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 #include "monitor_wrap.h" 44 45 void 46 kexgex_client(Kex *kex) 47 { 48 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 49 BIGNUM *p = NULL, *g = NULL; 50 Key *server_host_key; 51 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 52 u_int klen, kout, slen, sbloblen; 53 int min, max, nbits; 54 DH *dh; 55 56 nbits = dh_estimate(kex->we_need * 8); 57 58 if (datafellows & SSH_OLD_DHGEX) { 59 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent"); 60 61 /* Old GEX request */ 62 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD); 63 packet_put_int(nbits); 64 min = DH_GRP_MIN; 65 max = DH_GRP_MAX; 66 } else { 67 debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent"); 68 69 /* New GEX request */ 70 min = DH_GRP_MIN; 71 max = DH_GRP_MAX; 72 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST); 73 packet_put_int(min); 74 packet_put_int(nbits); 75 packet_put_int(max); 76 } 77 #ifdef DEBUG_KEXDH 78 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 79 min, nbits, max); 80 #endif 81 packet_send(); 82 83 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP"); 84 packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP); 85 86 if ((p = BN_new()) == NULL) 87 fatal("BN_new"); 88 packet_get_bignum2(p); 89 if ((g = BN_new()) == NULL) 90 fatal("BN_new"); 91 packet_get_bignum2(g); 92 packet_check_eom(); 93 94 if (BN_num_bits(p) < min || BN_num_bits(p) > max) 95 fatal("DH_GEX group out of range: %d !< %d !< %d", 96 min, BN_num_bits(p), max); 97 98 dh = dh_new_group(g, p); 99 dh_gen_key(dh, kex->we_need * 8); 100 101 #ifdef DEBUG_KEXDH 102 DHparams_print_fp(stderr, dh); 103 fprintf(stderr, "pub= "); 104 BN_print_fp(stderr, dh->pub_key); 105 fprintf(stderr, "\n"); 106 #endif 107 108 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 109 /* generate and send 'e', client DH public key */ 110 packet_start(SSH2_MSG_KEX_DH_GEX_INIT); 111 packet_put_bignum2(dh->pub_key); 112 packet_send(); 113 114 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY"); 115 packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY); 116 117 /* key, cert */ 118 server_host_key_blob = packet_get_string(&sbloblen); 119 server_host_key = key_from_blob(server_host_key_blob, sbloblen); 120 if (server_host_key == NULL) 121 fatal("cannot decode server_host_key_blob"); 122 if (server_host_key->type != kex->hostkey_type) 123 fatal("type mismatch for decoded server_host_key_blob"); 124 if (kex->verify_host_key == NULL) 125 fatal("cannot verify server_host_key"); 126 if (kex->verify_host_key(server_host_key) == -1) 127 fatal("server_host_key verification failed"); 128 129 /* DH paramter f, server public DH key */ 130 if ((dh_server_pub = BN_new()) == NULL) 131 fatal("dh_server_pub == NULL"); 132 packet_get_bignum2(dh_server_pub); 133 134 #ifdef DEBUG_KEXDH 135 fprintf(stderr, "dh_server_pub= "); 136 BN_print_fp(stderr, dh_server_pub); 137 fprintf(stderr, "\n"); 138 debug("bits %d", BN_num_bits(dh_server_pub)); 139 #endif 140 141 /* signed H */ 142 signature = packet_get_string(&slen); 143 packet_check_eom(); 144 145 if (!dh_pub_is_valid(dh, dh_server_pub)) 146 packet_disconnect("bad server public DH value"); 147 148 klen = DH_size(dh); 149 kbuf = xmalloc(klen); 150 kout = DH_compute_key(kbuf, dh_server_pub, dh); 151 #ifdef DEBUG_KEXDH 152 dump_digest("shared secret", kbuf, kout); 153 #endif 154 if ((shared_secret = BN_new()) == NULL) 155 fatal("kexgex_client: BN_new failed"); 156 BN_bin2bn(kbuf, kout, shared_secret); 157 memset(kbuf, 0, klen); 158 xfree(kbuf); 159 160 if (datafellows & SSH_OLD_DHGEX) 161 min = max = -1; 162 163 /* calc and verify H */ 164 hash = kexgex_hash( 165 kex->client_version_string, 166 kex->server_version_string, 167 buffer_ptr(&kex->my), buffer_len(&kex->my), 168 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 169 server_host_key_blob, sbloblen, 170 min, nbits, max, 171 dh->p, dh->g, 172 dh->pub_key, 173 dh_server_pub, 174 shared_secret 175 ); 176 /* have keys, free DH */ 177 DH_free(dh); 178 xfree(server_host_key_blob); 179 BN_clear_free(dh_server_pub); 180 181 if (key_verify(server_host_key, signature, slen, hash, 20) != 1) 182 fatal("key_verify failed for server_host_key"); 183 key_free(server_host_key); 184 xfree(signature); 185 186 /* save session id */ 187 if (kex->session_id == NULL) { 188 kex->session_id_len = 20; 189 kex->session_id = xmalloc(kex->session_id_len); 190 memcpy(kex->session_id, hash, kex->session_id_len); 191 } 192 kex_derive_keys(kex, hash, shared_secret); 193 BN_clear_free(shared_secret); 194 195 kex_finish(kex); 196 } 197