// RC4: Ron Rivest -> http://en.wikipedia.org/wiki/RC4_(cipher)
// Implementation By: B-Con -> http://b-con.us
///////////////////////////////////////////////////

#include <stdio.h>


// Key Scheduling Algorithm
void ksa(unsigned char s[], unsigned char key[])
{
   int i,j=0,l=strlen(key),t;
   
   for (i=0; i <= 255; i++)
      s[i] = i;
   for (i=0; i <= 255; i++) {
      j = (j + s[i] + key[i % l]) % 256;
      t = s[i];
      s[i] = s[j];
      s[j] = t;
   }   
}

// Pseudo-Random Generator Algorithm
void prga(unsigned char s[], int l)
{
   int i=0,j=0,x,t,key;
   
   for (x=o; x < l; x++) {
      i = (i + 1) % 256;
      j = (j + s[i]) % 256;
      t = s[i];
      s[i] = s[j];
      s[j] = t;
      // "key" contains the next keystream value produced
      key = s[(s[i] + s[j]) % 256];
      printf("%03d ",key);
      if (!(i % 15))
         printf("\n");
   }   
}   

// Driver
int main()
{
   unsigned char s[256],key[256];
   int len; 
   
   printf("Key: ");
   gets(key);
   printf("Number of keystream values: ");
   scanf("%d",&len);
   // Run the KSA with the initialization key
   ksa(s,key);
   printf("\nKeystream: \n");
   // Generate the keystream
   prga(s,len);
   fseek(stdin,0L,SEEK_END);
   getchar();
}