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/*
* RC4 stream cipher
* Copyright (c) 2002-2005, Jouni Malinen <j@w1.fi>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* Alternatively, this software may be distributed under the terms of BSD
* license.
*
* See README and COPYING for more details.
*/
#include "includes.h"
#include "common.h"
#include "crypto.h"
#define S_SWAP(a,b) do { u8 t = S[a]; S[a] = S[b]; S[b] = t; } while(0)
int rc4_skip(const u8 *key, size_t keylen, size_t skip,
u8 *data, size_t data_len)
{
u32 i, j, k;
u8 S[256], *pos;
size_t kpos;
/* Setup RC4 state */
for (i = 0; i < 256; i++)
S[i] = i;
j = 0;
kpos = 0;
for (i = 0; i < 256; i++) {
j = (j + S[i] + key[kpos]) & 0xff;
kpos++;
if (kpos >= keylen)
kpos = 0;
S_SWAP(i, j);
}
/* Skip the start of the stream */
i = j = 0;
for (k = 0; k < skip; k++) {
i = (i + 1) & 0xff;
j = (j + S[i]) & 0xff;
S_SWAP(i, j);
}
/* Apply RC4 to data */
pos = data;
for (k = 0; k < data_len; k++) {
i = (i + 1) & 0xff;
j = (j + S[i]) & 0xff;
S_SWAP(i, j);
*pos++ ^= S[(S[i] + S[j]) & 0xff];
}
return 0;
}
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