[Johnny555]

but if they know about a notebook where you wrote it they can require you to give up the notebook

But if you wrote in a made-up language that only you know, can they force you to translate it?

[Ntrails]

How would you know the translation was accurate if it was done?

[Johnny555]

Good question, similarly how do you know the right encryption key was given, maybe there's a hidden volume that you can only see if you have the right key.