crypto/openssh/kexdhs.c

   1 /* $OpenBSD: kexdhs.c,v 1.27 2018/04/10 00:10:49 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 #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 "openbsd-compat/openssl-compat.h"
  39
  40 #include "sshkey.h"
  41 #include "cipher.h"
  42 #include "digest.h"
  43 #include "kex.h"
  44 #include "log.h"
  45 #include "packet.h"
  46 #include "dh.h"
  47 #include "ssh2.h"
  48
  49 #include "dispatch.h"
  50 #include "compat.h"
  51 #include "ssherr.h"
  52 #include "sshbuf.h"
  53
  54 static int input_kex_dh_init(int, u_int32_t, struct ssh *);
  55
  56 int
  57 kexdh_server(struct ssh *ssh)
  58 {
  59         struct kex *kex = ssh->kex;
  60         int r;
  61
  62         /* generate server DH public key */
  63         switch (kex->kex_type) {
  64         case KEX_DH_GRP1_SHA1:
  65                 kex->dh = dh_new_group1();
  66                 break;
  67         case KEX_DH_GRP14_SHA1:
  68         case KEX_DH_GRP14_SHA256:
  69                 kex->dh = dh_new_group14();
  70                 break;
  71         case KEX_DH_GRP16_SHA512:
  72                 kex->dh = dh_new_group16();
  73                 break;
  74         case KEX_DH_GRP18_SHA512:
  75                 kex->dh = dh_new_group18();
  76                 break;
  77         default:
  78                 r = SSH_ERR_INVALID_ARGUMENT;
  79                 goto out;
  80         }
  81         if (kex->dh == NULL) {
  82                 r = SSH_ERR_ALLOC_FAIL;
  83                 goto out;
  84         }
  85         if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
  86                 goto out;
  87
  88         debug("expecting SSH2_MSG_KEXDH_INIT");
  89         ssh_dispatch_set(ssh, SSH2_MSG_KEXDH_INIT, &input_kex_dh_init);
  90         r = 0;
  91  out:
  92         return r;
  93 }
  94
  95 int
  96 input_kex_dh_init(int type, u_int32_t seq, struct ssh *ssh)
  97 {
  98         struct kex *kex = ssh->kex;
  99         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
 100         const BIGNUM *pub_key;
 101         struct sshkey *server_host_public, *server_host_private;
 102         u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL;
 103         u_char hash[SSH_DIGEST_MAX_LENGTH];
 104         size_t sbloblen, slen;
 105         size_t klen = 0, hashlen;
 106         int kout, r;
 107
 108         if (kex->load_host_public_key == NULL ||
 109             kex->load_host_private_key == NULL) {
 110                 r = SSH_ERR_INVALID_ARGUMENT;
 111                 goto out;
 112         }
 113         server_host_public = kex->load_host_public_key(kex->hostkey_type,
 114             kex->hostkey_nid, ssh);
 115         server_host_private = kex->load_host_private_key(kex->hostkey_type,
 116             kex->hostkey_nid, ssh);
 117         if (server_host_public == NULL) {
 118                 r = SSH_ERR_NO_HOSTKEY_LOADED;
 119                 goto out;
 120         }
 121
 122         /* key, cert */
 123         if ((dh_client_pub = BN_new()) == NULL) {
 124                 r = SSH_ERR_ALLOC_FAIL;
 125                 goto out;
 126         }
 127         DH_get0_key(kex->dh, &pub_key, NULL);
 128         if ((r = sshpkt_get_bignum2(ssh, dh_client_pub)) != 0 ||
 129             (r = sshpkt_get_end(ssh)) != 0)
 130                 goto out;
 131
 132 #ifdef DEBUG_KEXDH
 133         fprintf(stderr, "dh_client_pub= ");
 134         BN_print_fp(stderr, dh_client_pub);
 135         fprintf(stderr, "\n");
 136         debug("bits %d", BN_num_bits(dh_client_pub));
 137         DHparams_print_fp(stderr, kex->dh);
 138         fprintf(stderr, "pub= ");
 139         BN_print_fp(stderr, pub_key);
 140         fprintf(stderr, "\n");
 141 #endif
 142         if (!dh_pub_is_valid(kex->dh, dh_client_pub)) {
 143                 sshpkt_disconnect(ssh, "bad client public DH value");
 144                 r = SSH_ERR_MESSAGE_INCOMPLETE;
 145                 goto out;
 146         }
 147
 148         klen = DH_size(kex->dh);
 149         if ((kbuf = malloc(klen)) == NULL ||
 150             (shared_secret = BN_new()) == NULL) {
 151                 r = SSH_ERR_ALLOC_FAIL;
 152                 goto out;
 153         }
 154         if ((kout = DH_compute_key(kbuf, dh_client_pub, kex->dh)) < 0 ||
 155             BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
 156                 r = SSH_ERR_LIBCRYPTO_ERROR;
 157                 goto out;
 158         }
 159 #ifdef DEBUG_KEXDH
 160         dump_digest("shared secret", kbuf, kout);
 161 #endif
 162         if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob,
 163             &sbloblen)) != 0)
 164                 goto out;
 165         /* calc H */
 166         hashlen = sizeof(hash);
 167         if ((r = kex_dh_hash(
 168             kex->hash_alg,
 169             kex->client_version_string,
 170             kex->server_version_string,
 171             sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
 172             sshbuf_ptr(kex->my), sshbuf_len(kex->my),
 173             server_host_key_blob, sbloblen,
 174             dh_client_pub,
 175             pub_key,
 176             shared_secret,
 177             hash, &hashlen)) != 0)
 178                 goto out;
 179
 180         /* save session id := H */
 181         if (kex->session_id == NULL) {
 182                 kex->session_id_len = hashlen;
 183                 kex->session_id = malloc(kex->session_id_len);
 184                 if (kex->session_id == NULL) {
 185                         r = SSH_ERR_ALLOC_FAIL;
 186                         goto out;
 187                 }
 188                 memcpy(kex->session_id, hash, kex->session_id_len);
 189         }
 190
 191         /* sign H */
 192         if ((r = kex->sign(server_host_private, server_host_public, &signature,
 193              &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0)
 194                 goto out;
 195
 196         /* destroy_sensitive_data(); */
 197
 198         /* send server hostkey, DH pubkey 'f' and signed H */
 199         if ((r = sshpkt_start(ssh, SSH2_MSG_KEXDH_REPLY)) != 0 ||
 200             (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 ||
 201             (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||      /* f */
 202             (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
 203             (r = sshpkt_send(ssh)) != 0)
 204                 goto out;
 205
 206         if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
 207                 r = kex_send_newkeys(ssh);
 208  out:
 209         explicit_bzero(hash, sizeof(hash));
 210         DH_free(kex->dh);
 211         kex->dh = NULL;
 212         BN_clear_free(dh_client_pub);
 213         if (kbuf) {
 214                 explicit_bzero(kbuf, klen);
 215                 free(kbuf);
 216         }
 217         BN_clear_free(shared_secret);
 218         free(server_host_key_blob);
 219         free(signature);
 220         return r;
 221 }
 222 #endif /* WITH_OPENSSL */