wsutil/dot11decrypt_wep.c

   1 /* dot11decrypt_wep.c
   2  *
   3  * Copyright (c) 2002-2005 Sam Leffler, Errno Consulting
   4  * Copyright (c) 2006 CACE Technologies, Davis (California)
   5  * All rights reserved.
   6  *
   7  * SPDX-License-Identifier: BSD-3-Clause
   8  */
   9
  10 #include "config.h"
  11
  12 /************************************************************************/
  13 /*      File includes                                                   */
  14
  15 #include "crc32.h"
  16
  17 /************************************************************************/
  18 /* Note: copied from net80211/ieee80211_airpdcap_tkip.c                 */
  19 #define S_SWAP(a,b) { uint8_t t = S[a]; S[a] = S[b]; S[b] = t; }
  20
  21 /* Note: copied from FreeBSD source code, RELENG 6,                     */
  22 /*              sys/net80211/ieee80211_crypto_wep.c, 391                */
  23 int Dot11DecryptWepDecrypt(
  24         const unsigned char *seed,
  25         const size_t seed_len,
  26         unsigned char *cypher_text,
  27         const size_t data_len)
  28 {
  29         uint32_t i, j, k, crc;
  30         uint8_t S[256];
  31         uint8_t icv[4];
  32         size_t buflen;
  33
  34         /* Generate key stream (RC4 Pseudo-Random Number Generator) */
  35         for (i = 0; i < 256; i++)
  36                 S[i] = (uint8_t)i;
  37         for (j = i = 0; i < 256; i++) {
  38                 j = (j + S[i] + seed[i % seed_len]) & 0xff;
  39                 S_SWAP(i, j);
  40         }
  41
  42         /* Apply RC4 to data and compute CRC32 over decrypted data */
  43         crc = ~(uint32_t)0;
  44         buflen = data_len;
  45
  46         for (i = j = k = 0; k < buflen; k++) {
  47                 i = (i + 1) & 0xff;
  48                 j = (j + S[i]) & 0xff;
  49                 S_SWAP(i, j);
  50                 *cypher_text ^= S[(S[i] + S[j]) & 0xff];
  51                 crc = crc32_ccitt_table_lookup((crc ^ *cypher_text) & 0xff) ^ (crc >> 8);
  52                 cypher_text++;
  53         }
  54
  55         crc = ~crc;
  56
  57         /* Encrypt little-endian CRC32 and verify that it matches with the received ICV */
  58         icv[0] = (uint8_t)crc;
  59         icv[1] = (uint8_t)(crc >> 8);
  60         icv[2] = (uint8_t)(crc >> 16);
  61         icv[3] = (uint8_t)(crc >> 24);
  62         for (k = 0; k < 4; k++) {
  63                 i = (i + 1) & 0xff;
  64                 j = (j + S[i]) & 0xff;
  65                 S_SWAP(i, j);
  66                 if ((icv[k] ^ S[(S[i] + S[j]) & 0xff]) != *cypher_text++) {
  67                         /* ICV mismatch - drop frame */
  68                         return 1/*DOT11DECRYPT_RET_UNSUCCESS*/;
  69                 }
  70         }
  71
  72         return 0/*DOT11DECRYPT_RET_SUCCESS*/;
  73 }
  74
  75 /*
  76  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
  77  *
  78  * Local variables:
  79  * c-basic-offset: 8
  80  * tab-width: 8
  81  * indent-tabs-mode: t
  82  * End:
  83  *
  84  * vi: set shiftwidth=8 tabstop=8 noexpandtab:
  85  * :indentSize=8:tabSize=8:noTabs=false:
  86  */