The Wayback Machine - https://web.archive.org/web/20080207125928/http://cypherpunks.venona.com:80/archive/1994/09/msg00304.html
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Thank you Bob Anderson

SUBJECT:  RC4 Source Code


I've tested this.  It is compatible with the RC4 object module
that comes in the various RSA toolkits.  

/* 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;
 }