kexecdhs.c

   1 /* $OpenBSD: kexecdhs.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 #include <string.h>
  31 #include <signal.h>
  32
  33 #include "xmalloc.h"
  34 #include "buffer.h"
  35 #include "key.h"
  36 #include "cipher.h"
  37 #include "kex.h"
  38 #include "log.h"
  39 #include "packet.h"
  40 #include "dh.h"
  41 #include "ssh2.h"
  42 #ifdef GSSAPI
  43 #include "ssh-gss.h"
  44 #endif
  45 #include "monitor_wrap.h"
  46
  47 #ifdef OPENSSL_HAS_ECC
  48
  49 #include <openssl/ecdh.h>
  50
  51 void
  52 kexecdh_server(Kex *kex)
  53 {
  54         EC_POINT *client_public;
  55         EC_KEY *server_key;
  56         const EC_GROUP *group;
  57         BIGNUM *shared_secret;
  58         Key *server_host_private, *server_host_public;
  59         u_char *server_host_key_blob = NULL, *signature = NULL;
  60         u_char *kbuf, *hash;
  61         u_int klen, slen, sbloblen, hashlen;
  62         int curve_nid;
  63
  64         if ((curve_nid = kex_ecdh_name_to_nid(kex->name)) == -1)
  65                 fatal("%s: unsupported ECDH curve \"%s\"", __func__, kex->name);
  66         if ((server_key = EC_KEY_new_by_curve_name(curve_nid)) == NULL)
  67                 fatal("%s: EC_KEY_new_by_curve_name failed", __func__);
  68         if (EC_KEY_generate_key(server_key) != 1)
  69                 fatal("%s: EC_KEY_generate_key failed", __func__);
  70         group = EC_KEY_get0_group(server_key);
  71
  72 #ifdef DEBUG_KEXECDH
  73         fputs("server private key:\n", stderr);
  74         key_dump_ec_key(server_key);
  75 #endif
  76
  77         if (kex->load_host_public_key == NULL ||
  78             kex->load_host_private_key == NULL)
  79                 fatal("Cannot load hostkey");
  80         server_host_public = kex->load_host_public_key(kex->hostkey_type);
  81         if (server_host_public == NULL)
  82                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  83         server_host_private = kex->load_host_private_key(kex->hostkey_type);
  84         if (server_host_private == NULL)
  85                 fatal("Missing private key for hostkey type %d",
  86                     kex->hostkey_type);
  87
  88         debug("expecting SSH2_MSG_KEX_ECDH_INIT");
  89         packet_read_expect(SSH2_MSG_KEX_ECDH_INIT);
  90         if ((client_public = EC_POINT_new(group)) == NULL)
  91                 fatal("%s: EC_POINT_new failed", __func__);
  92         packet_get_ecpoint(group, client_public);
  93         packet_check_eom();
  94
  95         if (key_ec_validate_public(group, client_public) != 0)
  96                 fatal("%s: invalid client public key", __func__);
  97
  98 #ifdef DEBUG_KEXECDH
  99         fputs("client public key:\n", stderr);
 100         key_dump_ec_point(group, client_public);
 101 #endif
 102
 103         /* Calculate shared_secret */
 104         klen = (EC_GROUP_get_degree(group) + 7) / 8;
 105         kbuf = xmalloc(klen);
 106         if (ECDH_compute_key(kbuf, klen, client_public,
 107             server_key, NULL) != (int)klen)
 108                 fatal("%s: ECDH_compute_key failed", __func__);
 109
 110 #ifdef DEBUG_KEXDH
 111         dump_digest("shared secret", kbuf, klen);
 112 #endif
 113         if ((shared_secret = BN_new()) == NULL)
 114                 fatal("%s: BN_new failed", __func__);
 115         if (BN_bin2bn(kbuf, klen, shared_secret) == NULL)
 116                 fatal("%s: BN_bin2bn failed", __func__);
 117         memset(kbuf, 0, klen);
 118         xfree(kbuf);
 119
 120         /* calc H */
 121         key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
 122         kex_ecdh_hash(
 123             kex->evp_md,
 124             group,
 125             kex->client_version_string,
 126             kex->server_version_string,
 127             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 128             buffer_ptr(&kex->my), buffer_len(&kex->my),
 129             server_host_key_blob, sbloblen,
 130             client_public,
 131             EC_KEY_get0_public_key(server_key),
 132             shared_secret,
 133             &hash, &hashlen
 134         );
 135         EC_POINT_clear_free(client_public);
 136
 137         /* save session id := H */
 138         if (kex->session_id == NULL) {
 139                 kex->session_id_len = hashlen;
 140                 kex->session_id = xmalloc(kex->session_id_len);
 141                 memcpy(kex->session_id, hash, kex->session_id_len);
 142         }
 143
 144         /* sign H */
 145         if (PRIVSEP(key_sign(server_host_private, &signature, &slen,
 146             hash, hashlen)) < 0)
 147                 fatal("kexdh_server: key_sign failed");
 148
 149         /* destroy_sensitive_data(); */
 150
 151         /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
 152         packet_start(SSH2_MSG_KEX_ECDH_REPLY);
 153         packet_put_string(server_host_key_blob, sbloblen);
 154         packet_put_ecpoint(group, EC_KEY_get0_public_key(server_key));
 155         packet_put_string(signature, slen);
 156         packet_send();
 157
 158         xfree(signature);
 159         xfree(server_host_key_blob);
 160         /* have keys, free server key */
 161         EC_KEY_free(server_key);
 162
 163         kex_derive_keys(kex, hash, hashlen, shared_secret);
 164         BN_clear_free(shared_secret);
 165         kex_finish(kex);
 166 }
 167 #else /* OPENSSL_HAS_ECC */
 168 void
 169 kexecdh_server(Kex *kex)
 170 {
 171         fatal("ECC support is not enabled");
 172 }
 173 #endif /* OPENSSL_HAS_ECC */