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Sign commits with SSH keys (FREE)

Use SSH keys to sign Git commits in the same manner as GPG signed commits. When you sign commits with SSH keys, GitLab uses the SSH public keys associated with your GitLab account to cryptographically verify the commit signature. If successful, GitLab displays a Verified label on the commit.

You may use the same SSH keys for git+ssh authentication to GitLab and signing commit signatures as long as their usage type is Authentication & Signing. It can be verified on the page for adding an SSH key to your GitLab account.

For more information about managing the SSH keys associated with your GitLab account, see Use SSH keys to communicate with GitLab.

Configure Git to sign commits with your SSH key

After you create an SSH key and add it to your GitLab account or generate it using a password manager, configure Git to begin using the key.

Prerequisites:

  • Git 2.34.0 or newer.

  • OpenSSH 8.0 or newer.

    NOTE: OpenSSH 8.7 has broken signing functionality. If you are on OpenSSH 8.7, upgrade to OpenSSH 8.8.

  • A SSH key with the usage type of either Authentication & Signing or Signing. The SSH key must be one of these types:

To configure Git to use your key:

  1. Configure Git to use SSH for commit signing:

    git config --global gpg.format ssh

  2. Specify which SSH key should be used as the signing key, changing the filename (here, ~/.ssh/examplekey) to the location of your key. The filename may differ, depending on how you generated your key:

    git config --global user.signingkey ~/.ssh/examplekey

Sign commits with your SSH key

Prerequisites:

To sign a commit:

  1. Use the -S flag when signing your commits:

    git commit -S -m "My commit msg"

  2. Optional. If you don't want to type the -S flag every time you commit, tell Git to sign your commits automatically:

    git config --global commit.gpgsign true

  3. If your SSH key is protected, Git prompts you to enter your passphrase.

  4. Push to GitLab.

  5. Check that your commits are verified. Signature verification uses the allowed_signers file to associate emails and SSH keys. For help configuring this file, read Verify commits locally.

Verify commits

You can review commits for a merge request, or for an entire project, to confirm they are signed:

  1. To review commits for a project:
    1. On the top bar, select Main menu > Projects and find your project.
    2. On the left sidebar, select Repository > Commits.
  2. To review commits for a merge request:
    1. On the top bar, select Main menu > Projects and find your project.
    2. On the left sidebar, select Merge requests, then select your merge request.
    3. Select Commits.
  3. Identify the commit you want to review. Signed commits show either a Verified or Unverified badge, depending on the verification status of the signature. Unsigned commits do not display a badge.
  4. To display the signature details for a commit, select Verified. GitLab shows the SSH key's fingerprint.

Verify commits locally

To verify commits locally, create an allowed signers file for Git to associate SSH public keys with users:

  1. Create an allowed signers file:

    touch allowed_signers

  2. Configure the allowed_signers file in Git:

    git config gpg.ssh.allowedSignersFile "$(pwd)/allowed_signers"

  3. Add your entry to the allowed signers file. Use this command to add your email address and public SSH key to the allowed_signers file. Replace <MY_KEY> with the name of your key, and ~/.ssh/allowed_signers with the location of your project's allowed_signers file:

    # Modify this line to meet your needs.
# Declaring the `git` namespace helps prevent cross-protocol attacks.
echo "$(git config --get user.email) namespaces=\"git\" $(cat ~/.ssh/<MY_KEY>.pub)" >> ~/.ssh/allowed_signers

    The resulting entry in the allowed_signers file contains your email address, key type, and key contents, like this:

    example@gitlab.com namespaces="git" ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAmaTS47vRmsKyLyK1jlIFJn/i8wdGQ3J49LYyIYJ2hv

  4. Repeat the previous step for each user who you want to verify signatures for. Consider checking this file in to your Git repository if you want to locally verify signatures for many different contributors.

  5. Use git log --show-signature to view the signature status for the commits:

    $ git log --show-signature

commit e2406b6cd8ebe146835ceab67ff4a5a116e09154 (HEAD -> main, origin/main, origin/HEAD)
Good "git" signature for johndoe@example.com with ED25519 key SHA256:Ar44iySGgxic+U6Dph4Z9Rp+KDaix5SFGFawovZLAcc
Author: John Doe <johndoe@example.com>
Date:   Tue Nov 29 06:54:15 2022 -0600

    SSH signed commit

Revoke an SSH key for signing commits

Introduced in GitLab 15.9.

If an SSH key becomes compromised, revoke it. Revoking a key changes both future and past commits:

  • Past commits signed by this key are marked as unverified.
  • Future commits signed by this key are marked as unverified.

To revoke an SSH key:

  1. In the upper-right corner, select your avatar.
  2. Select Edit profile.
  3. On the left sidebar, select ({key}) SSH Keys.
  4. Select Revoke next to the SSH key you want to delete.

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