kexdh.c revision 76259
1/* 2 * Copyright (c) 2001 Markus Friedl. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 23 */ 24 25#include "includes.h" 26RCSID("$OpenBSD: kexdh.c,v 1.3 2001/04/04 09:48:34 markus Exp $"); 27 28#include <openssl/crypto.h> 29#include <openssl/bn.h> 30 31#include "xmalloc.h" 32#include "buffer.h" 33#include "bufaux.h" 34#include "key.h" 35#include "kex.h" 36#include "log.h" 37#include "packet.h" 38#include "dh.h" 39#include "ssh2.h" 40 41u_char * 42kex_dh_hash( 43 char *client_version_string, 44 char *server_version_string, 45 char *ckexinit, int ckexinitlen, 46 char *skexinit, int skexinitlen, 47 char *serverhostkeyblob, int sbloblen, 48 BIGNUM *client_dh_pub, 49 BIGNUM *server_dh_pub, 50 BIGNUM *shared_secret) 51{ 52 Buffer b; 53 static u_char digest[EVP_MAX_MD_SIZE]; 54 EVP_MD *evp_md = EVP_sha1(); 55 EVP_MD_CTX md; 56 57 buffer_init(&b); 58 buffer_put_string(&b, client_version_string, strlen(client_version_string)); 59 buffer_put_string(&b, server_version_string, strlen(server_version_string)); 60 61 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ 62 buffer_put_int(&b, ckexinitlen+1); 63 buffer_put_char(&b, SSH2_MSG_KEXINIT); 64 buffer_append(&b, ckexinit, ckexinitlen); 65 buffer_put_int(&b, skexinitlen+1); 66 buffer_put_char(&b, SSH2_MSG_KEXINIT); 67 buffer_append(&b, skexinit, skexinitlen); 68 69 buffer_put_string(&b, serverhostkeyblob, sbloblen); 70 buffer_put_bignum2(&b, client_dh_pub); 71 buffer_put_bignum2(&b, server_dh_pub); 72 buffer_put_bignum2(&b, shared_secret); 73 74#ifdef DEBUG_KEX 75 buffer_dump(&b); 76#endif 77 EVP_DigestInit(&md, evp_md); 78 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 79 EVP_DigestFinal(&md, digest, NULL); 80 81 buffer_free(&b); 82 83#ifdef DEBUG_KEX 84 dump_digest("hash", digest, evp_md->md_size); 85#endif 86 return digest; 87} 88 89/* client */ 90 91void 92kexdh_client(Kex *kex) 93{ 94 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 95 DH *dh; 96 Key *server_host_key; 97 char *server_host_key_blob = NULL, *signature = NULL; 98 u_char *kbuf, *hash; 99 u_int klen, kout, slen, sbloblen; 100 int dlen, plen; 101 102 /* generate and send 'e', client DH public key */ 103 dh = dh_new_group1(); 104 dh_gen_key(dh, kex->we_need * 8); 105 packet_start(SSH2_MSG_KEXDH_INIT); 106 packet_put_bignum2(dh->pub_key); 107 packet_send(); 108 109 debug("sending SSH2_MSG_KEXDH_INIT"); 110#ifdef DEBUG_KEXDH 111 DHparams_print_fp(stderr, dh); 112 fprintf(stderr, "pub= "); 113 BN_print_fp(stderr, dh->pub_key); 114 fprintf(stderr, "\n"); 115#endif 116 117 debug("expecting SSH2_MSG_KEXDH_REPLY"); 118 packet_read_expect(&plen, SSH2_MSG_KEXDH_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"); 125 126 if (kex->check_host_key == NULL) 127 fatal("cannot check server_host_key"); 128 kex->check_host_key(server_host_key); 129 130 /* DH paramter f, server public DH key */ 131 dh_server_pub = BN_new(); 132 if (dh_server_pub == NULL) 133 fatal("dh_server_pub == NULL"); 134 packet_get_bignum2(dh_server_pub, &dlen); 135 136#ifdef DEBUG_KEXDH 137 fprintf(stderr, "dh_server_pub= "); 138 BN_print_fp(stderr, dh_server_pub); 139 fprintf(stderr, "\n"); 140 debug("bits %d", BN_num_bits(dh_server_pub)); 141#endif 142 143 /* signed H */ 144 signature = packet_get_string(&slen); 145 packet_done(); 146 147 if (!dh_pub_is_valid(dh, dh_server_pub)) 148 packet_disconnect("bad server public DH value"); 149 150 klen = DH_size(dh); 151 kbuf = xmalloc(klen); 152 kout = DH_compute_key(kbuf, dh_server_pub, dh); 153#ifdef DEBUG_KEXDH 154 dump_digest("shared secret", kbuf, kout); 155#endif 156 shared_secret = BN_new(); 157 BN_bin2bn(kbuf, kout, shared_secret); 158 memset(kbuf, 0, klen); 159 xfree(kbuf); 160 161 /* calc and verify H */ 162 hash = kex_dh_hash( 163 kex->client_version_string, 164 kex->server_version_string, 165 buffer_ptr(&kex->my), buffer_len(&kex->my), 166 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 167 server_host_key_blob, sbloblen, 168 dh->pub_key, 169 dh_server_pub, 170 shared_secret 171 ); 172 xfree(server_host_key_blob); 173 BN_free(dh_server_pub); 174 DH_free(dh); 175 176 if (key_verify(server_host_key, (u_char *)signature, slen, hash, 20) != 1) 177 fatal("key_verify failed for server_host_key"); 178 key_free(server_host_key); 179 xfree(signature); 180 181 /* save session id */ 182 if (kex->session_id == NULL) { 183 kex->session_id_len = 20; 184 kex->session_id = xmalloc(kex->session_id_len); 185 memcpy(kex->session_id, hash, kex->session_id_len); 186 } 187 188 kex_derive_keys(kex, hash, shared_secret); 189 BN_clear_free(shared_secret); 190 kex_finish(kex); 191} 192 193/* server */ 194 195void 196kexdh_server(Kex *kex) 197{ 198 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 199 DH *dh; 200 Key *server_host_key; 201 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 202 u_int sbloblen, klen, kout; 203 int dlen, slen, plen; 204 205 /* generate server DH public key */ 206 dh = dh_new_group1(); 207 dh_gen_key(dh, kex->we_need * 8); 208 209 debug("expecting SSH2_MSG_KEXDH_INIT"); 210 packet_read_expect(&plen, SSH2_MSG_KEXDH_INIT); 211 212 if (kex->load_host_key == NULL) 213 fatal("Cannot load hostkey"); 214 server_host_key = kex->load_host_key(kex->hostkey_type); 215 if (server_host_key == NULL) 216 fatal("Unsupported hostkey type %d", kex->hostkey_type); 217 218 /* key, cert */ 219 dh_client_pub = BN_new(); 220 if (dh_client_pub == NULL) 221 fatal("dh_client_pub == NULL"); 222 packet_get_bignum2(dh_client_pub, &dlen); 223 224#ifdef DEBUG_KEXDH 225 fprintf(stderr, "dh_client_pub= "); 226 BN_print_fp(stderr, dh_client_pub); 227 fprintf(stderr, "\n"); 228 debug("bits %d", BN_num_bits(dh_client_pub)); 229#endif 230 231#ifdef DEBUG_KEXDH 232 DHparams_print_fp(stderr, dh); 233 fprintf(stderr, "pub= "); 234 BN_print_fp(stderr, dh->pub_key); 235 fprintf(stderr, "\n"); 236#endif 237 if (!dh_pub_is_valid(dh, dh_client_pub)) 238 packet_disconnect("bad client public DH value"); 239 240 klen = DH_size(dh); 241 kbuf = xmalloc(klen); 242 kout = DH_compute_key(kbuf, dh_client_pub, dh); 243#ifdef DEBUG_KEXDH 244 dump_digest("shared secret", kbuf, kout); 245#endif 246 shared_secret = BN_new(); 247 BN_bin2bn(kbuf, kout, shared_secret); 248 memset(kbuf, 0, klen); 249 xfree(kbuf); 250 251 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 252 253 /* calc H */ 254 hash = kex_dh_hash( 255 kex->client_version_string, 256 kex->server_version_string, 257 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 258 buffer_ptr(&kex->my), buffer_len(&kex->my), 259 (char *)server_host_key_blob, sbloblen, 260 dh_client_pub, 261 dh->pub_key, 262 shared_secret 263 ); 264 BN_free(dh_client_pub); 265 266 /* save session id := H */ 267 /* XXX hashlen depends on KEX */ 268 if (kex->session_id == NULL) { 269 kex->session_id_len = 20; 270 kex->session_id = xmalloc(kex->session_id_len); 271 memcpy(kex->session_id, hash, kex->session_id_len); 272 } 273 274 /* sign H */ 275 /* XXX hashlen depends on KEX */ 276 key_sign(server_host_key, &signature, &slen, hash, 20); 277 278 /* destroy_sensitive_data(); */ 279 280 /* send server hostkey, DH pubkey 'f' and singed H */ 281 packet_start(SSH2_MSG_KEXDH_REPLY); 282 packet_put_string((char *)server_host_key_blob, sbloblen); 283 packet_put_bignum2(dh->pub_key); /* f */ 284 packet_put_string((char *)signature, slen); 285 packet_send(); 286 287 xfree(signature); 288 xfree(server_host_key_blob); 289 /* have keys, free DH */ 290 DH_free(dh); 291 292 kex_derive_keys(kex, hash, shared_secret); 293 BN_clear_free(shared_secret); 294 kex_finish(kex); 295} 296 297void 298kexdh(Kex *kex) 299{ 300 if (kex->server) 301 kexdh_server(kex); 302 else 303 kexdh_client(kex); 304} 305