contrib/hostapd-0.4.9/rc4.c

   1 /*
   2  * RC4 stream cipher
   3  * Copyright (c) 2002-2005, Jouni Malinen <jkmaline@cc.hut.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 <stdio.h>
  16 #include "common.h"
  17 #include "rc4.h"
  18
  19 #define S_SWAP(a,b) do { u8 t = S[a]; S[a] = S[b]; S[b] = t; } while(0)
  20
  21 /**
  22  * rc4 - XOR RC4 stream to given data with skip-stream-start
  23  * @key: RC4 key
  24  * @keylen: RC4 key length
  25  * @skip: number of bytes to skip from the beginning of the RC4 stream
  26  * @data: data to be XOR'ed with RC4 stream
  27  * @data_len: buf length
  28  *
  29  * Generate RC4 pseudo random stream for the given key, skip beginning of the
  30  * stream, and XOR the end result with the data buffer to perform RC4
  31  * encryption/decryption.
  32  */
  33 void rc4_skip(const u8 *key, size_t keylen, size_t skip,
  34               u8 *data, size_t data_len)
  35 {
  36         u32 i, j, k;
  37         u8 S[256], *pos;
  38         int kpos;
  39
  40         /* Setup RC4 state */
  41         for (i = 0; i < 256; i++)
  42                 S[i] = i;
  43         j = 0;
  44         kpos = 0;
  45         for (i = 0; i < 256; i++) {
  46                 j = (j + S[i] + key[kpos]) & 0xff;
  47                 kpos++;
  48                 if (kpos >= keylen)
  49                         kpos = 0;
  50                 S_SWAP(i, j);
  51         }
  52
  53         /* Skip the start of the stream */
  54         i = j = 0;
  55         for (k = 0; k < skip; k++) {
  56                 i = (i + 1) & 0xff;
  57                 j = (j + S[i]) & 0xff;
  58                 S_SWAP(i, j);
  59         }
  60
  61         /* Apply RC4 to data */
  62         pos = data;
  63         for (k = 0; k < data_len; k++) {
  64                 i = (i + 1) & 0xff;
  65                 j = (j + S[i]) & 0xff;
  66                 S_SWAP(i, j);
  67                 *pos++ ^= S[(S[i] + S[j]) & 0xff];
  68         }
  69 }
  70
  71
  72 /**
  73  * rc4 - XOR RC4 stream to given data
  74  * @buf: data to be XOR'ed with RC4 stream
  75  * @len: buf length
  76  * @key: RC4 key
  77  * @key_len: RC4 key length
  78  *
  79  * Generate RC4 pseudo random stream for the given key and XOR this with the
  80  * data buffer to perform RC4 encryption/decryption.
  81  */
  82 void rc4(u8 *buf, size_t len, const u8 *key, size_t key_len)
  83 {
  84         rc4_skip(key, key_len, 0, buf, len);
  85 }