multibackend.py 文件源码

def create_symmetric_encryption_ctx(self, cipher, mode):
        for b in self._filtered_backends(CipherBackend):
            try:
                return b.create_symmetric_encryption_ctx(cipher, mode)
            except UnsupportedAlgorithm:
                pass
        raise UnsupportedAlgorithm(
            "cipher {0} in {1} mode is not supported by this backend.".format(
                cipher.name, mode.name if mode else mode),
            _Reasons.UNSUPPORTED_CIPHER
        )