The Locked Box

Aug 15, 2015

RAY: Imagine you have a friend who lives in an authoritarian country where the government spies on everyone and everything. You want to send a valuable object to this friend. So you have a box which is more than large enough to contain the object and you have several locks with keys.

Now this box, I suppose you could call it a strongbox, has a lock ring that can accommodate several padlocks. But your friend does not have the key to any lock that you have. You can't send a key in the mail because the government will intercept it and copy it. And you can’t leave the box unlocked, because the object is very valuable. You have to send it through the mail. You can't hand deliver it. You want to lock it so that your friend can open it, but the spies can't.

The question is, how would you do it?


RAY: Put the valuable thing in the box and put as many locks as you want on the clasp, making sure you leave room for at least one more. Put it in the mail. Your friend gets it. He leaves all of your locks on it and adds another lock for which he has the key. He mails it back to you. You remove all of your locks, and now you can't get it open. But you don't have to -- because he can when you mail it back to him. So who's our winner?

TOM: Our winner this week is Ken Smith of Springfield, Illinois. Congratulations!

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