BTCP-Rebase/contrib/verify-commits

Tooling for verification of PGP signed commits

This is an incomplete work in progress, but currently includes a pre-push hook script (pre-push-hook.sh) for maintainers to ensure that their own commits are PGP signed (nearly always merge commits), as well as a script to verify commits against a trusted keys list.

Using verify-commits.py safely

Remember that you can't use an untrusted script to verify itself. This means that checking out code, then running verify-commits.py against HEAD is not safe, because the version of verify-commits.py that you just ran could be backdoored. Instead, you need to use a trusted version of verify-commits prior to checkout to make sure you're checking out only code signed by trusted keys:

git fetch origin && \
  ./contrib/verify-commits/verify-commits.py origin/master && \
  git checkout origin/master

Note that the above isn't a good UI/UX yet, and needs significant improvements to make it more convenient and reduce the chance of errors; pull-reqs improving this process would be much appreciated.

Configuration files

• trusted-git-root: This file should contain a single git commit hash which is the first unsigned git commit (hence it is the "root of trust").
• trusted-sha512-root-commit: This file should contain a single git commit hash which is the first commit without a SHA512 root commitment.
• trusted-keys: This file should contain a \n-delimited list of all PGP fingerprints of authorized commit signers (primary, not subkeys).
• allow-revsig-commits: This file should contain a \n-delimited list of git commit hashes. See next section for more info.

Key expiry/revocation

When a key (or subkey) which has signed old commits expires or is revoked, verify-commits will start failing to verify all commits which were signed by said key. In order to avoid bumping the root-of-trust trusted-git-root file, individual commits which were signed by such a key can be added to the allow-revsig-commits file. That way, the PGP signatures are still verified but no new commits can be signed by any expired/revoked key. To easily build a list of commits which need to be added, verify-commits.py can be edited to test each commit with BITCOIN_VERIFY_COMMITS_ALLOW_REVSIG set to both 1 and 0, and those which need it set to 1 printed.