A basic example of how to perform symmetric key encryption/decryption using AES and Java's cryptography API.

CryptoHelper.java

import java.security.Key;
import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;

import org.apache.commons.codec.binary.Base64;

public class CryptoHelper {

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

		CryptoHelper crypto = new CryptoHelper();

		String plaintext = "This is a good secret.";
		System.out.println( plaintext );

		String ciphertext = crypto.encrypt( plaintext );
		System.out.println( ciphertext );

		String decrypted = crypto.decrypt( ciphertext );
		System.out.println( decrypted );

	}

	public String encrypt( String plaintext ) throws Exception {
		return encrypt( generateIV(), plaintext );
	}

	public String encrypt( byte [] iv, String plaintext ) throws Exception {

		byte [] decrypted = plaintext.getBytes();
		byte [] encrypted = encrypt( iv, decrypted );

		StringBuilder ciphertext = new StringBuilder();

		ciphertext.append( Base64.encodeBase64String( iv ) );
		ciphertext.append( ":" );
		ciphertext.append( Base64.encodeBase64String( encrypted ) );

		return ciphertext.toString();

	}

	public String decrypt( String ciphertext ) throws Exception {
		String [] parts = ciphertext.split( ":" );
		byte [] iv = Base64.decodeBase64( parts[0] );
		byte [] encrypted = Base64.decodeBase64( parts[1] );
		byte [] decrypted = decrypt( iv, encrypted );
		return new String( decrypted );
	}

	private Key key;

	public CryptoHelper( Key key ) {
		this.key = key;
	}

	public CryptoHelper() throws Exception {
		this( generateSymmetricKey() );
	}

	public Key getKey() {
		return key;
	}

	public void setKey( Key key ) {
		this.key = key;
	}

	public static byte [] generateIV() {
		SecureRandom random = new SecureRandom();
		byte [] iv = new byte [16];
		random.nextBytes( iv );
		return iv;
	}

	public static Key generateSymmetricKey() throws Exception {
		KeyGenerator generator = KeyGenerator.getInstance( "AES" );
		SecretKey key = generator.generateKey();
		return key;
	}

	public byte [] encrypt( byte [] iv, byte [] plaintext ) throws Exception {
		Cipher cipher = Cipher.getInstance( key.getAlgorithm() + "/CBC/PKCS5Padding" );
		cipher.init( Cipher.ENCRYPT_MODE, key, new IvParameterSpec( iv ) );
		return cipher.doFinal( plaintext );
	}

	public byte [] decrypt( byte [] iv, byte [] ciphertext ) throws Exception {
		Cipher cipher = Cipher.getInstance( key.getAlgorithm() + "/CBC/PKCS5Padding" );
		cipher.init( Cipher.DECRYPT_MODE, key, new IvParameterSpec( iv ) );
		return cipher.doFinal( ciphertext );
	}

}

Brilliant tutorial, just what I have been looking for

no brilliant tutorial !!

is this program an example of AES NI implementation? as there are no initialization vectors in NI ..according to my understanding!
Kindly reply soon

how do you generate the encryption key

For symmetric keys, is signing same as encryption?