385 lines
14 KiB
Markdown
385 lines
14 KiB
Markdown
# component_architecture_attestor.md — **Stella Ops Attestor** (2025Q4)
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> **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).
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---
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## 0) Mission & boundaries
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**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.
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**Boundaries.**
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* Attestor **does not sign**; it **must not** accept unsigned or third‑party‑signed bundles.
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* Attestor **does not decide PASS/FAIL**; it logs attestations for SBOMs, reports, and export artifacts.
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* Rekor v2 backends may be **local** (self‑hosted) or **remote**; Attestor handles both with retries, backoff, and idempotency.
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---
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## 1) Topology & dependencies
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**Process shape:** single stateless service `stellaops/attestor` behind mTLS.
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**Dependencies:**
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* **Signer** (caller) — authenticated via **mTLS** and **Authority** OpToks.
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* **Rekor v2** — tile‑backed transparency log endpoint(s).
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* **MinIO (S3)** — optional archive store for DSSE envelopes & verification bundles.
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* **MongoDB** — local cache of `{uuid, index, proof, artifactSha256, bundleSha256}`; job state; audit.
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* **Redis** — dedupe/idempotency keys and short‑lived rate‑limit buckets.
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* **Licensing Service (optional)** — “endorse” call for cross‑log publishing when customer opts‑in.
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Trust boundary: **Only the Signer** is allowed to call submission endpoints; enforced by **mTLS peer cert allowlist** + `aud=attestor` OpTok.
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---
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## 2) Data model (Mongo)
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Database: `attestor`
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**Collections & schemas**
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* `entries`
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```
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{ _id: "<rekor-uuid>",
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artifact: { sha256: "<sha256>", kind: "sbom|report|vex-export", imageDigest?, subjectUri? },
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bundleSha256: "<sha256>", // canonicalized DSSE
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index: <int>, // log index/sequence if provided by backend
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proof: { // inclusion proof
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checkpoint: { origin, size, rootHash, timestamp },
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inclusion: { leafHash, path[] } // Merkle path (tiles)
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},
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log: { url, logId? },
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createdAt, status: "included|pending|failed",
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signerIdentity: { mode: "keyless|kms", issuer, san?, kid? }
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}
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```
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* `dedupe`
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```
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{ key: "bundle:<sha256>", rekorUuid, createdAt, ttlAt } // idempotency key
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```
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* `audit`
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```
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{ _id, ts, caller: { cn, mTLSThumbprint, sub, aud }, // from mTLS + OpTok
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action: "submit|verify|fetch",
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artifactSha256, bundleSha256, rekorUuid?, index?, result, latencyMs, backend }
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```
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Indexes:
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* `entries` on `artifact.sha256`, `bundleSha256`, `createdAt`, and `{status:1, createdAt:-1}`.
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* `dedupe.key` unique (TTL 24–48h).
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* `audit.ts` for time‑range queries.
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---
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## 3) Input contract (from Signer)
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**Attestor accepts only** DSSE envelopes that satisfy all of:
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1. **mTLS** peer certificate maps to `signer` service (CA‑pinned).
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2. **Authority** OpTok with `aud=attestor`, `scope=attestor.write`, DPoP or mTLS bound.
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3. DSSE envelope is **signed by the Signer’s key** (or includes a **Fulcio‑issued** cert chain) and **chains to configured roots** (Fulcio/KMS).
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4. **Predicate type** is one of Stella Ops types (sbom/report/vex‑export) with valid schema.
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5. `subject[*].digest.sha256` is present and canonicalized.
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**Wire shape (JSON):**
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```json
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{
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"bundle": { "dsse": { "payloadType": "application/vnd.in-toto+json", "payload": "<b64>", "signatures": [ ... ] },
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"certificateChain": [ "-----BEGIN CERTIFICATE-----..." ],
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"mode": "keyless" },
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"meta": {
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"artifact": { "sha256": "<subject sha256>", "kind": "sbom|report|vex-export", "imageDigest": "sha256:..." },
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"bundleSha256": "<sha256 of canonical dsse>",
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"logPreference": "primary", // "primary" | "mirror" | "both"
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"archive": true // whether Attestor should archive bundle to S3
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}
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}
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```
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---
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## 4) APIs
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### 4.1 Submission
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`POST /api/v1/rekor/entries` *(mTLS + OpTok required)*
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* **Body**: as above.
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* **Behavior**:
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* Verify caller (mTLS + OpTok).
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* Validate DSSE bundle (signature, cert chain to Fulcio/KMS; DSSE structure; payloadType allowed).
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* Idempotency: compute `bundleSha256`; check `dedupe`. If present, return existing `rekorUuid`.
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* Submit canonicalized bundle to Rekor v2 (primary or mirror according to `logPreference`).
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* Retrieve **inclusion proof** (blocking until inclusion or up to `proofTimeoutMs`); if backend returns promise only, return `status=pending` and retry asynchronously.
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* Persist `entries` record; archive DSSE to S3 if `archive=true`.
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* **Response 200**:
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```json
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{
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"uuid": "…",
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"index": 123456,
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"proof": {
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"checkpoint": { "origin": "rekor@site", "size": 987654, "rootHash": "…", "timestamp": "…" },
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"inclusion": { "leafHash": "…", "path": ["…","…"] }
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},
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"logURL": "https://rekor…/api/v2/log/…/entries/…",
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"status": "included"
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}
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```
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* **Errors**: `401 invalid_token`, `403 not_signer|chain_untrusted`, `409 duplicate_bundle` (with existing `uuid`), `502 rekor_unavailable`, `504 proof_timeout`.
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### 4.2 Proof retrieval
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`GET /api/v1/rekor/entries/{uuid}`
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* Returns `entries` row (refreshes proof from Rekor if stale/missing).
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* Accepts `?refresh=true` to force backend query.
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### 4.3 Verification (third‑party or internal)
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`POST /api/v1/rekor/verify`
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* **Body** (one of):
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* `{ "uuid": "…" }`
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* `{ "bundle": { …DSSE… } }`
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* `{ "artifactSha256": "…" }` *(looks up most recent entry)*
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* **Checks**:
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1. **Bundle signature** → cert chain to Fulcio/KMS roots configured.
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2. **Inclusion proof** → recompute leaf hash; verify Merkle path against checkpoint root.
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3. Optionally verify **checkpoint** against local trust anchors (if Rekor signs checkpoints).
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4. Confirm **subject.digest** matches caller‑provided hash (when given).
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* **Response**:
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```json
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{ "ok": true, "uuid": "…", "index": 123, "logURL": "…", "checkedAt": "…" }
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```
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### 4.4 Batch submission (optional)
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`POST /api/v1/rekor/batch` accepts an array of submission objects; processes with per‑item results.
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---
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## 5) Rekor v2 driver (backend)
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* **Canonicalization**: DSSE envelopes are **normalized** (stable JSON ordering, no insignificant whitespace) before hashing and submission.
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* **Transport**: HTTP/2 with retries (exponential backoff, jitter), budgeted timeouts.
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* **Idempotency**: if backend returns “already exists,” map to existing `uuid`.
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* **Proof acquisition**:
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* In synchronous mode, poll the log for inclusion up to `proofTimeoutMs`.
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* In asynchronous mode, return `pending` and schedule a **proof fetcher** job (Mongo job doc + backoff).
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* **Mirrors/dual logs**:
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* When `logPreference="both"`, submit to primary and mirror; store **both** UUIDs (primary canonical).
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* Optional **cloud endorsement**: POST to the Stella Ops cloud `/attest/endorse` with `{uuid, artifactSha256}`; store returned endorsement id.
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---
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## 6) Security model
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* **mTLS required** for submission from **Signer** (CA‑pinned).
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* **Authority token** with `aud=attestor` and DPoP/mTLS binding must be presented; Attestor verifies both.
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* **Bundle acceptance policy**:
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* DSSE signature must chain to the configured **Fulcio** (keyless) or **KMS/HSM** roots.
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* SAN (Subject Alternative Name) must match **Signer identity** policy (e.g., `urn:stellaops:signer` or pinned OIDC issuer).
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* Predicate `predicateType` must be on allowlist (sbom/report/vex-export).
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* `subject.digest.sha256` values must be present and well‑formed (hex).
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* **No public submission** path. **Never** accept bundles from untrusted clients.
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* **Rate limits**: per mTLS thumbprint/license (from Signer‑forwarded claims) to avoid flooding the log.
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* **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.
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---
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## 7) Storage & archival
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* **Entries** in Mongo provide a local ledger keyed by `rekorUuid` and **artifact sha256** for quick reverse lookups.
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* **S3 archival** (if enabled):
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```
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s3://stellaops/attest/
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dsse/<bundleSha256>.json
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proof/<rekorUuid>.json
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bundle/<artifactSha256>.zip # optional verification bundle
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```
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* **Verification bundles** (zip):
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* DSSE (`*.dsse.json`), proof (`*.proof.json`), `chain.pem` (certs), `README.txt` with verification steps & hashes.
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---
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## 8) Observability & audit
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**Metrics** (Prometheus):
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* `attestor.submit_total{result,backend}`
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* `attestor.submit_latency_seconds{backend}`
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* `attestor.proof_fetch_total{result}`
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* `attestor.verify_total{result}`
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* `attestor.dedupe_hits_total`
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* `attestor.errors_total{type}`
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**Tracing**:
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* Spans: `validate`, `rekor.submit`, `rekor.poll`, `persist`, `archive`, `verify`.
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**Audit**:
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* Immutable `audit` rows (ts, caller, action, hashes, uuid, index, backend, result, latency).
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---
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## 9) Configuration (YAML)
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```yaml
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attestor:
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listen: "https://0.0.0.0:8444"
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security:
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mtls:
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caBundle: /etc/ssl/signer-ca.pem
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requireClientCert: true
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authority:
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issuer: "https://authority.internal"
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jwksUrl: "https://authority.internal/jwks"
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requireSenderConstraint: "dpop" # or "mtls"
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signerIdentity:
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mode: ["keyless","kms"]
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fulcioRoots: ["/etc/fulcio/root.pem"]
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allowedSANs: ["urn:stellaops:signer"]
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kmsKeys: ["kms://cluster-kms/stellaops-signer"]
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rekor:
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primary:
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url: "https://rekor-v2.internal"
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proofTimeoutMs: 15000
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pollIntervalMs: 250
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maxAttempts: 60
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mirror:
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enabled: false
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url: "https://rekor-v2.mirror"
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mongo:
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uri: "mongodb://mongo/attestor"
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s3:
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enabled: true
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endpoint: "http://minio:9000"
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bucket: "stellaops"
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prefix: "attest/"
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objectLock: "governance"
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redis:
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url: "redis://redis:6379/2"
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quotas:
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perCaller:
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qps: 50
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burst: 100
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```
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---
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## 10) End‑to‑end sequences
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**A) Submit & include (happy path)**
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```mermaid
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sequenceDiagram
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autonumber
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participant SW as Scanner.WebService
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participant SG as Signer
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participant AT as Attestor
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participant RK as Rekor v2
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SW->>SG: POST /sign/dsse (OpTok+PoE)
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SG-->>SW: DSSE bundle (+certs)
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SW->>AT: POST /rekor/entries (mTLS + OpTok)
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AT->>AT: Validate DSSE (chain to Fulcio/KMS; signer identity)
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AT->>RK: submit(bundle)
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RK-->>AT: {uuid, index?}
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AT->>RK: poll inclusion until proof or timeout
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RK-->>AT: inclusion proof (checkpoint + path)
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AT-->>SW: {uuid, index, proof, logURL}
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```
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**B) Verify by artifact digest (CLI)**
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```mermaid
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sequenceDiagram
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autonumber
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participant CLI as stellaops verify
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participant SW as Scanner.WebService
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participant AT as Attestor
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CLI->>SW: GET /catalog/artifacts/{id}
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SW-->>CLI: {artifactSha256, rekor: {uuid}}
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CLI->>AT: POST /rekor/verify { uuid }
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AT-->>CLI: { ok: true, index, logURL }
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```
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---
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## 11) Failure modes & responses
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| Condition | Return | Details | | |
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| ------------------------------------- | ----------------------- | --------------------------------------------------------- | -------- | ------------ |
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| mTLS/OpTok invalid | `401 invalid_token` | Include `WWW-Authenticate` DPoP challenge when applicable | | |
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| Bundle not signed by trusted identity | `403 chain_untrusted` | DSSE accepted only from Signer identities | | |
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| Duplicate bundle | `409 duplicate_bundle` | Return existing `uuid` (idempotent) | | |
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| Rekor unreachable/timeout | `502 rekor_unavailable` | Retry with backoff; surface `Retry-After` | | |
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| Inclusion proof timeout | `202 accepted` | `status=pending`, background job continues to fetch proof | | |
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| Archive failure | `207 multi-status` | Entry recorded; archive will retry asynchronously | | |
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| Verification mismatch | `400 verify_failed` | Include reason: chain | leafHash | rootMismatch |
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---
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## 12) Performance & scale
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* Stateless; scale horizontally.
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* **Targets**:
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* Submit+proof P95 ≤ **300 ms** (warm log; local Rekor).
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* Verify P95 ≤ **30 ms** from cache; ≤ **120 ms** with live proof fetch.
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* 1k submissions/minute per replica sustained.
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* **Hot caches**: `dedupe` (bundle hash → uuid), recent `entries` by artifact sha256.
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---
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## 13) Testing matrix
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* **Happy path**: valid DSSE, inclusion within timeout.
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* **Idempotency**: resubmit same `bundleSha256` → same `uuid`.
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* **Security**: reject non‑Signer mTLS, wrong `aud`, DPoP replay, untrusted cert chain, forbidden predicateType.
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* **Rekor variants**: promise‑then‑proof, proof delayed, mirror dual‑submit, mirror failure.
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* **Verification**: corrupt leaf path, wrong root, tampered bundle.
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* **Throughput**: soak test with 10k submissions; latency SLOs, zero drops.
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---
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## 14) Implementation notes
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* Language: **.NET 10** minimal API; `HttpClient` with **sockets handler** tuned for HTTP/2.
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* JSON: **canonical writer** for DSSE payload hashing.
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* Crypto: use **BouncyCastle**/**System.Security.Cryptography**; PEM parsing for cert chains.
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* Rekor client: pluggable driver; treat backend errors as retryable/non‑retryable with granular mapping.
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* Safety: size caps on bundles; decompress bombs guarded; strict UTF‑8.
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* CLI integration: `stellaops verify attestation <uuid|bundle|artifact>` calls `/rekor/verify`.
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---
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## 15) Optional features
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* **Dual‑log** write (primary + mirror) and **cross‑log proof** packaging.
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* **Cloud endorsement**: send `{uuid, artifactSha256}` to Stella Ops cloud; store returned endorsement id for marketing/chain‑of‑custody.
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* **Checkpoint pinning**: periodically pin latest Rekor checkpoints to an external audit store for independent monitoring.
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