A Secret Message

Alice wants to send a message to Bob in the mail. Unfortunately, Bob lives with Eve, and they share a letterbox. Bob doesn’t trust Eve when it comes to sniffing around in Bob’s mail. So Alice and Bob want to devise a method of sending the message in such a way that Eve will not be able to read the message.

Fortunately, Alice has a box into which she can place the message. The box can be secured with one or more padlocks. Unfortunately, they can’t send the key together with the box because Eve would then be able to open the box with the key and read the message.

Which method should Alice and Bob use to send the message?

This riddle is a relatively easy logic question, and I can think of two simple solutions to this problem. Can you find more?

I will publish and discuss the answer tomorrow.


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