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///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
#include "gsCommon.h"
#include "gsRC4.h"
///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
static void swap_byte (unsigned char *a, unsigned char *b)
{
unsigned char swapByte;
swapByte = *a;
*a = *b;
*b = swapByte;
}
///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
void RC4Init(RC4Context *context, const unsigned char *key, int len)
{
int i=0;
unsigned char stateIndex = 0;
unsigned char keyIndex = 0;
// must supply a key
assert(key != NULL && len != 0);
if (key == NULL || len == 0)
return;
context->x = 0;
context->y = 0;
for (i=0; i<256; i++)
context->state[i] = (unsigned char)i;
for (i=0; i<256; i++)
{
stateIndex = (unsigned char)(stateIndex + context->state[i] + key[keyIndex]);
swap_byte(&context->state[i], &context->state[stateIndex]);
keyIndex = (unsigned char)((keyIndex+1)%len);
}
}
///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
void RC4Encrypt(RC4Context *context, const unsigned char *src, unsigned char *dest, int len)
{
int i = 0;
for (i=0; i<len; i++)
{
context->x = (unsigned char)(context->x + 1); // ok to wrap around from overflow
context->y = (unsigned char)(context->y + context->state[context->x]); // ditto
swap_byte(&context->state[context->x], &context->state[context->y]);
dest[i] = (unsigned char)(src[i] ^ context->state[(unsigned char)(context->state[context->x]+context->state[context->y])]);
}
}
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