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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 (
AlreadyFinalized, UnsupportedAlgorithm, _Reasons
)
from cryptography.hazmat.backends.interfaces import CMACBackend
from cryptography.hazmat.primitives import interfaces
@utils.register_interface(interfaces.MACContext)
class CMAC(object):
def __init__(self, algorithm, backend, ctx=None):
if not isinstance(backend, CMACBackend):
raise UnsupportedAlgorithm(
"Backend object does not implement CMACBackend.",
_Reasons.BACKEND_MISSING_INTERFACE
)
if not isinstance(algorithm, interfaces.BlockCipherAlgorithm):
raise TypeError(
"Expected instance of interfaces.BlockCipherAlgorithm."
)
self._algorithm = algorithm
self._backend = backend
if ctx is None:
self._ctx = self._backend.create_cmac_ctx(self._algorithm)
else:
self._ctx = ctx
def update(self, data):
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
if not isinstance(data, bytes):
raise TypeError("data must be bytes.")
self._ctx.update(data)
def finalize(self):
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
digest = self._ctx.finalize()
self._ctx = None
return digest
def verify(self, signature):
if not isinstance(signature, bytes):
raise TypeError("signature must be bytes.")
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
ctx, self._ctx = self._ctx, None
ctx.verify(signature)
def copy(self):
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
return CMAC(
self._algorithm,
backend=self._backend,
ctx=self._ctx.copy()
)
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