Bazaar can sign revisions using GnuPG, a Free Software implementation of the OpenPGP digital signature format. By signing commits a person wanting to make use of a branch can be confident where the code came from, assuming the GnuPG keys used can be verified. This could for example prevent worry about compromised code in the case where a server hosting Bazaar branches has been hacked into. It could also be used to verify that all code is written by a select group of people, such as if contributor agreements are needed.
Signatures are passed around with commits during branch, push, merge and other operations.
There are many guides to creating a digital signature key with GnuPG. See for example the GnuPG Handbook or the Launchpad Wiki.
To sign commits as they are made turn on the create_signatures configuration option in your bazaar.conf or locations.conf file:
Homecreate_signatures = always
When you next make a commit it will ask for the pass phrase for your GnuPG key. If you want GnuPG to remember your password ensure you have gnupg-agent installed.
To sign previous commits to a branch use sign-my-commits. This will go through all revisions in the branch and sign any which match your commit name. You can also pass the name of a contributor to sign-my-commits to sign someone else’s commits or if your GnuPG key does not match your Bazaar name and e-mail:
bzr sign-my-commits . "Amy Pond <amy@example.com>"
It will not sign commits which already have a signature.
To sign a single commit or a range of commits use the (hidden) command re-sign:
bzr re-sign -r 24
re-sign is also useful to change an existing signature.
By default Bazaar will tell GnuPG to use a key with the same user identity as the one set with whoami. To override this set gpg_signing_key in bazaar.conf or locations.conf.
gpg_signing_key=DD4D5088
gpg_signing_key=amy@example.com
Signatures can be verified with the bzr verify-signatures command. By default this will check all commits in the branch and notify that all commits are signed by known trusted signatures. If not all commits have trusted signatures it will give a summary of the number of commits which are invalid, having missing keys or are not signed.
The verify-signatures command can be given a comma separated list of key patters to specify a list of acceptable keys. It can also take a range of commits to verify in the current branch. Finally using the verbose option will list each key that is valid or authors for commits which failed:
$bzr verify-signatures -kamy -v -r 1..5
1 commit with valid signature
Amy Pond <amy@example.com> signed 4 commits
0 commits with unknown keys
1 commit not valid
1 commit by author The Doctor <doctor@example.com>
0 commits not signed
There is still a number of digital signature related features which are hoped to be added to Bazaar soon. These include bzr explorer integration and setting branches to require signatures.