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# Copyright 2021-2025 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 logging
import operator
import secrets
try:
from bumble.crypto.cryptography import EccKey, aes_cmac, e
except ImportError:
logging.getLogger(__name__).debug(
"Unable to import cryptography, using built-in primitives."
)
from bumble.crypto.builtin import EccKey, aes_cmac, e # type: ignore[assignment]
_EccKey = EccKey # For the linter only
# -----------------------------------------------------------------------------
# Logging
# -----------------------------------------------------------------------------
logger = logging.getLogger(__name__)
# -----------------------------------------------------------------------------
# Functions
# -----------------------------------------------------------------------------
# -----------------------------------------------------------------------------
def generate_prand() -> bytes:
'''Generates random 3 bytes, with the 2 most significant bits of 0b01.
See Bluetooth spec, Vol 6, Part E - Table 1.2.
'''
prand_bytes = secrets.token_bytes(6)
return prand_bytes[:2] + bytes([(prand_bytes[2] & 0b01111111) | 0b01000000])
# -----------------------------------------------------------------------------
def xor(x: bytes, y: bytes) -> bytes:
assert len(x) == len(y)
return bytes(map(operator.xor, x, y))
# -----------------------------------------------------------------------------
def reverse(input: bytes) -> bytes:
'''
Returns bytes of input in reversed endianness.
'''
return input[::-1]
# -----------------------------------------------------------------------------
def r() -> bytes:
'''
Generate 16 bytes of random data
'''
return secrets.token_bytes(16)
# -----------------------------------------------------------------------------
def ah(k: bytes, r: bytes) -> bytes: # pylint: disable=redefined-outer-name
'''
See Bluetooth spec Vol 3, Part H - 2.2.2 Random Address Hash function ah
'''
padding = bytes(13)
r_prime = r + padding
return e(k, r_prime)[0:3]
# -----------------------------------------------------------------------------
def c1(
k: bytes,
r: bytes,
preq: bytes,
pres: bytes,
iat: int,
rat: int,
ia: bytes,
ra: bytes,
) -> bytes: # pylint: disable=redefined-outer-name
'''
See Bluetooth spec, Vol 3, Part H - 2.2.3 Confirm value generation function c1 for
LE Legacy Pairing
'''
p1 = bytes([iat, rat]) + preq + pres
p2 = ra + ia + bytes([0, 0, 0, 0])
return e(k, xor(e(k, xor(r, p1)), p2))
# -----------------------------------------------------------------------------
def s1(k: bytes, r1: bytes, r2: bytes) -> bytes:
'''
See Bluetooth spec, Vol 3, Part H - 2.2.4 Key generation function s1 for LE Legacy
Pairing
'''
return e(k, r2[0:8] + r1[0:8])
# -----------------------------------------------------------------------------
def f4(u: bytes, v: bytes, x: bytes, z: bytes) -> bytes:
'''
See Bluetooth spec, Vol 3, Part H - 2.2.6 LE Secure Connections Confirm Value
Generation Function f4
'''
return reverse(aes_cmac(reverse(u) + reverse(v) + z, reverse(x)))
# -----------------------------------------------------------------------------
def f5(w: bytes, n1: bytes, n2: bytes, a1: bytes, a2: bytes) -> tuple[bytes, bytes]:
'''
See Bluetooth spec, Vol 3, Part H - 2.2.7 LE Secure Connections Key Generation
Function f5
NOTE: this returns a tuple: (MacKey, LTK) in little-endian byte order
'''
salt = bytes.fromhex('6C888391AAF5A53860370BDB5A6083BE')
t = aes_cmac(reverse(w), salt)
key_id = bytes([0x62, 0x74, 0x6C, 0x65])
return (
reverse(
aes_cmac(
bytes([0])
+ key_id
+ reverse(n1)
+ reverse(n2)
+ reverse(a1)
+ reverse(a2)
+ bytes([1, 0]),
t,
)
),
reverse(
aes_cmac(
bytes([1])
+ key_id
+ reverse(n1)
+ reverse(n2)
+ reverse(a1)
+ reverse(a2)
+ bytes([1, 0]),
t,
)
),
)
# -----------------------------------------------------------------------------
def f6(
w: bytes, n1: bytes, n2: bytes, r: bytes, io_cap: bytes, a1: bytes, a2: bytes
) -> bytes: # pylint: disable=redefined-outer-name
'''
See Bluetooth spec, Vol 3, Part H - 2.2.8 LE Secure Connections Check Value
Generation Function f6
'''
return reverse(
aes_cmac(
reverse(n1)
+ reverse(n2)
+ reverse(r)
+ reverse(io_cap)
+ reverse(a1)
+ reverse(a2),
reverse(w),
)
)
# -----------------------------------------------------------------------------
def g2(u: bytes, v: bytes, x: bytes, y: bytes) -> int:
'''
See Bluetooth spec, Vol 3, Part H - 2.2.9 LE Secure Connections Numeric Comparison
Value Generation Function g2
'''
return int.from_bytes(
aes_cmac(
reverse(u) + reverse(v) + reverse(y),
reverse(x),
)[-4:],
byteorder='big',
)
# -----------------------------------------------------------------------------
def h6(w: bytes, key_id: bytes) -> bytes:
'''
See Bluetooth spec, Vol 3, Part H - 2.2.10 Link key conversion function h6
'''
return reverse(aes_cmac(key_id, reverse(w)))
# -----------------------------------------------------------------------------
def h7(salt: bytes, w: bytes) -> bytes:
'''
See Bluetooth spec, Vol 3, Part H - 2.2.11 Link key conversion function h7
'''
return reverse(aes_cmac(reverse(w), salt))
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