def perform_pair_setup_part1(
with_auth: bool = True,
) -> Generator[Tuple[List[Tuple[int, bytearray]], List[int]], None, Tuple[
bytearray, bytearray]]:
"""
Performs a pair setup operation as described in chapter 4.7 page 39 ff.
:return: a tuple of salt and server's public key
:raises UnavailableError: if the device is already paired
:raises MaxTriesError: if the device received more than 100 unsuccessful pairing attempts
:raises BusyError: if a parallel pairing is ongoing
:raises AuthenticationError: if the verification of the device's SRP proof fails
:raises MaxPeersError: if the device cannot accept an additional pairing
:raises IllegalData: if the verification of the accessory's data fails
"""
#
# Step #1 ios --> accessory (send SRP start Request) (see page 39)
#
logging.debug("#1 ios -> accessory: send SRP start request")
request_tlv = [
(TLV.kTLVType_State, TLV.M1),
(TLV.kTLVType_Method,
TLV.PairSetupWithAuth if with_auth else TLV.PairSetup),
]
step2_expectations = [
TLV.kTLVType_State,
TLV.kTLVType_Error,
TLV.kTLVType_PublicKey,
TLV.kTLVType_Salt,
]
response_tlv = yield (request_tlv, step2_expectations)
#
# Step #3 ios --> accessory (send SRP verify request) (see page 41)
#
logging.debug("#3 ios -> accessory: send SRP verify request")
response_tlv = TLV.reorder(response_tlv, step2_expectations)
assert (response_tlv[0][0] == TLV.kTLVType_State and response_tlv[0][1]
== TLV.M2), "perform_pair_setup: State not M2"
# the errors here can be:
# * kTLVError_Unavailable: Device is paired
# * kTLVError_MaxTries: More than 100 unsuccessful attempts
# * kTLVError_Busy: There is already a pairing going on
if response_tlv[1][0] == TLV.kTLVType_Error:
error_handler(response_tlv[1][1], "step 3")
assert (response_tlv[1][0] == TLV.kTLVType_PublicKey
), "perform_pair_setup: Not a public key"
assert response_tlv[2][
0] == TLV.kTLVType_Salt, "perform_pair_setup: Not a salt"
return response_tlv[2][1], response_tlv[1][1]
def test_reorder_2(self):
val = [
[TLV.kTLVType_State, TLV.M3],
[TLV.kTLVType_Salt, (16 * "a").encode()],
[TLV.kTLVType_PublicKey, (384 * "b").encode()],
]
tmp = TLV.reorder(val, [TLV.kTLVType_State, TLV.kTLVType_Salt])
self.assertEqual(tmp[0][0], TLV.kTLVType_State)
self.assertEqual(tmp[0][1], TLV.M3)
self.assertEqual(tmp[1][0], TLV.kTLVType_Salt)
self.assertEqual(tmp[1][1], (16 * "a").encode())
def get_session_keys(
pairing_data: Dict[str, Union[str, int, List[Any]]]
) -> Generator[Union[Tuple[List[Union[Tuple[int, bytearray], Tuple[
int, bytes]]], List[int]], Tuple[List[Tuple[
int, bytearray]], List[int]], ], None, Tuple[bytes, bytes], ]:
"""
HomeKit Controller state machine to perform a pair verify operation as described in chapter 4.8 page 47 ff.
:param pairing_data: the paring data as returned by perform_pair_setup
:return: tuple of the session keys (controller_to_accessory_key and accessory_to_controller_key)
:raises InvalidAuthTagError: if the auth tag could not be verified,
:raises IncorrectPairingIdError: if the accessory's LTPK could not be found
:raises InvalidSignatureError: if the accessory's signature could not be verified
:raises AuthenticationError: if the secured session could not be established
"""
#
# Step #1 ios --> accessory (send verify start Request) (page 47)
#
ios_key = x25519.X25519PrivateKey.generate()
ios_key_pub = ios_key.public_key().public_bytes(
encoding=serialization.Encoding.Raw,
format=serialization.PublicFormat.Raw)
request_tlv = [(TLV.kTLVType_State, TLV.M1),
(TLV.kTLVType_PublicKey, ios_key_pub)]
step2_expectations = [
TLV.kTLVType_State,
TLV.kTLVType_PublicKey,
TLV.kTLVType_EncryptedData,
]
response_tlv = yield (request_tlv, step2_expectations)
#
# Step #3 ios --> accessory (send SRP verify request) (page 49)
#
response_tlv = TLV.reorder(response_tlv, step2_expectations)
assert (response_tlv[0][0] == TLV.kTLVType_State
and response_tlv[0][1] == TLV.M2), "get_session_keys: not M2"
assert (response_tlv[1][0] == TLV.kTLVType_PublicKey
), "get_session_keys: no public key"
assert (response_tlv[2][0] == TLV.kTLVType_EncryptedData
), "get_session_keys: no encrypted data"
# 1) generate shared secret
accessorys_session_pub_key_bytes = bytes(response_tlv[1][1])
accessorys_session_pub_key = x25519.X25519PublicKey.from_public_bytes(
accessorys_session_pub_key_bytes)
shared_secret = ios_key.exchange(accessorys_session_pub_key)
# 2) derive session key
session_key = hkdf_derive(shared_secret, "Pair-Verify-Encrypt-Salt",
"Pair-Verify-Encrypt-Info")
# 3) verify auth tag on encrypted data and 4) decrypt
encrypted = response_tlv[2][1]
decrypted = chacha20_aead_decrypt(bytes(),
session_key, "PV-Msg02".encode(),
bytes([0, 0, 0, 0]), encrypted)
if type(decrypted) == bool and not decrypted:
raise InvalidAuthTagError("step 3")
d1 = TLV.decode_bytes(decrypted)
d1 = TLV.reorder(d1, [TLV.kTLVType_Identifier, TLV.kTLVType_Signature])
assert d1[0][
0] == TLV.kTLVType_Identifier, "get_session_keys: no identifier"
assert d1[1][0] == TLV.kTLVType_Signature, "get_session_keys: no signature"
# 5) look up pairing by accessory name
accessory_name = d1[0][1].decode()
if pairing_data["AccessoryPairingID"] != accessory_name:
raise IncorrectPairingIdError("step 3")
accessory_ltpk = ed25519.Ed25519PublicKey.from_public_bytes(
bytes.fromhex(pairing_data["AccessoryLTPK"]))
# 6) verify accessory's signature
accessory_sig = d1[1][1]
accessory_session_pub_key_bytes = response_tlv[1][1]
accessory_info = (accessory_session_pub_key_bytes +
accessory_name.encode() + ios_key_pub)
try:
accessory_ltpk.verify(bytes(accessory_sig), bytes(accessory_info))
except cryptography_exceptions.InvalidSignature:
raise InvalidSignatureError("step 3")
# 7) create iOSDeviceInfo
ios_device_info = (ios_key_pub + pairing_data["iOSPairingId"].encode() +
accessorys_session_pub_key_bytes)
# 8) sign iOSDeviceInfo with long term secret key
ios_device_ltsk_h = pairing_data["iOSDeviceLTSK"]
# ios_device_ltpk_h = pairing_data["iOSDeviceLTPK"]
ios_device_ltsk = ed25519.Ed25519PrivateKey.from_private_bytes(
bytes.fromhex(ios_device_ltsk_h))
# ios_device_ltsk = ed25519.SigningKey(
# bytes.fromhex(ios_device_ltsk_h) + bytes.fromhex(ios_device_ltpk_h)
# )
ios_device_signature = ios_device_ltsk.sign(ios_device_info)
# 9) construct sub tlv
sub_tlv = TLV.encode_list([
(TLV.kTLVType_Identifier, pairing_data["iOSPairingId"].encode()),
(TLV.kTLVType_Signature, ios_device_signature),
])
# 10) encrypt and sign
encrypted_data_with_auth_tag = chacha20_aead_encrypt(
bytes(), session_key, "PV-Msg03".encode(), bytes([0, 0, 0, 0]),
sub_tlv)
# 11) create tlv
request_tlv = [
(TLV.kTLVType_State, TLV.M3),
(TLV.kTLVType_EncryptedData, encrypted_data_with_auth_tag),
]
step3_expectations = [TLV.kTLVType_State, TLV.kTLVType_Error]
response_tlv = yield (request_tlv, step3_expectations)
#
# Post Step #4 verification (page 51)
#
response_tlv = TLV.reorder(response_tlv, step3_expectations)
assert (response_tlv[0][0] == TLV.kTLVType_State
and response_tlv[0][1] == TLV.M4), "get_session_keys: not M4"
if len(response_tlv) == 2 and response_tlv[1][0] == TLV.kTLVType_Error:
error_handler(response_tlv[1][1], "verification")
# calculate session keys
controller_to_accessory_key = hkdf_derive(shared_secret, "Control-Salt",
"Control-Write-Encryption-Key")
accessory_to_controller_key = hkdf_derive(shared_secret, "Control-Salt",
"Control-Read-Encryption-Key")
return controller_to_accessory_key, accessory_to_controller_key
def perform_pair_setup_part2(
pin: str, ios_pairing_id: str, salt: bytearray,
server_public_key: bytearray
) -> Generator[Tuple[List[Tuple[int, bytearray]], List[int]], None, Dict[str,
str]]:
"""
Performs a pair setup operation as described in chapter 4.7 page 39 ff.
:param pin: the setup code from the accessory
:param ios_pairing_id: the id of the simulated ios device
:return: a dict with the ios device's part of the pairing information
:raises UnavailableError: if the device is already paired
:raises MaxTriesError: if the device received more than 100 unsuccessful pairing attempts
:raises BusyError: if a parallel pairing is ongoing
:raises AuthenticationError: if the verification of the device's SRP proof fails
:raises MaxPeersError: if the device cannot accept an additional pairing
:raises IllegalData: if the verification of the accessory's data fails
"""
srp_client = SrpClient("Pair-Setup", pin)
srp_client.set_salt(salt)
srp_client.set_server_public_key(server_public_key)
client_pub_key = srp_client.get_public_key()
client_proof = srp_client.get_proof()
response_tlv = [
(TLV.kTLVType_State, TLV.M3),
(TLV.kTLVType_PublicKey, SrpClient.to_byte_array(client_pub_key)),
(TLV.kTLVType_Proof, SrpClient.to_byte_array(client_proof)),
]
step4_expectations = [
TLV.kTLVType_State, TLV.kTLVType_Error, TLV.kTLVType_Proof
]
response_tlv = yield (response_tlv, step4_expectations)
#
# Step #5 ios --> accessory (Exchange Request) (see page 43)
#
logging.debug("#5 ios -> accessory: send SRP exchange request")
# M4 Verification (page 43)
response_tlv = TLV.reorder(response_tlv, step4_expectations)
assert (response_tlv[0][0] == TLV.kTLVType_State and response_tlv[0][1]
== TLV.M4), "perform_pair_setup: State not M4"
if response_tlv[1][0] == TLV.kTLVType_Error:
error_handler(response_tlv[1][1], "step 5")
assert response_tlv[1][
0] == TLV.kTLVType_Proof, "perform_pair_setup: Not a proof"
if not srp_client.verify_servers_proof(response_tlv[1][1]):
raise AuthenticationError("Step #5: wrong proof!")
# M5 Request generation (page 44)
session_key = srp_client.get_session_key()
ios_device_ltsk = ed25519.Ed25519PrivateKey.generate()
ios_device_ltpk = ios_device_ltsk.public_key()
ios_device_public_bytes = ios_device_ltpk.public_bytes(
encoding=serialization.Encoding.Raw,
format=serialization.PublicFormat.Raw)
# reversed:
# Pair-Setup-Encrypt-Salt instead of Pair-Setup-Controller-Sign-Salt
# Pair-Setup-Encrypt-Info instead of Pair-Setup-Controller-Sign-Info
ios_device_x = hkdf_derive(
SrpClient.to_byte_array(session_key),
"Pair-Setup-Controller-Sign-Salt",
"Pair-Setup-Controller-Sign-Info",
)
session_key = hkdf_derive(
SrpClient.to_byte_array(session_key),
"Pair-Setup-Encrypt-Salt",
"Pair-Setup-Encrypt-Info",
)
ios_device_pairing_id = ios_pairing_id.encode()
ios_device_info = ios_device_x + ios_device_pairing_id + ios_device_public_bytes
ios_device_signature = ios_device_ltsk.sign(ios_device_info)
sub_tlv = [
(TLV.kTLVType_Identifier, ios_device_pairing_id),
(TLV.kTLVType_PublicKey, ios_device_public_bytes),
(TLV.kTLVType_Signature, ios_device_signature),
]
sub_tlv_b = TLV.encode_list(sub_tlv)
# taking tge iOSDeviceX as key was reversed from
# https://github.com/KhaosT/HAP-NodeJS/blob/2ea9d761d9bd7593dd1949fec621ab085af5e567/lib/HAPServer.js
# function handlePairStepFive calling encryption.encryptAndSeal
encrypted_data_with_auth_tag = chacha20_aead_encrypt(
bytes(), session_key, "PS-Msg05".encode(), bytes([0, 0, 0, 0]),
sub_tlv_b)
response_tlv = [
(TLV.kTLVType_State, TLV.M5),
(TLV.kTLVType_EncryptedData, encrypted_data_with_auth_tag),
]
step6_expectations = [
TLV.kTLVType_State,
TLV.kTLVType_Error,
TLV.kTLVType_EncryptedData,
]
response_tlv = yield (response_tlv, step6_expectations)
#
# Step #7 ios (Verification) (page 47)
#
response_tlv = TLV.reorder(response_tlv, step6_expectations)
assert (response_tlv[0][0] == TLV.kTLVType_State and response_tlv[0][1]
== TLV.M6), "perform_pair_setup: State not M6"
if response_tlv[1][0] == TLV.kTLVType_Error:
error_handler(response_tlv[1][1], "step 7")
assert (response_tlv[1][0] == TLV.kTLVType_EncryptedData
), "perform_pair_setup: No encrypted data"
decrypted_data = chacha20_aead_decrypt(
bytes(),
session_key,
"PS-Msg06".encode(),
bytes([0, 0, 0, 0]),
response_tlv[1][1],
)
if decrypted_data is False:
raise IllegalData("step 7")
response_tlv = TLV.decode_bytearray(decrypted_data)
response_tlv = TLV.reorder(
response_tlv,
[
TLV.kTLVType_Identifier, TLV.kTLVType_PublicKey,
TLV.kTLVType_Signature
],
)
assert (response_tlv[2][0] == TLV.kTLVType_Signature
), "perform_pair_setup: No signature"
accessory_sig = response_tlv[2][1]
assert (response_tlv[0][0] == TLV.kTLVType_Identifier
), "perform_pair_setup: No identifier"
accessory_pairing_id = response_tlv[0][1]
assert (response_tlv[1][0] == TLV.kTLVType_PublicKey
), "perform_pair_setup: No public key"
accessory_ltpk = response_tlv[1][1]
accessory_x = hkdf_derive(
SrpClient.to_byte_array(srp_client.get_session_key()),
"Pair-Setup-Accessory-Sign-Salt",
"Pair-Setup-Accessory-Sign-Info",
)
accessory_info = accessory_x + accessory_pairing_id + accessory_ltpk
e25519s = ed25519.Ed25519PublicKey.from_public_bytes(
bytes(response_tlv[1][1]))
try:
e25519s.verify(bytes(accessory_sig), bytes(accessory_info))
except cryptography_exceptions.InvalidSignature:
raise InvalidSignatureError("step #7")
ios_device_ltsk_private_bytes = ios_device_ltsk.private_bytes(
encoding=serialization.Encoding.Raw,
format=serialization.PrivateFormat.Raw,
encryption_algorithm=serialization.NoEncryption(),
)
return {
"AccessoryPairingID": response_tlv[0][1].decode(),
"AccessoryLTPK": hexlify(response_tlv[1][1]).decode(),
"iOSPairingId": ios_pairing_id,
"iOSDeviceLTSK": ios_device_ltsk_private_bytes.hex(),
"iOSDeviceLTPK": ios_device_public_bytes.hex(),
}