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Cryptography

Throughout history codes have been used to pass secure information. In these activities students will learn about past and present methods of cryptography while working hands-on to code and decode vital information.

Objective: Students will learn about modular (clock) arithmetic and how modular arithmetic can be used to encode messages using simple shift, multiple, and affine ciphers.

Materials: Each student will need

• Paper
• Pencil or Pen
• Computer with internet access (students can share computers if necessary)

Introduce the topic to students. Consider these exploration questions:

• Why is cryptography needed? Why do we put things into code?
• Where have you seen cryptography before? Online passwords, ATM machines, etc.
• Have you heard of it being used in the past? The Zimmermann telegram hastened the entry of the U.S. into World War I.
• Have you heard of Caesar Cipher?

The following sections will guide students through activities exploring cryptography.

• Introduction to Modular Arithmetic: Students will learn about modular arithmetic and begin discussing its applications in cryptography.
• Introduction to Cryptography: Shift Ciphers Students will learn how to encode messages using modular arithmetic to create a shift cipher.
• Introduction to Cryptography: Caesar Ciphers Students will learn how to encode messages using modular arithmetic to create a Caesar cipher.
• Codebreaking Activities Students practice codebreaking with a few additional activities.