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278 lines
8.5 KiB
Python
278 lines
8.5 KiB
Python
# Copyright 2021-2022 Google LLC
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# https://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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# -----------------------------------------------------------------------------
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# Crypto support
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#
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# See Bluetooth spec Vol 3, Part H - 2.2 CRYPTOGRAPHIC TOOLBOX
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# -----------------------------------------------------------------------------
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# -----------------------------------------------------------------------------
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# Imports
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# -----------------------------------------------------------------------------
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import logging
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import operator
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import platform
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if platform.system() != 'Emscripten':
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import secrets
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from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
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from cryptography.hazmat.primitives.asymmetric.ec import (
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generate_private_key,
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ECDH,
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EllipticCurvePublicNumbers,
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EllipticCurvePrivateNumbers,
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SECP256R1,
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)
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from cryptography.hazmat.primitives import cmac
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else:
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# TODO: implement stubs
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pass
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# -----------------------------------------------------------------------------
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# Logging
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# -----------------------------------------------------------------------------
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logger = logging.getLogger(__name__)
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# -----------------------------------------------------------------------------
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# Classes
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# -----------------------------------------------------------------------------
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class EccKey:
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def __init__(self, private_key):
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self.private_key = private_key
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@classmethod
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def generate(cls):
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private_key = generate_private_key(SECP256R1())
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return cls(private_key)
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@classmethod
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def from_private_key_bytes(cls, d_bytes, x_bytes, y_bytes):
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d = int.from_bytes(d_bytes, byteorder='big', signed=False)
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x = int.from_bytes(x_bytes, byteorder='big', signed=False)
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y = int.from_bytes(y_bytes, byteorder='big', signed=False)
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private_key = EllipticCurvePrivateNumbers(
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d, EllipticCurvePublicNumbers(x, y, SECP256R1())
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).private_key()
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return cls(private_key)
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@property
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def x(self):
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return (
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self.private_key.public_key()
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.public_numbers()
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.x.to_bytes(32, byteorder='big')
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)
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@property
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def y(self):
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return (
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self.private_key.public_key()
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.public_numbers()
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.y.to_bytes(32, byteorder='big')
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)
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def dh(self, public_key_x, public_key_y):
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x = int.from_bytes(public_key_x, byteorder='big', signed=False)
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y = int.from_bytes(public_key_y, byteorder='big', signed=False)
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public_key = EllipticCurvePublicNumbers(x, y, SECP256R1()).public_key()
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shared_key = self.private_key.exchange(ECDH(), public_key)
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return shared_key
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# -----------------------------------------------------------------------------
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# Functions
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# -----------------------------------------------------------------------------
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# -----------------------------------------------------------------------------
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def xor(x, y):
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assert len(x) == len(y)
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return bytes(map(operator.xor, x, y))
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# -----------------------------------------------------------------------------
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def r():
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'''
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Generate 16 bytes of random data
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'''
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return secrets.token_bytes(16)
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# -----------------------------------------------------------------------------
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def e(key, data):
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'''
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AES-128 ECB, expecting byte-swapped inputs and producing a byte-swapped output.
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See Bluetooth spec Vol 3, Part H - 2.2.1 Security function e
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'''
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cipher = Cipher(algorithms.AES(bytes(reversed(key))), modes.ECB())
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encryptor = cipher.encryptor()
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return bytes(reversed(encryptor.update(bytes(reversed(data)))))
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# -----------------------------------------------------------------------------
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def ah(k, r): # pylint: disable=redefined-outer-name
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'''
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See Bluetooth spec Vol 3, Part H - 2.2.2 Random Address Hash function ah
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'''
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padding = bytes(13)
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r_prime = r + padding
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return e(k, r_prime)[0:3]
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# -----------------------------------------------------------------------------
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def c1(k, r, preq, pres, iat, rat, ia, ra): # pylint: disable=redefined-outer-name
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'''
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See Bluetooth spec, Vol 3, Part H - 2.2.3 Confirm value generation function c1 for
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LE Legacy Pairing
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'''
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p1 = bytes([iat, rat]) + preq + pres
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p2 = ra + ia + bytes([0, 0, 0, 0])
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return e(k, xor(e(k, xor(r, p1)), p2))
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# -----------------------------------------------------------------------------
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def s1(k, r1, r2):
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'''
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See Bluetooth spec, Vol 3, Part H - 2.2.4 Key generation function s1 for LE Legacy
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Pairing
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'''
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return e(k, r2[0:8] + r1[0:8])
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# -----------------------------------------------------------------------------
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def aes_cmac(m, k):
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'''
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See Bluetooth spec, Vol 3, Part H - 2.2.5 FunctionAES-CMAC
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NOTE: the input and output of this internal function are in big-endian byte order
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'''
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mac = cmac.CMAC(algorithms.AES(k))
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mac.update(m)
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return mac.finalize()
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# -----------------------------------------------------------------------------
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def f4(u, v, x, z):
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'''
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See Bluetooth spec, Vol 3, Part H - 2.2.6 LE Secure Connections Confirm Value
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Generation Function f4
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'''
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return bytes(
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reversed(
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aes_cmac(bytes(reversed(u)) + bytes(reversed(v)) + z, bytes(reversed(x)))
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)
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)
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# -----------------------------------------------------------------------------
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def f5(w, n1, n2, a1, a2):
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'''
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See Bluetooth spec, Vol 3, Part H - 2.2.7 LE Secure Connections Key Generation
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Function f5
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NOTE: this returns a tuple: (MacKey, LTK) in little-endian byte order
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'''
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salt = bytes.fromhex('6C888391AAF5A53860370BDB5A6083BE')
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t = aes_cmac(bytes(reversed(w)), salt)
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key_id = bytes([0x62, 0x74, 0x6C, 0x65])
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return (
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bytes(
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reversed(
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aes_cmac(
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bytes([0])
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+ key_id
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+ bytes(reversed(n1))
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+ bytes(reversed(n2))
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+ bytes(reversed(a1))
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+ bytes(reversed(a2))
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+ bytes([1, 0]),
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t,
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)
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)
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),
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bytes(
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reversed(
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aes_cmac(
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bytes([1])
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+ key_id
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+ bytes(reversed(n1))
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+ bytes(reversed(n2))
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+ bytes(reversed(a1))
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+ bytes(reversed(a2))
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+ bytes([1, 0]),
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t,
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)
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)
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),
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)
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# -----------------------------------------------------------------------------
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def f6(w, n1, n2, r, io_cap, a1, a2): # pylint: disable=redefined-outer-name
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'''
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See Bluetooth spec, Vol 3, Part H - 2.2.8 LE Secure Connections Check Value
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Generation Function f6
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'''
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return bytes(
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reversed(
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aes_cmac(
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bytes(reversed(n1))
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+ bytes(reversed(n2))
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+ bytes(reversed(r))
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+ bytes(reversed(io_cap))
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+ bytes(reversed(a1))
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+ bytes(reversed(a2)),
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bytes(reversed(w)),
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)
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)
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)
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# -----------------------------------------------------------------------------
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def g2(u, v, x, y):
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'''
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See Bluetooth spec, Vol 3, Part H - 2.2.9 LE Secure Connections Numeric Comparison
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Value Generation Function g2
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'''
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return int.from_bytes(
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aes_cmac(
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bytes(reversed(u)) + bytes(reversed(v)) + bytes(reversed(y)),
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bytes(reversed(x)),
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)[-4:],
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byteorder='big',
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)
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# -----------------------------------------------------------------------------
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def h6(w, key_id):
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'''
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See Bluetooth spec, Vol 3, Part H - 2.2.10 Link key conversion function h6
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'''
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return aes_cmac(key_id, w)
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# -----------------------------------------------------------------------------
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def h7(salt, w):
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'''
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See Bluetooth spec, Vol 3, Part H - 2.2.11 Link key conversion function h7
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'''
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return aes_cmac(w, salt)
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