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