Verify given signature

        :param sign: Sign data
        :param data_filename: Assume signature is detached when not null
        :rtype: VerifyResult

def verify(self, sign, *args, **kwargs):
        '''
        Verify given signature

        :param sign: Sign data
        :param data_filename: Assume signature is detached when not null
        :rtype: VerifyResult
        '''
        return self.verify_file(self.create_stream(sign), *args, **kwargs)