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: kexgexs.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 #include "monitor_wrap.h" 38 39 void 40 kexgex_server(Kex *kex) 41 { 42 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 43 Key *server_host_key; 44 DH *dh; 45 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 46 u_int sbloblen, klen, kout, slen; 47 int min = -1, max = -1, nbits = -1, type; 48 49 if (kex->load_host_key == NULL) 50 fatal("Cannot load hostkey"); 51 server_host_key = kex->load_host_key(kex->hostkey_type); 52 if (server_host_key == NULL) 53 fatal("Unsupported hostkey type %d", kex->hostkey_type); 54 55 type = packet_read(); 56 switch (type) { 57 case SSH2_MSG_KEX_DH_GEX_REQUEST: 58 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 59 min = packet_get_int(); 60 nbits = packet_get_int(); 61 max = packet_get_int(); 62 min = MAX(DH_GRP_MIN, min); 63 max = MIN(DH_GRP_MAX, max); 64 break; 65 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 66 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 67 nbits = packet_get_int(); 68 min = DH_GRP_MIN; 69 max = DH_GRP_MAX; 70 /* unused for old GEX */ 71 break; 72 default: 73 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 74 } 75 packet_check_eom(); 76 77 if (max < min || nbits < min || max < nbits) 78 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 79 min, nbits, max); 80 81 /* Contact privileged parent */ 82 dh = PRIVSEP(choose_dh(min, nbits, max)); 83 if (dh == NULL) 84 packet_disconnect("Protocol error: no matching DH grp found"); 85 86 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 87 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 88 packet_put_bignum2(dh->p); 89 packet_put_bignum2(dh->g); 90 packet_send(); 91 92 /* flush */ 93 packet_write_wait(); 94 95 /* Compute our exchange value in parallel with the client */ 96 dh_gen_key(dh, kex->we_need * 8); 97 98 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 99 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 100 101 /* key, cert */ 102 if ((dh_client_pub = BN_new()) == NULL) 103 fatal("dh_client_pub == NULL"); 104 packet_get_bignum2(dh_client_pub); 105 packet_check_eom(); 106 107 #ifdef DEBUG_KEXDH 108 fprintf(stderr, "dh_client_pub= "); 109 BN_print_fp(stderr, dh_client_pub); 110 fprintf(stderr, "\n"); 111 debug("bits %d", BN_num_bits(dh_client_pub)); 112 #endif 113 114 #ifdef DEBUG_KEXDH 115 DHparams_print_fp(stderr, dh); 116 fprintf(stderr, "pub= "); 117 BN_print_fp(stderr, dh->pub_key); 118 fprintf(stderr, "\n"); 119 #endif 120 if (!dh_pub_is_valid(dh, dh_client_pub)) 121 packet_disconnect("bad client public DH value"); 122 123 klen = DH_size(dh); 124 kbuf = xmalloc(klen); 125 kout = DH_compute_key(kbuf, dh_client_pub, dh); 126 #ifdef DEBUG_KEXDH 127 dump_digest("shared secret", kbuf, kout); 128 #endif 129 if ((shared_secret = BN_new()) == NULL) 130 fatal("kexgex_server: BN_new failed"); 131 BN_bin2bn(kbuf, kout, shared_secret); 132 memset(kbuf, 0, klen); 133 xfree(kbuf); 134 135 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 136 137 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 138 min = max = -1; 139 140 /* calc H */ /* XXX depends on 'kex' */ 141 hash = kexgex_hash( 142 kex->client_version_string, 143 kex->server_version_string, 144 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 145 buffer_ptr(&kex->my), buffer_len(&kex->my), 146 server_host_key_blob, sbloblen, 147 min, nbits, max, 148 dh->p, dh->g, 149 dh_client_pub, 150 dh->pub_key, 151 shared_secret 152 ); 153 BN_clear_free(dh_client_pub); 154 155 /* save session id := H */ 156 /* XXX hashlen depends on KEX */ 157 if (kex->session_id == NULL) { 158 kex->session_id_len = 20; 159 kex->session_id = xmalloc(kex->session_id_len); 160 memcpy(kex->session_id, hash, kex->session_id_len); 161 } 162 163 /* sign H */ 164 /* XXX hashlen depends on KEX */ 165 PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, 20)); 166 167 /* destroy_sensitive_data(); */ 168 169 /* send server hostkey, DH pubkey 'f' and singed H */ 170 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 171 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 172 packet_put_string(server_host_key_blob, sbloblen); 173 packet_put_bignum2(dh->pub_key); /* f */ 174 packet_put_string(signature, slen); 175 packet_send(); 176 177 xfree(signature); 178 xfree(server_host_key_blob); 179 /* have keys, free DH */ 180 DH_free(dh); 181 182 kex_derive_keys(kex, hash, shared_secret); 183 BN_clear_free(shared_secret); 184 185 kex_finish(kex); 186 } 187