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From: Fabian Stelzer <>
Cc: Adam Szkoda <>,
	Adam Szkoda via GitGitGadget <>,
Subject: Re: [PATCH] ssh signing: better error message when key not in agent
Date: Mon, 23 Jan 2023 11:02:45 +0100	[thread overview]
Message-ID: <20230123100245.3qbscxkgvbnh7ilt@fs> (raw)
In-Reply-To: <>

On 23.01.2023 09:33, Phillip Wood wrote:
>On 20/01/2023 09:03, Fabian Stelzer wrote:
>>On 18.01.2023 16:29, Phillip Wood wrote:
>>>Hi Adam
>>>I've cc'd Fabian who knows more about the ssh signing code that I do.
>>>On 18/01/2023 15:28, Adam Szkoda wrote:
>>>>Hi Phillip,
>>>>Good point!  My first thought is to try doing a stat() syscall on the
>>>>path from 'user.signingKey' to see if it exists and if not, treat it
>>>>as a public key (and pass the -U option).  If that sounds reasonable,
>>>>I can update the patch.
>>>My reading of the documentation is that user.signingKey may point 
>>>to a public or private key so I'm not sure how stat()ing would 
>>>help. Looking at the code in sign_buffer_ssh() we have a function 
>>>is_literal_ssh_key() that checks if the config value is a public 
>>>key. When the user passes the path to a key we could read the file 
>>>check use is_literal_ssh_key() to check if it is a public key (or 
>>>possibly just check if the file begins with "ssh-"). Fabian - does 
>>>that sound reasonable?
>>I have encountered the mentioned problem before as well and tried to 
>>fix it but did not find a good / reasonable way to do so. Git just 
>>passes the user.signingKey to ssh-keygen which states:
>>`The key used for signing is specified using the -f option and may 
>>refer to either a private key, or a public key with the private half 
>>available via ssh-agent(1)`
>>I don't think it's a good idea for git to parse the key and try to 
>>determine if it's public or private. The fix should probably be in 
>>openssh (different error message) but when looking into it last time 
>>i remember that the logic for using the key is quite deeply embedded 
>>into the ssh code and not easily adjusted for the signing use case. 
>>At the moment I don't have the time to look into it but the openssh 
>>code for signing is quite readable so feel free to give it a try. 
>>Maybe you find a good way.
>Thanks Fabian, perhaps the easiest way forward is for us to only pass 
>"-U" when we have a literal key in user.signingKey as we know it must 
>a be public key in that case.

Yes, i think that's a good idea as long as the `-U` flag is ignored in older 
ssh versions and shouldn't be too hard to implement. And it should work just 
as well when using `defaultKeyCommand`.


>Best Wishes
>>Best regards,
>>>Best Wishes
>>>>— Adam
>>>>On Wed, Jan 18, 2023 at 3:34 PM Phillip Wood 
>>>><> wrote:
>>>>>On 18/01/2023 11:10, Phillip Wood wrote:
>>>>>>>the agent [1].  A fix is scheduled to be released in OpenSSH 9.1. All
>>>>>>>needs to be done is to pass an additional backward-compatible option
>>>>>>>-U to
>>>>>>>'ssh-keygen -Y sign' call.  With '-U', ssh-keygen always interprets
>>>>>>>the file
>>>>>>>as public key and expects to find the private key in the agent.
>>>>>>The documentation for user.signingKey says
>>>>>>  If gpg.format is set to ssh this can contain the path to either your
>>>>>>private ssh key or the public key when ssh-agent is used.
>>>>>>If I've understood correctly passing -U will prevent users 
>>>>>>from setting
>>>>>>this to a private key.
>>>>>If there is an easy way to tell if the user has given us a public key
>>>>>then we could pass "-U" in that case.
>>>>>Best Wishes

  reply	other threads:[~2023-01-23 10:03 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-18  8:17 [PATCH] ssh signing: better error message when key not in agent Adam Szkoda via GitGitGadget
2023-01-18 11:10 ` Phillip Wood
2023-01-18 14:34   ` Phillip Wood
2023-01-18 15:28     ` Adam Szkoda
2023-01-18 16:29       ` Phillip Wood
2023-01-20  9:03         ` Fabian Stelzer
2023-01-23  9:33           ` Phillip Wood
2023-01-23 10:02             ` Fabian Stelzer [this message]
2023-01-23 16:17               ` Adam Szkoda
2023-01-24 15:26 ` [PATCH v2] " Adam Szkoda via GitGitGadget
2023-01-24 17:52   ` Junio C Hamano
2023-01-25 12:46     ` Adam Szkoda
2023-01-25 17:04       ` Junio C Hamano
2023-01-25 17:17       ` Junio C Hamano
2023-01-25 21:42       ` Eric Sunshine
2023-01-25 22:22         ` Junio C Hamano
2023-02-15  1:22           ` Eric Sunshine
2023-01-25 12:40   ` [PATCH v3] " Adam Szkoda via GitGitGadget

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