def _th4_input(self) -> CBOR:
hash_func = config_cose(self.cipher_suite.hash).hash
input_th = [
self.transcript(hash_func, self._th3_input), self.msg_3.ciphertext
]
return b''.join([cbor2.dumps(part) for part in input_th])
def ciphertext_3(self):
# TODO: resolve magic key and IV lengths
iv_bytes = self._hkdf3(13, 'IV_3ae', self._prk3e2m)
hash_func = config_cose(self.cipher_suite.hash).hash
# TODO: resolve magic key and IV lengths
cose_key = self._create_cose_key(self._hkdf3, 16, 'K_3ae',
self._prk3e2m, KeyOps.ENCRYPT)
# create payload for the COSE_Encrypt0
payload = [self._p_3ae]
if self.aad3_cb is not None:
payload.append(self.aad3_cb())
payload = b''.join(payload)
# create the external data for the COSE_Encrypt0
th_3 = self.transcript(hash_func, self._th3_input)
# calculate the mac_2 using a COSE_Encrypt0 message
ciphertext = Enc0Message(payload=payload, external_aad=th_3).encrypt(
iv_bytes, cose_key)
return ciphertext
def _decrypt(self, ciphertext: bytes) -> bytes:
# TODO: resolve magic key and IV lengths
iv_bytes = self._hkdf3(13, 'IV_3ae', self._prk3e2m)
hash_func = config_cose(self.cipher_suite.hash).hash
# TODO: resolve magic key and IV lengths
cose_key = self._create_cose_key(self._hkdf3, 16, 'K_3ae', self._prk3e2m, KeyOps.DECRYPT)
th_3 = self.transcript(hash_func, self._th3_input)
return Enc0Message(payload=ciphertext, external_aad=th_3).decrypt(iv_bytes, cose_key)
def _prk(self, private_key: Key, pub_key: Key, salt: bytes) -> bytes:
h = self.cipher_suite.hash
secret = self.shared_secret(private_key, pub_key)
prk_2e = hmac.HMAC(algorithm=config_cose(h).hash(),
key=salt,
backend=default_backend())
prk_2e.update(secret)
prk = prk_2e.finalize()
return prk
def shared_secret(private_key: Key, public_key: Key) -> bytes:
""" Compute the shared secret. """
if public_key.crv == CoseEllipticCurves.X25519:
d = X25519PrivateKey.from_private_bytes(private_key.d)
x = X25519PublicKey.from_public_bytes(public_key.x)
elif public_key.crv == CoseEllipticCurves.X448:
d = X448PrivateKey.from_private_bytes(private_key.d)
x = X448PublicKey.from_public_bytes(public_key.x)
elif public_key.crv == CoseEllipticCurves.P_256:
d = ec.derive_private_key(int(hexlify(private_key.d), 16),
config_cose(public_key.crv).curve[1](),
default_backend())
x = ec.EllipticCurvePublicNumbers(
int(hexlify(public_key.x), 16), int(hexlify(public_key.y), 16),
config_cose(public_key.crv).curve[1]())
else:
raise CoseIllegalCurve(f"{public_key.crv} is unsupported")
secret = d.exchange(x)
return secret
def _external_aad(self, transcript: bytes,
aad_cb: Callable[..., bytes]) -> CBOR:
hash_func = config_cose(self.cipher_suite.hash).hash
aad = [cbor2.dumps(self.transcript(hash_func, transcript)), self.cred]
if aad_cb is not None:
ad = aad_cb()
if ad != b'':
aad.append(ad)
aad = b"".join(aad)
return aad
def test_initiator_message3(initiator, test_vectors):
initiator.msg_1 = MessageOne.decode(test_vectors['I']['message_1'])
initiator.msg_2 = MessageTwo.decode(test_vectors['R']['message_2'])
crv = CoseEllipticCurves(CipherSuite(initiator._selected_cipher).dh_curve)
hash_func = config_cose(CipherSuite(initiator._selected_cipher).hash).hash
assert initiator.data_2 == test_vectors['R']['data_2']
assert initiator._th2_input == test_vectors['R']['input_th_2']
assert initiator._prk2e == test_vectors['R']['prk_2e']
assert initiator._prk3e2m == test_vectors['R']['prk_3e2m']
assert initiator.transcript(
hash_func, initiator._th2_input) == test_vectors['R']['th_2']
assert initiator._decrypt(
initiator.msg_2.ciphertext) == test_vectors['R']['p_2e']
assert initiator.shared_secret(initiator.ephemeral_key,
OKP(x=initiator.g_y,
crv=crv)) == test_vectors['S']['g_xy']
assert initiator.data_3 == test_vectors['I']['data_3']
assert initiator._th3_input == test_vectors['I']['input_th_3']
assert initiator.transcript(
hash_func, initiator._th3_input) == test_vectors['I']['th_3']
assert initiator.cred_id == test_vectors['I']['id_cred']
assert initiator._prk4x3m == test_vectors['I']['prk_4x3m']
assert initiator._external_aad(
initiator._th3_input,
initiator.aad3_cb) == test_vectors['I']['eaad_3m']
assert initiator._hkdf3(16, 'K_3m',
initiator._prk4x3m) == test_vectors['I']['k_3m']
assert initiator._hkdf3(13, 'IV_3m',
initiator._prk4x3m) == test_vectors['I']['iv_3m']
assert initiator._mac(initiator._hkdf3, 'K_3m', 16, 'IV_3m', 13,
initiator._th3_input, initiator._prk4x3m,
initiator.aad2_cb) == test_vectors['I']['mac3']
assert initiator.signature_or_mac3(
test_vectors['I']['mac3']) == test_vectors['I']['sign_or_mac3']
assert initiator._p_3ae == test_vectors['I']['p_3ae']
assert initiator._hkdf3(16, 'K_3ae',
initiator._prk3e2m) == test_vectors['I']['k_3ae']
assert initiator._hkdf3(13, 'IV_3ae',
initiator._prk3e2m) == test_vectors['I']['iv_3ae']
assert initiator.ciphertext_3 == test_vectors['I']['ciphertext_3']
assert initiator.create_message_three(
test_vectors['R']['message_2']) == test_vectors['I']['message_3']
def _hkdf_expand(self, length: int, label: str, prk: bytes,
transcript: bytes) -> bytes:
"""
Derive the encryption key and the IV to protect the COSE_Encrypt0 message in the EDHOC message 2.
:return:
"""
hash_func = config_cose(self.cipher_suite.hash).hash
info = EdhocKDFInfo(edhoc_aead_id=self.cipher_suite.aead,
transcript_hash=self.transcript(
hash_func, transcript),
label=label,
length=length)
derived_bytes = HKDFExpand(algorithm=hash_func(),
length=info.length,
info=info.encode(),
backend=default_backend()).derive(prk)
return derived_bytes
def test_responder_message2(responder, test_vectors):
responder.msg_1 = MessageOne.decode(test_vectors['I']['message_1'])
hash_func = config_cose(CipherSuite(
responder.msg_1.selected_cipher).hash).hash
crv = CoseEllipticCurves(
CipherSuite(responder.msg_1.selected_cipher).dh_curve)
assert responder.shared_secret(responder.ephemeral_key,
OKP(x=responder.g_x,
crv=crv)) == test_vectors['S']['g_xy']
assert responder._prk2e == test_vectors['R']['prk_2e']
assert responder._prk3e2m == test_vectors['R']['prk_3e2m']
assert responder.data_2 == test_vectors['R']['data_2']
assert responder._th2_input == test_vectors['R']['input_th_2']
assert responder.cred_id == test_vectors['R']['id_cred']
assert responder.transcript(
hash_func, responder._th2_input) == test_vectors['R']['th_2']
assert responder._external_aad(
responder._th2_input,
responder.aad2_cb) == test_vectors['R']['eaad_2m']
assert responder._hkdf2(
16, 'K_2m', prk=responder._prk3e2m) == test_vectors['R']['k_2m']
assert responder._hkdf2(
13, 'IV_2m', prk=responder._prk3e2m) == test_vectors['R']['iv_2m']
assert responder._mac(responder._hkdf2, 'K_2m', 16, 'IV_2m', 13,
responder._th2_input, responder._prk3e2m,
responder.aad2_cb) == test_vectors['R']['mac2']
assert responder.signature_or_mac2(
test_vectors['R']['mac2']) == test_vectors['R']['sign_or_mac2']
assert responder._p_2e == test_vectors['R']['p_2e']
assert responder._hkdf2(len(responder._p_2e), 'K_2e',
prk=responder._prk2e) == test_vectors['R']['k_2e']
assert responder.ciphertext_2 == test_vectors['R']['ciphertext_2']
assert responder.create_message_two(
test_vectors['I']['message_1']) == test_vectors['R']['message_2']
def exporter(self, label: str, length: int):
hash_func = config_cose(self.cipher_suite.hash).hash
return self._hkdf_expand(length, label, self._prk4x3m,
self.transcript(hash_func, self._th4_input))
