Write a program to implement Caesar Cipher encryption - decryption.

 

Code:

import java.util.Scanner;

public class CaesarCipher {

    public static void main(String []args) {

        Scanner sc=new Scanner(System.in);

        System.out.print("1. Encryption 2. Decryption: ");
        int choice = sc.nextInt();
        switch (choice) {
            case 1:
                System.out.print("Enter plain text:");
                String text = sc.next();

                System.out.print("Enter Key:");
                int key = sc.nextInt();

                System.out.println("Encrypted text is: " + encrypted(text,key));
                break;
            case 2:
                System.out.print("Enter Encrypted text:");
                text = sc.next();

                System.out.print("Enter Key:");
                key = sc.nextInt();

                System.out.println("Decrypted text is: "+ decrypted(text,key));
                break;
            default:
                break;
        }
    }

    public static StringBuffer encrypted(String text, int key)
    {
        StringBuffer result = new StringBuffer();

        for (int i=0; i<text.length(); i++)
        {
            if (Character.isUpperCase(text.charAt(i)))
            {
                char ch = (char)(((int)text.charAt(i) +
                        key - 65) % 26 + 65);
                result.append(ch);
            }
            else
            {
                char ch = (char)(((int)text.charAt(i) +
                        key - 97) % 26 + 97);
                result.append(ch);
            }
        }
        return result;
    }

    public static StringBuffer decrypted(String text, int key)
    {
        StringBuffer result=new StringBuffer();

        for (int i=0; i<text.length(); i++)
        {
            if (Character.isUpperCase(text.charAt(i)))
            {
                char ch = (char)(((int)text.charAt(i) - key - 65+26) % 26 + 65);
                result.append(ch);
            }
            else
            {
                char ch = (char)(((int)text.charAt(i) - key - 97+26) % 26 + 97);
                result.append(ch);
            }
        }
        return result;
    }
}

Output: