/*rc4.c */
#include "rc4.h"
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 swapByte;
    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 = (key_data_ptr[index1] + state[counter] +
            index2) % 256;                
         swap_byte(&state[counter], &state[index2]);            

         index1 = (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;
    short counter;              
    
    x = key->x;     
    y = key->y;     
    
    state = &key->state[0];         
    for(counter = 0; counter < buffer_len; counter ++)      
    {               
         x = (x + 1) % 256;                      
         y = (state[x] + y) % 256;               
         swap_byte(&state[x], &state[y]);                        
              
         xorIndex = (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;
}