Rc4.c

   /*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;
    }