static int do_ssh2_transport(Ssh ssh, void *vin, int inlen,
			     struct Packet *pktin)
{
    unsigned char *in = (unsigned char *)vin;
    struct do_ssh2_transport_state {
	int nbits, pbits, warn_kex, warn_cscipher, warn_sccipher;
	Bignum p, g, e, f, K;
	void *our_kexinit;
	int our_kexinitlen;
	int kex_init_value, kex_reply_value;
	const struct ssh_mac **maclist;
	int nmacs;
	const struct ssh2_cipher *cscipher_tobe;
	const struct ssh2_cipher *sccipher_tobe;
	const struct ssh_mac *csmac_tobe;
	const struct ssh_mac *scmac_tobe;

	ssh2_pkt_addstring_start(s->pktout);
	/* First KEX packet does _not_ follow, because we're not that brave. */
	ssh2_pkt_addbool(s->pktout, FALSE);
	/* Reserved. */
	ssh2_pkt_adduint32(s->pktout, 0);
    }

    SHA_Init(&ssh->exhash);
    sha_string(&ssh->exhash, ssh->v_c, strlen(ssh->v_c));
    s->our_kexinitlen = s->pktout->length - 5;
    s->our_kexinit = snewn(s->our_kexinitlen, unsigned char);
    sha_string(&ssh->exhash, ssh->v_s, strlen(ssh->v_s));
    sha_string(&ssh->exhash, s->pktout->data + 5, s->pktout->length - 5);
    memcpy(s->our_kexinit, s->pktout->data + 5, s->our_kexinitlen); 

    ssh2_pkt_send_noqueue(ssh, s->pktout);

    if (!pktin)
	crWaitUntil(pktin);
    if (pktin->length > 5)
	sha_string(&ssh->exhash, pktin->data + 5, pktin->length - 5);

    /*
     * Now examine the other side's KEXINIT to see what we're up
     * to.
     */
    {
	char *str, *preferred;

	    ssh_set_frozen(ssh, 0);
	    if (s->dlgret == 0) {
		ssh_disconnect(ssh, "User aborted at cipher warning", NULL,
			       0, TRUE);
		crStop(0);
	    }
	}

	SHA_Init(&ssh->exhash);
	sha_string(&ssh->exhash, ssh->v_c, strlen(ssh->v_c));
	sha_string(&ssh->exhash, ssh->v_s, strlen(ssh->v_s));
	sha_string(&ssh->exhash, s->our_kexinit, s->our_kexinitlen);
	sfree(s->our_kexinit);
	if (pktin->length > 5)
	    sha_string(&ssh->exhash, pktin->data + 5, pktin->length - 5);


	if (s->ignorepkt) /* first_kex_packet_follows */
	    crWaitUntil(pktin);                /* Ignore packet */
    }

    /*
     * Work out the number of bits of key we will need from the key