text: /* $OpenBSD: kexc25519c.c,v 1.4 2014/01/12 08:13:13 djm Exp $ */
  /*
   * Copyright (c) 2001 Markus Friedl.  All rights reserved.
   * Copyright (c) 2010 Damien Miller.  All rights reserved.
   * Copyright (c) 2013 Aris Adamantiadis.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  #include "includes.h"
  
  #include <sys/types.h>
  
  #include <stdio.h>
  #include <string.h>
  #include <signal.h>
  
  #include "xmalloc.h"
  #include "buffer.h"
  #include "key.h"
  #include "cipher.h"
  #include "kex.h"
  #include "log.h"
  #include "packet.h"
  #include "ssh2.h"
  
  void
  kexc25519_client(Kex *kex)
  {
  	Key *server_host_key;
  	u_char client_key[CURVE25519_SIZE];
  	u_char client_pubkey[CURVE25519_SIZE];
  	u_char *server_pubkey = NULL;
  	u_char *server_host_key_blob = NULL, *signature = NULL;
  	u_char *hash;
  	u_int slen, sbloblen, hashlen;
  	Buffer shared_secret;
  
  	kexc25519_keygen(client_key, client_pubkey);
  
  	packet_start(SSH2_MSG_KEX_ECDH_INIT);
  	packet_put_string(client_pubkey, sizeof(client_pubkey));
  	packet_send();
  	debug("sending SSH2_MSG_KEX_ECDH_INIT");
  
  #ifdef DEBUG_KEXECDH
  	dump_digest("client private key:", client_key, sizeof(client_key));
  #endif
  
  	debug("expecting SSH2_MSG_KEX_ECDH_REPLY");
  	packet_read_expect(SSH2_MSG_KEX_ECDH_REPLY);
  
  	/* hostkey */
  	server_host_key_blob = packet_get_string(&sbloblen);
  	server_host_key = key_from_blob(server_host_key_blob, sbloblen);
  	if (server_host_key == NULL)
  		fatal("cannot decode server_host_key_blob");
  	if (server_host_key->type != kex->hostkey_type)
  		fatal("type mismatch for decoded server_host_key_blob");
  	if (kex->verify_host_key == NULL)
  		fatal("cannot verify server_host_key");
  	if (kex->verify_host_key(server_host_key) == -1)
  		fatal("server_host_key verification failed");
  
  	/* Q_S, server public key */
  	server_pubkey = packet_get_string(&slen);
  	if (slen != CURVE25519_SIZE)
  		fatal("Incorrect size for server Curve25519 pubkey: %d", slen);
  
  #ifdef DEBUG_KEXECDH
  	dump_digest("server public key:", server_pubkey, CURVE25519_SIZE);
  #endif
  
  	/* signed H */
  	signature = packet_get_string(&slen);
  	packet_check_eom();
  
  	buffer_init(&shared_secret);
  	kexc25519_shared_key(client_key, server_pubkey, &shared_secret);
  
  	/* calc and verify H */
  	kex_c25519_hash(
  	    kex->hash_alg,
  	    kex->client_version_string,
  	    kex->server_version_string,
  	    buffer_ptr(&kex->my), buffer_len(&kex->my),
  	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
  	    server_host_key_blob, sbloblen,
  	    client_pubkey,
  	    server_pubkey,
  	    buffer_ptr(&shared_secret), buffer_len(&shared_secret),
  	    &hash, &hashlen
  	);
  	free(server_host_key_blob);
  	free(server_pubkey);
  	if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
  		fatal("key_verify failed for server_host_key");
  	key_free(server_host_key);
  	free(signature);
  
  	/* save session id */
  	if (kex->session_id == NULL) {
  		kex->session_id_len = hashlen;
  		kex->session_id = xmalloc(kex->session_id_len);
  		memcpy(kex->session_id, hash, kex->session_id_len);
  	}
  	kex_derive_keys(kex, hash, hashlen,
  	    buffer_ptr(&shared_secret), buffer_len(&shared_secret));
  	buffer_free(&shared_secret);
  	kex_finish(kex);
  }
  