Lesson 2: Applying and Teaching Basic Cryptography

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Unit 3: Understanding How Cryptography Protects Digital Information

Lesson 2: Applying and Teaching Basic Cryptography

In this lesson, participants will apply a Caesar cipher to encode and decode messages. They will examine the limitations of simple encryption methods and explore how cryptography can be introduced through age-appropriate classroom activities.

Participants will then receive new evidence from the Riverside Middle School investigation. They will compare this information with their initial conclusions and revise their security recommendations when appropriate.

Instructional Content

1. Applying a Caesar cipher

A Caesar cipher replaces each letter with another letter a fixed number of positions away in the alphabet.

With a shift of three, A becomes D, B becomes E , and C becomes F .

2. Encoding and decoding messages

Encoding a message means moving each letter forward by a chosen number of positions in the alphabet.

Decoding reverses the process.

For example:

For example:

SAFE -> VDIH

VDIH-> SAFE

3. Understanding the limitations of a Caesar cipher

A Caesar cipher has only a few possible letter shifts. Someone who does not know the key can test the possible shifts until the message becomes readable.

Therefore, a Caesar cipher is useful for demonstrating encryption but does not provide meaningful protection for sensitive digital information.

4. Adapting cryptography activities

Teachers can adjust cryptography activities to students' grade levels.

Younger students may use alphabet strips and short messages. Middle school students may compare different shift values. High school students may investigate why simple substitution methods are vulnerable to attacks.

Existing Cybersecurity Resources

Access Information: Creating an account and accessing existing resources is free.

1. Code.org - Simple Encryption
   • Review the cipher activity and consider how its instructions, examples, and materials could be adapted for different grade levels.

Activity 1: Create and Decode a Secret Message

Instructions: Use the Caesar cipher below to practice encoding and decoding messages.

1. Encode CAT using a shift of three.
2. Decode VDIH using a shift of three.
3. Encode LEARN using a shift of three.
4. Explain why the Caesar cipher would not be suitable for protecting real school records.

Answer guide: FDW, SAFE, and OHDUQ. Caesar ciphers are vulnerable because there are few possible shifts to test.

Activity 2: Riverside Middle School — New Evidence

Case File 2: Investigation Update

The technology coordinator confirms that the cloud-based service used to store the document already provided encryption. However, the sharing permissions allowed anyone with the link to access its contents.

The investigation also reveals that several staff members did not understand how document-sharing permissions worked.The coordinator recommends reviewing both security settings and staff training procedures. Participant Instructions Return to the conclusions you recorded in Lesson 1.

1. What new information does this report provide?
2. How does this evidence change your understanding of the incident?
3. Which of your original recommendations remain appropriate?
4. Which recommendations would you revise?
5. Why is controlling access to information important even when encryption is available?

Facilitator answer guide

A strong response explains that the information was already protected by encryption in the cloud service, but the sharing permissions allowed unintended access.

Participants should recommend reviewing access settings, limiting document-sharing permissions, and providing staff training.

They should explain how the new evidence supports or changes their initial conclusions rather than changing their answers simply because new information was provided.

Classroom Teaching Example: Secret Messages

Suggested grade level: Grades 3–5.

Students encode short messages with a Caesar cipher. They exchange their encoded messages and attempt to decode them using the appropriate shift. Afterward, students discuss how the method works and why a simple cipher is not sufficient to protect sensitive information.

Participant reflection: How would you adapt this activity for middle school or high school students?

Unit 3 Final Teaching Application

Title: Adapting Cryptography for K–12 Instruction

Participants select a grade level and create a short classroom activity that introduces encryption and decryption. It should include a learning objective, materials, student instructions, an explanation of age-appropriate adaptations, and a brief assessment.

The activity can be used or expanded in the final cybersecurity lesson plan in Unit 4.

Click here to continue to Unit 4: Designing a Standards-Aligned Cybersecurity Lesson

Click here to return to Lesson 1: Understanding Encryption and Decryption or Unit 3: Understanding How Cryptography Protects Digital Information