Lesson 1: Understanding Encryption and Decryption
Navigation Links: ETAP 623 Fall 2026 Design Project Agenda | Taisha Dormil's Portfolio Page | Cybersecurity Awareness in the Classroom
Unit 3: Understanding How Cryptography Protects Digital Information
Lesson 1: Understanding Encryption and Decryption
Encryption helps protect digital information by transforming readable data into an encoded form. Decryption reverses this process so that authorized individuals can recover the original information. In this lesson, participants will examine the purpose of cryptography, identify plaintext and ciphertext, and explain the role of a cryptographic key.
They will then investigate a fictional incident involving exposed student information at Riverside Middle School. Using the available evidence, participants will explain how encryption could help protect information and identify additional safeguards that may be necessary.
Instructional Content
1. What is cryptography?
Modern cryptography supports secure communication, protects sensitive data, and helps verify information or identities. Students encounter cryptography when using secure websites, messaging services, and other digital platforms.
2. Understanding encryption and decryption
Encryption changes readable information into a coded form using a special method and key.
Decryption reverses the transformation so the original information can be recovered.
3. Plaintext, ciphertext, and cryptographic keys
Plaintext is the original readable information.
Ciphertext is the encoded result of encryption.
A cryptographic key is a piece of information used to encrypt or decrypt data.
For example, using a Caesar cipher with a shift of three changes HELLO into KHOOR.
4. What encryption can and cannot protect
Encryption helps protect the confidentiality of information. However, encryption does not automatically prevent every cybersecurity problem.
For example, information may be encrypted while stored on a digital service but still become accessible to unintended individuals if sharing permissions are incorrectly configured.
Understanding this distinction helps teachers explain why cybersecurity requires more than one safeguard.
Existing Cybersecurity Resources
Access Information: Creating an account and accessing existing resources is free.
- Code.org - Simple Encryption
- Review the introductory explanation of encryption and its classroom application. Consider how the activity introduces plaintext, ciphertext, and keys.
Activity 1: Understanding Plaintext and Ciphertext
Instructions: Examine the following example.
| Message A | Message B |
|---|---|
| HELLO | KHOOR |
Message B was created using a Caesar cipher with a shift of three.
Answer the following questions:
- Which message is plaintext?
- Which message is ciphertext?
- What transformation occurred?
- What information is needed to reverse the transformation?
Expected responses: Message A is plaintext; Message B is ciphertext. Each letter was shifted three positions forward. Decoding requires knowing the method and shift value.
Activity 2: Riverside Middle School Cybersecurity Investigation
Case File 1: Exposed Student Information
Riverside Middle School recently discovered that a document containing student names and school email addresses was accessible to individuals outside the school.
The document was stored on a cloud-based service, and its sharing settings allowed anyone with the link to view it.
School administrators are concerned about how the information became accessible and want to know whether encryption could have prevented the incident.
The school's technology coordinator has not yet completed the investigation.
Participant Instructions
You are reviewing the incident. Based on the information currently available, answer the following questions:
- What information was exposed?
- What cybersecurity concerns does this incident raise?
- How could encryption help protect student information?
- Would encryption alone prevent this type of exposure? Explain your reasoning.
- What two safeguards would you recommend?
- What additional evidence would help you understand the incident?
Record your Initial thinking. Save your responses. You will revisit them in Lesson 2 when new evidence becomes available.
Classroom Teaching Example: Who Can Read the Message?
Suggested grade level: Grades 6–8.
A teacher displays an ordinary message and an encrypted message. Students identify which message is readable and discuss how encryption changes information.
Next, the teacher introduces a situation where someone with permission to view a document shares its contents with another person.
Students explain why encryption does not automatically prevent someone with access from sharing information.
Participant reflection: How could this activity help students understand the difference between encryption and access permissions?
Click here to continue to Lesson 2: Applying and Teaching Basic Cryptography
Click here to return to Unit 3: Understanding How Cryptography Protects Digital Information