Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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" |
Ben Lindstrom | 664408d | 2001-06-09 01:42:01 +0000 | [diff] [blame] | 26 | RCSID("$OpenBSD: kexdh.c,v 1.4 2001/06/07 20:23:04 markus Exp $"); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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 | 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); |
Ben Lindstrom | 664408d | 2001-06-09 01:42:01 +0000 | [diff] [blame] | 58 | buffer_put_cstring(&b, client_version_string); |
| 59 | buffer_put_cstring(&b, server_version_string); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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 | 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->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); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 173 | BN_free(dh_server_pub); |
Ben Lindstrom | 238abf6 | 2001-04-04 17:52:53 +0000 | [diff] [blame] | 174 | DH_free(dh); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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); |
Ben Lindstrom | 238abf6 | 2001-04-04 17:52:53 +0000 | [diff] [blame] | 190 | kex_finish(kex); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 191 | } |
| 192 | |
| 193 | /* server */ |
| 194 | |
| 195 | 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 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(); |
Ben Lindstrom | 238abf6 | 2001-04-04 17:52:53 +0000 | [diff] [blame] | 286 | |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 287 | xfree(signature); |
| 288 | xfree(server_host_key_blob); |
Ben Lindstrom | 238abf6 | 2001-04-04 17:52:53 +0000 | [diff] [blame] | 289 | /* have keys, free DH */ |
| 290 | DH_free(dh); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 291 | |
| 292 | kex_derive_keys(kex, hash, shared_secret); |
| 293 | BN_clear_free(shared_secret); |
Ben Lindstrom | 238abf6 | 2001-04-04 17:52:53 +0000 | [diff] [blame] | 294 | kex_finish(kex); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 295 | } |
| 296 | |
| 297 | void |
| 298 | kexdh(Kex *kex) |
| 299 | { |
| 300 | if (kex->server) |
| 301 | kexdh_server(kex); |
| 302 | else |
| 303 | kexdh_client(kex); |
| 304 | } |