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_server(Kex *kex) 47 { 48 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 49 Key *server_host_key; 50 DH *dh; 51 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 52 u_int sbloblen, klen, kout, slen; 53 int min = -1, max = -1, nbits = -1, type; 54 55 if (kex->load_host_key == NULL) 56 fatal("Cannot load hostkey"); 57 server_host_key = kex->load_host_key(kex->hostkey_type); 58 if (server_host_key == NULL) 59 fatal("Unsupported hostkey type %d", kex->hostkey_type); 60 61 type = packet_read(); 62 switch (type) { 63 case SSH2_MSG_KEX_DH_GEX_REQUEST: 64 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 65 min = packet_get_int(); 66 nbits = packet_get_int(); 67 max = packet_get_int(); 68 min = MAX(DH_GRP_MIN, min); 69 max = MIN(DH_GRP_MAX, max); 70 break; 71 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 72 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 73 nbits = packet_get_int(); 74 min = DH_GRP_MIN; 75 max = DH_GRP_MAX; 76 /* unused for old GEX */ 77 break; 78 default: 79 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 80 } 81 packet_check_eom(); 82 83 if (max < min || nbits < min || max < nbits) 84 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 85 min, nbits, max); 86 87 /* Contact privileged parent */ 88 dh = PRIVSEP(choose_dh(min, nbits, max)); 89 if (dh == NULL) 90 packet_disconnect("Protocol error: no matching DH grp found"); 91 92 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 93 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 94 packet_put_bignum2(dh->p); 95 packet_put_bignum2(dh->g); 96 packet_send(); 97 98 /* flush */ 99 packet_write_wait(); 100 101 /* Compute our exchange value in parallel with the client */ 102 dh_gen_key(dh, kex->we_need * 8); 103 104 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 105 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 106 107 /* key, cert */ 108 if ((dh_client_pub = BN_new()) == NULL) 109 fatal("dh_client_pub == NULL"); 110 packet_get_bignum2(dh_client_pub); 111 packet_check_eom(); 112 113 #ifdef DEBUG_KEXDH 114 fprintf(stderr, "dh_client_pub= "); 115 BN_print_fp(stderr, dh_client_pub); 116 fprintf(stderr, "\n"); 117 debug("bits %d", BN_num_bits(dh_client_pub)); 118 #endif 119 120 #ifdef DEBUG_KEXDH 121 DHparams_print_fp(stderr, dh); 122 fprintf(stderr, "pub= "); 123 BN_print_fp(stderr, dh->pub_key); 124 fprintf(stderr, "\n"); 125 #endif 126 if (!dh_pub_is_valid(dh, dh_client_pub)) 127 packet_disconnect("bad client public DH value"); 128 129 klen = DH_size(dh); 130 kbuf = xmalloc(klen); 131 kout = DH_compute_key(kbuf, dh_client_pub, dh); 132 #ifdef DEBUG_KEXDH 133 dump_digest("shared secret", kbuf, kout); 134 #endif 135 if ((shared_secret = BN_new()) == NULL) 136 fatal("kexgex_server: BN_new failed"); 137 BN_bin2bn(kbuf, kout, shared_secret); 138 memset(kbuf, 0, klen); 139 xfree(kbuf); 140 141 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 142 143 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 144 min = max = -1; 145 146 /* calc H */ /* XXX depends on 'kex' */ 147 hash = kexgex_hash( 148 kex->client_version_string, 149 kex->server_version_string, 150 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 151 buffer_ptr(&kex->my), buffer_len(&kex->my), 152 server_host_key_blob, sbloblen, 153 min, nbits, max, 154 dh->p, dh->g, 155 dh_client_pub, 156 dh->pub_key, 157 shared_secret 158 ); 159 BN_clear_free(dh_client_pub); 160 161 /* save session id := H */ 162 /* XXX hashlen depends on KEX */ 163 if (kex->session_id == NULL) { 164 kex->session_id_len = 20; 165 kex->session_id = xmalloc(kex->session_id_len); 166 memcpy(kex->session_id, hash, kex->session_id_len); 167 } 168 169 /* sign H */ 170 /* XXX hashlen depends on KEX */ 171 PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, 20)); 172 173 /* destroy_sensitive_data(); */ 174 175 /* send server hostkey, DH pubkey 'f' and singed H */ 176 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 177 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 178 packet_put_string(server_host_key_blob, sbloblen); 179 packet_put_bignum2(dh->pub_key); /* f */ 180 packet_put_string(signature, slen); 181 packet_send(); 182 183 xfree(signature); 184 xfree(server_host_key_blob); 185 /* have keys, free DH */ 186 DH_free(dh); 187 188 kex_derive_keys(kex, hash, shared_secret); 189 BN_clear_free(shared_secret); 190 191 kex_finish(kex); 192 } 193