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/*********************************************************************
* Filename: arcfour.c
* Author: Brad Conte (brad AT bradconte.com)
* Copyright:
* Disclaimer: This code is presented "as is" without any guarantees.
* Details: Implementation of the ARCFOUR encryption algorithm.
Algorithm specification can be found here:
* http://en.wikipedia.org/wiki/RC4
*********************************************************************/
/*************************** HEADER FILES ***************************/
#include <stdlib.h>
#include "arcfour.h"
/*********************** FUNCTION DEFINITIONS ***********************/
void arcfour_key_setup(BYTE state[], const BYTE key[], int len)
{
int i, j;
BYTE t;
for (i = 0; i < 256; ++i)
state[i] = i;
for (i = 0, j = 0; i < 256; ++i) {
j = (j + state[i] + key[i % len]) % 256;
t = state[i];
state[i] = state[j];
state[j] = t;
}
}
// This does not hold state between calls. It always generates the
// stream starting from the first output byte.
void arcfour_generate_stream(BYTE state[], BYTE out[], size_t len)
{
int i, j;
size_t idx;
BYTE t;
for (idx = 0, i = 0, j = 0; idx < len; ++idx) {
i = (i + 1) % 256;
j = (j + state[i]) % 256;
t = state[i];
state[i] = state[j];
state[j] = t;
out[idx] = state[(state[i] + state[j]) % 256];
}
}
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