Summary

Currently, slsa-verifier verify-artifact requires actual artifact files as positional arguments.
I propose allowing it to also accept artifact digests instead of files.

Background

When verifying downloaded artifacts in CI using slsa-verifier verify-artifact, there are several challenges:

1. Verification takes some time
2. Dependency on slsa-verifier (requires installation)
3. Rekor access occasionally fails
4. Cannot verify in network-restricted environments where Rekor is inaccessible

A practical solution to these issues is:

1. Verify the digest once using provenance and record it in a lock file
2. Subsequently, verify artifacts against the digest recorded in the lock file

Step 1 only needs to be performed when adding or updating artifacts, while step 2 eliminates the issues mentioned above.

Digests can be obtained from files like checksums.txt or the GitHub Releases API without downloading large artifacts.
However, since slsa-verifier verify-artifact currently cannot accept digests as arguments, downloading the artifact is still required.
Supporting digest arguments would enable efficient verification in step 1.

Proposal

Allow verify-artifact to accept digest strings in the format sha256:<hex> or sha512:<hex> as positional arguments, in addition to file paths.

Example Usage

# Verify using digest instead of file
slsa-verifier verify-artifact sha256:b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9 \
  --provenance-path provenance.json \
  --source-uri github.com/org/repo

# Mix file paths and digests
slsa-verifier verify-artifact artifact.tar.gz sha256:abc123... \
  --provenance-path provenance.json \
  --source-uri github.com/org/repo

Proposed Behavior

• If an argument starts with sha256: or sha512:, treat it as a digest
• Validate the digest format (correct length, valid hex characters)
• Otherwise, treat the argument as a file path (current behavior)

Note

• sigstore/cosign’s cosign verify-blob also supports digests in the same usage
• Support SHA hash input for gh attestation verify and gh attestation download command cli/cli#12462
• I'll send a pull request for this issue