/* $OpenBSD: kexgexs.c,v 1.10 2006/11/06 21:25:28 markus Exp $ */

/*

* Copyright (c) 2000 Niels Provos. All rights reserved.

* Copyright (c) 2001 Markus Friedl. All rights reserved.

*

* Redistribution and use in source and binary forms, with or without

* modification, are permitted provided that the following conditions

* are met:

* 1. Redistributions of source code must retain the above copyright

* notice, this list of conditions and the following disclaimer.

* 2. Redistributions in binary form must reproduce the above copyright

* notice, this list of conditions and the following disclaimer in the

* documentation and/or other materials provided with the distribution.

*

* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

*/

#include "includes.h"

#include <sys/param.h>

#include <stdarg.h>

#include <stdio.h>

#include <string.h>

#include <signal.h>

#include "xmalloc.h"

#include "buffer.h"

#include "key.h"

#include "cipher.h"

#include "kex.h"

#include "log.h"

#include "packet.h"

#include "dh.h"

#include "ssh2.h"

#include "compat.h"

#ifdef GSSAPI

#include "ssh-gss.h"

#endif

#include "monitor_wrap.h"

#include "do_kex2_exchange.h"

extern common_info g_data;

void

kexgex_server(Kex *kex)

{

BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;

Key *server_host_key;

DH *dh;

u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;

u_int sbloblen, klen, slen, hashlen;

int min = -1, max = -1, nbits = -1, type, kout;

if (kex->load_host_key == NULL)

fatal("Cannot load hostkey");

server_host_key = kex->load_host_key(kex->hostkey_type);

if (server_host_key == NULL)

fatal("Unsupported hostkey type %d", kex->hostkey_type);

type = packet_read();

switch (type) {

case SSH2_MSG_KEX_DH_GEX_REQUEST:

printf("SSH2_MSG_KEX_DH_GEX_REQUEST received\r\n");

min = packet_get_int();

nbits = packet_get_int();

max = packet_get_int();

min = MAX(DH_GRP_MIN, min);

max = MIN(DH_GRP_MAX, max);

break;

case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:

debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");

nbits = packet_get_int();

min = DH_GRP_MIN;

max = DH_GRP_MAX;

/* unused for old GEX */

break;

default:

fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);

}

packet_check_eom();

if (max < min || nbits < min || max < nbits)

fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",

min, nbits, max);

/* Contact privileged parent */

dh = PRIVSEP(choose_dh(min, nbits, max));

if (dh == NULL)

packet_disconnect("Protocol error: no matching DH grp found");

printf("SSH2_MSG_KEX_DH_GEX_GROUP sent\r\n");

packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);

packet_put_bignum2(dh->p);

packet_put_bignum2(dh->g);

packet_send();

/* flush */

packet_write_wait();

/* Compute our exchange value in parallel with the client */

dh_gen_key(dh, kex->we_need * 8);

printf("expecting SSH2_MSG_KEX_DH_GEX_INIT\r\n");

packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);

/* key, cert */

if ((dh_client_pub = BN_new()) == NULL)

fatal("dh_client_pub == NULL");

packet_get_bignum2(dh_client_pub);

packet_check_eom();

#ifdef DEBUG_KEXDH

fprintf(stderr, "dh_client_pub= ");

BN_print_fp(stderr, dh_client_pub);

fprintf(stderr, "\n");

debug("bits %d", BN_num_bits(dh_client_pub));

#endif

#ifdef DEBUG_KEXDH

DHparams_print_fp(stderr, dh);

fprintf(stderr, "pub= ");

BN_print_fp(stderr, dh->pub_key);

fprintf(stderr, "\n");

#endif

if (!dh_pub_is_valid(dh, dh_client_pub))

packet_disconnect("bad client public DH value");

klen = DH_size(dh);

kbuf = xmalloc(klen);

if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)

fatal("DH_compute_key: failed");

#ifdef DEBUG_KEXDH

dump_digest("shared secret", kbuf, kout);

#endif

if ((shared_secret = BN_new()) == NULL)

fatal("kexgex_server: BN_new failed");

if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)

fatal("kexgex_server: BN_bin2bn failed");

memset(kbuf, 0, klen);

xfree(kbuf);

key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);

if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)

min = max = -1;

/* calc H */

kexgex_hash(

kex->evp_md,

kex->client_version_string,

kex->server_version_string,

buffer_ptr(&kex->peer), buffer_len(&kex->peer),

buffer_ptr(&kex->my), buffer_len(&kex->my),

server_host_key_blob, sbloblen,

min, nbits, max,

dh->p, dh->g,

dh_client_pub,

dh->pub_key,

shared_secret,

&hash, &hashlen

);

BN_clear_free(dh_client_pub);

/* save session id := H */

if (kex->session_id == NULL) {

kex->session_id_len = hashlen;

kex->session_id = xmalloc(kex->session_id_len);

memcpy(kex->session_id, hash, kex->session_id_len);

}

/* sign H */

PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));

/* destroy_sensitive_data(); */

/* send server hostkey, DH pubkey 'f' and singed H */

printf("SSH2_MSG_KEX_DH_GEX_REPLY sent\r\n");

packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);

packet_put_string(server_host_key_blob, sbloblen);

packet_put_bignum2(dh->pub_key); /* f */

packet_put_string(signature, slen);

packet_send();

xfree(signature);

xfree(server_host_key_blob);

/* have keys, free DH */

DH_free(dh);

kex_derive_keys(kex, hash, hashlen, shared_secret);

BN_clear_free(shared_secret);

kex_finish(kex);

}