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