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 <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 omin = -1, min = -1, omax = -1, max = -1, onbits = -1, nbits = -1; 57 int type, kout; 58 59 if (kex->load_host_key == NULL) 60 fatal("Cannot load hostkey"); 61 server_host_key = kex->load_host_key(kex->hostkey_type); 62 if (server_host_key == NULL) 63 fatal("Unsupported hostkey type %d", kex->hostkey_type); 64 65 type = packet_read(); 66 switch (type) { 67 case SSH2_MSG_KEX_DH_GEX_REQUEST: 68 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 69 omin = min = packet_get_int(); 70 onbits = nbits = packet_get_int(); 71 omax = max = packet_get_int(); 72 min = MAX(DH_GRP_MIN, min); 73 max = MIN(DH_GRP_MAX, max); 74 nbits = MAX(DH_GRP_MIN, nbits); 75 nbits = MIN(DH_GRP_MAX, nbits); 76 break; 77 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 78 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 79 onbits = nbits = packet_get_int(); 80 /* unused for old GEX */ 81 omin = min = DH_GRP_MIN; 82 omax = max = DH_GRP_MAX; 83 break; 84 default: 85 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 86 } 87 packet_check_eom(); 88 89 if (omax < omin || onbits < omin || omax < onbits) 90 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 91 omin, onbits, omax); 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 if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0) 138 fatal("DH_compute_key: failed"); 139 #ifdef DEBUG_KEXDH 140 dump_digest("shared secret", kbuf, kout); 141 #endif 142 if ((shared_secret = BN_new()) == NULL) 143 fatal("kexgex_server: BN_new failed"); 144 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL) 145 fatal("kexgex_server: BN_bin2bn failed"); 146 memset(kbuf, 0, klen); 147 xfree(kbuf); 148 149 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 150 151 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 152 omin = min = omax = max = -1; 153 154 /* calc H */ 155 kexgex_hash( 156 kex->evp_md, 157 kex->client_version_string, 158 kex->server_version_string, 159 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 160 buffer_ptr(&kex->my), buffer_len(&kex->my), 161 server_host_key_blob, sbloblen, 162 omin, onbits, omax, 163 dh->p, dh->g, 164 dh_client_pub, 165 dh->pub_key, 166 shared_secret, 167 &hash, &hashlen 168 ); 169 BN_clear_free(dh_client_pub); 170 171 /* save session id := H */ 172 if (kex->session_id == NULL) { 173 kex->session_id_len = hashlen; 174 kex->session_id = xmalloc(kex->session_id_len); 175 memcpy(kex->session_id, hash, kex->session_id_len); 176 } 177 178 /* sign H */ 179 if (PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, 180 hashlen)) < 0) 181 fatal("kexgex_server: key_sign failed"); 182 183 /* destroy_sensitive_data(); */ 184 185 /* send server hostkey, DH pubkey 'f' and singed H */ 186 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 187 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 188 packet_put_string(server_host_key_blob, sbloblen); 189 packet_put_bignum2(dh->pub_key); /* f */ 190 packet_put_string(signature, slen); 191 packet_send(); 192 193 xfree(signature); 194 xfree(server_host_key_blob); 195 /* have keys, free DH */ 196 DH_free(dh); 197 198 kex_derive_keys(kex, hash, hashlen, shared_secret); 199 BN_clear_free(shared_secret); 200 201 kex_finish(kex); 202 } 203