Activity Description Create your own affine cipher for encoding and decoding messages. Input your own constant and multiplier, then input a message to encode.

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Caesar Cipher

Place in mathematics curriculum:

• practice students' long division skills
• demonstrate the applications of modular arithmetic
• practice the students' logical reasoning skills

This activity allows the user to experiment with encoding and decoding messages using modular arithmetic. This activity would work well in mixed ability groups of four or five for about forty-five to fifty minutes if you use the exploration questions and twenty minutes otherwise.

Preparations for this activity:

• explain in detail and show examples of how Caesar Cipher works.
• be flexible on the time spent on this activity.
• encourage the students that they can do this if they give it a good try even though it is tricky and involved.