➜ sudo apt -y install git
GPG keys can be used to cryptographically sign your work when using Git for version control. This ties your identity to your work, whether that’s a commit, tag, or even a push. Gitea, GitHub, GitLab, and other popular Git hosting services support visualizing this feature when browsing changes, showing which commits are verified.
This tutorial describes how to use GPG to sign your work with Git, including command-line incantations and configuration options. It is assumed you already have a GPG key pair for your commit email. If not, I describe the exact steps in Generate a GPG Key. I also recommend you checkout my post Backup and Restore a GPG Key for ways to avoid the pain of losing your private key. The official Git Book contains a very useful section on this topic, Git Tools Signing Your Work. With that said, Ubuntu 20.04 is used as the reference system and familiarity with Git, GPG, and the command-line on Linux is assumed.
All Git configuration settings are done globally, i.e. for the user in these steps. They may just as easily be configured at the repository level.
Install Ubuntu’s git package, of course.
➜ sudo apt -y install git
Set your Git username.
➜ git config --global user.name "Ponder Stibbons"
Set your Git commit email address.
➜ git config --global user.email "firstname.lastname@example.org"
Identify the GPG secret key associated with your Git commit email address.
➜ gpg --list-secret-keys --keyid-format LONG /home/pstibbons/.gnupg/pubring.kbx ------------------------------- sec rsa4096/C8DE632E9A8A0BDD 2020-11-13 [SC] (1) F38915B041F5F1024AF95C30C8DE632E9A8A0BDD uid [ultimate] Ponder Stibbons <email@example.com> ssb rsa4096/DBCD8B98F2F9188C 2020-11-13 [E]
|1||The secret key’s id is
Configure this key as your default signing key for Git.
➜ git config --global user.signingKey C8DE632E9A8A0BDD
|The key can be provided when signing a tag, commit, or push, but it’s generally more convenient to configure your default key,|
Create a test directory for a test repository.
➜ mkdir git-signing-test
Change into the directory.
➜ cd git-signing-test
Initialize a new Git repository.
➜ git init
Create an example file.
➜ touch test
Stage this file in order to make a signed commit.
➜ git add test
-S short option to git-commit(1) to manually sign a commit.
➜ git commit -S -m 'Signed commit'
Enter the passphrase for your private key in the [Passphrase Prompt].
|If you value your sanity, check the Save in password manager box to avoid unlocking your key for every signature.|
Optionally, configure Git to sign commits by default with git-config(1) thus allowing you to omit the
➜ git config --global commit.gpgSign true
|This configuration setting applies to merge commits created when using git-merge(1) and git-pull(1).|
Check a signed commit by using the
--show-signature option with
➜ git log --show-signature -1 commit 48fafff3d24a89ec9c6d5940317588f9b10b4f43 (HEAD -> master) gpg: Signature made Sat 14 Nov 2020 09:53:05 AM CST gpg: using RSA key F38915B041F5F1024AF95C30C8DE632E9A8A0BDD gpg: Good signature from "Ponder Stibbons <firstname.lastname@example.org>" [ultimate] Author: Ponder Stibbons <email@example.com> Date: Sat Nov 14 09:53:05 2020 -0600 Signed commit
|When verifying GPG signatures, you will need to have the signer’s public key in your GPG keyring.|
Manually sign a tag with the
-s short option.
➜ git tag -s v1.0.0 -m 'Signed tag'
If desired, configure Git to sign all tags by default.
➜ git config --global tag.gpgSign true
Verify a tag with the
➜ git tag -v v1.0.0 object 48fafff3d24a89ec9c6d5940317588f9b10b4f43 type commit tag v1.0.0 tagger Ponder Stibbons <firstname.lastname@example.org> 1605369450 -0600 Signed tag gpg: Signature made Sat 14 Nov 2020 09:57:30 AM CST gpg: using RSA key F38915B041F5F1024AF95C30C8DE632E9A8A0BDD gpg: Good signature from "Ponder Stibbons <email@example.com>" [ultimate]
Create and switch to a new branch.
➜ git switch -c unsigned Switched to a new branch 'unsigned'
Create another file.
➜ touch test2
Stage the new file.
➜ git add test2
Now, commit the file without a signature.
➜ git commit --no-gpg-sign -m 'Unsigned commit'
Switch back to the main branch.
➜ git switch master Switched to branch 'master'
When using git-merge(1), sign a merge commit by passing the
-S option and verify all signatures in the merge with the
➜ git merge -S --verify-signatures unsigned fatal: Commit a3bf413 does not have a GPG signature.
Oh no! The unsigned commit in the unsigned branch couldn’t be verified so the merge failed.
To always verify signatures when merging, set the configuration option
➜ git config --global merge.verifySignatures true
|This configuration setting also applies to the git-pull(1) command.|
For git-pull(1), use the same options as with git-merge(1) to sign a merge commit and verify all signatures.
➜ git pull -S --verify-signatures
Sign pushes by using the
--signed long option with git-push(1).
This option takes more than just a true or false value.
if-asked value used here signs pushes if the server supports this feature, but doesn’t otherwise.
Signing pushed signifies intent, as Konstantin Ryabitsev describes in more detail in his article Signed git pushes.
➜ git push --signed=if-asked
Configure Git to sign pushes by default if the server supports it.
➜ git config --global push.gpgSign if-asked
Now go setup your key for use with your Git servers and start rolling out your signed commits!