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      1 /* $OpenBSD: kexdhs.c,v 1.12 2010/11/10 01:33:07 djm Exp $ */
      2 /*
      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 
     28 #include <sys/types.h>
     29 
     30 #include <stdarg.h>
     31 #include <string.h>
     32 #include <signal.h>
     33 
     34 #include <openssl/dh.h>
     35 
     36 #include "xmalloc.h"
     37 #include "buffer.h"
     38 #include "key.h"
     39 #include "cipher.h"
     40 #include "kex.h"
     41 #include "log.h"
     42 #include "packet.h"
     43 #include "dh.h"
     44 #include "ssh2.h"
     45 #ifdef GSSAPI
     46 #include "ssh-gss.h"
     47 #endif
     48 #include "monitor_wrap.h"
     49 
     50 void
     51 kexdh_server(Kex *kex)
     52 {
     53 	BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
     54 	DH *dh;
     55 	Key *server_host_public, *server_host_private;
     56 	u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
     57 	u_int sbloblen, klen, hashlen, slen;
     58 	int kout;
     59 
     60 	/* generate server DH public key */
     61 	switch (kex->kex_type) {
     62 	case KEX_DH_GRP1_SHA1:
     63 		dh = dh_new_group1();
     64 		break;
     65 	case KEX_DH_GRP14_SHA1:
     66 		dh = dh_new_group14();
     67 		break;
     68 	default:
     69 		fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
     70 	}
     71 	dh_gen_key(dh, kex->we_need * 8);
     72 
     73 	debug("expecting SSH2_MSG_KEXDH_INIT");
     74 	packet_read_expect(SSH2_MSG_KEXDH_INIT);
     75 
     76 	if (kex->load_host_public_key == NULL ||
     77 	    kex->load_host_private_key == NULL)
     78 		fatal("Cannot load hostkey");
     79 	server_host_public = kex->load_host_public_key(kex->hostkey_type);
     80 	if (server_host_public == NULL)
     81 		fatal("Unsupported hostkey type %d", kex->hostkey_type);
     82 	server_host_private = kex->load_host_private_key(kex->hostkey_type);
     83 	if (server_host_private == NULL)
     84 		fatal("Missing private key for hostkey type %d",
     85 		    kex->hostkey_type);
     86 
     87 	/* key, cert */
     88 	if ((dh_client_pub = BN_new()) == NULL)
     89 		fatal("dh_client_pub == NULL");
     90 	packet_get_bignum2(dh_client_pub);
     91 	packet_check_eom();
     92 
     93 #ifdef DEBUG_KEXDH
     94 	fprintf(stderr, "dh_client_pub= ");
     95 	BN_print_fp(stderr, dh_client_pub);
     96 	fprintf(stderr, "\n");
     97 	debug("bits %d", BN_num_bits(dh_client_pub));
     98 #endif
     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 	if (!dh_pub_is_valid(dh, dh_client_pub))
    107 		packet_disconnect("bad client public DH value");
    108 
    109 	klen = DH_size(dh);
    110 	kbuf = xmalloc(klen);
    111 	if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
    112 		fatal("DH_compute_key: failed");
    113 #ifdef DEBUG_KEXDH
    114 	dump_digest("shared secret", kbuf, kout);
    115 #endif
    116 	if ((shared_secret = BN_new()) == NULL)
    117 		fatal("kexdh_server: BN_new failed");
    118 	if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
    119 		fatal("kexdh_server: BN_bin2bn failed");
    120 	memset(kbuf, 0, klen);
    121 	xfree(kbuf);
    122 
    123 	key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
    124 
    125 	/* calc H */
    126 	kex_dh_hash(
    127 	    kex->client_version_string,
    128 	    kex->server_version_string,
    129 	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
    130 	    buffer_ptr(&kex->my), buffer_len(&kex->my),
    131 	    server_host_key_blob, sbloblen,
    132 	    dh_client_pub,
    133 	    dh->pub_key,
    134 	    shared_secret,
    135 	    &hash, &hashlen
    136 	);
    137 	BN_clear_free(dh_client_pub);
    138 
    139 	/* save session id := H */
    140 	if (kex->session_id == NULL) {
    141 		kex->session_id_len = hashlen;
    142 		kex->session_id = xmalloc(kex->session_id_len);
    143 		memcpy(kex->session_id, hash, kex->session_id_len);
    144 	}
    145 
    146 	/* sign H */
    147 	if (PRIVSEP(key_sign(server_host_private, &signature, &slen, hash,
    148 	    hashlen)) < 0)
    149 		fatal("kexdh_server: key_sign failed");
    150 
    151 	/* destroy_sensitive_data(); */
    152 
    153 	/* send server hostkey, DH pubkey 'f' and singed H */
    154 	packet_start(SSH2_MSG_KEXDH_REPLY);
    155 	packet_put_string(server_host_key_blob, sbloblen);
    156 	packet_put_bignum2(dh->pub_key);	/* f */
    157 	packet_put_string(signature, slen);
    158 	packet_send();
    159 
    160 	xfree(signature);
    161 	xfree(server_host_key_blob);
    162 	/* have keys, free DH */
    163 	DH_free(dh);
    164 
    165 	kex_derive_keys(kex, hash, hashlen, shared_secret);
    166 	BN_clear_free(shared_secret);
    167 	kex_finish(kex);
    168 }
    169