Section 3.6

Learning Goals

• IOC-2.B.5: Students will define the vocabulary terms:  encrypt, decrypt, symmetric encryption and Caesar cipher.

• Students will encrypt and decrypt a message using a Caesar cipher algorithm.

• Students will evaluate the limitations of symmetric encryption as it relates to personal data.

Objectives and General Description

Another method of protecting our personal data is to encrypt the data.  In this lesson, students will practice symmetric encryption by using a Caesar cipher algorithm.  Students will watch two short videos, encrypt a message, decrypt another message and evaluate the limitations of symmetric encryption.  

Activities

Activity 3.6.1 (budget  25 minutes)

1. Introduction: Each student needs a piece of notebook paper.  Have them fold it in half.  On the top half, have each student write a short, school appropriate text message or tweet to a friend inviting them to a party.  Put this away for a few minutes.

2. Now that we know about vulnerabilities in the transfer of data, what are ways that we can protect our data?  Have students brainstorm answers and add to a Padlet or a word cloud to promote discussion.

3. Watch this short video on Caesar cipher (2 minutes).

4. Have students take out their paper with the text message again.  Using a Caesar cipher, they should encrypt the message on the bottom of the page.  Cut the two halves apart.  They keep the original message.  They should put their name on the  encrypted message and give it to the teacher.

5. The teacher needs to randomly hand out the encrypted messages and challenge the students to decrypt without knowing the key.

6. Give students about 10 minutes to try to break the code.  If they can’t, the student should ask the message creator what the key is and then decrypt.

7. Discussion:  This is a symmetric encryption...the same key encrypts and decrypts.  What are the limitations of this type of encryption?

8. Watch Enigma Encryption machine video (10 minutes)

9. Discuss impact of the enigma machine.

10. Reflection questions:  Can be answered in journals, ticket out the door, verbally, etc.

    • How secure is symmetric encryption?  

    • Would a message that was encrypted with a symmetric encryption algorithm be challenging to hack?  

    • What is a hacker?  

    • Are there beneficial and/or harmful effects of hacking?

    • What are the limitations of symmetric encryption?

Resources

• 3.6.1: Caesar Cipher Video (teacher resource)

• 3.6.1: Enigma Encryption Machine Video (teacher resource)