Security Review for liboqs_dart

Review code for security issues specific to this post-quantum cryptography FFI library.

Security Checklist

1. Memory Management

Secret Data (keys, shared secrets):

• Use LibOQSUtils.secureFreePointer(ptr, length) - calls OQS_MEM_secure_free
• Never use LibOQSUtils.freePointer() for secrets

Non-sensitive Data (public keys, ciphertext):

• Use LibOQSUtils.freePointer(ptr) - standard free is OK

Always:

• Free memory in finally blocks to prevent leaks on exceptions

2. Classes Holding Secrets

Every class with secret data MUST have:

dart

// 1. Finalizer for automatic cleanup (defense-in-depth)
final Finalizer<Uint8List> _secretDataFinalizer = Finalizer((data) {
  LibOQSUtils.zeroMemory(data);
});

// 2. In constructor - attach finalizer
_secretDataFinalizer.attach(this, secretKey, detach: this);

// 3. clearSecrets() method for explicit cleanup
void clearSecrets() {
  LibOQSUtils.zeroMemory(secretKey);
}

3. Comparisons

• Use LibOQSUtils.constantTimeEquals() for comparing secrets
• NEVER use == or loop-based comparison for secret data (timing attacks!)

4. Function Pointers

Before calling .asFunction() on native function pointers:

dart

// CORRECT: Validate first
if (_ptr.ref.keypair == nullptr) {
  throw LibOQSException('keypair function pointer is null - corrupted');
}
final fn = _ptr.ref.keypair.asFunction<...>();

// WRONG: Direct call without validation
final fn = _ptr.ref.keypair.asFunction<...>(); // May crash!

5. dispose() Pattern

Order matters - prevents memory leaks if exception occurs:

dart

void dispose() {
  if (!_disposed) {
    oqs.OQS_KEM_free(_kemPtr);      // 1. Free native memory
    _kemFinalizer.detach(this);      // 2. Detach finalizer
    _disposed = true;                 // 3. Set flag
  }
}

6. Documentation

Methods exposing secrets MUST have:

dart

/// **Security Warning:** This method exports the SECRET KEY in plaintext.
/// Only use for secure storage. Never log the output.

7. What to Look For

Red Flags:

•freePointer used on secret keys or shared secrets
•Missing clearSecrets() method on classes with secrets
•Missing Finalizer attachment for secret data
•== used to compare keys or secrets
•Function pointer used without null check
•Missing finally block for memory cleanup
•Logging or printing of secret data

Good Patterns:

•secureFreePointer for all secrets
•constantTimeEquals for secret comparison
•Finalizers attached in constructors
•clearSecrets() available and documented
•Security warnings in docstrings

Example Review Output

code

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

### Issues Found

1. **Line 45**: Using `freePointer` for secret key
   - Severity: HIGH
   - Fix: Use `secureFreePointer(secretKeyPtr, secretKey.length)`

2. **Line 78**: Missing Finalizer for shared secret
   - Severity: MEDIUM
   - Fix: Add `_secretDataFinalizer.attach(this, sharedSecret, detach: this)`

### Recommendations

- Add `clearSecrets()` method to `NewResult` class
- Add security warning to `toStrings()` docstring