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/*
* 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;
}
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