text: /* $OpenBSD: kexgexc.c,v 1.17 2014/02/02 03:44:31 djm 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/types.h>
  
  #include <openssl/dh.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"
  
  void
  kexgex_client(Kex *kex)
  {
  	BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
  	BIGNUM *p = NULL, *g = NULL;
  	Key *server_host_key;
  	u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  	u_int klen, slen, sbloblen, hashlen;
  	int kout;
  	int min, max, nbits;
  	DH *dh;
  
  	nbits = dh_estimate(kex->dh_need * 8);
  
  	if (datafellows & SSH_OLD_DHGEX) {
  		/* Old GEX request */
  		packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
  		packet_put_int(nbits);
  		min = DH_GRP_MIN;
  		max = DH_GRP_MAX;
  
  		debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", nbits);
  	} else {
  		/* New GEX request */
  		min = DH_GRP_MIN;
  		max = DH_GRP_MAX;
  		packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
  		packet_put_int(min);
  		packet_put_int(nbits);
  		packet_put_int(max);
  
  		debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
  		    min, nbits, max);
  	}
  #ifdef DEBUG_KEXDH
  	fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
  	    min, nbits, max);
  #endif
  	packet_send();
  
  	debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
  	packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
  
  	if ((p = BN_new()) == NULL)
  		fatal("BN_new");
  	packet_get_bignum2(p);
  	if ((g = BN_new()) == NULL)
  		fatal("BN_new");
  	packet_get_bignum2(g);
  	packet_check_eom();
  
  	if (BN_num_bits(p) < min || BN_num_bits(p) > max)
  		fatal("DH_GEX group out of range: %d !< %d !< %d",
  		    min, BN_num_bits(p), max);
  
  	dh = dh_new_group(g, p);
  	dh_gen_key(dh, kex->we_need * 8);
  
  #ifdef DEBUG_KEXDH
  	DHparams_print_fp(stderr, dh);
  	fprintf(stderr, "pub= ");
  	BN_print_fp(stderr, dh->pub_key);
  	fprintf(stderr, "\n");
  #endif
  
  	debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
  	/* generate and send 'e', client DH public key */
  	packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
  	packet_put_bignum2(dh->pub_key);
  	packet_send();
  
  	debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
  	packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
  
  	/* key, cert */
  	server_host_key_blob = packet_get_string(&sbloblen);
  	server_host_key = key_from_blob(server_host_key_blob, sbloblen);
  	if (server_host_key == NULL)
  		fatal("cannot decode server_host_key_blob");
  	if (server_host_key->type != kex->hostkey_type)
  		fatal("type mismatch for decoded server_host_key_blob");
  	if (kex->verify_host_key == NULL)
  		fatal("cannot verify server_host_key");
  	if (kex->verify_host_key(server_host_key) == -1)
  		fatal("server_host_key verification failed");
  
  	/* DH parameter f, server public DH key */
  	if ((dh_server_pub = BN_new()) == NULL)
  		fatal("dh_server_pub == NULL");
  	packet_get_bignum2(dh_server_pub);
  
  #ifdef DEBUG_KEXDH
  	fprintf(stderr, "dh_server_pub= ");
  	BN_print_fp(stderr, dh_server_pub);
  	fprintf(stderr, "\n");
  	debug("bits %d", BN_num_bits(dh_server_pub));
  #endif
  
  	/* signed H */
  	signature = packet_get_string(&slen);
  	packet_check_eom();
  
  	if (!dh_pub_is_valid(dh, dh_server_pub))
  		packet_disconnect("bad server public DH value");
  
  	klen = DH_size(dh);
  	kbuf = xmalloc(klen);
  	if ((kout = DH_compute_key(kbuf, dh_server_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_client: BN_new failed");
  	if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
  		fatal("kexgex_client: BN_bin2bn failed");
  	explicit_bzero(kbuf, klen);
  	free(kbuf);
  
  	if (datafellows & SSH_OLD_DHGEX)
  		min = max = -1;
  
  	/* calc and verify H */
  	kexgex_hash(
  	    kex->hash_alg,
  	    kex->client_version_string,
  	    kex->server_version_string,
  	    buffer_ptr(&kex->my), buffer_len(&kex->my),
  	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
  	    server_host_key_blob, sbloblen,
  	    min, nbits, max,
  	    dh->p, dh->g,
  	    dh->pub_key,
  	    dh_server_pub,
  	    shared_secret,
  	    &hash, &hashlen
  	);
  
  	/* have keys, free DH */
  	DH_free(dh);
  	free(server_host_key_blob);
  	BN_clear_free(dh_server_pub);
  
  	if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
  		fatal("key_verify failed for server_host_key");
  	key_free(server_host_key);
  	free(signature);
  
  	/* save session id */
  	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);
  	}
  	kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
  	BN_clear_free(shared_secret);
  
  	kex_finish(kex);
  }
  