Question

Write a short Java program that uses private key (symmetric) encryption method to encrypt a short string. Approximate algorithm:

Enter a text string

Use Java to generate a key and encrypt the string

Use Java (and the key) to decrypt the string

Compare original and decrypted string to make sure it is the same

Note: Please make it as simple as possible

Answer 1

package com.javapapers.java.security;

import java.security.Security;

import javax.crypto.Cipher;

import javax.crypto.KeyGenerator;

import javax.crypto.SecretKey;

import java.util.Scanner;

public class EncryptTextEntered {

//initializing cipher Text as null

private static Cipher cipherText = null;

public static void main(String[] args) throws Exception {

//generating key using DESede key generator

KeyGenerator keyGenerator = KeyGenerator.getInstance("DESede");

// size of key must be 112 or 168 for this provider

keyGenerator.init(168);

//generating private key

SecretKey privateKey = keyGenerator.generateKey();

cipherText = Cipher.getInstance("DESede");

Scanner ss = new Scanner(System.in);

System.out.print("Enter text string : ");

// Below Statement used for getting String including sentence

String text = ss.nextLine();

System.out.println("Plain Text Before Encryption: " + text);

//encrypting the string into UTF8 key format

byte[] plainTextByte = text.getBytes("UTF8");

byte[] encryptedBytes = encrypt(plainTextByte, privateKey);

String encryptText = new String(encryptedBytes, "UTF8");

System.out.println("Encrypted Text After Encryption: " + encryptText);

byte[] decryptedBytes = decrypt(encryptedBytes, privateKey);

String decryptText = new String(decryptedBytes, "UTF8");

System.out.println("Decrypted Text After Decryption: " + decryptText);

}

static byte[] encrypt(byte[] plainTextByte, SecretKey privateKey)

throws Exception {

cipherText.init(Cipher.ENCRYPT_MODE, privateKey);

byte[] encryptedBytes = cipherText.doFinal(plainTextByte);

return encryptedBytes;

}

static byte[] decrypt(byte[] encryptedBytes, SecretKey privateKey)

throws Exception {

cipherText.init(Cipher.DECRYPT_MODE, privateKey);

byte[] decryptedBytes = cipherText.doFinal(encryptedBytes);

return decryptedBytes;

}

}

output:

Enter Text string : This is a text file.

Plain Text Before Encryption: This is a text file.

Encrypted Text After Encryption: ‡(?ê?z@ou7ÿ—pø"é³.Õ0Ò;jVi¶‚

Decrypted Text After Decryption: This is a text file.