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. How do you do it? Note that you cannot send a key in an unlocked box since it might be copied.
More Logic Riddles
More Riddles and Answers
What is it that you ought to keep after you have given it to someone else?
Not a Raincoat
What kind of coat can be put on only when wet?
Logic - Math - Miscellaneous - What Am I - Words