SKILL.md

--- frontmatter

name: security-review
description: Review libsignal Dart code for security issues. Use when reviewing code changes, checking for proper API usage, verifying secure patterns, or auditing cryptographic code.
allowed-tools:
  - Read
  - Grep
  - Glob

Security Review for libsignal_dart

Review code for security issues specific to this Signal Protocol library.

Architecture Context

This library uses Flutter Rust Bridge (FRB) with libsignal-protocol (pure Rust):

•Memory safety is handled by Rust (no manual FFI memory management)
•Cryptographic operations are implemented in libsignal-protocol
•Store callbacks use DartFn to bridge Dart stores to Rust

Security Categories

A: API Usage Correctness

• Correct constructor patterns used (PrivateKey.generate() not manual FFI)
• Proper async/await for store operations
• Store callbacks return correct data types

B: Store Security

• Production stores use secure storage (not in-memory)
• Session records persisted correctly (Double Ratchet state)
• Identity keys stored in secure storage (e.g., flutter_secure_storage)

dart

// ❌ WRONG - in-memory stores lose state on restart
final sessionStore = InMemorySessionStore();

// ✅ CORRECT - production stores persist securely
final sessionStore = SecureSqliteSessionStore();

C: Timing Attack Prevention

All cryptographic operations are handled by Rust's libsignal-protocol with constant-time implementations.

• Let library handle cryptographic comparisons
• Avoid comparing serialized cryptographic data directly in Dart

dart

// ✅ CORRECT - let Rust handle cryptographic verification
final isValid = publicKey.verifySignature(message: data, signature: sig);

// ✅ CORRECT - compare public keys using library methods
final keysMatch = key1.compare(other: key2) == 0;

// ❌ AVOID - comparing serialized cryptographic data in Dart
if (key1.serialize() == key2.serialize()) { ... }  // Not constant-time

D: DateTime UTC Consistency

• Use DateTime.now().toUtc() (not DateTime.now())
• Use DateTime.fromMillisecondsSinceEpoch(value, isUtc: true)
• Certificate validation uses UTC timestamps

dart

// ✅ CORRECT
final now = DateTime.now().toUtc();
final expiration = DateTime.fromMillisecondsSinceEpoch(ms, isUtc: true);

// ❌ WRONG - local time can cause certificate validation issues
final now = DateTime.now();

E: Key Material Handling

• Private keys not logged or printed
• Serialized keys not stored in plain text
• Keys not included in error messages

dart

// ❌ WRONG - exposes key material
print('Generated key: ${privateKey.serialize()}');
throw Exception('Failed with key: $keyBytes');

// ✅ CORRECT - no key material in logs
print('Generated new private key');
throw Exception('Key operation failed');

F: Certificate Validation

• Trust roots properly configured
• Certificate expiration checked
• Server certificates validated before use

dart

// ✅ CORRECT - validate before use
final isValid = senderCert.validate(
  trustRoot: serverTrustRoot,
  timestamp: DateTime.now().toUtc(),
);
if (!isValid) {
  throw SecurityException('Invalid sender certificate');
}

G: Error Handling

• Cryptographic failures don't leak information
• Proper exception types used
• Errors logged without sensitive data

dart

// ✅ CORRECT
try {
  final plaintext = await cipher.decrypt(ciphertext);
} catch (e) {
  // Log operation failure, not the ciphertext
  log.warning('Decryption failed for message from ${sender.name}');
  rethrow;
}

H: Concurrency Safety

• Store operations properly synchronized
• No race conditions in session updates

dart

// ✅ CORRECT - synchronized store access
class MySessionStore implements SessionStore {
  final _lock = Lock();

  @override
  Future<void> storeSession(ProtocolAddress addr, SessionRecord record) async {
    await _lock.synchronized(() async {
      await _db.insert('sessions', record.serialize());
    });
  }
}

I: Input Validation

• Device IDs validated (1-127 range)
• UUIDs properly formatted
• Serialized data length checked

dart

// ✅ FRB validates in Rust - but Dart code should also check
if (deviceId < 1 || deviceId > 127) {
  throw ArgumentError('Device ID must be 1-127');
}

J: Initialization

• LibSignal.init() called before use
• Proper cleanup on app termination (optional)

dart

void main() async {
  await LibSignal.init();  // Initialize FRB
  runApp(MyApp());
}

Quick Checklist

code

[ ] No in-memory stores in production code
[ ] No key material in logs/errors
[ ] UTC timestamps for certificates
[ ] Cryptographic comparisons via library methods (not raw bytes)
[ ] Proper async/await for store operations
[ ] LibSignal.init() called at startup
[ ] Store operations synchronized

Red Flags

•InMemorySessionStore in production code
•print() or logging with key bytes
•DateTime.now() without .toUtc()
•Comparing serialized cryptographic data with == in Dart
•Missing await on store operations
•Certificate validation without timestamp check

Example Review Output

code

## Security Review: lib/src/my_feature.dart

### Issues Found

1. **Line 45**: Using in-memory store in production
   - Category: B
   - Severity: HIGH
   - Fix: Implement persistent secure storage

2. **Line 78**: DateTime.now() without UTC
   - Category: D
   - Severity: MEDIUM
   - Fix: Change to `DateTime.now().toUtc()`

3. **Line 102**: Key bytes logged
   - Category: E
   - Severity: HIGH
   - Fix: Remove key material from log statement

### Recommendations

- Add lock synchronization to store operations
- Validate device IDs before creating addresses

Files to Review

Area	Files
Store implementations	`lib/src/stores/*/.dart`
Session operations	`lib/src/protocol/*.dart`
Certificate handling	`lib/src/sealed_sender/*.dart`
Group messaging	`lib/src/groups/*.dart`

Reference

•See SECURITY.md for full security guidelines
•See .claude/skills/stores-implementation/SKILL.md for production store patterns