cmac.py 文件源码

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, 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