/*
    * EL4J, the Extension Library for the J2EE, adds incremental enhancements to
    * the spring framework, http://el4j.sf.net
    * Copyright (C) 2005 by ELCA Informatique SA, Av. de la Harpe 22-24,
    * 1000 Lausanne, Switzerland, http://www.elca.ch
    *
    * EL4J is published under the GNU Lesser General Public License (LGPL)
    * Version 2.1. See http://www.gnu.org/licenses/
    *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
   * GNU Lesser General Public License for more details.
   *
   * For alternative licensing, please contact info@elca.ch
   */
  package ch.elca.el4j.services.security.encryption;
  
  import java.util.Arrays;
  
  import javax.crypto.Cipher;
  import javax.crypto.KeyGenerator;
  import javax.crypto.SecretKey;
  import javax.crypto.spec.SecretKeySpec;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import org.apache.commons.codec.binary.Base64;
  
  
  /**
   * This class can be used to en/decrypt Strings using the AES algorithm.
   *
   * @svnLink $Revision: 4010 $;$Date: 2009-12-01 10:59:54 +0100 (Di, 01. Dez 2009) $;$Author: jonasha $;$URL: https://el4j.svn.sourceforge.net/svnroot/el4j/branches/el4j_3_1/el4j/framework/modules/security/src/main/java/ch/elca/el4j/services/security/encryption/AESCipher.java $
   *
   * @author Stefan Wismer (SWI)
   */
  public class AESCipher {
  	/**
  	 * The prefix of encrypted messages.
  	 */
  	private static final String PREFIX = "{AES-128}";
  	
  	/**
  	 * The logger.
  	 */
  	private static Logger s_logger = LoggerFactory.getLogger(AESCipher.class);
  	
  	/**
  	 * Cipher used for encryption.
  	 */
  	private Cipher m_cipherEncypt;
  	
  	/**
  	 * Cipher used for decryption.
  	 */
  	private Cipher m_cipherDecypt;
  	
  	/**
  	 * @param base64encodedKey    a 128 bit AES key (base64 encoded) to use for en/decryption
  	 */
  	public AESCipher(String base64encodedKey) {
  		try {
  			byte[] key = Base64.decodeBase64(base64encodedKey.getBytes());
  			SecretKeySpec skeySpec = new SecretKeySpec(key, "AES");
  			
  			m_cipherEncypt = Cipher.getInstance("AES");
  			m_cipherEncypt.init(Cipher.ENCRYPT_MODE, skeySpec);
  			
  			m_cipherDecypt = Cipher.getInstance("AES");
  			m_cipherDecypt.init(Cipher.DECRYPT_MODE, skeySpec);
  		} catch (Exception e) {
  			s_logger.error("Error creating AESCipher", e);
  		}
  	}
  	
  	/**
  	 * @param plainText    plain text
  	 * @return             encrypted text
  	 */
  	public String encrypt(String plainText) {
  		try {
  			return PREFIX + new String(Base64.encodeBase64(m_cipherEncypt.doFinal(plainText.getBytes())));
  		} catch (Exception e) {
  			s_logger.error("Error while encrypting text", e);
  			return null;
  		}
  	}
  	
  	/**
  	 * @param encryptedText    encrypted text
  	 * @return                decrypted text
  	 */
  	public String decrypt(String encryptedText) {
  		try {
  			if (encryptedText.startsWith(PREFIX)) {
  				return new String(m_cipherDecypt.doFinal(
  						Base64.decodeBase64(encryptedText.substring(PREFIX.length()).getBytes())));
 			} else {
 				s_logger.error("Error while decrypting text: encyptedText does not start with " + PREFIX);
 				return encryptedText;
 			}
 		} catch (Exception e) {
 			s_logger.error("Error while decrypting text", e);
 			return null;
 		}
 	}
 
 	/**
 	 * @param args          (no arguments expected)
 	 * @throws Exception
 	 */
 	public static void main(String[] args) throws Exception {
 
 		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();
 
 		System.out.println("Generated AES-128 key:" + Arrays.toString(Base64.encodeBase64(raw)));
 	}
 
 }