static void ssh2_pkt_init(Ssh, int pkt_type);
static void ssh2_pkt_addbool(Ssh, unsigned char value);
static void ssh2_pkt_adduint32(Ssh, unsigned long value);
static void ssh2_pkt_addstring_start(Ssh);
static void ssh2_pkt_addstring_str(Ssh, char *data);
static void ssh2_pkt_addstring_data(Ssh, char *data, int len);
static void ssh2_pkt_addstring(Ssh, char *data);
static unsigned char *ssh2_mpint_fmt(Bignum b, int *len);
static void ssh2_pkt_addmp(Ssh, Bignum b);
static int ssh2_pkt_construct(Ssh);
static void ssh2_pkt_send(Ssh);

/*
 * Buffer management constants. There are several of these for
 * various different purposes:

    return biglen + 4;
}

static void s_wrpkt(Ssh ssh)
{
    int len, backlog;
    len = s_wrpkt_prepare(ssh);
    backlog = sk_write(ssh->s, (char *)ssh->pktout.data, len);
    if (backlog > SSH_MAX_BACKLOG)
	ssh_throttle_all(ssh, 1, backlog);
}

static void s_wrpkt_defer(Ssh ssh)
{
    int len;

	  case PKT_DATA:
	    (void) va_arg(ap1, unsigned char *);
	    arglen = va_arg(ap1, int);
	    pktlen += arglen;
	    break;
	  case PKT_STR:
	    argp = va_arg(ap1, unsigned char *);
	    arglen = strlen((char *)argp);
	    pktlen += 4 + arglen;
	    break;
	  case PKT_BIGNUM:
	    bn = va_arg(ap1, Bignum);
	    pktlen += ssh1_bignum_length(bn);
	    break;
	  default:

	    argp = va_arg(ap2, unsigned char *);
	    arglen = va_arg(ap2, int);
	    memcpy(p, argp, arglen);
	    p += arglen;
	    break;
	  case PKT_STR:
	    argp = va_arg(ap2, unsigned char *);
	    arglen = strlen((char *)argp);
	    PUT_32BIT(p, arglen);
	    memcpy(p + 4, argp, arglen);
	    p += 4 + arglen;
	    break;
	  case PKT_BIGNUM:
	    bn = va_arg(ap2, Bignum);
	    p += ssh1_write_bignum(p, bn);

	      ssh->pktout.length - ssh->pktout.savedpos);
}
static void ssh2_pkt_addstring(Ssh ssh, char *data)
{
    ssh2_pkt_addstring_start(ssh);
    ssh2_pkt_addstring_str(ssh, data);
}
static unsigned char *ssh2_mpint_fmt(Bignum b, int *len)
{
    unsigned char *p;
    int i, n = (bignum_bitcount(b) + 7) / 8;
    p = smalloc(n + 1);
    if (!p)
	fatalbox("out of memory");
    p[0] = 0;

}
static void ssh2_pkt_addmp(Ssh ssh, Bignum b)
{
    unsigned char *p;
    int len;
    p = ssh2_mpint_fmt(b, &len);
    ssh2_pkt_addstring_start(ssh);
    ssh2_pkt_addstring_data(ssh, (char *)p, len);
    sfree(p);
}

/*
 * Construct an SSH2 final-form packet: compress it, encrypt it,
 * put the MAC on it. Final packet, ready to be sent, is stored in
 * ssh->pktout.data. Total length is returned.

 * Construct and send an SSH2 packet immediately.
 */
static void ssh2_pkt_send(Ssh ssh)
{
    int len;
    int backlog;
    len = ssh2_pkt_construct(ssh);
    backlog = sk_write(ssh->s, (char *)ssh->pktout.data, len);
    if (backlog > SSH_MAX_BACKLOG)
	ssh_throttle_all(ssh, 1, backlog);
}

/*
 * Construct an SSH2 packet and add it to a deferred data block.
 * Useful for sending multiple packets in a single sk_write() call,

/*
 * Send the whole deferred data block constructed by
 * ssh2_pkt_defer() or SSH1's defer_packet().
 */
static void ssh_pkt_defersend(Ssh ssh)
{
    int backlog;
    backlog = sk_write(ssh->s, (char *)ssh->deferred_send_data,
		       ssh->deferred_len);
    ssh->deferred_len = ssh->deferred_size = 0;
    sfree(ssh->deferred_send_data);
    ssh->deferred_send_data = NULL;
    if (backlog > SSH_MAX_BACKLOG)
	ssh_throttle_all(ssh, 1, backlog);
}

    len = GET_32BIT(ssh->pktin.data + ssh->pktin.savedpos);
    if (len < 0)
	return;
    *length = len;
    ssh->pktin.savedpos += 4;
    if (ssh->pktin.length - ssh->pktin.savedpos < *length)
	return;
    *p = (char *)(ssh->pktin.data + ssh->pktin.savedpos);
    ssh->pktin.savedpos += *length;
}
static Bignum ssh2_pkt_getmp(Ssh ssh)
{
    char *p;
    int length;
    Bignum b;

    ssh2_pkt_getstring(ssh, &p, &length);
    if (!p)
	return NULL;
    if (p[0] & 0x80) {
	bombout((ssh,"internal error: Can't handle negative mpints"));
	return NULL;
    }
    b = bignum_from_bytes((unsigned char *)p, length);
    return b;
}

/*
 * Helper function to add an SSH2 signature blob to a packet.
 * Expects to be shown the public key blob as well as the signature
 * blob. Normally works just like ssh2_pkt_addstring, but will

	pos = 4+7;		       /* skip over "ssh-rsa" */
	siglen = GET_32BIT(sigblob+pos);
	/* debug(("signature length is %d\n", siglen)); */

	if (len != siglen) {
	    unsigned char newlen[4];
	    ssh2_pkt_addstring_start(ssh);
	    ssh2_pkt_addstring_data(ssh, (char *)sigblob, pos);
	    /* dmemdump(sigblob, pos); */
	    pos += 4;		       /* point to start of actual sig */
	    PUT_32BIT(newlen, len);
	    ssh2_pkt_addstring_data(ssh, (char *)newlen, 4);
	    /* dmemdump(newlen, 4); */
	    newlen[0] = 0;
	    while (len-- > siglen) {
		ssh2_pkt_addstring_data(ssh, (char *)newlen, 1);
		/* dmemdump(newlen, 1); */
	    }
	    ssh2_pkt_addstring_data(ssh, (char *)(sigblob+pos), siglen);
	    /* dmemdump(sigblob+pos, siglen); */
	    return;
	}

	/* Otherwise fall through and do it the easy way. */
    }

    ssh2_pkt_addstring_start(ssh);
    ssh2_pkt_addstring_data(ssh, (char *)sigblob, sigblob_len);
}

/*
 * Examine the remote side's version string and compare it against
 * a list of known buggy implementations.
 */
static void ssh_detect_bugs(Ssh ssh, char *vstring)

    }
    return 0;
}

static int ssh_receive(Plug plug, int urgent, char *data, int len)
{
    Ssh ssh = (Ssh) plug;
    ssh_gotdata(ssh, (unsigned char *)data, len);
    if (ssh->state == SSH_STATE_CLOSED) {
	if (ssh->s) {
	    sk_close(ssh->s);
	    ssh->s = NULL;
	}
	return 0;
    }

			s->tried_publickey = 1;
		    }
		    s->p += 4;
		    s->p += ssh1_read_bignum(s->p, &s->key.exponent);
		    s->p += ssh1_read_bignum(s->p, &s->key.modulus);
		    s->commentlen = GET_32BIT(s->p);
		    s->p += 4;
		    s->commentp = (char *)s->p;
		    s->p += s->commentlen;
		    send_packet(ssh, SSH1_CMSG_AUTH_RSA,
				PKT_BIGNUM, s->key.modulus, PKT_END);
		    crWaitUntil(ispkt);
		    if (ssh->pktin.type != SSH1_SMSG_AUTH_RSA_CHALLENGE) {
			logevent("Key refused");
			continue;

	if (ispkt) {
	    if (ssh->pktin.type == SSH1_SMSG_STDOUT_DATA ||
		ssh->pktin.type == SSH1_SMSG_STDERR_DATA) {
		long len = GET_32BIT(ssh->pktin.body);
		int bufsize =
		    from_backend(ssh->frontend,
				 ssh->pktin.type == SSH1_SMSG_STDERR_DATA,
				 (char *)(ssh->pktin.body) + 4, len);
		if (!ssh->v1_stdout_throttling && bufsize > SSH1_BUFFER_LIMIT) {
		    ssh->v1_stdout_throttling = 1;
		    ssh1_throttle(ssh, +1);
		}
	    } else if (ssh->pktin.type == SSH1_MSG_DISCONNECT) {
		ssh->state = SSH_STATE_CLOSED;
		logevent("Received disconnect request");

		int hostsize, port;
		char host[256], buf[1024];
		char *p, *h, *e;
		c = smalloc(sizeof(struct ssh_channel));
		c->ssh = ssh;

		hostsize = GET_32BIT(ssh->pktin.body+4);
		for (h = host, p = (char *)(ssh->pktin.body+8);
		     hostsize != 0; hostsize--) {
		    if (h+1 < host+sizeof(host))
			*h++ = *p;
		    p++;
		}
		*h = 0;
		port = GET_32BIT(p);

		unsigned char *p = ssh->pktin.body + 8;
		struct ssh_channel *c;
		c = find234(ssh->channels, &i, ssh_channelfind);
		if (c) {
		    int bufsize;
		    switch (c->type) {
		      case CHAN_X11:
			bufsize = x11_send(c->u.x11.s, (char *)p, len);
			break;
		      case CHAN_SOCKDATA:
			bufsize = pfd_send(c->u.pfd.s, (char *)p, len);
			break;
		      case CHAN_AGENT:
			/* Data for an agent message. Buffer it. */
			while (len > 0) {
			    if (c->u.a.lensofar < 4) {
				int l = min(4 - c->u.a.lensofar, len);
				memcpy(c->u.a.msglen + c->u.a.lensofar, p,

	haylen--, haystack++;	       /* skip over comma itself */
    }
}

/*
 * SSH2 key creation method.
 */
static void ssh2_mkkey(Ssh ssh, Bignum K, unsigned char *H,
		       unsigned char *sessid, char chr,
		       unsigned char *keyspace)
{
    SHA_State s;
    /* First 20 bytes. */
    SHA_Init(&s);
    if (!(ssh->remote_bugs & BUG_SSH2_DERIVEKEY))
	sha_mpint(&s, K);
    SHA_Bytes(&s, H, 20);

    debug(("Exchange hash is:\n"));
    dmemdump(s->exchange_hash, 20);
#endif

    s->hkey = ssh->hostkey->newkey(s->hostkeydata, s->hostkeylen);
    if (!s->hkey ||
	!ssh->hostkey->verifysig(s->hkey, s->sigdata, s->siglen,
				 (char *)s->exchange_hash, 20)) {
	bombout((ssh,"Server's host key did not match the signature supplied"));
	crReturn(0);
    }

    /*
     * Authenticate remote host: verify host key. (We've already
     * checked the signature of the exchange hash.)

			if (s->publickey_blob &&
			    s->pklen == s->publickey_bloblen &&
			    !memcmp(s->p, s->publickey_blob,
				    s->publickey_bloblen)) {
			    logevent("This key matches configured key file");
			    s->tried_pubkey_config = 1;
			}
			s->pkblob = (char *)s->p;
			s->p += s->pklen;
			s->alglen = GET_32BIT(s->pkblob);
			s->alg = s->pkblob + 4;
			s->commentlen = GET_32BIT(s->p);
			s->p += 4;
			s->commentp = (char *)s->p;
			s->p += s->commentlen;
			ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
			ssh2_pkt_addstring(ssh, s->username);
			ssh2_pkt_addstring(ssh, "ssh-connection");	/* service requested */
			ssh2_pkt_addstring(ssh, "publickey");	/* method */
			ssh2_pkt_addbool(ssh, FALSE);	/* no signature included */
			ssh2_pkt_addstring_start(ssh);

		/*
		 * Try the public key supplied in the configuration.
		 *
		 * First, offer the public blob to see if the server is
		 * willing to accept it.
		 */
		pub_blob =
		    (unsigned char *)ssh2_userkey_loadpub(cfg.keyfile,
							  &algorithm,
							  &pub_blob_len);
		if (pub_blob) {
		    ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
		    ssh2_pkt_addstring(ssh, s->username);
		    ssh2_pkt_addstring(ssh, "ssh-connection");	/* service requested */
		    ssh2_pkt_addstring(ssh, "publickey");	/* method */
		    ssh2_pkt_addbool(ssh, FALSE);	/* no signature included */
		    ssh2_pkt_addstring(ssh, algorithm);
		    ssh2_pkt_addstring_start(ssh);
		    ssh2_pkt_addstring_data(ssh, (char *)pub_blob,
					    pub_blob_len);
		    ssh2_pkt_send(ssh);
		    logevent("Offered public key");	/* FIXME */

		    crWaitUntilV(ispkt);
		    if (ssh->pktin.type != SSH2_MSG_USERAUTH_PK_OK) {
			s->gotit = TRUE;
			s->type = AUTH_TYPE_PUBLICKEY_OFFER_LOUD;

		    ssh2_pkt_addstring(ssh, s->username);
		    ssh2_pkt_addstring(ssh, "ssh-connection");	/* service requested */
		    ssh2_pkt_addstring(ssh, "publickey");	/* method */
		    ssh2_pkt_addbool(ssh, TRUE);
		    ssh2_pkt_addstring(ssh, key->alg->name);
		    pkblob = key->alg->public_blob(key->data, &pkblob_len);
		    ssh2_pkt_addstring_start(ssh);
		    ssh2_pkt_addstring_data(ssh, (char *)pkblob, pkblob_len);

		    /*
		     * The data to be signed is:
		     *
		     *   string  session-id
		     *
		     * followed by everything so far placed in the
		     * outgoing packet.
		     */
		    sigdata_len = ssh->pktout.length - 5 + 4 + 20;
		    sigdata = smalloc(sigdata_len);
		    PUT_32BIT(sigdata, 20);
		    memcpy(sigdata + 4, ssh->v2_session_id, 20);
		    memcpy(sigdata + 24, ssh->pktout.data + 5,
			   ssh->pktout.length - 5);
		    sigblob = key->alg->sign(key->data, (char *)sigdata,
					     sigdata_len, &sigblob_len);
		    ssh2_add_sigblob(ssh, pkblob, pkblob_len,
				     sigblob, sigblob_len);
		    sfree(pkblob);
		    sfree(sigblob);
		    sfree(sigdata);

		bombout((ssh,"Strange packet received: type %d", ssh->pktin.type));
		crReturnV;
	    }
	} else {
	    /*
	     * We have spare data. Add it to the channel buffer.
	     */
	    ssh2_add_channel_data(ssh->mainchan, (char *)in, inlen);
	    s->try_send = TRUE;
	}
	if (s->try_send) {
	    int i;
	    struct ssh_channel *c;
	    /*
	     * Try to send data on all channels if we can.

static int ssh_send(void *handle, char *buf, int len)
{
    Ssh ssh = (Ssh) handle;

    if (ssh == NULL || ssh->s == NULL || ssh->protocol == NULL)
	return 0;

    ssh->protocol(ssh, (unsigned char *)buf, len, 0);

    return ssh_sendbuffer(ssh);
}

/*
 * Called to query the current amount of buffered stdin data.
 */