code: public byte[] decrypt(byte[] msg) {
          if (msg == null) return null;
          try {
              Cipher cipher = Cipher.getInstance(ENCRYPTION_ALGORITHM_IMPLEMENTATION);
              SecretKeySpec key = new SecretKeySpec(getMd5(), ENCRYPTION_ALGORITHM);
              IvParameterSpec iv = new IvParameterSpec(getIv());
              cipher.init(Cipher.DECRYPT_MODE, key, iv);
              return cipher.doFinal(msg);
          } catch (Exception e) {
              return null;
          }
      }
docs: Decrypt a message with this token.
  @param msg The message to decrypt.
  @return The encrypted message. Null if decryption failed.