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      1 /*
      2  * Copyright (c) 2000 Niels Provos.  All rights reserved.
      3  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions
      7  * are met:
      8  * 1. Redistributions of source code must retain the above copyright
      9  *    notice, this list of conditions and the following disclaimer.
     10  * 2. Redistributions in binary form must reproduce the above copyright
     11  *    notice, this list of conditions and the following disclaimer in the
     12  *    documentation and/or other materials provided with the distribution.
     13  *
     14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     17  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     24  */
     25 
     26 #include "includes.h"
     27 RCSID("$OpenBSD: kexgex.c,v 1.22 2002/03/24 17:27:03 stevesk Exp $");
     28 
     29 #pragma ident	"%Z%%M%	%I%	%E% SMI"
     30 
     31 #include <openssl/bn.h>
     32 
     33 #include "xmalloc.h"
     34 #include "buffer.h"
     35 #include "bufaux.h"
     36 #include "key.h"
     37 #include "kex.h"
     38 #include "log.h"
     39 #include "packet.h"
     40 #include "dh.h"
     41 #include "ssh2.h"
     42 #include "compat.h"
     43 
     44 void
     45 kexgex_client(Kex *kex)
     46 {
     47 	BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
     48 	BIGNUM *p = NULL, *g = NULL;
     49 	Key *server_host_key;
     50 	u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
     51 	u_int klen, kout, slen, sbloblen;
     52 	int min, max, nbits;
     53 	DH *dh;
     54 
     55 	nbits = dh_estimate(kex->we_need * 8);
     56 
     57 	if (datafellows & SSH_OLD_DHGEX) {
     58 		debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent");
     59 
     60 		/* Old GEX request */
     61 		packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
     62 		packet_put_int(nbits);
     63 		min = DH_GRP_MIN;
     64 		max = DH_GRP_MAX;
     65 	} else {
     66 		debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent");
     67 
     68 		/* New GEX request */
     69 		min = DH_GRP_MIN;
     70 		max = DH_GRP_MAX;
     71 		packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
     72 		packet_put_int(min);
     73 		packet_put_int(nbits);
     74 		packet_put_int(max);
     75 	}
     76 #ifdef DEBUG_KEXDH
     77 	fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
     78 	    min, nbits, max);
     79 #endif
     80 	packet_send();
     81 
     82 	debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
     83 	packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
     84 
     85 	if ((p = BN_new()) == NULL)
     86 		fatal("BN_new");
     87 	packet_get_bignum2(p);
     88 	if ((g = BN_new()) == NULL)
     89 		fatal("BN_new");
     90 	packet_get_bignum2(g);
     91 	packet_check_eom();
     92 
     93 	if (BN_num_bits(p) < min || BN_num_bits(p) > max)
     94 		fatal("DH_GEX group out of range: %d !< %d !< %d",
     95 		    min, BN_num_bits(p), max);
     96 
     97 	dh = dh_new_group(g, p);
     98 	dh_gen_key(dh, kex->we_need * 8);
     99 
    100 #ifdef DEBUG_KEXDH
    101 	DHparams_print_fp(stderr, dh);
    102 	fprintf(stderr, "pub= ");
    103 	BN_print_fp(stderr, dh->pub_key);
    104 	fprintf(stderr, "\n");
    105 #endif
    106 
    107 	debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
    108 	/* generate and send 'e', client DH public key */
    109 	packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
    110 	packet_put_bignum2(dh->pub_key);
    111 	packet_send();
    112 
    113 	debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
    114 	packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
    115 
    116 	/* key, cert */
    117 	server_host_key_blob = packet_get_string(&sbloblen);
    118 	server_host_key = key_from_blob(server_host_key_blob, sbloblen);
    119 	if (server_host_key == NULL)
    120 		fatal("cannot decode server_host_key_blob");
    121 	if (server_host_key->type != kex->hostkey_type)
    122 		fatal("type mismatch for decoded server_host_key_blob");
    123 	if (kex->verify_host_key == NULL)
    124 		fatal("cannot verify server_host_key");
    125 	if (kex->verify_host_key(server_host_key) == -1)
    126 		fatal("server_host_key verification failed");
    127 
    128 	/* DH paramter f, server public DH key */
    129 	if ((dh_server_pub = BN_new()) == NULL)
    130 		fatal("dh_server_pub == NULL");
    131 	packet_get_bignum2(dh_server_pub);
    132 
    133 #ifdef DEBUG_KEXDH
    134 	fprintf(stderr, "dh_server_pub= ");
    135 	BN_print_fp(stderr, dh_server_pub);
    136 	fprintf(stderr, "\n");
    137 	debug("bits %d", BN_num_bits(dh_server_pub));
    138 #endif
    139 
    140 	/* signed H */
    141 	signature = packet_get_string(&slen);
    142 	packet_check_eom();
    143 
    144 	if (!dh_pub_is_valid(dh, dh_server_pub))
    145 		packet_disconnect("bad server public DH value");
    146 
    147 	klen = DH_size(dh);
    148 	kbuf = xmalloc(klen);
    149 	kout = DH_compute_key(kbuf, dh_server_pub, dh);
    150 #ifdef DEBUG_KEXDH
    151 	dump_digest("shared secret", kbuf, kout);
    152 #endif
    153 	if ((shared_secret = BN_new()) == NULL)
    154 		fatal("kexgex_client: BN_new failed");
    155 	BN_bin2bn(kbuf, kout, shared_secret);
    156 	memset(kbuf, 0, klen);
    157 	xfree(kbuf);
    158 
    159 	if (datafellows & SSH_OLD_DHGEX)
    160 		min = max = -1;
    161 
    162 	/* calc and verify H */
    163 	hash = kexgex_hash(
    164 	    kex->client_version_string,
    165 	    kex->server_version_string,
    166 	    buffer_ptr(&kex->my), buffer_len(&kex->my),
    167 	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
    168 	    server_host_key_blob, sbloblen,
    169 	    min, nbits, max,
    170 	    dh->p, dh->g,
    171 	    dh->pub_key,
    172 	    dh_server_pub,
    173 	    shared_secret
    174 	);
    175 	/* have keys, free DH */
    176 	DH_free(dh);
    177 	xfree(server_host_key_blob);
    178 	BN_clear_free(dh_server_pub);
    179 
    180 	if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
    181 		fatal("key_verify failed for server_host_key");
    182 	key_free(server_host_key);
    183 	xfree(signature);
    184 
    185 	/* save session id */
    186 	if (kex->session_id == NULL) {
    187 		kex->session_id_len = 20;
    188 		kex->session_id = xmalloc(kex->session_id_len);
    189 		memcpy(kex->session_id, hash, kex->session_id_len);
    190 	}
    191 	kex_derive_keys(kex, hash, shared_secret);
    192 	BN_clear_free(shared_secret);
    193 
    194 	kex_finish(kex);
    195 }
    196