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master 7e1b10d3b2 Rename Vexer to Excititor

2025-10-18 20:44:59 +03:00

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component_architecture_attestor.md — Stella Ops Attestor (2025Q4)

Scope. Implementation‑ready architecture for the Attestor: the service that submits DSSE envelopes to Rekor v2, retrieves/validates inclusion proofs, caches results, and exposes verification APIs. It accepts DSSE only from the Signer over mTLS, enforces chain‑of‑trust to Stella Ops roots, and returns {uuid, index, proof, logURL} to calling services (Scanner.WebService for SBOMs; backend for final reports; Excititor exports when configured).

0) Mission & boundaries

Mission. Turn a signed DSSE envelope from the Signer into a transparency‑logged, verifiable fact with a durable, replayable proof (Merkle inclusion + (optional) checkpoint anchoring). Provide fast verification for downstream consumers and a stable retrieval interface for UI/CLI.

Boundaries.

Attestor does not sign; it must not accept unsigned or third‑party‑signed bundles.
Attestor does not decide PASS/FAIL; it logs attestations for SBOMs, reports, and export artifacts.
Rekor v2 backends may be local (self‑hosted) or remote; Attestor handles both with retries, backoff, and idempotency.

1) Topology & dependencies

Process shape: single stateless service stellaops/attestor behind mTLS.

Dependencies:

Signer (caller) — authenticated via mTLS and Authority OpToks.
Rekor v2 — tile‑backed transparency log endpoint(s).
MinIO (S3) — optional archive store for DSSE envelopes & verification bundles.
MongoDB — local cache of {uuid, index, proof, artifactSha256, bundleSha256}; job state; audit.
Redis — dedupe/idempotency keys and short‑lived rate‑limit buckets.
Licensing Service (optional) — “endorse” call for cross‑log publishing when customer opts‑in.

Trust boundary: Only the Signer is allowed to call submission endpoints; enforced by mTLS peer cert allowlist + aud=attestor OpTok.

2) Data model (Mongo)

Database: attestor

Collections & schemas

entries

{ _id: "<rekor-uuid>",
  artifact: { sha256: "<sha256>", kind: "sbom|report|vex-export", imageDigest?, subjectUri? },
  bundleSha256: "<sha256>",                           // canonicalized DSSE
  index: <int>,                                       // log index/sequence if provided by backend
  proof: {                                            // inclusion proof
    checkpoint: { origin, size, rootHash, timestamp },
    inclusion: { leafHash, path[] }                   // Merkle path (tiles)
  },
  log: { url, logId? },
  createdAt, status: "included|pending|failed",
  signerIdentity: { mode: "keyless|kms", issuer, san?, kid? }
}

dedupe

{ key: "bundle:<sha256>", rekorUuid, createdAt, ttlAt }     // idempotency key

audit

{ _id, ts, caller: { cn, mTLSThumbprint, sub, aud },        // from mTLS + OpTok
  action: "submit|verify|fetch",
  artifactSha256, bundleSha256, rekorUuid?, index?, result, latencyMs, backend }

Indexes:

entries on artifact.sha256, bundleSha256, createdAt, and {status:1, createdAt:-1}.
dedupe.key unique (TTL 24–48h).
audit.ts for time‑range queries.

3) Input contract (from Signer)

Attestor accepts only DSSE envelopes that satisfy all of:

mTLS peer certificate maps to signer service (CA‑pinned).
Authority OpTok with aud=attestor, scope=attestor.write, DPoP or mTLS bound.
DSSE envelope is signed by the Signer’s key (or includes a Fulcio‑issued cert chain) and chains to configured roots (Fulcio/KMS).
Predicate type is one of Stella Ops types (sbom/report/vex‑export) with valid schema.
subject[*].digest.sha256 is present and canonicalized.

Wire shape (JSON):

{
  "bundle": { "dsse": { "payloadType": "application/vnd.in-toto+json", "payload": "<b64>", "signatures": [ ... ] },
              "certificateChain": [ "-----BEGIN CERTIFICATE-----..." ],
              "mode": "keyless" },
  "meta": {
    "artifact": { "sha256": "<subject sha256>", "kind": "sbom|report|vex-export", "imageDigest": "sha256:..." },
    "bundleSha256": "<sha256 of canonical dsse>",
    "logPreference": "primary",               // "primary" | "mirror" | "both"
    "archive": true                           // whether Attestor should archive bundle to S3
  }
}

4) APIs

4.1 Submission

POST /api/v1/rekor/entries (mTLS + OpTok required)

Body: as above.
Behavior:
- Verify caller (mTLS + OpTok).
- Validate DSSE bundle (signature, cert chain to Fulcio/KMS; DSSE structure; payloadType allowed).
- Idempotency: compute bundleSha256; check dedupe. If present, return existing rekorUuid.
- Submit canonicalized bundle to Rekor v2 (primary or mirror according to logPreference).
- Retrieve inclusion proof (blocking until inclusion or up to proofTimeoutMs); if backend returns promise only, return status=pending and retry asynchronously.
- Persist entries record; archive DSSE to S3 if archive=true.

Response 200:

{
  "uuid": "…",
  "index": 123456,
  "proof": {
    "checkpoint": { "origin": "rekor@site", "size": 987654, "rootHash": "…", "timestamp": "…" },
    "inclusion": { "leafHash": "…", "path": ["…","…"] }
  },
  "logURL": "https://rekor…/api/v2/log/…/entries/…",
  "status": "included"
}

Errors: 401 invalid_token, 403 not_signer|chain_untrusted, 409 duplicate_bundle (with existing uuid), 502 rekor_unavailable, 504 proof_timeout.

4.2 Proof retrieval

GET /api/v1/rekor/entries/{uuid}

Returns entries row (refreshes proof from Rekor if stale/missing).
Accepts ?refresh=true to force backend query.

4.3 Verification (third‑party or internal)

POST /api/v1/rekor/verify

Body (one of):
- { "uuid": "…" }
- { "bundle": { …DSSE… } }
- { "artifactSha256": "…" } (looks up most recent entry)
Checks:
1. Bundle signature → cert chain to Fulcio/KMS roots configured.
2. Inclusion proof → recompute leaf hash; verify Merkle path against checkpoint root.
3. Optionally verify checkpoint against local trust anchors (if Rekor signs checkpoints).
4. Confirm subject.digest matches caller‑provided hash (when given).

Response:

{ "ok": true, "uuid": "…", "index": 123, "logURL": "…", "checkedAt": "…" }

4.4 Batch submission (optional)

POST /api/v1/rekor/batch accepts an array of submission objects; processes with per‑item results.

5) Rekor v2 driver (backend)

Canonicalization: DSSE envelopes are normalized (stable JSON ordering, no insignificant whitespace) before hashing and submission.
Transport: HTTP/2 with retries (exponential backoff, jitter), budgeted timeouts.
Idempotency: if backend returns “already exists,” map to existing uuid.
Proof acquisition:
- In synchronous mode, poll the log for inclusion up to proofTimeoutMs.
- In asynchronous mode, return pending and schedule a proof fetcher job (Mongo job doc + backoff).
Mirrors/dual logs:
- When logPreference="both", submit to primary and mirror; store both UUIDs (primary canonical).
- Optional cloud endorsement: POST to the Stella Ops cloud /attest/endorse with {uuid, artifactSha256}; store returned endorsement id.

6) Security model

mTLS required for submission from Signer (CA‑pinned).
Authority token with aud=attestor and DPoP/mTLS binding must be presented; Attestor verifies both.
Bundle acceptance policy:
- DSSE signature must chain to the configured Fulcio (keyless) or KMS/HSM roots.
- SAN (Subject Alternative Name) must match Signer identity policy (e.g., urn:stellaops:signer or pinned OIDC issuer).
- Predicate predicateType must be on allowlist (sbom/report/vex-export).
- subject.digest.sha256 values must be present and well‑formed (hex).
No public submission path. Never accept bundles from untrusted clients.
Rate limits: per mTLS thumbprint/license (from Signer‑forwarded claims) to avoid flooding the log.
Redaction: Attestor never logs secret material; DSSE payloads should be public by design (SBOMs/reports). If customers require redaction, enforce policy at Signer (predicate minimization) before Attestor.

7) Storage & archival

Entries in Mongo provide a local ledger keyed by rekorUuid and artifact sha256 for quick reverse lookups.

S3 archival (if enabled):

s3://stellaops/attest/
  dsse/<bundleSha256>.json
  proof/<rekorUuid>.json
  bundle/<artifactSha256>.zip               # optional verification bundle

Verification bundles (zip):
- DSSE (*.dsse.json), proof (*.proof.json), chain.pem (certs), README.txt with verification steps & hashes.

8) Observability & audit

Metrics (Prometheus):

attestor.submit_total{result,backend}
attestor.submit_latency_seconds{backend}
attestor.proof_fetch_total{result}
attestor.verify_total{result}
attestor.dedupe_hits_total
attestor.errors_total{type}

Tracing:

Spans: validate, rekor.submit, rekor.poll, persist, archive, verify.

Audit:

Immutable audit rows (ts, caller, action, hashes, uuid, index, backend, result, latency).

9) Configuration (YAML)

attestor:
  listen: "https://0.0.0.0:8444"
  security:
    mtls:
      caBundle: /etc/ssl/signer-ca.pem
      requireClientCert: true
    authority:
      issuer: "https://authority.internal"
      jwksUrl: "https://authority.internal/jwks"
      requireSenderConstraint: "dpop"   # or "mtls"
    signerIdentity:
      mode: ["keyless","kms"]
      fulcioRoots: ["/etc/fulcio/root.pem"]
      allowedSANs: ["urn:stellaops:signer"]
      kmsKeys: ["kms://cluster-kms/stellaops-signer"]
  rekor:
    primary:
      url: "https://rekor-v2.internal"
      proofTimeoutMs: 15000
      pollIntervalMs: 250
      maxAttempts: 60
    mirror:
      enabled: false
      url: "https://rekor-v2.mirror"
  mongo:
    uri: "mongodb://mongo/attestor"
  s3:
    enabled: true
    endpoint: "http://minio:9000"
    bucket: "stellaops"
    prefix: "attest/"
    objectLock: "governance"
  redis:
    url: "redis://redis:6379/2"
  quotas:
    perCaller:
      qps: 50
      burst: 100

10) End‑to‑end sequences

A) Submit & include (happy path)

sequenceDiagram
  autonumber
  participant SW as Scanner.WebService
  participant SG as Signer
  participant AT as Attestor
  participant RK as Rekor v2

  SW->>SG: POST /sign/dsse (OpTok+PoE)
  SG-->>SW: DSSE bundle (+certs)
  SW->>AT: POST /rekor/entries (mTLS + OpTok)
  AT->>AT: Validate DSSE (chain to Fulcio/KMS; signer identity)
  AT->>RK: submit(bundle)
  RK-->>AT: {uuid, index?}
  AT->>RK: poll inclusion until proof or timeout
  RK-->>AT: inclusion proof (checkpoint + path)
  AT-->>SW: {uuid, index, proof, logURL}

B) Verify by artifact digest (CLI)

sequenceDiagram
  autonumber
  participant CLI as stellaops verify
  participant SW as Scanner.WebService
  participant AT as Attestor

  CLI->>SW: GET /catalog/artifacts/{id}
  SW-->>CLI: {artifactSha256, rekor: {uuid}}
  CLI->>AT: POST /rekor/verify { uuid }
  AT-->>CLI: { ok: true, index, logURL }

11) Failure modes & responses

Condition	Return	Details
mTLS/OpTok invalid	`401 invalid_token`	Include `WWW-Authenticate` DPoP challenge when applicable
Bundle not signed by trusted identity	`403 chain_untrusted`	DSSE accepted only from Signer identities
Duplicate bundle	`409 duplicate_bundle`	Return existing `uuid` (idempotent)
Rekor unreachable/timeout	`502 rekor_unavailable`	Retry with backoff; surface `Retry-After`
Inclusion proof timeout	`202 accepted`	`status=pending`, background job continues to fetch proof
Archive failure	`207 multi-status`	Entry recorded; archive will retry asynchronously
Verification mismatch	`400 verify_failed`	Include reason: chain	leafHash	rootMismatch

12) Performance & scale

Stateless; scale horizontally.
Targets:
- Submit+proof P95 ≤ 300 ms (warm log; local Rekor).
- Verify P95 ≤ 30 ms from cache; ≤ 120 ms with live proof fetch.
- 1k submissions/minute per replica sustained.
Hot caches: dedupe (bundle hash → uuid), recent entries by artifact sha256.

13) Testing matrix

Happy path: valid DSSE, inclusion within timeout.
Idempotency: resubmit same bundleSha256 → same uuid.
Security: reject non‑Signer mTLS, wrong aud, DPoP replay, untrusted cert chain, forbidden predicateType.
Rekor variants: promise‑then‑proof, proof delayed, mirror dual‑submit, mirror failure.
Verification: corrupt leaf path, wrong root, tampered bundle.
Throughput: soak test with 10k submissions; latency SLOs, zero drops.

14) Implementation notes

Language: .NET 10 minimal API; HttpClient with sockets handler tuned for HTTP/2.
JSON: canonical writer for DSSE payload hashing.
Crypto: use BouncyCastle/System.Security.Cryptography; PEM parsing for cert chains.
Rekor client: pluggable driver; treat backend errors as retryable/non‑retryable with granular mapping.
Safety: size caps on bundles; decompress bombs guarded; strict UTF‑8.
CLI integration: stellaops verify attestation <uuid|bundle|artifact> calls /rekor/verify.

15) Optional features

Dual‑log write (primary + mirror) and cross‑log proof packaging.
Cloud endorsement: send {uuid, artifactSha256} to Stella Ops cloud; store returned endorsement id for marketing/chain‑of‑custody.
Checkpoint pinning: periodically pin latest Rekor checkpoints to an external audit store for independent monitoring.

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component_architecture_attestor.md — Stella Ops Attestor (2025Q4)