/
concatkdf.py
127 lines (101 loc) · 3.67 KB
/
concatkdf.py
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
import typing
from cryptography import utils
from cryptography.exceptions import AlreadyFinalized, InvalidKey
from cryptography.hazmat.primitives import constant_time, hashes, hmac
from cryptography.hazmat.primitives.kdf import KeyDerivationFunction
def _int_to_u32be(n: int) -> bytes:
return n.to_bytes(length=4, byteorder="big")
def _common_args_checks(
algorithm: hashes.HashAlgorithm,
length: int,
otherinfo: typing.Optional[bytes],
) -> None:
max_length = algorithm.digest_size * (2**32 - 1)
if length > max_length:
raise ValueError(
"Cannot derive keys larger than {} bits.".format(max_length)
)
if otherinfo is not None:
utils._check_bytes("otherinfo", otherinfo)
def _concatkdf_derive(
key_material: bytes,
length: int,
auxfn: typing.Callable[[], hashes.HashContext],
otherinfo: bytes,
) -> bytes:
utils._check_byteslike("key_material", key_material)
output = [b""]
outlen = 0
counter = 1
while length > outlen:
h = auxfn()
h.update(_int_to_u32be(counter))
h.update(key_material)
h.update(otherinfo)
output.append(h.finalize())
outlen += len(output[-1])
counter += 1
return b"".join(output)[:length]
class ConcatKDFHash(KeyDerivationFunction):
def __init__(
self,
algorithm: hashes.HashAlgorithm,
length: int,
otherinfo: typing.Optional[bytes],
backend: typing.Any = None,
):
_common_args_checks(algorithm, length, otherinfo)
self._algorithm = algorithm
self._length = length
self._otherinfo: bytes = otherinfo if otherinfo is not None else b""
self._used = False
def _hash(self) -> hashes.Hash:
return hashes.Hash(self._algorithm)
def derive(self, key_material: bytes) -> bytes:
if self._used:
raise AlreadyFinalized
self._used = True
return _concatkdf_derive(
key_material, self._length, self._hash, self._otherinfo
)
def verify(self, key_material: bytes, expected_key: bytes) -> None:
if not constant_time.bytes_eq(self.derive(key_material), expected_key):
raise InvalidKey
class ConcatKDFHMAC(KeyDerivationFunction):
def __init__(
self,
algorithm: hashes.HashAlgorithm,
length: int,
salt: typing.Optional[bytes],
otherinfo: typing.Optional[bytes],
backend: typing.Any = None,
):
_common_args_checks(algorithm, length, otherinfo)
self._algorithm = algorithm
self._length = length
self._otherinfo: bytes = otherinfo if otherinfo is not None else b""
if algorithm.block_size is None:
raise TypeError(
"{} is unsupported for ConcatKDF".format(algorithm.name)
)
if salt is None:
salt = b"\x00" * algorithm.block_size
else:
utils._check_bytes("salt", salt)
self._salt = salt
self._used = False
def _hmac(self) -> hmac.HMAC:
return hmac.HMAC(self._salt, self._algorithm)
def derive(self, key_material: bytes) -> bytes:
if self._used:
raise AlreadyFinalized
self._used = True
return _concatkdf_derive(
key_material, self._length, self._hmac, self._otherinfo
)
def verify(self, key_material: bytes, expected_key: bytes) -> None:
if not constant_time.bytes_eq(self.derive(key_material), expected_key):
raise InvalidKey