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

/**
 * This program generates a AES key, retrieves its raw bytes, and then
 * reinstantiates a AES key from the key bytes. The reinstantiated key is used
 * to initialize a AES cipher for encryption and decryption.
 */

public class AES {

	/**
	 * Turns array of bytes into string
	 * 
	 * @param buf
	 *            Array of bytes to convert to hex string
	 * @return Generated hex string
	 */
	
	// static SecretKeySpec skeySpec = null;
	
	public static String asHex(byte buf[]) {
		StringBuffer strbuf = new StringBuffer(buf.length * 2);
		int i;
		for (i = 0; i < buf.length; i++) {
			if (((int) buf[i] & 0xff) < 0x10)
				strbuf.append("0");
			strbuf.append(Long.toString((int) buf[i] & 0xff));
		}
		return strbuf.toString();
	}

	public static byte[] encrypt_AES(String message) throws Exception {
		byte[] encrypted_text = null;

		KeyGenerator kgen = KeyGenerator.getInstance("AES");
		kgen.init(128); // 192 and 256 bits may not be available

		// Generate the secret key specs.
		SecretKey skey = kgen.generateKey();
		byte[] raw = skey.getEncoded();

		SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
		System.out.println(skeySpec);
		// Instantiate the cipher
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
		encrypted_text = cipher.doFinal((message).getBytes());
		return encrypted_text;
	}

	public static String decrypt_AES(byte[] encrypted_text) throws Exception {
		String decrypted_text = null;
		KeyGenerator kgen = KeyGenerator.getInstance("AES");
		kgen.init(128); // 192 and 256 bits may not be available
		// Generate the secret key specs.
		
		SecretKey skey = kgen.generateKey();
		byte[] raw = skey.getEncoded();
		SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
		Cipher cipher = Cipher.getInstance("AES");
		
		cipher.init(Cipher.DECRYPT_MODE, skeySpec);
		byte[] original = cipher.doFinal(encrypted_text);
		// decrypted_text = new String(original);
		return decrypted_text;
	}

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

		String message = "TEST";

		byte[] test_byte = encrypt_AES(message);
		System.out.println(asHex(test_byte));
		
		String test_string = decrypt_AES(test_byte);
		System.out.println(test_string);
	}
}

javax.crypto.spec.SecretKeySpec@17276
10167102211157604819423021711420307559149
Exception in thread "main" javax.crypto.BadPaddingException: Given final block not properly padded
	at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:811)
	at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:676)
	at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:313)
	at javax.crypto.Cipher.doFinal(Cipher.java:2086)
	at AES.decrypt_AES(AES.java:66)
	at AES.main(AES.java:78)