Git now has the ability to sign commits with git commit -S, which is great, but sometimes I forget the flag to commit, and sometimes I mail myself patches which I apply with am, and that command doesn't have a flag for signing.

Is there a way to add a signature to an already recorded commit?

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    For the record, you can tell git to always sign commits via configuration: git config commit.gpgsign true. – nicooga Oct 23 '18 at 12:47
  • @nicooga I wish your comment had more upvotes so I noticed this earlier. I've had to pull up this question at least half a dozen times, and setting that flag would've saved me a bunch of time. – Michael Ziluck Sep 16 '19 at 21:28
  1. Go into interactive rebase mode.
  2. Add the following line after each commit you want to sign

    exec git commit --amend --no-edit -S

This will run this command after picking each commit.


Easier way to do this is:

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

This rebases everything till development (or any hash) and you don't have to copy paste after every commit.

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    Oh I wish I had found this sooner. I read so many things, even from GitHub themselves, saying that you can't resign old commits. This proves that completely false! I could have saved hundreds of commits, which I have now squashed. Oh well... thanks for sharing! I made an alias out of this. resign = "!re() { git rebase --exec 'git commit --amend --no-edit -n -S' -i $1; }; re" becomes git resign HASH – BarryMode Jul 6 '17 at 21:16
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    This should be common knowledge! You have done a great service for humanity (no sarc!)! – hopeseekr Feb 3 '18 at 20:25
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    There's no reason to rebase at all. Just run git commit --amend --no-edit -n -S. – Quolonel Questions Mar 6 '18 at 1:51
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    Doesn’t this change the history, requiring a git push --force? – Steve Apr 14 '18 at 17:21
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    @Steve Yes, requiring force push depends on what commits you change and whether or not they are pushed already. – Shubham Chaudhary Apr 19 '18 at 6:34

Signing a commit changes its contents, so more recent commits depending on it will change their hash.

If you just want to sign the most recent commit, git commit -S --amend will work.

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  • Most of the time signing the most recent commit, or even creating an empty signed commit on top of it will be sufficient to guarantee authenticity. Git commits are a Merkle tree, so modification of any ancestor commit requires rewrite of its descendants, thus invalidating the signature. – gronostaj Jul 22 at 12:38

I use git rebase -i --root ( see Rewriting History ) and change pick to edit.

Then I use git commit -S --amend --no-edit && git rebase --continue (on Windows) for each commits.

This is manually sign for each commits. I hope we will found better solution.

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  • I have my home directory as a git repo (for dotfiles). Some programs interactively pick up changes as its rebasing, funny to see the history being replayed live. It's slow enough because signing is slow – Avindra Goolcharan Jan 22 '17 at 1:33

If you need to GPG sign all commits SINCE a particular commit on the current branch, you can use the following instead:

git filter-branch --commit-filter 'git commit-tree -S "$@";' <COMMIT>..HEAD

Where <COMMIT> is the commit id (e.g. abc123e5).

This has the added benefit that it does not disturb the commit metadata (including commit date). The commit hashes will change, though (since it's a digest of the contents of each commit, and a signature is being added to each commit).

If you also would like to stop getting prompted for your GPG passphrase on every commit, also see this answer: https://askubuntu.com/a/805550

NOTE: Switching from gpg to gpg2 for GIT signing will require you to re-import your private key in GPG 2.

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I also stumbled on the same problem and here is my solution:

git rebase -i --root --exec 'git commit --amend --no-edit --no-verify -S'

this will sign all of my commits from the first initial commit and also bypass commit hook that I set up using husky. No need to change pick to edit.

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If you want to filter only specific commits and sign only them you can use filter-branch:

git filter-branch --commit-filter 'if [ "$GIT_COMMITTER_EMAIL" = "user@domain.com" ];
  then git commit-tree -S "$@";
  else git commit-tree "$@";
  fi' HEAD

This is useful if, for some reason, you want to sign only your own commits.

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If no filtering on commit is needed, then it is preferred to use rebase than filter-branch:

git rebase -i master --exec 'git commit --amend --no-edit --no-verify -S --reset-author'

Else, you can leave untouched the commits you don't own.
Set the following alias in ~/.gitconfig (replace your@address.com with your email address):

resign = "!_() { : git checkout ; [ \"$#\" -eq 0 ] && echo 'Usage: resign <rev-list>' && exit 2; \
                   git filter-branch --commit-filter ' \
                   if [ \"$GIT_COMMITTER_EMAIL\" = \"your@address.com\" ]; then git commit-tree -S \"$@\"; else git commit-tree \"$@\"; fi' $1; }; _"

Then for instance, to resign all your commits in the current branch pulled from master, do:

git resign master..

Credits to previous answers by BarryMode and Roberto Leinardi

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here's the one I use for all commits, yes it will re-write history:

git rebase --exec 'git commit --amend --no-edit -n -S' -i --root
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To sign off last N commits, you can also do:

git rebase HEAD~N --signoff

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  • Note that --signoff is different than signing (e.g. when using git commit -S). AFAIK signoff just adds a line like Signed-off-by <author> <email> to the commit message. – stian Sep 18 at 7:33

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