Verifies artifact signatures and SLSA provenance using Sigstore's cosign (verify, verify-attestation, verify-blob-attestation) and slsa-verifier (verify-artifact), enforcing keyless OIDC builder identity and source repo against SLSA Build levels. Use in CI/CD before deploying artifacts, when consuming third-party attestations, establishing a SLSA Build L3 pipeline, or confirming provenance during incident response or admission control.
Installer avec Codex ou Claude Copiez ce prompt, collez-le dans Codex, Claude ou un autre assistant, puis laissez-le vérifier la page du skill et l'installer pour vous.
Une commande directe contourne le prompt de vérification. Examinez la source avant de l'exécuter.
Verifies artifact signatures and SLSA provenance using Sigstore's cosign (verify, verify-attestation, verify-blob-attestation) and slsa-verifier (verify-artifact), enforcing keyless OIDC builder identity and source repo against SLSA Build levels. Use in CI/CD before deploying artifacts, when consuming third-party attestations, establishing a SLSA Build L3 pipeline, or confirming provenance during incident response or admission control.
Build-provenance verification answers a question that defeats many supply-chain attacks: was this artifact actually built from the source I think it was, by the builder I trust, without tampering? Attackers who compromise a build system, swap a compiled release, or inject a malicious step (as in the SolarWinds and 3CX incidents) produce artifacts that look legitimate but lack verifiable provenance. SLSA (Supply-chain Levels for Software Artifacts, https://slsa.dev) defines Build levels (L1–L3) describing increasing provenance integrity, and Sigstore (https://www.sigstore.dev) provides the signing and transparency infrastructure: cosign for signing/verifying artifacts and attestations, Fulcio for short-lived keyless certificates bound to an OIDC identity, and Rekor as a tamper-evident transparency log.
This skill covers verifying signatures and SLSA provenance with cosign (cosign verify, cosign verify-attestation, cosign verify-blob-attestation) and slsa-verifier (slsa-verifier verify-artifact), enforcing the builder identity (the GitHub Actions workflow that produced the artifact) and the expected source repository. Keyless verification ties trust to an OIDC issuer (e.g., https://token.actions.githubusercontent.com) and a certificate identity rather than a long-lived private key.
This maps to MITRE ATT&CK T1195 — Supply Chain Compromise (provenance verification detects/blocks tampered artifacts) and NIST CSF PR.DS-01 (the confidentiality, integrity, and availability of data-at-rest are protected; CSF 2.0 absorbed the retired 1.1 PR.DS-06 integrity-checking outcome here).
When to Use
In CI/CD before deploying or promoting any container image or release binary.
When consuming third-party artifacts (base images, Go/npm releases) that publish attestations.
When establishing a SLSA Build L3 producer pipeline and enforcing it at the consumer side.
During incident response to confirm whether a deployed artifact's provenance is intact.
In admission control (e.g., Kubernetes via policy-controller / Kyverno) to admit only verified images.
Prerequisites
cosign (Sigstore CLI):
go install github.com/sigstore/cosign/v2/cmd/cosign@latest
# or download a release binary from https://github.com/sigstore/cosign/releases
Network access to Rekor (https://rekor.sigstore.dev) and Fulcio for transparency-log verification.
The artifact plus its provenance/attestation bundle (.sigstore, .intoto.jsonl, or attached OCI attestation).
Objectives
Verify a keyless cosign signature on a container image, pinning OIDC issuer and certificate identity.
Verify a SLSA provenance attestation on an image with cosign verify-attestation --type slsaprovenance.
Verify a release binary's provenance with slsa-verifier verify-artifact, pinning source repo and tag.
Verify GitHub artifact attestations / blob bundles with cosign verify-blob-attestation.
Gate CI and admission control on successful verification; understand SLSA Build L1–L3.
MITRE ATT&CK Mapping
ID
Tactic
Technique Name
Relevance
T1195
Initial Access
Supply Chain Compromise
Verifying provenance and signatures detects artifacts that were tampered with or substituted in the build/distribution chain, preventing supply-chain compromise from reaching deployment.
Workflow
Step 1: Verify a keyless cosign signature on an image
Pin both the OIDC issuer and the certificate identity (the exact workflow that signed). A bare cosign verify without identity pinning is meaningless — anyone can sign.
Step 4: Verify a release binary with slsa-verifier
For downloadable binaries (e.g., produced by slsa-github-generator), pin the source URI and the tag. slsa-verifier checks the cryptographic signature on the provenance and that the expected builder produced it.
Document the level each consumed artifact achieves:
Build L1 — provenance exists (the build process generates it), but it may be unsigned/forgeable.
Build L2 — provenance is signed by a hosted build service.
Build L3 — provenance is non-forgeable: generated on an isolated, hardened builder where secrets are unavailable to user-defined steps (e.g., slsa-github-generator reusable workflows). Require L3 for high-trust artifacts.
