# 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() )