allowed_signers file for SSH/git

Git 2.34 brings support for signing commits with SSH key and having a SSH-compatible smartcard, I have to try this. It likely getting more common in the future doesn’t hurt either and I have pgp-alt-wot which does about the same for PGP.

Where to find keys

• GitHub, Giteas and GitLabs expose user public keys (without useful names) when you append a .keys after their profile page
  • For example: https://github.com/Mikaela.keys https://gitea.blesmrt.net/Mikaela.keys https://gitlab.com/Mikaela.keys
• Good ideas are made to be copied, so maybe there will be more repositories like this 😉

Quick howto

I don’t mean this to be used directly, only to be took inspiration from. See the first link in further reading.

mkdir -p ~/src/gitea.blesmrt.net/Mikaela
cd ~/src/gitea.blesmrt.net/Mikaela
git clone https://gitea.blesmrt.net/Mikaela/ssh-allowed_signers.git
git config --global gpg.ssh.allowedSignersFile ~/src/gitea.blesmrt.net/Mikaela/ssh-allowed_signers/allowed_signers

Git commands, such as git verify-commit --raw HEAD or git log --show-signature, should now recognised commits signed with keys I have allowed. In the last command it’s fine to remove --global to only affect the single repository you are on (while I haven’t tested this), should that repository be something only I am signing in or something I need to verify otherwise enough to list it here.

On the last command, git config turns it into absolute path, while manually edited .gitconfig can literally have the above. I wonder if the command would understand -- before the file, but not enough to actually try it 😃

Further reading

• Caleb Hearth: Signing Git Commits with Your SSH Key (web.archive.org) inspired me to try this
• Andrew Ayer: It’s Now Possible To Sign Arbitrary Data With Your SSH Keys instructs on signing and verifying files outside of git

Forge support

• 🥇 Gitea v1.16.0 brought support for SSH signed commits on 2022-01-30. (tag)
• GitHub feedback: Allow using SSH keys to sign commits
  • TODO: notify here when it actually works, link to their guide or maybe remove the section?
• GitLab issues: Support for SSH signed commits
  • TODO: a better link when this happens