1/* $OpenBSD: kexgexs.c,v 1.16 2013/07/19 07:37:48 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 <openssl/dh.h> 37 38#include "xmalloc.h" 39#include "buffer.h" 40#include "key.h" 41#include "cipher.h" 42#include "kex.h" 43#include "log.h" 44#include "packet.h" 45#include "dh.h" 46#include "ssh2.h" 47#include "compat.h" 48#ifdef GSSAPI 49#include "ssh-gss.h" 50#endif 51#include "monitor_wrap.h" 52 53void 54kexgex_server(Kex *kex) 55{ 56 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 57 Key *server_host_public, *server_host_private; 58 DH *dh; 59 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 60 u_int sbloblen, klen, slen, hashlen; 61 int omin = -1, min = -1, omax = -1, max = -1, onbits = -1, nbits = -1; 62 int type, kout; 63 64 if (kex->load_host_public_key == NULL || 65 kex->load_host_private_key == NULL) 66 fatal("Cannot load hostkey"); 67 server_host_public = kex->load_host_public_key(kex->hostkey_type); 68 if (server_host_public == NULL) 69 fatal("Unsupported hostkey type %d", kex->hostkey_type); 70 server_host_private = kex->load_host_private_key(kex->hostkey_type); 71 72 type = packet_read(); 73 switch (type) { 74 case SSH2_MSG_KEX_DH_GEX_REQUEST: 75 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 76 omin = min = packet_get_int(); 77 onbits = nbits = packet_get_int(); 78 omax = max = packet_get_int(); 79 min = MAX(DH_GRP_MIN, min); 80 max = MIN(DH_GRP_MAX, max); 81 nbits = MAX(DH_GRP_MIN, nbits); 82 nbits = MIN(DH_GRP_MAX, nbits); 83 break; 84 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 85 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 86 onbits = nbits = packet_get_int(); 87 /* unused for old GEX */ 88 omin = min = DH_GRP_MIN; 89 omax = max = DH_GRP_MAX; 90 break; 91 default: 92 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 93 } 94 packet_check_eom(); 95 96 if (omax < omin || onbits < omin || omax < onbits) 97 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 98 omin, onbits, omax); 99 100 /* Contact privileged parent */ 101 dh = PRIVSEP(choose_dh(min, nbits, max)); 102 if (dh == NULL) 103 packet_disconnect("Protocol error: no matching DH grp found"); 104 105 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 106 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 107 packet_put_bignum2(dh->p); 108 packet_put_bignum2(dh->g); 109 packet_send(); 110 111 /* flush */ 112 packet_write_wait(); 113 114 /* Compute our exchange value in parallel with the client */ 115 dh_gen_key(dh, kex->we_need * 8); 116 117 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 118 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 119 120 /* key, cert */ 121 if ((dh_client_pub = BN_new()) == NULL) 122 fatal("dh_client_pub == NULL"); 123 packet_get_bignum2(dh_client_pub); 124 packet_check_eom(); 125 126#ifdef DEBUG_KEXDH 127 fprintf(stderr, "dh_client_pub= "); 128 BN_print_fp(stderr, dh_client_pub); 129 fprintf(stderr, "\n"); 130 debug("bits %d", BN_num_bits(dh_client_pub)); 131#endif 132 133#ifdef DEBUG_KEXDH 134 DHparams_print_fp(stderr, dh); 135 fprintf(stderr, "pub= "); 136 BN_print_fp(stderr, dh->pub_key); 137 fprintf(stderr, "\n"); 138#endif 139 if (!dh_pub_is_valid(dh, dh_client_pub)) 140 packet_disconnect("bad client public DH value"); 141 142 klen = DH_size(dh); 143 kbuf = xmalloc(klen); 144 if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0) 145 fatal("DH_compute_key: failed"); 146#ifdef DEBUG_KEXDH 147 dump_digest("shared secret", kbuf, kout); 148#endif 149 if ((shared_secret = BN_new()) == NULL) 150 fatal("kexgex_server: BN_new failed"); 151 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL) 152 fatal("kexgex_server: BN_bin2bn failed"); 153 memset(kbuf, 0, klen); 154 free(kbuf); 155 156 key_to_blob(server_host_public, &server_host_key_blob, &sbloblen); 157 158 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 159 omin = min = omax = max = -1; 160 161 /* calc H */ 162 kexgex_hash( 163 kex->evp_md, 164 kex->client_version_string, 165 kex->server_version_string, 166 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 167 buffer_ptr(&kex->my), buffer_len(&kex->my), 168 server_host_key_blob, sbloblen, 169 omin, onbits, omax, 170 dh->p, dh->g, 171 dh_client_pub, 172 dh->pub_key, 173 shared_secret, 174 &hash, &hashlen 175 ); 176 BN_clear_free(dh_client_pub); 177 178 /* save session id := H */ 179 if (kex->session_id == NULL) { 180 kex->session_id_len = hashlen; 181 kex->session_id = xmalloc(kex->session_id_len); 182 memcpy(kex->session_id, hash, kex->session_id_len); 183 } 184 185 /* sign H */ 186 kex->sign(server_host_private, server_host_public, &signature, &slen, 187 hash, hashlen); 188 189 /* destroy_sensitive_data(); */ 190 191 /* send server hostkey, DH pubkey 'f' and singed H */ 192 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 193 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 194 packet_put_string(server_host_key_blob, sbloblen); 195 packet_put_bignum2(dh->pub_key); /* f */ 196 packet_put_string(signature, slen); 197 packet_send(); 198 199 free(signature); 200 free(server_host_key_blob); 201 /* have keys, free DH */ 202 DH_free(dh); 203 204 kex_derive_keys(kex, hash, hashlen, shared_secret); 205 BN_clear_free(shared_secret); 206 207 kex_finish(kex); 208} 209