1 /* $OpenBSD: kexgexs.c,v 1.13 2010/02/26 20:29:54 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 "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_public, *server_host_private; 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_public_key == NULL || 63 kex->load_host_private_key == NULL) 64 fatal("Cannot load hostkey"); 65 server_host_public = kex->load_host_public_key(kex->hostkey_type); 66 if (server_host_public == NULL) 67 fatal("Unsupported hostkey type %d", kex->hostkey_type); 68 server_host_private = kex->load_host_private_key(kex->hostkey_type); 69 if (server_host_private == NULL) 70 fatal("Missing private key for hostkey type %d", 71 kex->hostkey_type); 72 73 74 type = packet_read(); 75 switch (type) { 76 case SSH2_MSG_KEX_DH_GEX_REQUEST: 77 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 78 omin = min = packet_get_int(); 79 onbits = nbits = packet_get_int(); 80 omax = max = packet_get_int(); 81 min = MAX(DH_GRP_MIN, min); 82 max = MIN(DH_GRP_MAX, max); 83 nbits = MAX(DH_GRP_MIN, nbits); 84 nbits = MIN(DH_GRP_MAX, nbits); 85 break; 86 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 87 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 88 onbits = nbits = packet_get_int(); 89 /* unused for old GEX */ 90 omin = min = DH_GRP_MIN; 91 omax = max = DH_GRP_MAX; 92 break; 93 default: 94 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 95 } 96 packet_check_eom(); 97 98 if (omax < omin || onbits < omin || omax < onbits) 99 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 100 omin, onbits, omax); 101 102 /* Contact privileged parent */ 103 dh = PRIVSEP(choose_dh(min, nbits, max)); 104 if (dh == NULL) 105 packet_disconnect("Protocol error: no matching DH grp found"); 106 107 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 108 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 109 packet_put_bignum2(dh->p); 110 packet_put_bignum2(dh->g); 111 packet_send(); 112 113 /* flush */ 114 packet_write_wait(); 115 116 /* Compute our exchange value in parallel with the client */ 117 dh_gen_key(dh, kex->we_need * 8); 118 119 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 120 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 121 122 /* key, cert */ 123 if ((dh_client_pub = BN_new()) == NULL) 124 fatal("dh_client_pub == NULL"); 125 packet_get_bignum2(dh_client_pub); 126 packet_check_eom(); 127 128 #ifdef DEBUG_KEXDH 129 fprintf(stderr, "dh_client_pub= "); 130 BN_print_fp(stderr, dh_client_pub); 131 fprintf(stderr, "\n"); 132 debug("bits %d", BN_num_bits(dh_client_pub)); 133 #endif 134 135 #ifdef DEBUG_KEXDH 136 DHparams_print_fp(stderr, dh); 137 fprintf(stderr, "pub= "); 138 BN_print_fp(stderr, dh->pub_key); 139 fprintf(stderr, "\n"); 140 #endif 141 if (!dh_pub_is_valid(dh, dh_client_pub)) 142 packet_disconnect("bad client public DH value"); 143 144 klen = DH_size(dh); 145 kbuf = xmalloc(klen); 146 if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0) 147 fatal("DH_compute_key: failed"); 148 #ifdef DEBUG_KEXDH 149 dump_digest("shared secret", kbuf, kout); 150 #endif 151 if ((shared_secret = BN_new()) == NULL) 152 fatal("kexgex_server: BN_new failed"); 153 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL) 154 fatal("kexgex_server: BN_bin2bn failed"); 155 memset(kbuf, 0, klen); 156 xfree(kbuf); 157 158 key_to_blob(server_host_public, &server_host_key_blob, &sbloblen); 159 160 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 161 omin = min = omax = max = -1; 162 163 /* calc H */ 164 kexgex_hash( 165 kex->evp_md, 166 kex->client_version_string, 167 kex->server_version_string, 168 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 169 buffer_ptr(&kex->my), buffer_len(&kex->my), 170 server_host_key_blob, sbloblen, 171 omin, onbits, omax, 172 dh->p, dh->g, 173 dh_client_pub, 174 dh->pub_key, 175 shared_secret, 176 &hash, &hashlen 177 ); 178 BN_clear_free(dh_client_pub); 179 180 /* save session id := H */ 181 if (kex->session_id == NULL) { 182 kex->session_id_len = hashlen; 183 kex->session_id = xmalloc(kex->session_id_len); 184 memcpy(kex->session_id, hash, kex->session_id_len); 185 } 186 187 /* sign H */ 188 if (PRIVSEP(key_sign(server_host_private, &signature, &slen, hash, 189 hashlen)) < 0) 190 fatal("kexgex_server: key_sign failed"); 191 192 /* destroy_sensitive_data(); */ 193 194 /* send server hostkey, DH pubkey 'f' and singed H */ 195 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 196 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 197 packet_put_string(server_host_key_blob, sbloblen); 198 packet_put_bignum2(dh->pub_key); /* f */ 199 packet_put_string(signature, slen); 200 packet_send(); 201 202 xfree(signature); 203 xfree(server_host_key_blob); 204 /* have keys, free DH */ 205 DH_free(dh); 206 207 kex_derive_keys(kex, hash, hashlen, shared_secret); 208 BN_clear_free(shared_secret); 209 210 kex_finish(kex); 211 } 212