Alan Turing Lesson Plan: Crack a Secret Code

Lesson Procedure:

1. Write the word “encryption” on the whiteboard. Ask students to brainstorm everything they know about encryption and secret codes, such as how and why people use them. After everyone has had a chance to respond, tell students that today they will learn about Alan Turing, a mathematician who was a war hero because of his ability to break the code of the Nazi encryption machine, known as Enigma.
2. Show the movie Alan Turing on the whiteboard to the whole class once through without pausing.
3. Have students watch the movie again in pairs or small groups within the Make-a-Map feature. As they watch, tell them to construct a concept map. Have them write Turing’s name in the center, then have them identifies facts and details about Turing and his role in cracking the code of the Engima. Remind them that they can use text, images, and clips from the movie in their concept map.
4. Next, display the Cryptogram Puzzle Worksheet on the whiteboard as students open it on their own computers/devices. Alternatively you can print out and distribute the puzzle.  Read the instructions aloud to the class. Point out that two of the letters have already been identified: G is I and Q is F. Ask students if they have any ideas how they might go about cracking this code? Give them a chance to share their ideas. You can try out their ideas, too. Show them how they can keep track of each letter they solve by putting it in the table at the bottom.
5. Model strategies for cracking the code as needed. Encourage students who do not want or need support, to solve the puzzle independently. For those who would like help, provide logic strategies. For example, point out that the second word is just one letter, and that there are just two words that have one letter (A and I). Remind them that we already know that G is I, so E must be A.  Now fill in all the As as they do the same. Now draw their attention to the sixth word in the puzzle. Ask what two-letter word begins with T. They should recognize that TO is the answer. So now have them fill in all the Os as you do the same.  

   Next, encourage them to figure out the other two-letter words. For example, for the fourth word ask what two-letter words begin with I. Make a list on the board: it, in, is, if.  But explain that it can’t be if because we know that Q is F.  and it can’t be it because we know that J is T, so it must be in or is. Use this same strategy for the other two letter words in the puzzle.

6. At this point, students may choose to continue on their own. For those who still would like help, continue to model strategies. For example, point out the double letters in several of the words, such as the double Bs in the second and last line. Tell them that the most common double letters are ss, tt, ff, ll, mm, ee, and oo. By process of elimination, they’ll know it’s not tt, ff, oo, and probably at this point they know it’s not ss. Encourage students by explaining that beyond these strategies, much of cracking the code is making educated guesses and using trial and error. As students work independently, circulate, listening in on their strategies and helping as needed.
7. When everyone is finished, you can display the secret message--which is a quote from Alan Turing--on the whiteboard: If a machine is expected to be infallible, it cannot also be intelligent. Ask students to share what they think this means. What is Turing saying about intelligence and human nature?
8. Now invite students to work in pairs to come up with their own cryptogram puzzle with each letter representing one other letter. Then have pairs swap and solve each other’s messages.