kexgexc.c revision 113908
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" 27RCSID("$OpenBSD: kexgexc.c,v 1.1 2003/02/16 17:09:57 markus Exp $"); 28 29#include "xmalloc.h" 30#include "key.h" 31#include "kex.h" 32#include "log.h" 33#include "packet.h" 34#include "dh.h" 35#include "ssh2.h" 36#include "compat.h" 37 38void 39kexgex_client(Kex *kex) 40{ 41 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 42 BIGNUM *p = NULL, *g = NULL; 43 Key *server_host_key; 44 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 45 u_int klen, kout, slen, sbloblen; 46 int min, max, nbits; 47 DH *dh; 48 49 nbits = dh_estimate(kex->we_need * 8); 50 51 if (datafellows & SSH_OLD_DHGEX) { 52 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent"); 53 54 /* Old GEX request */ 55 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD); 56 packet_put_int(nbits); 57 min = DH_GRP_MIN; 58 max = DH_GRP_MAX; 59 } else { 60 debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent"); 61 62 /* New GEX request */ 63 min = DH_GRP_MIN; 64 max = DH_GRP_MAX; 65 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST); 66 packet_put_int(min); 67 packet_put_int(nbits); 68 packet_put_int(max); 69 } 70#ifdef DEBUG_KEXDH 71 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 72 min, nbits, max); 73#endif 74 packet_send(); 75 76 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP"); 77 packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP); 78 79 if ((p = BN_new()) == NULL) 80 fatal("BN_new"); 81 packet_get_bignum2(p); 82 if ((g = BN_new()) == NULL) 83 fatal("BN_new"); 84 packet_get_bignum2(g); 85 packet_check_eom(); 86 87 if (BN_num_bits(p) < min || BN_num_bits(p) > max) 88 fatal("DH_GEX group out of range: %d !< %d !< %d", 89 min, BN_num_bits(p), max); 90 91 dh = dh_new_group(g, p); 92 dh_gen_key(dh, kex->we_need * 8); 93 94#ifdef DEBUG_KEXDH 95 DHparams_print_fp(stderr, dh); 96 fprintf(stderr, "pub= "); 97 BN_print_fp(stderr, dh->pub_key); 98 fprintf(stderr, "\n"); 99#endif 100 101 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 102 /* generate and send 'e', client DH public key */ 103 packet_start(SSH2_MSG_KEX_DH_GEX_INIT); 104 packet_put_bignum2(dh->pub_key); 105 packet_send(); 106 107 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY"); 108 packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY); 109 110 /* key, cert */ 111 server_host_key_blob = packet_get_string(&sbloblen); 112 server_host_key = key_from_blob(server_host_key_blob, sbloblen); 113 if (server_host_key == NULL) 114 fatal("cannot decode server_host_key_blob"); 115 if (server_host_key->type != kex->hostkey_type) 116 fatal("type mismatch for decoded server_host_key_blob"); 117 if (kex->verify_host_key == NULL) 118 fatal("cannot verify server_host_key"); 119 if (kex->verify_host_key(server_host_key) == -1) 120 fatal("server_host_key verification failed"); 121 122 /* DH paramter f, server public DH key */ 123 if ((dh_server_pub = BN_new()) == NULL) 124 fatal("dh_server_pub == NULL"); 125 packet_get_bignum2(dh_server_pub); 126 127#ifdef DEBUG_KEXDH 128 fprintf(stderr, "dh_server_pub= "); 129 BN_print_fp(stderr, dh_server_pub); 130 fprintf(stderr, "\n"); 131 debug("bits %d", BN_num_bits(dh_server_pub)); 132#endif 133 134 /* signed H */ 135 signature = packet_get_string(&slen); 136 packet_check_eom(); 137 138 if (!dh_pub_is_valid(dh, dh_server_pub)) 139 packet_disconnect("bad server public DH value"); 140 141 klen = DH_size(dh); 142 kbuf = xmalloc(klen); 143 kout = DH_compute_key(kbuf, dh_server_pub, dh); 144#ifdef DEBUG_KEXDH 145 dump_digest("shared secret", kbuf, kout); 146#endif 147 if ((shared_secret = BN_new()) == NULL) 148 fatal("kexgex_client: BN_new failed"); 149 BN_bin2bn(kbuf, kout, shared_secret); 150 memset(kbuf, 0, klen); 151 xfree(kbuf); 152 153 if (datafellows & SSH_OLD_DHGEX) 154 min = max = -1; 155 156 /* calc and verify H */ 157 hash = kexgex_hash( 158 kex->client_version_string, 159 kex->server_version_string, 160 buffer_ptr(&kex->my), buffer_len(&kex->my), 161 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 162 server_host_key_blob, sbloblen, 163 min, nbits, max, 164 dh->p, dh->g, 165 dh->pub_key, 166 dh_server_pub, 167 shared_secret 168 ); 169 /* have keys, free DH */ 170 DH_free(dh); 171 xfree(server_host_key_blob); 172 BN_clear_free(dh_server_pub); 173 174 if (key_verify(server_host_key, signature, slen, hash, 20) != 1) 175 fatal("key_verify failed for server_host_key"); 176 key_free(server_host_key); 177 xfree(signature); 178 179 /* save session id */ 180 if (kex->session_id == NULL) { 181 kex->session_id_len = 20; 182 kex->session_id = xmalloc(kex->session_id_len); 183 memcpy(kex->session_id, hash, kex->session_id_len); 184 } 185 kex_derive_keys(kex, hash, shared_secret); 186 BN_clear_free(shared_secret); 187 188 kex_finish(kex); 189} 190