PlainTextAttack.java

import java.util.*;
class Pair {

  private final int left;
  private final int right;

  public Pair(int left, int right) {
    this.left = left;
    this.right = right;
  }

  public int getLeft() { return left; }
  public int getRight() { return right; }

  

}


public class PlainTextAttack {
	public String getwordSets(String plainText,String cipherText)
    {
        ArrayList listOfPairsPos = new ArrayList();
		ArrayList listOfPairCrypt = new ArrayList();
		//finding position of equal pairs
		for(int i = 0; i < plainText.length(); i++){
			for(int j = i + 1; j < plainText.length(); j++)	{
				if(plainText.charAt(i) == plainText.charAt(j)){
					listOfPairsPos.add(new Pair(i,j));
					break;
				}
			}
		}
		
		int res = 0;
		int j;
		for(int i = 0; i < cipherText.length(); i++) {
			for(j = i; j < plainText.length(); j++) {
				for(int k = j + 1; k < plainText.length(); k++)	{
					if(cipherText.charAt(j) == plainText.charAt(k)){
						listOfPairCrypt.add(new Pair(j,k));
						break;
					}
				}
			}
			if(listOfPairsPos.equals(listOfPairCrypt)) {
				res = j;
				break;
			}
		}
		
		String resString = cipherText.substring(res, plainText.length());
		if(resString != null){
			return resString;
		}
        return null;
    }

    public static void main(String[] args){
        //TestCase 1
        try{
            String plainText="AMMUNITION";
            String cipherText="ASQWDFDFCOOWPKVKQPFGDFGDGCXVRFTWEA"; 
            PlainTextAttack obj = new PlainTextAttack();
            String output= obj.getwordSets(plainText,cipherText);
            System.out.println("TestCase 1");
            if(output!=null)
            System.out.println(output);
            else
            System.out.println("NULL");

        }
        catch(Exception e){
            e.printStackTrace();
        }
        //TestCase 2
        try{
            String plainText="AMMUNITION";
            String cipherText="QWERTYUIOPLKJHGFDSAZXCV";
            PlainTextAttack obj = new PlainTextAttack();
            String output= obj.getwordSets(plainText,cipherText);
            System.out.println("TestCase 2");
            if(output!=null)
            System.out.println(output);
            else
            System.out.println("NULL");

        }
        catch(Exception e){
            e.printStackTrace();
        }
        //TestCase 3
        try{
            String plainText="AMMUNITION";
            String cipherText="SDLKFJSDLKFJLJRLWRWEJRWLEJRWLERJs";
            PlainTextAttack obj = new PlainTextAttack();
            String output= obj.getwordSets(plainText,cipherText);
            System.out.println("TestCase 3");
            if(output!=null)
            System.out.println(output);
            else
            System.out.println("NULL");

        }
        catch(Exception e){
            e.printStackTrace();
        }

    }


}