You want to send a valuable object to a friend. You have a box 
which is more than large enough to contain the object. You have 
several locks with keys. The box has a locking ring which is more 
than large enough to have a lock attached. But your friend does 
not have the key to any lock that you have. Note that you cannot send 
a key in an unlocked box, since it might be copied. How is this done?

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