I think that this riddle isn’t very commonly known so it might be something new even for riddle experts :o)

Imagine you want to send a valuable item to your friend. You have 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.


Item can be sent more than once.

You both can place locks on it.


Lock the item in the box and send it to your friend. He ads his padlock on the box and sends it back to you. Take off your padlock and send it to your friend –now he only removes his padlock and box is opened...