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# 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
#
# http://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.
from __future__ import absolute_import, division, print_function
from cryptography import utils
from cryptography.exceptions import (
InvalidTag, UnsupportedAlgorithm, _Reasons
)
from cryptography.hazmat.primitives import constant_time, interfaces
from cryptography.hazmat.primitives.ciphers.modes import (
CFB, CFB8, CTR, OFB
)
@utils.register_interface(interfaces.CipherContext)
class _CipherContext(object):
def __init__(self, backend, cipher, mode, operation):
self._backend = backend
self._cipher = cipher
self._mode = mode
self._operation = operation
# There is a bug in CommonCrypto where block ciphers do not raise
# kCCAlignmentError when finalizing if you supply non-block aligned
# data. To work around this we need to keep track of the block
# alignment ourselves, but only for alg+mode combos that require
# block alignment. OFB, CFB, and CTR make a block cipher algorithm
# into a stream cipher so we don't need to track them (and thus their
# block size is effectively 1 byte just like OpenSSL/CommonCrypto
# treat RC4 and other stream cipher block sizes).
# This bug has been filed as rdar://15589470
self._bytes_processed = 0
if (isinstance(cipher, interfaces.BlockCipherAlgorithm) and not
isinstance(mode, (OFB, CFB, CFB8, CTR))):
self._byte_block_size = cipher.block_size // 8
else:
self._byte_block_size = 1
registry = self._backend._cipher_registry
try:
cipher_enum, mode_enum = registry[type(cipher), type(mode)]
except KeyError:
raise UnsupportedAlgorithm(
"cipher {0} in {1} mode is not supported "
"by this backend.".format(
cipher.name, mode.name if mode else mode),
_Reasons.UNSUPPORTED_CIPHER
)
ctx = self._backend._ffi.new("CCCryptorRef *")
ctx = self._backend._ffi.gc(ctx, self._backend._release_cipher_ctx)
if isinstance(mode, interfaces.ModeWithInitializationVector):
iv_nonce = mode.initialization_vector
elif isinstance(mode, interfaces.ModeWithNonce):
iv_nonce = mode.nonce
else:
iv_nonce = self._backend._ffi.NULL
if isinstance(mode, CTR):
mode_option = self._backend._lib.kCCModeOptionCTR_BE
else:
mode_option = 0
res = self._backend._lib.CCCryptorCreateWithMode(
operation,
mode_enum, cipher_enum,
self._backend._lib.ccNoPadding, iv_nonce,
cipher.key, len(cipher.key),
self._backend._ffi.NULL, 0, 0, mode_option, ctx)
self._backend._check_cipher_response(res)
self._ctx = ctx
def update(self, data):
# Count bytes processed to handle block alignment.
self._bytes_processed += len(data)
buf = self._backend._ffi.new(
"unsigned char[]", len(data) + self._byte_block_size - 1)
outlen = self._backend._ffi.new("size_t *")
res = self._backend._lib.CCCryptorUpdate(
self._ctx[0], data, len(data), buf,
len(data) + self._byte_block_size - 1, outlen)
self._backend._check_cipher_response(res)
return self._backend._ffi.buffer(buf)[:outlen[0]]
def finalize(self):
# Raise error if block alignment is wrong.
if self._bytes_processed % self._byte_block_size:
raise ValueError(
"The length of the provided data is not a multiple of "
"the block length."
)
buf = self._backend._ffi.new("unsigned char[]", self._byte_block_size)
outlen = self._backend._ffi.new("size_t *")
res = self._backend._lib.CCCryptorFinal(
self._ctx[0], buf, len(buf), outlen)
self._backend._check_cipher_response(res)
self._backend._release_cipher_ctx(self._ctx)
return self._backend._ffi.buffer(buf)[:outlen[0]]
@utils.register_interface(interfaces.AEADCipherContext)
@utils.register_interface(interfaces.AEADEncryptionContext)
class _GCMCipherContext(object):
def __init__(self, backend, cipher, mode, operation):
self._backend = backend
self._cipher = cipher
self._mode = mode
self._operation = operation
self._tag = None
registry = self._backend._cipher_registry
try:
cipher_enum, mode_enum = registry[type(cipher), type(mode)]
except KeyError:
raise UnsupportedAlgorithm(
"cipher {0} in {1} mode is not supported "
"by this backend.".format(
cipher.name, mode.name if mode else mode),
_Reasons.UNSUPPORTED_CIPHER
)
ctx = self._backend._ffi.new("CCCryptorRef *")
ctx = self._backend._ffi.gc(ctx, self._backend._release_cipher_ctx)
self._ctx = ctx
res = self._backend._lib.CCCryptorCreateWithMode(
operation,
mode_enum, cipher_enum,
self._backend._lib.ccNoPadding,
self._backend._ffi.NULL,
cipher.key, len(cipher.key),
self._backend._ffi.NULL, 0, 0, 0, self._ctx)
self._backend._check_cipher_response(res)
res = self._backend._lib.CCCryptorGCMAddIV(
self._ctx[0],
mode.initialization_vector,
len(mode.initialization_vector)
)
self._backend._check_cipher_response(res)
# CommonCrypto has a bug where calling update without at least one
# call to authenticate_additional_data will result in null byte output
# for ciphertext. The following empty byte string call prevents the
# issue, which is present in at least 10.8 and 10.9.
# Filed as rdar://18314544
self.authenticate_additional_data(b"")
def update(self, data):
buf = self._backend._ffi.new("unsigned char[]", len(data))
args = (self._ctx[0], data, len(data), buf)
if self._operation == self._backend._lib.kCCEncrypt:
res = self._backend._lib.CCCryptorGCMEncrypt(*args)
else:
res = self._backend._lib.CCCryptorGCMDecrypt(*args)
self._backend._check_cipher_response(res)
return self._backend._ffi.buffer(buf)[:]
def finalize(self):
# CommonCrypto has a yet another bug where you must make at least one
# call to update. If you pass just AAD and call finalize without a call
# to update you'll get null bytes for tag. The following update call
# prevents this issue, which is present in at least 10.8 and 10.9.
# Filed as rdar://18314580
self.update(b"")
tag_size = self._cipher.block_size // 8
tag_buf = self._backend._ffi.new("unsigned char[]", tag_size)
tag_len = self._backend._ffi.new("size_t *", tag_size)
res = self._backend._lib.CCCryptorGCMFinal(
self._ctx[0], tag_buf, tag_len
)
self._backend._check_cipher_response(res)
self._backend._release_cipher_ctx(self._ctx)
self._tag = self._backend._ffi.buffer(tag_buf)[:]
if (self._operation == self._backend._lib.kCCDecrypt and
not constant_time.bytes_eq(
self._tag[:len(self._mode.tag)], self._mode.tag
)):
raise InvalidTag
return b""
def authenticate_additional_data(self, data):
res = self._backend._lib.CCCryptorGCMAddAAD(
self._ctx[0], data, len(data)
)
self._backend._check_cipher_response(res)
tag = utils.read_only_property("_tag")
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