cmac.py 文件源码

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()

            assert ctx != self._backend._ffi.NULL
            ctx = self._backend._ffi.gc(ctx, self._backend._lib.CMAC_CTX_free)

            self._backend._lib.CMAC_Init(
                ctx, self._key, len(self._key),
                evp_cipher, self._backend._ffi.NULL
            )

        self._ctx = ctx