Set Breaker #28: Clowning it
Imagine you want to send a valuable item to your friend. You have a big enough box on which you can place several padlocks. You both have enough padlocks but the problem is that you don’t have keys to padlocks of the other one.
How do you send the valuable item so that it doesn’t go unlocked? Sending just a key doesn’t help because someone could replicate it.