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Notes to the Instructor

In this lesson, students try their hand at cryptography, the science of codes and code breaking. They start by decoding example messages and then encode their own messages which are, in turn, decoded by their peers. Lastly, they decode the “secret” message found at the scene of the crime.

Across history, many types of codes have been developed and used by different groups for different purposes. Morse code was created by Samuel Morse as a way to send telegraphic messages. It uses a series of dots and dashes to represent letters and slash marks to separate words.

Other well known codes that are not necessarily secret codes are ASCII, used in computers, and Code 39, commonly used in bar code scanners, such as those used in supermarkets. Both operate from a binary code, using only two numbers: 1 and 0. 1 indicates a computer switch is on, and 0 indicates a switch is off. This seemingly simple system can translate 1s and 0s into an infinite arrangement of numbers and letters, such as the name and price of a grocery item that appears on the register.

Substituting numbers for letters, letters for letters, and writing words or entire messages backwards are all examples of ways to encode messages. These tips below can help you with decoding:

  1. Consider if symbols have been used to represent letters or entire words.
  2. Decode short words first.
  3. Remember that identical symbols represent identical letters or words.
  4. The order of frequency for letters in the English language is:
    ETOANIRSHDLCWUMFYGPBVKXQJZ
  5. Replacing symbols that appear repeatedly in the coded message with one of these letters can help.
  6. Spaces between symbols may indicate a space between words.
  7. Once a symbol has been decoded, the correct letter or word should be substituted immediately in the message wherever it appears.

The activities in this lesson address Common Core State Standards CCSS.ELA-Literacy.CCRA.SL.1 and CCSS.ELA Literacy.CCRA.SL.2. See the Standards Matrix included in the appendix for more detailed information.