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Tanmay Jain
014f8d1bbe
* feat(provenance): add SLSA provenance and attestation signing libraries Add internal/provenance for deriving in-toto subjects from Packer artifacts, building SLSA Provenance v1 predicates, wrapping in-toto statements, and best-effort git/CI source detection. Add internal/attestation for DSSE envelope handling and a pluggable Signer/Verifier backend supporting key (local PEM), kms (aws/gcp/ azure/hashivault), and keyless (Sigstore Fulcio) modes, plus Sigstore bundle handling and DSSE/policy verification. Add the supporting module dependencies in go.mod/go.sum. * feat(provenance): add provenance post-processor Add the opt-in "provenance" post-processor that runs after a build, derives subjects from the artifact, emits DSSE-wrapped SLSA provenance (and optional SBOM) attestations, signs them via the configured signing backend, and writes sidecar files (including *.sigstore.json bundles in keyless mode). Register it in the core post-processor set. The provenance enable flag is a tri-state so an unset value stays enabled through HCL2 decoding instead of being silently disabled. * feat(provenance): add verify-attestation command Add "packer verify-attestation" to verify signed DSSE attestations against key, KMS, and keyless policy inputs, including optional Sigstore bundle checks for Rekor and timestamp evidence. Register the command in the CLI. * docs(provenance): add reference CI workflows and changelog Add reference GitHub Actions workflows under examples/ci for SLSA L2 keyless signing and L3-compatible delegated signing * fix: lint and tests * Added docs for Provenance PostProcessor
Provenance CI reference workflows
These are copy-paste reference workflows for producing SLSA provenance with the
Packer provenance post-processor. They are not wired into this
repository's own CI — copy them into your project's .github/workflows/
directory and adapt the template and artifact paths.
SLSA levels and Packer
SLSA Build levels are mostly properties of the build platform, not the build tool. Packer is a tool, so its reach is:
| SLSA Build level | Requirement | Packer's role | What Packer provides |
|---|---|---|---|
| L1 | Provenance exists and is distributed | Fully in Packer | Provenance generation |
| L2 | Provenance signed by a hosted platform | Packer signs via CI OIDC identity | Keyless signing in CI |
| L3 | Hardened platform; build steps cannot reach the signing key | Platform property; Packer is compatible | Delegated-signing pattern |
| L4 | — | Not defined in SLSA v1.0 | — |
Packer generates SLSA Provenance v1 and reaches Build L1, and L2 when run on a hosted CI with keyless signing. L3 is a property of the build platform: it requires the signing key to be unreachable by the build steps. Packer does not confer L3 on its own, but the delegated-signing pattern below is compatible with an L3 platform.
Workflows
github-actions-l2-keyless.yml— L2: Packer signs provenance keyless using the workflow's OIDC identity, uploads to Rekor, and verifies the signed attestation withpacker verify-attestation.github-actions-l3-delegated.yml— L3-compatible: the build job only builds and publishes a digest; provenance generation and signing are delegated to an isolated reusable workflow so the build steps cannot reach the signing material.