kexecdhc.c

   1 /* $OpenBSD: kexecdhc.c,v 1.2 2010/09/22 05:01:29 djm 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 #include <sys/types.h>
  30
  31 #include <stdio.h>
  32 #include <string.h>
  33 #include <signal.h>
  34
  35 #include "xmalloc.h"
  36 #include "buffer.h"
  37 #include "key.h"
  38 #include "cipher.h"
  39 #include "kex.h"
  40 #include "log.h"
  41 #include "packet.h"
  42 #include "dh.h"
  43 #include "ssh2.h"
  44
  45 #ifdef OPENSSL_HAS_ECC
  46
  47 #include <openssl/ecdh.h>
  48
  49 void
  50 kexecdh_client(Kex *kex)
  51 {
  52         EC_KEY *client_key;
  53         EC_POINT *server_public;
  54         const EC_GROUP *group;
  55         BIGNUM *shared_secret;
  56         Key *server_host_key;
  57         u_char *server_host_key_blob = NULL, *signature = NULL;
  58         u_char *kbuf, *hash;
  59         u_int klen, slen, sbloblen, hashlen;
  60         int curve_nid;
  61
  62         if ((curve_nid = kex_ecdh_name_to_nid(kex->name)) == -1)
  63                 fatal("%s: unsupported ECDH curve \"%s\"", __func__, kex->name);
  64         if ((client_key = EC_KEY_new_by_curve_name(curve_nid)) == NULL)
  65                 fatal("%s: EC_KEY_new_by_curve_name failed", __func__);
  66         if (EC_KEY_generate_key(client_key) != 1)
  67                 fatal("%s: EC_KEY_generate_key failed", __func__);
  68         group = EC_KEY_get0_group(client_key);
  69
  70         packet_start(SSH2_MSG_KEX_ECDH_INIT);
  71         packet_put_ecpoint(group, EC_KEY_get0_public_key(client_key));
  72         packet_send();
  73         debug("sending SSH2_MSG_KEX_ECDH_INIT");
  74
  75 #ifdef DEBUG_KEXECDH
  76         fputs("client private key:\n", stderr);
  77         key_dump_ec_key(client_key);
  78 #endif
  79
  80         debug("expecting SSH2_MSG_KEX_ECDH_REPLY");
  81         packet_read_expect(SSH2_MSG_KEX_ECDH_REPLY);
  82
  83         /* hostkey */
  84         server_host_key_blob = packet_get_string(&sbloblen);
  85         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
  86         if (server_host_key == NULL)
  87                 fatal("cannot decode server_host_key_blob");
  88         if (server_host_key->type != kex->hostkey_type)
  89                 fatal("type mismatch for decoded server_host_key_blob");
  90         if (kex->verify_host_key == NULL)
  91                 fatal("cannot verify server_host_key");
  92         if (kex->verify_host_key(server_host_key) == -1)
  93                 fatal("server_host_key verification failed");
  94
  95         /* Q_S, server public key */
  96         if ((server_public = EC_POINT_new(group)) == NULL)
  97                 fatal("%s: EC_POINT_new failed", __func__);
  98         packet_get_ecpoint(group, server_public);
  99
 100         if (key_ec_validate_public(group, server_public) != 0)
 101                 fatal("%s: invalid server public key", __func__);
 102
 103 #ifdef DEBUG_KEXECDH
 104         fputs("server public key:\n", stderr);
 105         key_dump_ec_point(group, server_public);
 106 #endif
 107
 108         /* signed H */
 109         signature = packet_get_string(&slen);
 110         packet_check_eom();
 111
 112         klen = (EC_GROUP_get_degree(group) + 7) / 8;
 113         kbuf = xmalloc(klen);
 114         if (ECDH_compute_key(kbuf, klen, server_public,
 115             client_key, NULL) != (int)klen)
 116                 fatal("%s: ECDH_compute_key failed", __func__);
 117
 118 #ifdef DEBUG_KEXECDH
 119         dump_digest("shared secret", kbuf, klen);
 120 #endif
 121         if ((shared_secret = BN_new()) == NULL)
 122                 fatal("%s: BN_new failed", __func__);
 123         if (BN_bin2bn(kbuf, klen, shared_secret) == NULL)
 124                 fatal("%s: BN_bin2bn failed", __func__);
 125         memset(kbuf, 0, klen);
 126         xfree(kbuf);
 127
 128         /* calc and verify H */
 129         kex_ecdh_hash(
 130             kex->evp_md,
 131             group,
 132             kex->client_version_string,
 133             kex->server_version_string,
 134             buffer_ptr(&kex->my), buffer_len(&kex->my),
 135             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 136             server_host_key_blob, sbloblen,
 137             EC_KEY_get0_public_key(client_key),
 138             server_public,
 139             shared_secret,
 140             &hash, &hashlen
 141         );
 142         xfree(server_host_key_blob);
 143         EC_POINT_clear_free(server_public);
 144         EC_KEY_free(client_key);
 145
 146         if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
 147                 fatal("key_verify failed for server_host_key");
 148         key_free(server_host_key);
 149         xfree(signature);
 150
 151         /* save session id */
 152         if (kex->session_id == NULL) {
 153                 kex->session_id_len = hashlen;
 154                 kex->session_id = xmalloc(kex->session_id_len);
 155                 memcpy(kex->session_id, hash, kex->session_id_len);
 156         }
 157
 158         kex_derive_keys(kex, hash, hashlen, shared_secret);
 159         BN_clear_free(shared_secret);
 160         kex_finish(kex);
 161 }
 162 #else /* OPENSSL_HAS_ECC */
 163 void
 164 kexecdh_client(Kex *kex)
 165 {
 166         fatal("ECC support is not enabled");
 167 }
 168 #endif /* OPENSSL_HAS_ECC */