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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 cryptography import utils
from cryptography.exceptions import (
AlreadyFinalized,
UnsupportedAlgorithm,
_Reasons,
)
from cryptography.hazmat.backends import _get_backend
from cryptography.hazmat.backends.interfaces import CMACBackend
from cryptography.hazmat.primitives import ciphers
class CMAC(object):
def __init__(
self, algorithm: ciphers.BlockCipherAlgorithm, backend=None, ctx=None
):
backend = _get_backend(backend)
if not isinstance(backend, CMACBackend):
raise UnsupportedAlgorithm(
"Backend object does not implement CMACBackend.",
_Reasons.BACKEND_MISSING_INTERFACE,
)
if not isinstance(algorithm, ciphers.BlockCipherAlgorithm):
raise TypeError("Expected instance of 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: bytes) -> None:
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
utils._check_bytes("data", data)
self._ctx.update(data)
def finalize(self) -> bytes:
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
digest = self._ctx.finalize()
self._ctx = None
return digest
def verify(self, signature: bytes) -> None:
utils._check_bytes("signature", signature)
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
ctx, self._ctx = self._ctx, None
ctx.verify(signature)
def copy(self) -> "CMAC":
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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