1/* $OpenBSD: kexgexs.c,v 1.14 2010/11/10 01:33:07 djm 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#ifdef __APPLE_CRYPTO__ 37#include "ossl-dh.h" 38#else 39#include <openssl/dh.h> 40#endif 41 42#include "xmalloc.h" 43#include "buffer.h" 44#include "key.h" 45#include "cipher.h" 46#include "kex.h" 47#include "log.h" 48#include "packet.h" 49#include "dh.h" 50#include "ssh2.h" 51#include "compat.h" 52#ifdef GSSAPI 53#include "ssh-gss.h" 54#endif 55#include "monitor_wrap.h" 56 57void 58kexgex_server(Kex *kex) 59{ 60 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 61 Key *server_host_public, *server_host_private; 62 DH *dh; 63 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 64 u_int sbloblen, klen, slen, hashlen; 65 int omin = -1, min = -1, omax = -1, max = -1, onbits = -1, nbits = -1; 66 int type, kout; 67 68 if (kex->load_host_public_key == NULL || 69 kex->load_host_private_key == NULL) 70 fatal("Cannot load hostkey"); 71 server_host_public = kex->load_host_public_key(kex->hostkey_type); 72 if (server_host_public == NULL) 73 fatal("Unsupported hostkey type %d", kex->hostkey_type); 74 server_host_private = kex->load_host_private_key(kex->hostkey_type); 75 if (server_host_private == NULL) 76 fatal("Missing private key for hostkey type %d", 77 kex->hostkey_type); 78 79 80 type = packet_read(); 81 switch (type) { 82 case SSH2_MSG_KEX_DH_GEX_REQUEST: 83 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 84 omin = min = packet_get_int(); 85 onbits = nbits = packet_get_int(); 86 omax = max = packet_get_int(); 87 min = MAX(DH_GRP_MIN, min); 88 max = MIN(DH_GRP_MAX, max); 89 nbits = MAX(DH_GRP_MIN, nbits); 90 nbits = MIN(DH_GRP_MAX, nbits); 91 break; 92 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 93 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 94 onbits = nbits = packet_get_int(); 95 /* unused for old GEX */ 96 omin = min = DH_GRP_MIN; 97 omax = max = DH_GRP_MAX; 98 break; 99 default: 100 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 101 } 102 packet_check_eom(); 103 104 if (omax < omin || onbits < omin || omax < onbits) 105 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 106 omin, onbits, omax); 107 108 /* Contact privileged parent */ 109 dh = PRIVSEP(choose_dh(min, nbits, max)); 110 if (dh == NULL) 111 packet_disconnect("Protocol error: no matching DH grp found"); 112 113 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 114 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 115 packet_put_bignum2(dh->p); 116 packet_put_bignum2(dh->g); 117 packet_send(); 118 119 /* flush */ 120 packet_write_wait(); 121 122 /* Compute our exchange value in parallel with the client */ 123 dh_gen_key(dh, kex->we_need * 8); 124 125 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 126 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 127 128 /* key, cert */ 129 if ((dh_client_pub = BN_new()) == NULL) 130 fatal("dh_client_pub == NULL"); 131 packet_get_bignum2(dh_client_pub); 132 packet_check_eom(); 133 134#ifdef DEBUG_KEXDH 135 fprintf(stderr, "dh_client_pub= "); 136 BN_print_fp(stderr, dh_client_pub); 137 fprintf(stderr, "\n"); 138 debug("bits %d", BN_num_bits(dh_client_pub)); 139#endif 140 141#ifdef DEBUG_KEXDH 142 DHparams_print_fp(stderr, dh); 143 fprintf(stderr, "pub= "); 144 BN_print_fp(stderr, dh->pub_key); 145 fprintf(stderr, "\n"); 146#endif 147 if (!dh_pub_is_valid(dh, dh_client_pub)) 148 packet_disconnect("bad client public DH value"); 149 150 klen = DH_size(dh); 151 kbuf = xmalloc(klen); 152 if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0) 153 fatal("DH_compute_key: failed"); 154#ifdef DEBUG_KEXDH 155 dump_digest("shared secret", kbuf, kout); 156#endif 157 if ((shared_secret = BN_new()) == NULL) 158 fatal("kexgex_server: BN_new failed"); 159 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL) 160 fatal("kexgex_server: BN_bin2bn failed"); 161 memset(kbuf, 0, klen); 162 xfree(kbuf); 163 164 key_to_blob(server_host_public, &server_host_key_blob, &sbloblen); 165 166 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 167 omin = min = omax = max = -1; 168 169 /* calc H */ 170 kexgex_hash( 171 kex->evp_md, 172 kex->client_version_string, 173 kex->server_version_string, 174 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 175 buffer_ptr(&kex->my), buffer_len(&kex->my), 176 server_host_key_blob, sbloblen, 177 omin, onbits, omax, 178 dh->p, dh->g, 179 dh_client_pub, 180 dh->pub_key, 181 shared_secret, 182 &hash, &hashlen 183 ); 184 BN_clear_free(dh_client_pub); 185 186 /* save session id := H */ 187 if (kex->session_id == NULL) { 188 kex->session_id_len = hashlen; 189 kex->session_id = xmalloc(kex->session_id_len); 190 memcpy(kex->session_id, hash, kex->session_id_len); 191 } 192 193 /* sign H */ 194 if (PRIVSEP(key_sign(server_host_private, &signature, &slen, hash, 195 hashlen)) < 0) 196 fatal("kexgex_server: key_sign failed"); 197 198 /* destroy_sensitive_data(); */ 199 200 /* send server hostkey, DH pubkey 'f' and singed H */ 201 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 202 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 203 packet_put_string(server_host_key_blob, sbloblen); 204 packet_put_bignum2(dh->pub_key); /* f */ 205 packet_put_string(signature, slen); 206 packet_send(); 207 208 xfree(signature); 209 xfree(server_host_key_blob); 210 /* have keys, free DH */ 211 DH_free(dh); 212 213 kex_derive_keys(kex, hash, hashlen, shared_secret); 214 BN_clear_free(shared_secret); 215 216 kex_finish(kex); 217} 218