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 <sys/param.h> 28 29 #include <stdio.h> 30 #include <string.h> 31 #include <signal.h> 32 33 #include "xmalloc.h" 34 #include "buffer.h" 35 #include "key.h" 36 #include "cipher.h" 37 #include "kex.h" 38 #include "log.h" 39 #include "packet.h" 40 #include "dh.h" 41 #include "ssh2.h" 42 #include "compat.h" 43 #ifdef GSSAPI 44 #include "ssh-gss.h" 45 #endif 46 #include "monitor_wrap.h" 47 48 void 49 kexgex_server(Kex *kex) 50 { 51 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 52 Key *server_host_key; 53 DH *dh; 54 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 55 u_int sbloblen, klen, slen, hashlen; 56 int min = -1, max = -1, nbits = -1, type, kout; 57 58 if (kex->load_host_key == NULL) 59 fatal("Cannot load hostkey"); 60 server_host_key = kex->load_host_key(kex->hostkey_type); 61 if (server_host_key == NULL) 62 fatal("Unsupported hostkey type %d", kex->hostkey_type); 63 64 type = packet_read(); 65 switch (type) { 66 case SSH2_MSG_KEX_DH_GEX_REQUEST: 67 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 68 min = packet_get_int(); 69 nbits = packet_get_int(); 70 max = packet_get_int(); 71 min = MAX(DH_GRP_MIN, min); 72 max = MIN(DH_GRP_MAX, max); 73 break; 74 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 75 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 76 nbits = packet_get_int(); 77 min = DH_GRP_MIN; 78 max = DH_GRP_MAX; 79 /* unused for old GEX */ 80 break; 81 default: 82 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 83 } 84 packet_check_eom(); 85 86 if (max < min || nbits < min || max < nbits) 87 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 88 min, nbits, max); 89 90 /* Contact privileged parent */ 91 dh = PRIVSEP(choose_dh(min, nbits, max)); 92 if (dh == NULL) 93 packet_disconnect("Protocol error: no matching DH grp found"); 94 95 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 96 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 97 packet_put_bignum2(dh->p); 98 packet_put_bignum2(dh->g); 99 packet_send(); 100 101 /* flush */ 102 packet_write_wait(); 103 104 /* Compute our exchange value in parallel with the client */ 105 dh_gen_key(dh, kex->we_need * 8); 106 107 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 108 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 109 110 /* key, cert */ 111 if ((dh_client_pub = BN_new()) == NULL) 112 fatal("dh_client_pub == NULL"); 113 packet_get_bignum2(dh_client_pub); 114 packet_check_eom(); 115 116 #ifdef DEBUG_KEXDH 117 fprintf(stderr, "dh_client_pub= "); 118 BN_print_fp(stderr, dh_client_pub); 119 fprintf(stderr, "\n"); 120 debug("bits %d", BN_num_bits(dh_client_pub)); 121 #endif 122 123 #ifdef DEBUG_KEXDH 124 DHparams_print_fp(stderr, dh); 125 fprintf(stderr, "pub= "); 126 BN_print_fp(stderr, dh->pub_key); 127 fprintf(stderr, "\n"); 128 #endif 129 if (!dh_pub_is_valid(dh, dh_client_pub)) 130 packet_disconnect("bad client public DH value"); 131 132 klen = DH_size(dh); 133 kbuf = xmalloc(klen); 134 if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0) 135 fatal("DH_compute_key: failed"); 136 #ifdef DEBUG_KEXDH 137 dump_digest("shared secret", kbuf, kout); 138 #endif 139 if ((shared_secret = BN_new()) == NULL) 140 fatal("kexgex_server: BN_new failed"); 141 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL) 142 fatal("kexgex_server: BN_bin2bn failed"); 143 memset(kbuf, 0, klen); 144 xfree(kbuf); 145 146 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 147 148 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 149 min = max = -1; 150 151 /* calc H */ 152 kexgex_hash( 153 kex->evp_md, 154 kex->client_version_string, 155 kex->server_version_string, 156 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 157 buffer_ptr(&kex->my), buffer_len(&kex->my), 158 server_host_key_blob, sbloblen, 159 min, nbits, max, 160 dh->p, dh->g, 161 dh_client_pub, 162 dh->pub_key, 163 shared_secret, 164 &hash, &hashlen 165 ); 166 BN_clear_free(dh_client_pub); 167 168 /* save session id := H */ 169 if (kex->session_id == NULL) { 170 kex->session_id_len = hashlen; 171 kex->session_id = xmalloc(kex->session_id_len); 172 memcpy(kex->session_id, hash, kex->session_id_len); 173 } 174 175 /* sign H */ 176 PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen)); 177 178 /* destroy_sensitive_data(); */ 179 180 /* send server hostkey, DH pubkey 'f' and singed H */ 181 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 182 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 183 packet_put_string(server_host_key_blob, sbloblen); 184 packet_put_bignum2(dh->pub_key); /* f */ 185 packet_put_string(signature, slen); 186 packet_send(); 187 188 xfree(signature); 189 xfree(server_host_key_blob); 190 /* have keys, free DH */ 191 DH_free(dh); 192 193 kex_derive_keys(kex, hash, hashlen, shared_secret); 194 BN_clear_free(shared_secret); 195 196 kex_finish(kex); 197 } 198