ns/RC4.cpp

#include <iostream>
using namespace std;
int main() {
    
    int key_size,plain_text_size,N=8,l=8,k=0;
    cout<<"Enter the size of key\n";
    cin>>key_size;
    
    cout<<"Enter the size of plain text\n";
    cin>>plain_text_size;
    
    int i,j=0,key[key_size],plain_text[plain_text_size],S[N],Z[key_size],cipher_text[plain_text_size];
  
    cout<<"Enter the key\n";
    
    for(i=0;i<key_size;i++)
    cin>>key[i];
    
    cout<<"Enter the plain text\n";
    
    for(i=0;i<plain_text_size;i++)
    cin>>plain_text[i];

    //KSA
    for(i=0;i<N;i++)
        S[i]=i;
    
    for(i=0;i<N;i++)
    {
        j=(j+S[i]+(key[i%key_size]))%l;
        
        S[i]=S[i]+S[j];
        S[j]=S[i]-S[j];
        S[i]=S[i]-S[j];
      
    }
    

    i=0;j=0;
        
    //PRGA
    for(k=0;i<key_size;k++)
    {
        i++;
        j=(j+S[i])%l;

        int temp;
        temp=S[i];
        S[i]=S[j];
        S[j]=temp;
        
        Z[k]=S[(S[i]+S[j])%l];
        
        cipher_text[k]=plain_text[k] ^ Z[k];
        
        
        
    }
    
    cout<<"Cipher Text is ";
    
    for(i=0;i<plain_text_size;i++)
        cout<<cipher_text[i];
    
    
    cout<<endl;
    return 0;
}

/*
OUTPUT:-
 

 Enter the size of key
 4
 Enter the size of plain text
 4
 Enter the key
 1 2 3 6
 Enter the plain text
 1 2 2 2
 Cipher Text is 4323
 
 */