def ssh_KEX_DH_GEX_INIT(self, packet):
        """
        Called when we get a MSG_KEX_DH_GEX_INIT message.  Payload::
            integer e (client DH public key)

        We send the MSG_KEX_DH_GEX_REPLY message with our host key and
        signature.

        @type packet: L{bytes}
        @param packet: The message data.
        """
        clientDHpublicKey, foo = getMP(packet)
        # TODO: we should also look at the value they send to us and reject
        # insecure values of f (if g==2 and f has a single '1' bit while the
        # rest are '0's, then they must have used a small y also).

        # TODO: This could be computed when self.p is set up
        #  or do as openssh does and scan f for a single '1' bit instead

        sharedSecret = self._finishEphemeralDH(clientDHpublicKey)
        h = _kex.getHashProcessor(self.kexAlg)()
        h.update(NS(self.otherVersionString))
        h.update(NS(self.ourVersionString))
        h.update(NS(self.otherKexInitPayload))
        h.update(NS(self.ourKexInitPayload))
        h.update(NS(self.factory.publicKeys[self.keyAlg].blob()))
        h.update(self.dhGexRequest)
        h.update(MP(self.p))
        h.update(MP(self.g))
        h.update(MP(clientDHpublicKey))
        h.update(self.dhSecretKeyPublicMP)
        h.update(sharedSecret)
        exchangeHash = h.digest()
        self.sendPacket(
            MSG_KEX_DH_GEX_REPLY,
            NS(self.factory.publicKeys[self.keyAlg].blob()) +
            self.dhSecretKeyPublicMP +
            NS(self.factory.privateKeys[self.keyAlg].sign(exchangeHash)))
        self._keySetup(sharedSecret, exchangeHash)

        Called when we get a MSG_KEX_DH_GEX_INIT message.  Payload::
            integer e (client DH public key)

        We send the MSG_KEX_DH_GEX_REPLY message with our host key and
        signature.

        @type packet: L{bytes}
        @param packet: The message data.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/ssh/transport.py