The Dishonest Courier January 1st, 2002

Ah, were we expecting a subtle and complex chess question on the first day of the new year? Well, the only connection this problem has with chess is that it was given to us by Shay Bushinsky, one of the authors of the chess program Junior (and spiritus rector of Kasparov Chess) some years ago. We have used this puzzle before, to drive a lot of good people nuts. Hopefully you have not seen it before and will enjoy wrestling with the accursed thing.

The courier problem

We need to send a valuable item to an associate in a different city. There is a very fast, very inexpensive courier service we would really like to use. Unfortunately the couriers themselves are extremely dishonest and steal everything that we put into the box. Fortunately the box has a latch which we can secure with a padlock (as shown in the picture), making it impossible for the courier to get at the contents. Unfortunately our partner in the other city does not have the keys to our padlocks. How do we send the goods safely?

Here are some points to note:

• We can only use regular padlocks, of which we and our associate have an ample supply.
• No, neither of us has a combination lock where we could transmit the numbers by phone.
• We do not use any other form of delivery, e.g. send the key by regular post.
• The courier service is very inexpensive, we can use it as often as we like.
• Sending a key in an unlocked box or attaching it to the outside of the box is pointless: the courier steals keys.
• Transmitting information on the shape of the key, e.g. by fax, doesn't work either: our associate does not have the tools or the skill to quickly manufacture a key.

The solution is not a silly little trick but straight-forward and very satisfying. If you do not think to youself "Wow, that is so simple and so elegant!" you have not yet found the correct strategy.

The entry form for all the Christmas puzzles will appear on January 3, 2001. You have until the end of the month to submit your solutions. It will not be necessary to solve all the puzzles, so do not be discouraged if you have not worked out everything. The prize will be a Fritz 7 program signed by some of the world's top players.

A very harmonious and peaceful New Year to all of you!

Frederic Friedel

Solution