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Verifying releases with cosign

Releases are signed with cosign as part of the release process. The build produces additional attestation bundles during this process, which can be used to verify both binaries and Docker images.

For binaries, bundles are present in the tar.gz archive created by the release. For images, bundles are stored in the OCI registry alongside the image itself.

Obtaining cosign

Download from the sigstore/cosign project on GitHub, and verify the release as you prefer.

Release identity

The certificates issued by the release are issued for the GitHub Actions OIDC provider, and the identity is the executed workflow, referenced by the Git tag being built.

Field Format
Issuer https://token.actions.githubusercontent.com
Identity https://github.com/jamestelfer/chinmina-bridge/.github/workflows/release.yaml@refs/tags/<tag name>

Important

Git tags are not static: they can be updated to point to a different commit SHA. Examine the recorded claims for the exact commit.

There are claims recorded for the exact commit of both the workflow that produced the artifact and the commit that the artifact source was built from.

Verifying an image release

Images are published to Docker Hub in the chinmina repository. The images are named chinmina-bridge and are labelled with their release tag (vX.Y.Z).

An image can be verified with the following cosign command:

TAG=vX.Y.Z \
cosign verify "chinmina/chinmina-bridge:$TAG" \
  --certificate-oidc-issuer 'https://token.actions.githubusercontent.com' \
  --certificate-identity "https://github.com/jamestelfer/chinmina-bridge/.github/workflows/release.yaml@refs/tags/$TAG" \
  --output text

# more details are available if you use JSON output:
TAG=vX.Y.Z \
cosign verify "chinmina/chinmina-bridge:$TAG" \
  --certificate-oidc-issuer 'https://token.actions.githubusercontent.com' \
  --certificate-identity "https://github.com/jamestelfer/chinmina-bridge/.github/workflows/release.yaml@refs/tags/$TAG" \
  --output json | jq

The path .[].optional.Bundle.Payload.logIndex is the index entry in the public transparency log, recording the details of the signing event. The details of the event can be found at: https://search.sigstore.dev/.

Verifying the binary releases

Download and extract the tar.gz of the binary you're interested in. The artifacts present include both the binary itself (named chinmina-bridge) and the signing bundle (chinmina-bridge.cosign.bundle).

# declare the release details for download
TAG=vX.Y.Z
ARCH=arm64

# download the binary
curl -L -o chinmina-bridge_linux_${ARCH}.tar.gz \
  https://github.com/jamestelfer/chinmina-bridge/releases/download/${TAG}/chinmina-bridge_linux_${ARCH}.tar.gz

# extract to the current directory
tar xvf chinmina-bridge_linux_${ARCH}.tar.gz

# verify
cosign verify-blob \
  chinmina-bridge \
  --bundle chinmina-bridge.cosign.bundle \
  --certificate-oidc-issuer 'https://token.actions.githubusercontent.com' \
  --certificate-identity "https://github.com/jamestelfer/chinmina-bridge/.github/workflows/release.yaml@refs/tags/$TAG"

# peek the details
jq -r '.rekorBundle.Payload.logIndex | "https://search.sigstore.dev/?logIndex=\(.)"' < chinmina-bridge.cosign.bundle

# open the URL that is shown