Falcon-512 Security-Focused API Documentation

Version: 1.0
Last Updated: 2025-07-05
**Security Classification: PUBLIC
Author: Phantom (phantom@metamui.id)

Overview

Falcon-512 is a post-quantum digital signature scheme based on the NTRU lattice and selected as one of NIST’s post-quantum cryptography standards. It provides 128-bit classical security and strong quantum resistance through compact signatures and efficient verification. Falcon uses a trapdoor sampler over NTRU lattices with Gaussian sampling for security.

Security Level: NIST Level 1 (128-bit classical, ~2^64 quantum)
Public Key Size: 897 bytes
Private Key Size: 1281 bytes
Signature Size: ~666 bytes (variable)
Quantum Security: Strong lattice-based resistance

Security Warnings ⚠️

Post-Quantum Ready: Designed specifically for quantum-resistant security
Variable Signatures: Signature sizes vary due to rejection sampling
Side-Channel Sensitive: Implementation must protect against timing/power attacks
Key Generation Critical: Requires high-quality randomness for security
Not Deterministic: Same message produces different signatures

API Functions

`falcon512_keygen() -> (PublicKey[897], PrivateKey[1281])`

Security Contract:

Preconditions:
- System CSPRNG must be available
- Sufficient entropy for lattice sampling
- Implementation protects against side-channels
Postconditions:
- Returns mathematically valid key pair
- Private key enables signing, public key enables verification
- Keys are independent across generations

Security Requirements:

Use cryptographically secure randomness
Protect private key generation from observation
Implement constant-time operations where possible
Secure key storage with proper access controls

Secure Usage Example:

import secrets
import hashlib
from typing import Tuple, Optional
import time
import json

class SecureFalcon512:
    """Secure Falcon-512 implementation with best practices"""
    
    def __init__(self):
        self.key_pair = None
        self.key_generation_time = None
        self.usage_counter = 0
        
    def generate_keypair(self, entropy_sources: Optional[list] = None) -> dict:
        """Generate Falcon-512 key pair with enhanced entropy"""
        
        # Gather entropy from multiple sources
        entropy_pool = bytearray()
        
        # System randomness
        entropy_pool.extend(secrets.token_bytes(64))
        
        # High-resolution timing
        import time
        timing_entropy = str(time.perf_counter_ns()).encode()
        entropy_pool.extend(hashlib.sha256(timing_entropy).digest())
        
        # Additional entropy sources if provided
        if entropy_sources:
            for source in entropy_sources:
                if hasattr(source, 'read'):
                    # File-like entropy source
                    entropy_pool.extend(source.read(32))
                else:
                    # Byte entropy source
                    entropy_pool.extend(bytes(source)[:32])
        
        # Process entropy
        final_seed = hashlib.shake_256(
            b"Falcon512-KeyGen-v1:" + bytes(entropy_pool)
        ).digest(64)
        
        # Clear entropy pool
        for i in range(len(entropy_pool)):
            entropy_pool[i] = 0
        
        # Generate key pair (using final_seed for deterministic generation)
        public_key, private_key = self._falcon512_keygen_from_seed(final_seed)
        
        # Store key pair
        self.key_pair = {
            'public_key': public_key,
            'private_key': private_key,
            'generated_at': time.time(),
            'algorithm': 'Falcon-512',
            'version': '1.0'
        }
        
        self.key_generation_time = time.time()
        
        # Clear seed
        for i in range(len(final_seed)):
            final_seed[i] = 0
        
        return {
            'public_key': public_key.hex(),
            'key_id': self._compute_key_id(public_key),
            'algorithm': 'Falcon-512',
            'generated_at': self.key_generation_time
        }
    
    def _falcon512_keygen_from_seed(self, seed: bytes) -> Tuple[bytes, bytes]:
        """Generate Falcon-512 keys from seed (implementation placeholder)"""
        
        # This would call the actual Falcon-512 implementation
        # For security, this should be implemented with:
        # - Constant-time operations where possible
        # - Secure sampling procedures
        # - Protection against timing attacks
        
        # Placeholder implementation
        from falcon_crypto import falcon512_keygen_seeded
        return falcon512_keygen_seeded(seed)
    
    def _compute_key_id(self, public_key: bytes) -> str:
        """Compute stable identifier for public key"""
        
        key_hash = hashlib.sha256(
            b"Falcon512-KeyID:" + public_key
        ).digest()
        
        return key_hash[:16].hex()
    
    def export_public_key(self, format: str = "raw") -> dict:
        """Export public key in specified format"""
        
        if not self.key_pair:
            raise ValueError("No key pair generated")
        
        public_key = self.key_pair['public_key']
        
        if format == "raw":
            return {
                'public_key': public_key.hex(),
                'format': 'raw',
                'algorithm': 'Falcon-512'
            }
        elif format == "der":
            # DER encoding would be implemented here
            der_encoded = self._encode_public_key_der(public_key)
            return {
                'public_key': der_encoded.hex(),
                'format': 'DER',
                'algorithm': 'Falcon-512'
            }
        else:
            raise ValueError(f"Unsupported format: {format}")
    
    def should_rotate_keys(self, max_age_days: int = 365) -> bool:
        """Check if keys should be rotated"""
        
        if not self.key_generation_time:
            return True
        
        age_seconds = time.time() - self.key_generation_time
        age_days = age_seconds / (24 * 3600)
        
        return age_days > max_age_days

# SECURE: Long-term key management
class Falcon512KeyManager:
    def __init__(self, storage_backend):
        self.storage = storage_backend
        self.active_keys = {}
        self.rotation_policy = {
            'max_age_days': 365,
            'max_signatures': 1000000,
            'emergency_rotation': False
        }
    
    def create_signing_key(self, key_id: str, context: str) -> dict:
        """Create new signing key with metadata"""
        
        falcon = SecureFalcon512()
        key_data = falcon.generate_keypair()
        
        # Add metadata
        metadata = {
            'key_id': key_id,
            'context': context,
            'created_at': time.time(),
            'signature_count': 0,
            'status': 'active',
            'public_key': key_data['public_key'],
            'algorithm': 'Falcon-512'
        }
        
        # Store securely
        self.storage.store_private_key(
            key_id,
            falcon.key_pair['private_key'],
            metadata
        )
        
        self.active_keys[key_id] = {
            'falcon': falcon,
            'metadata': metadata
        }
        
        return metadata
    
    def get_verification_key(self, key_id: str) -> Optional[bytes]:
        """Get public key for verification"""
        
        if key_id in self.active_keys:
            return self.active_keys[key_id]['falcon'].key_pair['public_key']
        
        # Try loading from storage
        metadata = self.storage.get_key_metadata(key_id)
        if metadata:
            return bytes.fromhex(metadata['public_key'])
        
        return None
    
    def rotate_key_if_needed(self, key_id: str) -> bool:
        """Rotate key if policy requires it"""
        
        if key_id not in self.active_keys:
            return False
        
        key_data = self.active_keys[key_id]
        metadata = key_data['metadata']
        
        # Check rotation conditions
        age_days = (time.time() - metadata['created_at']) / (24 * 3600)
        
        should_rotate = (
            age_days > self.rotation_policy['max_age_days'] or
            metadata['signature_count'] > self.rotation_policy['max_signatures'] or
            self.rotation_policy['emergency_rotation']
        )
        
        if should_rotate:
            # Create new key
            new_key_id = f"{key_id}-rotated-{int(time.time())}"
            self.create_signing_key(new_key_id, metadata['context'])
            
            # Mark old key as deprecated
            metadata['status'] = 'deprecated'
            metadata['deprecated_at'] = time.time()
            
            return True
        
        return False

# SECURE: Message signing with domain separation
def falcon512_sign_message(
    private_key: bytes,
    message: bytes,
    context: str = "",
    timestamp: bool = True
) -> dict:
    """Sign message with Falcon-512 including context"""
    
    # Build signing input with domain separation
    signing_input = bytearray()
    
    # Add context for domain separation
    if context:
        signing_input.extend(b"Falcon512-Context:")
        signing_input.extend(context.encode())
        signing_input.extend(b"\n")
    
    # Add timestamp if requested
    if timestamp:
        ts = int(time.time())
        signing_input.extend(b"Timestamp:")
        signing_input.extend(str(ts).encode())
        signing_input.extend(b"\n")
    
    # Add message
    signing_input.extend(b"Message:")
    signing_input.extend(message)
    
    # Hash the complete input
    message_hash = hashlib.sha256(signing_input).digest()
    
    # Sign the hash
    signature = _falcon512_sign_hash(private_key, message_hash)
    
    result = {
        'signature': signature.hex(),
        'message_hash': message_hash.hex(),
        'algorithm': 'Falcon-512',
        'version': '1.0'
    }
    
    if context:
        result['context'] = context
    
    if timestamp:
        result['timestamp'] = ts
    
    return result

Common Mistakes:

# INSECURE: Weak randomness for key generation
import random
seed = random.getrandbits(256)  # NOT cryptographically secure!

# INSECURE: Reusing ephemeral values
# Falcon uses randomness in signing - implementation must be secure

# INSECURE: No side-channel protection
# Timing attacks can reveal private key information

# INSECURE: Storing private key in plaintext
with open('private.key', 'w') as f:
    f.write(private_key.hex())  # Unencrypted storage!

# INSECURE: No domain separation
sig1 = falcon512_sign(key, message)  # Could be replayed in other contexts

`falcon512_sign(private_key: bytes[1281], message: bytes) -> bytes[~666]`

Security Contract:

Preconditions:
- private_key must be valid Falcon-512 private key
- message can be any length
- Implementation uses secure randomness for signing
Postconditions:
- Returns valid signature for message
- Signature size varies (rejection sampling)
- Non-deterministic (different each time)

Security Requirements:

Use fresh randomness for each signature
Protect signing process from observation
Include context/domain separation
Implement proper rejection sampling

Secure Usage Example:

use falcon::{Falcon512, PrivateKey, Signature};
use rand::{RngCore, thread_rng};
use zeroize::Zeroize;

/// Secure Falcon-512 signing with context
pub struct SecureFalconSigner {
    private_key: PrivateKey,
    signature_count: u64,
    context: String,
}

impl SecureFalconSigner {
    pub fn new(private_key: PrivateKey, context: String) -> Self {
        Self {
            private_key,
            signature_count: 0,
            context,
        }
    }
    
    pub fn sign_with_metadata(
        &mut self,
        message: &[u8],
        additional_context: Option<&str>,
    ) -> Result<SignedMessage, Error> {
        // Build complete message with metadata
        let mut signing_data = Vec::new();
        
        // Add primary context
        signing_data.extend_from_slice(b"Context:");
        signing_data.extend_from_slice(self.context.as_bytes());
        signing_data.push(b'\n');
        
        // Add additional context if provided
        if let Some(ctx) = additional_context {
            signing_data.extend_from_slice(b"AdditionalContext:");
            signing_data.extend_from_slice(ctx.as_bytes());
            signing_data.push(b'\n');
        }
        
        // Add sequence number
        signing_data.extend_from_slice(b"Sequence:");
        signing_data.extend_from_slice(&self.signature_count.to_le_bytes());
        signing_data.push(b'\n');
        
        // Add timestamp
        let timestamp = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap()
            .as_secs();
        signing_data.extend_from_slice(b"Timestamp:");
        signing_data.extend_from_slice(&timestamp.to_le_bytes());
        signing_data.push(b'\n');
        
        // Add actual message
        signing_data.extend_from_slice(b"Message:");
        signing_data.extend_from_slice(message);
        
        // Sign the complete data
        let signature = self.private_key.sign(&signing_data, &mut thread_rng())?;
        
        self.signature_count += 1;
        
        Ok(SignedMessage {
            message: message.to_vec(),
            signature,
            context: self.context.clone(),
            additional_context: additional_context.map(|s| s.to_string()),
            sequence: self.signature_count - 1,
            timestamp,
        })
    }
    
    pub fn sign_digest(
        &mut self,
        digest: &[u8; 32],
        algorithm: &str,
    ) -> Result<Signature, Error> {
        // For pre-hashed signing
        let mut signing_data = Vec::new();
        signing_data.extend_from_slice(b"PrehashedMessage:");
        signing_data.extend_from_slice(algorithm.as_bytes());
        signing_data.push(b':');
        signing_data.extend_from_slice(digest);
        
        self.private_key.sign(&signing_data, &mut thread_rng())
    }
}

impl Drop for SecureFalconSigner {
    fn drop(&mut self) {
        // Zeroize private key on drop
        self.private_key.zeroize();
    }
}

#[derive(Debug)]
pub struct SignedMessage {
    pub message: Vec<u8>,
    pub signature: Signature,
    pub context: String,
    pub additional_context: Option<String>,
    pub sequence: u64,
    pub timestamp: u64,
}

/// Batch signing for efficiency
pub struct BatchFalconSigner {
    signer: SecureFalconSigner,
}

impl BatchFalconSigner {
    pub fn sign_batch(
        &mut self,
        messages: &[&[u8]],
    ) -> Result<Vec<Signature>, Error> {
        let mut signatures = Vec::with_capacity(messages.len());
        
        for message in messages {
            let signed = self.signer.sign_with_metadata(message, None)?;
            signatures.push(signed.signature);
        }
        
        Ok(signatures)
    }
    
    pub fn sign_merkle_tree(
        &mut self,
        leaves: &[&[u8]],
    ) -> Result<TreeSignature, Error> {
        // Create Merkle tree and sign root
        let tree = MerkleTree::new(leaves)?;
        let root_signature = self.signer.sign_with_metadata(
            &tree.root(),
            Some("MerkleTree")
        )?;
        
        Ok(TreeSignature {
            root_signature,
            tree,
        })
    }
}

`falcon512_verify(public_key: bytes[897], message: bytes, signature: bytes) -> bool`

Security Contract:

Preconditions:
- public_key must be valid Falcon-512 public key
- message is the original signed message
- signature is putative Falcon-512 signature
Postconditions:
- Returns true if signature is valid
- Returns false for any invalid signature
- Constant-time verification preferred

Security Requirements:

Verify signature format before processing
Use constant-time comparison operations
Validate public key format
Check signature bounds

Secure Usage Example:

class Falcon512Verifier:
    """Secure Falcon-512 signature verification"""
    
    def __init__(self):
        self.trusted_keys = {}
        self.verification_cache = {}
        
    def add_trusted_key(self, key_id: str, public_key: bytes, metadata: dict):
        """Add trusted public key"""
        
        # Validate public key format
        if len(public_key) != 897:
            raise ValueError("Invalid Falcon-512 public key size")
        
        # Verify key structure (implementation specific)
        if not self._validate_public_key_structure(public_key):
            raise ValueError("Invalid Falcon-512 public key structure")
        
        self.trusted_keys[key_id] = {
            'public_key': public_key,
            'metadata': metadata,
            'added_at': time.time()
        }
    
    def verify_signed_message(
        self,
        signed_message: dict,
        key_id: str,
        expected_context: str = ""
    ) -> bool:
        """Verify complete signed message"""
        
        if key_id not in self.trusted_keys:
            return False
        
        public_key = self.trusted_keys[key_id]['public_key']
        
        # Reconstruct signing input
        signing_input = bytearray()
        
        # Add context if present
        if 'context' in signed_message:
            if expected_context and signed_message['context'] != expected_context:
                return False
            
            signing_input.extend(b"Falcon512-Context:")
            signing_input.extend(signed_message['context'].encode())
            signing_input.extend(b"\n")
        
        # Add timestamp if present
        if 'timestamp' in signed_message:
            # Check timestamp freshness (optional)
            current_time = int(time.time())
            if abs(current_time - signed_message['timestamp']) > 3600:  # 1 hour
                return False
            
            signing_input.extend(b"Timestamp:")
            signing_input.extend(str(signed_message['timestamp']).encode())
            signing_input.extend(b"\n")
        
        # Add message
        signing_input.extend(b"Message:")
        signing_input.extend(signed_message['message'].encode())
        
        # Hash the complete input
        message_hash = hashlib.sha256(signing_input).digest()
        
        # Verify signature
        signature = bytes.fromhex(signed_message['signature'])
        
        return self._falcon512_verify_hash(public_key, message_hash, signature)
    
    def verify_with_caching(
        self,
        public_key: bytes,
        message: bytes,
        signature: bytes
    ) -> bool:
        """Verify with result caching for performance"""
        
        # Create cache key
        cache_key = hashlib.sha256(
            public_key + message + signature
        ).digest()[:16].hex()
        
        # Check cache
        if cache_key in self.verification_cache:
            cached_result, cached_time = self.verification_cache[cache_key]
            
            # Use cached result if recent (within 5 minutes)
            if time.time() - cached_time < 300:
                return cached_result
        
        # Perform verification
        result = self._falcon512_verify_hash(public_key, message, signature)
        
        # Cache result
        self.verification_cache[cache_key] = (result, time.time())
        
        # Limit cache size
        if len(self.verification_cache) > 1000:
            # Remove oldest entries
            sorted_cache = sorted(
                self.verification_cache.items(),
                key=lambda x: x[1][1]
            )
            
            # Keep newest 800 entries
            self.verification_cache = dict(sorted_cache[-800:])
        
        return result
    
    def batch_verify(
        self,
        verifications: list
    ) -> list:
        """Batch verify multiple signatures"""
        
        results = []
        
        for verification in verifications:
            public_key = verification['public_key']
            message = verification['message']
            signature = verification['signature']
            
            result = self.verify_with_caching(public_key, message, signature)
            results.append(result)
        
        return results
    
    def _validate_public_key_structure(self, public_key: bytes) -> bool:
        """Validate Falcon-512 public key structure"""
        
        # Implementation would check:
        # - Key coefficients are in valid range
        # - Key follows Falcon format specification
        # - Mathematical constraints are satisfied
        
        # Placeholder implementation
        return True
    
    def _falcon512_verify_hash(
        self,
        public_key: bytes,
        message_hash: bytes,
        signature: bytes
    ) -> bool:
        """Low-level Falcon-512 verification"""
        
        # This would call the actual Falcon-512 implementation
        from falcon_crypto import falcon512_verify
        
        try:
            return falcon512_verify(public_key, message_hash, signature)
        except Exception:
            return False

Security Best Practices

Key Lifecycle Management

/// Complete key lifecycle for Falcon-512
pub struct Falcon512Lifecycle {
    key_store: SecureKeyStore,
    audit_log: AuditLogger,
}

impl Falcon512Lifecycle {
    pub fn create_key_with_ceremony(
        &mut self,
        key_id: &str,
        ceremony_participants: &[&str],
    ) -> Result<KeyCeremonyResult, Error> {
        // Key generation ceremony with multiple participants
        let mut entropy_contributions = Vec::new();
        
        // Collect entropy from each participant
        for participant in ceremony_participants {
            let contribution = self.collect_entropy_from_participant(participant)?;
            entropy_contributions.push(contribution);
        }
        
        // Combine entropy sources
        let combined_entropy = self.combine_entropy_sources(&entropy_contributions)?;
        
        // Generate key pair
        let (public_key, private_key) = self.generate_key_from_entropy(&combined_entropy)?;
        
        // Create key shares for distributed storage
        let key_shares = self.create_key_shares(&private_key, ceremony_participants.len())?;
        
        // Store key metadata
        let metadata = KeyMetadata {
            key_id: key_id.to_string(),
            created_at: chrono::Utc::now(),
            ceremony_participants: ceremony_participants.iter().map(|s| s.to_string()).collect(),
            key_type: "Falcon-512".to_string(),
            status: KeyStatus::Active,
        };
        
        self.key_store.store_public_key(key_id, &public_key, &metadata)?;
        
        // Distribute private key shares
        for (i, share) in key_shares.iter().enumerate() {
            self.key_store.store_key_share(
                key_id,
                ceremony_participants[i],
                share,
            )?;
        }
        
        // Log the ceremony
        self.audit_log.log_key_generation_ceremony(key_id, ceremony_participants)?;
        
        // Clear sensitive data
        combined_entropy.zeroize();
        private_key.zeroize();
        
        Ok(KeyCeremonyResult {
            key_id: key_id.to_string(),
            public_key,
            metadata,
        })
    }
    
    pub fn reconstruct_key_for_signing(
        &self,
        key_id: &str,
        participant_shares: &[(String, KeyShare)],
        threshold: usize,
    ) -> Result<TemporarySigningKey, Error> {
        if participant_shares.len() < threshold {
            return Err(Error::InsufficientShares);
        }
        
        // Verify shares
        for (participant, share) in participant_shares {
            if !self.key_store.verify_key_share(key_id, participant, share)? {
                return Err(Error::InvalidKeyShare);
            }
        }
        
        // Reconstruct private key
        let private_key = self.reconstruct_private_key(participant_shares)?;
        
        // Create temporary signing key with time limit
        Ok(TemporarySigningKey::new(
            private_key,
            std::time::Duration::from_secs(300), // 5 minutes
        ))
    }
}

Certificate Authority Integration

class Falcon512CertificateAuthority:
    """Post-quantum certificate authority using Falcon-512"""
    
    def __init__(self, ca_private_key: bytes, ca_cert: dict):
        self.ca_private_key = ca_private_key
        self.ca_cert = ca_cert
        self.issued_certificates = {}
        self.revoked_certificates = set()
        
    def issue_certificate(
        self,
        subject_public_key: bytes,
        subject_info: dict,
        validity_period_days: int = 365
    ) -> dict:
        """Issue post-quantum certificate"""
        
        # Create certificate structure
        cert_data = {
            'version': 3,
            'serial_number': self._generate_serial_number(),
            'issuer': self.ca_cert['subject'],
            'subject': subject_info,
            'public_key': {
                'algorithm': 'Falcon-512',
                'key': subject_public_key.hex()
            },
            'validity': {
                'not_before': int(time.time()),
                'not_after': int(time.time()) + (validity_period_days * 24 * 3600)
            },
            'extensions': {
                'key_usage': ['digital_signature', 'key_agreement'],
                'extended_key_usage': ['client_auth', 'server_auth'],
                'subject_alt_name': subject_info.get('alt_names', [])
            }
        }
        
        # Serialize certificate for signing
        cert_bytes = self._serialize_certificate(cert_data)
        
        # Sign certificate with CA key
        signature_data = falcon512_sign_message(
            self.ca_private_key,
            cert_bytes,
            context="X.509-Certificate-v3",
            timestamp=True
        )
        
        # Complete certificate
        certificate = {
            **cert_data,
            'signature': {
                'algorithm': 'Falcon-512',
                'value': signature_data['signature']
            }
        }
        
        # Store issued certificate
        serial = cert_data['serial_number']
        self.issued_certificates[serial] = certificate
        
        return certificate
    
    def verify_certificate_chain(
        self,
        cert_chain: list,
        trusted_roots: list
    ) -> bool:
        """Verify post-quantum certificate chain"""
        
        if not cert_chain:
            return False
        
        # Check each certificate in chain
        for i, cert in enumerate(cert_chain):
            if i == 0:
                # End entity certificate
                if not self._verify_certificate_validity(cert):
                    return False
            else:
                # Intermediate or root certificate
                if not self._verify_certificate_validity(cert):
                    return False
                
                # Verify signature on previous certificate
                prev_cert = cert_chain[i-1]
                if not self._verify_certificate_signature(prev_cert, cert):
                    return False
        
        # Verify root certificate is trusted
        root_cert = cert_chain[-1]
        if not any(self._certificates_equal(root_cert, trusted) 
                  for trusted in trusted_roots):
            return False
        
        return True
    
    def revoke_certificate(self, serial_number: str, reason: str):
        """Revoke certificate"""
        
        self.revoked_certificates.add(serial_number)
        
        # Update Certificate Revocation List
        self._update_crl(serial_number, reason)
    
    def generate_crl(self) -> dict:
        """Generate Certificate Revocation List"""
        
        crl_data = {
            'version': 2,
            'issuer': self.ca_cert['subject'],
            'this_update': int(time.time()),
            'next_update': int(time.time()) + (7 * 24 * 3600),  # 7 days
            'revoked_certificates': [
                {
                    'serial_number': serial,
                    'revocation_date': int(time.time()),
                    'reason': 'unspecified'
                }
                for serial in self.revoked_certificates
            ]
        }
        
        # Sign CRL
        crl_bytes = self._serialize_crl(crl_data)
        signature_data = falcon512_sign_message(
            self.ca_private_key,
            crl_bytes,
            context="X.509-CRL-v2"
        )
        
        return {
            **crl_data,
            'signature': {
                'algorithm': 'Falcon-512',
                'value': signature_data['signature']
            }
        }

Common Integration Patterns

Hybrid Classical/Post-Quantum Signatures

/// Dual signature with classical and post-quantum algorithms
pub struct HybridSigner {
    ecdsa_key: EcdsaPrivateKey,
    falcon_key: Falcon512PrivateKey,
}

impl HybridSigner {
    pub fn sign_hybrid(&self, message: &[u8]) -> HybridSignature {
        // Sign with both algorithms
        let ecdsa_sig = self.ecdsa_key.sign(message);
        let falcon_sig = self.falcon_key.sign(message);
        
        HybridSignature {
            ecdsa: ecdsa_sig,
            falcon: falcon_sig,
        }
    }
    
    pub fn verify_hybrid(
        &self,
        message: &[u8],
        signature: &HybridSignature,
    ) -> bool {
        // Both signatures must be valid
        self.ecdsa_key.verify(message, &signature.ecdsa) &&
        self.falcon_key.verify(message, &signature.falcon)
    }
}

Blockchain Integration

def falcon512_blockchain_transaction_signing():
    """Example of Falcon-512 in blockchain context"""
    
    class PostQuantumTransaction:
        def __init__(self, sender_key, recipient, amount):
            self.sender_key = sender_key
            self.recipient = recipient
            self.amount = amount
            self.timestamp = int(time.time())
            self.nonce = secrets.token_bytes(32)
            
        def sign_transaction(self):
            # Create transaction data
            tx_data = {
                'sender': self.sender_key['public_key'],
                'recipient': self.recipient,
                'amount': self.amount,
                'timestamp': self.timestamp,
                'nonce': self.nonce.hex()
            }
            
            # Serialize for signing
            tx_bytes = json.dumps(tx_data, sort_keys=True).encode()
            
            # Sign with Falcon-512
            signature = falcon512_sign_message(
                self.sender_key['private_key'],
                tx_bytes,
                context="Blockchain-Transaction-v1"
            )
            
            return {
                **tx_data,
                'signature': signature['signature']
            }

Performance Considerations

Operation	Time (ms)	Size (bytes)	Notes
Key Generation	15-25	-	Variable due to rejection sampling
Signing	5-15	~666	Variable signature size
Verification	0.1-0.2	-	Fast verification
Public Key	-	897	Fixed size
Private Key	-	1281	Fixed size

Optimization Strategies

Pre-generate key pairs for batch operations
Cache verification results for repeated checks
Use hardware acceleration where available
Implement tree signatures for bulk signing

Security Auditing

Verification Checklist

Using cryptographically secure randomness
Protecting key generation from side-channels
Implementing proper rejection sampling
Adding domain separation to signatures
Securing private key storage
Implementing key rotation policies
Validating signature formats before verification

Common Vulnerabilities

# AUDIT: Look for these patterns

# ❌ Weak randomness
import random
private_key = generate_falcon_key(random.getrandbits(256))

# ❌ Deterministic signing (if incorrectly implemented)
# Falcon should be probabilistic

# ❌ No domain separation
sig1 = falcon512_sign(key, message)  # Could be replayed

# ❌ Side-channel vulnerable implementation
# Timing/power attacks on key generation or signing

# ❌ Insecure key storage
pickle.dump(private_key, open('key.pkl', 'wb'))

Security Analysis

Threat Model: Falcon-512 Threat Model

The comprehensive threat analysis covers:

Algorithm-specific attack vectors
Implementation vulnerabilities
Side-channel considerations
Quantum resistance analysis (where applicable)
Deployment recommendations

For complete security analysis and risk assessment, see the dedicated threat model documentation.

References

Support

Security Issues: security@metamui.id
Documentation Updates: phantom@metamui.id
Vulnerability Disclosure: See SECURITY.md

Document Version: 1.0
Review Cycle: Quarterly
Next Review: 2025-04-05
Classification: PUBLIC