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