rc4.cpp

#include "rc4.hpp"

static void swap_byte(unsigned char *a, unsigned char *b);

void prepare_key(unsigned char *key_data_ptr, int key_data_len, rc4_key *key) {
unsigned char index1;
unsigned char index2;
unsigned char* state;
short counter;

     state = &key->state[0];
     for(counter = 0; counter < 256; counter++)
     state[counter] = counter;
     key->x = 0;
     key->y = 0;
     index1 = 0;
     index2 = 0;
     for(counter = 0; counter < 256; counter++) {
          index2 = (unsigned char)((key_data_ptr[index1] + state[counter] + index2) % 256);
          swap_byte(&state[counter], &state[index2]);
          index1 = (unsigned char)((index1 + 1) % key_data_len);
     }
}

void rc4(unsigned char *buffer_ptr, int buffer_len, rc4_key *key) {
unsigned char x;
unsigned char y;
unsigned char* state;
unsigned char xorIndex;
int counter;

    x = key->x;
    y = key->y;

    state = &key->state[0];
    for(counter = 0; counter < buffer_len; counter ++) {
         x = (unsigned char)((x + 1) % 256);
         y = (unsigned char)((state[x] + y) % 256);
         swap_byte(&state[x], &state[y]);

         xorIndex = (unsigned char)((state[x] + state[y]) % 256);

         buffer_ptr[counter] ^= state[xorIndex];
     }
     key->x = x;
     key->y = y;
}

static void swap_byte(unsigned char *a, unsigned char *b) {
unsigned char swapByte;

    swapByte = *a;
    *a = *b;
    *b = swapByte;
}