REPL ---> http://repl.it/yHs

AdditiveCipher

package me.rahulthakur;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

class Main {

	private static final char[] ciphertext = "OTWEWNGWCBPQABIZVQAPMLJGZWTTQVOBQUMAPMIDGZCABEQVBMZLZIXMLAXZQVOQVLMMXAVWEIVLLIZSNZWABJQZLWNLMTQOPBVIUMLGWCBPAEQNBTGTMNBBPMVMABITIAKWCTLVBBQUMQBEPQTMQBEIAQVUGBZCAB".toCharArray();
	private static final char[] alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
	private static final char[] targets = "ETAOINSHRDLCUMWFGYPBVKJQXZ".toCharArray();
	private static short loopCounter = 0;
	private static Scanner reader = null;

	public static void main(String[] args) {

		System.out.println("Press 1: Initiate Statistical Attack\nPress 2: Initiate Brute Force Attack");
		System.out.print("Your choice: ");
		try {
			reader = new Scanner(System.in);
			switch (reader.nextInt()) {
				case 1:
					statisticalAttack();
					break;
				case 2:
					bruteForceAttack();
					break;
				default:
					System.out.println("Bad Input!");
					break;
			}
		} catch (Exception e) {
		} finally {
			try {
				reader.close();
			} catch (Exception e) {
			}
		}
	}

	private static void statisticalAttack() {

		System.out.println("\n\nInitiating Statistical Attack\n==============================");
		Map<String, Integer> frequencyMap = new HashMap<String, Integer>();
		for (char a : alphabets)
			frequencyMap.put(String.valueOf(a), 0);
		for (char c : ciphertext)
			frequencyMap.put(String.valueOf(c), frequencyMap.get(String.valueOf(c)) + 1);
		System.out.println("Generating frequency map for the ciphertext:");
		for (String s : frequencyMap.keySet())
			System.out.println(s + " => " + frequencyMap.get(s));
		loopCounter = 0;
		for (char t : targets)
			for (char a : alphabets) {
				loopCounter++;
				String s = Collections.max(frequencyMap.entrySet(), (entry1, entry2) -> entry1.getValue() > entry2.getValue() ? 1 : -1).getKey();
				System.out.println("\n\nAttempt " + loopCounter + " with target " + t + ":");
				transform(s.charAt(0), t);
				exitOrContinue();
				frequencyMap.put(s, 0);
			}
		System.out.println("This is impossible! I'm out of here!");
	}

	private static void bruteForceAttack() {

		System.out.println("\n\nInitiating Brute Force Attack\n==============================");
		loopCounter = 0;
		for (char a : alphabets) {
			if (a == 'A')
				continue;
			loopCounter++;
			System.out.println("\n\nAttempt " + loopCounter + " with target " + a + ":");
			transform(a, 'A');
			exitOrContinue();
		}
		System.out.println("This is impossible! I'm out of here!");
	}

	private static void transform(char value, char target) {

		System.out.println("Assuming " + value + " as " + target + " --->");
		int offset = 0;
		if (target > value)
			offset = value - target;
		else
			offset = target - value;
		for (char c : ciphertext) {
			int x = c + offset;
			if (x < Integer.valueOf('A'))
				x = 'Z' - ('A' - x) + 1;
			System.out.print(Character.toChars(x));
		}
		System.out.print("\n\n");
	}

	private static void exitOrContinue() {

		System.out.print("Does that make sense?(1 to exit/0 to continue):");
		if (reader.nextInt() == 0)
			System.out.println("\nMoving on then..");
		else {
			System.out.println("\nWe did it, and in only " + loopCounter + " attempts!");
			System.exit(0);
		}
	}
}