1 /* $OpenBSD: kexgexs.c,v 1.8 2006/08/03 03:34:42 deraadt 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 51 void 52 kexgex_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, kout, slen, hashlen; 59 int min = -1, max = -1, nbits = -1, type; 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 kout = DH_compute_key(kbuf, dh_client_pub, dh); 138 #ifdef DEBUG_KEXDH 139 dump_digest("shared secret", kbuf, kout); 140 #endif 141 if ((shared_secret = BN_new()) == NULL) 142 fatal("kexgex_server: BN_new failed"); 143 BN_bin2bn(kbuf, kout, shared_secret); 144 memset(kbuf, 0, klen); 145 xfree(kbuf); 146 147 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 148 149 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 150 min = max = -1; 151 152 /* calc H */ 153 kexgex_hash( 154 kex->evp_md, 155 kex->client_version_string, 156 kex->server_version_string, 157 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 158 buffer_ptr(&kex->my), buffer_len(&kex->my), 159 server_host_key_blob, sbloblen, 160 min, nbits, max, 161 dh->p, dh->g, 162 dh_client_pub, 163 dh->pub_key, 164 shared_secret, 165 &hash, &hashlen 166 ); 167 BN_clear_free(dh_client_pub); 168 169 /* save session id := H */ 170 if (kex->session_id == NULL) { 171 kex->session_id_len = hashlen; 172 kex->session_id = xmalloc(kex->session_id_len); 173 memcpy(kex->session_id, hash, kex->session_id_len); 174 } 175 176 /* sign H */ 177 PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen)); 178 179 /* destroy_sensitive_data(); */ 180 181 /* send server hostkey, DH pubkey 'f' and singed H */ 182 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 183 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 184 packet_put_string(server_host_key_blob, sbloblen); 185 packet_put_bignum2(dh->pub_key); /* f */ 186 packet_put_string(signature, slen); 187 packet_send(); 188 189 xfree(signature); 190 xfree(server_host_key_blob); 191 /* have keys, free DH */ 192 DH_free(dh); 193 194 kex_derive_keys(kex, hash, hashlen, shared_secret); 195 BN_clear_free(shared_secret); 196 197 kex_finish(kex); 198 } 199