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Professional Java Security : Symmetric Encryption

Simple Encryption Example

Now that we've gone over some of the classes and methods we'll need for symmetric encryption, we're going to create a simple program that utilizes them. Our program will create a DESede key, and then encrypt a string with it. We'll then decrypt the encrypted string and display it along with the plaintext and ciphertext bytes as and when we use them.

Here we're using the name DESede rather than TripleDES since that's the term used in the Bouncy Castle provider. You may have to change this if you using a different provider.

import java.security.*;
import javax.crypto.*;

/**
 * 	SimpleExample.java
 */

public class SimpleExample
{
	public static void main (String[] args)
			throws Exception
	{
		if (args.length != 1) {
			System.err.println("Usage: java SimpleExample text");
			System.exit(1);
		}
		String text = args[0];

		System.out.println("Generating a DESede (TripleDES) key...");

		// Create a TripleDES key

		KeyGenerator keyGenerator = KeyGenerator.getInstance("DESede");
		keyGenerator.init(168);   // need to initialize with the keysize
		Key key = keyGenerator.generateKey();

		System.out.println("Done generating the key.");

		// Create a cipher using that key to initialize it

		Cipher cipher = Cipher.getInstance("DESede/ECB/PKCS5Padding");
		cipher.init(Cipher.ENCRYPT_MODE, key);

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

		// Print out the bytes of the plaintext

		System.out.println("\nPlaintext: ");
		for (int i=0;i<plaintext.length;i++) {
			System.out.print(plaintext[i]+" ");
		}

		// Perform the actual encryption

		byte[] ciphertext = cipher.doFinal(plaintext);

		// Print out the ciphertext

		System.out.println("\n\nCiphertext: ");
		for (int i=0;i<ciphertext.length;i++) {
			System.out.print(ciphertext[i]+" ");
		}

		// Re-initialize the cipher to decrypt mode

		cipher.init(Cipher.DECRYPT_MODE, key);

		// Perform the decryption

		byte[] decryptedText = cipher.doFinal(ciphertext);

		String output = new String(decryptedText,"UTF8");

		System.out.println("\n\nDecrypted text: "+output);
	}
}

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