/*
 * challenge.c
 * ptunnel is licensed under the BSD license:
 *
 * Copyright (c) 2004-2011, Daniel Stoedle <daniels@cs.uit.no>,
 * Yellow Lemon Software. All rights reserved.
 *
 * Copyright (c) 2017-2019, Toni Uhlig <matzeton@googlemail.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 *
 * - 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.
 *
 * - Neither the name of the Yellow Lemon Software nor the names of its
 *   contributors may be used to endorse or promote products derived from this
 *   software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT OWNER OR CONTRIBUTORS 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.
 *
 * Contacting the author:
 * You can get in touch with me, Daniel Stødle (that's the Norwegian letter oe,
 * in case your text editor didn't realize), here: <daniels@cs.uit.no>
 *
 * The official ptunnel website is here:
 * <http://www.cs.uit.no/~daniels/PingTunnel/>
 *
 * Note that the source code is best viewed with tabs set to 4 spaces.
 */

#include <stdlib.h>
#include <string.h>
#include <sys/time.h>

#include "challenge.h"
#include "options.h"
#include "md5.h"
#include "utils.h"

/* generate_challenge: Generates a random challenge, incorporating the current
 * local timestamp to avoid replay attacks.
 */
challenge_t* generate_challenge(void) {
	struct timeval  tt;
	challenge_t     *c;
	int             i;

	c = (challenge_t *) calloc(1, sizeof(challenge_t));
	gettimeofday(&tt, 0);
	c->sec      = tt.tv_sec;
	c->usec_rnd = tt.tv_usec + pt_random();
	for (i=0;i<6;i++)
		c->random[i] = pt_random();

	return c;
}

/* generate_response: Generates a response to the given challenge. The response
 * is generated by combining the concatenating the challenge data with the
 * md5 digest of the password, and then calculating the MD5 digest of the
 * entire buffer. The result is stored in the passed-in challenge, overwriting
 * the challenge data.
 */
void generate_response(challenge_t *challenge) {
	md5_byte_t  buf[sizeof(challenge_t)+kMD5_digest_size];
	md5_state_t state;

	memcpy(buf, challenge, sizeof(challenge_t));
	memcpy(&buf[sizeof(challenge_t)], opts.password_digest, kMD5_digest_size);
	memset(challenge, 0, sizeof(challenge_t));
	md5_init(&state);
	md5_append(&state, buf, sizeof(challenge_t)+kMD5_digest_size);
	md5_finish(&state, (md5_byte_t*)challenge);
}

/* validate_challenge: Checks whether a given response matches the expected
 * response, returning 1 if validation succeeded, and 0 otherwise. Note that
 * overwriting the local challenge with the challenge result is not a problem,
 * as the data will not be used again anyway (authentication either succeeds,
 * or the connection is closed down).
 */
int validate_challenge(challenge_t *local, challenge_t *remote) {
	generate_response(local);
	if (memcmp(local, remote, sizeof(challenge_t)) == 0)
		return 1;
	return 0;
}