FeistelCipher.java

import java.util.Scanner;
public class FeistelCipher {
    public static int feistelFunction(int halfBlock, int key) {
        return halfBlock ^ key;  
    }
    public static String encrypt(String plainText, int key) {
        int L = plainText.charAt(0);  
        int R = plainText.charAt(1);  
        int newL = R;
        int newR = L ^ feistelFunction(R, key);
        return "" + (char)newL + (char)newR;
    }
    public static String decrypt(String cipherText, int key) {
        int L = cipherText.charAt(0);  
        int R = cipherText.charAt(1);  
        int newR = L;
        int newL = R ^ feistelFunction(L, key);
        return "" + (char)newL + (char)newR;
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a two-character plain text: ");
        String plainText = scanner.nextLine();
        int key = 5;
        String cipherText = encrypt(plainText, key);
        System.out.println("Encrypted Text: " + cipherText);
        String decryptedText = decrypt(cipherText, key);
        System.out.println("Decrypted Text: " + decryptedText);
    }
}