git.stella-ops.org/docs/product-advisories/15-Nov-2026 - embedded in-toto provenance events.md

Here’s a compact, practical way to think about embedding in‑toto provenance attestations directly inside your event payloads (instead of sidecar files), so your vuln/build graph stays temporally consistent.

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Why embed?

• Atomicity: build → publish → scan → VEX decisions share one event ID and clock; no dangling sidecars.
• Replayability: the event stream alone reproduces state (great for offline kits/audits).
• Causal joins: vulnerability findings can cite the exact provenance that led to an image/digest.

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Event shape (single, self‑contained envelope)

{
  "eventId": "01JDN2Q0YB8M…",
  "eventType": "build.provenance.v1",
  "occurredAt": "2025-11-13T10:22:31Z",
  "subject": {
    "artifactPurl": "pkg:docker/acme/api@sha256:…",
    "digest": {"sha256": "…"}
  },
  "provenance": {
    "kind": "in-toto-provenance",
    "dsse": {
      "payloadType": "application/vnd.in-toto+json",
      "payload": "<base64(in-toto Statement)>",
      "signatures": [{"keyid":"…","sig":"…"}]
    },
    "transparency": {
      "rekor": {"logIndex": 123456, "logID": "…", "entryUUID": "…"}
    }
  },
  "sig": {
    "envelope": "dsse",
    "alg": "Ed25519", 
    "bundle": { "certChain": ["…"], "timestamp": "…" }
  },
  "meta": {
    "builderId": "https://builder.stella-ops.local/gha",
    "buildInvocationId": "gha-run-457812",
    "slsa": {"level": 3}
  }
}

Notes

• provenance.dsse.payload holds the raw in‑toto Statement (Statement + Subject + Predicate).
• Keep both artifact digest (subject) and statement subject (inside payload) and verify they match on ingest.

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DB model (Mongo-esque)

• events collection: one doc per event (above schema).
• Compound index: { "subject.digest.sha256": 1, "occurredAt": 1 }
• Causal index: { "meta.buildInvocationId": 1 }
• Uniq guard: { "eventId": 1 } unique

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Ingest pipeline (deterministic)

1. Verify DSSE: check signature, cert roots (or offline trust bundle).
2. Validate Statement: subject digests, builder ID, predicateType.
3. Upsert artifact node: keyed by digest; attach lastProvenanceEventId.
4. Append event: write once; never mutate (event‑sourced).
5. Emit derived edges: (builderId) --built--> (artifact@digest) with occurredAt.

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Joining scans to provenance (temporal consistency)

• When a scan event arrives, resolve the latest provenance event with occurredAt ≤ scan.occurredAt for the same digest.
• Store an edge (artifact@digest) --scannedWith--> (scanner@version) with a pointer to the provenance eventId used for policy.

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Minimal .NET 10 contracts

public sealed record DsseEnvelope(string PayloadType, string Payload, IReadOnlyList<DsseSig> Signatures);
public sealed record Provenance(string Kind, DsseEnvelope Dsse, Transparency? Transparency);
public sealed record EventSubject(string ArtifactPurl, Digest Digest);
public sealed record EventEnvelope(
    string EventId, string EventType, DateTime OccurredAt,
    EventSubject Subject, Provenance Provenance, SigMeta Sig, Meta Meta);

public interface IEventVerifier {
    ValueTask VerifyAsync(EventEnvelope ev, CancellationToken ct);
}
public interface IEventIngestor {
    ValueTask IngestAsync(EventEnvelope ev, CancellationToken ct); // verify->validate->append->derive
}

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Policy hooks (VEX/Trust Algebra)

• Rule: “Only trust findings if the scan’s referenced provenance has builderId ∈ AllowedBuilders and SLSA ≥ 3 and time(scan) − time(prov) ≤ 24h.”
• Effect: drops stale/forged results and aligns all scoring to one timeline.

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Migration from sidecars

1. Dual‑write for one sprint: keep emitting sidecars, but also embed DSSE in events.
2. Add backfill job: wraps historical sidecars into build.provenance.v1 events (preserve original timestamps).
3. Flip consumers (scoring/VEX) to require provenance in the event; keep sidecar reader only for legacy imports.

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Failure & edge cases

• Oversized payloads: gzip the DSSE payload; cap event body (e.g., 512 KB) and store overflow in provenance.ref (content‑addressed blob) while hash‑linking it in the event.
• Multiple subjects: keep the Statement intact; still key the event by the primary digest you care about, but validate all subjects.

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Quick checklist to ship

• Event schema & JSON schema with strict types (no additionalProperties).
• DSSE + in‑toto validators (offline trust bundles supported).
• Mongo indexes + append‑only writer.
• Temporal join in scanner consumer (≤ O(log n) via index).
• VEX rules referencing event.meta & provenance.dsse.
• Backfill task for legacy sidecars.
• Replay test: rebuild graph from events only → identical results.

If you want, I can turn this into ready‑to‑drop .proto + C# models, plus a Mongo migration script and a tiny verifier service.