Built-in Signature Schemes

Psy provides two built-in signature schemes that serve different use cases and performance requirements.

ZK Key Signature

The ZK signature scheme is Psy's optimized zero-knowledge signature system.

Characteristics

• Signature Type: zk
• Proof Generation Time: 2-5 seconds
• Circuit Optimization: Highly optimized for fast proving
• Security Model: Zero-knowledge proof of secret knowledge
• Quantum Resistance: Designed with post-quantum considerations

When to Use ZK Keys

✅ Recommended for:

• General-purpose transaction signing
• High-frequency trading applications
• Real-time user interactions
• Mobile and web applications requiring responsive UX
• Applications prioritizing performance

Technical Details

QED ZK Signature Scheme:

public_key_params = hash(private_key, private_key_constants)
fingerprint = hash(verifier_data)
public_key = hash(public_key_params, fingerprint)
sig_action_hash = hash(data, network_magic, nonce)

circuit = private_inputs.private_key.get_public_key() == public_inputs_preimage[0..4]
public_inputs = hash(public_key_params, sig_action_hash)
private_inputs = private_key

Key Features:

• Custom Signature Logic: Supports transaction introspection and custom constraints
• ECDSA Compatibility: Can integrate with existing ECDSA infrastructure
• Quantum Resistance: Designed to be resistant to quantum computing attacks
• Optimized Circuit: Minimal constraint count for fast proving (~2-5 seconds)

SECP256K1 Signature

The SECP256K1 scheme provides compatibility with existing elliptic curve tooling through zero-knowledge proofs.

Characteristics

• Signature Type: secp256k1
• Proof Generation Time: 10-20 seconds
• Circuit Complexity: Higher constraint count
• Security Model: Elliptic curve discrete logarithm
• Compatibility: Works with existing ECDSA tooling

Technical Details

QED Software Defined Signature (SECP256K1):

public_key_hash = hash(secp256k1_public_key)
public_key_params = public_key_hash
fingerprint = hash(verifier_data)
public_key = hash(public_key_params, fingerprint)
sig_action_hash = hash(data, network_magic, nonce)

circuit = {
  hash(private_inputs.secp256k1_public_key) == public_inputs[0..4]
  secp256k1_verify(private_inputs.secp256k1_public_key, secp256k1_signature, sig_action_hash)
}
public_inputs = hash(public_key_params, sig_action_hash)
private_inputs = secp256k1_public_key, secp256k1_signature, sig_action_hash_preimage

Circuit Implementation:

• ECDSA Verification: Implements SECP256K1 signature verification in ZK circuit
• Public Key Validation: Proves knowledge of private key without revealing it
• Higher Complexity: More constraints result in longer proving times
• Backward Compatibility: Enables migration from traditional ECDSA systems

When to Use SECP256K1

⚠️ Use only when:

• Migrating from existing ECDSA-based systems
• Requiring compatibility with external tools
• Working with legacy applications
• Development and testing scenarios

Performance Impact

The longer proof generation time of SECP256K1 makes it less suitable for:

• Interactive applications requiring quick responses
• High-throughput systems
• Mobile applications with limited computational resources
• Real-time trading platforms

Comparison Table

Choosing the Right Scheme

Default Choice: ZK Key

For most applications, ZK key (zk) is the recommended choice because:

# Fast and efficient for most use cases
psy_user_cli register-user --private-key <key> --sign-type zk

When SECP256K1 Might Be Needed

# Only for specific compatibility requirements
psy_user_cli register-user --private-key <key> --sign-type secp256k1

Consider SECP256K1 only if you have specific requirements for:

• Integration with existing ECDSA infrastructure
• Migration scenarios from traditional blockchain systems
• Development environments requiring ECDSA tooling

Performance Benchmarks

Proof Generation Times

Based on standard hardware configurations:

ZK Key Performance:

• Consumer laptop: ~2-3 seconds
• Server hardware: ~1-2 seconds
• Mobile device: ~4-5 seconds

SECP256K1 Performance:

• Consumer laptop: ~12-15 seconds
• Server hardware: ~8-10 seconds
• Mobile device: ~18-25 seconds

Resource Usage

ZK Key:

• Memory usage: Moderate
• CPU utilization: Efficient
• Battery impact: Low (mobile)

SECP256K1:

• Memory usage: Higher
• CPU utilization: Intensive
• Battery impact: Significant (mobile)

Migration Considerations

Upgrading from SECP256K1 to ZK

If you're currently using SECP256K1 and want to upgrade:

1. Generate a new ZK key pair
2. Register the new public key
3. Update applications to use the new key
4. Gradually migrate transaction signing

Backward Compatibility

Both signature schemes can coexist in the same application:

• Different users can use different schemes
• Applications can support both simultaneously
• Gradual migration strategies are supported

Best Practices

For New Applications

# Always prefer ZK keys for new implementations
SIGN_TYPE=zk
psy_user_cli wallet create
psy_user_cli register-user --sign-type ${SIGN_TYPE}

For Existing Systems

1. Evaluate Requirements: Determine if ECDSA compatibility is truly needed
2. Performance Testing: Measure actual proof generation times in your environment
3. User Experience: Consider the impact of longer signing times
4. Migration Planning: Plan for eventual upgrade to ZK keys

Development vs Production

Development:

# Fast iteration with ZK keys
SIGN_TYPE=zk make register-user

Legacy Testing:

# When testing ECDSA compatibility
SIGN_TYPE=secp256k1 make register-user

Future Considerations

Roadmap

• Custom Circuits: Support for user-defined signature circuits
• Aggregated Signatures: Batch verification optimizations
• Hardware Acceleration: GPU and specialized hardware support
• Mobile Optimization: Further optimizations for mobile devices

Deprecation Timeline

While SECP256K1 support will continue, new features and optimizations will focus on ZK-based schemes. Plan migration to ZK keys for long-term compatibility.