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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_server(Kex *kex)
     46 {
     47 	BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
     48 	Key *server_host_key;
     49 	DH *dh;
     50 	u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
     51 	u_int sbloblen, klen, kout, slen;
     52 	int min = -1, max = -1, nbits = -1, type;
     53 
     54 	if (kex->load_host_key == NULL)
     55 		fatal("Cannot load hostkey");
     56 	server_host_key = kex->load_host_key(kex->hostkey_type);
     57 	if (server_host_key == NULL)
     58 		fatal("Unsupported hostkey type %d", kex->hostkey_type);
     59 
     60 	type = packet_read();
     61 	switch (type) {
     62 	case SSH2_MSG_KEX_DH_GEX_REQUEST:
     63 		debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
     64 		min = packet_get_int();
     65 		nbits = packet_get_int();
     66 		max = packet_get_int();
     67 		min = MAX(DH_GRP_MIN, min);
     68 		max = MIN(DH_GRP_MAX, max);
     69 		break;
     70 	case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
     71 		debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
     72 		nbits = packet_get_int();
     73 		min = DH_GRP_MIN;
     74 		max = DH_GRP_MAX;
     75 		/* unused for old GEX */
     76 		break;
     77 	default:
     78 		fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
     79 	}
     80 	packet_check_eom();
     81 
     82 	if (max < min || nbits < min || max < nbits)
     83 		fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
     84 		    min, nbits, max);
     85 
     86 	/* Contact privileged parent */
     87 	dh = choose_dh(min, nbits, max);
     88 	if (dh == NULL)
     89 		packet_disconnect("Protocol error: no matching DH grp found");
     90 
     91 	debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
     92 	packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
     93 	packet_put_bignum2(dh->p);
     94 	packet_put_bignum2(dh->g);
     95 	packet_send();
     96 
     97 	/* flush */
     98 	packet_write_wait();
     99 
    100 	/* Compute our exchange value in parallel with the client */
    101 	dh_gen_key(dh, kex->we_need * 8);
    102 
    103 	debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
    104 	packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
    105 
    106 	/* key, cert */
    107 	if ((dh_client_pub = BN_new()) == NULL)
    108 		fatal("dh_client_pub == NULL");
    109 	packet_get_bignum2(dh_client_pub);
    110 	packet_check_eom();
    111 
    112 #ifdef DEBUG_KEXDH
    113 	fprintf(stderr, "dh_client_pub= ");
    114 	BN_print_fp(stderr, dh_client_pub);
    115 	fprintf(stderr, "\n");
    116 	debug("bits %d", BN_num_bits(dh_client_pub));
    117 #endif
    118 
    119 #ifdef DEBUG_KEXDH
    120 	DHparams_print_fp(stderr, dh);
    121 	fprintf(stderr, "pub= ");
    122 	BN_print_fp(stderr, dh->pub_key);
    123 	fprintf(stderr, "\n");
    124 #endif
    125 	if (!dh_pub_is_valid(dh, dh_client_pub))
    126 		packet_disconnect("bad client public DH value");
    127 
    128 	klen = DH_size(dh);
    129 	kbuf = xmalloc(klen);
    130 	kout = DH_compute_key(kbuf, dh_client_pub, dh);
    131 #ifdef DEBUG_KEXDH
    132 	dump_digest("shared secret", kbuf, kout);
    133 #endif
    134 	if ((shared_secret = BN_new()) == NULL)
    135 		fatal("kexgex_server: BN_new failed");
    136 	BN_bin2bn(kbuf, kout, shared_secret);
    137 	memset(kbuf, 0, klen);
    138 	xfree(kbuf);
    139 
    140 	key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
    141 
    142 	if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
    143 		min = max = -1;
    144 
    145 	/* calc H */			/* XXX depends on 'kex' */
    146 	hash = kexgex_hash(
    147 	    kex->client_version_string,
    148 	    kex->server_version_string,
    149 	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
    150 	    buffer_ptr(&kex->my), buffer_len(&kex->my),
    151 	    server_host_key_blob, sbloblen,
    152 	    min, nbits, max,
    153 	    dh->p, dh->g,
    154 	    dh_client_pub,
    155 	    dh->pub_key,
    156 	    shared_secret
    157 	);
    158 	BN_clear_free(dh_client_pub);
    159 
    160 	/* save session id := H */
    161 	/* XXX hashlen depends on KEX */
    162 	if (kex->session_id == NULL) {
    163 		kex->session_id_len = 20;
    164 		kex->session_id = xmalloc(kex->session_id_len);
    165 		memcpy(kex->session_id, hash, kex->session_id_len);
    166 	}
    167 
    168 	/* sign H */
    169 	/* XXX hashlen depends on KEX */
    170 	key_sign(server_host_key, &signature, &slen, hash, 20);
    171 
    172 	/* destroy_sensitive_data(); */
    173 
    174 	/* send server hostkey, DH pubkey 'f' and singed H */
    175 	debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
    176 	packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
    177 	packet_put_string(server_host_key_blob, sbloblen);
    178 	packet_put_bignum2(dh->pub_key);	/* f */
    179 	packet_put_string(signature, slen);
    180 	packet_send();
    181 
    182 	xfree(signature);
    183 	xfree(server_host_key_blob);
    184 	/* have keys, free DH */
    185 	DH_free(dh);
    186 
    187 	kex_derive_keys(kex, hash, shared_secret);
    188 	BN_clear_free(shared_secret);
    189 
    190 	kex_finish(kex);
    191 }
    192