1 /* $OpenBSD: kexgexc.c,v 1.11 2006/11/06 21:25:28 markus 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, slen, sbloblen, hashlen; 55 int kout; 56 int min, max, nbits; 57 DH *dh; 58 59 nbits = dh_estimate(kex->we_need * 8); 60 61 if (datafellows & SSH_OLD_DHGEX) { 62 /* Old GEX request */ 63 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD); 64 packet_put_int(nbits); 65 min = DH_GRP_MIN; 66 max = DH_GRP_MAX; 67 68 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", nbits); 69 } else { 70 /* New GEX request */ 71 min = DH_GRP_MIN; 72 max = DH_GRP_MAX; 73 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST); 74 packet_put_int(min); 75 packet_put_int(nbits); 76 packet_put_int(max); 77 78 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent", 79 min, nbits, max); 80 } 81 #ifdef DEBUG_KEXDH 82 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 83 min, nbits, max); 84 #endif 85 packet_send(); 86 87 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP"); 88 packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP); 89 90 if ((p = BN_new()) == NULL) 91 fatal("BN_new"); 92 packet_get_bignum2(p); 93 if ((g = BN_new()) == NULL) 94 fatal("BN_new"); 95 packet_get_bignum2(g); 96 packet_check_eom(); 97 98 if (BN_num_bits(p) < min || BN_num_bits(p) > max) 99 fatal("DH_GEX group out of range: %d !< %d !< %d", 100 min, BN_num_bits(p), max); 101 102 dh = dh_new_group(g, p); 103 dh_gen_key(dh, kex->we_need * 8); 104 105 #ifdef DEBUG_KEXDH 106 DHparams_print_fp(stderr, dh); 107 fprintf(stderr, "pub= "); 108 BN_print_fp(stderr, dh->pub_key); 109 fprintf(stderr, "\n"); 110 #endif 111 112 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 113 /* generate and send 'e', client DH public key */ 114 packet_start(SSH2_MSG_KEX_DH_GEX_INIT); 115 packet_put_bignum2(dh->pub_key); 116 packet_send(); 117 118 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY"); 119 packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY); 120 121 /* key, cert */ 122 server_host_key_blob = packet_get_string(&sbloblen); 123 server_host_key = key_from_blob(server_host_key_blob, sbloblen); 124 if (server_host_key == NULL) 125 fatal("cannot decode server_host_key_blob"); 126 if (server_host_key->type != kex->hostkey_type) 127 fatal("type mismatch for decoded server_host_key_blob"); 128 if (kex->verify_host_key == NULL) 129 fatal("cannot verify server_host_key"); 130 if (kex->verify_host_key(server_host_key) == -1) 131 fatal("server_host_key verification failed"); 132 133 /* DH parameter f, server public DH key */ 134 if ((dh_server_pub = BN_new()) == NULL) 135 fatal("dh_server_pub == NULL"); 136 packet_get_bignum2(dh_server_pub); 137 138 #ifdef DEBUG_KEXDH 139 fprintf(stderr, "dh_server_pub= "); 140 BN_print_fp(stderr, dh_server_pub); 141 fprintf(stderr, "\n"); 142 debug("bits %d", BN_num_bits(dh_server_pub)); 143 #endif 144 145 /* signed H */ 146 signature = packet_get_string(&slen); 147 packet_check_eom(); 148 149 if (!dh_pub_is_valid(dh, dh_server_pub)) 150 packet_disconnect("bad server public DH value"); 151 152 klen = DH_size(dh); 153 kbuf = xmalloc(klen); 154 if ((kout = DH_compute_key(kbuf, dh_server_pub, dh)) < 0) 155 fatal("DH_compute_key: failed"); 156 #ifdef DEBUG_KEXDH 157 dump_digest("shared secret", kbuf, kout); 158 #endif 159 if ((shared_secret = BN_new()) == NULL) 160 fatal("kexgex_client: BN_new failed"); 161 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL) 162 fatal("kexgex_client: BN_bin2bn failed"); 163 memset(kbuf, 0, klen); 164 xfree(kbuf); 165 166 if (datafellows & SSH_OLD_DHGEX) 167 min = max = -1; 168 169 /* calc and verify H */ 170 kexgex_hash( 171 kex->evp_md, 172 kex->client_version_string, 173 kex->server_version_string, 174 buffer_ptr(&kex->my), buffer_len(&kex->my), 175 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 176 server_host_key_blob, sbloblen, 177 min, nbits, max, 178 dh->p, dh->g, 179 dh->pub_key, 180 dh_server_pub, 181 shared_secret, 182 &hash, &hashlen 183 ); 184 185 /* have keys, free DH */ 186 DH_free(dh); 187 xfree(server_host_key_blob); 188 BN_clear_free(dh_server_pub); 189 190 if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1) 191 fatal("key_verify failed for server_host_key"); 192 key_free(server_host_key); 193 xfree(signature); 194 195 /* save session id */ 196 if (kex->session_id == NULL) { 197 kex->session_id_len = hashlen; 198 kex->session_id = xmalloc(kex->session_id_len); 199 memcpy(kex->session_id, hash, kex->session_id_len); 200 } 201 kex_derive_keys(kex, hash, hashlen, shared_secret); 202 BN_clear_free(shared_secret); 203 204 kex_finish(kex); 205 } 206