1 /* $OpenBSD: kexgexs.c,v 1.19 2014/02/02 03:44:31 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 <sys/param.h> 28 29 #include <stdio.h> 30 #include <string.h> 31 #include <signal.h> 32 33 #include <openssl/dh.h> 34 35 #include "xmalloc.h" 36 #include "buffer.h" 37 #include "key.h" 38 #include "cipher.h" 39 #include "kex.h" 40 #include "log.h" 41 #include "packet.h" 42 #include "dh.h" 43 #include "ssh2.h" 44 #include "compat.h" 45 #ifdef GSSAPI 46 #include "ssh-gss.h" 47 #endif 48 #include "monitor_wrap.h" 49 50 void 51 kexgex_server(Kex *kex) 52 { 53 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 54 Key *server_host_public, *server_host_private; 55 DH *dh; 56 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 57 u_int sbloblen, klen, slen, hashlen; 58 int omin = -1, min = -1, omax = -1, max = -1, onbits = -1, nbits = -1; 59 int type, kout; 60 61 if (kex->load_host_public_key == NULL || 62 kex->load_host_private_key == NULL) 63 fatal("Cannot load hostkey"); 64 server_host_public = kex->load_host_public_key(kex->hostkey_type); 65 if (server_host_public == NULL) 66 fatal("Unsupported hostkey type %d", kex->hostkey_type); 67 server_host_private = kex->load_host_private_key(kex->hostkey_type); 68 69 type = packet_read(); 70 switch (type) { 71 case SSH2_MSG_KEX_DH_GEX_REQUEST: 72 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 73 omin = min = packet_get_int(); 74 onbits = nbits = packet_get_int(); 75 omax = max = packet_get_int(); 76 min = MAX(DH_GRP_MIN, min); 77 max = MIN(DH_GRP_MAX, max); 78 nbits = MAX(DH_GRP_MIN, nbits); 79 nbits = MIN(DH_GRP_MAX, nbits); 80 break; 81 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 82 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 83 onbits = nbits = packet_get_int(); 84 /* unused for old GEX */ 85 omin = min = DH_GRP_MIN; 86 omax = max = DH_GRP_MAX; 87 break; 88 default: 89 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 90 } 91 packet_check_eom(); 92 93 if (omax < omin || onbits < omin || omax < onbits) 94 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 95 omin, onbits, omax); 96 97 /* Contact privileged parent */ 98 dh = PRIVSEP(choose_dh(min, nbits, max)); 99 if (dh == NULL) 100 packet_disconnect("Protocol error: no matching DH grp found"); 101 102 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 103 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 104 packet_put_bignum2(dh->p); 105 packet_put_bignum2(dh->g); 106 packet_send(); 107 108 /* flush */ 109 packet_write_wait(); 110 111 /* Compute our exchange value in parallel with the client */ 112 dh_gen_key(dh, kex->we_need * 8); 113 114 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 115 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 116 117 /* key, cert */ 118 if ((dh_client_pub = BN_new()) == NULL) 119 fatal("dh_client_pub == NULL"); 120 packet_get_bignum2(dh_client_pub); 121 packet_check_eom(); 122 123 #ifdef DEBUG_KEXDH 124 fprintf(stderr, "dh_client_pub= "); 125 BN_print_fp(stderr, dh_client_pub); 126 fprintf(stderr, "\n"); 127 debug("bits %d", BN_num_bits(dh_client_pub)); 128 #endif 129 130 #ifdef DEBUG_KEXDH 131 DHparams_print_fp(stderr, dh); 132 fprintf(stderr, "pub= "); 133 BN_print_fp(stderr, dh->pub_key); 134 fprintf(stderr, "\n"); 135 #endif 136 if (!dh_pub_is_valid(dh, dh_client_pub)) 137 packet_disconnect("bad client public DH value"); 138 139 klen = DH_size(dh); 140 kbuf = xmalloc(klen); 141 if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0) 142 fatal("DH_compute_key: failed"); 143 #ifdef DEBUG_KEXDH 144 dump_digest("shared secret", kbuf, kout); 145 #endif 146 if ((shared_secret = BN_new()) == NULL) 147 fatal("kexgex_server: BN_new failed"); 148 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL) 149 fatal("kexgex_server: BN_bin2bn failed"); 150 explicit_bzero(kbuf, klen); 151 free(kbuf); 152 153 key_to_blob(server_host_public, &server_host_key_blob, &sbloblen); 154 155 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 156 omin = min = omax = max = -1; 157 158 /* calc H */ 159 kexgex_hash( 160 kex->hash_alg, 161 kex->client_version_string, 162 kex->server_version_string, 163 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 164 buffer_ptr(&kex->my), buffer_len(&kex->my), 165 server_host_key_blob, sbloblen, 166 omin, onbits, omax, 167 dh->p, dh->g, 168 dh_client_pub, 169 dh->pub_key, 170 shared_secret, 171 &hash, &hashlen 172 ); 173 BN_clear_free(dh_client_pub); 174 175 /* save session id := H */ 176 if (kex->session_id == NULL) { 177 kex->session_id_len = hashlen; 178 kex->session_id = xmalloc(kex->session_id_len); 179 memcpy(kex->session_id, hash, kex->session_id_len); 180 } 181 182 /* sign H */ 183 kex->sign(server_host_private, server_host_public, &signature, &slen, 184 hash, hashlen); 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 free(signature); 197 free(server_host_key_blob); 198 /* have keys, free DH */ 199 DH_free(dh); 200 201 kex_derive_keys_bn(kex, hash, hashlen, shared_secret); 202 BN_clear_free(shared_secret); 203 204 kex_finish(kex); 205 } 206