import java.net.*;

import java.io.*;

import javax.swing.*;

import java.util.regex.*;

import java.util.*;

import java.security.*;

import java.security.spec.*;

import javax.crypto.*;

import javax.crypto.spec.*;

public class main {

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

    byte[] data = "hello".getBytes("UTF-8");

    printHex(data);

    Random ranGen = new SecureRandom();

    byte[] salt = new byte[8]; // 8 grains of salt

    ranGen.nextBytes(salt);

    String pw = "pw";

    byte[] enc = encrypt(data, pw.toCharArray(), salt);

    printHex(enc);

    System.out.println("enc length: " + enc.length);

    byte[] dec = decrypt(enc, pw.toCharArray(), salt);

    System.out.println("decrypted: " + new String(dec, "UTF-8"));

  }

  static void printHex(byte[] data) {

    System.out.println(bytesToHex(data));

  }

  static String bytesToHex(byte[] bytes) {

    return bytesToHex(bytes, 0, bytes.length);

  }

  static String bytesToHex(byte[] bytes, int ofs, int len) {

    StringBuilder stringBuilder = new StringBuilder(len*2);

    for (int i = 0; i < len; i++) {

      String s = "0" + Integer.toHexString(bytes[ofs+i]);

      stringBuilder.append(s.substring(s.length()-2, s.length()));

    }

    return stringBuilder.toString();

  }

  static SecretKey makeKey(char[] password, byte[] salt) throws Exception {

    /* Derive the key, given password and salt. */

    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");

    // only with unlimited strength:

    //KeySpec spec = new PBEKeySpec(password, salt, 65536, 256);

    // Let's try this:

    KeySpec spec = new PBEKeySpec(password, salt, 65536, 128);

    SecretKey tmp = factory.generateSecret(spec);

    SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");

    return secret;

  }

  public static byte[] encrypt(byte[] data, char[] password, byte[] salt) {

    try {

      SecretKey secret = makeKey(password, salt);

      /* Encrypt the message. */

      Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

      cipher.init(Cipher.ENCRYPT_MODE, secret);

      AlgorithmParameters params = cipher.getParameters();

      byte[] iv = params.getParameterSpec(IvParameterSpec.class).getIV();

      ByteArrayOutputStream baos = new ByteArrayOutputStream();

      baos.write(cipher.update(data));

      baos.write(cipher.doFinal());

      byte[] ciphertext = baos.toByteArray();

      return ciphertext;

    } catch (Exception e) {

      throw new RuntimeException(e);

    }

  }

  static byte[] decrypt(byte[] ciphertext, char[] password, byte[] salt) {

    try {

      SecretKey secret = makeKey(password, salt);

      Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

      cipher.init(Cipher.ENCRYPT_MODE, secret);

      AlgorithmParameters params = cipher.getParameters();

      byte[] iv = params.getParameterSpec(IvParameterSpec.class).getIV();

      /* Decrypt the message, given derived key and initialization vector. */

      cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

      ByteArrayOutputStream baos = new ByteArrayOutputStream();

      cipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(iv));

      baos.write(cipher.update(ciphertext));

      baos.write(cipher.doFinal());

      return baos.toByteArray(); 

    } catch (Exception e) {

      throw new RuntimeException(e);

    }

  }

}