File: rc4.c

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/*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 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;
}