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Learn: Supply Chain — reference

Definitions, commands, and gotchas to look up. The orientation walks through how the pieces fit.

The pipeline (produce the trustworthy artifact)

Section titled “The pipeline (produce the trustworthy artifact)”

One shared, reusable workflow the platform owns (asanexample/trusted-ci/build-sign.yml) does the whole backbone; each app’s CI is a thin caller:

build → push to ECR → cosign sign (keyless) → SLSA provenance (isolated) → SBOM
  • Keyless signing — cosign / Sigstore: the CI’s GitHub Actions OIDC identity → Fulcio issues a short-lived cert → sign → logged in Rekor (public transparency log). No private key exists.
  • SLSA Build L3 provenance — generated in an isolated workflow the app team can’t write, so the build can’t forge its own.
  • SBOM — the image’s ingredient list (vuln queryability).

Inspect it yourself (real commands)

Section titled “Inspect it yourself (real commands)”
Terminal window
$ cosign tree <platform-acct>.dkr.ecr.us-east-1.amazonaws.com/team-alpha/shop-storefront@sha256:f6b37d…
└── 🔐 Signatures …          # 1 signature
└── 💾 Attestations …        # 2: SLSA provenance (v0.2) + CycloneDX SBOM


$ cosign verify … team-alpha/shop-storefront@sha256:f6b37d…
Issuer:  https://token.actions.githubusercontent.com          # keyless (GitHub Actions OIDC)
Subject: …/asanexample/trusted-ci/…/build-sign.yml@…          # the shared signer
githubWorkflowRepository: asanexample/alpha-shop            # the caller repo = the trust anchor

The trust rule

Section titled “The trust rule”

An image is trusted iff its signing cert’s githubWorkflowRepository equals the Product’s declared spec.repo (Product registry). Per-product and registry-derived, not “any signed image.” A validly-signed image from the wrong repo is rejected.

Verify at admission (the enforce half)

Section titled “Verify at admission (the enforce half)”

Kyverno fetches signature + attestations from ECR (via Pod Identity ECR-read) and enforces, per product:

  • verify-images-product-<team>-<product> — signed by the shared workflow, cert repo = the product’s repo.
  • verify-attestations-product-<team>-<product> — SLSA provenance + SBOM present.

Both Enforce on preprod — unsigned, unattested, or wrong-repo images never admit. (Platform-owned; the Policy & Admission module covers the admission mechanics. Per-product image registry scoping is separate — owned by the Environment Composition.)

Gotchas

Section titled “Gotchas”
  • Signed ≠ safe. Signing and provenance prove origin and integrity, not that the code is free of bugs or poisoned deps — a compromised upstream dependency is legitimately signed. SLSA’s threat model is explicit: it covers build tampering, not a malicious author. Layer SBOM-driven vulnerability scanning on top; signing is necessary, not sufficient.
  • Repo rename breaks trust. Trust is keyed on the repo in the cert; renaming a Product’s repo without updating spec.repo makes every new image fail verification. Update the registry with the rename.
  • Signature and attestation are separate policies. An image can be signed but missing attestations (or vice versa) — both must pass. cosign tree shows what’s actually attached.
  • Isolation is the point of L3. Provenance the build could edit is L2 at best. The isolated trusted-ci workflow (app-team-unwritable) is what makes it L3 — don’t inline it back into the app repo.

Glossary

Section titled “Glossary”
  • cosign / Sigstore — the keyless signing toolchain (Fulcio CA + Rekor transparency log).
  • keyless — signing with a short-lived OIDC identity + momentary cert instead of a stored private key.
  • SLSA provenance — a signed statement of how/where/from-what-commit an artifact was built.
  • SBOM — Software Bill of Materials; the image’s dependency inventory.
  • attestation — a signed claim about an artifact (provenance and SBOM are attestations).
  • thin caller — an app CI that invokes the shared signing workflow rather than implementing signing.

Go deeper

Section titled “Go deeper”