Phase 5: Security Audit & Documentation (FINAL)

[kevalyq]

📌 Parent Epic

#143 (Client-Side File Encryption for Zero-Knowledge Architecture)

🎯 Goal

Perform comprehensive security audit, create architecture documentation, and ensure no vulnerabilities before merging.

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📋 Implementation Tasks

1. Security Checklist

Key Management:

• Keys never logged or exposed (verify no console.log with keys)
• Keys non-extractable (Web Crypto API)
• HKDF used for key derivation (not simple hash)
• Unique IV for each encryption operation
• No hardcoded keys or test keys in production code

Encryption:

• AES-GCM-256 with 128-bit auth tag
• Known test vectors validated (NIST)
• Tampering detection works (auth tag)
• IV never reused
• Ciphertext authenticated (GCM mode)

Integrity:

• SHA-256 checksums before/after encryption
• Checksum verification enforced on download
• File corruption detected
• No checksum bypass possible

Error Handling:

• Decryption failures handled gracefully
• User-friendly error messages (no key exposure)
• Network failures don't expose keys
• Stack traces sanitized (no sensitive data)

Testing:

• ≥80% code coverage for all crypto code
• Known test vectors pass
• Roundtrip encryption/decryption works
• Tampering detection works
• Edge cases covered (large files, network errors, empty files)

2. CodeQL Security Scan

File: .github/workflows/codeql.yml (verify enabled)

• Run CodeQL scan on all crypto code
• Fix any security alerts (High/Medium)
• Document any suppressed warnings (with justification)
• Verify no XSS vulnerabilities
• Verify no SQL injection (if applicable)
• Verify no hardcoded secrets

3. Documentation

File: frontend/docs/CRYPTO_ARCHITECTURE.md (NEW)

• Overview of encryption architecture
• Key hierarchy diagram
• Encryption flow diagram
• Decryption flow diagram
• Security guarantees
• Threat model
• Known limitations
• API reference

File: frontend/README.md (UPDATE)

• Add "File Encryption" section
• Link to CRYPTO_ARCHITECTURE.md
• Mention zero-knowledge architecture
• Security highlights

File: frontend/CHANGELOG.md (UPDATE)

• Add Phase 3 feature (Client-Side File Encryption)
• List all 5 sub-issues completed
• Mention security enhancements
• Breaking changes (if any)

File: frontend/PWA_PHASE3_TESTING.md (UPDATE)

• Add encryption test scenarios
• Manual testing guide for file encryption
• Edge cases to test
• Security testing procedures

4. Performance Profiling

File: frontend/docs/PERFORMANCE_BENCHMARKS.md (NEW)

• Benchmark encryption speed (1MB, 5MB, 10MB files)
• Benchmark decryption speed
• Benchmark key derivation speed
• Benchmark checksum calculation
• Document results
• Identify bottlenecks (if any)

5. Accessibility (a11y) Audit

File: frontend/docs/ACCESSIBILITY.md (UPDATE)

• Verify encryption progress indicators are screen-reader friendly
• Verify error messages are accessible
• Verify keyboard navigation works
• Verify focus management during encryption
• Run axe DevTools audit
• Fix any violations

6. Final Review

• 4-Pass Self-Review completed (copilot-instructions.md)
• All quality gates passing (TypeScript, ESLint, Prettier, Tests)
• REUSE compliance (SPDX headers)
• Domain policy compliance (secpal.app/secpal.dev)
• No TODO/FIXME comments left in code
• All console.log statements removed
• All test.skip removed

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✅ Acceptance Criteria

• Security checklist 100% complete
• CodeQL scan passing (no High/Medium alerts)
• Documentation comprehensive (architecture, API, testing)
• Performance benchmarks documented
• Accessibility audit passed
• All tests passing (100% green)
• Code coverage ≥80% overall
• 4-Pass Self-Review completed
• No security vulnerabilities found
• No hardcoded keys or secrets
• CHANGELOG updated
• README updated

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🔗 Dependencies

• Depends on: #TBD (Phase 4 - Download & Decryption)
• Blocks: Epic [EPIC] Client-Side File Encryption for Zero-Knowledge Architecture #143 closure
• Part of: Epic [EPIC] Client-Side File Encryption for Zero-Knowledge Architecture #143 (FINAL sub-issue)

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📝 Documentation Structure

CRYPTO_ARCHITECTURE.md

# Client-Side Encryption Architecture

## Overview

SecPal implements end-to-end encryption for file attachments using Web Crypto API with AES-GCM-256.

## Key Hierarchy

User Master Key (from authentication)
└─> Secret Master Key (per Secret)
└─> File Encryption Key (derived via HKDF + filename salt)

## Encryption Flow

1. User shares file via Share Target API
2. Derive file key from Secret's master key (HKDF)
3. Encrypt file with AES-GCM-256 (random IV)
4. Calculate checksums (before/after)
5. Upload encrypted blob to backend
6. Backend stores encrypted file (cannot decrypt)

## Decryption Flow

1. Download encrypted blob from backend
2. Derive file key from Secret's master key (HKDF)
3. Decrypt file with AES-GCM-256
4. Verify checksum (SHA-256)
5. Restore original filename and MIME type

## Security Guarantees

- **Zero-Knowledge Backend**: Server cannot decrypt files
- **End-to-End Encryption**: Only client can decrypt
- **Integrity Verification**: SHA-256 checksums + GCM auth tag
- **Tampering Detection**: Modified files rejected
- **Forward Secrecy**: Unique IV per encryption

## Threat Model

### Mitigated Threats

- Server-side data breaches (encrypted at rest)
- Man-in-the-middle attacks (HTTPS + E2EE)
- File tampering (checksums + auth tag)

### Out of Scope

- Quantum computing attacks (future work)
- Physical device compromise (user responsibility)
- Social engineering (user awareness)

## API Reference

See `src/lib/crypto/encryption.ts` for implementation details.

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🚀 Branch Strategy

# Create feature branch FROM Phase 4 branch
git checkout feat/download-decryption-phase4
git checkout -b feat/security-audit-phase5

# Complete audit tasks
git commit -S -m "docs: add crypto architecture documentation (Phase 5.1)"
git commit -S -m "test: add performance benchmarks (Phase 5.2)"
git commit -S -m "docs: update CHANGELOG with encryption feature (Phase 5.3)"
git commit -S -m "chore: remove debug logs and TODOs (Phase 5.4)"
git commit -S -m "docs: complete accessibility audit (Phase 5.5)"

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📏 PR Linking Instructions

When creating the PR for this sub-issue (FINAL), use this in your PR description:

Fixes #TBD
Closes #143
Depends on: #TBD (Phase 4)

⚠️ Important:

• USE Closes #143 - this is the FINAL sub-issue, closes the Epic
• Wait for Phase 4 PR to be merged before starting
• This PR is documentation/audit only (no new features)
• PR size: ~200-300 LOC (docs + audit)

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🔒 Security Audit Checklist

# Run security checks
npm audit                          # Check for vulnerable dependencies
npm run typecheck                  # TypeScript strict mode
npm run lint                       # ESLint security rules
npm test                           # All tests passing
npm run test:coverage              # ≥80% coverage

# Manual review
grep -r "console.log" src/lib/crypto/  # No debug logs
grep -r "CryptoKey" src/              # No key exposure
grep -r "TODO\|FIXME" src/lib/crypto/  # No unfinished work

# CodeQL scan (GitHub Actions)
# https://github.com/SecPal/frontend/security/code-scanning

# Performance benchmark
npm run benchmark:crypto           # If script exists

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Type: Sub-Issue (Phase 5/5 - FINAL)
Priority: High (Security-Critical)
Estimated Effort: 1 day
Sprint: Security Audit & Documentation

[github-actions]

✅ This issue has been added to the SecPal Feature Roadmap with status: 💡 Ideas

New idea - needs discussion and evaluation

Status Flow:
💡 Ideas → 💬 Discussion → 📥 Backlog → 📋 Planned → 🚧 In Progress → 👀 In Review → ✅ Done

Note: Ideas that won't be implemented should be moved to 🚫 Won't Do with a reason.