# Advisory: SBOM Evidence Verification and Auditability Pipeline

**Date:** 2026-02-19
**Status:** ARCHIVED (translated to sprint tasks)
**Reviewed:** 2026-02-19

## Review Outcome

Advisory reviewed against current codebase. ~85% of proposed capabilities already exist in Stella Ops across Scanner, Signer, Attestor, Excititor, VexLens, Signals, EvidenceLocker, and ReachGraph modules.

### Capabilities Confirmed (no action needed)
- CycloneDX v1.7 SBOM generation (Scanner.Emit)
- DSSE/in-toto attestation with 10+ predicate types (Attestor.Envelope)
- Cosign-compatible signing via Signer (keyless Fulcio + keyful KMS/HSM)
- Rekor v2 anchoring with RFC 6962 tile verification and offline mode (Attestor)
- Deterministic VEX ingestion with AOC enforcement (Excititor + VexLens)
- eBPF micro-witness collection with cross-distro replay (Signals + Scanner)
- Evidence bundle storage with Merkle roots and portable audit packs (EvidenceLocker)
- Offline verification for air-gapped deployments

### Gaps Identified → Sprint Tasks Created
1. **Unified canonical_id contract** → SPRINT_20260219_009 (CID-01, CID-02)
2. **Artifact Canonical Record** → SPRINT_20260219_009 (CID-03, CID-04)
3. **Predicate Schema Registry** → SPRINT_20260219_010 (PSR-01, PSR-02)
4. **CI Assertion Pack** → SPRINT_20260219_011 (CIAP-01 through CIAP-04)
5. **Micro-witness → VEX Auto-Suppress workflow** → SPRINT_20260219_012 (MWS-01 through MWS-03)

### Proposals Explicitly Rejected
- Replacing Signer with raw cosign CLI (Signer adds PoE, quotas, DPoP/mTLS)
- Simplifying VEX handling (Excititor+VexLens+AOC is more sophisticated)
- Adopting advisory's simplified schema URIs (keep existing Stella URIs, add to registry)
- `replay_token` pointing to external S3 (keep CAS with BLAKE3 digests)

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## Original Advisory Content

(Inline advisory provided by user — full text preserved below for audit trail.)

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# Why this matters (quick primer)

* **SBOM** (software bill of materials) says what's inside an artifact.
* **DSSE / in-toto** wraps evidence in a tamper-evident envelope.
* **cosign** signs/verifies those envelopes.
* **Rekor (transparency log)** proves *when/what* was published.
* **VEX** states whether known CVEs affect your artifact.
* **Micro-witnesses** are runtime breadcrumbs you can join back to SBOM/VEX for triage.

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# NOW (MVP you can ship immediately)

**Goal:** Minimal, reproducible spine with canonical SBOMs, signed attestations, Rekor v2 anchoring, and deterministic VEX ingestion.

### Canonical SBOM & ID

1. Emit CycloneDX v1.7 JSON.
2. Canonicalize via JSON-JCS -> `canonical_id := sha256(JCS(sbom.json))`.

### DSSE attestation (SBOM predicate)

* Wrap CycloneDX content (or pointer) in an **in-toto Statement**.
* `subject[0].digest.sha256 == canonical_id`.
* Sign with cosign (**DSSE mode**).
* Capture Rekor v2 tile pointer / entry id and embed it in predicate metadata.

### Rekor v2 anchoring

* cosign publish creates the log entry.
* Store the **tile URL** and **entry id** in your artifact record.

### Deterministic VEX ingestion (OpenVEX & CycloneDX VEX)

* Ingest OpenVEX or CycloneDX VEX, map to a **canonical CycloneDX VEX** form.
* Apply strict merge rules (source priority, timestamp, exact `canonical_id` target).

### CI assertions (must-pass)

* **Unit:** `cyclonedx-cli validate ./bom.json && jcs_canonicalize ./bom.json | sha256sum` -> equals expected `canonical_id`.
* **Integration:**
  `cosign attest --predicate predicate.json --key cosign.key <subject-ref>`
  `cosign verify-attestation --key <pubkey> --type in-toto <subject-ref>`
  Rekor proof: `rekor-cli tile get --entry <entry_id>` -> inclusion proof valid.
* **VEX mapping:** jsonschema validate; assert `vulnerabilities[].analysis.state` and target match `canonical_id`.

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# LATER (scale/hardening)

* Rekor v2 **tile batching** & multi-tile reconciliation.
* **Signed micro-witness aggregation** service.
* **Deterministic replay** harness (nightly) for large volumes.
* Predicate **schema registry** (stable `predicateType` URIs, semver).

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# Flow A: Build-time SBOM + Attestation Anchor (end-to-end)

1. **Producer:** CycloneDX v1.7 -> validate -> JCS canonicalize -> `canonical_id = sha256(canonical_bytes)`.
2. **Predicate:** in-toto Statement with CycloneDX JCS content.
3. **Sign & anchor:** cosign attest -> capture Rekor tile URL and entry_id.
4. **Verify:** Fetch referrers, extract DSSE, cosign verify-attestation, recompute canonical_id, validate Rekor inclusion proof.

# Flow B: VEX -> Apply -> Runtime Micro-witness Join

1. **VEX provider:** Publish OpenVEX or CycloneDX VEX; DSSE-sign; optionally anchor in Rekor.
2. **Ingest & map:** OpenVEX -> canonical CycloneDX VEX; store DSSE + rekor_tile + provenance.
3. **Runtime micro-witness:** Emit DSSE micro-witness predicate referencing canonical_id.
4. **Correlate:** Join micro-witness DSSE with VEX; if not_affected -> auto-suppress; else surface audit pack.

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# Failure modes

* Payload > Rekor limit: Put artifact in immutable store; Rekor entry contains digest + pointer.
* Missing symbol bundle: Emit unknown_state micro-witness entry.
* Digest mismatch anywhere: fail the build.