Security Documentation Index

Last Updated: November 15, 2025 Version: 1.0.0 Target Audience: Development team, security reviewers

This directory contains comprehensive security guidance for the Sonar Quiz System offline browser application.

📚 Document Structure

1. SECURITY_BEST_PRACTICES.md (55 KB) - Read This First

Purpose: Comprehensive reference guide covering all security areas

Contents:

Executive summary
6 detailed security areas with implementation patterns:
1. Password configuration & environment variables
2. XSS prevention (Safe DOM manipulation)
3. Browser encryption (Web Crypto API)
4. Rate limiting (Client-side authentication)
5. Timing attack prevention (Constant-time comparison)
6. Cross-tab message validation (BroadcastChannel security)
Security considerations for each area
Browser compatibility matrices
Implementation priority (Phase 1-3)
Testing & validation checklist
References & resources

Best For: Understanding the "why" behind each security measure

Time to Read: 30-45 minutes

2. SECURITY_IMPLEMENTATION_GUIDE.md (20 KB) - Copy-Paste Ready Code

Purpose: Practical implementation patterns you can use directly

Contents:

Quick start checklist
Implementation patterns for each security area
Simplified, focused code examples
Setup instructions for each feature
Integration checklist
Deployment verification steps
Common patterns (Safe Input → Store → Display, Rate Limited Actions, etc.)
Troubleshooting guide

Best For: Developers implementing security features

Time to Read: 20-30 minutes

3. SECURITY_QUICK_REFERENCE.md (11 KB) - One-Page Checklist

Purpose: Quick reference for daily development work

Contents:

Developer security checklist (before each commit)
Code snippets for common patterns (✓ DO vs ✗ DON'T)
Security checklist by phase
Common security patterns (4 key patterns)
Dangerous code patterns (red flags)
Security decision tree
Browser compatibility matrix
Pre-commit hook template
Quick troubleshooting

Best For: Developers during code review and implementation

Time to Read: 5-10 minutes (reference card)

4. SECURITY_TEST_EXAMPLES.md (30 KB) - Test Code & Examples

Purpose: Complete test suite you can copy into your project

Contents:

Testing setup & configuration
Test 1: XSS Prevention (Lit safety, input sanitization)
Test 2: Rate Limiting (blocking, exponential backoff)
Test 3: Timing-Safe Comparison (constant-time verification)
Test 4: Web Crypto API (encryption/decryption)
Test 5: BroadcastChannel Signing (message validation)
Running security tests
Coverage targets
CI/CD integration
Real-world scenarios in each test

Best For: Writing and validating security tests

Time to Read: 25-35 minutes

🚀 Quick Start Path

For New Team Members (1 hour)

Read: SECURITY_QUICK_REFERENCE.md (5 min)
Skim: SECURITY_BEST_PRACTICES.md sections 1-3 (15 min)
Reference: SECURITY_IMPLEMENTATION_GUIDE.md as needed (40 min)

For Implementing New Security Feature (2-3 hours)

Read: Relevant section in SECURITY_BEST_PRACTICES.md
Copy: Code from SECURITY_IMPLEMENTATION_GUIDE.md
Test: Using SECURITY_TEST_EXAMPLES.md
Check: SECURITY_QUICK_REFERENCE.md before committing

For Code Review (30 minutes)

Open: SECURITY_QUICK_REFERENCE.md
Check: "Dangerous Code Patterns" section
Verify: All items on developer checklist

🔐 Security Areas Covered

Area	Best Practices	Implementation	Quick Ref	Tests
1. Environment Variables	✓	✓	✓	Setup only
2. XSS Prevention	✓	✓	✓	✓
3. Encryption	✓	✓	✓	✓
4. Rate Limiting	✓	✓	✓	✓
5. Timing Attacks	✓	✓	✓	✓
6. Cross-Tab Messages	✓	✓	✓	✓

📋 Pre-Implementation Checklist

Before implementing any security feature:

🎯 Implementation Priority

Phase 1: Essential (Week 1)

For immediate deployment

✓ Environment variables (.env, Vite define)
✓ XSS prevention (Lit templates, sanitizeInput)
✓ Input validation (length limits, type checks)

Checklist:

npm run build && npm run audit:secrets  # Verify no secrets exposed
npm run test -- xss                     # XSS tests pass

Phase 2: Important (Week 2-3)

For production hardening

Rate limiting (max 5 attempts/minute)
Timing-safe comparison (constantTimeCompare)
Message validation setup

Checklist:

npm run test -- rate-limiter            # Rate limiting tests
npm run test -- timing-safe             # Timing tests
npm run test                            # All tests pass

Phase 3: Enhanced (Week 4+)

For maximum security

sessionStorage encryption (optional)
IndexedDB encryption (optional)
BroadcastChannel signing (for multi-window)

Checklist:

npm run test -- crypto                  # Crypto tests
npm run test -- broadcast               # Broadcast tests
npm run build && npm run size-check     # Verify bundle size

🧪 Testing & Validation

Local Development

# Run all security tests
npm run test -- tests/security

# Run specific test area
npm run test -- xss                     # XSS tests only
npm run test -- rate-limiter            # Rate limiter tests
npm run test -- timing-safe             # Timing tests

# Watch mode for development
npm run test:watch -- tests/security

# Check code quality
npm run lint
npm run format:check
npm run build

Before Committing

# Run everything
npm run test
npm run lint
npm run format:check
npm run build
npm run audit:secrets

# Verify .env not in git
git check-ignore .env  # Should exit 0

Pre-Deploy Checklist

npm run test          # All tests pass
npm run lint          # Zero errors
npm run build         # Successful build
npm run audit:secrets # No secrets in bundle
npm run size-check    # Under 25KB gzipped

🔍 Security Review Checklist

Use this when reviewing security-related PRs:

Code Review

No hardcoded credentials (check for: password, secret, apikey, token)
No console.log() of sensitive data
No innerHTML with user input
No eval() or Function() with untrusted data
All user input sanitized
Rate limiting on sensitive actions
Timing-safe comparison for secrets
.env file NOT committed
Environment variables injected at build time only

Testing

Build & Deployment

Build succeeds: npm run build
No errors: npm run lint
Secrets audit passes: npm run audit:secrets
Bundle size OK: npm run size-check
All tests pass: npm run test

📖 Key Concepts

XSS Prevention

Why: Attackers can inject malicious scripts through user input How: Lit auto-escapes, sanitizeInput removes dangerous patterns, textContent for plain text Test: See SECURITY_TEST_EXAMPLES.md - XSS tests

Rate Limiting

Why: Prevents brute-force attacks on authentication How: Track attempts, block after threshold, exponential backoff Test: See SECURITY_TEST_EXAMPLES.md - Rate Limiter tests

Timing Attacks

Why: Different timing for different answers reveals secret structure How: constantTimeCompare always checks all bytes Test: See SECURITY_TEST_EXAMPLES.md - Timing-Safe Comparison tests

Encryption (Optional)

Why: Data at-rest protection if device is stolen How: Web Crypto API with AES-GCM and PBKDF2 derivation Test: See SECURITY_TEST_EXAMPLES.md - Crypto tests

Message Validation

Why: Prevent tampering/replay attacks between browser tabs How: HMAC signatures + nonce + timestamp validation Test: See SECURITY_TEST_EXAMPLES.md - Broadcast Channel tests

🌐 Browser Compatibility

All security features are supported in target browsers without polyfills:

Browser	Version	Support	Notes
Chrome	≥96	✓ Full	Includes Web Components
Firefox	≥102	✓ Full	Full Web Crypto support
Edge	≥96	✓ Full	Chromium-based
Safari	≥14	✓ Full	Web Crypto available

⚡ Performance Impact

Security measures add minimal overhead:

Feature	Impact	Notes
Input sanitization	<1ms	Per input event
XSS prevention	<1ms	Lit built-in
Rate limiting	<1ms	In-memory check
Constant-time compare	<10ms	Full string check
Encryption (optional)	50-200ms	PBKDF2 intentionally slow
HMAC signing	<5ms	Per message

Result: No user-visible performance degradation

🚨 Critical Reminders

Never Do This

// NEVER commit this
password = 'hardcoded123';
const SECRET = process.env.MY_SECRET;
element.innerHTML = userInput;
if (userCode === CORRECT_CODE) { /* timing leak */ }

Always Do This

// ALWAYS use this pattern
// .env file (DO NOT COMMIT)
// vite.config.ts
define: {
  __UNLOCK_HASH__: JSON.stringify(env.UNLOCK_HASH)
}

// Usage
const safe = sanitizeInput(userInput);
html`<div>${safe}</div>`;  // Lit auto-escapes

if (constantTimeCompare(userHash, storedHash)) { /* safe */ }

📞 Getting Help

Questions About...

Best Practices: Read SECURITY_BEST_PRACTICES.md
Implementation: Check SECURITY_IMPLEMENTATION_GUIDE.md
Code Review: Use SECURITY_QUICK_REFERENCE.md
Testing: See SECURITY_TEST_EXAMPLES.md

Reporting Security Issues

Do NOT create public GitHub issue
Use GitHub Security Advisory
Email security team privately
Follow responsible disclosure (90 days)

For Implementation Help

Copy code from SECURITY_IMPLEMENTATION_GUIDE.md
Adapt tests from SECURITY_TEST_EXAMPLES.md
Review patterns in SECURITY_QUICK_REFERENCE.md
Ask team in code review

📚 Related Documents

CLAUDE.md: Project constitution and constraints
System_Requirements.md: Functional requirements
Technical_Design.md: Architecture overview
Contracts.md: Frozen type definitions
Delivery_Plan.md: 8-phase plan
demo/README.md: Manual testing guide

🔄 Maintenance & Updates

This documentation should be reviewed:

Quarterly (every 3 months)
When new browser features arrive
When security vulnerabilities discovered
Before each major release

Last Review: November 15, 2025 Next Review: February 15, 2026

Document Statistics

Document	Size	Topics	Code Examples
SECURITY_BEST_PRACTICES.md	55 KB	6 areas	15+
SECURITY_IMPLEMENTATION_GUIDE.md	20 KB	Setup + patterns	20+
SECURITY_QUICK_REFERENCE.md	11 KB	Checklist + reference	8
SECURITY_TEST_EXAMPLES.md	30 KB	5 test suites	50+
Total	116 KB	Complete coverage	90+ examples

Summary

You now have:

✅ Comprehensive security guide (SECURITY_BEST_PRACTICES.md) ✅ Implementation-ready code (SECURITY_IMPLEMENTATION_GUIDE.md) ✅ Quick reference card (SECURITY_QUICK_REFERENCE.md) ✅ Complete test suite (SECURITY_TEST_EXAMPLES.md) ✅ This index (SECURITY_README.md)

Total: 116 KB of practical, actionable security guidance for your offline browser application.

Start Here

First time? → Read SECURITY_QUICK_REFERENCE.md (5 min)
Need to understand why? → Read SECURITY_BEST_PRACTICES.md (30 min)
Ready to code? → Use SECURITY_IMPLEMENTATION_GUIDE.md + SECURITY_TEST_EXAMPLES.md (2-3 hours)
Reviewing code? → Use SECURITY_QUICK_REFERENCE.md checklist (5 min per PR)

Version: 1.0.0 Status: Complete & Production-Ready Last Updated: November 15, 2025 Maintained By: Security Team

Questions? Check the relevant section above or use the "Getting Help" section.

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Security Documentation Index

📚 Document Structure

1. SECURITY_BEST_PRACTICES.md (55 KB) - Read This First

2. SECURITY_IMPLEMENTATION_GUIDE.md (20 KB) - Copy-Paste Ready Code

3. SECURITY_QUICK_REFERENCE.md (11 KB) - One-Page Checklist

4. SECURITY_TEST_EXAMPLES.md (30 KB) - Test Code & Examples

🚀 Quick Start Path

For New Team Members (1 hour)

For Implementing New Security Feature (2-3 hours)

For Code Review (30 minutes)

🔐 Security Areas Covered

📋 Pre-Implementation Checklist

🎯 Implementation Priority

Phase 1: Essential (Week 1)

Phase 2: Important (Week 2-3)

Phase 3: Enhanced (Week 4+)

🧪 Testing & Validation

Local Development

Before Committing

Pre-Deploy Checklist

🔍 Security Review Checklist

Code Review

Testing

Build & Deployment

📖 Key Concepts

XSS Prevention

Rate Limiting

Timing Attacks

Encryption (Optional)

Message Validation

🌐 Browser Compatibility

⚡ Performance Impact

🚨 Critical Reminders

Never Do This

Always Do This

📞 Getting Help

Questions About...

Reporting Security Issues

For Implementation Help

📚 Related Documents

🔄 Maintenance & Updates

Document Statistics

Summary

Start Here