1 /* $OpenBSD: kexgexc.c,v 1.9 2006/08/03 03:34:42 deraadt 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/types.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 47 void 48 kexgex_client(Kex *kex) 49 { 50 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 51 BIGNUM *p = NULL, *g = NULL; 52 Key *server_host_key; 53 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 54 u_int klen, kout, slen, sbloblen, hashlen; 55 int min, max, nbits; 56 DH *dh; 57 58 nbits = dh_estimate(kex->we_need * 8); 59 60 if (datafellows & SSH_OLD_DHGEX) { 61 /* Old GEX request */ 62 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD); 63 packet_put_int(nbits); 64 min = DH_GRP_MIN; 65 max = DH_GRP_MAX; 66 67 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", nbits); 68 } else { 69 /* New GEX request */ 70 min = DH_GRP_MIN; 71 max = DH_GRP_MAX; 72 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST); 73 packet_put_int(min); 74 packet_put_int(nbits); 75 packet_put_int(max); 76 77 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent", 78 min, nbits, max); 79 } 80 #ifdef DEBUG_KEXDH 81 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 82 min, nbits, max); 83 #endif 84 packet_send(); 85 86 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP"); 87 packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP); 88 89 if ((p = BN_new()) == NULL) 90 fatal("BN_new"); 91 packet_get_bignum2(p); 92 if ((g = BN_new()) == NULL) 93 fatal("BN_new"); 94 packet_get_bignum2(g); 95 packet_check_eom(); 96 97 if (BN_num_bits(p) < min || BN_num_bits(p) > max) 98 fatal("DH_GEX group out of range: %d !< %d !< %d", 99 min, BN_num_bits(p), max); 100 101 dh = dh_new_group(g, p); 102 dh_gen_key(dh, kex->we_need * 8); 103 104 #ifdef DEBUG_KEXDH 105 DHparams_print_fp(stderr, dh); 106 fprintf(stderr, "pub= "); 107 BN_print_fp(stderr, dh->pub_key); 108 fprintf(stderr, "\n"); 109 #endif 110 111 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 112 /* generate and send 'e', client DH public key */ 113 packet_start(SSH2_MSG_KEX_DH_GEX_INIT); 114 packet_put_bignum2(dh->pub_key); 115 packet_send(); 116 117 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY"); 118 packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY); 119 120 /* key, cert */ 121 server_host_key_blob = packet_get_string(&sbloblen); 122 server_host_key = key_from_blob(server_host_key_blob, sbloblen); 123 if (server_host_key == NULL) 124 fatal("cannot decode server_host_key_blob"); 125 if (server_host_key->type != kex->hostkey_type) 126 fatal("type mismatch for decoded server_host_key_blob"); 127 if (kex->verify_host_key == NULL) 128 fatal("cannot verify server_host_key"); 129 if (kex->verify_host_key(server_host_key) == -1) 130 fatal("server_host_key verification failed"); 131 132 /* DH parameter f, server public DH key */ 133 if ((dh_server_pub = BN_new()) == NULL) 134 fatal("dh_server_pub == NULL"); 135 packet_get_bignum2(dh_server_pub); 136 137 #ifdef DEBUG_KEXDH 138 fprintf(stderr, "dh_server_pub= "); 139 BN_print_fp(stderr, dh_server_pub); 140 fprintf(stderr, "\n"); 141 debug("bits %d", BN_num_bits(dh_server_pub)); 142 #endif 143 144 /* signed H */ 145 signature = packet_get_string(&slen); 146 packet_check_eom(); 147 148 if (!dh_pub_is_valid(dh, dh_server_pub)) 149 packet_disconnect("bad server public DH value"); 150 151 klen = DH_size(dh); 152 kbuf = xmalloc(klen); 153 kout = DH_compute_key(kbuf, dh_server_pub, dh); 154 #ifdef DEBUG_KEXDH 155 dump_digest("shared secret", kbuf, kout); 156 #endif 157 if ((shared_secret = BN_new()) == NULL) 158 fatal("kexgex_client: BN_new failed"); 159 BN_bin2bn(kbuf, kout, shared_secret); 160 memset(kbuf, 0, klen); 161 xfree(kbuf); 162 163 if (datafellows & SSH_OLD_DHGEX) 164 min = max = -1; 165 166 /* calc and verify H */ 167 kexgex_hash( 168 kex->evp_md, 169 kex->client_version_string, 170 kex->server_version_string, 171 buffer_ptr(&kex->my), buffer_len(&kex->my), 172 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 173 server_host_key_blob, sbloblen, 174 min, nbits, max, 175 dh->p, dh->g, 176 dh->pub_key, 177 dh_server_pub, 178 shared_secret, 179 &hash, &hashlen 180 ); 181 182 /* have keys, free DH */ 183 DH_free(dh); 184 xfree(server_host_key_blob); 185 BN_clear_free(dh_server_pub); 186 187 if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1) 188 fatal("key_verify failed for server_host_key"); 189 key_free(server_host_key); 190 xfree(signature); 191 192 /* save session id */ 193 if (kex->session_id == NULL) { 194 kex->session_id_len = hashlen; 195 kex->session_id = xmalloc(kex->session_id_len); 196 memcpy(kex->session_id, hash, kex->session_id_len); 197 } 198 kex_derive_keys(kex, hash, hashlen, shared_secret); 199 BN_clear_free(shared_secret); 200 201 kex_finish(kex); 202 } 203