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_server(Kex *kex) 46 { 47 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 48 Key *server_host_key; 49 DH *dh; 50 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 51 u_int sbloblen, klen, kout, slen; 52 int min = -1, max = -1, nbits = -1, type; 53 54 if (kex->load_host_key == NULL) 55 fatal("Cannot load hostkey"); 56 server_host_key = kex->load_host_key(kex->hostkey_type); 57 if (server_host_key == NULL) 58 fatal("Unsupported hostkey type %d", kex->hostkey_type); 59 60 type = packet_read(); 61 switch (type) { 62 case SSH2_MSG_KEX_DH_GEX_REQUEST: 63 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 64 min = packet_get_int(); 65 nbits = packet_get_int(); 66 max = packet_get_int(); 67 min = MAX(DH_GRP_MIN, min); 68 max = MIN(DH_GRP_MAX, max); 69 break; 70 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 71 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 72 nbits = packet_get_int(); 73 min = DH_GRP_MIN; 74 max = DH_GRP_MAX; 75 /* unused for old GEX */ 76 break; 77 default: 78 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 79 } 80 packet_check_eom(); 81 82 if (max < min || nbits < min || max < nbits) 83 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 84 min, nbits, max); 85 86 /* Contact privileged parent */ 87 dh = choose_dh(min, nbits, max); 88 if (dh == NULL) 89 packet_disconnect("Protocol error: no matching DH grp found"); 90 91 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 92 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 93 packet_put_bignum2(dh->p); 94 packet_put_bignum2(dh->g); 95 packet_send(); 96 97 /* flush */ 98 packet_write_wait(); 99 100 /* Compute our exchange value in parallel with the client */ 101 dh_gen_key(dh, kex->we_need * 8); 102 103 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 104 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 105 106 /* key, cert */ 107 if ((dh_client_pub = BN_new()) == NULL) 108 fatal("dh_client_pub == NULL"); 109 packet_get_bignum2(dh_client_pub); 110 packet_check_eom(); 111 112 #ifdef DEBUG_KEXDH 113 fprintf(stderr, "dh_client_pub= "); 114 BN_print_fp(stderr, dh_client_pub); 115 fprintf(stderr, "\n"); 116 debug("bits %d", BN_num_bits(dh_client_pub)); 117 #endif 118 119 #ifdef DEBUG_KEXDH 120 DHparams_print_fp(stderr, dh); 121 fprintf(stderr, "pub= "); 122 BN_print_fp(stderr, dh->pub_key); 123 fprintf(stderr, "\n"); 124 #endif 125 if (!dh_pub_is_valid(dh, dh_client_pub)) 126 packet_disconnect("bad client public DH value"); 127 128 klen = DH_size(dh); 129 kbuf = xmalloc(klen); 130 kout = DH_compute_key(kbuf, dh_client_pub, dh); 131 #ifdef DEBUG_KEXDH 132 dump_digest("shared secret", kbuf, kout); 133 #endif 134 if ((shared_secret = BN_new()) == NULL) 135 fatal("kexgex_server: BN_new failed"); 136 BN_bin2bn(kbuf, kout, shared_secret); 137 memset(kbuf, 0, klen); 138 xfree(kbuf); 139 140 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 141 142 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 143 min = max = -1; 144 145 /* calc H */ /* XXX depends on 'kex' */ 146 hash = kexgex_hash( 147 kex->client_version_string, 148 kex->server_version_string, 149 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 150 buffer_ptr(&kex->my), buffer_len(&kex->my), 151 server_host_key_blob, sbloblen, 152 min, nbits, max, 153 dh->p, dh->g, 154 dh_client_pub, 155 dh->pub_key, 156 shared_secret 157 ); 158 BN_clear_free(dh_client_pub); 159 160 /* save session id := H */ 161 /* XXX hashlen depends on KEX */ 162 if (kex->session_id == NULL) { 163 kex->session_id_len = 20; 164 kex->session_id = xmalloc(kex->session_id_len); 165 memcpy(kex->session_id, hash, kex->session_id_len); 166 } 167 168 /* sign H */ 169 /* XXX hashlen depends on KEX */ 170 key_sign(server_host_key, &signature, &slen, hash, 20); 171 172 /* destroy_sensitive_data(); */ 173 174 /* send server hostkey, DH pubkey 'f' and singed H */ 175 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 176 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 177 packet_put_string(server_host_key_blob, sbloblen); 178 packet_put_bignum2(dh->pub_key); /* f */ 179 packet_put_string(signature, slen); 180 packet_send(); 181 182 xfree(signature); 183 xfree(server_host_key_blob); 184 /* have keys, free DH */ 185 DH_free(dh); 186 187 kex_derive_keys(kex, hash, shared_secret); 188 BN_clear_free(shared_secret); 189 190 kex_finish(kex); 191 } 192