def response_status(self, value):
        """
        The overall status of the response. Only a "successful" response will
        include information about the certificate. Other response types are for
        signaling info about the OCSP responder. Valid values include:

         - "successful" - when the response includes information about the certificate
         - "malformed_request" - when the request could not be understood
         - "internal_error" - when an internal error occured with the OCSP responder
         - "try_later" - when the OCSP responder is temporarily unavailable
         - "sign_required" - when the OCSP request must be signed
         - "unauthorized" - when the responder is not the correct responder for the certificate
        """

        if not isinstance(value, str_cls):
            raise TypeError(_pretty_message(
                '''
                response_status must be a unicode string, not %s
                ''',
                _type_name(value)
            ))

        valid_response_statuses = set([
            'successful',
            'malformed_request',
            'internal_error',
            'try_later',
            'sign_required',
            'unauthorized'
        ])
        if value not in valid_response_statuses:
            raise ValueError(_pretty_message(
                '''
                response_status must be one of "successful",
                "malformed_request", "internal_error", "try_later",
                "sign_required", "unauthorized", not %s
                ''',
                repr(value)
            ))

        self._response_status = value