HMAC for hashing secret, AES for encrypting/decrypting data

Crypto.java

package com.puppycloud.game.cheat;
import java.security.MessageDigest;

import javax.crypto.Cipher;
import javax.crypto.Mac;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class Crypto {

	public static byte[] HMACMD5(String s, String keyString) {
		try {
			SecretKeySpec key = new SecretKeySpec(
					(keyString).getBytes("UTF-8"), "HmacMD5");
			Mac mac = Mac.getInstance("HmacMD5");
			mac.init(key);

			byte[] bytes = mac.doFinal(s.getBytes("ASCII"));
			return bytes;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	public static String bytesToHexString(byte[] bytes) {
		StringBuffer buffer = new StringBuffer();
		for (int i = 0; i < bytes.length; i++) {
			String hex = String.format("%02x", 0xFF & bytes[i]);
			buffer.append(hex);
		}
		return buffer.toString();
	}

	public static byte[] stringToHexBytes(String s) {
		if ((s.length() % 2) == 1) {
			return new byte[0];
		}
		
		byte[] buffer = new byte[s.length() >> 1];
		for (int i = 0; i < s.length(); i += 2) {
			buffer[i >> 1] = (byte) Integer.parseInt(s.substring(i, i + 2), 16);
		}
		return buffer;
	}

	public static byte[] AES(boolean encrypt, byte[] key, byte[] iv, byte[] plain) {
		int mode = encrypt ? Cipher.ENCRYPT_MODE : Cipher.DECRYPT_MODE;
		Cipher cipher;
		try {
			cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
			cipher.init(mode, new SecretKeySpec(key, "AES"), new IvParameterSpec(iv));
			return cipher.doFinal(plain);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	public static byte[] MD5(String message) {
		try {
			byte[] bytes = message.getBytes("UTF-8");
			MessageDigest md = MessageDigest.getInstance("MD5");
			return md.digest(bytes);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}
}