code: private SecretKey loadSecretKey() throws IOException, ClassNotFoundException {
          final File file = getKeyPath(KeyType.SECRET);
          SecretKey key;
          try (InputStream fis = Files.newInputStream(file.toPath());
               ObjectInputStream ois = new ObjectInputStream(fis)) {
  
              key = (SecretKey) ois.readObject();
          }
          return this.secretKey = key;
      }
docs: Loads the secret key.
  @return a SecretKey
  @throws IOException if the file cannot be read
  @throws ClassNotFoundException if deserialization of the SecretKey fails