[PATCH v2 8/9] gpg-interface: introduce new signature format "x509" using gpgsm

[Henning Schild <henning.schild@siemens.com>]

This commit allows git to create and check x509 type signatures using
gpgsm.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
---
 Documentation/config.txt |  2 +-
 gpg-interface.c          | 10 +++++++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index c0bd80954..b6f9b47d5 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1830,7 +1830,7 @@ gpg.program::
 
 gpg.format::
 	Specifies which key format to use when signing with `--gpg-sign`.
-	Default is "openpgp", that is also the only supported value.
+	Default is "opengpg" and another possible value is "x509".
 
 gpg.<format>.program::
 	Use this to customize the program used for the signing format you
diff --git a/gpg-interface.c b/gpg-interface.c
index 65098430f..bf8d567a4 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -16,13 +16,18 @@ struct gpg_format_data {
 
 #define PGP_SIGNATURE "-----BEGIN PGP SIGNATURE-----"
 #define PGP_MESSAGE "-----BEGIN PGP MESSAGE-----"
+#define X509_SIGNATURE "-----BEGIN SIGNED MESSAGE-----"
 
-enum gpgformats { PGP_FMT };
+enum gpgformats { PGP_FMT, X509_FMT };
 struct gpg_format_data gpg_formats[] = {
 	{ .format = "openpgp", .program = "gpg",
 	  .extra_args_verify = { "--keyid-format=long" },
 	  .sigs = { PGP_SIGNATURE, PGP_MESSAGE }
 	},
+	{ .format = "x509", .program = "gpgsm",
+	  .extra_args_verify = { NULL },
+	  .sigs = { X509_SIGNATURE, NULL }
+	},
 };
 static const char *gpg_format = "openpgp";
 
@@ -182,6 +187,9 @@ int git_gpg_config(const char *var, const char *value, void *cb)
 	if (!strcmp(var, "gpg.program") || !strcmp(var, "gpg.openpgp.program"))
 		return git_config_string(&gpg_formats[PGP_FMT].program, var,
 					 value);
+	if (!strcmp(var, "gpg.x509.program"))
+		return git_config_string(&gpg_formats[X509_FMT].program, var,
+					 value);
 	return 0;
 }
 
-- 
2.16.4