Build a mechanical representaiton of encryption and signing via public/secret key systems

Inspired from https://blog.vrypan.net/2013/08/28/public-key-cryptography-for-non-geeks/ create a lock with 2 keys of which one can only unlock and the other can only lock

Either the lock in in a box and allows to open it, or the design is like a padlock and allows to lock/sign any item

Prototype is done and people are amazed. This sounds good.