/usr/lib/python3/dist-packages/Cryptodome/Cipher/_mode_ocb.py is in python3-pycryptodome 3.4.7-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 | # ===================================================================
#
# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# 1. Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
# notice, this list of conditions and the following disclaimer in
# the documentation and/or other materials provided with the
# distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
# ===================================================================
"""
Offset Codebook (OCB) mode.
OCB is Authenticated Encryption with Associated Data (AEAD) cipher mode
designed by Prof. Phillip Rogaway and specified in `RFC7253`_.
The algorithm provides both authenticity and privacy, it is very efficient,
it uses only one key and it can be used in online mode (so that encryption
or decryption can start before the end of the message is available).
This module implements the third and last variant of OCB (OCB3) and it only
works in combination with a 128-bit block symmetric cipher, like AES.
OCB is patented in US but `free licenses`_ exist for software implementations
meant for non-military purposes.
Example:
>>> from Cryptodome.Cipher import AES
>>> from Cryptodome.Random import get_random_bytes
>>>
>>> key = get_random_bytes(32)
>>> cipher = AES.new(key, AES.MODE_OCB)
>>> plaintext = b"Attack at dawn"
>>> ciphertext, mac = cipher.encrypt_and_digest(plaintext)
>>> # Deliver cipher.nonce, ciphertext and mac
...
>>> cipher = AES.new(key, AES.MODE_OCB, nonce=nonce)
>>> try:
>>> plaintext = cipher.decrypt_and_verify(ciphertext, mac)
>>> except ValueError:
>>> print "Invalid message"
>>> else:
>>> print plaintext
:undocumented: __package__
.. _RFC7253: http://www.rfc-editor.org/info/rfc7253
.. _free licenses: http://web.cs.ucdavis.edu/~rogaway/ocb/license.htm
"""
from Cryptodome.Util.py3compat import b, bord, bchr, unhexlify
from Cryptodome.Util.number import long_to_bytes, bytes_to_long
from Cryptodome.Util.strxor import strxor
from Cryptodome.Hash import BLAKE2s
from Cryptodome.Random import get_random_bytes
from Cryptodome.Util._raw_api import (load_pycryptodome_raw_lib, VoidPointer,
create_string_buffer, get_raw_buffer,
SmartPointer, c_size_t, expect_byte_string,
)
_raw_ocb_lib = load_pycryptodome_raw_lib("Cryptodome.Cipher._raw_ocb", """
int OCB_start_operation(void *cipher,
const uint8_t *offset_0,
size_t offset_0_len,
void **pState);
int OCB_encrypt(void *state,
const uint8_t *in,
uint8_t *out,
size_t data_len);
int OCB_decrypt(void *state,
const uint8_t *in,
uint8_t *out,
size_t data_len);
int OCB_update(void *state,
const uint8_t *in,
size_t data_len);
int OCB_digest(void *state,
uint8_t *tag,
size_t tag_len);
int OCB_stop_operation(void *state);
""")
class OcbMode(object):
"""Offset Codebook (OCB) mode.
:undocumented: __init__
"""
def __init__(self, factory, nonce, mac_len, cipher_params):
if factory.block_size != 16:
raise ValueError("OCB mode is only available for ciphers"
" that operate on 128 bits blocks")
self.block_size = 16
"""The block size of the underlying cipher, in bytes."""
self.nonce = nonce
"""Nonce used for this session."""
if len(nonce) not in list(range(1, 16)):
raise ValueError("Nonce must be at most 15 bytes long")
self._mac_len = mac_len
if not 8 <= mac_len <= 16:
raise ValueError("MAC tag must be between 8 and 16 bytes long")
# Cache for MAC tag
self._mac_tag = None
# Cache for unaligned associated data
self._cache_A = b("")
# Cache for unaligned ciphertext/plaintext
self._cache_P = b("")
# Allowed transitions after initialization
self._next = [self.update, self.encrypt, self.decrypt,
self.digest, self.verify]
# Compute Offset_0
params_without_key = dict(cipher_params)
key = params_without_key.pop("key")
nonce = (bchr(self._mac_len << 4 & 0xFF) +
bchr(0) * (14 - len(self.nonce)) +
bchr(1) +
self.nonce)
bottom = bord(nonce[15]) & 0x3F # 6 bits, 0..63
ktop = factory.new(key, factory.MODE_ECB, **params_without_key)\
.encrypt(nonce[:15] + bchr(bord(nonce[15]) & 0xC0))
stretch = ktop + strxor(ktop[:8], ktop[1:9]) # 192 bits
offset_0 = long_to_bytes(bytes_to_long(stretch) >>
(64 - bottom), 24)[8:]
# Create low-level cipher instance
raw_cipher = factory._create_base_cipher(cipher_params)
if cipher_params:
raise TypeError("Unknown keywords: " + str(cipher_params))
self._state = VoidPointer()
result = _raw_ocb_lib.OCB_start_operation(raw_cipher.get(),
offset_0,
c_size_t(len(offset_0)),
self._state.address_of())
if result:
raise ValueError("Error %d while instantiating the OCB mode"
% result)
# Ensure that object disposal of this Python object will (eventually)
# free the memory allocated by the raw library for the cipher mode
self._state = SmartPointer(self._state.get(),
_raw_ocb_lib.OCB_stop_operation)
# Memory allocated for the underlying block cipher is now owed
# by the cipher mode
raw_cipher.release()
def _update(self, assoc_data, assoc_data_len):
expect_byte_string(assoc_data)
result = _raw_ocb_lib.OCB_update(self._state.get(),
assoc_data,
c_size_t(assoc_data_len))
if result:
raise ValueError("Error %d while MAC-ing in OCB mode" % result)
def update(self, assoc_data):
"""Process the associated data.
If there is any associated data, the caller has to invoke
this method one or more times, before using
``decrypt`` or ``encrypt``.
By *associated data* it is meant any data (e.g. packet headers) that
will not be encrypted and will be transmitted in the clear.
However, the receiver shall still able to detect modifications.
If there is no associated data, this method must not be called.
The caller may split associated data in segments of any size, and
invoke this method multiple times, each time with the next segment.
:Parameters:
assoc_data : byte string
A piece of associated data.
"""
if self.update not in self._next:
raise TypeError("update() can only be called"
" immediately after initialization")
self._next = [self.encrypt, self.decrypt, self.digest,
self.verify, self.update]
if len(self._cache_A) > 0:
filler = min(16 - len(self._cache_A), len(assoc_data))
self._cache_A += assoc_data[:filler]
assoc_data = assoc_data[filler:]
if len(self._cache_A) < 16:
return self
# Clear the cache, and proceeding with any other aligned data
self._cache_A, seg = b(""), self._cache_A
self.update(seg)
update_len = len(assoc_data) // 16 * 16
self._cache_A = assoc_data[update_len:]
self._update(assoc_data, update_len)
return self
def _transcrypt_aligned(self, in_data, in_data_len,
trans_func, trans_desc):
out_data = create_string_buffer(in_data_len)
result = trans_func(self._state.get(),
in_data,
out_data,
c_size_t(in_data_len))
if result:
raise ValueError("Error %d while %sing in OCB mode"
% (result, trans_desc))
return get_raw_buffer(out_data)
def _transcrypt(self, in_data, trans_func, trans_desc):
# Last piece to encrypt/decrypt
if in_data is None:
out_data = self._transcrypt_aligned(self._cache_P,
len(self._cache_P),
trans_func,
trans_desc)
self._cache_P = b("")
return out_data
# Try to fill up the cache, if it already contains something
expect_byte_string(in_data)
prefix = b("")
if len(self._cache_P) > 0:
filler = min(16 - len(self._cache_P), len(in_data))
self._cache_P += in_data[:filler]
in_data = in_data[filler:]
if len(self._cache_P) < 16:
# We could not manage to fill the cache, so there is certainly
# no output yet.
return b("")
# Clear the cache, and proceeding with any other aligned data
prefix = self._transcrypt_aligned(self._cache_P,
len(self._cache_P),
trans_func,
trans_desc)
self._cache_P = b("")
# Process data in multiples of the block size
trans_len = len(in_data) // 16 * 16
result = self._transcrypt_aligned(in_data,
trans_len,
trans_func,
trans_desc)
if prefix:
result = prefix + result
# Left-over
self._cache_P = in_data[trans_len:]
return result
def encrypt(self, plaintext=None):
"""Encrypt the next piece of plaintext.
After the entire plaintext has been passed (but before `digest`),
you **must** call this method one last time with no arguments to collect
the final piece of ciphertext.
If possible, use the method `encrypt_and_digest` instead.
:Parameters:
plaintext : byte string
The next piece of data to encrypt or ``None`` to signify
that encryption has finished and that any remaining ciphertext
has to be produced.
:Return:
the ciphertext, as a byte string.
Its length may not match the length of the *plaintext*.
"""
if self.encrypt not in self._next:
raise TypeError("encrypt() can only be called after"
" initialization or an update()")
if plaintext is None:
self._next = [self.digest]
else:
self._next = [self.encrypt]
return self._transcrypt(plaintext, _raw_ocb_lib.OCB_encrypt, "encrypt")
def decrypt(self, ciphertext=None):
"""Decrypt the next piece of ciphertext.
After the entire ciphertext has been passed (but before `verify`),
you **must** call this method one last time with no arguments to collect
the remaining piece of plaintext.
If possible, use the method `decrypt_and_verify` instead.
:Parameters:
ciphertext : byte string
The next piece of data to decrypt or ``None`` to signify
that decryption has finished and that any remaining plaintext
has to be produced.
:Return:
the plaintext, as a byte string.
Its length may not match the length of the *ciphertext*.
"""
if self.decrypt not in self._next:
raise TypeError("decrypt() can only be called after"
" initialization or an update()")
if ciphertext is None:
self._next = [self.verify]
else:
self._next = [self.decrypt]
return self._transcrypt(ciphertext,
_raw_ocb_lib.OCB_decrypt,
"decrypt")
def _compute_mac_tag(self):
if self._mac_tag is not None:
return
if self._cache_A:
self._update(self._cache_A, len(self._cache_A))
self._cache_A = b("")
mac_tag = create_string_buffer(16)
result = _raw_ocb_lib.OCB_digest(self._state.get(),
mac_tag,
c_size_t(len(mac_tag))
)
if result:
raise ValueError("Error %d while computing digest in OCB mode"
% result)
self._mac_tag = get_raw_buffer(mac_tag)[:self._mac_len]
def digest(self):
"""Compute the *binary* MAC tag.
Call this method after the final `encrypt` (the one with no arguments)
to obtain the MAC tag.
The MAC tag is needed by the receiver to determine authenticity
of the message.
:Return: the MAC, as a byte string.
"""
if self.digest not in self._next:
raise TypeError("digest() cannot be called now for this cipher")
assert(len(self._cache_P) == 0)
self._next = [self.digest]
if self._mac_tag is None:
self._compute_mac_tag()
return self._mac_tag
def hexdigest(self):
"""Compute the *printable* MAC tag.
This method is like `digest`.
:Return: the MAC, as a hexadecimal string.
"""
return "".join(["%02x" % bord(x) for x in self.digest()])
def verify(self, received_mac_tag):
"""Validate the *binary* MAC tag.
Call this method after the final `decrypt` (the one with no arguments)
to check if the message is authentic and valid.
:Parameters:
received_mac_tag : byte string
This is the *binary* MAC, as received from the sender.
:Raises ValueError:
if the MAC does not match. The message has been tampered with
or the key is incorrect.
"""
if self.verify not in self._next:
raise TypeError("verify() cannot be called now for this cipher")
assert(len(self._cache_P) == 0)
self._next = [self.verify]
if self._mac_tag is None:
self._compute_mac_tag()
secret = get_random_bytes(16)
mac1 = BLAKE2s.new(digest_bits=160, key=secret, data=self._mac_tag)
mac2 = BLAKE2s.new(digest_bits=160, key=secret, data=received_mac_tag)
if mac1.digest() != mac2.digest():
raise ValueError("MAC check failed")
def hexverify(self, hex_mac_tag):
"""Validate the *printable* MAC tag.
This method is like `verify`.
:Parameters:
hex_mac_tag : string
This is the *printable* MAC, as received from the sender.
:Raises ValueError:
if the MAC does not match. The message has been tampered with
or the key is incorrect.
"""
self.verify(unhexlify(hex_mac_tag))
def encrypt_and_digest(self, plaintext):
"""Encrypt the message and create the MAC tag in one step.
:Parameters:
plaintext : byte string
The entire message to encrypt.
:Return:
a tuple with two byte strings:
- the encrypted data
- the MAC
"""
return self.encrypt(plaintext) + self.encrypt(), self.digest()
def decrypt_and_verify(self, ciphertext, received_mac_tag):
"""Decrypted the message and verify its authenticity in one step.
:Parameters:
ciphertext : byte string
The entire message to decrypt.
received_mac_tag : byte string
This is the *binary* MAC, as received from the sender.
:Return: the decrypted data (byte string).
:Raises ValueError:
if the MAC does not match. The message has been tampered with
or the key is incorrect.
"""
plaintext = self.decrypt(ciphertext) + self.decrypt()
self.verify(received_mac_tag)
return plaintext
def _create_ocb_cipher(factory, **kwargs):
"""Create a new block cipher, configured in OCB mode.
:Parameters:
factory : module
A symmetric cipher module from `Cryptodome.Cipher`
(like `Cryptodome.Cipher.AES`).
:Keywords:
nonce : byte string
A value that must never be reused for any other encryption.
Its length can vary from 1 to 15 bytes.
If not specified, a random 15 bytes long nonce is generated.
mac_len : integer
Length of the MAC, in bytes.
It must be in the range ``[8..16]``.
The default is 16 (128 bits).
Any other keyword will be passed to the underlying block cipher.
See the relevant documentation for details (at least ``key`` will need
to be present).
"""
try:
nonce = kwargs.pop("nonce", None)
if nonce is None:
nonce = get_random_bytes(15)
mac_len = kwargs.pop("mac_len", 16)
except KeyError as e:
raise TypeError("Keyword missing: " + str(e))
return OcbMode(factory, nonce, mac_len, kwargs)
|