kexdhs.c

   1 /* $OpenBSD: kexdhs.c,v 1.26 2018/02/07 02:06:51 jsing 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 #ifdef WITH_OPENSSL
  29
  30 #include <sys/types.h>
  31
  32 #include <stdarg.h>
  33 #include <string.h>
  34 #include <signal.h>
  35
  36 #include <openssl/dh.h>
  37
  38 #include "sshkey.h"
  39 #include "cipher.h"
  40 #include "digest.h"
  41 #include "kex.h"
  42 #include "log.h"
  43 #include "packet.h"
  44 #include "dh.h"
  45 #include "ssh2.h"
  46
  47 #include "dispatch.h"
  48 #include "compat.h"
  49 #include "ssherr.h"
  50 #include "sshbuf.h"
  51
  52 static int input_kex_dh_init(int, u_int32_t, struct ssh *);
  53
  54 int
  55 kexdh_server(struct ssh *ssh)
  56 {
  57         struct kex *kex = ssh->kex;
  58         int r;
  59
  60         /* generate server DH public key */
  61         switch (kex->kex_type) {
  62         case KEX_DH_GRP1_SHA1:
  63                 kex->dh = dh_new_group1();
  64                 break;
  65         case KEX_DH_GRP14_SHA1:
  66         case KEX_DH_GRP14_SHA256:
  67                 kex->dh = dh_new_group14();
  68                 break;
  69         case KEX_DH_GRP16_SHA512:
  70                 kex->dh = dh_new_group16();
  71                 break;
  72         case KEX_DH_GRP18_SHA512:
  73                 kex->dh = dh_new_group18();
  74                 break;
  75         default:
  76                 r = SSH_ERR_INVALID_ARGUMENT;
  77                 goto out;
  78         }
  79         if (kex->dh == NULL) {
  80                 r = SSH_ERR_ALLOC_FAIL;
  81                 goto out;
  82         }
  83         if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
  84                 goto out;
  85
  86         debug("expecting SSH2_MSG_KEXDH_INIT");
  87         ssh_dispatch_set(ssh, SSH2_MSG_KEXDH_INIT, &input_kex_dh_init);
  88         r = 0;
  89  out:
  90         return r;
  91 }
  92
  93 int
  94 input_kex_dh_init(int type, u_int32_t seq, struct ssh *ssh)
  95 {
  96         struct kex *kex = ssh->kex;
  97         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  98         struct sshkey *server_host_public, *server_host_private;
  99         u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL;
 100         u_char hash[SSH_DIGEST_MAX_LENGTH];
 101         size_t sbloblen, slen;
 102         size_t klen = 0, hashlen;
 103         int kout, r;
 104
 105         if (kex->load_host_public_key == NULL ||
 106             kex->load_host_private_key == NULL) {
 107                 r = SSH_ERR_INVALID_ARGUMENT;
 108                 goto out;
 109         }
 110         server_host_public = kex->load_host_public_key(kex->hostkey_type,
 111             kex->hostkey_nid, ssh);
 112         server_host_private = kex->load_host_private_key(kex->hostkey_type,
 113             kex->hostkey_nid, ssh);
 114         if (server_host_public == NULL) {
 115                 r = SSH_ERR_NO_HOSTKEY_LOADED;
 116                 goto out;
 117         }
 118
 119         /* key, cert */
 120         if ((dh_client_pub = BN_new()) == NULL) {
 121                 r = SSH_ERR_ALLOC_FAIL;
 122                 goto out;
 123         }
 124         if ((r = sshpkt_get_bignum2(ssh, dh_client_pub)) != 0 ||
 125             (r = sshpkt_get_end(ssh)) != 0)
 126                 goto out;
 127
 128 #ifdef DEBUG_KEXDH
 129         fprintf(stderr, "dh_client_pub= ");
 130         BN_print_fp(stderr, dh_client_pub);
 131         fprintf(stderr, "\n");
 132         debug("bits %d", BN_num_bits(dh_client_pub));
 133 #endif
 134
 135 #ifdef DEBUG_KEXDH
 136         DHparams_print_fp(stderr, kex->dh);
 137         fprintf(stderr, "pub= ");
 138         BN_print_fp(stderr, kex->dh->pub_key);
 139         fprintf(stderr, "\n");
 140 #endif
 141         if (!dh_pub_is_valid(kex->dh, dh_client_pub)) {
 142                 sshpkt_disconnect(ssh, "bad client public DH value");
 143                 r = SSH_ERR_MESSAGE_INCOMPLETE;
 144                 goto out;
 145         }
 146
 147         klen = DH_size(kex->dh);
 148         if ((kbuf = malloc(klen)) == NULL ||
 149             (shared_secret = BN_new()) == NULL) {
 150                 r = SSH_ERR_ALLOC_FAIL;
 151                 goto out;
 152         }
 153         if ((kout = DH_compute_key(kbuf, dh_client_pub, kex->dh)) < 0 ||
 154             BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
 155                 r = SSH_ERR_LIBCRYPTO_ERROR;
 156                 goto out;
 157         }
 158 #ifdef DEBUG_KEXDH
 159         dump_digest("shared secret", kbuf, kout);
 160 #endif
 161         if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob,
 162             &sbloblen)) != 0)
 163                 goto out;
 164         /* calc H */
 165         hashlen = sizeof(hash);
 166         {
 167         const BIGNUM *pub_key;
 168         DH_get0_key(kex->dh, &pub_key, NULL);
 169         if ((r = kex_dh_hash(
 170             kex->hash_alg,
 171             kex->client_version_string,
 172             kex->server_version_string,
 173             sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
 174             sshbuf_ptr(kex->my), sshbuf_len(kex->my),
 175             server_host_key_blob, sbloblen,
 176             dh_client_pub,
 177             pub_key,
 178             shared_secret,
 179             hash, &hashlen)) != 0) {
 180                 goto out;
 181         }
 182         }
 183
 184         /* save session id := H */
 185         if (kex->session_id == NULL) {
 186                 kex->session_id_len = hashlen;
 187                 kex->session_id = malloc(kex->session_id_len);
 188                 if (kex->session_id == NULL) {
 189                         r = SSH_ERR_ALLOC_FAIL;
 190                         goto out;
 191                 }
 192                 memcpy(kex->session_id, hash, kex->session_id_len);
 193         }
 194
 195         /* sign H */
 196         if ((r = kex->sign(server_host_private, server_host_public, &signature,
 197              &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0)
 198                 goto out;
 199
 200         /* destroy_sensitive_data(); */
 201
 202         /* send server hostkey, DH pubkey 'f' and singed H */
 203         {
 204         const BIGNUM *pub_key;
 205         DH_get0_key(kex->dh, &pub_key, NULL);
 206         if ((r = sshpkt_start(ssh, SSH2_MSG_KEXDH_REPLY)) != 0 ||
 207             (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 ||
 208             (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||      /* f */
 209             (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
 210             (r = sshpkt_send(ssh)) != 0) {
 211                 goto out;
 212         }
 213         }
 214
 215         if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
 216                 r = kex_send_newkeys(ssh);
 217  out:
 218         explicit_bzero(hash, sizeof(hash));
 219         DH_free(kex->dh);
 220         kex->dh = NULL;
 221         BN_clear_free(dh_client_pub);
 222         if (kbuf) {
 223                 explicit_bzero(kbuf, klen);
 224                 free(kbuf);
 225         }
 226         BN_clear_free(shared_secret);
 227         free(server_host_key_blob);
 228         free(signature);
 229         return r;
 230 }
 231 #endif /* WITH_OPENSSL */