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# Copyright 2021-2023 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# -----------------------------------------------------------------------------
# Imports
# -----------------------------------------------------------------------------
from __future__ import annotations
import enum
import struct
from bumble import core, crypto, device, gatt, gatt_client
# -----------------------------------------------------------------------------
# Constants
# -----------------------------------------------------------------------------
SET_IDENTITY_RESOLVING_KEY_LENGTH = 16
class SirkType(enum.IntEnum):
'''Coordinated Set Identification Service - 5.1 Set Identity Resolving Key.'''
ENCRYPTED = 0x00
PLAINTEXT = 0x01
class MemberLock(enum.IntEnum):
'''Coordinated Set Identification Service - 5.3 Set Member Lock.'''
UNLOCKED = 0x01
LOCKED = 0x02
# -----------------------------------------------------------------------------
# Crypto Toolbox
# -----------------------------------------------------------------------------
def s1(m: bytes) -> bytes:
'''
Coordinated Set Identification Service - 4.3 s1 SALT generation function.
'''
return crypto.aes_cmac(m[::-1], bytes(16))[::-1]
def k1(n: bytes, salt: bytes, p: bytes) -> bytes:
'''
Coordinated Set Identification Service - 4.4 k1 derivation function.
'''
t = crypto.aes_cmac(n[::-1], salt[::-1])
return crypto.aes_cmac(p[::-1], t)[::-1]
def sef(k: bytes, r: bytes) -> bytes:
'''
Coordinated Set Identification Service - 4.5 SIRK encryption function sef.
SIRK decryption function sdf shares the same algorithm. The only difference is that argument r is:
* Plaintext in encryption
* Cipher in decryption
'''
return crypto.xor(k1(k, s1(b'SIRKenc'[::-1]), b'csis'[::-1]), r)
def sih(k: bytes, r: bytes) -> bytes:
'''
Coordinated Set Identification Service - 4.7 Resolvable Set Identifier hash function sih.
'''
return crypto.e(k, r + bytes(13))[:3]
def generate_rsi(sirk: bytes) -> bytes:
'''
Coordinated Set Identification Service - 4.8 Resolvable Set Identifier generation operation.
'''
prand = crypto.generate_prand()
return sih(sirk, prand) + prand
# -----------------------------------------------------------------------------
# Server
# -----------------------------------------------------------------------------
class CoordinatedSetIdentificationService(gatt.TemplateService):
UUID = gatt.GATT_COORDINATED_SET_IDENTIFICATION_SERVICE
set_identity_resolving_key: bytes
set_identity_resolving_key_characteristic: gatt.Characteristic[bytes]
coordinated_set_size_characteristic: gatt.Characteristic[bytes] | None = None
set_member_lock_characteristic: gatt.Characteristic[bytes] | None = None
set_member_rank_characteristic: gatt.Characteristic[bytes] | None = None
def __init__(
self,
set_identity_resolving_key: bytes,
set_identity_resolving_key_type: SirkType,
coordinated_set_size: int | None = None,
set_member_lock: MemberLock | None = None,
set_member_rank: int | None = None,
) -> None:
if len(set_identity_resolving_key) != SET_IDENTITY_RESOLVING_KEY_LENGTH:
raise core.InvalidArgumentError(
f'Invalid SIRK length {len(set_identity_resolving_key)}, expected {SET_IDENTITY_RESOLVING_KEY_LENGTH}'
)
characteristics = []
self.set_identity_resolving_key = set_identity_resolving_key
self.set_identity_resolving_key_type = set_identity_resolving_key_type
self.set_identity_resolving_key_characteristic = gatt.Characteristic(
uuid=gatt.GATT_SET_IDENTITY_RESOLVING_KEY_CHARACTERISTIC,
properties=gatt.Characteristic.Properties.READ
| gatt.Characteristic.Properties.NOTIFY,
permissions=gatt.Characteristic.Permissions.READ_REQUIRES_ENCRYPTION,
value=gatt.CharacteristicValue(read=self.on_sirk_read),
)
characteristics.append(self.set_identity_resolving_key_characteristic)
if coordinated_set_size is not None:
self.coordinated_set_size_characteristic = gatt.Characteristic(
uuid=gatt.GATT_COORDINATED_SET_SIZE_CHARACTERISTIC,
properties=gatt.Characteristic.Properties.READ
| gatt.Characteristic.Properties.NOTIFY,
permissions=gatt.Characteristic.Permissions.READ_REQUIRES_ENCRYPTION,
value=struct.pack('B', coordinated_set_size),
)
characteristics.append(self.coordinated_set_size_characteristic)
if set_member_lock is not None:
self.set_member_lock_characteristic = gatt.Characteristic(
uuid=gatt.GATT_SET_MEMBER_LOCK_CHARACTERISTIC,
properties=gatt.Characteristic.Properties.READ
| gatt.Characteristic.Properties.NOTIFY
| gatt.Characteristic.Properties.WRITE,
permissions=gatt.Characteristic.Permissions.READ_REQUIRES_ENCRYPTION
| gatt.Characteristic.Permissions.WRITEABLE,
value=struct.pack('B', set_member_lock),
)
characteristics.append(self.set_member_lock_characteristic)
if set_member_rank is not None:
self.set_member_rank_characteristic = gatt.Characteristic(
uuid=gatt.GATT_SET_MEMBER_RANK_CHARACTERISTIC,
properties=gatt.Characteristic.Properties.READ
| gatt.Characteristic.Properties.NOTIFY,
permissions=gatt.Characteristic.Permissions.READ_REQUIRES_ENCRYPTION,
value=struct.pack('B', set_member_rank),
)
characteristics.append(self.set_member_rank_characteristic)
super().__init__(characteristics)
async def on_sirk_read(self, connection: device.Connection) -> bytes:
if self.set_identity_resolving_key_type == SirkType.PLAINTEXT:
sirk_bytes = self.set_identity_resolving_key
else:
if connection.transport == core.PhysicalTransport.LE:
key = await connection.device.get_long_term_key(
connection_handle=connection.handle, rand=b'', ediv=0
)
else:
key = await connection.device.get_link_key(connection.peer_address)
if not key:
raise core.InvalidOperationError('LTK or LinkKey is not present')
sirk_bytes = sef(key, self.set_identity_resolving_key)
return bytes([self.set_identity_resolving_key_type]) + sirk_bytes
def get_advertising_data(self) -> bytes:
return bytes(
core.AdvertisingData(
[
(
core.AdvertisingData.RESOLVABLE_SET_IDENTIFIER,
generate_rsi(self.set_identity_resolving_key),
),
]
)
)
# -----------------------------------------------------------------------------
# Client
# -----------------------------------------------------------------------------
class CoordinatedSetIdentificationProxy(gatt_client.ProfileServiceProxy):
SERVICE_CLASS = CoordinatedSetIdentificationService
set_identity_resolving_key: gatt_client.CharacteristicProxy[bytes]
coordinated_set_size: gatt_client.CharacteristicProxy[bytes] | None = None
set_member_lock: gatt_client.CharacteristicProxy[bytes] | None = None
set_member_rank: gatt_client.CharacteristicProxy[bytes] | None = None
def __init__(self, service_proxy: gatt_client.ServiceProxy) -> None:
self.service_proxy = service_proxy
self.set_identity_resolving_key = service_proxy.get_characteristics_by_uuid(
gatt.GATT_SET_IDENTITY_RESOLVING_KEY_CHARACTERISTIC
)[0]
if characteristics := service_proxy.get_characteristics_by_uuid(
gatt.GATT_COORDINATED_SET_SIZE_CHARACTERISTIC
):
self.coordinated_set_size = characteristics[0]
if characteristics := service_proxy.get_characteristics_by_uuid(
gatt.GATT_SET_MEMBER_LOCK_CHARACTERISTIC
):
self.set_member_lock = characteristics[0]
if characteristics := service_proxy.get_characteristics_by_uuid(
gatt.GATT_SET_MEMBER_RANK_CHARACTERISTIC
):
self.set_member_rank = characteristics[0]
async def read_set_identity_resolving_key(self) -> tuple[SirkType, bytes]:
'''Reads SIRK and decrypts if encrypted.'''
response = await self.set_identity_resolving_key.read_value()
if len(response) != SET_IDENTITY_RESOLVING_KEY_LENGTH + 1:
raise core.InvalidPacketError('Invalid SIRK value')
sirk_type = SirkType(response[0])
if sirk_type == SirkType.PLAINTEXT:
sirk = response[1:]
else:
connection = self.service_proxy.client.connection
device = connection.device
if connection.transport == core.PhysicalTransport.LE:
key = await device.get_long_term_key(
connection_handle=connection.handle, rand=b'', ediv=0
)
else:
key = await device.get_link_key(connection.peer_address)
if not key:
raise core.InvalidOperationError('LTK or LinkKey is not present')
sirk = sef(key, response[1:])
return (sirk_type, sirk)
|
