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.
Best regards,
Fabian
Best Wishes
Phillip
Best
— Adam
On Wed, Jan 18, 2023 at 3:34 PM Phillip Wood <phillip.wood123@xxxxxxxxx> 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
