About Secret (and not so Secret) Codes Overview: Secret Codes and Mathematics Secret codes are a terrific source of enrichment material for mathematics. The process of encoding and decoding is inherently mathematical, and much sophisticated mathematics has been used and/or developed in connection with cryptography. The German Enigma Code was cracked by the famous British mathematician and conceptual inventor of the computer, Alan Turing. Cryptography appears regularly in articles on teaching children mathematics. Some of the sources (not an exhaustive list) are "Developing Mathematical Thinking Using Codes and Ciphers" by Lisa Evered and Serigne Gningue in Teaching Children Mathematics vol 8 no. 1 p. 8 "An Application of Number Theory to Cryptology" by Joanne R. Snow in The Mathematics Teacher January 1989 p. 18 "Using Clock Arithmetic to Send Secret Messages" by Catherine A. Gorini in The Mathematics Teacher vol 89 no. 2 p. 100 The Activities The activities the children can choose from are 1. Sending and receiving Morse code messages 2. Decoding a transposition code (the message to decode is on the handout and on the trifold display). 3. Decoding a Caesar cipher and using the sample code wheel to decode a message. (Both on the same handout). 4. Making a code wheel and sending a message to a friend. In addition there are a few historical notes to read and some extra information on the mathematics of substitution codes. Assembling the material The trifold The printable material includes a left, a right, and a middle panel for the trifold display. A photo of a bust of Caesar for the middle panel is on a separate pdf. You will also need to print a second copy of the page containing the Morse Code key (part of the left panel) and tape it on the back of the display. Supplementary papers There are supplementary pages of text with more detailed explanations of how the codes work. The intent is to be able to spread those across the table so that not everyone is crowded around the display trying to read the details. There is a sample code wheel which you will need to cut out and assemble with a paper fastener. The messages to decode are intended as handouts--each child can have a copy and sit down and work out the message. They're printed two to a page. Other Materials There should be an adequate supply of pencils, of course. You'll also need scissors and paper for the code wheel. Last, you'll need a Morse Code silent transmitter, which should be built ahead of time. The Morse Code transmitter is a doorbell button connected in a series circuit to a flashlight bulb in a light bulb holder, powered by a pair of C batteries. You need two of these. Each side of the trifold should have a doorbell button and a flashlight bulb. Diagram: Radio Shack and similar electronics stores carry flashlight bulbs, flashlight bulb holders, and battery holders. Most stores with a hardware department carry doorbell buttons. I found them at Walmart. Ordinary (not krypton) flashlight bulbs work best. A photo of the transmitters. A couple of books would be a good addition to this module--check a kid's book on codes and The Navajo Code by Nathan Aaseng out of the library and put it on the table with the activity materials. Materials Summary Copies of the transposition code message to decode Copies of the other two messages (on the same page) to decode Copies of the code wheel with blank inner wheel Paper fasteners for the code wheel A pair of transmitter-receivers for the Morse Code Scissors Scrap paper Pencils Instruction pages Reference Material A good kids' book about codes: Lu & Clancy's Secret Codes by Adrienne Mason and Pat Cupples The Cub Scout Handbooks each have an elective on codes and Morse Code. The book In Code written by Sarah Flannery at age 17 about becoming involved through a science project in designing a code on the frontiers of cryptography is inspirational. This website by Tony Sales has a clear and comprehensive explanation of how the German Enigma machine worked. http://www.codesandciphers.org.uk/enigma/index.htm A website about the history of the Bombe (the machine to decode Enigma. http://home.earthlink.net/~nbrass1/enigma.htm About the invention of the telegraph. http://165.29.91.7/classes/humanities/amstud/97-98/telecom/telephone_and_telegraph.htm http://www.morsehistoricsite.org/morse/history.html Acknowlegements I would like to thank the Herbert F. Johnson Museum of Art at Cornell University for donating the image of Caesar's head for this display. I would like to thank Morton Swimmer for permission to use one of his photos of the Enigma machine. His comprehensive collection of photos of the machine can be found at http://www.swimmer.org/morton/enigma.html. I'd like to thank Wendy Ashlock for many of the basic ideas which went into this module, and Susan Minks for clever ideas on the staging of the activities--recruiting the Secret Agents at the Math Night! The telegraph key in the photo for the display is the property of the Des Moines Radio Amateurs Association. Don Whitmer and Dennis O'Brien kindly allowed me to photograph it for this activity when they were hosting a radio display at the Science Center of Central Iowa in Des Moines. Written by Janet A. Dixon March 15, 2002 Revised January 28, 2006