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Codebreakers

Classroom Activity

Objective
To encipher a message.

• copy of "Codemaker's Guidelines" student handout (PDF or HTML)

1. To introduce some of the basic strategies used in breaking codes, ask students to select a few paragraphs from a newspaper article to analyze.

   • Count and graph the frequency with which each letter of the alphabet appears in a single article.

   • Determine the five most and least used letters in the texts.

   • Determine common two-letter combinations and their frequencies (e.g., how often does "th" occur, compared to "t" followed by anything else?)

   • Search for any other patterns that might be consistent in English (e.g., "I" and "a" are the only one-letter words.

   • Calculate class averages for these data. Brainstorm ideas about how to use the findings to interpret a coded English message.

2. Photocopy and distribute the "Codemaker's Guidelines" student handout. Ask each student to use one of the methods to encipher a message.

3. Encourage students to utilize the data they collected in the first part of the activity to break each others' enciphered messages. This exercise will give the students a sense for the large number of text samples that a codebreaker would have to analyze in order to produce a reliable guide for decoding a language. (This activity can also be conducted using foreign language documents.)

Student responses will vary depending on which method of coding they choose. Encourage them to think of more difficult coding methods and try them on fellow students.