Mono-alphabetic substitution cipher.

[ SENDER SIDE ]

import java.io.*;
import java.net.*;
public class sender
{
public static void main(String args[])throws Exception
{
char ch,ch1;
int i,pos;
String input="",output="";
String plaintext="abcdefghijklmnopqrstuvwxyz";
String ciphertext="QWERTYUIOPASDFGHJKLZXCVBNM";
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
Socket soc=new Socket("localhost",3030);
DataOutputStream dos=new DataOutputStream(soc.getOutputStream());

System.out.print("Enter Data To Send : ");
input=br.readLine(); //attack
for(i=0;i<input.length();i++)
{
ch=input.charAt(i);
pos=plaintext.indexOf(ch);
ch1=ciphertext.charAt(pos);
output=output+ch1;
}
System.out.println("ENCRYPTED DATA IS "+output);
dos.writeUTF(output);
}
}

[ RECEIVER SIDE ]

import java.io.*;
import java.net.*;
public class receiver
{
public static void main(String args[])throws Exception
{
char ch,ch1;
int i,pos;
String input="",output="";
String plaintext="abcdefghijklmnopqrstuvwxyz";
String ciphertext="QWERTYUIOPASDFGHJKLZXCVBNM";
ServerSocket ss=new ServerSocket(3030);
Socket soc=ss.accept();
DataInputStream dis=new DataInputStream(soc.getInputStream());
input=dis.readUTF();
for(i=0;i<input.length();i++)
{
ch=input.charAt(i);
pos=ciphertext.indexOf(ch);
ch1=plaintext.charAt(pos);
output=output+ch1;
}
System.out.println("Decrypted Message : "+output);
}
}