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 1.18 2002/03/18 17:50:31 provos Exp $"); 27 28 #pragma ident "%Z%%M% %I% %E% SMI" 29 30 #include <openssl/crypto.h> 31 #include <openssl/bn.h> 32 33 #include "xmalloc.h" 34 #include "buffer.h" 35 #include "bufaux.h" 36 #include "key.h" 37 #include "kex.h" 38 #include "log.h" 39 #include "packet.h" 40 #include "dh.h" 41 #include "ssh2.h" 42 #include "monitor_wrap.h" 43 44 void 45 kexdh_client(Kex *kex) 46 { 47 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 48 DH *dh; 49 Key *server_host_key; 50 u_char *server_host_key_blob = NULL, *signature = NULL; 51 u_char *kbuf, *hash; 52 u_int klen, kout, slen, sbloblen; 53 54 /* generate and send 'e', client DH public key */ 55 dh = dh_new_group1(); 56 dh_gen_key(dh, kex->we_need * 8); 57 packet_start(SSH2_MSG_KEXDH_INIT); 58 packet_put_bignum2(dh->pub_key); 59 packet_send(); 60 61 debug("sending SSH2_MSG_KEXDH_INIT"); 62 #ifdef DEBUG_KEXDH 63 DHparams_print_fp(stderr, dh); 64 fprintf(stderr, "pub= "); 65 BN_print_fp(stderr, dh->pub_key); 66 fprintf(stderr, "\n"); 67 #endif 68 69 debug("expecting SSH2_MSG_KEXDH_REPLY"); 70 packet_read_expect(SSH2_MSG_KEXDH_REPLY); 71 72 /* key, cert */ 73 server_host_key_blob = packet_get_string(&sbloblen); 74 server_host_key = key_from_blob(server_host_key_blob, sbloblen); 75 if (server_host_key == NULL) 76 fatal("cannot decode server_host_key_blob"); 77 if (server_host_key->type != kex->hostkey_type) 78 fatal("type mismatch for decoded server_host_key_blob"); 79 if (kex->verify_host_key == NULL) 80 fatal("cannot verify server_host_key"); 81 if (kex->verify_host_key(server_host_key) == -1) 82 fatal("server_host_key verification failed"); 83 84 /* DH paramter f, server public DH key */ 85 if ((dh_server_pub = BN_new()) == NULL) 86 fatal("dh_server_pub == NULL"); 87 packet_get_bignum2(dh_server_pub); 88 89 #ifdef DEBUG_KEXDH 90 fprintf(stderr, "dh_server_pub= "); 91 BN_print_fp(stderr, dh_server_pub); 92 fprintf(stderr, "\n"); 93 debug("bits %d", BN_num_bits(dh_server_pub)); 94 #endif 95 96 /* signed H */ 97 signature = packet_get_string(&slen); 98 packet_check_eom(); 99 100 if (!dh_pub_is_valid(dh, dh_server_pub)) 101 packet_disconnect("bad server public DH value"); 102 103 klen = DH_size(dh); 104 kbuf = xmalloc(klen); 105 kout = DH_compute_key(kbuf, dh_server_pub, dh); 106 #ifdef DEBUG_KEXDH 107 dump_digest("shared secret", kbuf, kout); 108 #endif 109 if ((shared_secret = BN_new()) == NULL) 110 fatal("kexdh_client: BN_new failed"); 111 BN_bin2bn(kbuf, kout, shared_secret); 112 memset(kbuf, 0, klen); 113 xfree(kbuf); 114 115 /* calc and verify H */ 116 hash = kex_dh_hash( 117 kex->client_version_string, 118 kex->server_version_string, 119 buffer_ptr(&kex->my), buffer_len(&kex->my), 120 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 121 server_host_key_blob, sbloblen, 122 dh->pub_key, 123 dh_server_pub, 124 shared_secret 125 ); 126 xfree(server_host_key_blob); 127 BN_clear_free(dh_server_pub); 128 DH_free(dh); 129 130 if (key_verify(server_host_key, signature, slen, hash, 20) != 1) 131 fatal("key_verify failed for server_host_key"); 132 key_free(server_host_key); 133 xfree(signature); 134 135 /* save session id */ 136 if (kex->session_id == NULL) { 137 kex->session_id_len = 20; 138 kex->session_id = xmalloc(kex->session_id_len); 139 memcpy(kex->session_id, hash, kex->session_id_len); 140 } 141 142 kex_derive_keys(kex, hash, shared_secret); 143 BN_clear_free(shared_secret); 144 kex_finish(kex); 145 } 146