Practical No-8

AIM: Write a program to Implement RC4 algorithm .

import java.io.*;

class rc4

{

public static void main(String args[])throws IOException

            {          int temp=0;

                        String ptext;

                        String key;

                        int s[]=new int[256];

                        int k[]=new int[256];

                        DataInputStream in=new DataInputStream(System.in);

                        System.out.print("\nENTER PLAIN TEXT\t");

                        ptext=in.readLine();

                        System.out.print("\n\nENTER KEY TEXT\t\t");

                        key=in.readLine();

                        char ptextc[]=ptext.toCharArray();

                        char keyc[]=key.toCharArray();

                        int cipher[]=new int[ptext.length()];

                        int decrypt[]=new int[ptext.length()];

int ptexti[]=new int[ptext.length()];

                        int keyi[]=new int[key.length()];

                        for(int i=0;i<ptext.length();i++)

                        {          ptexti[i]=(int)ptextc[i];

                        }

                        for(int i=0;i<key.length();i++)

                        {          keyi[i]=(int)keyc[i];

                        }

                        for(int i=0;i<255;i++)

                        {

                                    s[i]=i;

                                    k[i]=keyi[i%key.length()];

                        }

                        int j=0;

                        for(int i=0;i<255;i++)

                        {

                                    j=(j+s[i]+k[i])%256;

                                    temp=s[i];

                                    s[i]=s[j];

                                    s[j]=temp;

                        }

                        int i=0;

                        j=0;

                        int z=0;

                        for(int l=0;l<ptext.length();l++)

                        {

                                    i=(l+1)%256;

                                    j=(j+s[i])%256;

                                    temp=s[i];

                                    s[i]=s[j];

                                    s[j]=temp;

                                    z=s[(s[i]+s[j])%256];

                                    cipher[l]=z^ptexti[l];

                                    decrypt[l]=z^cipher[l];

                        }

                        System.out.print("\n\nENCRYPTED:\t\t");

                        display(cipher);

                        System.out.print("\n\nDECRYPTED:\t\t");

                        display(decrypt);

            }

            static void display(int disp[])

            {

                        char convert[]=new char[disp.length];

                        for(int l=0;l<disp.length;l++)

                        {

                                    convert[l]=(char)disp[l];

                                    System.out.print(convert[l]);

                        }

            }

}