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From: Phillip Wood <>
To: 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 09:33:09 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20230120090331.37dxkko6bgxbjae7@fs>

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?
> Hi,
> 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.

Best Wishes


> Best regards,
> Fabian
>> Best Wishes
>> Phillip
>>> Best
>>> — 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
>>>>>> that
>>>>>> 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
>>>> Phillip

  reply	other threads:[~2023-01-23  9:33 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 [this message]
2023-01-23 10:02             ` Fabian Stelzer
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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