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# 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 absolute_import, division, print_function
from cryptography import utils
from cryptography.exceptions import (
InvalidSignature, UnsupportedAlgorithm, _Reasons
)
from cryptography.hazmat.primitives import constant_time
from cryptography.hazmat.primitives.ciphers.modes import CBC
class _CMACContext(object):
def __init__(self, backend, algorithm, ctx=None):
if not backend.cmac_algorithm_supported(algorithm):
raise UnsupportedAlgorithm("This backend does not support CMAC.",
_Reasons.UNSUPPORTED_CIPHER)
self._backend = backend
self._key = algorithm.key
self._algorithm = algorithm
self._output_length = algorithm.block_size // 8
if ctx is None:
registry = self._backend._cipher_registry
adapter = registry[type(algorithm), CBC]
evp_cipher = adapter(self._backend, algorithm, CBC)
ctx = self._backend._lib.CMAC_CTX_new()
self._backend.openssl_assert(ctx != self._backend._ffi.NULL)
ctx = self._backend._ffi.gc(ctx, self._backend._lib.CMAC_CTX_free)
key_ptr = self._backend._ffi.from_buffer(self._key)
res = self._backend._lib.CMAC_Init(
ctx, key_ptr, len(self._key),
evp_cipher, self._backend._ffi.NULL
)
self._backend.openssl_assert(res == 1)
self._ctx = ctx
algorithm = utils.read_only_property("_algorithm")
def update(self, data):
res = self._backend._lib.CMAC_Update(self._ctx, data, len(data))
self._backend.openssl_assert(res == 1)
def finalize(self):
buf = self._backend._ffi.new("unsigned char[]", self._output_length)
length = self._backend._ffi.new("size_t *", self._output_length)
res = self._backend._lib.CMAC_Final(
self._ctx, buf, length
)
self._backend.openssl_assert(res == 1)
self._ctx = None
return self._backend._ffi.buffer(buf)[:]
def copy(self):
copied_ctx = self._backend._lib.CMAC_CTX_new()
copied_ctx = self._backend._ffi.gc(
copied_ctx, self._backend._lib.CMAC_CTX_free
)
res = self._backend._lib.CMAC_CTX_copy(
copied_ctx, self._ctx
)
self._backend.openssl_assert(res == 1)
return _CMACContext(
self._backend, self._algorithm, ctx=copied_ctx
)
def verify(self, signature):
digest = self.finalize()
if not constant_time.bytes_eq(digest, signature):
raise InvalidSignature("Signature did not match digest.")
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