crypto/openssh/kexgexc.c

   1 /* $OpenBSD: kexgexc.c,v 1.22 2015/05/26 23:23:40 dtucker Exp $ */
   2 /*
   3  * Copyright (c) 2000 Niels Provos.  All rights reserved.
   4  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #include "includes.h"
  28
  29 #ifdef WITH_OPENSSL
  30
  31 #include <sys/param.h>
  32 #include <sys/types.h>
  33
  34 #include <openssl/dh.h>
  35
  36 #include <stdarg.h>
  37 #include <stdio.h>
  38 #include <string.h>
  39 #include <signal.h>
  40
  41 #include "sshkey.h"
  42 #include "cipher.h"
  43 #include "digest.h"
  44 #include "kex.h"
  45 #include "log.h"
  46 #include "packet.h"
  47 #include "dh.h"
  48 #include "ssh2.h"
  49 #include "compat.h"
  50 #include "dispatch.h"
  51 #include "ssherr.h"
  52 #include "sshbuf.h"
  53
  54 static int input_kex_dh_gex_group(int, u_int32_t, void *);
  55 static int input_kex_dh_gex_reply(int, u_int32_t, void *);
  56
  57 int
  58 kexgex_client(struct ssh *ssh)
  59 {
  60         struct kex *kex = ssh->kex;
  61         int r;
  62         u_int nbits;
  63
  64         nbits = dh_estimate(kex->dh_need * 8);
  65
  66         kex->min = DH_GRP_MIN;
  67         kex->max = DH_GRP_MAX;
  68         kex->nbits = nbits;
  69         if (datafellows & SSH_BUG_DHGEX_LARGE)
  70                 kex->nbits = MIN(kex->nbits, 4096);
  71         /* New GEX request */
  72         if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
  73             (r = sshpkt_put_u32(ssh, kex->min)) != 0 ||
  74             (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 ||
  75             (r = sshpkt_put_u32(ssh, kex->max)) != 0 ||
  76             (r = sshpkt_send(ssh)) != 0)
  77                 goto out;
  78         debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
  79             kex->min, kex->nbits, kex->max);
  80 #ifdef DEBUG_KEXDH
  81         fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
  82             kex->min, kex->nbits, kex->max);
  83 #endif
  84         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP,
  85             &input_kex_dh_gex_group);
  86         r = 0;
  87  out:
  88         return r;
  89 }
  90
  91 static int
  92 input_kex_dh_gex_group(int type, u_int32_t seq, void *ctxt)
  93 {
  94         struct ssh *ssh = ctxt;
  95         struct kex *kex = ssh->kex;
  96         BIGNUM *p = NULL, *g = NULL;
  97         int r, bits;
  98
  99         debug("got SSH2_MSG_KEX_DH_GEX_GROUP");
 100
 101         if ((p = BN_new()) == NULL ||
 102             (g = BN_new()) == NULL) {
 103                 r = SSH_ERR_ALLOC_FAIL;
 104                 goto out;
 105         }
 106         if ((r = sshpkt_get_bignum2(ssh, p)) != 0 ||
 107             (r = sshpkt_get_bignum2(ssh, g)) != 0 ||
 108             (r = sshpkt_get_end(ssh)) != 0)
 109                 goto out;
 110         if ((bits = BN_num_bits(p)) < 0 ||
 111             (u_int)bits < kex->min || (u_int)bits > kex->max) {
 112                 r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
 113                 goto out;
 114         }
 115         if ((kex->dh = dh_new_group(g, p)) == NULL) {
 116                 r = SSH_ERR_ALLOC_FAIL;
 117                 goto out;
 118         }
 119         p = g = NULL; /* belong to kex->dh now */
 120
 121         /* generate and send 'e', client DH public key */
 122         if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0 ||
 123             (r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 ||
 124             (r = sshpkt_put_bignum2(ssh, kex->dh->pub_key)) != 0 ||
 125             (r = sshpkt_send(ssh)) != 0)
 126                 goto out;
 127         debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
 128 #ifdef DEBUG_KEXDH
 129         DHparams_print_fp(stderr, kex->dh);
 130         fprintf(stderr, "pub= ");
 131         BN_print_fp(stderr, kex->dh->pub_key);
 132         fprintf(stderr, "\n");
 133 #endif
 134         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, NULL);
 135         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply);
 136         r = 0;
 137 out:
 138         if (p)
 139                 BN_clear_free(p);
 140         if (g)
 141                 BN_clear_free(g);
 142         return r;
 143 }
 144
 145 static int
 146 input_kex_dh_gex_reply(int type, u_int32_t seq, void *ctxt)
 147 {
 148         struct ssh *ssh = ctxt;
 149         struct kex *kex = ssh->kex;
 150         BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
 151         struct sshkey *server_host_key = NULL;
 152         u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL;
 153         u_char hash[SSH_DIGEST_MAX_LENGTH];
 154         size_t klen = 0, slen, sbloblen, hashlen;
 155         int kout, r;
 156
 157         debug("got SSH2_MSG_KEX_DH_GEX_REPLY");
 158         if (kex->verify_host_key == NULL) {
 159                 r = SSH_ERR_INVALID_ARGUMENT;
 160                 goto out;
 161         }
 162         /* key, cert */
 163         if ((r = sshpkt_get_string(ssh, &server_host_key_blob,
 164             &sbloblen)) != 0 ||
 165             (r = sshkey_from_blob(server_host_key_blob, sbloblen,
 166             &server_host_key)) != 0)
 167                 goto out;
 168         if (server_host_key->type != kex->hostkey_type) {
 169                 r = SSH_ERR_KEY_TYPE_MISMATCH;
 170                 goto out;
 171         }
 172         if (server_host_key->type != kex->hostkey_type ||
 173             (kex->hostkey_type == KEY_ECDSA &&
 174             server_host_key->ecdsa_nid != kex->hostkey_nid)) {
 175                 r = SSH_ERR_KEY_TYPE_MISMATCH;
 176                 goto out;
 177         }
 178         if (kex->verify_host_key(server_host_key, ssh) == -1) {
 179                 r = SSH_ERR_SIGNATURE_INVALID;
 180                 goto out;
 181         }
 182         /* DH parameter f, server public DH key */
 183         if ((dh_server_pub = BN_new()) == NULL) {
 184                 r = SSH_ERR_ALLOC_FAIL;
 185                 goto out;
 186         }
 187         /* signed H */
 188         if ((r = sshpkt_get_bignum2(ssh, dh_server_pub)) != 0 ||
 189             (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
 190             (r = sshpkt_get_end(ssh)) != 0)
 191                 goto out;
 192 #ifdef DEBUG_KEXDH
 193         fprintf(stderr, "dh_server_pub= ");
 194         BN_print_fp(stderr, dh_server_pub);
 195         fprintf(stderr, "\n");
 196         debug("bits %d", BN_num_bits(dh_server_pub));
 197 #endif
 198         if (!dh_pub_is_valid(kex->dh, dh_server_pub)) {
 199                 sshpkt_disconnect(ssh, "bad server public DH value");
 200                 r = SSH_ERR_MESSAGE_INCOMPLETE;
 201                 goto out;
 202         }
 203
 204         klen = DH_size(kex->dh);
 205         if ((kbuf = malloc(klen)) == NULL ||
 206             (shared_secret = BN_new()) == NULL) {
 207                 r = SSH_ERR_ALLOC_FAIL;
 208                 goto out;
 209         }
 210         if ((kout = DH_compute_key(kbuf, dh_server_pub, kex->dh)) < 0 ||
 211             BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
 212                 r = SSH_ERR_LIBCRYPTO_ERROR;
 213                 goto out;
 214         }
 215 #ifdef DEBUG_KEXDH
 216         dump_digest("shared secret", kbuf, kout);
 217 #endif
 218         if (ssh->compat & SSH_OLD_DHGEX)
 219                 kex->min = kex->max = -1;
 220
 221         /* calc and verify H */
 222         hashlen = sizeof(hash);
 223         if ((r = kexgex_hash(
 224             kex->hash_alg,
 225             kex->client_version_string,
 226             kex->server_version_string,
 227             sshbuf_ptr(kex->my), sshbuf_len(kex->my),
 228             sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
 229             server_host_key_blob, sbloblen,
 230             kex->min, kex->nbits, kex->max,
 231             kex->dh->p, kex->dh->g,
 232             kex->dh->pub_key,
 233             dh_server_pub,
 234             shared_secret,
 235             hash, &hashlen)) != 0)
 236                 goto out;
 237
 238         if ((r = sshkey_verify(server_host_key, signature, slen, hash,
 239             hashlen, ssh->compat)) != 0)
 240                 goto out;
 241
 242         /* save session id */
 243         if (kex->session_id == NULL) {
 244                 kex->session_id_len = hashlen;
 245                 kex->session_id = malloc(kex->session_id_len);
 246                 if (kex->session_id == NULL) {
 247                         r = SSH_ERR_ALLOC_FAIL;
 248                         goto out;
 249                 }
 250                 memcpy(kex->session_id, hash, kex->session_id_len);
 251         }
 252
 253         if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
 254                 r = kex_send_newkeys(ssh);
 255  out:
 256         explicit_bzero(hash, sizeof(hash));
 257         DH_free(kex->dh);
 258         kex->dh = NULL;
 259         if (dh_server_pub)
 260                 BN_clear_free(dh_server_pub);
 261         if (kbuf) {
 262                 explicit_bzero(kbuf, klen);
 263                 free(kbuf);
 264         }
 265         if (shared_secret)
 266                 BN_clear_free(shared_secret);
 267         sshkey_free(server_host_key);
 268         free(server_host_key_blob);
 269         free(signature);
 270         return r;
 271 }
 272 #endif /* WITH_OPENSSL */