ct-provenance-keeper

name

ct-provenance-keeper

description

Generates in-toto v1 attestations, SLSA-level provenance records, SBOMs (CycloneDX or SPDX), and sigstore/cosign signatures for published artifacts. Invoked by ct-artifact-publisher as a delegation for signing and attestation. Records the full commit, then build, then artifact, then attestation, then registry chain in .cleo/releases.json and rejects publishes whose digest does not match the attestation. Triggers when artifact-publish reaches the provenance step or when a release needs SLSA L2+ attestation.

Provenance Keeper

Overview

Sub-protocol of ct-artifact-publisher. Generates cryptographic evidence for every published artifact: SHA-256 digests, in-toto Statement v1 attestations, SBOMs (CycloneDX 1.5+ or SPDX 2.3+), and signatures via sigstore/cosign keyless or gpg. Records the full commit-to-registry chain in .cleo/releases.json, verifies chain integrity before publishing attestations, and refuses to bind an attestation to an artifact whose digest does not match.

Core Principle

Provenance is non-falsifiable or it is not provenance.

Immutable Constraints

ID	Rule	Enforcement
PROV-001	Chain MUST be recorded from source commit to published artifact.	record_release() writes the full chain; missing links set metadata.completeness: incomplete.
PROV-002	SHA-256 digest MUST be computed for every produced artifact.	Digest binds to the in-toto subject; mismatch exits 93.
PROV-003	Attestation MUST be in in-toto Statement v1 format.	Validator rejects other schemas; exit 94.
PROV-004	SLSA Build Level MUST be recorded (L1 minimum).	Level stored in releases.json; L1 is the floor.
PROV-005	Provenance record MUST be stored in .cleo/releases.json via record_release().	Missing record fails validation.
PROV-006	Chain integrity MUST be verified before publishing the attestation.	verify_provenance_chain() runs before emit.
PROV-007	Manifest entry MUST set agent_type: "provenance".	Validator rejects any other value.

SLSA Compliance Levels

The skill records the achieved SLSA level in every provenance record. A minimum of L1 is mandatory; L3 is the target for npm + docker releases via OIDC keyless signing.

Level	Requirements	Typical achievement
L1	Provenance exists, basic metadata recorded.	Any run of the skill produces at least L1.
L2	Signed provenance, build on a hosted platform.	Requires sigstore keyless OR gpg signing + CI build.
L3	Non-falsifiable provenance, hermetic build environment.	CI runs with isolated runners and OIDC-bound identity (this is the default for npm + docker releases).
L4	Reproducible builds, two-party review, all deps signed.	Rare; requires pinned dependencies and second-reviewer sign-off.

Full requirements and per-level checklists are in references/slsa.md.

Signing Methods

Three methods are supported; the skill selects based on release.security.provenance.signing.method:

Method	Command	Output	When to use
sigstore (default, keyless)	cosign sign-blob --yes --output-signature <sig> --output-certificate <cert> <artifact>	.sig + .pem + Rekor transparency log entry	Default. Requires OIDC identity (CI).
sigstore (key)	cosign sign-blob --key <ref> <artifact>	.sig	Offline or self-hosted without OIDC.
gpg	gpg --detach-sign --armor -u <key-id> <artifact>	.asc	Legacy workflows, regulated environments.
none	(skip)	(none)	SLSA L1 only; explicit opt-out.

The decision matrix, including GPG_KEY_ID and OIDC trusted-publisher setup, lives in references/signing.md.

Provenance Chain

The skill walks and records the full chain for every release:

commit  -->  build  -->  artifact  -->  attestation  -->  registry
  |           |            |               |                |
  sha        log         digest        signature        published
  |           |            |               |                |
source    env capture   sha256 file    cert bundle        URL

Each link MUST reference the previous link's output. The chain is append-only in releases.json: no link is ever modified after creation. Missing links are recorded as incomplete, never elided. Offline verification MUST be possible — every digest is stored locally, not fetched per verification.

SBOM Generation

SBOMs are mandatory for artifacts with runtime dependencies (docker images, npm packages) and recommended for standalone binaries.

Format	Spec	Use case
CycloneDX	1.5+	Default. Machine-readable JSON.
SPDX	2.3+	Compliance-focused (FedRAMP, regulated environments).

Storage locations:

• .cleo/sbom/<artifact-name>-<version>.cdx.json (CycloneDX)
• .cleo/sbom/<artifact-name>-<version>.spdx.json (SPDX)
• <artifact>.sbom.json (bundled alongside the artifact)

Generate with syft packages dir:. -o cyclonedx-json or equivalent.

.cleo/releases.json Record Structure

Each release appends a record in the following shape. The skill MUST populate every field that can be known; the remainder stay as explicit nulls (never absent).

{
  "version": "v2026.4.5",
  "commitSha": "3a2f1e9c4b8d7e6a5f2c1d0e9f8a7b6c5d4e3f2a",
  "gitTag": "v2026.4.5",
  "buildInvocationId": "gh-actions-12345",
  "builder": { "id": "https://github.com/actions/runner" },
  "artifacts": [
    {
      "type": "npm-package",
      "name": "@cleocode/core",
      "sha256": "a1b2c3...",
      "registry": "https://registry.npmjs.org",
      "publishedAt": "2026-04-06T19:50:00Z",
      "attestation": ".cleo/attestations/v2026.4.5-core.intoto.jsonl",
      "signature": {
        "method": "sigstore",
        "keyless": true,
        "transparencyLog": {
          "index": "123456789",
          "url": "https://rekor.sigstore.dev"
        }
      }
    }
  ],
  "sbom": {
    "format": "CycloneDX",
    "specVersion": "1.5",
    "path": ".cleo/sbom/cleocode-core-2026.4.5.cdx.json"
  },
  "slsaLevel": "SLSA_BUILD_LEVEL_3",
  "chainVerified": true,
  "recordedAt": "2026-04-06T19:51:00Z"
}

Integration

Validate the provenance entry through cleo check protocol:

cleo check protocol \
  --protocolType provenance \
  --taskId T4902 \
  --hasAttestation true \
  --hasSbom true

Exit code 0 = provenance record is complete and verified. Exit code 90 = invalid config. Exit code 91 = signing key missing. Exit code 92 = signature invalid. Exit code 93 = digest mismatch (refuse to bind attestation). Exit code 94 = attestation format or subject is invalid.

Anti-Patterns

Pattern	Problem	Solution
Skipping digest computation	Chain integrity cannot be verified (violates PROV-002)	Always compute SHA-256 for every artifact before attesting
Hardcoding signing keys in config	Key exposure, credentials in VCS	Reference env vars by name; actual keys stay in the environment
Generating attestation without matching digest	Attestation binds to the wrong artifact (violates PROV-006)	Compute the digest first, then attest; refuse to attest a mismatched pair
Publishing artifact before signing	Cannot retrofit signatures after publish	Sign before push; the sub-protocol order is build → sign → publish
Modifying provenance records after creation	Breaks immutability, corrupts the audit trail	.cleo/releases.json is append-only; never rewrite old entries
Skipping SBOM for artifacts with dependencies	Hidden supply-chain risk	Generate CycloneDX for every artifact with runtime deps
Using SHA-1 or MD5 for digests	Cryptographically broken; non-compliant with SLSA	SHA-256 is mandatory; SHA-512 is optional for high-security contexts
Storing private keys inside .cleo/	Key compromise if the repo is leaked	Keys live in the keystore / OIDC / HSM — never in the worktree

Critical Rules Summary

1. Compute SHA-256 for every artifact; bind the attestation to the exact digest.
2. Produce attestations in in-toto Statement v1 format only.
3. Record the full chain in .cleo/releases.json via record_release().
4. Verify chain integrity before publishing the attestation.
5. Default to sigstore keyless signing via OIDC in CI; fall back to gpg only when configured.
6. Generate CycloneDX SBOMs for every artifact with runtime dependencies.
7. .cleo/releases.json is append-only; never mutate past entries.
8. Validate every run via cleo check protocol --protocolType provenance.