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" 26 RCSID("$OpenBSD: kexdh.c,v 1.6 2001/06/23 15:12:18 itojun 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 41 static u_char * 42 kex_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_cstring(&b, client_version_string); 59 buffer_put_cstring(&b, 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 91 static void 92 kexdh_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->verify_host_key == NULL) 127 fatal("cannot verify server_host_key"); 128 if (kex->verify_host_key(server_host_key) == -1) 129 fatal("server_host_key verification failed"); 130 131 /* DH paramter f, server public DH key */ 132 dh_server_pub = BN_new(); 133 if (dh_server_pub == NULL) 134 fatal("dh_server_pub == NULL"); 135 packet_get_bignum2(dh_server_pub, &dlen); 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_done(); 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 shared_secret = BN_new(); 158 BN_bin2bn(kbuf, kout, shared_secret); 159 memset(kbuf, 0, klen); 160 xfree(kbuf); 161 162 /* calc and verify H */ 163 hash = kex_dh_hash( 164 kex->client_version_string, 165 kex->server_version_string, 166 buffer_ptr(&kex->my), buffer_len(&kex->my), 167 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 168 server_host_key_blob, sbloblen, 169 dh->pub_key, 170 dh_server_pub, 171 shared_secret 172 ); 173 xfree(server_host_key_blob); 174 BN_free(dh_server_pub); 175 DH_free(dh); 176 177 if (key_verify(server_host_key, (u_char *)signature, slen, hash, 20) != 1) 178 fatal("key_verify failed for server_host_key"); 179 key_free(server_host_key); 180 xfree(signature); 181 182 /* save session id */ 183 if (kex->session_id == NULL) { 184 kex->session_id_len = 20; 185 kex->session_id = xmalloc(kex->session_id_len); 186 memcpy(kex->session_id, hash, kex->session_id_len); 187 } 188 189 kex_derive_keys(kex, hash, shared_secret); 190 BN_clear_free(shared_secret); 191 kex_finish(kex); 192 } 193 194 /* server */ 195 196 static void 197 kexdh_server(Kex *kex) 198 { 199 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 200 DH *dh; 201 Key *server_host_key; 202 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 203 u_int sbloblen, klen, kout; 204 int dlen, slen, plen; 205 206 /* generate server DH public key */ 207 dh = dh_new_group1(); 208 dh_gen_key(dh, kex->we_need * 8); 209 210 debug("expecting SSH2_MSG_KEXDH_INIT"); 211 packet_read_expect(&plen, SSH2_MSG_KEXDH_INIT); 212 213 if (kex->load_host_key == NULL) 214 fatal("Cannot load hostkey"); 215 server_host_key = kex->load_host_key(kex->hostkey_type); 216 if (server_host_key == NULL) 217 fatal("Unsupported hostkey type %d", kex->hostkey_type); 218 219 /* key, cert */ 220 dh_client_pub = BN_new(); 221 if (dh_client_pub == NULL) 222 fatal("dh_client_pub == NULL"); 223 packet_get_bignum2(dh_client_pub, &dlen); 224 225 #ifdef DEBUG_KEXDH 226 fprintf(stderr, "dh_client_pub= "); 227 BN_print_fp(stderr, dh_client_pub); 228 fprintf(stderr, "\n"); 229 debug("bits %d", BN_num_bits(dh_client_pub)); 230 #endif 231 232 #ifdef DEBUG_KEXDH 233 DHparams_print_fp(stderr, dh); 234 fprintf(stderr, "pub= "); 235 BN_print_fp(stderr, dh->pub_key); 236 fprintf(stderr, "\n"); 237 #endif 238 if (!dh_pub_is_valid(dh, dh_client_pub)) 239 packet_disconnect("bad client public DH value"); 240 241 klen = DH_size(dh); 242 kbuf = xmalloc(klen); 243 kout = DH_compute_key(kbuf, dh_client_pub, dh); 244 #ifdef DEBUG_KEXDH 245 dump_digest("shared secret", kbuf, kout); 246 #endif 247 shared_secret = BN_new(); 248 BN_bin2bn(kbuf, kout, shared_secret); 249 memset(kbuf, 0, klen); 250 xfree(kbuf); 251 252 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 253 254 /* calc H */ 255 hash = kex_dh_hash( 256 kex->client_version_string, 257 kex->server_version_string, 258 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 259 buffer_ptr(&kex->my), buffer_len(&kex->my), 260 (char *)server_host_key_blob, sbloblen, 261 dh_client_pub, 262 dh->pub_key, 263 shared_secret 264 ); 265 BN_free(dh_client_pub); 266 267 /* save session id := H */ 268 /* XXX hashlen depends on KEX */ 269 if (kex->session_id == NULL) { 270 kex->session_id_len = 20; 271 kex->session_id = xmalloc(kex->session_id_len); 272 memcpy(kex->session_id, hash, kex->session_id_len); 273 } 274 275 /* sign H */ 276 /* XXX hashlen depends on KEX */ 277 key_sign(server_host_key, &signature, &slen, hash, 20); 278 279 /* destroy_sensitive_data(); */ 280 281 /* send server hostkey, DH pubkey 'f' and singed H */ 282 packet_start(SSH2_MSG_KEXDH_REPLY); 283 packet_put_string((char *)server_host_key_blob, sbloblen); 284 packet_put_bignum2(dh->pub_key); /* f */ 285 packet_put_string((char *)signature, slen); 286 packet_send(); 287 288 xfree(signature); 289 xfree(server_host_key_blob); 290 /* have keys, free DH */ 291 DH_free(dh); 292 293 kex_derive_keys(kex, hash, shared_secret); 294 BN_clear_free(shared_secret); 295 kex_finish(kex); 296 } 297 298 void 299 kexdh(Kex *kex) 300 { 301 if (kex->server) 302 kexdh_server(kex); 303 else 304 kexdh_client(kex); 305 } 306