Secure your supply chain using Cosign and Sigstore. This 2026 checklist covers keyless signing, Rekor log verification, and OCI security. Full breakdown.
What Sigstore and Cosign actually verify
Sigstore is a public infrastructure for signing software artifacts and recording those signatures in a transparency log. Cosign is the CLI and library most teams use to create and check those signatures against container images and other OCI artifacts. Together they answer a practical question at deploy time: did this image come from the publisher you expect, and has anyone tampered with it since it was signed?
Integrity verification is not the same as vulnerability scanning. A clean scan only tells you about known defects in the contents. A valid signature plus a matching log entry tells you the bits match what the signer published and that the signing event was recorded where others can audit it. You still need both layers; neither replaces the other.
Keyless signing without long-lived secrets
Traditional signing relies on private keys you generate, store, and rotate. Keyless signing with Sigstore short-circuits that lifecycle. At sign time, the signer authenticates to an identity provider, receives a short-lived certificate bound to that identity, signs the artifact digest, and discards the private material. Verifiers later check the certificate chain and the signature against the artifact, not a key you had to distribute yourself.
For CI pipelines this removes a common failure mode: a leaked long-lived signing key that can mint “valid” artifacts forever. Your verification policy should still pin who is allowed to sign—typically a specific identity or issuer claim—so that any authenticated party cannot silently replace your releases. Treat identity claims as part of the trust policy, not as optional metadata.
Rekor log verification
Rekor is Sigstore’s append-only transparency log. When Cosign signs, it can upload an entry that binds the signature, certificate, and artifact digest. On verify, Cosign can fetch that entry and check inclusion so you are not relying only on a signature blob that might have been copied or replayed offline.
- Confirm the log entry’s artifact digest matches the image or blob you are about to run.
- Confirm the signing identity in the entry matches your allowlist for that repository or product.
- Fail closed when the log cannot be reached or inclusion proof fails—do not “best effort” past it in production gates.
- Keep a record of the entry IDs or digests you accepted so incidents can be traced later.
Transparency does not stop a compromised identity from signing once. It makes that signing event hard to hide and easy to revoke from policy after discovery.
OCI security checklist for day-to-day use
Apply Cosign and Sigstore at the points where artifacts move: build, push, pull, and deploy. Sign the digest of the image you push, not a mutable tag. In the registry, prefer immutable digests in deployment manifests so a tag flip cannot bypass a prior verification. In the cluster or runtime, enforce signature and identity checks before the image is scheduled—admission policies and pull-time hooks are the usual places.
Operationally, document the exact Cosign verify flags and identity constraints your team requires, wire them into CI and production the same way, and treat unsigned or policy-failing artifacts as blocked, not warned. That checklist—keyless identity, Rekor inclusion, digest-based OCI references, and fail-closed enforcement—is the minimum useful bar for supply-chain integrity with Sigstore in 2026.