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 1.12 2001/12/28 14:50:54 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 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 u_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 u_char *server_host_key_blob = NULL, *signature = NULL; 98 u_char *kbuf, *hash; 99 u_int klen, kout, slen, sbloblen; 100 101 /* generate and send 'e', client DH public key */ 102 dh = dh_new_group1(); 103 dh_gen_key(dh, kex->we_need * 8); 104 packet_start(SSH2_MSG_KEXDH_INIT); 105 packet_put_bignum2(dh->pub_key); 106 packet_send(); 107 108 debug("sending SSH2_MSG_KEXDH_INIT"); 109 #ifdef DEBUG_KEXDH 110 DHparams_print_fp(stderr, dh); 111 fprintf(stderr, "pub= "); 112 BN_print_fp(stderr, dh->pub_key); 113 fprintf(stderr, "\n"); 114 #endif 115 116 debug("expecting SSH2_MSG_KEXDH_REPLY"); 117 packet_read_expect(SSH2_MSG_KEXDH_REPLY); 118 119 /* key, cert */ 120 server_host_key_blob = packet_get_string(&sbloblen); 121 server_host_key = key_from_blob(server_host_key_blob, sbloblen); 122 if (server_host_key == NULL) 123 fatal("cannot decode server_host_key_blob"); 124 125 if (kex->verify_host_key == NULL) 126 fatal("cannot verify server_host_key"); 127 if (kex->verify_host_key(server_host_key) == -1) 128 fatal("server_host_key verification failed"); 129 130 /* DH paramter f, server public DH key */ 131 if ((dh_server_pub = BN_new()) == NULL) 132 fatal("dh_server_pub == NULL"); 133 packet_get_bignum2(dh_server_pub); 134 135 #ifdef DEBUG_KEXDH 136 fprintf(stderr, "dh_server_pub= "); 137 BN_print_fp(stderr, dh_server_pub); 138 fprintf(stderr, "\n"); 139 debug("bits %d", BN_num_bits(dh_server_pub)); 140 #endif 141 142 /* signed H */ 143 signature = packet_get_string(&slen); 144 packet_check_eom(); 145 146 if (!dh_pub_is_valid(dh, dh_server_pub)) 147 packet_disconnect("bad server public DH value"); 148 149 klen = DH_size(dh); 150 kbuf = xmalloc(klen); 151 kout = DH_compute_key(kbuf, dh_server_pub, dh); 152 #ifdef DEBUG_KEXDH 153 dump_digest("shared secret", kbuf, kout); 154 #endif 155 if ((shared_secret = BN_new()) == NULL) 156 fatal("kexdh_client: BN_new failed"); 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_clear_free(dh_server_pub); 174 DH_free(dh); 175 176 if (key_verify(server_host_key, 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 */ 194 195 static void 196 kexdh_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 slen; 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(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 if ((dh_client_pub = BN_new()) == NULL) 220 fatal("dh_client_pub == NULL"); 221 packet_get_bignum2(dh_client_pub); 222 223 #ifdef DEBUG_KEXDH 224 fprintf(stderr, "dh_client_pub= "); 225 BN_print_fp(stderr, dh_client_pub); 226 fprintf(stderr, "\n"); 227 debug("bits %d", BN_num_bits(dh_client_pub)); 228 #endif 229 230 #ifdef DEBUG_KEXDH 231 DHparams_print_fp(stderr, dh); 232 fprintf(stderr, "pub= "); 233 BN_print_fp(stderr, dh->pub_key); 234 fprintf(stderr, "\n"); 235 #endif 236 if (!dh_pub_is_valid(dh, dh_client_pub)) 237 packet_disconnect("bad client public DH value"); 238 239 klen = DH_size(dh); 240 kbuf = xmalloc(klen); 241 kout = DH_compute_key(kbuf, dh_client_pub, dh); 242 #ifdef DEBUG_KEXDH 243 dump_digest("shared secret", kbuf, kout); 244 #endif 245 if ((shared_secret = BN_new()) == NULL) 246 fatal("kexdh_server: BN_new failed"); 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 server_host_key_blob, sbloblen, 260 dh_client_pub, 261 dh->pub_key, 262 shared_secret 263 ); 264 BN_clear_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(server_host_key_blob, sbloblen); 283 packet_put_bignum2(dh->pub_key); /* f */ 284 packet_put_string(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 } 296 297 void 298 kexdh(Kex *kex) 299 { 300 if (kex->server) 301 kexdh_server(kex); 302 else 303 kexdh_client(kex); 304 } 305