def sign(message: bytes, sign_key: SignKey) -> Signature:
        """
        Signs the message and returns signature.

        :param: message - Message to sign
        :param: sign_key - Sign key
        :return: Signature
        """

        logger = logging.getLogger(__name__)
        logger.debug("Bls::sign: >>> message: %r, sign_key: %r", message, sign_key)

        c_instance = c_void_p()
        do_call('indy_crypto_bls_sign',
                message, len(message),
                sign_key.c_instance,
                byref(c_instance))

        res = Signature(c_instance)

        logger.debug("Bls::sign: <<< res: %r", res)
        return res
Signs the message and returns signature.

        :param: message - Message to sign
        :param: sign_key - Sign key
        :return: Signature