git - change the signature of a signed commit

December 12, 2024

Change the signature of the last commit:

$ git commit --amend --no-edit -n -S <keyid>
  --amend:      Replace the tip of the current branch by creating a new commit.
  --no-edit:    Use the selected commit message without launching an editor. The commit message won't change.
  -n:           Bypass the pre-commit and commit-msg hooks.
  -S:           [--gpg-sign]: GPG-sign commits. The keyid argument is optional and defaults to the committer identity[.]

# Example:
$ git commit --amend --no-edit -n -S D7E9F238FD9F7A68BBA4F57AA59953E41FEBB5F2

# Note: The <keyid> is optional.

Change the signature of older commits:

Interactively git rebase everything until my_branch (or any hash).
--exec is applied to each and every commit in the range.

$ git rebase --exec 'git commit --amend --no-edit -n -S' -i my_branch

The result of the above one-liner can also be accomplished in a more manual manner:

$ git rebase -i my_branch

pick 12345 commit message
exec git commit --amend --no-edit -n -S
pick 67890 commit message
exec git commit --amend --no-edit -n -S

Always sign commits: * Add to the git configuration:

$ git config commit.gpgsign true

A gpg configuration could look like this - including a specific gpg key:

$ git config -l
...
user.signingkey=A17BEB9EBF763280A57B0C8DA7F8A1CFB1B0FDH4
commit.gpgsign=true
...

Helpful commands:

$ git log --show-signature