		sigc->result = 'G';
+		sigc->trust_level = TRUST_FULLY;
+
+		/* Search for the last "with" to get the full principal */
+		principal = line;
+		do {
+			search = strstr(line, " with ");
+			if (search)
+				line = search + 1;
+		} while (search != NULL);
+		sigc->signer = xmemdupz(principal, line - principal - 1);
+		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);
+		sigc->key = xstrdup(sigc->fingerprint);
+	} else if (skip_prefix(line, "Good \"git\" signature with ", &line)) {
+		/* Valid signature, but key unknown */
+		sigc->result = 'G';
+		sigc->trust_level = TRUST_UNDEFINED;
+		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);
+		sigc->key = xstrdup(sigc->fingerprint);
+	}
+}
+
+static int verify_ssh_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size)
+{
+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
+	struct tempfile *buffer_file;
+	int ret = -1;
+	const char *line;
+	size_t trust_size;
+	char *principal;
+	struct strbuf ssh_keygen_out = STRBUF_INIT;
+	struct strbuf ssh_keygen_err = STRBUF_INIT;
+
+	if (!ssh_allowed_signers) {
+		error(_("gpg.ssh.allowedSignersFile needs to be configured and exist for ssh signature verification"));
+		return -1;
+	}
+
+	buffer_file = mks_tempfile_t(".git_vtag_tmpXXXXXX");
+	if (!buffer_file)
+		return error_errno(_("could not create temporary file"));
+	if (write_in_full(buffer_file->fd, signature, signature_size) < 0 ||
+	    close_tempfile_gently(buffer_file) < 0) {
+		error_errno(_("failed writing detached signature to '%s'"),
+			    buffer_file->filename.buf);
+		delete_tempfile(&buffer_file);
+		return -1;
+	}
+
+	/* Find the principal from the signers */
+	strvec_pushl(&ssh_keygen.args, fmt->program,
+		     "-Y", "find-principals",
+		     "-f", ssh_allowed_signers,
+		     "-s", buffer_file->filename.buf,
+		     NULL);
+	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0,
+			   &ssh_keygen_err, 0);
+	if (ret && strstr(ssh_keygen_err.buf, "usage:")) {
+		error(_("ssh-keygen -Y find-principals/verify is needed for ssh signature verification (available in openssh version 8.2p1+)"));
+		goto out;
+	}
+	if (ret || !ssh_keygen_out.len) {
+		/* We did not find a matching principal in the allowedSigners - Check
+		 * without validation */
+		child_process_init(&ssh_keygen);
+		strvec_pushl(&ssh_keygen.args, fmt->program,
+			     "-Y", "check-novalidate",
+			     "-n", "git",
+			     "-s", buffer_file->filename.buf,
+			     NULL);
+		ret = pipe_command(&ssh_keygen, payload, payload_size,
+				   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
+	} else {
+		/* Check every principal we found (one per line) */
+		for (line = ssh_keygen_out.buf; *line;
+		     line = strchrnul(line + 1, '\n')) {
+			while (*line == '\n')
+				line++;
+			if (!*line)
+				break;
+
+			trust_size = strcspn(line, "\n");
+			principal = xmemdupz(line, trust_size);
+
+			child_process_init(&ssh_keygen);
+			strbuf_release(&ssh_keygen_out);
+			strbuf_release(&ssh_keygen_err);
+			strvec_push(&ssh_keygen.args, fmt->program);
+			/* We found principals - Try with each until we find a
+			 * match */
+			strvec_pushl(&ssh_keygen.args, "-Y", "verify",
+				     "-n", "git",
+				     "-f", ssh_allowed_signers,
+				     "-I", principal,
+				     "-s", buffer_file->filename.buf,
+				     NULL);
+
+			if (ssh_revocation_file) {
+				if (file_exists(ssh_revocation_file)) {
+					strvec_pushl(&ssh_keygen.args, "-r",
+						     ssh_revocation_file, NULL);
+				} else {
+					warning(_("ssh signing revocation file configured but not found: %s"),
+						ssh_revocation_file);
+				}
+			}
+
+			sigchain_push(SIGPIPE, SIG_IGN);
+			ret = pipe_command(&ssh_keygen, payload, payload_size,
+					   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
+			sigchain_pop(SIGPIPE);
+
+			FREE_AND_NULL(principal);
+
+			ret &= starts_with(ssh_keygen_out.buf, "Good");
+			if (ret == 0)
+				break;
+		}
+	}
+
+	sigc->payload = xmemdupz(payload, payload_size);
+	strbuf_stripspace(&ssh_keygen_out, 0);
+	strbuf_stripspace(&ssh_keygen_err, 0);
+	strbuf_add(&ssh_keygen_out, ssh_keygen_err.buf, ssh_keygen_err.len);
+	sigc->output = strbuf_detach(&ssh_keygen_out, NULL);
+	sigc->gpg_status = xstrdup(sigc->output);
+
+	parse_ssh_output(sigc);
+
+out:
+	if (buffer_file)
+		delete_tempfile(&buffer_file);
+	strbuf_release(&ssh_keygen_out);
+	strbuf_release(&ssh_keygen_err);
+
+	return ret;
+}
+
 int check_signature(const char *payload, size_t plen, const char *signature,
 	size_t slen, struct signature_check *sigc)
 {
@@ -453,6 +618,18 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(var, "gpg.ssh.allowedsignersfile")) {
+		if (!value)
+			return config_error_nonbool(var);
+		return git_config_string(&ssh_allowed_signers, var, value);
+	}
+
+	if (!strcmp(var, "gpg.ssh.revocationFile")) {
+		if (!value)
+			return config_error_nonbool(var);
+		return git_config_string(&ssh_revocation_file, var, value);
+	}
+
 	if (!strcmp(var, "gpg.program") || !strcmp(var, "gpg.openpgp.program"))
 		fmtname = "openpgp";
 
-- 
gitgitgadget

[PATCH v5 6/9] ssh signing: add test prereqs

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

generate some ssh keys and a allowedSignersFile for testing

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/lib-gpg.sh | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/t/lib-gpg.sh b/t/lib-gpg.sh
index 9fc5241228e..b4fbcad4bf3 100644
--- a/t/lib-gpg.sh
+++ b/t/lib-gpg.sh
@@ -87,6 +87,33 @@ test_lazy_prereq RFC1991 '
 	echo | gpg --homedir "${GNUPGHOME}" -b --rfc1991 >/dev/null
 '
 
+test_lazy_prereq GPGSSH '
+	ssh_version=$(ssh-keygen -Y find-principals -n "git" 2>&1)
+	test $? != 127 || exit 1
+	echo $ssh_version | grep -q "find-principals:missing signature file"
+	test $? = 0 || exit 1;
+	mkdir -p "${GNUPGHOME}" &&
+	chmod 0700 "${GNUPGHOME}" &&
+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/ed25519_ssh_signing_key" >/dev/null &&
+	ssh-keygen -t rsa -b 2048 -N "" -f "${GNUPGHOME}/rsa_2048_ssh_signing_key" >/dev/null &&
+	ssh-keygen -t ed25519 -N "super_secret" -f "${GNUPGHOME}/protected_ssh_signing_key" >/dev/null &&
+	find "${GNUPGHOME}" -name *ssh_signing_key.pub -exec cat {} \; | awk "{print \"\\\"principal with number \" NR \"\\\" \" \$0}" > "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
+	cat "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/untrusted_ssh_signing_key" >/dev/null
+'
+
+SIGNING_KEY_PRIMARY="${GNUPGHOME}/ed25519_ssh_signing_key"
+SIGNING_KEY_SECONDARY="${GNUPGHOME}/rsa_2048_ssh_signing_key"
+SIGNING_KEY_UNTRUSTED="${GNUPGHOME}/untrusted_ssh_signing_key"
+SIGNING_KEY_WITH_PASSPHRASE="${GNUPGHOME}/protected_ssh_signing_key"
+SIGNING_KEY_PASSPHRASE="super_secret"
+SIGNING_ALLOWED_SIGNERS="${GNUPGHOME}/ssh.all_valid.allowedSignersFile"
+
+GOOD_SIGNATURE_TRUSTED='Good "git" signature for'
+GOOD_SIGNATURE_UNTRUSTED='Good "git" signature with'
+KEY_NOT_TRUSTED="No principal matched"
+BAD_SIGNATURE="Signature verification failed"
+
 sanitize_pgp() {
 	perl -ne '
 		/^-----END PGP/ and $in_pgp = 0;
-- 
gitgitgadget

[PATCH v5 7/9] ssh signing: duplicate t7510 tests for commits

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/t7528-signed-commit-ssh.sh | 398 +++++++++++++++++++++++++++++++++++
 1 file changed, 398 insertions(+)
 create mode 100755 t/t7528-signed-commit-ssh.sh

diff --git a/t/t7528-signed-commit-ssh.sh b/t/t7528-signed-commit-ssh.sh
new file mode 100755
index 00000000000..e2c48f69e6d
--- /dev/null
+++ b/t/t7528-signed-commit-ssh.sh
@@ -0,0 +1,398 @@
+#!/bin/sh
+
+test_description='ssh signed commit tests'
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+GNUPGHOME_NOT_USED=$GNUPGHOME
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPGSSH 'create signed commits' '
+	test_oid_cache <<-\EOF &&
+	header sha1:gpgsig
+	header sha256:gpgsig-sha256
+	EOF
+
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+
+	echo 1 >file && git add file &&
+	test_tick && git commit -S -m initial &&
+	git tag initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -S -m second &&
+	git tag second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout main &&
+	test_tick && git merge -S side &&
+	git tag merge &&
+
+	echo 4 >file && test_tick && git commit -a -m "fourth unsigned" &&
+	git tag fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag fourth-signed &&
+
+	git config commit.gpgsign true &&
+	echo 5 >file && test_tick && git commit -a -m "fifth signed" &&
+	git tag fifth-signed &&
+
+	git config commit.gpgsign false &&
+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
+	git tag sixth-unsigned &&
+
+	git config commit.gpgsign true &&
+	echo 7 >file && test_tick && git commit -a -m "seventh" --no-gpg-sign &&
+	git tag seventh-unsigned &&
+
+	test_tick && git rebase -f HEAD^^ && git tag sixth-signed HEAD^ &&
+	git tag seventh-signed &&
+
+	echo 8 >file && test_tick && git commit -a -m eighth -S"${SIGNING_KEY_UNTRUSTED}" &&
+	git tag eighth-signed-alt &&
+
+	# commit.gpgsign is still on but this must not be signed
+	echo 9 | git commit-tree HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag ninth-unsigned $(cat oid) &&
+	# explicit -S of course must sign.
+	echo 10 | git commit-tree -S HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag tenth-signed $(cat oid) &&
+
+	# --gpg-sign[=<key-id>] must sign.
+	echo 11 | git commit-tree --gpg-sign HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag eleventh-signed $(cat oid) &&
+	echo 12 | git commit-tree --gpg-sign="${SIGNING_KEY_UNTRUSTED}" HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag twelfth-signed-alt $(cat oid)
+'
+
+test_expect_success GPGSSH 'verify and show signatures' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config gpg.mintrustlevel UNDEFINED &&
+	(
+		for commit in initial second merge fourth-signed \
+			fifth-signed sixth-signed seventh-signed tenth-signed \
+			eleventh-signed
+		do
+			git verify-commit $commit &&
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in merge^2 fourth-unsigned sixth-unsigned \
+			seventh-unsigned ninth-unsigned
+		do
+			test_must_fail git verify-commit $commit &&
+			git show --pretty=short --show-signature $commit >actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in eighth-signed-alt twelfth-signed-alt
+		do
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			grep "${KEY_NOT_TRUSTED}" actual &&
+			echo $commit OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'verify-commit exits success on untrusted signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git verify-commit eighth-signed-alt 2>actual &&
+	grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual &&
+	grep "${KEY_NOT_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH 'verify-commit exits success with matching minTrustLevel' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config gpg.minTrustLevel fully &&
+	git verify-commit sixth-signed
+'
+
+test_expect_success GPGSSH 'verify-commit exits success with low minTrustLevel' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config gpg.minTrustLevel marginal &&
+	git verify-commit sixth-signed
+'
+
+test_expect_success GPGSSH 'verify-commit exits failure with high minTrustLevel' '
+	test_config gpg.minTrustLevel ultimate &&
+	test_must_fail git verify-commit eighth-signed-alt
+'
+
+test_expect_success GPGSSH 'verify signatures with --raw' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	(
+		for commit in initial second merge fourth-signed fifth-signed sixth-signed seventh-signed
+		do
+			git verify-commit --raw $commit 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in merge^2 fourth-unsigned sixth-unsigned seventh-unsigned
+		do
+			test_must_fail git verify-commit --raw $commit 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in eighth-signed-alt
+		do
+			git verify-commit --raw $commit 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'proper header is used for hash algorithm' '
+	git cat-file commit fourth-signed >output &&
+	grep "^$(test_oid header) -----BEGIN SSH SIGNATURE-----" output
+'
+
+test_expect_success GPGSSH 'show signed commit with signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git show -s initial >commit &&
+	git show -s --show-signature initial >show &&
+	git verify-commit -v initial >verify.1 2>verify.2 &&
+	git cat-file commit initial >cat &&
+	grep -v -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.commit &&
+	grep -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.gpg &&
+	grep -v "^ " cat | grep -v "^gpgsig.* " >cat.commit &&
+	test_cmp show.commit commit &&
+	test_cmp show.gpg verify.2 &&
+	test_cmp cat.commit verify.1
+'
+
+test_expect_success GPGSSH 'detect fudged signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git cat-file commit seventh-signed >raw &&
+	sed -e "s/^seventh/7th forged/" raw >forged1 &&
+	git hash-object -w -t commit forged1 >forged1.commit &&
+	test_must_fail git verify-commit $(cat forged1.commit) &&
+	git show --pretty=short --show-signature $(cat forged1.commit) >actual1 &&
+	grep "${BAD_SIGNATURE}" actual1 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
+'
+
+test_expect_success GPGSSH 'detect fudged signature with NUL' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git cat-file commit seventh-signed >raw &&
+	cat raw >forged2 &&
+	echo Qwik | tr "Q" "\000" >>forged2 &&
+	git hash-object -w -t commit forged2 >forged2.commit &&
+	test_must_fail git verify-commit $(cat forged2.commit) &&
+	git show --pretty=short --show-signature $(cat forged2.commit) >actual2 &&
+	grep "${BAD_SIGNATURE}" actual2 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual2
+'
+
+test_expect_success GPGSSH 'amending already signed commit' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git checkout fourth-signed^0 &&
+	git commit --amend -S --no-edit &&
+	git verify-commit HEAD &&
+	git show -s --show-signature HEAD >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual
+'
+
+test_expect_success GPGSSH 'show good signature with custom format' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	cat >expect.tmpl <<-\EOF &&
+	G
+	FINGERPRINT
+	principal with number 1
+	FINGERPRINT
+
+	EOF
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show bad signature with custom format' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect <<-\EOF &&
+	B
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat forged1.commit) >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with custom format' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect.tmpl <<-\EOF &&
+	U
+	FINGERPRINT
+
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with undefined trust level' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect.tmpl <<-\EOF &&
+	undefined
+	FINGERPRINT
+
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with ultimate trust level' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect.tmpl <<-\EOF &&
+	fully
+	FINGERPRINT
+	principal with number 1
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show lack of signature with custom format' '
+	cat >expect <<-\EOF &&
+	N
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" seventh-unsigned >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'log.showsignature behaves like --show-signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config log.showsignature true &&
+	git show initial >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH 'check config gpg.format values' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_config gpg.format ssh &&
+	git commit -S --amend -m "success" &&
+	test_config gpg.format OpEnPgP &&
+	test_must_fail git commit -S --amend -m "fail"
+'
+
+test_expect_failure GPGSSH 'detect fudged commit with double signature (TODO)' '
+	sed -e "/gpgsig/,/END PGP/d" forged1 >double-base &&
+	sed -n -e "/gpgsig/,/END PGP/p" forged1 | \
+		sed -e "s/^$(test_oid header)//;s/^ //" | gpg --dearmor >double-sig1.sig &&
+	gpg -o double-sig2.sig -u 29472784 --detach-sign double-base &&
+	cat double-sig1.sig double-sig2.sig | gpg --enarmor >double-combined.asc &&
+	sed -e "s/^\(-.*\)ARMORED FILE/\1SIGNATURE/;1s/^/$(test_oid header) /;2,\$s/^/ /" \
+		double-combined.asc > double-gpgsig &&
+	sed -e "/committer/r double-gpgsig" double-base >double-commit &&
+	git hash-object -w -t commit double-commit >double-commit.commit &&
+	test_must_fail git verify-commit $(cat double-commit.commit) &&
+	git show --pretty=short --show-signature $(cat double-commit.commit) >double-actual &&
+	grep "BAD signature from" double-actual &&
+	grep "Good signature from" double-actual
+'
+
+test_expect_failure GPGSSH 'show double signature with custom format (TODO)' '
+	cat >expect <<-\EOF &&
+	E
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat double-commit.commit) >actual &&
+	test_cmp expect actual
+'
+
+
+test_expect_failure GPGSSH 'verify-commit verifies multiply signed commits (TODO)' '
+	git init multiply-signed &&
+	cd multiply-signed &&
+	test_commit first &&
+	echo 1 >second &&
+	git add second &&
+	tree=$(git write-tree) &&
+	parent=$(git rev-parse HEAD^{commit}) &&
+	git commit --gpg-sign -m second &&
+	git cat-file commit HEAD &&
+	# Avoid trailing whitespace.
+	sed -e "s/^Q//" -e "s/^Z/ /" >commit <<-EOF &&
+	Qtree $tree
+	Qparent $parent
+	Qauthor A U Thor <author@example.com> 1112912653 -0700
+	Qcommitter C O Mitter <committer@example.com> 1112912653 -0700
+	Qgpgsig -----BEGIN PGP SIGNATURE-----
+	QZ
+	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBDRYcY29tbWl0dGVy
+	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMNd+8AoK1I8mhLHviPH+q2I5fIVgPsEtYC
+	Q AKCTqBh+VabJceXcGIZuF0Ry+udbBQ==
+	Q =tQ0N
+	Q -----END PGP SIGNATURE-----
+	Qgpgsig-sha256 -----BEGIN PGP SIGNATURE-----
+	QZ
+	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBIBYcY29tbWl0dGVy
+	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMN/NEAn0XO9RYSBj2dFyozi0JKSbssYMtO
+	Q AJwKCQ1BQOtuwz//IjU8TiS+6S4iUw==
+	Q =pIwP
+	Q -----END PGP SIGNATURE-----
+	Q
+	Qsecond
+	EOF
+	head=$(git hash-object -t commit -w commit) &&
+	git reset --hard $head &&
+	git verify-commit $head 2>actual &&
+	grep "Good signature from" actual &&
+	! grep "BAD signature from" actual
+'
+
+test_done
-- 
gitgitgadget

[PATCH v5 8/9] ssh signing: add more tests for logs, tags & push certs

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/t4202-log.sh                   |  23 +++++
 t/t5534-push-signed.sh           | 101 +++++++++++++++++++
 t/t7031-verify-tag-signed-ssh.sh | 161 +++++++++++++++++++++++++++++++
 3 files changed, 285 insertions(+)
 create mode 100755 t/t7031-verify-tag-signed-ssh.sh

diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index 39e746fbcbe..afd7f2516ee 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -1616,6 +1616,16 @@ test_expect_success GPGSM 'setup signed branch x509' '
 	git commit -S -m signed_commit
 '
 
+test_expect_success GPGSSH 'setup sshkey signed branch' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_when_finished "git reset --hard && git checkout main" &&
+	git checkout -b signed-ssh main &&
+	echo foo >foo &&
+	git add foo &&
+	git commit -S -m signed_commit
+'
+
 test_expect_success GPGSM 'log x509 fingerprint' '
 	echo "F8BF62E0693D0694816377099909C779FA23FD65 | " >expect &&
 	git log -n1 --format="%GF | %GP" signed-x509 >actual &&
@@ -1628,6 +1638,13 @@ test_expect_success GPGSM 'log OpenPGP fingerprint' '
 	test_cmp expect actual
 '
 
+test_expect_success GPGSSH 'log ssh key fingerprint' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	ssh-keygen -lf  "${SIGNING_KEY_PRIMARY}" | awk "{print \$2\" | \"}" >expect &&
+	git log -n1 --format="%GF | %GP" signed-ssh >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success GPG 'log --graph --show-signature' '
 	git log --graph --show-signature -n1 signed >actual &&
 	grep "^| gpg: Signature made" actual &&
@@ -1640,6 +1657,12 @@ test_expect_success GPGSM 'log --graph --show-signature x509' '
 	grep "^| gpgsm: Good signature" actual
 '
 
+test_expect_success GPGSSH 'log --graph --show-signature ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git log --graph --show-signature -n1 signed-ssh >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual
+'
+
 test_expect_success GPG 'log --graph --show-signature for merged tag' '
 	test_when_finished "git reset --hard && git checkout main" &&
 	git checkout -b plain main &&
diff --git a/t/t5534-push-signed.sh b/t/t5534-push-signed.sh
index bba768f5ded..d590249b995 100755
--- a/t/t5534-push-signed.sh
+++ b/t/t5534-push-signed.sh
@@ -137,6 +137,53 @@ test_expect_success GPG 'signed push sends push certificate' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPGSSH 'ssh signed push sends push certificate' '
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=principal with number 1
+		KEY=FINGERPRINT
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
+
+	noop=$(git rev-parse noop) &&
+	ff=$(git rev-parse ff) &&
+	noff=$(git rev-parse noff) &&
+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_expect_success GPG 'inconsistent push options in signed push not allowed' '
 	# First, invoke receive-pack with dummy input to obtain its preamble.
 	prepare_dst &&
@@ -276,6 +323,60 @@ test_expect_success GPGSM 'fail without key and heed user.signingkey x509' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPGSSH 'fail without key and heed user.signingkey ssh' '
+	test_config gpg.format ssh &&
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	test_config user.email hasnokey@nowhere.com &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "" &&
+	(
+		sane_unset GIT_COMMITTER_EMAIL &&
+		test_must_fail git push --signed dst noop ff +noff
+	) &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=principal with number 1
+		KEY=FINGERPRINT
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
+
+	noop=$(git rev-parse noop) &&
+	ff=$(git rev-parse ff) &&
+	noff=$(git rev-parse noff) &&
+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_expect_success GPG 'failed atomic push does not execute GPG' '
 	prepare_dst &&
 	git -C dst config receive.certnonceseed sekrit &&
diff --git a/t/t7031-verify-tag-signed-ssh.sh b/t/t7031-verify-tag-signed-ssh.sh
new file mode 100755
index 00000000000..05bf520a332
--- /dev/null
+++ b/t/t7031-verify-tag-signed-ssh.sh
@@ -0,0 +1,161 @@
+#!/bin/sh
+
+test_description='signed tag tests'
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPGSSH 'create signed tags ssh' '
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+
+	echo 1 >file && git add file &&
+	test_tick && git commit -m initial &&
+	git tag -s -m initial initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -m second &&
+	git tag -s -m second second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout main &&
+	test_tick && git merge -S side &&
+	git tag -s -m merge merge &&
+
+	echo 4 >file && test_tick && git commit -a -S -m "fourth unsigned" &&
+	git tag -a -m fourth-unsigned fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag -s -m fourth fourth-signed &&
+
+	echo 5 >file && test_tick && git commit -a -m "fifth" &&
+	git tag fifth-unsigned &&
+
+	git config commit.gpgsign true &&
+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
+	git tag -a -m sixth sixth-unsigned &&
+
+	test_tick && git rebase -f HEAD^^ && git tag -s -m 6th sixth-signed HEAD^ &&
+	git tag -m seventh -s seventh-signed &&
+
+	echo 8 >file && test_tick && git commit -a -m eighth &&
+	git tag -u"${SIGNING_KEY_UNTRUSTED}" -m eighth eighth-signed-alt
+'
+
+test_expect_success GPGSSH 'verify and show ssh signatures' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	(
+		for tag in initial second merge fourth-signed sixth-signed seventh-signed
+		do
+			git verify-tag $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
+		do
+			test_must_fail git verify-tag $tag 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in eighth-signed-alt
+		do
+			git verify-tag $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			grep "${KEY_NOT_TRUSTED}" actual &&
+			echo $tag OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'detect fudged ssh signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git cat-file tag seventh-signed >raw &&
+	sed -e "/^tag / s/seventh/7th forged/" raw >forged1 &&
+	git hash-object -w -t tag forged1 >forged1.tag &&
+	test_must_fail git verify-tag $(cat forged1.tag) 2>actual1 &&
+	grep "${BAD_SIGNATURE}" actual1 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
+'
+
+test_expect_success GPGSSH 'verify ssh signatures with --raw' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	(
+		for tag in initial second merge fourth-signed sixth-signed seventh-signed
+		do
+			git verify-tag --raw $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
+		do
+			test_must_fail git verify-tag --raw $tag 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in eighth-signed-alt
+		do
+			git verify-tag --raw $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'verify signatures with --raw ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git verify-tag --raw sixth-signed 2>actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual &&
+	echo sixth-signed OK
+'
+
+test_expect_success GPGSSH 'verify multiple tags ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	tags="seventh-signed sixth-signed" &&
+	for i in $tags
+	do
+		git verify-tag -v --raw $i || return 1
+	done >expect.stdout 2>expect.stderr.1 &&
+	grep "^${GOOD_SIGNATURE_TRUSTED}" <expect.stderr.1 >expect.stderr &&
+	git verify-tag -v --raw $tags >actual.stdout 2>actual.stderr.1 &&
+	grep "^${GOOD_SIGNATURE_TRUSTED}" <actual.stderr.1 >actual.stderr &&
+	test_cmp expect.stdout actual.stdout &&
+	test_cmp expect.stderr actual.stderr
+'
+
+test_expect_success GPGSSH 'verifying tag with --format - ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect <<-\EOF &&
+	tagname : fourth-signed
+	EOF
+	git verify-tag --format="tagname : %(tag)" "fourth-signed" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'verifying a forged tag with --format should fail silently - ssh' '
+	test_must_fail git verify-tag --format="tagname : %(tag)" $(cat forged1.tag) >actual-forged &&
+	test_must_be_empty actual-forged
+'
+
+test_done
-- 
gitgitgadget

[PATCH v5 9/9] ssh signing: add documentation

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 Documentation/config/gpg.txt  | 39 +++++++++++++++++++++++++++++++++--
 Documentation/config/user.txt |  6 ++++++
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
index d94025cb368..dc790512e86 100644
--- a/Documentation/config/gpg.txt
+++ b/Documentation/config/gpg.txt
@@ -11,13 +11,13 @@ gpg.program::
 
 gpg.format::
 	Specifies which key format to use when signing with `--gpg-sign`.
-	Default is "openpgp" and another possible value is "x509".
+	Default is "openpgp". Other possible values are "x509", "ssh".
 
 gpg.<format>.program::
 	Use this to customize the program used for the signing format you
 	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
 	be used as a legacy synonym for `gpg.openpgp.program`. The default
-	value for `gpg.x509.program` is "gpgsm".
+	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
 
 gpg.minTrustLevel::
 	Specifies a minimum trust level for signature verification.  If
@@ -33,3 +33,38 @@ gpg.minTrustLevel::
 * `marginal`
 * `fully`
 * `ultimate`
+
+gpg.ssh.allowedSignersFile::
+	A file containing ssh public keys which you are willing to trust.
+	The file consists of one or more lines of principals followed by an ssh
+	public key.
+	e.g.: user1@example.com,user2@example.com ssh-rsa AAAAX1...
+	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
+	The principal is only used to identify the key and is available when
+	verifying a signature.
++
+SSH has no concept of trust levels like gpg does. To be able to differentiate
+between valid signatures and trusted signatures the trust level of a signature
+verification is set to `fully` when the public key is present in the allowedSignersFile.
+Therefore to only mark fully trusted keys as verified set gpg.minTrustLevel to `fully`.
+Otherwise valid but untrusted signatures will still verify but show no principal
+name of the signer.
++
+This file can be set to a location outside of the repository and every developer
+maintains their own trust store. A central repository server could generate this
+file automatically from ssh keys with push access to verify the code against.
+In a corporate setting this file is probably generated at a global location
+from automation that already handles developer ssh keys.
++
+A repository that only allows signed commits can store the file
+in the repository itself using a path relative to the top-level of the working tree.
+This way only committers with an already valid key can add or change keys in the keyring.
++
+Using a SSH CA key with the cert-authority option
+(see ssh-keygen(1) "CERTIFICATES") is also valid.
+
+gpg.ssh.revocationFile::
+	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
+	See ssh-keygen(1) for details.
+	If a public key is found in this file then it will always be treated
+	as having trust level "never" and signatures will show as invalid.
diff --git a/Documentation/config/user.txt b/Documentation/config/user.txt
index 59aec7c3aed..b3c2f2c541e 100644
--- a/Documentation/config/user.txt
+++ b/Documentation/config/user.txt
@@ -36,3 +36,9 @@ user.signingKey::
 	commit, you can override the default selection with this variable.
 	This option is passed unchanged to gpg's --local-user parameter,
 	so you may specify a key using any method that gpg supports.
+	If gpg.format is set to "ssh" this can contain the literal ssh public
+	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and
+	corresponds to the private key used for signing. The private key
+	needs to be available via ssh-agent. Alternatively it can be set to
+	a file containing a private key directly. If not set git will call
+	"ssh-add -L" and try to use the first key available.
-- 
gitgitgadget

[PATCH v6 0/9] ssh signing: Add commit & tag signing/verification via SSH keys using ssh-keygen

[Fabian Stelzer via GitGitGadget]

I have added support for using keyfiles directly, lots of tests and
generally cleaned up the signing & verification code a lot.

I can still rename things from being gpg specific to a more general
"signing" but thats rather cosmetic. Also i'm not sure if i named the new
test files correctly.

openssh 8.7 will add valid-after, valid-before options to the allowed keys
keyring. This allows us to pass the commit timestamp to the verification
call and make key rollover possible and still be able to verify older
commits. Set valid-after=NOW when adding your key to the keyring and set
valid-before to make it fail if used after a certain date. Software like
gitolite/github or corporate automation can do this automatically when ssh
push keys are addded / removed I will add this feature in a follow up patch
afterwards.

v3 addresses some issues & refactoring and splits the large commit into
several smaller ones.

v4:

 * restructures and cleans up the whole patch set - patches build on its own
   now and commit messages try to explain whats going on
 * got rid of the if branches and used callback functions in the format
   struct
 * fixed a bug with whitespace in principal identifiers that required a
   rewrite of the parse_ssh_output function
 * rewrote documentation to be more clear - also renamed keyring back to
   allowedSignersFile

v5:

 * moved t7527 to t7528 to not collide with another patch in "seen"
 * clean up return logic for failed signing & verification
 * some minor renames / reformatting to make things clearer

v6: fixed tests when using shm output dir

Fabian Stelzer (9):
  ssh signing: preliminary refactoring and clean-up
  ssh signing: add ssh signature format and signing using ssh keys
  ssh signing: retrieve a default key from ssh-agent
  ssh signing: provide a textual representation of the signing key
  ssh signing: parse ssh-keygen output and verify signatures
  ssh signing: add test prereqs
  ssh signing: duplicate t7510 tests for commits
  ssh signing: add more tests for logs, tags & push certs
  ssh signing: add documentation

 Documentation/config/gpg.txt     |  39 ++-
 Documentation/config/user.txt    |   6 +
 builtin/receive-pack.c           |   2 +
 fmt-merge-msg.c                  |   6 +-
 gpg-interface.c                  | 490 +++++++++++++++++++++++++++----
 gpg-interface.h                  |   8 +-
 log-tree.c                       |   8 +-
 pretty.c                         |   4 +-
 send-pack.c                      |   8 +-
 t/lib-gpg.sh                     |  29 ++
 t/t4202-log.sh                   |  23 ++
 t/t5534-push-signed.sh           | 101 +++++++
 t/t7031-verify-tag-signed-ssh.sh | 161 ++++++++++
 t/t7528-signed-commit-ssh.sh     | 398 +++++++++++++++++++++++++
 14 files changed, 1218 insertions(+), 65 deletions(-)
 create mode 100755 t/t7031-verify-tag-signed-ssh.sh
 create mode 100755 t/t7528-signed-commit-ssh.sh


base-commit: eb27b338a3e71c7c4079fbac8aeae3f8fbb5c687
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1041%2FFStelzer%2Fsshsign-v6
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1041/FStelzer/sshsign-v6
Pull-Request: https://github.com/git/git/pull/1041

Range-diff vs v5:

  1:  7c8502c65b8 =  1:  7c8502c65b8 ssh signing: preliminary refactoring and clean-up
  2:  f05bab16096 =  2:  f05bab16096 ssh signing: add ssh signature format and signing using ssh keys
  3:  071e6173d8e =  3:  071e6173d8e ssh signing: retrieve a default key from ssh-agent
  4:  7d1d131ff5b =  4:  7d1d131ff5b ssh signing: provide a textual representation of the signing key
  5:  725764018ce =  5:  725764018ce ssh signing: parse ssh-keygen output and verify signatures
  6:  eb677b1b6a8 !  6:  18a26ca49e7 ssh signing: add test prereqs
     @@ t/lib-gpg.sh: test_lazy_prereq RFC1991 '
      +	test $? = 0 || exit 1;
      +	mkdir -p "${GNUPGHOME}" &&
      +	chmod 0700 "${GNUPGHOME}" &&
     -+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/ed25519_ssh_signing_key" >/dev/null &&
     -+	ssh-keygen -t rsa -b 2048 -N "" -f "${GNUPGHOME}/rsa_2048_ssh_signing_key" >/dev/null &&
     -+	ssh-keygen -t ed25519 -N "super_secret" -f "${GNUPGHOME}/protected_ssh_signing_key" >/dev/null &&
     -+	find "${GNUPGHOME}" -name *ssh_signing_key.pub -exec cat {} \; | awk "{print \"\\\"principal with number \" NR \"\\\" \" \$0}" > "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
     ++	ssh-keygen -t ed25519 -N "" -C "git ed25519 key" -f "${GNUPGHOME}/ed25519_ssh_signing_key" >/dev/null &&
     ++	echo "\"principal with number 1\" $(cat "${GNUPGHOME}/ed25519_ssh_signing_key.pub")" >> "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
     ++	ssh-keygen -t rsa -b 2048 -N "" -C "git rsa2048 key" -f "${GNUPGHOME}/rsa_2048_ssh_signing_key" >/dev/null &&
     ++	echo "\"principal with number 2\" $(cat "${GNUPGHOME}/rsa_2048_ssh_signing_key.pub")" >> "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
     ++	ssh-keygen -t ed25519 -N "super_secret" -C "git ed25519 encrypted key" -f "${GNUPGHOME}/protected_ssh_signing_key" >/dev/null &&
     ++	echo "\"principal with number 3\" $(cat "${GNUPGHOME}/protected_ssh_signing_key.pub")" >> "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
      +	cat "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
      +	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/untrusted_ssh_signing_key" >/dev/null
      +'
  7:  c877951df23 =  7:  01da9a07934 ssh signing: duplicate t7510 tests for commits
  8:  60265e8c399 =  8:  d9707443f5c ssh signing: add more tests for logs, tags & push certs
  9:  f758ce0ade4 =  9:  275af516eba ssh signing: add documentation

-- 
gitgitgadget

[PATCH v6 1/9] ssh signing: preliminary refactoring and clean-up

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Openssh v8.2p1 added some new options to ssh-keygen for signature
creation and verification. These allow us to use ssh keys for git
signatures easily.

In our corporate environment we use PIV x509 Certs on Yubikeys for email
signing/encryption and ssh keys which I think is quite common
(at least for the email part). This way we can establish the correct
trust for the SSH Keys without setting up a separate GPG Infrastructure
(which is still quite painful for users) or implementing x509 signing
support for git (which lacks good forwarding mechanisms).
Using ssh agent forwarding makes this feature easily usable in todays
development environments where code is often checked out in remote VMs / containers.
In such a setup the keyring & revocationKeyring can be centrally
generated from the x509 CA information and distributed to the users.

To be able to implement new signing formats this commit:
 - makes the sigc structure more generic by renaming "gpg_output" to
   "output"
 - introduces function pointers in the gpg_format structure to call
   format specific signing and verification functions
 - moves format detection from verify_signed_buffer into the check_signature
   api function and calls the format specific verify
 - renames and wraps sign_buffer to handle format specific signing logic
   as well

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 fmt-merge-msg.c |   6 +--
 gpg-interface.c | 104 +++++++++++++++++++++++++++++-------------------
 gpg-interface.h |   2 +-
 log-tree.c      |   8 ++--
 pretty.c        |   4 +-
 5 files changed, 74 insertions(+), 50 deletions(-)

diff --git a/fmt-merge-msg.c b/fmt-merge-msg.c
index 0f66818e0f8..fb300bb4b67 100644
--- a/fmt-merge-msg.c
+++ b/fmt-merge-msg.c
@@ -526,11 +526,11 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 			buf = payload.buf;
 			len = payload.len;
 			if (check_signature(payload.buf, payload.len, sig.buf,
-					 sig.len, &sigc) &&
-				!sigc.gpg_output)
+					    sig.len, &sigc) &&
+			    !sigc.output)
 				strbuf_addstr(&sig, "gpg verification failed.\n");
 			else
-				strbuf_addstr(&sig, sigc.gpg_output);
+				strbuf_addstr(&sig, sigc.output);
 		}
 		signature_check_clear(&sigc);
 
diff --git a/gpg-interface.c b/gpg-interface.c
index 127aecfc2b0..31cf4ba3938 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -15,6 +15,12 @@ struct gpg_format {
 	const char *program;
 	const char **verify_args;
 	const char **sigs;
+	int (*verify_signed_buffer)(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size);
+	int (*sign_buffer)(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key);
 };
 
 static const char *openpgp_verify_args[] = {
@@ -35,14 +41,29 @@ static const char *x509_sigs[] = {
 	NULL
 };
 
+static int verify_gpg_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size);
+static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key);
+
 static struct gpg_format gpg_format[] = {
-	{ .name = "openpgp", .program = "gpg",
-	  .verify_args = openpgp_verify_args,
-	  .sigs = openpgp_sigs
+	{
+		.name = "openpgp",
+		.program = "gpg",
+		.verify_args = openpgp_verify_args,
+		.sigs = openpgp_sigs,
+		.verify_signed_buffer = verify_gpg_signed_buffer,
+		.sign_buffer = sign_buffer_gpg,
 	},
-	{ .name = "x509", .program = "gpgsm",
-	  .verify_args = x509_verify_args,
-	  .sigs = x509_sigs
+	{
+		.name = "x509",
+		.program = "gpgsm",
+		.verify_args = x509_verify_args,
+		.sigs = x509_sigs,
+		.verify_signed_buffer = verify_gpg_signed_buffer,
+		.sign_buffer = sign_buffer_gpg,
 	},
 };
 
@@ -72,7 +93,7 @@ static struct gpg_format *get_format_by_sig(const char *sig)
 void signature_check_clear(struct signature_check *sigc)
 {
 	FREE_AND_NULL(sigc->payload);
-	FREE_AND_NULL(sigc->gpg_output);
+	FREE_AND_NULL(sigc->output);
 	FREE_AND_NULL(sigc->gpg_status);
 	FREE_AND_NULL(sigc->signer);
 	FREE_AND_NULL(sigc->key);
@@ -257,16 +278,16 @@ error:
 	FREE_AND_NULL(sigc->key);
 }
 
-static int verify_signed_buffer(const char *payload, size_t payload_size,
-				const char *signature, size_t signature_size,
-				struct strbuf *gpg_output,
-				struct strbuf *gpg_status)
+static int verify_gpg_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
-	struct gpg_format *fmt;
 	struct tempfile *temp;
 	int ret;
-	struct strbuf buf = STRBUF_INIT;
+	struct strbuf gpg_stdout = STRBUF_INIT;
+	struct strbuf gpg_stderr = STRBUF_INIT;
 
 	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
 	if (!temp)
@@ -279,10 +300,6 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 		return -1;
 	}
 
-	fmt = get_format_by_sig(signature);
-	if (!fmt)
-		BUG("bad signature '%s'", signature);
-
 	strvec_push(&gpg.args, fmt->program);
 	strvec_pushv(&gpg.args, fmt->verify_args);
 	strvec_pushl(&gpg.args,
@@ -290,18 +307,22 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 		     "--verify", temp->filename.buf, "-",
 		     NULL);
 
-	if (!gpg_status)
-		gpg_status = &buf;
-
 	sigchain_push(SIGPIPE, SIG_IGN);
-	ret = pipe_command(&gpg, payload, payload_size,
-			   gpg_status, 0, gpg_output, 0);
+	ret = pipe_command(&gpg, payload, payload_size, &gpg_stdout, 0,
+			   &gpg_stderr, 0);
 	sigchain_pop(SIGPIPE);
 
 	delete_tempfile(&temp);
 
-	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
-	strbuf_release(&buf); /* no matter it was used or not */
+	ret |= !strstr(gpg_stdout.buf, "\n[GNUPG:] GOODSIG ");
+	sigc->payload = xmemdupz(payload, payload_size);
+	sigc->output = strbuf_detach(&gpg_stderr, NULL);
+	sigc->gpg_status = strbuf_detach(&gpg_stdout, NULL);
+
+	parse_gpg_output(sigc);
+
+	strbuf_release(&gpg_stdout);
+	strbuf_release(&gpg_stderr);
 
 	return ret;
 }
@@ -309,35 +330,32 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
 int check_signature(const char *payload, size_t plen, const char *signature,
 	size_t slen, struct signature_check *sigc)
 {
-	struct strbuf gpg_output = STRBUF_INIT;
-	struct strbuf gpg_status = STRBUF_INIT;
+	struct gpg_format *fmt;
 	int status;
 
 	sigc->result = 'N';
 	sigc->trust_level = -1;
 
-	status = verify_signed_buffer(payload, plen, signature, slen,
-				      &gpg_output, &gpg_status);
-	if (status && !gpg_output.len)
-		goto out;
-	sigc->payload = xmemdupz(payload, plen);
-	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
-	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
-	parse_gpg_output(sigc);
+	fmt = get_format_by_sig(signature);
+	if (!fmt)
+		return error(_("bad/incompatible signature '%s'"), signature);
+
+	status = fmt->verify_signed_buffer(sigc, fmt, payload, plen, signature,
+					   slen);
+
+	if (status && !sigc->output)
+		return !!status;
+
 	status |= sigc->result != 'G';
 	status |= sigc->trust_level < configured_min_trust_level;
 
- out:
-	strbuf_release(&gpg_status);
-	strbuf_release(&gpg_output);
-
 	return !!status;
 }
 
 void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
 {
-	const char *output = flags & GPG_VERIFY_RAW ?
-		sigc->gpg_status : sigc->gpg_output;
+	const char *output = flags & GPG_VERIFY_RAW ? sigc->gpg_status :
+							    sigc->output;
 
 	if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
 		fputs(sigc->payload, stdout);
@@ -441,6 +459,12 @@ const char *get_signing_key(void)
 }
 
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
+{
+	return use_format->sign_buffer(buffer, signature, signing_key);
+}
+
+static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
+		    const char *signing_key)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
 	int ret;
diff --git a/gpg-interface.h b/gpg-interface.h
index 80567e48948..feac4decf8b 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -17,7 +17,7 @@ enum signature_trust_level {
 
 struct signature_check {
 	char *payload;
-	char *gpg_output;
+	char *output;
 	char *gpg_status;
 
 	/*
diff --git a/log-tree.c b/log-tree.c
index 7b823786c2c..20af9bd1c82 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -513,10 +513,10 @@ static void show_signature(struct rev_info *opt, struct commit *commit)
 
 	status = check_signature(payload.buf, payload.len, signature.buf,
 				 signature.len, &sigc);
-	if (status && !sigc.gpg_output)
+	if (status && !sigc.output)
 		show_sig_lines(opt, status, "No signature\n");
 	else
-		show_sig_lines(opt, status, sigc.gpg_output);
+		show_sig_lines(opt, status, sigc.output);
 	signature_check_clear(&sigc);
 
  out:
@@ -583,8 +583,8 @@ static int show_one_mergetag(struct commit *commit,
 		/* could have a good signature */
 		status = check_signature(payload.buf, payload.len,
 					 signature.buf, signature.len, &sigc);
-		if (sigc.gpg_output)
-			strbuf_addstr(&verify_message, sigc.gpg_output);
+		if (sigc.output)
+			strbuf_addstr(&verify_message, sigc.output);
 		else
 			strbuf_addstr(&verify_message, "No signature\n");
 		signature_check_clear(&sigc);
diff --git a/pretty.c b/pretty.c
index b1ecd039cef..daa71394efd 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1432,8 +1432,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 			check_commit_signature(c->commit, &(c->signature_check));
 		switch (placeholder[1]) {
 		case 'G':
-			if (c->signature_check.gpg_output)
-				strbuf_addstr(sb, c->signature_check.gpg_output);
+			if (c->signature_check.output)
+				strbuf_addstr(sb, c->signature_check.output);
 			break;
 		case '?':
 			switch (c->signature_check.result) {
-- 
gitgitgadget

[PATCH v6 2/9] ssh signing: add ssh signature format and signing using ssh keys

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

implements the actual sign_buffer_ssh operation and move some shared
cleanup code into a strbuf function

Set gpg.format = ssh and user.signingkey to either a ssh public key
string (like from an authorized_keys file), or a ssh key file.
If the key file or the config value itself contains only a public key
then the private key needs to be available via ssh-agent.

gpg.ssh.program can be set to an alternative location of ssh-keygen.
A somewhat recent openssh version (8.2p1+) of ssh-keygen is needed for
this feature. Since only ssh-keygen is needed it can this way be
installed seperately without upgrading your system openssh packages.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 137 +++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 129 insertions(+), 8 deletions(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index 31cf4ba3938..c131977b347 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -41,12 +41,20 @@ static const char *x509_sigs[] = {
 	NULL
 };
 
+static const char *ssh_verify_args[] = { NULL };
+static const char *ssh_sigs[] = {
+	"-----BEGIN SSH SIGNATURE-----",
+	NULL
+};
+
 static int verify_gpg_signed_buffer(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
 				    size_t payload_size, const char *signature,
 				    size_t signature_size);
 static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 			   const char *signing_key);
+static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key);
 
 static struct gpg_format gpg_format[] = {
 	{
@@ -65,6 +73,14 @@ static struct gpg_format gpg_format[] = {
 		.verify_signed_buffer = verify_gpg_signed_buffer,
 		.sign_buffer = sign_buffer_gpg,
 	},
+	{
+		.name = "ssh",
+		.program = "ssh-keygen",
+		.verify_args = ssh_verify_args,
+		.sigs = ssh_sigs,
+		.verify_signed_buffer = NULL, /* TODO */
+		.sign_buffer = sign_buffer_ssh
+	},
 };
 
 static struct gpg_format *use_format = &gpg_format[0];
@@ -443,6 +459,9 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	if (!strcmp(var, "gpg.x509.program"))
 		fmtname = "x509";
 
+	if (!strcmp(var, "gpg.ssh.program"))
+		fmtname = "ssh";
+
 	if (fmtname) {
 		fmt = get_format_by_name(fmtname);
 		return git_config_string(&fmt->program, var, value);
@@ -463,12 +482,30 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
 	return use_format->sign_buffer(buffer, signature, signing_key);
 }
 
+/*
+ * Strip CR from the line endings, in case we are on Windows.
+ * NEEDSWORK: make it trim only CRs before LFs and rename
+ */
+static void remove_cr_after(struct strbuf *buffer, size_t offset)
+{
+	size_t i, j;
+
+	for (i = j = offset; i < buffer->len; i++) {
+		if (buffer->buf[i] != '\r') {
+			if (i != j)
+				buffer->buf[j] = buffer->buf[i];
+			j++;
+		}
+	}
+	strbuf_setlen(buffer, j);
+}
+
 static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 		    const char *signing_key)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
 	int ret;
-	size_t i, j, bottom;
+	size_t bottom;
 	struct strbuf gpg_status = STRBUF_INIT;
 
 	strvec_pushl(&gpg.args,
@@ -494,13 +531,97 @@ static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 		return error(_("gpg failed to sign the data"));
 
 	/* Strip CR from the line endings, in case we are on Windows. */
-	for (i = j = bottom; i < signature->len; i++)
-		if (signature->buf[i] != '\r') {
-			if (i != j)
-				signature->buf[j] = signature->buf[i];
-			j++;
-		}
-	strbuf_setlen(signature, j);
+	remove_cr_after(signature, bottom);
 
 	return 0;
 }
+
+static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
+			   const char *signing_key)
+{
+	struct child_process signer = CHILD_PROCESS_INIT;
+	int ret = -1;
+	size_t bottom, keylen;
+	struct strbuf signer_stderr = STRBUF_INIT;
+	struct tempfile *key_file = NULL, *buffer_file = NULL;
+	char *ssh_signing_key_file = NULL;
+	struct strbuf ssh_signature_filename = STRBUF_INIT;
+
+	if (!signing_key || signing_key[0] == '\0')
+		return error(
+			_("user.signingkey needs to be set for ssh signing"));
+
+	if (starts_with(signing_key, "ssh-")) {
+		/* A literal ssh key */
+		key_file = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
+		if (!key_file)
+			return error_errno(
+				_("could not create temporary file"));
+		keylen = strlen(signing_key);
+		if (write_in_full(key_file->fd, signing_key, keylen) < 0 ||
+		    close_tempfile_gently(key_file) < 0) {
+			error_errno(_("failed writing ssh signing key to '%s'"),
+				    key_file->filename.buf);
+			goto out;
+		}
+		ssh_signing_key_file = key_file->filename.buf;
+	} else {
+		/* We assume a file */
+		ssh_signing_key_file = expand_user_path(signing_key, 1);
+	}
+
+	buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
+	if (!buffer_file) {
+		error_errno(_("could not create temporary file"));
+		goto out;
+	}
+
+	if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
+	    close_tempfile_gently(buffer_file) < 0) {
+		error_errno(_("failed writing ssh signing key buffer to '%s'"),
+			    buffer_file->filename.buf);
+		goto out;
+	}
+
+	strvec_pushl(&signer.args, use_format->program,
+		     "-Y", "sign",
+		     "-n", "git",
+		     "-f", ssh_signing_key_file,
+		     buffer_file->filename.buf,
+		     NULL);
+
+	sigchain_push(SIGPIPE, SIG_IGN);
+	ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
+	sigchain_pop(SIGPIPE);
+
+	if (ret) {
+		if (strstr(signer_stderr.buf, "usage:"))
+			error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
+
+		error("%s", signer_stderr.buf);
+		goto out;
+	}
+
+	bottom = signature->len;
+
+	strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
+	strbuf_addstr(&ssh_signature_filename, ".sig");
+	if (strbuf_read_file(signature, ssh_signature_filename.buf, 0) < 0) {
+		error_errno(
+			_("failed reading ssh signing data buffer from '%s'"),
+			ssh_signature_filename.buf);
+	}
+	unlink_or_warn(ssh_signature_filename.buf);
+
+	/* Strip CR from the line endings, in case we are on Windows. */
+	remove_cr_after(signature, bottom);
+
+out:
+	if (key_file)
+		delete_tempfile(&key_file);
+	if (buffer_file)
+		delete_tempfile(&buffer_file);
+	strbuf_release(&signer_stderr);
+	strbuf_release(&ssh_signature_filename);
+	return ret;
+}
-- 
gitgitgadget

[PATCH v6 3/9] ssh signing: retrieve a default key from ssh-agent

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

if user.signingkey is not set and a ssh signature is requested we call
ssh-add -L and use the first key we get

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index c131977b347..3afacb48900 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -470,11 +470,35 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	return 0;
 }
 
+/* Returns the first public key from an ssh-agent to use for signing */
+static char *get_default_ssh_signing_key(void)
+{
+	struct child_process ssh_add = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf key_stdout = STRBUF_INIT;
+	struct strbuf **keys;
+
+	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
+	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
+	if (!ret) {
+		keys = strbuf_split_max(&key_stdout, '\n', 2);
+		if (keys[0])
+			return strbuf_detach(keys[0], NULL);
+	}
+
+	strbuf_release(&key_stdout);
+	return "";
+}
+
 const char *get_signing_key(void)
 {
 	if (configured_signing_key)
 		return configured_signing_key;
-	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
+	if (!strcmp(use_format->name, "ssh")) {
+		return get_default_ssh_signing_key();
+	} else {
+		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
+	}
 }
 
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
-- 
gitgitgadget

[PATCH v6 4/9] ssh signing: provide a textual representation of the signing key

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

for ssh the user.signingkey can be a filename/path or even a literal ssh pubkey.
in push certs and textual output we prefer the ssh fingerprint instead.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 gpg-interface.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 gpg-interface.h |  6 ++++++
 send-pack.c     |  8 ++++----
 3 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index 3afacb48900..ec48a37b6cc 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -470,6 +470,41 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	return 0;
 }
 
+static char *get_ssh_key_fingerprint(const char *signing_key)
+{
+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf fingerprint_stdout = STRBUF_INIT;
+	struct strbuf **fingerprint;
+
+	/*
+	 * With SSH Signing this can contain a filename or a public key
+	 * For textual representation we usually want a fingerprint
+	 */
+	if (istarts_with(signing_key, "ssh-")) {
+		strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf", "-", NULL);
+		ret = pipe_command(&ssh_keygen, signing_key,
+				   strlen(signing_key), &fingerprint_stdout, 0,
+				   NULL, 0);
+	} else {
+		strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf",
+			     configured_signing_key, NULL);
+		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0,
+				   NULL, 0);
+	}
+
+	if (!!ret)
+		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
+			  signing_key);
+
+	fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
+	if (!fingerprint[1])
+		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
+			  signing_key);
+
+	return strbuf_detach(fingerprint[1], NULL);
+}
+
 /* Returns the first public key from an ssh-agent to use for signing */
 static char *get_default_ssh_signing_key(void)
 {
@@ -490,6 +525,17 @@ static char *get_default_ssh_signing_key(void)
 	return "";
 }
 
+/* Returns a textual but unique representation ot the signing key */
+const char *get_signing_key_id(void)
+{
+	if (!strcmp(use_format->name, "ssh")) {
+		return get_ssh_key_fingerprint(get_signing_key());
+	} else {
+		/* GPG/GPGSM only store a key id on this variable */
+		return get_signing_key();
+	}
+}
+
 const char *get_signing_key(void)
 {
 	if (configured_signing_key)
diff --git a/gpg-interface.h b/gpg-interface.h
index feac4decf8b..beefacbb1e9 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -64,6 +64,12 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
 int git_gpg_config(const char *, const char *, void *);
 void set_signing_key(const char *);
 const char *get_signing_key(void);
+
+/*
+ * Returns a textual unique representation of the signing key in use
+ * Either a GPG KeyID or a SSH Key Fingerprint
+ */
+const char *get_signing_key_id(void);
 int check_signature(const char *payload, size_t plen,
 		    const char *signature, size_t slen,
 		    struct signature_check *sigc);
diff --git a/send-pack.c b/send-pack.c
index 5a79e0e7110..50cca7e439b 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -341,13 +341,13 @@ static int generate_push_cert(struct strbuf *req_buf,
 {
 	const struct ref *ref;
 	struct string_list_item *item;
-	char *signing_key = xstrdup(get_signing_key());
+	char *signing_key_id = xstrdup(get_signing_key_id());
 	const char *cp, *np;
 	struct strbuf cert = STRBUF_INIT;
 	int update_seen = 0;
 
 	strbuf_addstr(&cert, "certificate version 0.1\n");
-	strbuf_addf(&cert, "pusher %s ", signing_key);
+	strbuf_addf(&cert, "pusher %s ", signing_key_id);
 	datestamp(&cert);
 	strbuf_addch(&cert, '\n');
 	if (args->url && *args->url) {
@@ -374,7 +374,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 	if (!update_seen)
 		goto free_return;
 
-	if (sign_buffer(&cert, &cert, signing_key))
+	if (sign_buffer(&cert, &cert, get_signing_key()))
 		die(_("failed to sign the push certificate"));
 
 	packet_buf_write(req_buf, "push-cert%c%s", 0, cap_string);
@@ -386,7 +386,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 	packet_buf_write(req_buf, "push-cert-end\n");
 
 free_return:
-	free(signing_key);
+	free(signing_key_id);
 	strbuf_release(&cert);
 	return update_seen;
 }
-- 
gitgitgadget

[PATCH v6 5/9] ssh signing: parse ssh-keygen output and verify signatures

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

to verify a ssh signature we first call ssh-keygen -Y find-principal to
look up the signing principal by their public key from the
allowedSignersFile. If the key is found then we do a verify. Otherwise
we only validate the signature but can not verify the signers identity.

Verification uses the gpg.ssh.allowedSignersFile (see ssh-keygen(1) "ALLOWED
SIGNERS") which contains valid public keys and a principal (usually
user@domain). Depending on the environment this file can be managed by
the individual developer or for example generated by the central
repository server from known ssh keys with push access. If the
repository only allows signed commits / pushes then the file can even be
stored inside it.

To revoke a key put the public key without the principal prefix into
gpg.ssh.revocationKeyring or generate a KRL (see ssh-keygen(1)
"KEY REVOCATION LISTS"). The same considerations about who to trust for
verification as with the allowedSignersFile apply.

Using SSH CA Keys with these files is also possible. Add
"cert-authority" as key option between the principal and the key to mark
it as a CA and all keys signed by it as valid for this CA.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 builtin/receive-pack.c |   2 +
 gpg-interface.c        | 179 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 180 insertions(+), 1 deletion(-)

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index a34742513ac..62b11c5f3a4 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -131,6 +131,8 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 {
 	int status = parse_hide_refs_config(var, value, "receive");
 
+	git_gpg_config(var, value, NULL);
+
 	if (status)
 		return status;
 
diff --git a/gpg-interface.c b/gpg-interface.c
index ec48a37b6cc..703225c3cd3 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -3,11 +3,13 @@
 #include "config.h"
 #include "run-command.h"
 #include "strbuf.h"
+#include "dir.h"
 #include "gpg-interface.h"
 #include "sigchain.h"
 #include "tempfile.h"
 
 static char *configured_signing_key;
+static const char *ssh_allowed_signers, *ssh_revocation_file;
 static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
 
 struct gpg_format {
@@ -51,6 +53,10 @@ static int verify_gpg_signed_buffer(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
 				    size_t payload_size, const char *signature,
 				    size_t signature_size);
+static int verify_ssh_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size);
 static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 			   const char *signing_key);
 static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
@@ -78,7 +84,7 @@ static struct gpg_format gpg_format[] = {
 		.program = "ssh-keygen",
 		.verify_args = ssh_verify_args,
 		.sigs = ssh_sigs,
-		.verify_signed_buffer = NULL, /* TODO */
+		.verify_signed_buffer = verify_ssh_signed_buffer,
 		.sign_buffer = sign_buffer_ssh
 	},
 };
@@ -343,6 +349,165 @@ static int verify_gpg_signed_buffer(struct signature_check *sigc,
 	return ret;
 }
 
+static void parse_ssh_output(struct signature_check *sigc)
+{
+	const char *line, *principal, *search;
+
+	/*
+	 * ssh-keysign output should be:
+	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
+	 * Good "git" signature for PRINCIPAL WITH WHITESPACE with RSA key SHA256:FINGERPRINT
+	 * or for valid but unknown keys:
+	 * Good "git" signature with RSA key SHA256:FINGERPRINT
+	 */
+	sigc->result = 'B';
+	sigc->trust_level = TRUST_NEVER;
+
+	line = xmemdupz(sigc->output, strcspn(sigc->output, "\n"));
+
+	if (skip_prefix(line, "Good \"git\" signature for ", &line)) {
+		/* Valid signature and known principal */
+		sigc->result = 'G';
+		sigc->trust_level = TRUST_FULLY;
+
+		/* Search for the last "with" to get the full principal */
+		principal = line;
+		do {
+			search = strstr(line, " with ");
+			if (search)
+				line = search + 1;
+		} while (search != NULL);
+		sigc->signer = xmemdupz(principal, line - principal - 1);
+		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);
+		sigc->key = xstrdup(sigc->fingerprint);
+	} else if (skip_prefix(line, "Good \"git\" signature with ", &line)) {
+		/* Valid signature, but key unknown */
+		sigc->result = 'G';
+		sigc->trust_level = TRUST_UNDEFINED;
+		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);
+		sigc->key = xstrdup(sigc->fingerprint);
+	}
+}
+
+static int verify_ssh_signed_buffer(struct signature_check *sigc,
+				    struct gpg_format *fmt, const char *payload,
+				    size_t payload_size, const char *signature,
+				    size_t signature_size)
+{
+	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
+	struct tempfile *buffer_file;
+	int ret = -1;
+	const char *line;
+	size_t trust_size;
+	char *principal;
+	struct strbuf ssh_keygen_out = STRBUF_INIT;
+	struct strbuf ssh_keygen_err = STRBUF_INIT;
+
+	if (!ssh_allowed_signers) {
+		error(_("gpg.ssh.allowedSignersFile needs to be configured and exist for ssh signature verification"));
+		return -1;
+	}
+
+	buffer_file = mks_tempfile_t(".git_vtag_tmpXXXXXX");
+	if (!buffer_file)
+		return error_errno(_("could not create temporary file"));
+	if (write_in_full(buffer_file->fd, signature, signature_size) < 0 ||
+	    close_tempfile_gently(buffer_file) < 0) {
+		error_errno(_("failed writing detached signature to '%s'"),
+			    buffer_file->filename.buf);
+		delete_tempfile(&buffer_file);
+		return -1;
+	}
+
+	/* Find the principal from the signers */
+	strvec_pushl(&ssh_keygen.args, fmt->program,
+		     "-Y", "find-principals",
+		     "-f", ssh_allowed_signers,
+		     "-s", buffer_file->filename.buf,
+		     NULL);
+	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0,
+			   &ssh_keygen_err, 0);
+	if (ret && strstr(ssh_keygen_err.buf, "usage:")) {
+		error(_("ssh-keygen -Y find-principals/verify is needed for ssh signature verification (available in openssh version 8.2p1+)"));
+		goto out;
+	}
+	if (ret || !ssh_keygen_out.len) {
+		/* We did not find a matching principal in the allowedSigners - Check
+		 * without validation */
+		child_process_init(&ssh_keygen);
+		strvec_pushl(&ssh_keygen.args, fmt->program,
+			     "-Y", "check-novalidate",
+			     "-n", "git",
+			     "-s", buffer_file->filename.buf,
+			     NULL);
+		ret = pipe_command(&ssh_keygen, payload, payload_size,
+				   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
+	} else {
+		/* Check every principal we found (one per line) */
+		for (line = ssh_keygen_out.buf; *line;
+		     line = strchrnul(line + 1, '\n')) {
+			while (*line == '\n')
+				line++;
+			if (!*line)
+				break;
+
+			trust_size = strcspn(line, "\n");
+			principal = xmemdupz(line, trust_size);
+
+			child_process_init(&ssh_keygen);
+			strbuf_release(&ssh_keygen_out);
+			strbuf_release(&ssh_keygen_err);
+			strvec_push(&ssh_keygen.args, fmt->program);
+			/* We found principals - Try with each until we find a
+			 * match */
+			strvec_pushl(&ssh_keygen.args, "-Y", "verify",
+				     "-n", "git",
+				     "-f", ssh_allowed_signers,
+				     "-I", principal,
+				     "-s", buffer_file->filename.buf,
+				     NULL);
+
+			if (ssh_revocation_file) {
+				if (file_exists(ssh_revocation_file)) {
+					strvec_pushl(&ssh_keygen.args, "-r",
+						     ssh_revocation_file, NULL);
+				} else {
+					warning(_("ssh signing revocation file configured but not found: %s"),
+						ssh_revocation_file);
+				}
+			}
+
+			sigchain_push(SIGPIPE, SIG_IGN);
+			ret = pipe_command(&ssh_keygen, payload, payload_size,
+					   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
+			sigchain_pop(SIGPIPE);
+
+			FREE_AND_NULL(principal);
+
+			ret &= starts_with(ssh_keygen_out.buf, "Good");
+			if (ret == 0)
+				break;
+		}
+	}
+
+	sigc->payload = xmemdupz(payload, payload_size);
+	strbuf_stripspace(&ssh_keygen_out, 0);
+	strbuf_stripspace(&ssh_keygen_err, 0);
+	strbuf_add(&ssh_keygen_out, ssh_keygen_err.buf, ssh_keygen_err.len);
+	sigc->output = strbuf_detach(&ssh_keygen_out, NULL);
+	sigc->gpg_status = xstrdup(sigc->output);
+
+	parse_ssh_output(sigc);
+
+out:
+	if (buffer_file)
+		delete_tempfile(&buffer_file);
+	strbuf_release(&ssh_keygen_out);
+	strbuf_release(&ssh_keygen_err);
+
+	return ret;
+}
+
 int check_signature(const char *payload, size_t plen, const char *signature,
 	size_t slen, struct signature_check *sigc)
 {
@@ -453,6 +618,18 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(var, "gpg.ssh.allowedsignersfile")) {
+		if (!value)
+			return config_error_nonbool(var);
+		return git_config_string(&ssh_allowed_signers, var, value);
+	}
+
+	if (!strcmp(var, "gpg.ssh.revocationFile")) {
+		if (!value)
+			return config_error_nonbool(var);
+		return git_config_string(&ssh_revocation_file, var, value);
+	}
+
 	if (!strcmp(var, "gpg.program") || !strcmp(var, "gpg.openpgp.program"))
 		fmtname = "openpgp";
 
-- 
gitgitgadget

[PATCH v6 6/9] ssh signing: add test prereqs

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

generate some ssh keys and a allowedSignersFile for testing

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/lib-gpg.sh | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/t/lib-gpg.sh b/t/lib-gpg.sh
index 9fc5241228e..600c8d1a026 100644
--- a/t/lib-gpg.sh
+++ b/t/lib-gpg.sh
@@ -87,6 +87,35 @@ test_lazy_prereq RFC1991 '
 	echo | gpg --homedir "${GNUPGHOME}" -b --rfc1991 >/dev/null
 '
 
+test_lazy_prereq GPGSSH '
+	ssh_version=$(ssh-keygen -Y find-principals -n "git" 2>&1)
+	test $? != 127 || exit 1
+	echo $ssh_version | grep -q "find-principals:missing signature file"
+	test $? = 0 || exit 1;
+	mkdir -p "${GNUPGHOME}" &&
+	chmod 0700 "${GNUPGHOME}" &&
+	ssh-keygen -t ed25519 -N "" -C "git ed25519 key" -f "${GNUPGHOME}/ed25519_ssh_signing_key" >/dev/null &&
+	echo "\"principal with number 1\" $(cat "${GNUPGHOME}/ed25519_ssh_signing_key.pub")" >> "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
+	ssh-keygen -t rsa -b 2048 -N "" -C "git rsa2048 key" -f "${GNUPGHOME}/rsa_2048_ssh_signing_key" >/dev/null &&
+	echo "\"principal with number 2\" $(cat "${GNUPGHOME}/rsa_2048_ssh_signing_key.pub")" >> "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
+	ssh-keygen -t ed25519 -N "super_secret" -C "git ed25519 encrypted key" -f "${GNUPGHOME}/protected_ssh_signing_key" >/dev/null &&
+	echo "\"principal with number 3\" $(cat "${GNUPGHOME}/protected_ssh_signing_key.pub")" >> "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
+	cat "${GNUPGHOME}/ssh.all_valid.allowedSignersFile" &&
+	ssh-keygen -t ed25519 -N "" -f "${GNUPGHOME}/untrusted_ssh_signing_key" >/dev/null
+'
+
+SIGNING_KEY_PRIMARY="${GNUPGHOME}/ed25519_ssh_signing_key"
+SIGNING_KEY_SECONDARY="${GNUPGHOME}/rsa_2048_ssh_signing_key"
+SIGNING_KEY_UNTRUSTED="${GNUPGHOME}/untrusted_ssh_signing_key"
+SIGNING_KEY_WITH_PASSPHRASE="${GNUPGHOME}/protected_ssh_signing_key"
+SIGNING_KEY_PASSPHRASE="super_secret"
+SIGNING_ALLOWED_SIGNERS="${GNUPGHOME}/ssh.all_valid.allowedSignersFile"
+
+GOOD_SIGNATURE_TRUSTED='Good "git" signature for'
+GOOD_SIGNATURE_UNTRUSTED='Good "git" signature with'
+KEY_NOT_TRUSTED="No principal matched"
+BAD_SIGNATURE="Signature verification failed"
+
 sanitize_pgp() {
 	perl -ne '
 		/^-----END PGP/ and $in_pgp = 0;
-- 
gitgitgadget

[PATCH v6 7/9] ssh signing: duplicate t7510 tests for commits

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/t7528-signed-commit-ssh.sh | 398 +++++++++++++++++++++++++++++++++++
 1 file changed, 398 insertions(+)
 create mode 100755 t/t7528-signed-commit-ssh.sh

diff --git a/t/t7528-signed-commit-ssh.sh b/t/t7528-signed-commit-ssh.sh
new file mode 100755
index 00000000000..e2c48f69e6d
--- /dev/null
+++ b/t/t7528-signed-commit-ssh.sh
@@ -0,0 +1,398 @@
+#!/bin/sh
+
+test_description='ssh signed commit tests'
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+GNUPGHOME_NOT_USED=$GNUPGHOME
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPGSSH 'create signed commits' '
+	test_oid_cache <<-\EOF &&
+	header sha1:gpgsig
+	header sha256:gpgsig-sha256
+	EOF
+
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+
+	echo 1 >file && git add file &&
+	test_tick && git commit -S -m initial &&
+	git tag initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -S -m second &&
+	git tag second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout main &&
+	test_tick && git merge -S side &&
+	git tag merge &&
+
+	echo 4 >file && test_tick && git commit -a -m "fourth unsigned" &&
+	git tag fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag fourth-signed &&
+
+	git config commit.gpgsign true &&
+	echo 5 >file && test_tick && git commit -a -m "fifth signed" &&
+	git tag fifth-signed &&
+
+	git config commit.gpgsign false &&
+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
+	git tag sixth-unsigned &&
+
+	git config commit.gpgsign true &&
+	echo 7 >file && test_tick && git commit -a -m "seventh" --no-gpg-sign &&
+	git tag seventh-unsigned &&
+
+	test_tick && git rebase -f HEAD^^ && git tag sixth-signed HEAD^ &&
+	git tag seventh-signed &&
+
+	echo 8 >file && test_tick && git commit -a -m eighth -S"${SIGNING_KEY_UNTRUSTED}" &&
+	git tag eighth-signed-alt &&
+
+	# commit.gpgsign is still on but this must not be signed
+	echo 9 | git commit-tree HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag ninth-unsigned $(cat oid) &&
+	# explicit -S of course must sign.
+	echo 10 | git commit-tree -S HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag tenth-signed $(cat oid) &&
+
+	# --gpg-sign[=<key-id>] must sign.
+	echo 11 | git commit-tree --gpg-sign HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag eleventh-signed $(cat oid) &&
+	echo 12 | git commit-tree --gpg-sign="${SIGNING_KEY_UNTRUSTED}" HEAD^{tree} >oid &&
+	test_line_count = 1 oid &&
+	git tag twelfth-signed-alt $(cat oid)
+'
+
+test_expect_success GPGSSH 'verify and show signatures' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config gpg.mintrustlevel UNDEFINED &&
+	(
+		for commit in initial second merge fourth-signed \
+			fifth-signed sixth-signed seventh-signed tenth-signed \
+			eleventh-signed
+		do
+			git verify-commit $commit &&
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in merge^2 fourth-unsigned sixth-unsigned \
+			seventh-unsigned ninth-unsigned
+		do
+			test_must_fail git verify-commit $commit &&
+			git show --pretty=short --show-signature $commit >actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in eighth-signed-alt twelfth-signed-alt
+		do
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			grep "${KEY_NOT_TRUSTED}" actual &&
+			echo $commit OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'verify-commit exits success on untrusted signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git verify-commit eighth-signed-alt 2>actual &&
+	grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual &&
+	grep "${KEY_NOT_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH 'verify-commit exits success with matching minTrustLevel' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config gpg.minTrustLevel fully &&
+	git verify-commit sixth-signed
+'
+
+test_expect_success GPGSSH 'verify-commit exits success with low minTrustLevel' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config gpg.minTrustLevel marginal &&
+	git verify-commit sixth-signed
+'
+
+test_expect_success GPGSSH 'verify-commit exits failure with high minTrustLevel' '
+	test_config gpg.minTrustLevel ultimate &&
+	test_must_fail git verify-commit eighth-signed-alt
+'
+
+test_expect_success GPGSSH 'verify signatures with --raw' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	(
+		for commit in initial second merge fourth-signed fifth-signed sixth-signed seventh-signed
+		do
+			git verify-commit --raw $commit 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in merge^2 fourth-unsigned sixth-unsigned seventh-unsigned
+		do
+			test_must_fail git verify-commit --raw $commit 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	) &&
+	(
+		for commit in eighth-signed-alt
+		do
+			git verify-commit --raw $commit 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $commit OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'proper header is used for hash algorithm' '
+	git cat-file commit fourth-signed >output &&
+	grep "^$(test_oid header) -----BEGIN SSH SIGNATURE-----" output
+'
+
+test_expect_success GPGSSH 'show signed commit with signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git show -s initial >commit &&
+	git show -s --show-signature initial >show &&
+	git verify-commit -v initial >verify.1 2>verify.2 &&
+	git cat-file commit initial >cat &&
+	grep -v -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.commit &&
+	grep -e "${GOOD_SIGNATURE_TRUSTED}" -e "Warning: " show >show.gpg &&
+	grep -v "^ " cat | grep -v "^gpgsig.* " >cat.commit &&
+	test_cmp show.commit commit &&
+	test_cmp show.gpg verify.2 &&
+	test_cmp cat.commit verify.1
+'
+
+test_expect_success GPGSSH 'detect fudged signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git cat-file commit seventh-signed >raw &&
+	sed -e "s/^seventh/7th forged/" raw >forged1 &&
+	git hash-object -w -t commit forged1 >forged1.commit &&
+	test_must_fail git verify-commit $(cat forged1.commit) &&
+	git show --pretty=short --show-signature $(cat forged1.commit) >actual1 &&
+	grep "${BAD_SIGNATURE}" actual1 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
+'
+
+test_expect_success GPGSSH 'detect fudged signature with NUL' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git cat-file commit seventh-signed >raw &&
+	cat raw >forged2 &&
+	echo Qwik | tr "Q" "\000" >>forged2 &&
+	git hash-object -w -t commit forged2 >forged2.commit &&
+	test_must_fail git verify-commit $(cat forged2.commit) &&
+	git show --pretty=short --show-signature $(cat forged2.commit) >actual2 &&
+	grep "${BAD_SIGNATURE}" actual2 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual2
+'
+
+test_expect_success GPGSSH 'amending already signed commit' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git checkout fourth-signed^0 &&
+	git commit --amend -S --no-edit &&
+	git verify-commit HEAD &&
+	git show -s --show-signature HEAD >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual
+'
+
+test_expect_success GPGSSH 'show good signature with custom format' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	cat >expect.tmpl <<-\EOF &&
+	G
+	FINGERPRINT
+	principal with number 1
+	FINGERPRINT
+
+	EOF
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show bad signature with custom format' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect <<-\EOF &&
+	B
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat forged1.commit) >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with custom format' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect.tmpl <<-\EOF &&
+	U
+	FINGERPRINT
+
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with undefined trust level' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect.tmpl <<-\EOF &&
+	undefined
+	FINGERPRINT
+
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" eighth-signed-alt >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_UNTRUSTED}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show untrusted signature with ultimate trust level' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect.tmpl <<-\EOF &&
+	fully
+	FINGERPRINT
+	principal with number 1
+	FINGERPRINT
+
+	EOF
+	git log -1 --format="%GT%n%GK%n%GS%n%GF%n%GP" sixth-signed >actual &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	sed "s|FINGERPRINT|$FINGERPRINT|g" expect.tmpl >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'show lack of signature with custom format' '
+	cat >expect <<-\EOF &&
+	N
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" seventh-unsigned >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'log.showsignature behaves like --show-signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	test_config log.showsignature true &&
+	git show initial >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH 'check config gpg.format values' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_config gpg.format ssh &&
+	git commit -S --amend -m "success" &&
+	test_config gpg.format OpEnPgP &&
+	test_must_fail git commit -S --amend -m "fail"
+'
+
+test_expect_failure GPGSSH 'detect fudged commit with double signature (TODO)' '
+	sed -e "/gpgsig/,/END PGP/d" forged1 >double-base &&
+	sed -n -e "/gpgsig/,/END PGP/p" forged1 | \
+		sed -e "s/^$(test_oid header)//;s/^ //" | gpg --dearmor >double-sig1.sig &&
+	gpg -o double-sig2.sig -u 29472784 --detach-sign double-base &&
+	cat double-sig1.sig double-sig2.sig | gpg --enarmor >double-combined.asc &&
+	sed -e "s/^\(-.*\)ARMORED FILE/\1SIGNATURE/;1s/^/$(test_oid header) /;2,\$s/^/ /" \
+		double-combined.asc > double-gpgsig &&
+	sed -e "/committer/r double-gpgsig" double-base >double-commit &&
+	git hash-object -w -t commit double-commit >double-commit.commit &&
+	test_must_fail git verify-commit $(cat double-commit.commit) &&
+	git show --pretty=short --show-signature $(cat double-commit.commit) >double-actual &&
+	grep "BAD signature from" double-actual &&
+	grep "Good signature from" double-actual
+'
+
+test_expect_failure GPGSSH 'show double signature with custom format (TODO)' '
+	cat >expect <<-\EOF &&
+	E
+
+
+
+
+	EOF
+	git log -1 --format="%G?%n%GK%n%GS%n%GF%n%GP" $(cat double-commit.commit) >actual &&
+	test_cmp expect actual
+'
+
+
+test_expect_failure GPGSSH 'verify-commit verifies multiply signed commits (TODO)' '
+	git init multiply-signed &&
+	cd multiply-signed &&
+	test_commit first &&
+	echo 1 >second &&
+	git add second &&
+	tree=$(git write-tree) &&
+	parent=$(git rev-parse HEAD^{commit}) &&
+	git commit --gpg-sign -m second &&
+	git cat-file commit HEAD &&
+	# Avoid trailing whitespace.
+	sed -e "s/^Q//" -e "s/^Z/ /" >commit <<-EOF &&
+	Qtree $tree
+	Qparent $parent
+	Qauthor A U Thor <author@example.com> 1112912653 -0700
+	Qcommitter C O Mitter <committer@example.com> 1112912653 -0700
+	Qgpgsig -----BEGIN PGP SIGNATURE-----
+	QZ
+	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBDRYcY29tbWl0dGVy
+	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMNd+8AoK1I8mhLHviPH+q2I5fIVgPsEtYC
+	Q AKCTqBh+VabJceXcGIZuF0Ry+udbBQ==
+	Q =tQ0N
+	Q -----END PGP SIGNATURE-----
+	Qgpgsig-sha256 -----BEGIN PGP SIGNATURE-----
+	QZ
+	Q iHQEABECADQWIQRz11h0S+chaY7FTocTtvUezd5DDQUCX/uBIBYcY29tbWl0dGVy
+	Q QGV4YW1wbGUuY29tAAoJEBO29R7N3kMN/NEAn0XO9RYSBj2dFyozi0JKSbssYMtO
+	Q AJwKCQ1BQOtuwz//IjU8TiS+6S4iUw==
+	Q =pIwP
+	Q -----END PGP SIGNATURE-----
+	Q
+	Qsecond
+	EOF
+	head=$(git hash-object -t commit -w commit) &&
+	git reset --hard $head &&
+	git verify-commit $head 2>actual &&
+	grep "Good signature from" actual &&
+	! grep "BAD signature from" actual
+'
+
+test_done
-- 
gitgitgadget

[PATCH v6 8/9] ssh signing: add more tests for logs, tags & push certs

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/t4202-log.sh                   |  23 +++++
 t/t5534-push-signed.sh           | 101 +++++++++++++++++++
 t/t7031-verify-tag-signed-ssh.sh | 161 +++++++++++++++++++++++++++++++
 3 files changed, 285 insertions(+)
 create mode 100755 t/t7031-verify-tag-signed-ssh.sh

diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index 39e746fbcbe..afd7f2516ee 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -1616,6 +1616,16 @@ test_expect_success GPGSM 'setup signed branch x509' '
 	git commit -S -m signed_commit
 '
 
+test_expect_success GPGSSH 'setup sshkey signed branch' '
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	test_when_finished "git reset --hard && git checkout main" &&
+	git checkout -b signed-ssh main &&
+	echo foo >foo &&
+	git add foo &&
+	git commit -S -m signed_commit
+'
+
 test_expect_success GPGSM 'log x509 fingerprint' '
 	echo "F8BF62E0693D0694816377099909C779FA23FD65 | " >expect &&
 	git log -n1 --format="%GF | %GP" signed-x509 >actual &&
@@ -1628,6 +1638,13 @@ test_expect_success GPGSM 'log OpenPGP fingerprint' '
 	test_cmp expect actual
 '
 
+test_expect_success GPGSSH 'log ssh key fingerprint' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	ssh-keygen -lf  "${SIGNING_KEY_PRIMARY}" | awk "{print \$2\" | \"}" >expect &&
+	git log -n1 --format="%GF | %GP" signed-ssh >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success GPG 'log --graph --show-signature' '
 	git log --graph --show-signature -n1 signed >actual &&
 	grep "^| gpg: Signature made" actual &&
@@ -1640,6 +1657,12 @@ test_expect_success GPGSM 'log --graph --show-signature x509' '
 	grep "^| gpgsm: Good signature" actual
 '
 
+test_expect_success GPGSSH 'log --graph --show-signature ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git log --graph --show-signature -n1 signed-ssh >actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual
+'
+
 test_expect_success GPG 'log --graph --show-signature for merged tag' '
 	test_when_finished "git reset --hard && git checkout main" &&
 	git checkout -b plain main &&
diff --git a/t/t5534-push-signed.sh b/t/t5534-push-signed.sh
index bba768f5ded..d590249b995 100755
--- a/t/t5534-push-signed.sh
+++ b/t/t5534-push-signed.sh
@@ -137,6 +137,53 @@ test_expect_success GPG 'signed push sends push certificate' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPGSSH 'ssh signed push sends push certificate' '
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=principal with number 1
+		KEY=FINGERPRINT
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
+
+	noop=$(git rev-parse noop) &&
+	ff=$(git rev-parse ff) &&
+	noff=$(git rev-parse noff) &&
+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_expect_success GPG 'inconsistent push options in signed push not allowed' '
 	# First, invoke receive-pack with dummy input to obtain its preamble.
 	prepare_dst &&
@@ -276,6 +323,60 @@ test_expect_success GPGSM 'fail without key and heed user.signingkey x509' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPGSSH 'fail without key and heed user.signingkey ssh' '
+	test_config gpg.format ssh &&
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	test_config user.email hasnokey@nowhere.com &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "" &&
+	(
+		sane_unset GIT_COMMITTER_EMAIL &&
+		test_must_fail git push --signed dst noop ff +noff
+	) &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+	FINGERPRINT=$(ssh-keygen -lf "${SIGNING_KEY_PRIMARY}" | awk "{print \$2;}") &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=principal with number 1
+		KEY=FINGERPRINT
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) | sed -e "s|FINGERPRINT|$FINGERPRINT|" >expect &&
+
+	noop=$(git rev-parse noop) &&
+	ff=$(git rev-parse ff) &&
+	noff=$(git rev-parse noff) &&
+	grep "$noop $ff refs/heads/ff" dst/push-cert &&
+	grep "$noop $noff refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_expect_success GPG 'failed atomic push does not execute GPG' '
 	prepare_dst &&
 	git -C dst config receive.certnonceseed sekrit &&
diff --git a/t/t7031-verify-tag-signed-ssh.sh b/t/t7031-verify-tag-signed-ssh.sh
new file mode 100755
index 00000000000..05bf520a332
--- /dev/null
+++ b/t/t7031-verify-tag-signed-ssh.sh
@@ -0,0 +1,161 @@
+#!/bin/sh
+
+test_description='signed tag tests'
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPGSSH 'create signed tags ssh' '
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	test_config user.signingkey "${SIGNING_KEY_PRIMARY}" &&
+
+	echo 1 >file && git add file &&
+	test_tick && git commit -m initial &&
+	git tag -s -m initial initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -m second &&
+	git tag -s -m second second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout main &&
+	test_tick && git merge -S side &&
+	git tag -s -m merge merge &&
+
+	echo 4 >file && test_tick && git commit -a -S -m "fourth unsigned" &&
+	git tag -a -m fourth-unsigned fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag -s -m fourth fourth-signed &&
+
+	echo 5 >file && test_tick && git commit -a -m "fifth" &&
+	git tag fifth-unsigned &&
+
+	git config commit.gpgsign true &&
+	echo 6 >file && test_tick && git commit -a -m "sixth" &&
+	git tag -a -m sixth sixth-unsigned &&
+
+	test_tick && git rebase -f HEAD^^ && git tag -s -m 6th sixth-signed HEAD^ &&
+	git tag -m seventh -s seventh-signed &&
+
+	echo 8 >file && test_tick && git commit -a -m eighth &&
+	git tag -u"${SIGNING_KEY_UNTRUSTED}" -m eighth eighth-signed-alt
+'
+
+test_expect_success GPGSSH 'verify and show ssh signatures' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	(
+		for tag in initial second merge fourth-signed sixth-signed seventh-signed
+		do
+			git verify-tag $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
+		do
+			test_must_fail git verify-tag $tag 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in eighth-signed-alt
+		do
+			git verify-tag $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			grep "${KEY_NOT_TRUSTED}" actual &&
+			echo $tag OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'detect fudged ssh signature' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git cat-file tag seventh-signed >raw &&
+	sed -e "/^tag / s/seventh/7th forged/" raw >forged1 &&
+	git hash-object -w -t tag forged1 >forged1.tag &&
+	test_must_fail git verify-tag $(cat forged1.tag) 2>actual1 &&
+	grep "${BAD_SIGNATURE}" actual1 &&
+	! grep "${GOOD_SIGNATURE_TRUSTED}" actual1 &&
+	! grep "${GOOD_SIGNATURE_UNTRUSTED}" actual1
+'
+
+test_expect_success GPGSSH 'verify ssh signatures with --raw' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	(
+		for tag in initial second merge fourth-signed sixth-signed seventh-signed
+		do
+			git verify-tag --raw $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in fourth-unsigned fifth-unsigned sixth-unsigned
+		do
+			test_must_fail git verify-tag --raw $tag 2>actual &&
+			! grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	) &&
+	(
+		for tag in eighth-signed-alt
+		do
+			git verify-tag --raw $tag 2>actual &&
+			grep "${GOOD_SIGNATURE_UNTRUSTED}" actual &&
+			! grep "${BAD_SIGNATURE}" actual &&
+			echo $tag OK || exit 1
+		done
+	)
+'
+
+test_expect_success GPGSSH 'verify signatures with --raw ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	git verify-tag --raw sixth-signed 2>actual &&
+	grep "${GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${BAD_SIGNATURE}" actual &&
+	echo sixth-signed OK
+'
+
+test_expect_success GPGSSH 'verify multiple tags ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	tags="seventh-signed sixth-signed" &&
+	for i in $tags
+	do
+		git verify-tag -v --raw $i || return 1
+	done >expect.stdout 2>expect.stderr.1 &&
+	grep "^${GOOD_SIGNATURE_TRUSTED}" <expect.stderr.1 >expect.stderr &&
+	git verify-tag -v --raw $tags >actual.stdout 2>actual.stderr.1 &&
+	grep "^${GOOD_SIGNATURE_TRUSTED}" <actual.stderr.1 >actual.stderr &&
+	test_cmp expect.stdout actual.stdout &&
+	test_cmp expect.stderr actual.stderr
+'
+
+test_expect_success GPGSSH 'verifying tag with --format - ssh' '
+	test_config gpg.ssh.allowedSignersFile "${SIGNING_ALLOWED_SIGNERS}" &&
+	cat >expect <<-\EOF &&
+	tagname : fourth-signed
+	EOF
+	git verify-tag --format="tagname : %(tag)" "fourth-signed" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success GPGSSH 'verifying a forged tag with --format should fail silently - ssh' '
+	test_must_fail git verify-tag --format="tagname : %(tag)" $(cat forged1.tag) >actual-forged &&
+	test_must_be_empty actual-forged
+'
+
+test_done
-- 
gitgitgadget

[PATCH v6 9/9] ssh signing: add documentation

[Fabian Stelzer via GitGitGadget]

From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 Documentation/config/gpg.txt  | 39 +++++++++++++++++++++++++++++++++--
 Documentation/config/user.txt |  6 ++++++
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
index d94025cb368..dc790512e86 100644
--- a/Documentation/config/gpg.txt
+++ b/Documentation/config/gpg.txt
@@ -11,13 +11,13 @@ gpg.program::
 
 gpg.format::
 	Specifies which key format to use when signing with `--gpg-sign`.
-	Default is "openpgp" and another possible value is "x509".
+	Default is "openpgp". Other possible values are "x509", "ssh".
 
 gpg.<format>.program::
 	Use this to customize the program used for the signing format you
 	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
 	be used as a legacy synonym for `gpg.openpgp.program`. The default
-	value for `gpg.x509.program` is "gpgsm".
+	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
 
 gpg.minTrustLevel::
 	Specifies a minimum trust level for signature verification.  If
@@ -33,3 +33,38 @@ gpg.minTrustLevel::
 * `marginal`
 * `fully`
 * `ultimate`
+
+gpg.ssh.allowedSignersFile::
+	A file containing ssh public keys which you are willing to trust.
+	The file consists of one or more lines of principals followed by an ssh
+	public key.
+	e.g.: user1@example.com,user2@example.com ssh-rsa AAAAX1...
+	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
+	The principal is only used to identify the key and is available when
+	verifying a signature.
++
+SSH has no concept of trust levels like gpg does. To be able to differentiate
+between valid signatures and trusted signatures the trust level of a signature
+verification is set to `fully` when the public key is present in the allowedSignersFile.
+Therefore to only mark fully trusted keys as verified set gpg.minTrustLevel to `fully`.
+Otherwise valid but untrusted signatures will still verify but show no principal
+name of the signer.
++
+This file can be set to a location outside of the repository and every developer
+maintains their own trust store. A central repository server could generate this
+file automatically from ssh keys with push access to verify the code against.
+In a corporate setting this file is probably generated at a global location
+from automation that already handles developer ssh keys.
++
+A repository that only allows signed commits can store the file
+in the repository itself using a path relative to the top-level of the working tree.
+This way only committers with an already valid key can add or change keys in the keyring.
++
+Using a SSH CA key with the cert-authority option
+(see ssh-keygen(1) "CERTIFICATES") is also valid.
+
+gpg.ssh.revocationFile::
+	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
+	See ssh-keygen(1) for details.
+	If a public key is found in this file then it will always be treated
+	as having trust level "never" and signatures will show as invalid.
diff --git a/Documentation/config/user.txt b/Documentation/config/user.txt
index 59aec7c3aed..b3c2f2c541e 100644
--- a/Documentation/config/user.txt
+++ b/Documentation/config/user.txt
@@ -36,3 +36,9 @@ user.signingKey::
 	commit, you can override the default selection with this variable.
 	This option is passed unchanged to gpg's --local-user parameter,
 	so you may specify a key using any method that gpg supports.
+	If gpg.format is set to "ssh" this can contain the literal ssh public
+	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and
+	corresponds to the private key used for signing. The private key
+	needs to be available via ssh-agent. Alternatively it can be set to
+	a file containing a private key directly. If not set git will call
+	"ssh-add -L" and try to use the first key available.
-- 
gitgitgadget

Re: [PATCH v6 3/9] ssh signing: retrieve a default key from ssh-agent

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Fabian Stelzer <fs@gigacodes.de>
>
> if user.signingkey is not set and a ssh signature is requested we call
> ssh-add -L and use the first key we get
>
> Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
> ---
>  gpg-interface.c | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)

I would have expected that this also would become a method call into
*use_format object (instead of dispatching on use_format->name), but
let's not go overboard.  I think this is good enough for now.


> diff --git a/gpg-interface.c b/gpg-interface.c
> index c131977b347..3afacb48900 100644
> --- a/gpg-interface.c
> +++ b/gpg-interface.c
> @@ -470,11 +470,35 @@ int git_gpg_config(const char *var, const char *value, void *cb)
>  	return 0;
>  }
>  
> +/* Returns the first public key from an ssh-agent to use for signing */
> +static char *get_default_ssh_signing_key(void)
> +{
> +	struct child_process ssh_add = CHILD_PROCESS_INIT;
> +	int ret = -1;
> +	struct strbuf key_stdout = STRBUF_INIT;
> +	struct strbuf **keys;
> +
> +	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
> +	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
> +	if (!ret) {
> +		keys = strbuf_split_max(&key_stdout, '\n', 2);
> +		if (keys[0])
> +			return strbuf_detach(keys[0], NULL);
> +	}
> +
> +	strbuf_release(&key_stdout);
> +	return "";
> +}
> +
>  const char *get_signing_key(void)
>  {
>  	if (configured_signing_key)
>  		return configured_signing_key;
> -	return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
> +	if (!strcmp(use_format->name, "ssh")) {
> +		return get_default_ssh_signing_key();
> +	} else {
> +		return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
> +	}
>  }
>  
>  int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)

Re: [PATCH v6 4/9] ssh signing: provide a textual representation of the signing key

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Fabian Stelzer <fs@gigacodes.de>
>
> for ssh the user.signingkey can be a filename/path or even a literal ssh pubkey.
> in push certs and textual output we prefer the ssh fingerprint instead.

These sentences that lack the initial capital letters would look
unusual and distracting in our "git log --no-merges" stream.

> +static char *get_ssh_key_fingerprint(const char *signing_key)
> +{
> +	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
> +	int ret = -1;
> +	struct strbuf fingerprint_stdout = STRBUF_INIT;
> +	struct strbuf **fingerprint;
> +
> +	/*
> +	 * With SSH Signing this can contain a filename or a public key
> +	 * For textual representation we usually want a fingerprint
> +	 */
> +	if (istarts_with(signing_key, "ssh-")) {
> +		strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf", "-", NULL);
> +		ret = pipe_command(&ssh_keygen, signing_key,
> +				   strlen(signing_key), &fingerprint_stdout, 0,
> +				   NULL, 0);
> +	} else {
> +		strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf",
> +			     configured_signing_key, NULL);
> +		ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0,
> +				   NULL, 0);
> +	}
> +
> +	if (!!ret)
> +		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
> +			  signing_key);
> +
> +	fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
> +	if (!fingerprint[1])
> +		die_errno(_("failed to get the ssh fingerprint for key '%s'"),
> +			  signing_key);
> +
> +	return strbuf_detach(fingerprint[1], NULL);
> +}
> +
>  /* Returns the first public key from an ssh-agent to use for signing */
>  static char *get_default_ssh_signing_key(void)
>  {
> @@ -490,6 +525,17 @@ static char *get_default_ssh_signing_key(void)
>  	return "";
>  }
>  
> +/* Returns a textual but unique representation ot the signing key */

"ot" -> "of".

> +const char *get_signing_key_id(void)
> +{
> +	if (!strcmp(use_format->name, "ssh")) {
> +		return get_ssh_key_fingerprint(get_signing_key());
> +	} else {
> +		/* GPG/GPGSM only store a key id on this variable */
> +		return get_signing_key();

Hmph, we could ask gpg key fingerprint if we wanted to, and we
cannot tell why "ssh" side needs a separate "key" and "key_id"
while "gpg" side does not.  Hopefully it will become clear as we
read on?

Again, dispatching on use_format->name looked rather unexpected.

> +	}
> +}
> +
>  const char *get_signing_key(void)
>  {
>  	if (configured_signing_key)
> diff --git a/gpg-interface.h b/gpg-interface.h
> index feac4decf8b..beefacbb1e9 100644
> --- a/gpg-interface.h
> +++ b/gpg-interface.h
> @@ -64,6 +64,12 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
>  int git_gpg_config(const char *, const char *, void *);
>  void set_signing_key(const char *);
>  const char *get_signing_key(void);
> +
> +/*
> + * Returns a textual unique representation of the signing key in use
> + * Either a GPG KeyID or a SSH Key Fingerprint
> + */
> +const char *get_signing_key_id(void);
>  int check_signature(const char *payload, size_t plen,
>  		    const char *signature, size_t slen,
>  		    struct signature_check *sigc);
> diff --git a/send-pack.c b/send-pack.c
> index 5a79e0e7110..50cca7e439b 100644
> --- a/send-pack.c
> +++ b/send-pack.c
> @@ -341,13 +341,13 @@ static int generate_push_cert(struct strbuf *req_buf,
>  {
>  	const struct ref *ref;
>  	struct string_list_item *item;
> -	char *signing_key = xstrdup(get_signing_key());
> +	char *signing_key_id = xstrdup(get_signing_key_id());
>  	const char *cp, *np;
>  	struct strbuf cert = STRBUF_INIT;
>  	int update_seen = 0;
>  
>  	strbuf_addstr(&cert, "certificate version 0.1\n");
> -	strbuf_addf(&cert, "pusher %s ", signing_key);
> +	strbuf_addf(&cert, "pusher %s ", signing_key_id);

Ahh...  We do not send GPG fingerprint in push certificate but you
want to use the fingerprint when signing with SSH keys, and that is
where the need for signing_key_id comes from?

OK.

Re: [PATCH v6 5/9] ssh signing: parse ssh-keygen output and verify signatures

[Junio C Hamano]

"Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Fabian Stelzer <fs@gigacodes.de>
>
> to verify a ssh signature we first call ssh-keygen -Y find-principal to

"to" -> "To".

> look up the signing principal by their public key from the
> allowedSignersFile. If the key is found then we do a verify. Otherwise
> we only validate the signature but can not verify the signers identity.
>
> Verification uses the gpg.ssh.allowedSignersFile (see ssh-keygen(1) "ALLOWED
> SIGNERS") which contains valid public keys and a principal (usually
> user@domain). Depending on the environment this file can be managed by
> the individual developer or for example generated by the central
> repository server from known ssh keys with push access. If the
> repository only allows signed commits / pushes then the file can even be
> stored inside it.
>
> To revoke a key put the public key without the principal prefix into
> gpg.ssh.revocationKeyring or generate a KRL (see ssh-keygen(1)
> "KEY REVOCATION LISTS"). The same considerations about who to trust for
> verification as with the allowedSignersFile apply.
>
> Using SSH CA Keys with these files is also possible. Add
> "cert-authority" as key option between the principal and the key to mark
> it as a CA and all keys signed by it as valid for this CA.
>
> Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
> ---
>  builtin/receive-pack.c |   2 +
>  gpg-interface.c        | 179 ++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 180 insertions(+), 1 deletion(-)

A lot of additions to support a new system, all looking quite
straight-forward.

> @@ -78,7 +84,7 @@ static struct gpg_format gpg_format[] = {
>  		.program = "ssh-keygen",
>  		.verify_args = ssh_verify_args,
>  		.sigs = ssh_sigs,
> -		.verify_signed_buffer = NULL, /* TODO */
> +		.verify_signed_buffer = verify_ssh_signed_buffer,
>  		.sign_buffer = sign_buffer_ssh
>  	},
>  };

Nice.

> @@ -343,6 +349,165 @@ static int verify_gpg_signed_buffer(struct signature_check *sigc,
>  	return ret;
>  }
>  
> +static void parse_ssh_output(struct signature_check *sigc)
> +{
> +	const char *line, *principal, *search;
> +
> +	/*
> +	 * ssh-keysign output should be:
> +	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
> +	 * Good "git" signature for PRINCIPAL WITH WHITESPACE with RSA key SHA256:FINGERPRINT

A bit unfortunate line that is overly long.  These two are not
mutually exclusive two different choices, but one is a special case
of the other, no?  How about phrasing it like so instead?

	/*
	 * ssh-keysign output should be:
	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
         *
	 * or for valid but unknown keys:
	 * Good "git" signature with RSA key SHA256:FINGERPRINT
         *
	 * Note that "PRINCIPAL" can contain whitespace, "RSA" and
	 * "SHA256" part could be a different token that names of
	 * the algorithms used, and "FINGERPRINT" is a hexadecimal
         * string.  By finding the last occurence of " with ", we can
         * reliably parse out the PRINCIPAL.
	 */

> +	 * or for valid but unknown keys:
> +	 * Good "git" signature with RSA key SHA256:FINGERPRINT
> +	 */
> +	sigc->result = 'B';
> +	sigc->trust_level = TRUST_NEVER;
> +
> +	line = xmemdupz(sigc->output, strcspn(sigc->output, "\n"));
> +
> +	if (skip_prefix(line, "Good \"git\" signature for ", &line)) {
> +		/* Valid signature and known principal */
> +		sigc->result = 'G';
> +		sigc->trust_level = TRUST_FULLY;
> +
> +		/* Search for the last "with" to get the full principal */
> +		principal = line;
> +		do {
> +			search = strstr(line, " with ");
> +			if (search)
> +				line = search + 1;
> +		} while (search != NULL);
> +		sigc->signer = xmemdupz(principal, line - principal - 1);
> +		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);

OK.  This does not care the "RSA" part, which is future resistant.
It assumes the <algo>:<fingerprint> comes after literal " key ",
which I think is a reasonable thing to do.

However, we never checked if the line has "key" in it, so
strstr(line, "key") + 4 may not be pointing at where this code
expects.

> +		sigc->key = xstrdup(sigc->fingerprint);
> +	} else if (skip_prefix(line, "Good \"git\" signature with ", &line)) {
> +		/* Valid signature, but key unknown */
> +		sigc->result = 'G';
> +		sigc->trust_level = TRUST_UNDEFINED;
> +		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);
> +		sigc->key = xstrdup(sigc->fingerprint);

Likewise, I guess.

> +	}
> +}
> +
> +static int verify_ssh_signed_buffer(struct signature_check *sigc,
> +				    struct gpg_format *fmt, const char *payload,
> +				    size_t payload_size, const char *signature,
> +				    size_t signature_size)
> +{
> +	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
> +	struct tempfile *buffer_file;
> +	int ret = -1;
> +	const char *line;
> +	size_t trust_size;
> +	char *principal;
> +	struct strbuf ssh_keygen_out = STRBUF_INIT;
> +	struct strbuf ssh_keygen_err = STRBUF_INIT;
> +
> +	if (!ssh_allowed_signers) {
> +		error(_("gpg.ssh.allowedSignersFile needs to be configured and exist for ssh signature verification"));
> +		return -1;
> +	}
> +
> +	buffer_file = mks_tempfile_t(".git_vtag_tmpXXXXXX");
> +	if (!buffer_file)
> +		return error_errno(_("could not create temporary file"));
> +	if (write_in_full(buffer_file->fd, signature, signature_size) < 0 ||
> +	    close_tempfile_gently(buffer_file) < 0) {
> +		error_errno(_("failed writing detached signature to '%s'"),
> +			    buffer_file->filename.buf);
> +		delete_tempfile(&buffer_file);
> +		return -1;
> +	}
> +
> +	/* Find the principal from the signers */
> +	strvec_pushl(&ssh_keygen.args, fmt->program,
> +		     "-Y", "find-principals",
> +		     "-f", ssh_allowed_signers,
> +		     "-s", buffer_file->filename.buf,
> +		     NULL);
> +	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_keygen_out, 0,
> +			   &ssh_keygen_err, 0);
> +	if (ret && strstr(ssh_keygen_err.buf, "usage:")) {
> +		error(_("ssh-keygen -Y find-principals/verify is needed for ssh signature verification (available in openssh version 8.2p1+)"));
> +		goto out;
> +	}
> +	if (ret || !ssh_keygen_out.len) {
> +		/* We did not find a matching principal in the allowedSigners - Check
> +		 * without validation */
> +		child_process_init(&ssh_keygen);
> +		strvec_pushl(&ssh_keygen.args, fmt->program,
> +			     "-Y", "check-novalidate",
> +			     "-n", "git",
> +			     "-s", buffer_file->filename.buf,
> +			     NULL);
> +		ret = pipe_command(&ssh_keygen, payload, payload_size,
> +				   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
> +	} else {
> +		/* Check every principal we found (one per line) */
> +		for (line = ssh_keygen_out.buf; *line;
> +		     line = strchrnul(line + 1, '\n')) {
> +			while (*line == '\n')
> +				line++;
> +			if (!*line)
> +				break;
> +
> +			trust_size = strcspn(line, "\n");
> +			principal = xmemdupz(line, trust_size);
> +
> +			child_process_init(&ssh_keygen);
> +			strbuf_release(&ssh_keygen_out);
> +			strbuf_release(&ssh_keygen_err);
> +			strvec_push(&ssh_keygen.args, fmt->program);
> +			/* We found principals - Try with each until we find a
> +			 * match */

                        /*
                         * Do not forget our multi-line comment
                         * style, please.
                         */

> +			strvec_pushl(&ssh_keygen.args, "-Y", "verify",
> +				     "-n", "git",
> +				     "-f", ssh_allowed_signers,
> +				     "-I", principal,
> +				     "-s", buffer_file->filename.buf,
> +				     NULL);
> +
> +			if (ssh_revocation_file) {
> +				if (file_exists(ssh_revocation_file)) {
> +					strvec_pushl(&ssh_keygen.args, "-r",
> +						     ssh_revocation_file, NULL);
> +				} else {
> +					warning(_("ssh signing revocation file configured but not found: %s"),
> +						ssh_revocation_file);
> +				}
> +			}
> +
> +			sigchain_push(SIGPIPE, SIG_IGN);
> +			ret = pipe_command(&ssh_keygen, payload, payload_size,
> +					   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
> +			sigchain_pop(SIGPIPE);
> +
> +			FREE_AND_NULL(principal);
> +
> +			ret &= starts_with(ssh_keygen_out.buf, "Good");

This is somewhat unusual construct in our codebase, I suspect.  And
probably is even wrong.  Didn't you mean

			if (!ret)
				ret = starts_with(...);

instead?  Surely, when pipe_command() failed, it is likely that
ssh_keygen_out may not have anything useful, and checking what the
first up-to-four bytes of it contain unconditionally may be cheap
enough, but the person reading the code would expect you to peek
into the result only when you actually got the result, no?

> +			if (ret == 0)
> +				break;

It's more common to do

			if (!ret)
				break;

in our codebase; in other words, we prefer not to compare with
literal 0, like "if (x == 0)" or "if (y != 0)".

Thanks.

Re: [PATCH v6 1/9] ssh signing: preliminary refactoring and clean-up

[Jonathan Tan]

I think this patch set is beyond the "is this a good idea in general"
phase (in particular, I think that being able to sign Git commits by
using SSH infrastructure is very useful), so I'll proceed to critiquing
the commits in more detail.

Firstly, in commit messages, the left side of the colon is usually the
name of the subsystem - in this case, "gpg-interface".

> To be able to implement new signing formats this commit:
>  - makes the sigc structure more generic by renaming "gpg_output" to
>    "output"
>  - introduces function pointers in the gpg_format structure to call
>    format specific signing and verification functions
>  - moves format detection from verify_signed_buffer into the check_signature
>    api function and calls the format specific verify
>  - renames and wraps sign_buffer to handle format specific signing logic
>    as well

I think that this commit should be further split up - in particular, it
is hard for reviewers to verify that there is no difference in
functionality before and after this commit. I already spotted one
difference - perhaps there are more. For me, splitting the above 4
points into 4 commits would be an acceptable split.

> diff --git a/gpg-interface.c b/gpg-interface.c
> index 127aecfc2b0..31cf4ba3938 100644
> --- a/gpg-interface.c
> +++ b/gpg-interface.c
> @@ -15,6 +15,12 @@ struct gpg_format {
>  	const char *program;
>  	const char **verify_args;
>  	const char **sigs;
> +	int (*verify_signed_buffer)(struct signature_check *sigc,
> +				    struct gpg_format *fmt, const char *payload,
> +				    size_t payload_size, const char *signature,
> +				    size_t signature_size);
> +	int (*sign_buffer)(struct strbuf *buffer, struct strbuf *signature,
> +			   const char *signing_key);
>  };

[snip]

>  static struct gpg_format gpg_format[] = {
> -	{ .name = "openpgp", .program = "gpg",
> -	  .verify_args = openpgp_verify_args,
> -	  .sigs = openpgp_sigs
> +	{
> +		.name = "openpgp",
> +		.program = "gpg",
> +		.verify_args = openpgp_verify_args,
> +		.sigs = openpgp_sigs,
> +		.verify_signed_buffer = verify_gpg_signed_buffer,
> +		.sign_buffer = sign_buffer_gpg,
>  	},
> -	{ .name = "x509", .program = "gpgsm",
> -	  .verify_args = x509_verify_args,
> -	  .sigs = x509_sigs
> +	{
> +		.name = "x509",
> +		.program = "gpgsm",
> +		.verify_args = x509_verify_args,
> +		.sigs = x509_sigs,
> +		.verify_signed_buffer = verify_gpg_signed_buffer,
> +		.sign_buffer = sign_buffer_gpg,
>  	},
>  };

I think that verify_signed_buffer and sign_buffer should replace
verify_args and sigs, not be alongside them. In particular, I see from
later patches that a new entry will be introduced for SSH, and the
corresponding new "verify" function does not use verify_args or sigs.

> @@ -279,10 +300,6 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
>  		return -1;
>  	}
>  
> -	fmt = get_format_by_sig(signature);
> -	if (!fmt)
> -		BUG("bad signature '%s'", signature);

Here is the difference in functionality that I spotted. Here, lack of
fmt is fatal...

> @@ -309,35 +330,32 @@ static int verify_signed_buffer(const char *payload, size_t payload_size,
>  int check_signature(const char *payload, size_t plen, const char *signature,
>  	size_t slen, struct signature_check *sigc)
>  {
> -	struct strbuf gpg_output = STRBUF_INIT;
> -	struct strbuf gpg_status = STRBUF_INIT;
> +	struct gpg_format *fmt;
>  	int status;
>  
>  	sigc->result = 'N';
>  	sigc->trust_level = -1;
>  
> -	status = verify_signed_buffer(payload, plen, signature, slen,
> -				      &gpg_output, &gpg_status);
> -	if (status && !gpg_output.len)
> -		goto out;
> -	sigc->payload = xmemdupz(payload, plen);
> -	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
> -	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
> -	parse_gpg_output(sigc);
> +	fmt = get_format_by_sig(signature);
> +	if (!fmt)
> +		return error(_("bad/incompatible signature '%s'"), signature);

...but here it is not.

Re: [PATCH v6 2/9] ssh signing: add ssh signature format and signing using ssh keys

[Jonathan Tan]

Keep the commit titles to 50 characters or fewer. E.g.:

  gpg-interface: teach "ssh" gpg.format

> implements the actual sign_buffer_ssh operation and move some shared
> cleanup code into a strbuf function

Capitalization and punctuation.

> Set gpg.format = ssh and user.signingkey to either a ssh public key
> string (like from an authorized_keys file), or a ssh key file.
> If the key file or the config value itself contains only a public key
> then the private key needs to be available via ssh-agent.
> 
> gpg.ssh.program can be set to an alternative location of ssh-keygen.
> A somewhat recent openssh version (8.2p1+) of ssh-keygen is needed for
> this feature. Since only ssh-keygen is needed it can this way be
> installed seperately without upgrading your system openssh packages.

I notice that end-user documentation (e.g. about gpg.ssh.program) is in
its own patch, but could that be added as functionality is being
implemented? That makes it easier for reviewers to understand what's
being implemented in each patch.

> @@ -463,12 +482,30 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
>  	return use_format->sign_buffer(buffer, signature, signing_key);
>  }
>  
> +/*
> + * Strip CR from the line endings, in case we are on Windows.
> + * NEEDSWORK: make it trim only CRs before LFs and rename
> + */
> +static void remove_cr_after(struct strbuf *buffer, size_t offset)
> +{
> +	size_t i, j;
> +
> +	for (i = j = offset; i < buffer->len; i++) {
> +		if (buffer->buf[i] != '\r') {
> +			if (i != j)
> +				buffer->buf[j] = buffer->buf[i];
> +			j++;
> +		}
> +	}
> +	strbuf_setlen(buffer, j);
> +}

In the future, I would prefer refactoring like this to be in its own
patch. For the moment, this should probably be called "remove_cr" (no
"after" as CRs are removed wherever they are in the string).

> +static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
> +			   const char *signing_key)
> +{
> +	struct child_process signer = CHILD_PROCESS_INIT;
> +	int ret = -1;
> +	size_t bottom, keylen;
> +	struct strbuf signer_stderr = STRBUF_INIT;
> +	struct tempfile *key_file = NULL, *buffer_file = NULL;
> +	char *ssh_signing_key_file = NULL;
> +	struct strbuf ssh_signature_filename = STRBUF_INIT;
> +
> +	if (!signing_key || signing_key[0] == '\0')
> +		return error(
> +			_("user.signingkey needs to be set for ssh signing"));
> +
> +	if (starts_with(signing_key, "ssh-")) {
> +		/* A literal ssh key */
> +		key_file = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
> +		if (!key_file)
> +			return error_errno(
> +				_("could not create temporary file"));
> +		keylen = strlen(signing_key);
> +		if (write_in_full(key_file->fd, signing_key, keylen) < 0 ||
> +		    close_tempfile_gently(key_file) < 0) {
> +			error_errno(_("failed writing ssh signing key to '%s'"),
> +				    key_file->filename.buf);
> +			goto out;
> +		}
> +		ssh_signing_key_file = key_file->filename.buf;
> +	} else {
> +		/* We assume a file */
> +		ssh_signing_key_file = expand_user_path(signing_key, 1);
> +	}

A config that has 2 modes of operation is quite error-prone, I think.
For example, a user could put a path starting with "ssh-" (admittedly
unlikely since it would usually be an absolute path, but not
impossible). And also from an implementation point of view, here the
"ssh-" is case-sensitive, but in a future patch, there is a "ssh-" that
is case-insensitive.

Can this just always take a path?

> +	if (ret) {
> +		if (strstr(signer_stderr.buf, "usage:"))
> +			error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
> +
> +		error("%s", signer_stderr.buf);
> +		goto out;
> +	}

Checking for "usage:" seems fragile -  a binary running in a different
locale might emit a different string, and legitimate output may somehow
contain the string "usage:". Is there a different way to detect a
version mismatch?

Re: [PATCH v6 3/9] ssh signing: retrieve a default key from ssh-agent

[Jonathan Tan]

> if user.signingkey is not set and a ssh signature is requested we call
> ssh-add -L and use the first key we get

[snip]

> +/* Returns the first public key from an ssh-agent to use for signing */
> +static char *get_default_ssh_signing_key(void)
> +{
> +	struct child_process ssh_add = CHILD_PROCESS_INIT;
> +	int ret = -1;
> +	struct strbuf key_stdout = STRBUF_INIT;
> +	struct strbuf **keys;
> +
> +	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
> +	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
> +	if (!ret) {
> +		keys = strbuf_split_max(&key_stdout, '\n', 2);
> +		if (keys[0])
> +			return strbuf_detach(keys[0], NULL);
> +	}
> +
> +	strbuf_release(&key_stdout);
> +	return "";
> +}

Could the commit message have a better explanation of why we need this?
(Also, I would think that the command being run needs to be configurable
instead of being just the first "ssh-add" in $PATH, and the parsing of
the output should be more rigorous. But this is moot if we don't need
this feature in the first place.)

Re: [PATCH v6 5/9] ssh signing: parse ssh-keygen output and verify signatures

[Jonathan Tan]

> to verify a ssh signature we first call ssh-keygen -Y find-principal to
> look up the signing principal by their public key from the
> allowedSignersFile. If the key is found then we do a verify. Otherwise
> we only validate the signature but can not verify the signers identity.

Is this the same behavior as GPG signing in Git?

> Verification uses the gpg.ssh.allowedSignersFile (see ssh-keygen(1) "ALLOWED
> SIGNERS") which contains valid public keys and a principal (usually
> user@domain). Depending on the environment this file can be managed by
> the individual developer or for example generated by the central
> repository server from known ssh keys with push access. If the
> repository only allows signed commits / pushes then the file can even be
> stored inside it.

Storing the allowedSignersFile in the repo is technically possible even
if the repository does not allow signed commits/pushes, right? I would
reword the last sentence as "This file is usually stored outside the
repository, but if the repository only allows signed commits/pushes, the
user might choose to store it in the repository".

> Using SSH CA Keys with these files is also possible. Add
> "cert-authority" as key option between the principal and the key to mark
> it as a CA and all keys signed by it as valid for this CA.

Is this functionality provided by SSH? I don't see "cert-authority"
anywhere in the diff below.

Also, I notice that the tests are all provided at the end. I think that
it would be better for the tests to be incrementally provided along with
the commit that introduces the relevant functionality, so it is clearer
to the reviewers how it is supposed to work (and also for us to observe
test coverage).

> diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
> index a34742513ac..62b11c5f3a4 100644
> --- a/builtin/receive-pack.c
> +++ b/builtin/receive-pack.c
> @@ -131,6 +131,8 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
>  {
>  	int status = parse_hide_refs_config(var, value, "receive");
>  
> +	git_gpg_config(var, value, NULL);
> +
>  	if (status)
>  		return status;

Check the return value of git_gpg_config() to see if that config was
processed by that function - if yes, we can return early.

> +static void parse_ssh_output(struct signature_check *sigc)
> +{
> +	const char *line, *principal, *search;
> +
> +	/*
> +	 * ssh-keysign output should be:
> +	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
> +	 * Good "git" signature for PRINCIPAL WITH WHITESPACE with RSA key SHA256:FINGERPRINT
> +	 * or for valid but unknown keys:
> +	 * Good "git" signature with RSA key SHA256:FINGERPRINT
> +	 */

Is this "ssh-keysign" or "ssh-keygen" output?

Also, is this output documented to be stable even across locales?

> +	sigc->result = 'B';
> +	sigc->trust_level = TRUST_NEVER;

A discussion of trust levels should also be in the commit message or
user documentation.

> +	if (!strcmp(var, "gpg.ssh.revocationFile")) {

The "F" in "revocationFile" has to be lowercase. (If tests were
included, as I suggested above, it might have been easier to catch
this.)

Re: [PATCH v6 1/9] ssh signing: preliminary refactoring and clean-up

[Junio C Hamano]

Jonathan Tan <jonathantanmy@google.com> writes:

>> -	fmt = get_format_by_sig(signature);
>> -	if (!fmt)
>> -		BUG("bad signature '%s'", signature);
>
> Here is the difference in functionality that I spotted. Here, lack of
> fmt is fatal...
>
>> +	fmt = get_format_by_sig(signature);
>> +	if (!fmt)
>> +		return error(_("bad/incompatible signature '%s'"), signature);
>
> ...but here it is not.

While I was reviewing this step, I was assumign that the callers
would respond to this error return appropriately.  If it is not the
case, then we do have to fix that.

The original's use of BUG() is wrong in any case, I woud think.  The
"signature" there is an external input, so we were reporting a data
error (it should have been die()), not a program logic error.

Thanks.

Re: [PATCH v6 2/9] ssh signing: add ssh signature format and signing using ssh keys

[Junio C Hamano]

Jonathan Tan <jonathantanmy@google.com> writes:

>> +/*
>> + * Strip CR from the line endings, in case we are on Windows.
>> + * NEEDSWORK: make it trim only CRs before LFs and rename
>> + */
>> +static void remove_cr_after(struct strbuf *buffer, size_t offset)
>> +{
>> +	size_t i, j;
>> +
>> +	for (i = j = offset; i < buffer->len; i++) {
>> +		if (buffer->buf[i] != '\r') {
>> +			if (i != j)
>> +				buffer->buf[j] = buffer->buf[i];
>> +			j++;
>> +		}
>> +	}
>> +	strbuf_setlen(buffer, j);
>> +}
>
> In the future, I would prefer refactoring like this to be in its own
> patch. For the moment, this should probably be called "remove_cr" (no
> "after" as CRs are removed wherever they are in the string).

You have me to blame for that "after".  It was meant to signal that
CR's before the given "offset" are retained.

> A config that has 2 modes of operation is quite error-prone, I think.
> For example, a user could put a path starting with "ssh-" (admittedly
> unlikely since it would usually be an absolute path, but not
> impossible). And also from an implementation point of view, here the
> "ssh-" is case-sensitive, but in a future patch, there is a "ssh-" that
> is case-insensitive.
>
> Can this just always take a path?

Sensible simplification, I guess.

Thanks for a careful review.

>> +	if (ret) {
>> +		if (strstr(signer_stderr.buf, "usage:"))
>> +			error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
>> +
>> +		error("%s", signer_stderr.buf);
>> +		goto out;
>> +	}
>
> Checking for "usage:" seems fragile -  a binary running in a different
> locale might emit a different string, and legitimate output may somehow
> contain the string "usage:". Is there a different way to detect a
> version mismatch?

Re: [PATCH v6 1/9] ssh signing: preliminary refactoring and clean-up

[Fabian Stelzer]

On 29.07.21 02:58, Junio C Hamano wrote:
> Jonathan Tan <jonathantanmy@google.com> writes:
> 
>>> -	fmt = get_format_by_sig(signature);
>>> -	if (!fmt)
>>> -		BUG("bad signature '%s'", signature);
>>
>> Here is the difference in functionality that I spotted. Here, lack of
>> fmt is fatal...
>>
>>> +	fmt = get_format_by_sig(signature);
>>> +	if (!fmt)
>>> +		return error(_("bad/incompatible signature '%s'"), signature);
>>
>> ...but here it is not.
> 
> While I was reviewing this step, I was assumign that the callers
> would respond to this error return appropriately.  If it is not the
> case, then we do have to fix that.
> 
> The original's use of BUG() is wrong in any case, I woud think.  The
> "signature" there is an external input, so we were reporting a data
> error (it should have been die()), not a program logic error.
> 
> Thanks.
> 

My intention was to actually change this behavior (i should have made 
that clear in the commit message). When the current git version 
encounters an unknown signature format it will BUG() and leave the user 
with a coredump.
I assume that some repos will have multiple different signature formats 
in their history in the future and the effect i would have liked was to 
only mark the commits with unknown signatures as bad/unknown when using 
git log --show-signature for example.
I have checked all the calls to check_signature and unfortunately the 
result check is really inconsistent. Some ignore it completely, others 
check but still then dereference fields from the sigcheck struct.
So for now a die() is probably the correct way to go.

In the future we might want to differentiate between verifying a single 
commit (in which case we can die()) and a list of commits. Or fix all 
the calls to check_signature to check the return code.

Thanks

Re: [PATCH v6 0/9] ssh signing: Add commit & tag signing/verification via SSH keys using ssh-keygen

[Bagas Sanjaya]

On 29/07/21 02.36, Fabian Stelzer via GitGitGadget wrote:
> openssh 8.7 will add valid-after, valid-before options to the allowed keys
> keyring. This allows us to pass the commit timestamp to the verification
> call and make key rollover possible and still be able to verify older
> commits. Set valid-after=NOW when adding your key to the keyring and set
> valid-before to make it fail if used after a certain date. Software like
> gitolite/github or corporate automation can do this automatically when ssh
> push keys are addded / removed I will add this feature in a follow up patch
> afterwards.
> 

I read above as "set valid-before=<some date> and valid-after=<now> to 
limit key validity for several days from now". Is it right?

-- 
An old man doll... just what I always wanted! - Clara

Re: [PATCH v6 4/9] ssh signing: provide a textual representation of the signing key

[Fabian Stelzer]

On 28.07.21 23:34, Junio C Hamano wrote:
> "Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> From: Fabian Stelzer <fs@gigacodes.de>
>>
>> for ssh the user.signingkey can be a filename/path or even a literal ssh pubkey.
>> in push certs and textual output we prefer the ssh fingerprint instead.
> 
> These sentences that lack the initial capital letters would look
> unusual and distracting in our "git log --no-merges" stream.
> 

Fixed

>>   
>> +/* Returns a textual but unique representation ot the signing key */
> 
> "ot" -> "of".
> 

Fixed

>> +const char *get_signing_key_id(void)
>> +{
>> +	if (!strcmp(use_format->name, "ssh")) {
>> +		return get_ssh_key_fingerprint(get_signing_key());
>> +	} else {
>> +		/* GPG/GPGSM only store a key id on this variable */
>> +		return get_signing_key();
> 
> Hmph, we could ask gpg key fingerprint if we wanted to, and we
> cannot tell why "ssh" side needs a separate "key" and "key_id"
> while "gpg" side does not.  Hopefully it will become clear as we
> read on?
> 
> Again, dispatching on use_format->name looked rather unexpected.
> 

i will put the two strcmp(ssh) ifs on my todo list to also replace with 
a callback function.

>> -	char *signing_key = xstrdup(get_signing_key());
>> +	char *signing_key_id = xstrdup(get_signing_key_id());
>>   	const char *cp, *np;
>>   	struct strbuf cert = STRBUF_INIT;
>>   	int update_seen = 0;
>>   
>>   	strbuf_addstr(&cert, "certificate version 0.1\n");
>> -	strbuf_addf(&cert, "pusher %s ", signing_key);
>> +	strbuf_addf(&cert, "pusher %s ", signing_key_id);
> 
> Ahh...  We do not send GPG fingerprint in push certificate but you
> want to use the fingerprint when signing with SSH keys, and that is
> where the need for signing_key_id comes from?
> 
> OK.
> 

Previously the push certs contained the configured user.signingkey as 
"pusher". For gpg this is usually the key id. (e.g.: ABCDEF01)
For ssh signing this can now be a file path which would not make much 
sense to put into the push cert. I did not use the public ssh key since 
the file can also contain an encrypted private key, so i would have to 
ask ssh-keygen for the public key anyway.
Since the ssh fingerprint more resembles the gpg key id i used it instead.

As far as i understand the actual contents of the "pusher" header is not 
really relevant for the push-cert. The unique nonce is important but 
besides that its just a signed text blob.
If we don't care about having a local users file path in this header we 
could drop this commit.

Re: [PATCH v6 1/9] ssh signing: preliminary refactoring and clean-up

[Fabian Stelzer]

On 29.07.21 00:32, Jonathan Tan wrote:
> I think this patch set is beyond the "is this a good idea in general"
> phase (in particular, I think that being able to sign Git commits by
> using SSH infrastructure is very useful), so I'll proceed to critiquing
> the commits in more detail.

Thanks for your help.

> 
> Firstly, in commit messages, the left side of the colon is usually the
> name of the subsystem - in this case, "gpg-interface".
> 

The docs call this "name of the component you're working on". Since this 
code does not actually change any gpg functionality (at least it should 
not) i think gpg-interface in the commits might be a bit misleading.


>> To be able to implement new signing formats this commit:
>>   - makes the sigc structure more generic by renaming "gpg_output" to
>>     "output"
>>   - introduces function pointers in the gpg_format structure to call
>>     format specific signing and verification functions
>>   - moves format detection from verify_signed_buffer into the check_signature
>>     api function and calls the format specific verify
>>   - renames and wraps sign_buffer to handle format specific signing logic
>>     as well
> 
> I think that this commit should be further split up - in particular, it
> is hard for reviewers to verify that there is no difference in
> functionality before and after this commit. I already spotted one
> difference - perhaps there are more. For me, splitting the above 4
> points into 4 commits would be an acceptable split.
> 

The rename can of course be easily separated. The others would probably 
require some code in between commits that's not present in the final 
patch result to make the individual commits compile / work. Otherwise 
those would only add unused code with the last commit then actually 
using everything. I don't think that would make things easier to verify, 
would it?


> [snip]
> 
>>   static struct gpg_format gpg_format[] = {
>> -	{ .name = "openpgp", .program = "gpg",
>> -	  .verify_args = openpgp_verify_args,
>> -	  .sigs = openpgp_sigs
>> +	{
>> +		.name = "openpgp",
>> +		.program = "gpg",
>> +		.verify_args = openpgp_verify_args,
>> +		.sigs = openpgp_sigs,
>> +		.verify_signed_buffer = verify_gpg_signed_buffer,
>> +		.sign_buffer = sign_buffer_gpg,
>>   	},
>> -	{ .name = "x509", .program = "gpgsm",
>> -	  .verify_args = x509_verify_args,
>> -	  .sigs = x509_sigs
>> +	{
>> +		.name = "x509",
>> +		.program = "gpgsm",
>> +		.verify_args = x509_verify_args,
>> +		.sigs = x509_sigs,
>> +		.verify_signed_buffer = verify_gpg_signed_buffer,
>> +		.sign_buffer = sign_buffer_gpg,
>>   	},
>>   };
> 
> I think that verify_signed_buffer and sign_buffer should replace
> verify_args and sigs, not be alongside them. In particular, I see from
> later patches that a new entry will be introduced for SSH, and the
> corresponding new "verify" function does not use verify_args or sigs.
> 

I kept the verify_args since i would either have to duplicate the 
verify_gpg_signed_buffer for gpg & gpgsm or have an if within deciding 
what format to use.
Also this is something that we might want to make a configuration option 
in the future and pass to ssh-keygen as well (there are a couple of -O 
options for it users might want)

sigs is still needed for the parse_signed_buffer api function.

Re: [PATCH v6 3/9] ssh signing: retrieve a default key from ssh-agent

[Fabian Stelzer]

On 29.07.21 00:48, Jonathan Tan wrote:
>> if user.signingkey is not set and a ssh signature is requested we call
>> ssh-add -L and use the first key we get
> 
> [snip]
> 
> Could the commit message have a better explanation of why we need this?
> (Also, I would think that the command being run needs to be configurable
> instead of being just the first "ssh-add" in $PATH, and the parsing of
> the output should be more rigorous. But this is moot if we don't need
> this feature in the first place.)
> 

How about:
If user.signingkey ist not set and a ssh signature is requested we call 
ssh-add -L und use the first key we get. This enables us to activate 
commit signing globally for all users on a shared server when ssh-agent 
forwarding is already in use without the need to touch an individual 
users gitconfig.

Maybe a general gpg.ssh.signingKeyDefaultCommand that we call and use 
the first returned line as key would be useful and achieve the same goal 
without having this default for everyone.
On the other hand i like having less configuration / good defaults for 
individual users. But I'm coming from a corporate environment, not an 
open source project.

Re: [PATCH v6 5/9] ssh signing: parse ssh-keygen output and verify signatures

[Fabian Stelzer]

On 28.07.21 23:55, Junio C Hamano wrote:
> "Fabian Stelzer via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> From: Fabian Stelzer <fs@gigacodes.de>
>>
>> to verify a ssh signature we first call ssh-keygen -Y find-principal to
> 
> "to" -> "To".

fixed

[snip]

>> +	/*
>> +	 * ssh-keysign output should be:
>> +	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
>> +	 * Good "git" signature for PRINCIPAL WITH WHITESPACE with RSA key SHA256:FINGERPRINT
> 
> A bit unfortunate line that is overly long.  These two are not
> mutually exclusive two different choices, but one is a special case
> of the other, no?  How about phrasing it like so instead?
> 
> 	/*
> 	 * ssh-keysign output should be:
> 	 * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
>           *
> 	 * or for valid but unknown keys:
> 	 * Good "git" signature with RSA key SHA256:FINGERPRINT
>           *
> 	 * Note that "PRINCIPAL" can contain whitespace, "RSA" and
> 	 * "SHA256" part could be a different token that names of
> 	 * the algorithms used, and "FINGERPRINT" is a hexadecimal
>           * string.  By finding the last occurence of " with ", we can
>           * reliably parse out the PRINCIPAL.
> 	 */
> 

Yes, it's a special case that makes it a bit harder to parse. I will 
change the comment like you suggested. That makes it clear.

>> +		/* Search for the last "with" to get the full principal */
>> +		principal = line;
>> +		do {
>> +			search = strstr(line, " with ");
>> +			if (search)
>> +				line = search + 1;
>> +		} while (search != NULL);
>> +		sigc->signer = xmemdupz(principal, line - principal - 1);
>> +		sigc->fingerprint = xstrdup(strstr(line, "key") + 4);
> 
> OK.  This does not care the "RSA" part, which is future resistant.
> It assumes the <algo>:<fingerprint> comes after literal " key ",
> which I think is a reasonable thing to do.
> 
> However, we never checked if the line has "key" in it, so
> strstr(line, "key") + 4 may not be pointing at where this code
> expects.
> 

Hmm. What would i do if i don't find "key"? Still mark the signature as 
valid an just leave fingerprint & key empty?

>> +			/* We found principals - Try with each until we find a
>> +			 * match */
> 
>                          /*
>                           * Do not forget our multi-line comment
>                           * style, please.
>                           */
> 

fixed. clang-format wordwrapped those :/


>> +
>> +			ret &= starts_with(ssh_keygen_out.buf, "Good");
> 
> This is somewhat unusual construct in our codebase, I suspect.  And
> probably is even wrong.  Didn't you mean
> 
> 			if (!ret)
> 				ret = starts_with(...);
> 
> instead?  Surely, when pipe_command() failed, it is likely that
> ssh_keygen_out may not have anything useful, and checking what the
> first up-to-four bytes of it contain unconditionally may be cheap
> enough, but the person reading the code would expect you to peek
> into the result only when you actually got the result, no?

you are correct. we don't need to look at the output when the command fails.

> 
>> +			if (ret == 0)
>> +				break;
> 
> It's more common to do
> 
> 			if (!ret)
> 				break;
> 

changed.

Thanks