def encrypt(self, x):
        """
        Called to encrypt the packet.  Simply record that encryption was used
        and return the data unchanged.
        """
        self.usedEncrypt = True
        if (len(x) % self.encBlockSize) != 0:
            raise RuntimeError("length %i modulo blocksize %i is not 0: %i" %
                    (len(x), self.encBlockSize, len(x) % self.encBlockSize))
        return x

        Called to encrypt the packet.  Simply record that encryption was used
        and return the data unchanged.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_transport.py