You want to send a valuable object to a friend securely. You have a box which can be fitted with multiple locks, and you have several locks and their corresponding keys. However, your friend does not have any keys to your locks, and if you send a key in an unlocked box, the key could be copied en route.
How can you send the object securely?
(In reply to
re(2): solution by exoticorn)
That's all fine and dandy, but I think that you are assuming that the box would arrive safely before the key. Countering this assumption, I would suggest that a box interceptor forge a receipt or impersonate your friend on the telephone to convince you to send the first key after he has intercepted the box.
Such a solution and counter attack are out of scope, I think.
I like your first solution better.
re(3): solution
