def derive_secrets(self,
initiator_nonce: bytes,
responder_nonce: bytes,
remote_ephemeral_pubkey: datatypes.PublicKey,
auth_init_ciphertext: bytes,
auth_ack_ciphertext: bytes
) -> Tuple[bytes, bytes, sha3.keccak_256, sha3.keccak_256]:
"""Derive base secrets from ephemeral key agreement."""
# ecdhe-shared-secret = ecdh.agree(ephemeral-privkey, remote-ephemeral-pubk)
ecdhe_shared_secret = ecies.ecdh_agree(
self.ephemeral_privkey, remote_ephemeral_pubkey)
# shared-secret = sha3(ecdhe-shared-secret || sha3(nonce || initiator-nonce))
shared_secret = keccak(
ecdhe_shared_secret + keccak(responder_nonce + initiator_nonce))
# aes-secret = sha3(ecdhe-shared-secret || shared-secret)
aes_secret = keccak(ecdhe_shared_secret + shared_secret)
# mac-secret = sha3(ecdhe-shared-secret || aes-secret)
mac_secret = keccak(ecdhe_shared_secret + aes_secret)
# setup sha3 instances for the MACs
# egress-mac = sha3.update(mac-secret ^ recipient-nonce || auth-sent-init)
mac1 = sha3.keccak_256(sxor(mac_secret, responder_nonce) + auth_init_ciphertext)
# ingress-mac = sha3.update(mac-secret ^ initiator-nonce || auth-recvd-ack)
mac2 = sha3.keccak_256(sxor(mac_secret, initiator_nonce) + auth_ack_ciphertext)
if self._is_initiator:
egress_mac, ingress_mac = mac1, mac2
else:
egress_mac, ingress_mac = mac2, mac1
return aes_secret, mac_secret, egress_mac, ingress_mac
def create_auth_message(self, nonce: bytes) -> bytes:
ecdh_shared_secret = ecies.ecdh_agree(self.privkey, self.remote.pubkey)
secret_xor_nonce = sxor(ecdh_shared_secret, nonce)
# S(ephemeral-privk, ecdh-shared-secret ^ nonce)
S = self.ephemeral_privkey.sign_msg_hash(secret_xor_nonce).to_bytes()
# S || H(ephemeral-pubk) || pubk || nonce || 0x0
return (S + keccak(self.ephemeral_pubkey.to_bytes()) +
self.pubkey.to_bytes() + nonce + b'\x00')
def decode_authentication(self, ciphertext: bytes) -> Tuple[datatypes.PublicKey, bytes]:
"""Decrypts and decodes the auth_init message.
Returns the initiator's ephemeral pubkey and nonce.
"""
if len(ciphertext) < ENCRYPTED_AUTH_MSG_LEN:
raise ValueError("Auth msg too short: {}".format(len(ciphertext)))
elif len(ciphertext) == ENCRYPTED_AUTH_MSG_LEN:
sig, initiator_pubkey, initiator_nonce, version = decode_auth_plain(
ciphertext, self.privkey)
else:
sig, initiator_pubkey, initiator_nonce, version = decode_auth_eip8(
ciphertext, self.privkey)
self.got_eip8_auth = True
# recover initiator ephemeral pubkey from sig
# S(ephemeral-privk, ecdh-shared-secret ^ nonce)
shared_secret = ecies.ecdh_agree(self.privkey, initiator_pubkey)
ephem_pubkey = sig.recover_public_key_from_msg_hash(
sxor(shared_secret, initiator_nonce))
return ephem_pubkey, initiator_nonce
def test_ecdh(privkey_hex, pubkey_hex, ecdh_expected):
privkey = keys.PrivateKey(decode_hex(privkey_hex))
pubkey = keys.PublicKey(decode_hex(pubkey_hex))
assert ecdh_expected == encode_hex(ecies.ecdh_agree(privkey, pubkey))