git.stella-ops.org/docs/reachability/hybrid-attestation.md

# Hybrid Reachability Attestation (Graph + Edge-Bundle)

> Decision date: 2025-12-11 · Owners: Scanner Guild, Attestor Guild, Signals Guild, Policy Guild

## 0. Context: Four Capabilities

This document supports **Signed Reachability**—one of four capabilities no competitor offers together:

1. **Signed Reachability** – Every reachability graph is sealed with DSSE; optional edge-bundle attestations for runtime/init/contested paths. Both static call-graph edges and runtime-derived edges can be attested—true hybrid reachability.
2. **Deterministic Replay** – Scans run bit-for-bit identical from frozen feeds and analyzer manifests.
3. **Explainable Policy (Lattice VEX)** – Evidence-linked VEX decisions with explicit "Unknown" state handling.
4. **Sovereign + Offline Operation** – FIPS/eIDAS/GOST/SM/PQC profiles and offline mirrors as first-class toggles.

All evidence is sealed in **Decision Capsules** for audit-grade reproducibility.

---

## 1. Purpose
- Guarantee replayable, signed reachability evidence with **graph-level DSSE** for every scan while enabling **selective edge-level DSSE bundles** when finer provenance or dispute handling is required.
- Keep CI/offline bundles lean (graph-first), but allow auditors/regulators to quarantine or prove individual edges without regenerating whole graphs.
- Support **hybrid reachability** by attesting both static call-graph edges and runtime-derived edges.

## 2. Attestation levels
- **Level 0 (Graph DSSE) — Required**
  - Payload: canonical `richgraph-v1` (nodes, edges, roots, graph_hash, analyzer metadata, policy_hash).
  - Signature: one DSSE envelope per graph; submit digest to Rekor (or mirror) always.
  - CAS: `cas://reachability/graphs/{blake3}` (body) + `cas://reachability/graphs/{blake3}.dsse` (envelope).
- **Level 1 (Edge-Bundle DSSE) — Optional/Selective**
  - Payload: batch of edges (size ≤ 512) with per-edge reason, evidence hashes, `symbol_digest`, `purl`, `confidence`, and `phase`.
  - Criteria to emit bundles:
    - Edge reason is `runtime`, `init_array`/constructors/TLS callbacks, or comes from third-party provenance.
    - Edge is contested/flagged in Unknowns registry or under policy quarantine.
  - Signature: one DSSE envelope per bundle; Rekor submission **configurable** (default on for contested/high-risk bundles, off for bulk benign bundles in sealed mode).
  - CAS: `cas://reachability/edges/{graph_hash}/{bundle_id}` JSON + `.../{bundle_id}.dsse`.

## 3. Producer responsibilities
- **Scanner**
  - Always emit Level 0 graph + manifest.
  - When criteria match, emit Level 1 bundles; include `bundle_reason` (e.g., `runtime-hit`, `init-root`, `third-party`, `disputed`).
  - Canonicalise JSON (sorted keys/arrays) before hashing; BLAKE3 as graph hash, SHA-256 inside bundles.
  - For hybrid reachability: tag edges with `source: static` or `source: runtime` to distinguish call-graph derived vs. runtime-observed edges.
- **Attestor/Signer**
  - Apply DSSE for both levels; respect sovereign crypto modes (FIPS/GOST/SM/PQC) from environment.
  - Rekor: push graph envelope digests; push edge-bundle digests only when `rekor_publish=true` (policy/default for high-risk bundles).

## 4. Consumer responsibilities
- **Signals**
  - Ingest graph DSSE as the canonical source; ingest edge-bundles when present and attach to the same `graph_hash`.
  - Store per-edge DSSE metadata for quarantine/override flows; surface missing edges as Unknowns only when absent from both graph and bundles.
- **Policy**
  - Default trust path: graph DSSE + CAS object.
  - When an edge is quarantined/contested, drop it from consideration if an edge-bundle DSSE marks it `revoked=true` or if the Unknowns registry lists it with policy quarantine flag.
  - For "evidence-required" rules, require either (a) graph DSSE + policy_hash match **or** (b) edge-bundle DSSE that covers the vulnerable path edges.
- **Replay/Bench/CLI**
  - `stella graph verify` should accept `--graph {hash}` and optional `--edge-bundles` to validate deeper provenance offline.

## 5. Verification and quarantine flows
- **Happy path**: verify graph DSSE → verify Rekor inclusion (or mirror) → hash graph body → match `graph_hash` in policy/replay manifest → accept.
- **Dispute/quarantine**: mark specific `edge_id` as `revoked` in an edge-bundle DSSE; Policy/Signals exclude it, recompute reachability, and surface delta in explainers.
- **Offline**: retain graph DSSE and selected edge-bundles inside replay pack; Rekor proofs cached when available.
- **Sovereign Verification Mode**: Even with no internet, all signatures and transparency proofs can be locally verified using Offline Update Kits.

## 6. Performance & storage guardrails
- Default: only graph DSSE is mandatory; edge-bundles capped at 512 edges per envelope and emitted only on criteria above.
- Rekor flood control: cap edge-bundle Rekor submissions per graph (config `reachability.edgeBundles.maxRekorPublishes`, default 5). Others stay CAS-only.
- Determinism: bundle ordering = stable sort by `(bundle_reason, edge_id)`; hash before signing.

## 7. Hybrid Reachability Details

Stella Ops provides **true hybrid reachability** by combining:

| Signal Type | Source | Attestation |
|-------------|--------|-------------|
| Static call-graph edges | IL/bytecode analysis, framework routing models, entry-point proximity | Graph DSSE (Level 0) |
| Runtime-observed edges | EventPipe, JFR, Node inspector, Go/Rust probes | Edge-bundle DSSE (Level 1) with `source: runtime` |

**Why hybrid matters:**
- Static analysis catches code paths that may not execute during observed runtime
- Runtime analysis catches dynamic dispatch, reflection, and framework-injected paths
- Combining both provides confidence across build and runtime contexts
- Each edge type is separately attestable for audit and dispute resolution

**Evidence linking:** Each edge in the graph or bundle includes `evidenceRefs` pointing to the underlying proof artifacts (static analysis artifacts, runtime traces), enabling **evidence-linked VEX decisions**.

## 8. Decisions (Frozen 2025-12-13)

### 8.1 DSSE/Rekor Budget by Deployment Tier

| Tier | Graph DSSE | Edge-Bundle DSSE | Rekor Publish | Max Bundles/Graph |
|------|------------|------------------|---------------|-------------------|
| **Regulated** (SOC2, FedRAMP, PCI) | Required | Required for runtime/contested | Required | 10 |
| **Standard** | Required | Optional (criteria-based) | Graph only | 5 |
| **Air-gapped** | Required | Optional | Offline checkpoint | 5 |
| **Dev/Test** | Optional | Optional | Disabled | Unlimited |

**Budget enforcement:**
- Graph DSSE: Always submit digest to Rekor (or offline checkpoint for air-gapped)
- Edge-bundle DSSE: Submit to Rekor only when `bundle_reason` is `disputed`, `runtime-hit`, or `security-critical`
- Cap enforced by `reachability.edgeBundles.maxRekorPublishes` config (per tier defaults above)

### 8.2 Signing Layout and CAS Paths

```
cas://reachability/
  graphs/
    {blake3}/                  # richgraph-v1 body (JSON)
    {blake3}.dsse              # Graph DSSE envelope
    {blake3}.rekor             # Rekor inclusion proof (optional)
  edges/
    {graph_hash}/
      {bundle_id}.json         # Edge bundle body
      {bundle_id}.dsse         # Edge bundle DSSE envelope
      {bundle_id}.rekor        # Rekor inclusion proof (if published)
  revisions/
    {revision_id}/             # Revision manifest + lineage
```

**Signing workflow:**
1. Canonicalize richgraph-v1 JSON (sorted keys, arrays by deterministic key)
2. Compute BLAKE3-256 hash -> `graph_hash`
3. Create DSSE envelope with `stella.ops/graph@v1` predicate
4. Submit digest to Rekor (online) or cache checkpoint (offline)
5. Store graph body + envelope + proof in CAS

### 8.3 CLI UX for Selective Bundle Verification

```bash
# Verify graph DSSE only (default)
stella graph verify --hash blake3:a1b2c3d4...

# Verify graph + all edge bundles
stella graph verify --hash blake3:a1b2c3d4... --include-bundles

# Verify specific edge bundle
stella graph verify --hash blake3:a1b2c3d4... --bundle bundle:001

# Offline verification with local CAS
stella graph verify --hash blake3:a1b2c3d4... --cas-root ./offline-cas/

# Verify Rekor inclusion
stella graph verify --hash blake3:a1b2c3d4... --rekor-proof

# Output formats
stella graph verify --hash blake3:a1b2c3d4... --format json|table|summary
```

### 8.4 Golden Fixture Plan

**Fixture location:** `tests/Reachability/Hybrid/`

**Required fixtures:**
| Fixture | Description | Expected Verification Time |
|---------|-------------|---------------------------|
| `graph-only.golden.json` | Minimal richgraph-v1 with DSSE | < 100ms |
| `graph-with-runtime.golden.json` | Graph + 1 runtime edge bundle | < 200ms |
| `graph-with-contested.golden.json` | Graph + 1 contested/revoked edge bundle | < 200ms |
| `large-graph.golden.json` | 10K nodes, 50K edges, 5 bundles | < 2s |
| `offline-bundle.golden.tgz` | Complete offline replay pack | < 5s |

**CI integration:**
- `.gitea/workflows/hybrid-attestation.yml` runs verification fixtures
- Size gate: Graph body < 10MB, individual bundle < 1MB
- Time gate: Full verification < 5s for standard tier

### 8.5 Implementation Status

| Component | Status | Notes |
|-----------|--------|-------|
| Graph DSSE predicate | Done | `stella.ops/graph@v1` in PredicateTypes.cs |
| Edge-bundle DSSE predicate | Done | `stella.ops/edgeBundle@v1` via EdgeBundlePublisher |
| Edge-bundle models | Done | EdgeBundle.cs, EdgeBundleReason, EdgeReason enums |
| Edge-bundle CAS publisher | Done | EdgeBundlePublisher.cs with deterministic DSSE |
| Edge-bundle ingestion | Done | EdgeBundleIngestionService in Signals |
| CAS layout | Done | Per section 8.2 |
| Runtime-facts CAS storage | Done | IRuntimeFactsArtifactStore, FileSystemRuntimeFactsArtifactStore |
| CLI verify command | Planned | Per section 8.3 |
| Golden fixtures | Planned | Per section 8.4 |
| Rekor integration | Done | Via Attestor module |
| Quarantine enforcement | Done | HasQuarantinedEdges in ReachabilityFactDocument |

---

## 9. Verification Runbook

This section provides step-by-step guidance for verifying hybrid attestations in different scenarios.

### 9.1 Graph-Only Verification

Use this workflow when only graph-level attestation is required (default for most use cases).

**Prerequisites:**
- Access to CAS storage (local or remote)
- `stella` CLI installed
- Optional: Rekor instance access for transparency verification

**Steps:**

1. **Retrieve graph DSSE envelope:**
   ```bash
   stella graph fetch --hash blake3:<graph_hash> --output ./verification/
   ```

2. **Verify DSSE signature:**
   ```bash
   stella graph verify --hash blake3:<graph_hash>
   # Output: ✓ Graph signature valid (key: <key_id>)
   ```

3. **Verify content integrity:**
   ```bash
   stella graph verify --hash blake3:<graph_hash> --check-content
   # Output: ✓ Content hash matches BLAKE3:<graph_hash>
   ```

4. **Verify Rekor inclusion (online):**
   ```bash
   stella graph verify --hash blake3:<graph_hash> --rekor-proof
   # Output: ✓ Rekor inclusion verified (log index: <index>)
   ```

5. **Verify policy hash binding:**
   ```bash
   stella graph verify --hash blake3:<graph_hash> --policy-hash sha256:<policy_hash>
   # Output: ✓ Policy hash matches graph metadata
   ```

### 9.2 Graph + Edge-Bundle Verification

Use this workflow when finer-grained verification of specific edges is required.

**When to use:**
- Auditing runtime-observed paths
- Investigating contested/disputed edges
- Verifying init-section or TLS callback roots
- Regulatory compliance requiring edge-level attestation

**Steps:**

1. **List available edge bundles:**
   ```bash
   stella graph bundles --hash blake3:<graph_hash>
   # Output:
   # Bundle ID          Reason          Edges  Rekor
   # bundle:001         runtime-hit     42     ✓
   # bundle:002         init-root       15     ✓
   # bundle:003         third-party     128    -
   ```

2. **Verify specific bundle:**
   ```bash
   stella graph verify --hash blake3:<graph_hash> --bundle bundle:001
   # Output:
   # ✓ Bundle DSSE signature valid
   # ✓ All 42 edges link to graph_hash
   # ✓ Rekor inclusion verified
   ```

3. **Verify all bundles:**
   ```bash
   stella graph verify --hash blake3:<graph_hash> --include-bundles
   # Output:
   # ✓ Graph signature valid
   # ✓ 3 bundles verified (185 edges total)
   ```

4. **Check for revoked edges:**
   ```bash
   stella graph verify --hash blake3:<graph_hash> --check-revoked
   # Output:
   # ⚠ 2 edges marked revoked in bundle:002
   #   - edge:func_a→func_b (reason: policy-quarantine)
   #   - edge:func_c→func_d (reason: revoked)
   ```

### 9.3 Verification Decision Matrix

| Scenario | Graph DSSE | Edge Bundles | Rekor | Policy Hash |
|----------|------------|--------------|-------|-------------|
| Standard CI/CD | Required | Optional | Recommended | Required |
| Regulated audit | Required | Required | Required | Required |
| Dispute resolution | Required | Required (contested) | Required | Optional |
| Offline replay | Required | As available | Cached proof | Required |
| Dev/test | Optional | Optional | Disabled | Optional |

---

## 10. Rekor Guidance

### 10.1 Rekor Integration Overview

Rekor provides an immutable transparency log for attestation artifacts. StellaOps integrates with Rekor (or compatible mirrors) to provide verifiable timestamps and inclusion proofs.

### 10.2 What Gets Published to Rekor

| Artifact Type | Rekor Publish | Condition |
|---------------|---------------|-----------|
| Graph DSSE digest | Always | All deployment tiers (except dev/test) |
| Edge-bundle DSSE digest | Conditional | Only for `disputed`, `runtime-hit`, `security-critical` reasons |
| VEX decision DSSE digest | Always | When VEX decisions are generated |

### 10.3 Rekor Configuration

```yaml
# etc/signals.yaml
reachability:
  rekor:
    enabled: true
    endpoint: "https://rekor.sigstore.dev"  # Or private mirror
    timeout: 30s
    retry:
      attempts: 3
      backoff: exponential
  edgeBundles:
    maxRekorPublishes: 5  # Per graph, configurable by tier
    publishReasons:
      - disputed
      - runtime-hit
      - security-critical
```

### 10.4 Private Rekor Mirror

For air-gapped or regulated environments:

```yaml
reachability:
  rekor:
    enabled: true
    endpoint: "https://rekor.internal.example.com"
    tls:
      ca: /etc/stellaops/ca.crt
      clientCert: /etc/stellaops/client.crt
      clientKey: /etc/stellaops/client.key
```

### 10.5 Rekor Proof Caching

Inclusion proofs are cached locally for offline verification:

```
cas://reachability/graphs/{blake3}.rekor    # Graph inclusion proof
cas://reachability/edges/{graph_hash}/{bundle_id}.rekor  # Bundle proof
```

**Proof format:**
```json
{
  "logIndex": 12345678,
  "logId": "c0d23d6ad406973f9559f3ba2d1ca01f84147d8ffc5b8445c224f98b9591801d",
  "integratedTime": 1702492800,
  "inclusionProof": {
    "logIndex": 12345678,
    "rootHash": "abc123...",
    "treeSize": 50000000,
    "hashes": ["def456...", "ghi789..."]
  }
}
```

---

## 11. Offline Replay Steps

### 11.1 Overview

Offline replay enables full verification of reachability attestations without network access. This is essential for air-gapped deployments and regulatory compliance scenarios.

### 11.2 Creating an Offline Replay Pack

**Step 1: Export graph and bundles**
```bash
stella graph export --hash blake3:<graph_hash> \
  --include-bundles \
  --include-rekor-proofs \
  --output ./offline-pack/
```

**Step 2: Include required artifacts**
The export creates:
```
offline-pack/
├── manifest.json              # Replay manifest v2
├── graphs/
│   └── <blake3>/
│       ├── richgraph-v1.json  # Graph body
│       ├── graph.dsse         # DSSE envelope
│       └── graph.rekor        # Inclusion proof
├── edges/
│   └── <graph_hash>/
│       ├── bundle-001.json
│       ├── bundle-001.dsse
│       └── bundle-001.rekor
├── runtime-facts/
│   └── <hash>/
│       └── runtime-facts.ndjson
└── checkpoints/
    └── rekor-checkpoint.json  # Transparency log checkpoint
```

**Step 3: Bundle for transfer**
```bash
stella offline pack --input ./offline-pack/ --output offline-replay.tgz
```

### 11.3 Verifying an Offline Pack

**Step 1: Extract pack**
```bash
stella offline unpack --input offline-replay.tgz --output ./verify/
```

**Step 2: Verify manifest integrity**
```bash
stella offline verify --manifest ./verify/manifest.json
# Output:
# ✓ Manifest version: 2
# ✓ Hash algorithm: blake3
# ✓ All CAS entries present
# ✓ All hashes verified
```

**Step 3: Verify attestations offline**
```bash
stella graph verify --hash blake3:<graph_hash> \
  --cas-root ./verify/ \
  --offline
# Output:
# ✓ Graph DSSE signature valid (offline mode)
# ✓ Rekor proof verified against checkpoint
# ✓ 3 bundles verified offline
```

### 11.4 Offline Verification Trust Model

```
┌─────────────────────────────────────────────────────────┐
│                   Offline Pack                          │
├─────────────────────────────────────────────────────────┤
│  ┌──────────────┐   ┌──────────────┐   ┌─────────────┐ │
│  │ Graph DSSE   │   │ Edge Bundle  │   │ Rekor       │ │
│  │ Envelope     │   │ DSSE         │   │ Checkpoint  │ │
│  └──────┬───────┘   └──────┬───────┘   └──────┬──────┘ │
│         │                  │                  │        │
│         ▼                  ▼                  ▼        │
│  ┌──────────────────────────────────────────────────┐  │
│  │           Local Verification Engine              │  │
│  │  1. Verify DSSE signatures against trusted keys  │  │
│  │  2. Verify content hashes match DSSE payloads    │  │
│  │  3. Verify Rekor proofs against checkpoint       │  │
│  │  4. Verify policy hash binding                   │  │
│  └──────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────┘
```

### 11.5 Air-Gapped Deployment Checklist

- [ ] Trusted signing keys pre-installed
- [ ] Rekor checkpoint from last sync included
- [ ] All referenced CAS artifacts bundled
- [ ] Policy hash recorded in manifest
- [ ] Analyzer manifests included for replay
- [ ] Runtime-facts artifacts included (if applicable)

---

## 12. Release Notes

### 12.1 Version History

| Version | Date | Changes |
|---------|------|---------|
| 1.0 | 2025-12-11 | Initial hybrid attestation design |
| 1.1 | 2025-12-13 | Added edge-bundle ingestion, CAS storage, verification runbook |

### 12.2 Breaking Changes

None. Hybrid attestation is additive; existing graph-only workflows remain unchanged.

### 12.3 Migration Guide

**From graph-only to hybrid:**
1. No migration required for existing graphs
2. Enable edge-bundle emission in scanner config:
   ```yaml
   scanner:
     reachability:
       edgeBundles:
         enabled: true
         emitRuntime: true
         emitContested: true
   ```
3. Signals automatically ingests edge bundles when present

---

## 13. Cross-References

- **Sprint:** SPRINT_0401_0001_0001_reachability_evidence_chain.md (Tasks 53-56)
- **Contracts:** docs/contracts/richgraph-v1.md, docs/contracts/edge-bundle-v1.md
- **Implementation:**
  - Scanner: `src/Scanner/__Libraries/StellaOps.Scanner.Reachability/EdgeBundle*.cs`
  - Signals: `src/Signals/StellaOps.Signals/Ingestion/EdgeBundleIngestionService.cs`
  - Policy: `src/Policy/StellaOps.Policy.Engine/Gates/PolicyGateEvaluator.cs`
- **Related docs:**
  - docs/reachability/function-level-evidence.md
  - docs/reachability/lattice.md
  - docs/replay/DETERMINISTIC_REPLAY.md
  - docs/07_HIGH_LEVEL_ARCHITECTURE.md