kexdh.c revision 92555
1193326Sed/* 2193326Sed * Copyright (c) 2001 Markus Friedl. All rights reserved. 3193326Sed * 4193326Sed * Redistribution and use in source and binary forms, with or without 5193326Sed * modification, are permitted provided that the following conditions 6193326Sed * are met: 7193326Sed * 1. Redistributions of source code must retain the above copyright 8193326Sed * notice, this list of conditions and the following disclaimer. 9193326Sed * 2. Redistributions in binary form must reproduce the above copyright 10193326Sed * notice, this list of conditions and the following disclaimer in the 11193326Sed * documentation and/or other materials provided with the distribution. 12193326Sed * 13193326Sed * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 14193326Sed * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 15249423Sdim * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 16263508Sdim * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 17249423Sdim * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 18249423Sdim * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 19249423Sdim * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 20193326Sed * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 21239462Sdim * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 22212904Sdim * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 23212904Sdim */ 24249423Sdim 25193326Sed#include "includes.h" 26234353SdimRCSID("$OpenBSD: kexdh.c,v 1.17 2002/02/28 15:46:33 markus Exp $"); 27226633Sdim 28193326Sed#include <openssl/crypto.h> 29193326Sed#include <openssl/bn.h> 30193326Sed 31193326Sed#include "xmalloc.h" 32193326Sed#include "buffer.h" 33193326Sed#include "bufaux.h" 34193326Sed#include "key.h" 35193326Sed#include "kex.h" 36193326Sed#include "log.h" 37193326Sed#include "packet.h" 38193326Sed#include "dh.h" 39218893Sdim#include "ssh2.h" 40224145Sdim 41224145Sdimstatic u_char * 42249423Sdimkex_dh_hash( 43249423Sdim char *client_version_string, 44234353Sdim char *server_version_string, 45239462Sdim char *ckexinit, int ckexinitlen, 46239462Sdim char *skexinit, int skexinitlen, 47234353Sdim u_char *serverhostkeyblob, int sbloblen, 48193326Sed BIGNUM *client_dh_pub, 49221345Sdim BIGNUM *server_dh_pub, 50249423Sdim BIGNUM *shared_secret) 51249423Sdim{ 52234353Sdim Buffer b; 53224145Sdim static u_char digest[EVP_MAX_MD_SIZE]; 54224145Sdim const EVP_MD *evp_md = EVP_sha1(); 55193326Sed EVP_MD_CTX md; 56193326Sed 57218893Sdim buffer_init(&b); 58193326Sed buffer_put_cstring(&b, client_version_string); 59193326Sed buffer_put_cstring(&b, server_version_string); 60193326Sed 61193326Sed /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ 62193326Sed buffer_put_int(&b, ckexinitlen+1); 63193326Sed buffer_put_char(&b, SSH2_MSG_KEXINIT); 64193326Sed buffer_append(&b, ckexinit, ckexinitlen); 65210299Sed buffer_put_int(&b, skexinitlen+1); 66193326Sed buffer_put_char(&b, SSH2_MSG_KEXINIT); 67193326Sed buffer_append(&b, skexinit, skexinitlen); 68226633Sdim 69226633Sdim buffer_put_string(&b, serverhostkeyblob, sbloblen); 70226633Sdim buffer_put_bignum2(&b, client_dh_pub); 71226633Sdim buffer_put_bignum2(&b, server_dh_pub); 72226633Sdim buffer_put_bignum2(&b, shared_secret); 73226633Sdim 74226633Sdim#ifdef DEBUG_KEX 75226633Sdim buffer_dump(&b); 76226633Sdim#endif 77199990Srdivacky EVP_DigestInit(&md, evp_md); 78193326Sed EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 79193326Sed EVP_DigestFinal(&md, digest, NULL); 80193326Sed 81193326Sed buffer_free(&b); 82193326Sed 83193326Sed#ifdef DEBUG_KEX 84193326Sed dump_digest("hash", digest, EVP_MD_size(evp_md)); 85193326Sed#endif 86193326Sed return digest; 87193326Sed} 88193326Sed 89193326Sed/* client */ 90193326Sed 91193326Sedstatic void 92193326Sedkexdh_client(Kex *kex) 93193326Sed{ 94193326Sed BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 95193326Sed DH *dh; 96193326Sed Key *server_host_key; 97193326Sed u_char *server_host_key_blob = NULL, *signature = NULL; 98193326Sed u_char *kbuf, *hash; 99193326Sed u_int klen, kout, slen, sbloblen; 100193326Sed 101193326Sed /* generate and send 'e', client DH public key */ 102198092Srdivacky dh = dh_new_group1(); 103263508Sdim dh_gen_key(dh, kex->we_need * 8); 104263508Sdim packet_start(SSH2_MSG_KEXDH_INIT); 105193326Sed packet_put_bignum2(dh->pub_key); 106263508Sdim packet_send(); 107263508Sdim 108263508Sdim debug("sending SSH2_MSG_KEXDH_INIT"); 109263508Sdim#ifdef DEBUG_KEXDH 110263508Sdim DHparams_print_fp(stderr, dh); 111263508Sdim fprintf(stderr, "pub= "); 112263508Sdim BN_print_fp(stderr, dh->pub_key); 113263508Sdim fprintf(stderr, "\n"); 114263508Sdim#endif 115263508Sdim 116234353Sdim debug("expecting SSH2_MSG_KEXDH_REPLY"); 117263508Sdim packet_read_expect(SSH2_MSG_KEXDH_REPLY); 118218893Sdim 119226633Sdim /* key, cert */ 120226633Sdim server_host_key_blob = packet_get_string(&sbloblen); 121199990Srdivacky server_host_key = key_from_blob(server_host_key_blob, sbloblen); 122198092Srdivacky if (server_host_key == NULL) 123193326Sed fatal("cannot decode server_host_key_blob"); 124193326Sed if (server_host_key->type != kex->hostkey_type) 125193326Sed fatal("type mismatch for decoded server_host_key_blob"); 126193326Sed if (kex->verify_host_key == NULL) 127263508Sdim fatal("cannot verify server_host_key"); 128218893Sdim if (kex->verify_host_key(server_host_key) == -1) 129193326Sed fatal("server_host_key verification failed"); 130193326Sed 131263508Sdim /* DH paramter f, server public DH key */ 132218893Sdim if ((dh_server_pub = BN_new()) == NULL) 133193326Sed fatal("dh_server_pub == NULL"); 134193326Sed packet_get_bignum2(dh_server_pub); 135193326Sed 136193326Sed#ifdef DEBUG_KEXDH 137198092Srdivacky fprintf(stderr, "dh_server_pub= "); 138193326Sed BN_print_fp(stderr, dh_server_pub); 139193326Sed fprintf(stderr, "\n"); 140193326Sed debug("bits %d", BN_num_bits(dh_server_pub)); 141193326Sed#endif 142193326Sed 143193326Sed /* signed H */ 144193326Sed signature = packet_get_string(&slen); 145198092Srdivacky packet_check_eom(); 146226633Sdim 147226633Sdim if (!dh_pub_is_valid(dh, dh_server_pub)) 148234353Sdim packet_disconnect("bad server public DH value"); 149226633Sdim 150226633Sdim klen = DH_size(dh); 151226633Sdim kbuf = xmalloc(klen); 152198092Srdivacky kout = DH_compute_key(kbuf, dh_server_pub, dh); 153234353Sdim#ifdef DEBUG_KEXDH 154234353Sdim dump_digest("shared secret", kbuf, kout); 155243830Sdim#endif 156234353Sdim if ((shared_secret = BN_new()) == NULL) 157234353Sdim fatal("kexdh_client: BN_new failed"); 158226633Sdim BN_bin2bn(kbuf, kout, shared_secret); 159226633Sdim memset(kbuf, 0, klen); 160198092Srdivacky xfree(kbuf); 161226633Sdim 162226633Sdim /* calc and verify H */ 163226633Sdim hash = kex_dh_hash( 164226633Sdim kex->client_version_string, 165226633Sdim kex->server_version_string, 166243830Sdim buffer_ptr(&kex->my), buffer_len(&kex->my), 167243830Sdim buffer_ptr(&kex->peer), buffer_len(&kex->peer), 168193326Sed server_host_key_blob, sbloblen, 169193326Sed dh->pub_key, 170263508Sdim dh_server_pub, 171263508Sdim shared_secret 172193326Sed ); 173193326Sed xfree(server_host_key_blob); 174193326Sed BN_clear_free(dh_server_pub); 175263508Sdim DH_free(dh); 176199990Srdivacky 177263508Sdim if (key_verify(server_host_key, signature, slen, hash, 20) != 1) 178263508Sdim fatal("key_verify failed for server_host_key"); 179218893Sdim key_free(server_host_key); 180218893Sdim xfree(signature); 181193326Sed 182193326Sed /* save session id */ 183193326Sed if (kex->session_id == NULL) { 184263508Sdim kex->session_id_len = 20; 185263508Sdim kex->session_id = xmalloc(kex->session_id_len); 186263508Sdim memcpy(kex->session_id, hash, kex->session_id_len); 187263508Sdim } 188263508Sdim 189263508Sdim kex_derive_keys(kex, hash, shared_secret); 190263508Sdim BN_clear_free(shared_secret); 191263508Sdim kex_finish(kex); 192263508Sdim} 193263508Sdim 194263508Sdim/* server */ 195251662Sdim 196251662Sdimstatic void 197226633Sdimkexdh_server(Kex *kex) 198263508Sdim{ 199263508Sdim BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 200263508Sdim DH *dh; 201263508Sdim Key *server_host_key; 202263508Sdim u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 203263508Sdim u_int sbloblen, klen, kout; 204263508Sdim u_int slen; 205263508Sdim 206263508Sdim /* generate server DH public key */ 207263508Sdim dh = dh_new_group1(); 208263508Sdim dh_gen_key(dh, kex->we_need * 8); 209263508Sdim 210263508Sdim debug("expecting SSH2_MSG_KEXDH_INIT"); 211263508Sdim packet_read_expect(SSH2_MSG_KEXDH_INIT); 212263508Sdim 213263508Sdim if (kex->load_host_key == NULL) 214263508Sdim fatal("Cannot load hostkey"); 215263508Sdim server_host_key = kex->load_host_key(kex->hostkey_type); 216263508Sdim if (server_host_key == NULL) 217263508Sdim fatal("Unsupported hostkey type %d", kex->hostkey_type); 218263508Sdim 219263508Sdim /* key, cert */ 220263508Sdim if ((dh_client_pub = BN_new()) == NULL) 221263508Sdim fatal("dh_client_pub == NULL"); 222263508Sdim packet_get_bignum2(dh_client_pub); 223263508Sdim packet_check_eom(); 224263508Sdim 225263508Sdim#ifdef DEBUG_KEXDH 226263508Sdim fprintf(stderr, "dh_client_pub= "); 227263508Sdim BN_print_fp(stderr, dh_client_pub); 228263508Sdim fprintf(stderr, "\n"); 229263508Sdim debug("bits %d", BN_num_bits(dh_client_pub)); 230263508Sdim#endif 231263508Sdim 232263508Sdim#ifdef DEBUG_KEXDH 233263508Sdim DHparams_print_fp(stderr, dh); 234263508Sdim fprintf(stderr, "pub= "); 235263508Sdim BN_print_fp(stderr, dh->pub_key); 236263508Sdim fprintf(stderr, "\n"); 237263508Sdim#endif 238263508Sdim if (!dh_pub_is_valid(dh, dh_client_pub)) 239263508Sdim packet_disconnect("bad client public DH value"); 240243830Sdim 241243830Sdim klen = DH_size(dh); 242226633Sdim kbuf = xmalloc(klen); 243226633Sdim kout = DH_compute_key(kbuf, dh_client_pub, dh); 244226633Sdim#ifdef DEBUG_KEXDH 245243830Sdim dump_digest("shared secret", kbuf, kout); 246243830Sdim#endif 247243830Sdim if ((shared_secret = BN_new()) == NULL) 248243830Sdim fatal("kexdh_server: BN_new failed"); 249226633Sdim BN_bin2bn(kbuf, kout, shared_secret); 250226633Sdim memset(kbuf, 0, klen); 251226633Sdim xfree(kbuf); 252263508Sdim 253263508Sdim key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 254263508Sdim 255226633Sdim /* calc H */ 256263508Sdim hash = kex_dh_hash( 257263508Sdim kex->client_version_string, 258263508Sdim kex->server_version_string, 259226633Sdim buffer_ptr(&kex->peer), buffer_len(&kex->peer), 260226633Sdim buffer_ptr(&kex->my), buffer_len(&kex->my), 261226633Sdim server_host_key_blob, sbloblen, 262263508Sdim dh_client_pub, 263263508Sdim dh->pub_key, 264263508Sdim shared_secret 265226633Sdim ); 266226633Sdim BN_clear_free(dh_client_pub); 267226633Sdim 268226633Sdim /* save session id := H */ 269239462Sdim /* XXX hashlen depends on KEX */ 270263508Sdim if (kex->session_id == NULL) { 271239462Sdim kex->session_id_len = 20; 272239462Sdim kex->session_id = xmalloc(kex->session_id_len); 273239462Sdim memcpy(kex->session_id, hash, kex->session_id_len); 274263508Sdim } 275263508Sdim 276263508Sdim /* sign H */ 277263508Sdim /* XXX hashlen depends on KEX */ 278263508Sdim key_sign(server_host_key, &signature, &slen, hash, 20); 279226633Sdim 280263508Sdim /* destroy_sensitive_data(); */ 281263508Sdim 282226633Sdim /* send server hostkey, DH pubkey 'f' and singed H */ 283263508Sdim packet_start(SSH2_MSG_KEXDH_REPLY); 284226633Sdim packet_put_string(server_host_key_blob, sbloblen); 285263508Sdim packet_put_bignum2(dh->pub_key); /* f */ 286263508Sdim packet_put_string(signature, slen); 287263508Sdim packet_send(); 288249423Sdim 289263508Sdim xfree(signature); 290263508Sdim xfree(server_host_key_blob); 291263508Sdim /* have keys, free DH */ 292263508Sdim DH_free(dh); 293263508Sdim 294263508Sdim kex_derive_keys(kex, hash, shared_secret); 295249423Sdim BN_clear_free(shared_secret); 296234353Sdim kex_finish(kex); 297263508Sdim} 298263508Sdim 299234353Sdimvoid 300234353Sdimkexdh(Kex *kex) 301263508Sdim{ 302234353Sdim if (kex->server) 303263508Sdim kexdh_server(kex); 304226633Sdim else 305226633Sdim kexdh_client(kex); 306234353Sdim} 307234353Sdim