/* airpcap_wep.c
 *
 *  $Id$
 *
 * Copyright (c) 2002-2005 Sam Leffler, Errno Consulting
 * Copyright (c) 2006 CACE Technologies, Davis (California)
 * 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.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * Alternatively, this software may be distributed under the terms of the
 * GNU General Public License ("GPL") version 2 as published by the Free
 * Software Foundation.
 *
 * 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 "config.h"

/************************************************************************/
/*	File includes							*/

#include <glib.h>
#include "crc32.h"

/************************************************************************/
/* Note: copied from net80211/ieee80211_airpdcap_tkip.c			*/
#define S_SWAP(a,b) { guint8 t = S[a]; S[a] = S[b]; S[b] = t; }

/* Note: copied from FreeBSD source code, RELENG 6,			*/
/*		sys/net80211/ieee80211_crypto_wep.c, 391		*/
int AirPDcapWepDecrypt(
	const guchar *seed,
	const size_t seed_len,
	guchar *cypher_text,
	const size_t data_len)
{
	guint32 i, j, k, crc;
	guint8 S[256];
	guint8 icv[4];
	size_t buflen;

	/* Generate key stream (RC4 Pseudo-Random Number Generator) */
	for (i = 0; i < 256; i++)
		S[i] = (guint8)i;
	for (j = i = 0; i < 256; i++) {
		j = (j + S[i] + seed[i % seed_len]) & 0xff;
		S_SWAP(i, j);
	}

	/* Apply RC4 to data and compute CRC32 over decrypted data */
	crc = ~(guint32)0;
	buflen = data_len;

	for (i = j = k = 0; k < buflen; k++) {
		i = (i + 1) & 0xff;
		j = (j + S[i]) & 0xff;
		S_SWAP(i, j);
		*cypher_text ^= S[(S[i] + S[j]) & 0xff];
		crc = crc32_ccitt_table_lookup((crc ^ *cypher_text) & 0xff) ^ (crc >> 8);
		cypher_text++;
	}

	crc = ~crc;

	/* Encrypt little-endian CRC32 and verify that it matches with the received ICV */
	icv[0] = (guint8)crc;
	icv[1] = (guint8)(crc >> 8);
	icv[2] = (guint8)(crc >> 16);
	icv[3] = (guint8)(crc >> 24);
	for (k = 0; k < 4; k++) {
		i = (i + 1) & 0xff;
		j = (j + S[i]) & 0xff;
		S_SWAP(i, j);
		if ((icv[k] ^ S[(S[i] + S[j]) & 0xff]) != *cypher_text++) {
			/* ICV mismatch - drop frame */
			return 1/*AIRPDCAP_RET_UNSUCCESS*/;
		}
	}

	return 0/*AIRPDCAP_RET_SUCCESS*/;
}
