public class SSL {

    private final static String HEX = "0123456789ABCDEF";
    private final static String ENC = "US-ASCII";

    private static final String RANDOM_ALGORITHM = "SHA1PRNG";
    private static final String CIPHER_ALGORITHM = "AES/CBC/PKCS5Padding";
    private static final String SECRET_KEY_ALGORITHM = "AES";

    private static IvParameterSpec ips;

    public static void init(byte[] iv) {
    	if(iv == null) {
    		iv = new byte[16];

        	Random random = new Random();
        	random.nextBytes(iv);
    	}

    	ips = new IvParameterSpec(iv);
    }

    public static byte[] getCertificate() {
    	return ips.getIV();
    }

	public static String encrypt(Session current, String cleartext) throws Exception {
		byte[] rawKey = getRawKey(current.getCurrentSession().getBytes(ENC));
		byte[] result = encrypt(rawKey, cleartext.getBytes(ENC));
		return toHex(result);
	}

	public static String decrypt(Session current, String encrypted) throws Exception {
		byte[] rawKey = getRawKey(current.getCurrentSession().getBytes(ENC));
		byte[] enc = toByte(encrypted);
		byte[] result = decrypt(rawKey, enc);
		return new String(result, ENC);
	}

	private static byte[] getRawKey(byte[] seed) throws Exception {
		KeyGenerator kgen = KeyGenerator.getInstance("AES");
		SecureRandom sr = SecureRandom.getInstance(RANDOM_ALGORITHM);
		sr.setSeed(seed);
	    kgen.init(128, sr); // 192 and 256 bits may not be available
	    SecretKey skey = kgen.generateKey();
	    byte[] raw = skey.getEncoded();
	    return raw;
	}


	private static byte[] encrypt(byte[] raw, byte[] clear) throws Exception {
	    SecretKeySpec skeySpec = new SecretKeySpec(raw, SECRET_KEY_ALGORITHM);
		Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
	    cipher.init(Cipher.ENCRYPT_MODE, skeySpec, ips);
	    byte[] encrypted = cipher.doFinal(clear);
		return encrypted;
	}

	private static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception {
	    SecretKeySpec skeySpec = new SecretKeySpec(raw, SECRET_KEY_ALGORITHM);
		Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
	    cipher.init(Cipher.DECRYPT_MODE, skeySpec, ips);
	    byte[] decrypted = cipher.doFinal(encrypted);
		return decrypted;
	}

	public static String toHex(String txt) throws UnsupportedEncodingException {
		return toHex(txt.getBytes(ENC));
	}
	public static String fromHex(String hex) throws UnsupportedEncodingException {
		return new String(toByte(hex), ENC);
	}

	public static byte[] toByte(String hexString) {
		int len = hexString.length()/2;
		byte[] result = new byte[len];
		for (int i = 0; i < len; i++)
			result[i] = Integer.valueOf(hexString.substring(2*i, 2*i+2), 16).byteValue();
		return result;
	}

	public static String toHex(byte[] buf) {
		if (buf == null)
			return "";
		StringBuffer result = new StringBuffer(2*buf.length);
		for (int i = 0; i < buf.length; i++) {
			appendHex(result, buf[i]);
		}
		return result.toString();
	}

	private static void appendHex(StringBuffer sb, byte b) {
		sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f));
	}
}