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      1 /*
      2  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
      3  *
      4  * Redistribution and use in source and binary forms, with or without
      5  * modification, are permitted provided that the following conditions
      6  * are met:
      7  * 1. Redistributions of source code must retain the above copyright
      8  *    notice, this list of conditions and the following disclaimer.
      9  * 2. Redistributions in binary form must reproduce the above copyright
     10  *    notice, this list of conditions and the following disclaimer in the
     11  *    documentation and/or other materials provided with the distribution.
     12  *
     13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     23  */
     24 
     25 #include "includes.h"
     26 RCSID("$OpenBSD: kexdh.c,v 1.18 2002/03/18 17:50:31 provos Exp $");
     27 
     28 #pragma ident	"%Z%%M%	%I%	%E% SMI"
     29 
     30 #include <openssl/crypto.h>
     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 
     43 void
     44 kexdh_client(Kex *kex)
     45 {
     46 	BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
     47 	DH *dh;
     48 	Key *server_host_key;
     49 	u_char *server_host_key_blob = NULL, *signature = NULL;
     50 	u_char *kbuf, *hash;
     51 	u_int klen, kout, slen, sbloblen;
     52 
     53 	/* generate and send 'e', client DH public key */
     54 	dh = dh_new_group1();
     55 	dh_gen_key(dh, kex->we_need * 8);
     56 	packet_start(SSH2_MSG_KEXDH_INIT);
     57 	packet_put_bignum2(dh->pub_key);
     58 	packet_send();
     59 
     60 	debug("sending SSH2_MSG_KEXDH_INIT");
     61 #ifdef DEBUG_KEXDH
     62 	DHparams_print_fp(stderr, dh);
     63 	fprintf(stderr, "pub= ");
     64 	BN_print_fp(stderr, dh->pub_key);
     65 	fprintf(stderr, "\n");
     66 #endif
     67 
     68 	debug("expecting SSH2_MSG_KEXDH_REPLY");
     69 	packet_read_expect(SSH2_MSG_KEXDH_REPLY);
     70 
     71 	/* key, cert */
     72 	server_host_key_blob = packet_get_string(&sbloblen);
     73 	server_host_key = key_from_blob(server_host_key_blob, sbloblen);
     74 	if (server_host_key == NULL)
     75 		fatal("cannot decode server_host_key_blob");
     76 	if (server_host_key->type != kex->hostkey_type)
     77 		fatal("type mismatch for decoded server_host_key_blob");
     78 	if (kex->verify_host_key == NULL)
     79 		fatal("cannot verify server_host_key");
     80 	if (kex->verify_host_key(server_host_key) == -1)
     81 		fatal("server_host_key verification failed");
     82 
     83 	/* DH paramter f, server public DH key */
     84 	if ((dh_server_pub = BN_new()) == NULL)
     85 		fatal("dh_server_pub == NULL");
     86 	packet_get_bignum2(dh_server_pub);
     87 
     88 #ifdef DEBUG_KEXDH
     89 	fprintf(stderr, "dh_server_pub= ");
     90 	BN_print_fp(stderr, dh_server_pub);
     91 	fprintf(stderr, "\n");
     92 	debug("bits %d", BN_num_bits(dh_server_pub));
     93 #endif
     94 
     95 	/* signed H */
     96 	signature = packet_get_string(&slen);
     97 	packet_check_eom();
     98 
     99 	if (!dh_pub_is_valid(dh, dh_server_pub))
    100 		packet_disconnect("bad server public DH value");
    101 
    102 	klen = DH_size(dh);
    103 	kbuf = xmalloc(klen);
    104 	kout = DH_compute_key(kbuf, dh_server_pub, dh);
    105 #ifdef DEBUG_KEXDH
    106 	dump_digest("shared secret", kbuf, kout);
    107 #endif
    108 	if ((shared_secret = BN_new()) == NULL)
    109 		fatal("kexdh_client: BN_new failed");
    110 	BN_bin2bn(kbuf, kout, shared_secret);
    111 	memset(kbuf, 0, klen);
    112 	xfree(kbuf);
    113 
    114 	/* calc and verify H */
    115 	hash = kex_dh_hash(
    116 	    kex->client_version_string,
    117 	    kex->server_version_string,
    118 	    buffer_ptr(&kex->my), buffer_len(&kex->my),
    119 	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
    120 	    server_host_key_blob, sbloblen,
    121 	    dh->pub_key,
    122 	    dh_server_pub,
    123 	    shared_secret
    124 	);
    125 	xfree(server_host_key_blob);
    126 	BN_clear_free(dh_server_pub);
    127 	DH_free(dh);
    128 
    129 	if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
    130 		fatal("key_verify failed for server_host_key");
    131 	key_free(server_host_key);
    132 	xfree(signature);
    133 
    134 	/* save session id */
    135 	if (kex->session_id == NULL) {
    136 		kex->session_id_len = 20;
    137 		kex->session_id = xmalloc(kex->session_id_len);
    138 		memcpy(kex->session_id, hash, kex->session_id_len);
    139 	}
    140 
    141 	kex_derive_keys(kex, hash, shared_secret);
    142 	BN_clear_free(shared_secret);
    143 	kex_finish(kex);
    144 }
    145