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verifying-build-provenance-with-slsa-sigstore

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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.

skills/verifying-build-provenance-with-slsa-sigstore/SKILL.md

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Aug 31, 2026
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Apache-2.0

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# Verifying Build Provenance with SLSA and Sigstore

## Overview

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.
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