crypto/openssh/kexecdhs.c

   1 /* $OpenBSD: kexecdhs.c,v 1.16 2017/05/30 14:23:52 markus Exp $ */
   2 /*
   3  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
   4  * Copyright (c) 2010 Damien Miller.  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 #if defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC)
  30
  31 #include <sys/types.h>
  32 #include <string.h>
  33 #include <signal.h>
  34
  35 #include <openssl/ecdh.h>
  36
  37 #include "sshkey.h"
  38 #include "cipher.h"
  39 #include "digest.h"
  40 #include "kex.h"
  41 #include "log.h"
  42 #include "packet.h"
  43 #include "ssh2.h"
  44
  45 #include "dispatch.h"
  46 #include "compat.h"
  47 #include "ssherr.h"
  48 #include "sshbuf.h"
  49
  50 static int input_kex_ecdh_init(int, u_int32_t, struct ssh *);
  51
  52 int
  53 kexecdh_server(struct ssh *ssh)
  54 {
  55         debug("expecting SSH2_MSG_KEX_ECDH_INIT");
  56         ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_ecdh_init);
  57         return 0;
  58 }
  59
  60 static int
  61 input_kex_ecdh_init(int type, u_int32_t seq, struct ssh *ssh)
  62 {
  63         struct kex *kex = ssh->kex;
  64         EC_POINT *client_public;
  65         EC_KEY *server_key = NULL;
  66         const EC_GROUP *group;
  67         const EC_POINT *public_key;
  68         BIGNUM *shared_secret = NULL;
  69         struct sshkey *server_host_private, *server_host_public;
  70         u_char *server_host_key_blob = NULL, *signature = NULL;
  71         u_char *kbuf = NULL;
  72         u_char hash[SSH_DIGEST_MAX_LENGTH];
  73         size_t slen, sbloblen;
  74         size_t klen = 0, hashlen;
  75         int r;
  76
  77         if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
  78                 r = SSH_ERR_ALLOC_FAIL;
  79                 goto out;
  80         }
  81         if (EC_KEY_generate_key(server_key) != 1) {
  82                 r = SSH_ERR_LIBCRYPTO_ERROR;
  83                 goto out;
  84         }
  85         group = EC_KEY_get0_group(server_key);
  86
  87 #ifdef DEBUG_KEXECDH
  88         fputs("server private key:\n", stderr);
  89         sshkey_dump_ec_key(server_key);
  90 #endif
  91
  92         if (kex->load_host_public_key == NULL ||
  93             kex->load_host_private_key == NULL) {
  94                 r = SSH_ERR_INVALID_ARGUMENT;
  95                 goto out;
  96         }
  97         server_host_public = kex->load_host_public_key(kex->hostkey_type,
  98             kex->hostkey_nid, ssh);
  99         server_host_private = kex->load_host_private_key(kex->hostkey_type,
 100             kex->hostkey_nid, ssh);
 101         if (server_host_public == NULL) {
 102                 r = SSH_ERR_NO_HOSTKEY_LOADED;
 103                 goto out;
 104         }
 105         if ((client_public = EC_POINT_new(group)) == NULL) {
 106                 r = SSH_ERR_ALLOC_FAIL;
 107                 goto out;
 108         }
 109         if ((r = sshpkt_get_ec(ssh, client_public, group)) != 0 ||
 110             (r = sshpkt_get_end(ssh)) != 0)
 111                 goto out;
 112
 113 #ifdef DEBUG_KEXECDH
 114         fputs("client public key:\n", stderr);
 115         sshkey_dump_ec_point(group, client_public);
 116 #endif
 117         if (sshkey_ec_validate_public(group, client_public) != 0) {
 118                 sshpkt_disconnect(ssh, "invalid client public key");
 119                 r = SSH_ERR_MESSAGE_INCOMPLETE;
 120                 goto out;
 121         }
 122
 123         /* Calculate shared_secret */
 124         klen = (EC_GROUP_get_degree(group) + 7) / 8;
 125         if ((kbuf = malloc(klen)) == NULL ||
 126             (shared_secret = BN_new()) == NULL) {
 127                 r = SSH_ERR_ALLOC_FAIL;
 128                 goto out;
 129         }
 130         if (ECDH_compute_key(kbuf, klen, client_public,
 131             server_key, NULL) != (int)klen ||
 132             BN_bin2bn(kbuf, klen, shared_secret) == NULL) {
 133                 r = SSH_ERR_LIBCRYPTO_ERROR;
 134                 goto out;
 135         }
 136
 137 #ifdef DEBUG_KEXECDH
 138         dump_digest("shared secret", kbuf, klen);
 139 #endif
 140         /* calc H */
 141         if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob,
 142             &sbloblen)) != 0)
 143                 goto out;
 144         hashlen = sizeof(hash);
 145         if ((r = kex_ecdh_hash(
 146             kex->hash_alg,
 147             group,
 148             kex->client_version_string,
 149             kex->server_version_string,
 150             sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
 151             sshbuf_ptr(kex->my), sshbuf_len(kex->my),
 152             server_host_key_blob, sbloblen,
 153             client_public,
 154             EC_KEY_get0_public_key(server_key),
 155             shared_secret,
 156             hash, &hashlen)) != 0)
 157                 goto out;
 158
 159         /* save session id := H */
 160         if (kex->session_id == NULL) {
 161                 kex->session_id_len = hashlen;
 162                 kex->session_id = malloc(kex->session_id_len);
 163                 if (kex->session_id == NULL) {
 164                         r = SSH_ERR_ALLOC_FAIL;
 165                         goto out;
 166                 }
 167                 memcpy(kex->session_id, hash, kex->session_id_len);
 168         }
 169
 170         /* sign H */
 171         if ((r = kex->sign(server_host_private, server_host_public, &signature,
 172              &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0)
 173                 goto out;
 174
 175         /* destroy_sensitive_data(); */
 176
 177         public_key = EC_KEY_get0_public_key(server_key);
 178         /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
 179         if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 ||
 180             (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 ||
 181             (r = sshpkt_put_ec(ssh, public_key, group)) != 0 ||
 182             (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
 183             (r = sshpkt_send(ssh)) != 0)
 184                 goto out;
 185
 186         if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
 187                 r = kex_send_newkeys(ssh);
 188  out:
 189         explicit_bzero(hash, sizeof(hash));
 190         if (kex->ec_client_key) {
 191                 EC_KEY_free(kex->ec_client_key);
 192                 kex->ec_client_key = NULL;
 193         }
 194         if (server_key)
 195                 EC_KEY_free(server_key);
 196         if (kbuf) {
 197                 explicit_bzero(kbuf, klen);
 198                 free(kbuf);
 199         }
 200         if (shared_secret)
 201                 BN_clear_free(shared_secret);
 202         free(server_host_key_blob);
 203         free(signature);
 204         return r;
 205 }
 206 #endif /* defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC) */
 207