contrib/hostapd/src/crypto/rc4.c

   1 /*
   2  * RC4 stream cipher
   3  * Copyright (c) 2002-2005, Jouni Malinen <j@w1.fi>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License version 2 as
   7  * published by the Free Software Foundation.
   8  *
   9  * Alternatively, this software may be distributed under the terms of BSD
  10  * license.
  11  *
  12  * See README and COPYING for more details.
  13  */
  14
  15 #include "includes.h"
  16
  17 #include "common.h"
  18 #include "rc4.h"
  19
  20 #define S_SWAP(a,b) do { u8 t = S[a]; S[a] = S[b]; S[b] = t; } while(0)
  21
  22 /**
  23  * rc4 - XOR RC4 stream to given data with skip-stream-start
  24  * @key: RC4 key
  25  * @keylen: RC4 key length
  26  * @skip: number of bytes to skip from the beginning of the RC4 stream
  27  * @data: data to be XOR'ed with RC4 stream
  28  * @data_len: buf length
  29  *
  30  * Generate RC4 pseudo random stream for the given key, skip beginning of the
  31  * stream, and XOR the end result with the data buffer to perform RC4
  32  * encryption/decryption.
  33  */
  34 void rc4_skip(const u8 *key, size_t keylen, size_t skip,
  35               u8 *data, size_t data_len)
  36 {
  37         u32 i, j, k;
  38         u8 S[256], *pos;
  39         size_t kpos;
  40
  41         /* Setup RC4 state */
  42         for (i = 0; i < 256; i++)
  43                 S[i] = i;
  44         j = 0;
  45         kpos = 0;
  46         for (i = 0; i < 256; i++) {
  47                 j = (j + S[i] + key[kpos]) & 0xff;
  48                 kpos++;
  49                 if (kpos >= keylen)
  50                         kpos = 0;
  51                 S_SWAP(i, j);
  52         }
  53
  54         /* Skip the start of the stream */
  55         i = j = 0;
  56         for (k = 0; k < skip; k++) {
  57                 i = (i + 1) & 0xff;
  58                 j = (j + S[i]) & 0xff;
  59                 S_SWAP(i, j);
  60         }
  61
  62         /* Apply RC4 to data */
  63         pos = data;
  64         for (k = 0; k < data_len; k++) {
  65                 i = (i + 1) & 0xff;
  66                 j = (j + S[i]) & 0xff;
  67                 S_SWAP(i, j);
  68                 *pos++ ^= S[(S[i] + S[j]) & 0xff];
  69         }
  70 }