offline encrypted address book

Hello everybody,
even though I am not a trisquel user (I use Debian) I really appreciate your work and like this forum. That's the reason why I ask my question here.

May sound like stupid to some of you, but only now after years of being aware of the internet control I decided to get rid of all the awful stuff in my virtual life (gmail? Yes, I have it. Facebook? Too.).

It is a slow process and I would like your support for one problem.
Once I'll shut down all my accounts and stuff I will find myself with the necessity of keeping the contact details of many of the people I know. So, where to put it?

My first idea was to just use a spreadsheet, but it not really efficient (cant do things like "sort by name", or "display contact with phone number only", "sort by country" etc.) and I should encrypt it to make it a but safer.
I also thought of writing one down myself but I'm not really confident with encryption, so I can also come up with a functioning python program but I would not be sure of how to protect it.

Is there any free program to do that? GUI does not matter.

Thank you very much for reading my post and, eventually, for helping me out.