This lesson introduces the concept of algorithms through activities about encryption and security. It was originally delivered to a group of seven middle school students who were assumed to have no background knowledge in computer science.
In this lesson, students are introduced to encryption and decryption by thinking about information they (and the computer) need to keep secret, such as passwords. Then they pretend they are CIA agents who must decrypt a secret code intercepted from criminals, which turns out to be Caesar's Cipher. Finally, the students come up with their own encryption system and write "algorithms" for their classmates to decode their secret messages. In between the activities, the class discusses effective encryption systems and how computer algorithms can help us encrypt and decrypt text.
The goal of this lesson was to spark student interest about computer science by evoking the mysterious, high-stakes world of cybersecurity. Although cybersecurity and cryptography are complex fields, Caesar's Cipher provides an accessible introduction to core concepts in CS and security.
Below is my lesson plan, followed by additional materials.
Additional materials: Encryption activity worksheet (the teacher can fill in the numbers that correspond to the letters on the cipher to help students' thought process, or just leave the spaces blank so the students can fill in the shifted alphabet)
The additional message to decrypt in the first activity is: AQW JCXG ETCEMGF VJG EQFG!