Two factor authentication

To further protect subjects’ personal data against compromised or weak passwords, Castellum can and should be used with two-factor authentication (2FA).

If enabled, you need to enter an additional code before you can log in to Castellum (similar to a TAN for online banking).

Currently we support any generic TOTP application or FIDO2 hardware security tokens.

Smartphone apps (TOTP)

We recommend to use a 2FA application on your phone. Just ask your local IT on suggestions for appropriate apps to be used at your institution.


By the time of writing (June 2021) the MPI for Human Development recommends its Castellum users to install either Google Authenticator or andOTP for Android or Microsoft Authenticator on iOS.

TOTP stands for “Time-based One-Time Password”. As the name suggests, each TOTP code can only be used once.

Most TOTP apps work the same:

  1. Install an authenticator app on a phone

    1. For Android phone users:

      1. Open Google Play Store on your phone.

      2. Type in the search bar: “Google Authenticator”, “andOTP” or any other authenticator app you can trust.

      3. Press the “Install” button.

    2. For iOS phone users:

      1. Open App Store on your phone.

      2. Type in the search bar: “Microsoft Authenticator” or any other authenticator app you can trust.

      3. Press the “Get” button.


    Some apps may require additional setup steps, like setting a password for the app, choosing database encryption, enabling Android sync, etc.

  2. Register that phone on Castellum with the authenticator app, by scanning a QR Code.

    Example from Google Authenticator

    Example from Google Authenticator

    By selecting this option you will be asked to allow the app to take pictures and record video. Press “Allow” and scan the QR Code.

  3. The app will now generate a new 6-digit numeric code every 30 seconds

    Whenever you want to log in to Castellum, you will need to input this numeric code, along with your private password.

  4. The code depends on the current time, so make sure that the phone has the correct time set


If you have acquired a new smartphone device, it is important that you keep your old device in use until you set up the new one. Procceed by installing an authenticator app on the new device, as described above. Then log in to Castellum using your old device’s TOTP and register your new device.

Hardware Keys (FIDO2)

If you do not want to use your phone and TOTP, you can also chose to use FIDO2-based hardware keys (tokens). In that case we recommend Yubico FIDO2 tokens, but any FIDO2-compatible token should work.

The tokens are connected to your device with USB and, when registered successfully, usually just require a tap / key press when prompted on login.

To register your FIDO2 hardware key:

  1. Insert your hardware key in any USB port.

  2. When prompted by Castellum, click “Register security key”.

  3. When prompted by Castellum, press your hardware key to complete its registration.

For additional details about supported hardware tokens or Authenticator apps, contact your local IT department or security officer.