How to sign/verify a Git tags and commits (using GnuPG)

  • git-tag@man is used to create, list, delete or verify a tag object signed with gnupg.
# install gnupg
$ sudo apt-get install gnupg2 | sudo yum install gnupg2

# from git-tag
'-s/--sign' make a GPG-signed tag, using the default e-mail address’s key
'-u/--local-user=<key-id>' make a GPG-signed tag, using the given key (defaults to 'user.signingkey')
'-v/--verify' verify the gpg signature of the given tag names.

# create key pair, asks for; note: use rng-tools to increase entropy
$ gpg --gen-key
$ gpg --list-secret-keys | grep ^sec
# either use '-u' or
$ git config --global user.signingkey [gpg-key-id]

# create a signed tab with private key
$ git tag --sign [signed-tag-name] -m "message"

# make public key available by storing as raw object and importing them
$ gpg --list-keys
$ gpg -a --export [gpg-key-id] | git hash-object -w --stdin
[object SHA]
# tag key with a name
$ git tag -a [object SHA] maintainer-pgp-pub
# import keys
$ git show maintainer-pgp-pub | gpg --import

# verify a tag signature
$ git tag --verify [signed-tag-name]

from Git Tools – Signing Your Work

  • git-commit@man record changes to the repository.
    As of 1.7.9 it’s possible to sign your commits with your private/secret key.
    As of 1.8.3 and later, “git merge” and “git pull” can be told to inspect and reject when merging a commit that does not carry a trusted GPG signature with the –verify-signatures command.
# from git-commit
'-S<keyid>/--gpg-sign=<keyid>' GPG-sign commit using the given key (defaults to 'user.signingkey')
# from git-log
'--show-signature' check the validity of a signed commit object by passing the signature to 'gpg --verify' and show the output
# from git-merge
'--verify-signatures' verify that the commits being merged have good and trusted GPG signatures and abort the merge in case they do not
'-S' sign the resulting merge commit itself

# sign commit
$ git config --global user.signingkey 8EE30EAB
$ git commit -m "message" -S

# show and verify signature in commit message
$ git log --show-signature 
gpg: Signature made ...
gpg: Good signature from ...

# verify and reject merge if has commits not signed
$ git merge --verify-signatures non-verify
fatal: Commit ab06180 does not have a GPG signature.

from Git Tools – Signing Your Work


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