pppd/chap-md5.c

/*
 * chap-md5.c - New CHAP/MD5 implementation.
 *
 * Copyright (c) 2003 Paul Mackerras. 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. The name(s) of the authors of this software must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission.
 *
 * 3. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by Paul Mackerras
 *     <paulus@samba.org>".
 *
 * THE AUTHORS OF THIS SOFTWARE DISCLAIM ALL WARRANTIES WITH REGARD TO
 * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS, IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
 * SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
 * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#define RCSID	"$Id: chap-md5.c,v 1.4 2004/11/09 22:39:25 paulus Exp $"

#include <stdlib.h>
#include <string.h>
#include "pppd.h"
#include "chap-new.h"
#include "chap-md5.h"
#include "magic.h"
#include "md5.h"

#define MD5_HASH_SIZE		16
#define MD5_MIN_CHALLENGE	16
#define MD5_MAX_CHALLENGE	24

static void
chap_md5_generate_challenge(unsigned char *cp)
{
	int clen;

	clen = (int)(drand48() * (MD5_MAX_CHALLENGE - MD5_MIN_CHALLENGE))
		+ MD5_MIN_CHALLENGE;
	*cp++ = clen;
	random_bytes(cp, clen);
}

static int
chap_md5_verify_response(int id, char *name,
			 unsigned char *secret, int secret_len,
			 unsigned char *challenge, unsigned char *response,
			 char *message, int message_space)
{
	MD5_CTX ctx;
	unsigned char idbyte = id;
	unsigned char hash[MD5_HASH_SIZE];
	int challenge_len, response_len;

	challenge_len = *challenge++;
	response_len = *response++;
	if (response_len == MD5_HASH_SIZE) {
		/* Generate hash of ID, secret, challenge */
		MD5_Init(&ctx);
		MD5_Update(&ctx, &idbyte, 1);
		MD5_Update(&ctx, secret, secret_len);
		MD5_Update(&ctx, challenge, challenge_len);
		MD5_Final(hash, &ctx);

		/* Test if our hash matches the peer's response */
		if (memcmp(hash, response, MD5_HASH_SIZE) == 0) {
			slprintf(message, message_space, "Access granted");
			return 1;
		}
	}
	slprintf(message, message_space, "Access denied");
	return 0;
}

static void
chap_md5_make_response(unsigned char *response, int id, char *our_name,
		       unsigned char *challenge, char *secret, int secret_len,
		       unsigned char *private)
{
	MD5_CTX ctx;
	unsigned char idbyte = id;
	int challenge_len = *challenge++;

	MD5_Init(&ctx);
	MD5_Update(&ctx, &idbyte, 1);
	MD5_Update(&ctx, secret, secret_len);
	MD5_Update(&ctx, challenge, challenge_len);
	MD5_Final(&response[1], &ctx);
	response[0] = MD5_HASH_SIZE;
}

static struct chap_digest_type md5_digest = {
	CHAP_MD5,		/* code */
	chap_md5_generate_challenge,
	chap_md5_verify_response,
	chap_md5_make_response,
	NULL,			/* check_success */
	NULL,			/* handle_failure */
};

void
chap_md5_init(void)
{
	chap_register_digest(&md5_digest);
}