Protocol Overview

The Privacy Engine supports multiple cryptographic protocols, allowing secure communication between parties using different cryptographic schemes.

Protocol Overview

Protocol	Curve	Key Size	Signature	Key Recovery	Use Case
Starknet	Stark Curve	32 bytes	✅ ECDSA	✅ Yes	Blockchain, ZK systems
X25519	Curve25519	32 bytes	❌ No	❌ No	Standard key exchange

Protocol Selection

When to Use Starknet Protocol

• Blockchain Integration: When working with Starknet or compatible blockchains

• Zero-Knowledge Systems: For applications requiring ZK proof compatibility

• Signature Recovery: When you need to recover public keys from signatures

• Advanced Features: When you need ECDSA signing and verification

When to Use X25519 Protocol

• Standard Key Exchange: For traditional Diffie-Hellman key exchange

• Performance: When you need maximum performance for key agreement

• Compatibility: When working with systems that expect standard X25519

• Simplicity: When you only need key exchange without signatures

Protocol Comparison

Cryptographic Properties

Property	Starknet	X25519
Curve	Stark curve (y² = x³ + x + b)	Curve25519
Key Agreement	ECDH on Stark curve	X25519 Diffie-Hellman
Signature	ECDSA with recovery	Not supported
Key Derivation	SHA-256 of shared secret	Direct use
Ephemeral Key Size	64 bytes (x || y)	32 bytes
Security Level	128-bit	128-bit

Performance Characteristics

Metric	Starknet	X25519
Key Generation	~2ms	~1ms
Key Agreement	~3ms	~2ms
Signature	~5ms	N/A
Verification	~4ms	N/A
Memory Usage	Higher	Lower

Protocol Implementation Details

Starknet Protocol

Detailed documentation for the Starknet protocol implementation, including:

• Cryptographic primitives

• Key recovery mechanisms

• Signature schemes

• Integration with Starknet ecosystem

X25519 Protocol

Comprehensive guide for the X25519 protocol, covering:

• Curve25519 mathematics

• Diffie-Hellman key exchange

• Performance optimizations

• Standard compliance

Cross-Protocol Communication

The Privacy Engine enables secure communication between users using different protocols:

// User A uses Starknet, User B uses X25519
let recipients = vec![
    RecipientInfo {
        pubkey: starknet_user_pubkey,
        protocol: Protocol::Starknet,
    },
    RecipientInfo {
        pubkey: x25519_user_pubkey,
        protocol: Protocol::X25519,
    },
];

// Both users can decrypt the same message using their respective protocols
let result = encrypt_message(message, recipients)?;

Adding New Protocols

To add support for a new cryptographic protocol:

1. Implement the Protocol Trait

   impl CryptoProtocol for NewProtocol {
       fn encrypt_key(&self, recipient_identifier: &[u8], msg_hash: Option<&[u8]>, key: &[u8]) -> Result<EncryptedData, CryptoError> {
           // Implementation
       }
       
       fn decrypt_key(&self, encrypted_data: &EncryptedData, privkey: &[u8]) -> Result<Vec<u8>, CryptoError> {
           // Implementation
       }
       
       // ... other methods
   }

2. Add to Protocol Enum

   pub enum Protocol {
       Starknet,
       X25519,
       NewProtocol, // Add here
   }

3. Register in Protocol Registry

   fn get_protocol_impl(protocol: Protocol) -> Box<dyn CryptoProtocol> {
       match protocol {
           Protocol::Starknet => Box::new(StarknetProtocol),
           Protocol::X25519 => Box::new(X25519Protocol::new()),
           Protocol::NewProtocol => Box::new(NewProtocol::new()), // Add here
       }
   }

4. Update Documentation

   • Add protocol-specific documentation

   • Update this overview page

   • Include examples and use cases

Security Considerations

Protocol-Specific Security

• Starknet: Based on well-established ECDSA and ECDH on the Stark curve

• X25519: Standard Curve25519 implementation with proven security

Cross-Protocol Security

• Each protocol maintains its own security properties

• No security degradation when mixing protocols

• All protocols provide equivalent security levels

Key Management

• Each protocol has its own key format and validation

• Keys are never converted between protocols

• Protocol-specific key derivation ensures isolation

Future Protocol Support

Planned protocol additions:

• Secp256k1: For Bitcoin/Ethereum compatibility

• Ed25519: For high-performance signature schemes

• P-256: For FIPS compliance

• Custom Curves: For specialized use cases

Protocol Testing

Each protocol includes comprehensive tests:

# Test specific protocol
cargo test --test starknet_protocol
cargo test --test x25519_protocol

# Test cross-protocol functionality
cargo test --test cross_protocol

Getting Help

• Check protocol-specific documentation for detailed information

• Review the API Reference for function documentation

• See Examples for practical use cases

• Open an issue for protocol-specific questions or bugs