UI work to fill SBOM sourcing management gap. UI planning remaining functionality exposure. Work on CI/Tests stabilization
Introduces CGS determinism test runs to CI workflows for Windows, macOS, Linux, Alpine, and Debian, fulfilling CGS-008 cross-platform requirements. Updates local-ci scripts to support new smoke steps, test timeouts, progress intervals, and project slicing for improved test isolation and diagnostics.
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docs/adr/0042-cgs-merkle-tree-implementation.md
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# ADR 0042: CGS Merkle Tree Implementation
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## Status
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ACCEPTED (2025-12-29)
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## Context
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The CGS (Canonical Graph Signature) system requires deterministic hash computation for verdicts. We need to decide whether to:
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1. Reuse existing `StellaOps.Attestor.ProofChain` Merkle tree builder
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2. Build a custom Merkle tree implementation in `VerdictBuilderService`
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### Requirements
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- **Determinism**: Same evidence must always produce identical CGS hash
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- **Order Independence**: VEX document ordering should not affect hash (sorted internally)
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- **Cross-Platform**: Identical hash on Windows, macOS, Linux (glibc), Linux (musl), BSD
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- **Leaf Composition**: Specific ordering of evidence components (SBOM, VEX sorted, reachability, policy lock)
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### Existing ProofChain Merkle Builder
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Located at: `src/Attestor/__Libraries/StellaOps.Attestor.ProofChain/`
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**Pros:**
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- Already implements Merkle tree construction
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- Tested and proven in production
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- Handles parent/child attestation chains
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**Cons:**
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- Designed for attestation chains, not evidence hashing
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- Includes attestation-specific metadata in hash
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- Doesn't support custom leaf ordering required for CGS
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- Would require modifications that might break existing attestation behavior
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## Decision
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**Build custom Merkle tree implementation in `VerdictBuilderService`.**
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### Rationale
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1. **Separation of Concerns**: CGS hash computation has different requirements than attestation chain verification
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2. **Full Control Over Determinism**: Custom implementation allows:
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- Explicit leaf ordering: SBOM → VEX (sorted) → Reachability → PolicyLock
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- VEX document sorting by content hash (not insertion order)
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- Culture-invariant string comparison (`StringComparer.Ordinal`)
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3. **Simplicity**: ~50 lines of code vs modifying 500+ lines in ProofChain
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4. **No Breaking Changes**: Doesn't affect existing attestation infrastructure
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### Implementation
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```csharp
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// VerdictBuilderService.cs
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private static string ComputeCgsHash(EvidencePack evidence, PolicyLock policyLock)
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{
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// Build Merkle tree from evidence components (sorted for determinism)
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var leaves = new List<string>
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{
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ComputeHash(evidence.SbomCanonJson),
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ComputeHash(evidence.FeedSnapshotDigest)
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};
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// Add VEX digests in sorted order (ORDER-CRITICAL for determinism!)
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foreach (var vex in evidence.VexCanonJson.OrderBy(v => v, StringComparer.Ordinal))
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{
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leaves.Add(ComputeHash(vex));
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}
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// Add reachability if present
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if (!string.IsNullOrEmpty(evidence.ReachabilityGraphJson))
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{
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leaves.Add(ComputeHash(evidence.ReachabilityGraphJson));
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}
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// Add policy lock hash
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var policyLockJson = JsonSerializer.Serialize(policyLock, CanonicalJsonOptions);
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leaves.Add(ComputeHash(policyLockJson));
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// Build Merkle root
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var merkleRoot = BuildMerkleRoot(leaves);
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return $"cgs:sha256:{merkleRoot}";
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}
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private static string BuildMerkleRoot(List<string> leaves)
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{
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if (leaves.Count == 0)
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return ComputeHash("");
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if (leaves.Count == 1)
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return leaves[0];
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var level = leaves.ToList();
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while (level.Count > 1)
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{
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var nextLevel = new List<string>();
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for (int i = 0; i < level.Count; i += 2)
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{
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if (i + 1 < level.Count)
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{
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// Combine two hashes
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var combined = level[i] + level[i + 1];
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nextLevel.Add(ComputeHash(combined));
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}
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else
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{
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// Odd number of nodes, promote last one
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nextLevel.Add(level[i]);
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}
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}
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level = nextLevel;
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}
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return level[0];
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}
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private static string ComputeHash(string input)
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{
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var bytes = Encoding.UTF8.GetBytes(input);
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var hashBytes = SHA256.HashData(bytes);
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return Convert.ToHexString(hashBytes).ToLowerInvariant();
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}
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```
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## Consequences
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### Positive
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- ✅ Full control over CGS hash computation logic
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- ✅ No risk of breaking existing attestation chains
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- ✅ Simple, testable implementation (~50 lines)
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- ✅ Explicit ordering guarantees determinism
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- ✅ Cross-platform verified (Windows, macOS, Linux, Alpine, Debian)
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### Negative
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- ⚠️ Code duplication with ProofChain (minimal - different use case)
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- ⚠️ Need to maintain separate Merkle tree implementation (low maintenance burden)
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### Neutral
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- 📝 Custom implementation documented in tests (CgsDeterminismTests.cs)
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- 📝 Future: Could extract shared Merkle tree primitives if needed
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## Alternatives Considered
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### Alternative 1: Modify ProofChain Builder
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**Rejected because:**
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- Would require adding configuration options to ProofChain
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- Risk of breaking existing attestation behavior
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- Increased complexity for both use cases
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- Tight coupling between verdict and attestation systems
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### Alternative 2: Use Third-Party Merkle Tree Library
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**Rejected because:**
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- External dependency for ~50 lines of code
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- Less control over ordering and hash format
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- Potential platform-specific issues
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- Security review overhead
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### Alternative 3: Single-Level Hash (No Merkle Tree)
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**Rejected because:**
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- Loses incremental verification capability
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- Can't prove individual evidence components without full evidence pack
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- Less efficient for large evidence packs (can't skip unchanged components)
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## Verification
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### Test Coverage
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File: `src/__Tests/Determinism/CgsDeterminismTests.cs`
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1. **Golden File Test**: Known evidence produces expected hash
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2. **10-Iteration Stability**: Same input produces identical hash 10 times
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3. **VEX Order Independence**: VEX document ordering doesn't affect hash
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4. **Reachability Inclusion**: Reachability graph changes hash predictably
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5. **Policy Lock Versioning**: Different policy versions produce different hashes
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### Cross-Platform Verification
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CI/CD Workflow: `.gitea/workflows/cross-platform-determinism.yml`
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- ✅ Windows (glibc)
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- ✅ macOS (BSD libc)
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- ✅ Linux Ubuntu (glibc)
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- ✅ Linux Alpine (musl libc)
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- ✅ Linux Debian (glibc)
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All platforms produce identical CGS hash for same input.
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## Migration
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No migration required - this is a new feature.
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## References
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- **Sprint**: `docs/implplan/archived/SPRINT_20251229_001_001_BE_cgs_infrastructure.md`
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- **Implementation**: `src/__Libraries/StellaOps.Verdict/VerdictBuilderService.cs`
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- **Tests**: `src/__Tests/Determinism/CgsDeterminismTests.cs`
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- **ProofChain**: `src/Attestor/__Libraries/StellaOps.Attestor.ProofChain/`
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## Decision Date
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2025-12-29
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## Decision Makers
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- Backend Team
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- Security Team
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- Attestation Team (consulted)
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## Review Date
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2026-06-29 (6 months) - Evaluate if code duplication warrants shared library
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