wsutil/airpdcap_wep.c

   1 /* airpcap_wep.c
   2  *
   3  *  $Id$
   4  *
   5  * Copyright (c) 2002-2005 Sam Leffler, Errno Consulting
   6  * Copyright (c) 2006 CACE Technologies, Davis (California)
   7  * All rights reserved.
   8  *
   9  * Redistribution and use in source and binary forms, with or without
  10  * modification, are permitted provided that the following conditions
  11  * are met:
  12  * 1. Redistributions of source code must retain the above copyright
  13  *    notice, this list of conditions and the following disclaimer.
  14  * 2. Redistributions in binary form must reproduce the above copyright
  15  *    notice, this list of conditions and the following disclaimer in the
  16  *    documentation and/or other materials provided with the distribution.
  17  * 3. The name of the author may not be used to endorse or promote products
  18  *    derived from this software without specific prior written permission.
  19  *
  20  * Alternatively, this software may be distributed under the terms of the
  21  * GNU General Public License ("GPL") version 2 as published by the Free
  22  * Software Foundation.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  25  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  26  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  27  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  28  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  29  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  30  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  31  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  32  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  33  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  34  */
  35
  36 #include "config.h"
  37
  38 /************************************************************************/
  39 /*      File includes                                                   */
  40
  41 #include <glib.h>
  42 #include "crc32.h"
  43
  44 /************************************************************************/
  45 /* Note: copied from net80211/ieee80211_airpdcap_tkip.c                 */
  46 #define S_SWAP(a,b) { guint8 t = S[a]; S[a] = S[b]; S[b] = t; }
  47
  48 /* Note: copied from FreeBSD source code, RELENG 6,                     */
  49 /*              sys/net80211/ieee80211_crypto_wep.c, 391                */
  50 int AirPDcapWepDecrypt(
  51         const guchar *seed,
  52         const size_t seed_len,
  53         guchar *cypher_text,
  54         const size_t data_len)
  55 {
  56         guint32 i, j, k, crc;
  57         guint8 S[256];
  58         guint8 icv[4];
  59         size_t buflen;
  60
  61         /* Generate key stream (RC4 Pseudo-Random Number Generator) */
  62         for (i = 0; i < 256; i++)
  63                 S[i] = (guint8)i;
  64         for (j = i = 0; i < 256; i++) {
  65                 j = (j + S[i] + seed[i % seed_len]) & 0xff;
  66                 S_SWAP(i, j);
  67         }
  68
  69         /* Apply RC4 to data and compute CRC32 over decrypted data */
  70         crc = ~(guint32)0;
  71         buflen = data_len;
  72
  73         for (i = j = k = 0; k < buflen; k++) {
  74                 i = (i + 1) & 0xff;
  75                 j = (j + S[i]) & 0xff;
  76                 S_SWAP(i, j);
  77                 *cypher_text ^= S[(S[i] + S[j]) & 0xff];
  78                 crc = crc32_ccitt_table_lookup((crc ^ *cypher_text) & 0xff) ^ (crc >> 8);
  79                 cypher_text++;
  80         }
  81
  82         crc = ~crc;
  83
  84         /* Encrypt little-endian CRC32 and verify that it matches with the received ICV */
  85         icv[0] = (guint8)crc;
  86         icv[1] = (guint8)(crc >> 8);
  87         icv[2] = (guint8)(crc >> 16);
  88         icv[3] = (guint8)(crc >> 24);
  89         for (k = 0; k < 4; k++) {
  90                 i = (i + 1) & 0xff;
  91                 j = (j + S[i]) & 0xff;
  92                 S_SWAP(i, j);
  93                 if ((icv[k] ^ S[(S[i] + S[j]) & 0xff]) != *cypher_text++) {
  94                         /* ICV mismatch - drop frame */
  95                         return 1/*AIRPDCAP_RET_UNSUCCESS*/;
  96                 }
  97         }
  98
  99         return 0/*AIRPDCAP_RET_SUCCESS*/;
 100 }