Java Program to Implement Caesar Cypher

This is a java program to implement Caesar Cipher Encryption algorithm. This is the simplest of all, where every character of the message is replaced by its next 3rd character.

Here is the source code of the Java Program to Implement Caesar Cypher. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

package com.maixuanviet.setandstring;
 
import java.util.Scanner;
 
public class CaesarCipher
{
    public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyz";
 
    public static String encrypt(String plainText, int shiftKey)
    {
        plainText = plainText.toLowerCase();
        String cipherText = "";
        for (int i = 0; i < plainText.length(); i++)
        {
            int charPosition = ALPHABET.indexOf(plainText.charAt(i));
            int keyVal = (shiftKey + charPosition) % 26;
            char replaceVal = ALPHABET.charAt(keyVal);
            cipherText += replaceVal;
        }
        return cipherText;
    }
 
    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)
    {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the String for Encryption: ");
        String message = new String();
        message = sc.next();
        System.out.println(encrypt(message, 3));
        System.out.println(decrypt(encrypt(message, 3), 3));
        sc.close();
    }
}

Output:

$ javac CaesarCipher.java
$ java CaesarCipher
 
Enter the String for Encryption: 
Sanfoundry
vdqirxqgub
sanfoundry