Question

Vignere cipher.

Suppose that I have the message One if by land and two if by sea and the key ABC To encrypt the message, conceptually we line up the key at the beginning of the message and then concatenate the message onto it, giving:

One if by land and two if by sea

ABC One if by land and two if by sea

 

Answer 1

import java.io.*;

import java.util.*;

class Cipher{

  public String encrypt(String msg,String key){

    String res = "";

    msg = msg.toUpperCase();

    int len = 0;

    char ch_len,ch_j;

    int j = 0;

    while (len < msg.length()){

      ch_len = msg.charAt(len);

      if ( (int)ch_len >= 65 && (int)ch_len <= 90 ){

        ch_j = msg.charAt(j);

        res += (char) (((int)ch_len + (int)ch_j - 2* (int)'A') % 26 + (int)'A');

        j += 1;

        j %= key.length();

      }

      len++;

    }

    return res;

  }

  

  public String decrypt(String msg,String key){

    String res = "";

    msg = msg.toUpperCase();

    int len = 0;

    char ch_len,ch_j;

    int j = 0;

    while (len < msg.length()){

      ch_len = msg.charAt(len);

      if ( (int)ch_len >= 65 && (int)ch_len <= 90 ){

        ch_j = msg.charAt(j);

        res += (char) (((int)ch_len - (int)ch_j + 26) % 26 + (int)'A');

        j += 1;

        j %= key.length();

      }

      len++;

    }

    return res;

  }

}

class main{

  public static void main(String[] args){

    String key = "VIGENERECIPHER";

    String message = "Beware the Jabberwock, my son! The jaws that bite, the claws that catch!";

    System.out.println("String L => " + message);

    

    Cipher c=new Cipher();

    String encryptedMsg = c.encrypt(message, key);

    System.out.println("Encrypted message => " + encryptedMsg);

    

    String decryptedMsg = c.decrypt(encryptedMsg, key);

    System.out.println("Decrypted message => " + decryptedMsg);   

  }

}