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
Possible Solution by DJ)
While that would certainly work, IF the friend had his own set of key+lock, the problem doesn't give us any information about whether this is the case. So the solution to the problem shouldn't depend on this.
re: Possible Solution
