Sign git commits in GitHub Actions

README.md

Sign git commits with GPG in GitHub Actions

• Generate a GPG key (see here)

gpg --full-generate-key

• Save the GPG passphrase to secrets as GPG_KEY_PASSPHRASE

• Save the GPG key ID (ex. 3AA5C34371567BD2)

gpg --list-secret-keys --keyid-format=long
/Users/hubot/.gnupg/secring.gpg
------------------------------------
sec   4096R/3AA5C34371567BD2 2016-03-10 [expires: 2017-03-10]
uid                          Michael West (GitHub GPG key) <michael.west@example.com>
ssb   4096R/42B317FD4BA89E7A 2016-03-10

to secrets as GPG_KEY_ID

• Save the name (ex. Michael West) to secrets as GIT_COMMITTER_NAME

• Save the email (ex. michael.west@example.com) to secrets as GIT_COMMITTER_EMAIL

• Save the GPG key (base64)

gpg --export-secret-keys 3AA5C34371567BD2 | base64

to secrets as GPG_KEY

• Add the following (preliminary) steps

steps:
  - name: Import GPG key
    run: echo $GPG_KEY | base64 --decode | gpg --batch --import
    env:
      GPG_KEY: ${{ secrets.GPG_KEY }}

  - name: Add the custom gpg siging program that passes the passphrase to the gpg CLI
    run: |
      rm -rf /tmp/gpg.sh
      echo '#!/bin/bash' >> /tmp/gpg.sh
      echo 'gpg --batch --pinentry-mode=loopback --passphrase $GPG_KEY_PASSPHRASE $@' >> /tmp/gpg.sh
      chmod +x /tmp/gpg.sh

  - name: Setup git
    run: |
      git config commit.gpgsign true
      git config user.signingkey $GPG_KEY_ID
      git config gpg.program /tmp/gpg.sh
    env:
      GPG_KEY_ID: ${{ secrets.GPG_KEY_ID }}

Example

steps:
  - name: Test sign
    run: |
      echo 'Something' >> test.md
      git add test.md
      git commit -m "test commit"
      git verify-commit $( git rev-parse HEAD )
    env:
      GPG_KEY_PASSPHRASE: ${{ secrets.GPG_KEY_PASSPHRASE }}
      GIT_COMMITTER_NAME: ${{ secrets.GIT_COMMITTER_NAME }}
      GIT_COMMITTER_EMAIL: ${{ secrets.GIT_COMMITTER_EMAIL }}
      GIT_AUTHOR_NAME: SomeBot
      GIT_AUTHOR_EMAIL: somebot@example.com