Add cross-chain attestation verifier for Phase III→IV governance - #42

Summary

Implements higher-order attestation verification across multiple experiments, enabling Phase III→IV transition (Evidence Chain Ledger → Chain-of-Chains Governance). Detects chain breaks, duplicate IDs, dual-root mismatches, hash drift, schema drift, and timestamp violations.

Strategic Impact

Differentiator Tag: [X] [FM]

Strategic Value: Multi-experiment attestation chain verification with cryptographic integrity enforcement (H_t = SHA256(R_t || U_t))

Acquisition Narrative: Demonstrates mature governance layer for cross-experiment evidence chains—critical for multi-phase research integrity

Measurable Outcomes:

• 4 critical issue types detected (chain breaks, duplicates, dual-root mismatches, prev_hash inconsistencies)
• 3 warning types detected (hash drift, schema drift, timestamp violations)
• 68 tests passing (25 new cross-chain, 43 existing dual-root)
• 0 CodeQL alerts

Doctrine Alignment: Formal methods (cryptographic verification), automation (CI guard), reliability (chain integrity)

Scope

Type: [X] Feature [X] Quality Assurance

Components Modified:

• Backend (attestation module)
• Scripts (CI attestation guard)
• Documentation (usage guide)
• Tests (comprehensive cross-chain test suite)

Files Changed:

• attestation/cross_chain_verifier.py - Core verification logic with drift detection
• attestation/__init__.py - Export cross-chain classes
• scripts/ci_attestation_guard.py - CI guard with exit codes (0=PASS, 1=PARTIAL, 2=FAIL, 3=CRITICAL)
• tests/test_cross_chain_attestation.py - 25 tests covering all verification scenarios
• attestation/CROSS_CHAIN_VERIFICATION_GUIDE.md - Usage guide with examples

Risk Assessment

Risk Level: [X] Low

Potential Impact:

• Performance impact: Minimal—verification is O(n) on manifest count
• Breaking changes
• Database schema changes
• Configuration changes required
• Deployment considerations: New CI guard script available for workflow integration

Rollback Plan:

• Simple revert possible (new module, no breaking changes to existing code)

Test Plan

Unit Tests

# Cross-chain attestation tests
python3 -m pytest tests/test_cross_chain_attestation.py -v
# Verify no regression in dual-root attestation
python3 -m pytest tests/test_dual_root_attestation.py -v
# Test CI guard
python3 scripts/ci_attestation_guard.py artifacts/ --fail-on-warnings

Test Results:

• All existing tests pass (43 dual-root tests)
• New tests added for new functionality (25 cross-chain tests)
• Coverage maintained or improved
• Network-free test requirement met

Integration Testing

• CI guard tested with all exit codes (0, 1, 2, 3)
• Artifacts directory scanning verified
• Strict/lenient schema modes tested
• Dual-root integrity validation confirmed

Performance Testing

• Baseline performance maintained (verification is lightweight hash comparison)
• No memory leaks detected
• Response times within acceptable limits (25 tests complete in 0.13s)

Conflict Watch

Files Also Modified by Other PRs:

• None identified

Coordination Notes:

• No conflicts expected (new module in attestation package)

Checklist

Code Quality

• Code follows project style guidelines
• ASCII-only content in docs/scripts
• No hardcoded secrets or credentials
• Error handling implemented (graceful handling of malformed manifests)
• Logging added where appropriate

Documentation

• README updated (attestation guide added)
• API documentation updated (inline docstrings)
• Inline code comments added (dataclasses and verification logic)
• Migration notes included (N/A—no breaking changes)

Security

• No sensitive data exposed
• Input validation implemented (schema checking)
• Authentication/authorization considered (read-only verification)
• Dependencies security reviewed (CodeQL: 0 alerts)

Performance

• No significant performance regression
• Memory usage considered (lightweight dataclasses)
• Database query optimization (N/A—filesystem only)
• Caching strategy implemented (N/A—stateless verification)

Deployment

• Environment variables documented (none required)
• Database migrations included (N/A—no DB changes)
• Configuration changes documented (CI guard flags in guide)
• Deployment instructions provided (usage guide)

Additional Notes

Architecture

Cross-Chain Verifier (CrossChainVerifier):

• Validates prev_hash chain continuity
• Enforces dual-root invariant: H_t = SHA256(R_t || U_t)
• Detects experiment ID collisions
• Tracks configuration hash drift
• Validates schema (strict/lenient modes)
• Checks timestamp monotonicity

CI Guard Exit Codes:

0 = PASS All valid
1 = PARTIAL Warnings (hash drift, schema drift, timestamp issues)
2 = FAIL Critical (chain breaks, duplicates, dual-root mismatches)
3 = CRITICAL System failure (missing artifacts, crashes)

Usage Example:

from attestation.cross_chain_verifier import CrossChainVerifier
verifier = CrossChainVerifier()
result = verifier.verify_artifacts_directory(Path('artifacts/'))
if not result.is_valid:
 print(f"Chain breaks: {len(result.chain_discontinuities)}")
 print(f"Dual-root mismatches: {len(result.dual_root_mismatches)}")
 
print(result.summary())

Integration Pattern:

# GitHub Actions
- name: Verify Attestation Chain
 run: python scripts/ci_attestation_guard.py artifacts/ --fail-on-warnings

Code Review Improvements Applied

• Hash drift detection preserves all indices (not just first occurrence)
• valid_experiments counts unique invalid experiment IDs (not issue count)
• Import fallback for CI guard script (try direct import first)
• Tests use canonical compute_composite_root() consistently

Reviewer Notes:

• New attestation module follows existing dual_root.py patterns
• Reuses canonical dual-root functions (no duplicate crypto primitives)
• Test coverage complete: 6 test classes, 25 scenarios, 100% pass rate
• Ready for Phase IV chain-of-chains governance workflows

Custom agent used: attestation-auditor
Audits attestation artifacts, experiment manifests, and result logs for integrity issues. Detects mismatches between declared and actual hashes, empty or truncated JSONL files, missing parent references, and manifest-to-preregistration inconsistencies. Does NOT generate proofs or run derivations.

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