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
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
|
# 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.
from __future__ import annotations
import abc
import typing
from cryptography import utils
from cryptography.exceptions import UnsupportedAlgorithm, _Reasons
from cryptography.hazmat.primitives._cipheralgorithm import (
BlockCipherAlgorithm,
CipherAlgorithm,
)
from cryptography.hazmat.primitives.ciphers import algorithms
class Mode(metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def name(self) -> str:
"""
A string naming this mode (e.g. "ECB", "CBC").
"""
@abc.abstractmethod
def validate_for_algorithm(self, algorithm: CipherAlgorithm) -> None:
"""
Checks that all the necessary invariants of this (mode, algorithm)
combination are met.
"""
class ModeWithInitializationVector(Mode, metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def initialization_vector(self) -> bytes:
"""
The value of the initialization vector for this mode as bytes.
"""
class ModeWithTweak(Mode, metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def tweak(self) -> bytes:
"""
The value of the tweak for this mode as bytes.
"""
class ModeWithNonce(Mode, metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def nonce(self) -> bytes:
"""
The value of the nonce for this mode as bytes.
"""
class ModeWithAuthenticationTag(Mode, metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def tag(self) -> typing.Optional[bytes]:
"""
The value of the tag supplied to the constructor of this mode.
"""
def _check_aes_key_length(self: Mode, algorithm: CipherAlgorithm) -> None:
if algorithm.key_size > 256 and algorithm.name == "AES":
raise ValueError(
"Only 128, 192, and 256 bit keys are allowed for this AES mode"
)
def _check_iv_length(
self: ModeWithInitializationVector, algorithm: BlockCipherAlgorithm
) -> None:
if len(self.initialization_vector) * 8 != algorithm.block_size:
raise ValueError(
"Invalid IV size ({}) for {}.".format(
len(self.initialization_vector), self.name
)
)
def _check_nonce_length(
nonce: bytes, name: str, algorithm: CipherAlgorithm
) -> None:
if not isinstance(algorithm, BlockCipherAlgorithm):
raise UnsupportedAlgorithm(
f"{name} requires a block cipher algorithm",
_Reasons.UNSUPPORTED_CIPHER,
)
if len(nonce) * 8 != algorithm.block_size:
raise ValueError(f"Invalid nonce size ({len(nonce)}) for {name}.")
def _check_iv_and_key_length(
self: ModeWithInitializationVector, algorithm: CipherAlgorithm
) -> None:
if not isinstance(algorithm, BlockCipherAlgorithm):
raise UnsupportedAlgorithm(
f"{self} requires a block cipher algorithm",
_Reasons.UNSUPPORTED_CIPHER,
)
_check_aes_key_length(self, algorithm)
_check_iv_length(self, algorithm)
class CBC(ModeWithInitializationVector):
name = "CBC"
def __init__(self, initialization_vector: bytes):
utils._check_byteslike("initialization_vector", initialization_vector)
self._initialization_vector = initialization_vector
@property
def initialization_vector(self) -> bytes:
return self._initialization_vector
validate_for_algorithm = _check_iv_and_key_length
class XTS(ModeWithTweak):
name = "XTS"
def __init__(self, tweak: bytes):
utils._check_byteslike("tweak", tweak)
if len(tweak) != 16:
raise ValueError("tweak must be 128-bits (16 bytes)")
self._tweak = tweak
@property
def tweak(self) -> bytes:
return self._tweak
def validate_for_algorithm(self, algorithm: CipherAlgorithm) -> None:
if isinstance(algorithm, (algorithms.AES128, algorithms.AES256)):
raise TypeError(
"The AES128 and AES256 classes do not support XTS, please use "
"the standard AES class instead."
)
if algorithm.key_size not in (256, 512):
raise ValueError(
"The XTS specification requires a 256-bit key for AES-128-XTS"
" and 512-bit key for AES-256-XTS"
)
class ECB(Mode):
name = "ECB"
validate_for_algorithm = _check_aes_key_length
class OFB(ModeWithInitializationVector):
name = "OFB"
def __init__(self, initialization_vector: bytes):
utils._check_byteslike("initialization_vector", initialization_vector)
self._initialization_vector = initialization_vector
@property
def initialization_vector(self) -> bytes:
return self._initialization_vector
validate_for_algorithm = _check_iv_and_key_length
class CFB(ModeWithInitializationVector):
name = "CFB"
def __init__(self, initialization_vector: bytes):
utils._check_byteslike("initialization_vector", initialization_vector)
self._initialization_vector = initialization_vector
@property
def initialization_vector(self) -> bytes:
return self._initialization_vector
validate_for_algorithm = _check_iv_and_key_length
class CFB8(ModeWithInitializationVector):
name = "CFB8"
def __init__(self, initialization_vector: bytes):
utils._check_byteslike("initialization_vector", initialization_vector)
self._initialization_vector = initialization_vector
@property
def initialization_vector(self) -> bytes:
return self._initialization_vector
validate_for_algorithm = _check_iv_and_key_length
class CTR(ModeWithNonce):
name = "CTR"
def __init__(self, nonce: bytes):
utils._check_byteslike("nonce", nonce)
self._nonce = nonce
@property
def nonce(self) -> bytes:
return self._nonce
def validate_for_algorithm(self, algorithm: CipherAlgorithm) -> None:
_check_aes_key_length(self, algorithm)
_check_nonce_length(self.nonce, self.name, algorithm)
class GCM(ModeWithInitializationVector, ModeWithAuthenticationTag):
name = "GCM"
_MAX_ENCRYPTED_BYTES = (2**39 - 256) // 8
_MAX_AAD_BYTES = (2**64) // 8
def __init__(
self,
initialization_vector: bytes,
tag: typing.Optional[bytes] = None,
min_tag_length: int = 16,
):
# OpenSSL 3.0.0 constrains GCM IVs to [64, 1024] bits inclusive
# This is a sane limit anyway so we'll enforce it here.
utils._check_byteslike("initialization_vector", initialization_vector)
if len(initialization_vector) < 8 or len(initialization_vector) > 128:
raise ValueError(
"initialization_vector must be between 8 and 128 bytes (64 "
"and 1024 bits)."
)
self._initialization_vector = initialization_vector
if tag is not None:
utils._check_bytes("tag", tag)
if min_tag_length < 4:
raise ValueError("min_tag_length must be >= 4")
if len(tag) < min_tag_length:
raise ValueError(
"Authentication tag must be {} bytes or longer.".format(
min_tag_length
)
)
self._tag = tag
self._min_tag_length = min_tag_length
@property
def tag(self) -> typing.Optional[bytes]:
return self._tag
@property
def initialization_vector(self) -> bytes:
return self._initialization_vector
def validate_for_algorithm(self, algorithm: CipherAlgorithm) -> None:
_check_aes_key_length(self, algorithm)
if not isinstance(algorithm, BlockCipherAlgorithm):
raise UnsupportedAlgorithm(
"GCM requires a block cipher algorithm",
_Reasons.UNSUPPORTED_CIPHER,
)
block_size_bytes = algorithm.block_size // 8
if self._tag is not None and len(self._tag) > block_size_bytes:
raise ValueError(
"Authentication tag cannot be more than {} bytes.".format(
block_size_bytes
)
)
|
