RC4 Source Code

Maaf aja walaupun yang saya share ini terkesan agak basi, tapi ini akan tetap saya posting untuk kepentingan saya sendiri :) 

/* rc4.h */
typedef struct rc4_key
{     
     unsigned char state[256];      
     unsigned char x;       
     unsigned char y;
} rc4_key;
void prepare_key(unsigned char *key_data_ptr,int key_data_len,
rc4_key *key);
void rc4(unsigned char *buffer_ptr,int buffer_len,rc4_key * key);


/*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;
 }