mirror of
https://github.com/vanhoefm/fragattacks.git
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71 lines
1.6 KiB
C
71 lines
1.6 KiB
C
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/*
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* RC4 stream cipher
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* Copyright (c) 2002-2005, Jouni Malinen <j@w1.fi>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* Alternatively, this software may be distributed under the terms of BSD
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* license.
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*
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* See README and COPYING for more details.
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*/
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#include "includes.h"
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#include "common.h"
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#include "rc4.h"
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#define S_SWAP(a,b) do { u8 t = S[a]; S[a] = S[b]; S[b] = t; } while(0)
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/**
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* rc4 - XOR RC4 stream to given data with skip-stream-start
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* @key: RC4 key
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* @keylen: RC4 key length
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* @skip: number of bytes to skip from the beginning of the RC4 stream
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* @data: data to be XOR'ed with RC4 stream
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* @data_len: buf length
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*
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* Generate RC4 pseudo random stream for the given key, skip beginning of the
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* stream, and XOR the end result with the data buffer to perform RC4
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* encryption/decryption.
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*/
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void rc4_skip(const u8 *key, size_t keylen, size_t skip,
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u8 *data, size_t data_len)
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{
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u32 i, j, k;
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u8 S[256], *pos;
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size_t kpos;
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/* Setup RC4 state */
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for (i = 0; i < 256; i++)
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S[i] = i;
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j = 0;
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kpos = 0;
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for (i = 0; i < 256; i++) {
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j = (j + S[i] + key[kpos]) & 0xff;
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kpos++;
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if (kpos >= keylen)
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kpos = 0;
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S_SWAP(i, j);
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}
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/* Skip the start of the stream */
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i = j = 0;
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for (k = 0; k < skip; k++) {
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i = (i + 1) & 0xff;
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j = (j + S[i]) & 0xff;
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S_SWAP(i, j);
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}
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/* Apply RC4 to data */
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pos = data;
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for (k = 0; k < data_len; k++) {
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i = (i + 1) & 0xff;
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j = (j + S[i]) & 0xff;
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S_SWAP(i, j);
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*pos++ ^= S[(S[i] + S[j]) & 0xff];
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}
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}
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