As I mentioned in the post (Nitrokey Storage and Open Keychain => Lack of power supply?) I had a problem with the touch keyboard and the Nitrokey Storage.
The Nitrokey registered himself as a keyboard when pluged, and so the soft keyboard disapears stopping you from typing any text (like text to encrypt or even the pin number).
You can change this behavior in the settings:
Language and Input(Sprache und Eingabe) =>Current Keyboard(Aktuelles Keyboard) => Hardware show input method (Hardware Eingabemethode anzeigen). Then there will be a button that you can type to display the touch keyboard, and to enter your pin.