ptunnel-ng/src/challenge.c

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

#include "challenge.h"
#include "options.h"
#include "md5.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 + rand();
	for (i=0;i<6;i++)
		c->random[i] = rand();

	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;
}