Write a program to lunch a brute-force attack on a ciphertext encrypted using th

Question

Write a program to lunch a brute-force attack on a ciphertext encrypted using the Caesar Cipher. The program should be able to read a ciphertext stored in a file then print in another file all the possible plaintexts. Can you find a way to figure out which one from the resulted plaintexts is the original message? Write a program to lunch a brute-force attack on a ciphertext encrypted using the Caesar Cipher. The program should be able to read a ciphertext stored in a file then print in another file all the possible plaintexts. Can you find a way to figure out which one from the resulted plaintexts is the original message? Write a program to lunch a brute-force attack on a ciphertext encrypted using the Caesar Cipher. The program should be able to read a ciphertext stored in a file then print in another file all the possible plaintexts. Can you find a way to figure out which one from the resulted plaintexts is the original message?

Explanation / Answer

The Caesar cipher is one of the earliest known and simplest ciphers. It is a type of substitution cipher in which each letter in the plaintext is 'shifted' a certain number of places down the alphabet. For example, with a shift of 1, A would be replaced by B, B would become C, and so on.

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import java.util.Scanner;

import java.io.*;

import java.util.*;

public class CaesarCipher

{

  

public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyz";

public static String decrypt(String cipherText, int shiftKey)

{

cipherText = cipherText.toLowerCase();

String plainText = "";

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

{

int charPosition = ALPHABET.indexOf(cipherText.charAt(i));

int keyVal = (charPosition - shiftKey) % 26;

if (keyVal < 0)

{

keyVal = ALPHABET.length() + keyVal;

}

char replaceVal = ALPHABET.charAt(keyVal);

plainText += replaceVal;

}

return plainText;

}

public static void main(String[] args)

{

BufferedReader br = null;

BufferedReader br2 = null;

BufferedWriter bw = null;

FileWriter fw = null;

try{

br = new BufferedReader(new FileReader("B:\ciphertext.txt"));

//One way of reading the file

System.out.println("Reading the file using readLine() method:");

String contentLine = br.readLine();

while (contentLine != null)

{

System.out.println("chipher text"+contentLine);

String originalMessage =decrypt(contentLine, 3);

System.out.println("original text"+originalMessage);

fw = new FileWriter("B:\originalmessage.txt");

bw = new BufferedWriter(fw);

bw.write(originalMessage);

System.out.println("Done");

contentLine = br.readLine();

}

}//try

catch (IOException e)

{

e.printStackTrace();

}

}//main

  

  

}//class

output:

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