code: public static byte[] generateKey()
          throws GeneralSecurityException
      {
          KeyGenerator keyGenerator = KeyGenerator.getInstance(KEY_ALGORITHM);
          // java max 128
          keyGenerator.init(128);
          SecretKey secretKey = keyGenerator.generateKey();
          return secretKey.getEncoded();
      }
docs: Generate key.
  
  @return the byte[]
  @throws GeneralSecurityException the general security exception