kexdhc.c revision 264377
1/* $OpenBSD: kexdhc.c,v 1.15 2014/02/02 03:44:31 djm Exp $ */ 2/* 3 * Copyright (c) 2001 Markus Friedl. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 */ 25 26#include "includes.h" 27 28#include <sys/types.h> 29 30#include <openssl/dh.h> 31 32#include <stdarg.h> 33#include <stdio.h> 34#include <string.h> 35#include <signal.h> 36 37#include "xmalloc.h" 38#include "buffer.h" 39#include "key.h" 40#include "cipher.h" 41#include "kex.h" 42#include "log.h" 43#include "packet.h" 44#include "dh.h" 45#include "ssh2.h" 46 47void 48kexdh_client(Kex *kex) 49{ 50 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 51 DH *dh; 52 Key *server_host_key; 53 u_char *server_host_key_blob = NULL, *signature = NULL; 54 u_char *kbuf, *hash; 55 u_int klen, slen, sbloblen, hashlen; 56 int kout; 57 58 /* generate and send 'e', client DH public key */ 59 switch (kex->kex_type) { 60 case KEX_DH_GRP1_SHA1: 61 dh = dh_new_group1(); 62 break; 63 case KEX_DH_GRP14_SHA1: 64 dh = dh_new_group14(); 65 break; 66 default: 67 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type); 68 } 69 dh_gen_key(dh, kex->we_need * 8); 70 packet_start(SSH2_MSG_KEXDH_INIT); 71 packet_put_bignum2(dh->pub_key); 72 packet_send(); 73 74 debug("sending SSH2_MSG_KEXDH_INIT"); 75#ifdef DEBUG_KEXDH 76 DHparams_print_fp(stderr, dh); 77 fprintf(stderr, "pub= "); 78 BN_print_fp(stderr, dh->pub_key); 79 fprintf(stderr, "\n"); 80#endif 81 82 debug("expecting SSH2_MSG_KEXDH_REPLY"); 83 packet_read_expect(SSH2_MSG_KEXDH_REPLY); 84 85 /* key, cert */ 86 server_host_key_blob = packet_get_string(&sbloblen); 87 server_host_key = key_from_blob(server_host_key_blob, sbloblen); 88 if (server_host_key == NULL) 89 fatal("cannot decode server_host_key_blob"); 90 if (server_host_key->type != kex->hostkey_type) 91 fatal("type mismatch for decoded server_host_key_blob"); 92 if (kex->verify_host_key == NULL) 93 fatal("cannot verify server_host_key"); 94 if (kex->verify_host_key(server_host_key) == -1) 95 fatal("server_host_key verification failed"); 96 97 /* DH parameter f, server public DH key */ 98 if ((dh_server_pub = BN_new()) == NULL) 99 fatal("dh_server_pub == NULL"); 100 packet_get_bignum2(dh_server_pub); 101 102#ifdef DEBUG_KEXDH 103 fprintf(stderr, "dh_server_pub= "); 104 BN_print_fp(stderr, dh_server_pub); 105 fprintf(stderr, "\n"); 106 debug("bits %d", BN_num_bits(dh_server_pub)); 107#endif 108 109 /* signed H */ 110 signature = packet_get_string(&slen); 111 packet_check_eom(); 112 113 if (!dh_pub_is_valid(dh, dh_server_pub)) 114 packet_disconnect("bad server public DH value"); 115 116 klen = DH_size(dh); 117 kbuf = xmalloc(klen); 118 if ((kout = DH_compute_key(kbuf, dh_server_pub, dh)) < 0) 119 fatal("DH_compute_key: failed"); 120#ifdef DEBUG_KEXDH 121 dump_digest("shared secret", kbuf, kout); 122#endif 123 if ((shared_secret = BN_new()) == NULL) 124 fatal("kexdh_client: BN_new failed"); 125 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL) 126 fatal("kexdh_client: BN_bin2bn failed"); 127 explicit_bzero(kbuf, klen); 128 free(kbuf); 129 130 /* calc and verify H */ 131 kex_dh_hash( 132 kex->client_version_string, 133 kex->server_version_string, 134 buffer_ptr(&kex->my), buffer_len(&kex->my), 135 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 136 server_host_key_blob, sbloblen, 137 dh->pub_key, 138 dh_server_pub, 139 shared_secret, 140 &hash, &hashlen 141 ); 142 free(server_host_key_blob); 143 BN_clear_free(dh_server_pub); 144 DH_free(dh); 145 146 if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1) 147 fatal("key_verify failed for server_host_key"); 148 key_free(server_host_key); 149 free(signature); 150 151 /* save session id */ 152 if (kex->session_id == NULL) { 153 kex->session_id_len = hashlen; 154 kex->session_id = xmalloc(kex->session_id_len); 155 memcpy(kex->session_id, hash, kex->session_id_len); 156 } 157 158 kex_derive_keys_bn(kex, hash, hashlen, shared_secret); 159 BN_clear_free(shared_secret); 160 kex_finish(kex); 161} 162