Software supply chain attacks targeting container images have surged, making image provenance and integrity verification essential for production Kubernetes deployments. Sigstore provides keyless signing and verification for container images, while SLSA (Supply-chain Levels for Software Artifacts) defines a framework of increasingly rigorous build integrity guarantees.
Implementing Container Supply Chain Security
Cosign, part of the Sigstore project, signs container images using ephemeral keys backed by certificate authorities and transparency logs. This keyless approach eliminates the burden of managing long-lived signing keys while providing cryptographic proof of image origin and build environment through verifiable provenance attestations.
SLSA levels define a maturity model from Level 1 (documented build process) through Level 4 (hermetic, reproducible builds on hardened infrastructure). Achieving SLSA Level 3 with GitHub Actions or Tekton Chains ensures that build artifacts have tamper-evident provenance and were produced by a version-controlled, auditable pipeline.
Kubernetes admission controllers like Kyverno and OPA Gatekeeper can enforce policies requiring valid Sigstore signatures and minimum SLSA levels before admitting images to the cluster. This creates a cryptographic chain of trust from source code through build to deployment, making supply chain attacks detectable and preventable.