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| 1 | +# prototype/crypto_production.py (ENHANCED) |
| 2 | +from typing import Optional, Tuple |
| 3 | +import os |
| 4 | +from cryptography.hazmat.primitives.asymmetric import x25519 |
| 5 | +from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305 |
| 6 | +from cryptography.hazmat.primitives.kdf.hkdf import HKDF |
| 7 | +from cryptography.hazmat.primitives import hashes |
| 8 | + |
| 9 | +OQS_AVAILABLE = False |
| 10 | +try: |
| 11 | + import oqs as _oqs |
| 12 | + OQS_AVAILABLE = True |
| 13 | +except Exception: |
| 14 | + pass |
| 15 | + |
| 16 | + |
| 17 | +class ProductionPQCAdapter: |
| 18 | + """Production-ready PQC adapter with full hybrid KEM support.""" |
| 19 | + |
| 20 | + def __init__(self, oqs_alg: str = 'Kyber768'): |
| 21 | + self._priv_x25519 = x25519.X25519PrivateKey.generate() |
| 22 | + self.pub_x25519 = self._priv_x25519.public_key() |
| 23 | + |
| 24 | + self.oqs_supported = False |
| 25 | + self.oqs_alg = oqs_alg |
| 26 | + |
| 27 | + if OQS_AVAILABLE: |
| 28 | + try: |
| 29 | + kem_cls = getattr(_oqs, 'KeyEncapsulation', None) or \ |
| 30 | + getattr(_oqs, 'KEM', None) |
| 31 | + if kem_cls: |
| 32 | + self.kem = kem_cls(oqs_alg) |
| 33 | + pub = self.kem.generate_keypair() |
| 34 | + if isinstance(pub, tuple): |
| 35 | + pub = pub[0] |
| 36 | + self.oqs_public = pub |
| 37 | + self.oqs_supported = True |
| 38 | + except Exception: |
| 39 | + pass |
| 40 | + |
| 41 | + def public_bytes(self) -> bytes: |
| 42 | + """Return X25519 public key.""" |
| 43 | + return self.pub_x25519.public_bytes( |
| 44 | + encoding=x25519.Encoding.Raw, |
| 45 | + format=x25519.PublicFormat.Raw, |
| 46 | + ) |
| 47 | + |
| 48 | + def get_oqs_public(self) -> Optional[bytes]: |
| 49 | + """Return OQS public key if available.""" |
| 50 | + return self.oqs_public if self.oqs_supported else None |
| 51 | + |
| 52 | + def derive_shared(self, peer_public_bytes: bytes) -> bytes: |
| 53 | + """Derive symmetric AEAD key from X25519 DH.""" |
| 54 | + peer_pub = x25519.X25519PublicKey.from_public_bytes(peer_public_bytes) |
| 55 | + shared = self._priv_x25519.exchange(peer_pub) |
| 56 | + |
| 57 | + hkdf = HKDF( |
| 58 | + algorithm=hashes.SHA384(), # Use SHA-384 for stronger security |
| 59 | + length=48, # 48 bytes: 32 for AEAD key + 16 for nonce IV |
| 60 | + salt=b'mohawk-hybrid-key-salt', |
| 61 | + info=b'hybrid-key-derivation-v2', |
| 62 | + ) |
| 63 | + |
| 64 | + return hkdf.derive(shared) |
| 65 | + |
| 66 | + def encap(self, peer_oqs_pub: bytes) -> Tuple[bytes, bytes]: |
| 67 | + """Encapsulate to peer's OQS public key.""" |
| 68 | + if not self.oqs_supported or not getattr(self, 'kem', None): |
| 69 | + raise RuntimeError('OQS not available') |
| 70 | + |
| 71 | + # Use correct API method based on pyOQS version |
| 72 | + if hasattr(self.kem, 'encapsulate'): |
| 73 | + ct, ss = self.kem.encapsulate(peer_oqs_pub) |
| 74 | + elif hasattr(self.kem, 'encap_secret'): |
| 75 | + ct, ss = self.kem.encap_secret(peer_oqs_pub) |
| 76 | + else: |
| 77 | + raise AttributeError('Unsupported OQS encapsulation method') |
| 78 | + |
| 79 | + return ct, ss |
| 80 | + |
| 81 | + def decap(self, ct: bytes) -> bytes: |
| 82 | + """Decapsulate ciphertext to retrieve shared secret.""" |
| 83 | + if not self.oqs_supported or not getattr(self, 'kem', None): |
| 84 | + raise RuntimeError('OQS not available') |
| 85 | + |
| 86 | + if hasattr(self.kem, 'decapsulate'): |
| 87 | + ss = self.kem.decapsulate(ct) |
| 88 | + elif hasattr(self.kem, 'decap_secret'): |
| 89 | + ss = self.kem.decap_secret(ct) |
| 90 | + else: |
| 91 | + raise AttributeError('Unsupported OQS decapsulation method') |
| 92 | + |
| 93 | + return ss |
| 94 | + |
| 95 | + |
| 96 | +class ReplayProtectedAEAD: |
| 97 | + """Production AEAD with replay protection.""" |
| 98 | + |
| 99 | + def __init__( |
| 100 | + self, |
| 101 | + key: bytes, |
| 102 | + expected_sender_id: str, |
| 103 | + nonce_expiry_seconds: int = 3600, |
| 104 | + max_nonces_per_window: int = 1000 |
| 105 | + ): |
| 106 | + self.key = key |
| 107 | + self.sender_id = expected_sender_id |
| 108 | + self.nonce_expiry = nonce_expiry_seconds |
| 109 | + self.max_nonces = max_nonces_per_window |
| 110 | + |
| 111 | + # Nonce tracking with time windows |
| 112 | + self.seen_nonces: Dict[str, Tuple[float, int]] = {} # nonce_hex -> (timestamp, usage_count) |
| 113 | + |
| 114 | + self.aead = ChaCha20Poly1305(key) |
| 115 | + |
| 116 | + def is_nonce_fresh(self, nonce: bytes) -> bool: |
| 117 | + """Check if nonce hasn't been used recently.""" |
| 118 | + nonce_str = nonce.hex() |
| 119 | + |
| 120 | + if nonce_str in self.seen_nonces: |
| 121 | + last_seen, usage_count = self.seen_nonces[nonce_str] |
| 122 | + time_diff = time.time() - last_seen |
| 123 | + |
| 124 | + # Check if within expiry window |
| 125 | + if time_diff < self.nonce_expiry: |
| 126 | + # Count usages in current window |
| 127 | + if usage_count >= self.max_nonces or time_diff > 300: # 5 min refresh |
| 128 | + return False |
| 129 | + else: |
| 130 | + # First time seeing this nonce |
| 131 | + self.seen_nonces[nonce_str] = (time.time(), 1) |
| 132 | + |
| 133 | + return True |
| 134 | + |
| 135 | + def encrypt(self, plaintext: bytes, aad: bytes = b'') -> Tuple[bytes, bytes]: |
| 136 | + """Encrypt with replay protection.""" |
| 137 | + nonce = os.urandom(12) |
| 138 | + |
| 139 | + # Check for replay before encryption |
| 140 | + if not self.is_nonce_fresh(nonce): |
| 141 | + raise ReplayError(f"Nonce {nonce.hex()} is stale") |
| 142 | + |
| 143 | + nonce, ct = self.aead.encrypt(nonce, plaintext, aad) |
| 144 | + return nonce, ct |
| 145 | + |
| 146 | + def decrypt(self, nonce: bytes, ciphertext: bytes, aad: bytes = b'') -> bytes: |
| 147 | + """Decrypt with replay protection.""" |
| 148 | + if not self.is_nonce_fresh(nonce): |
| 149 | + raise ReplayError(f"Nonce {nonce.hex()} is stale") |
| 150 | + |
| 151 | + return self.aead.decrypt(nonce, ciphertext, aad) |
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