kexgexs.c revision 164147
1/* $OpenBSD: kexgexs.c,v 1.10 2006/11/06 21:25:28 markus Exp $ */ 2/* 3 * Copyright (c) 2000 Niels Provos. All rights reserved. 4 * Copyright (c) 2001 Markus Friedl. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25 */ 26 27#include "includes.h" 28 29#include <sys/param.h> 30 31#include <stdarg.h> 32#include <stdio.h> 33#include <string.h> 34#include <signal.h> 35 36#include "xmalloc.h" 37#include "buffer.h" 38#include "key.h" 39#include "cipher.h" 40#include "kex.h" 41#include "log.h" 42#include "packet.h" 43#include "dh.h" 44#include "ssh2.h" 45#include "compat.h" 46#ifdef GSSAPI 47#include "ssh-gss.h" 48#endif 49#include "monitor_wrap.h" 50 51void 52kexgex_server(Kex *kex) 53{ 54 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 55 Key *server_host_key; 56 DH *dh; 57 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 58 u_int sbloblen, klen, slen, hashlen; 59 int min = -1, max = -1, nbits = -1, type, kout; 60 61 if (kex->load_host_key == NULL) 62 fatal("Cannot load hostkey"); 63 server_host_key = kex->load_host_key(kex->hostkey_type); 64 if (server_host_key == NULL) 65 fatal("Unsupported hostkey type %d", kex->hostkey_type); 66 67 type = packet_read(); 68 switch (type) { 69 case SSH2_MSG_KEX_DH_GEX_REQUEST: 70 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 71 min = packet_get_int(); 72 nbits = packet_get_int(); 73 max = packet_get_int(); 74 min = MAX(DH_GRP_MIN, min); 75 max = MIN(DH_GRP_MAX, max); 76 break; 77 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 78 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 79 nbits = packet_get_int(); 80 min = DH_GRP_MIN; 81 max = DH_GRP_MAX; 82 /* unused for old GEX */ 83 break; 84 default: 85 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 86 } 87 packet_check_eom(); 88 89 if (max < min || nbits < min || max < nbits) 90 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 91 min, nbits, max); 92 93 /* Contact privileged parent */ 94 dh = PRIVSEP(choose_dh(min, nbits, max)); 95 if (dh == NULL) 96 packet_disconnect("Protocol error: no matching DH grp found"); 97 98 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 99 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 100 packet_put_bignum2(dh->p); 101 packet_put_bignum2(dh->g); 102 packet_send(); 103 104 /* flush */ 105 packet_write_wait(); 106 107 /* Compute our exchange value in parallel with the client */ 108 dh_gen_key(dh, kex->we_need * 8); 109 110 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 111 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 112 113 /* key, cert */ 114 if ((dh_client_pub = BN_new()) == NULL) 115 fatal("dh_client_pub == NULL"); 116 packet_get_bignum2(dh_client_pub); 117 packet_check_eom(); 118 119#ifdef DEBUG_KEXDH 120 fprintf(stderr, "dh_client_pub= "); 121 BN_print_fp(stderr, dh_client_pub); 122 fprintf(stderr, "\n"); 123 debug("bits %d", BN_num_bits(dh_client_pub)); 124#endif 125 126#ifdef DEBUG_KEXDH 127 DHparams_print_fp(stderr, dh); 128 fprintf(stderr, "pub= "); 129 BN_print_fp(stderr, dh->pub_key); 130 fprintf(stderr, "\n"); 131#endif 132 if (!dh_pub_is_valid(dh, dh_client_pub)) 133 packet_disconnect("bad client public DH value"); 134 135 klen = DH_size(dh); 136 kbuf = xmalloc(klen); 137 if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0) 138 fatal("DH_compute_key: failed"); 139#ifdef DEBUG_KEXDH 140 dump_digest("shared secret", kbuf, kout); 141#endif 142 if ((shared_secret = BN_new()) == NULL) 143 fatal("kexgex_server: BN_new failed"); 144 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL) 145 fatal("kexgex_server: BN_bin2bn failed"); 146 memset(kbuf, 0, klen); 147 xfree(kbuf); 148 149 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 150 151 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 152 min = max = -1; 153 154 /* calc H */ 155 kexgex_hash( 156 kex->evp_md, 157 kex->client_version_string, 158 kex->server_version_string, 159 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 160 buffer_ptr(&kex->my), buffer_len(&kex->my), 161 server_host_key_blob, sbloblen, 162 min, nbits, max, 163 dh->p, dh->g, 164 dh_client_pub, 165 dh->pub_key, 166 shared_secret, 167 &hash, &hashlen 168 ); 169 BN_clear_free(dh_client_pub); 170 171 /* save session id := H */ 172 if (kex->session_id == NULL) { 173 kex->session_id_len = hashlen; 174 kex->session_id = xmalloc(kex->session_id_len); 175 memcpy(kex->session_id, hash, kex->session_id_len); 176 } 177 178 /* sign H */ 179 PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen)); 180 181 /* destroy_sensitive_data(); */ 182 183 /* send server hostkey, DH pubkey 'f' and singed H */ 184 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 185 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 186 packet_put_string(server_host_key_blob, sbloblen); 187 packet_put_bignum2(dh->pub_key); /* f */ 188 packet_put_string(signature, slen); 189 packet_send(); 190 191 xfree(signature); 192 xfree(server_host_key_blob); 193 /* have keys, free DH */ 194 DH_free(dh); 195 196 kex_derive_keys(kex, hash, hashlen, shared_secret); 197 BN_clear_free(shared_secret); 198 199 kex_finish(kex); 200} 201