1 /* $OpenBSD: kexgexs.c,v 1.12 2009/06/21 07:37:15 dtucker 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, slen, hashlen; 59 int omin = -1, min = -1, omax = -1, max = -1, onbits = -1, nbits = -1; 60 int type, kout; 61 62 if (kex->load_host_key == NULL) 63 fatal("Cannot load hostkey"); 64 server_host_key = kex->load_host_key(kex->hostkey_type); 65 if (server_host_key == NULL) 66 fatal("Unsupported hostkey type %d", kex->hostkey_type); 67 68 type = packet_read(); 69 switch (type) { 70 case SSH2_MSG_KEX_DH_GEX_REQUEST: 71 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 72 omin = min = packet_get_int(); 73 onbits = nbits = packet_get_int(); 74 omax = max = packet_get_int(); 75 min = MAX(DH_GRP_MIN, min); 76 max = MIN(DH_GRP_MAX, max); 77 nbits = MAX(DH_GRP_MIN, nbits); 78 nbits = MIN(DH_GRP_MAX, nbits); 79 break; 80 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 81 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 82 onbits = nbits = packet_get_int(); 83 /* unused for old GEX */ 84 omin = min = DH_GRP_MIN; 85 omax = max = DH_GRP_MAX; 86 break; 87 default: 88 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 89 } 90 packet_check_eom(); 91 92 if (omax < omin || onbits < omin || omax < onbits) 93 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 94 omin, onbits, omax); 95 96 /* Contact privileged parent */ 97 dh = PRIVSEP(choose_dh(min, nbits, max)); 98 if (dh == NULL) 99 packet_disconnect("Protocol error: no matching DH grp found"); 100 101 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 102 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 103 packet_put_bignum2(dh->p); 104 packet_put_bignum2(dh->g); 105 packet_send(); 106 107 /* flush */ 108 packet_write_wait(); 109 110 /* Compute our exchange value in parallel with the client */ 111 dh_gen_key(dh, kex->we_need * 8); 112 113 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 114 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 115 116 /* key, cert */ 117 if ((dh_client_pub = BN_new()) == NULL) 118 fatal("dh_client_pub == NULL"); 119 packet_get_bignum2(dh_client_pub); 120 packet_check_eom(); 121 122 #ifdef DEBUG_KEXDH 123 fprintf(stderr, "dh_client_pub= "); 124 BN_print_fp(stderr, dh_client_pub); 125 fprintf(stderr, "\n"); 126 debug("bits %d", BN_num_bits(dh_client_pub)); 127 #endif 128 129 #ifdef DEBUG_KEXDH 130 DHparams_print_fp(stderr, dh); 131 fprintf(stderr, "pub= "); 132 BN_print_fp(stderr, dh->pub_key); 133 fprintf(stderr, "\n"); 134 #endif 135 if (!dh_pub_is_valid(dh, dh_client_pub)) 136 packet_disconnect("bad client public DH value"); 137 138 klen = DH_size(dh); 139 kbuf = xmalloc(klen); 140 if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0) 141 fatal("DH_compute_key: failed"); 142 #ifdef DEBUG_KEXDH 143 dump_digest("shared secret", kbuf, kout); 144 #endif 145 if ((shared_secret = BN_new()) == NULL) 146 fatal("kexgex_server: BN_new failed"); 147 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL) 148 fatal("kexgex_server: BN_bin2bn failed"); 149 memset(kbuf, 0, klen); 150 xfree(kbuf); 151 152 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 153 154 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 155 omin = min = omax = max = -1; 156 157 /* calc H */ 158 kexgex_hash( 159 kex->evp_md, 160 kex->client_version_string, 161 kex->server_version_string, 162 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 163 buffer_ptr(&kex->my), buffer_len(&kex->my), 164 server_host_key_blob, sbloblen, 165 omin, onbits, omax, 166 dh->p, dh->g, 167 dh_client_pub, 168 dh->pub_key, 169 shared_secret, 170 &hash, &hashlen 171 ); 172 BN_clear_free(dh_client_pub); 173 174 /* save session id := H */ 175 if (kex->session_id == NULL) { 176 kex->session_id_len = hashlen; 177 kex->session_id = xmalloc(kex->session_id_len); 178 memcpy(kex->session_id, hash, kex->session_id_len); 179 } 180 181 /* sign H */ 182 if (PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, 183 hashlen)) < 0) 184 fatal("kexgex_server: key_sign failed"); 185 186 /* destroy_sensitive_data(); */ 187 188 /* send server hostkey, DH pubkey 'f' and singed H */ 189 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 190 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 191 packet_put_string(server_host_key_blob, sbloblen); 192 packet_put_bignum2(dh->pub_key); /* f */ 193 packet_put_string(signature, slen); 194 packet_send(); 195 196 xfree(signature); 197 xfree(server_host_key_blob); 198 /* have keys, free DH */ 199 DH_free(dh); 200 201 kex_derive_keys(kex, hash, hashlen, shared_secret); 202 BN_clear_free(shared_secret); 203 204 kex_finish(kex); 205 } 206