The Arizona STEM Acceleration Project

What is Cryptography?: Part 1

What is Cryptography?- Part 1

A High School STEM Lesson

Tabatha Hancock

April 2024

Notes for Teachers

This is part 1 of a two-part series. This lesson introduces the history of cryptography and popular ciphers.

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This lesson can be taught in a classroom setting or after-school club (such as a cybersecurity club).

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This lesson can be simplified for younger grades (consider using a video to supplement/replace articles). If students are too young to research on their own, have websites or articles to provide to groups.

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Part 2 will require purchasing an electronics kit and involve soldering and is not recommended for younger students.

List of Materials:

• White copy paper
• Markers
• Poster board
• Scissors
• Glue/tape

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Optional:

• “Rise of the Hackers” video by PBS�
• Top Secret: a handbook of codes, ciphers, and secret writing, by Paul B. Janeczko

Standards

Technology

Standard 1. Empowered Learner

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Standard 3. Knowledge Constructor

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Standard 4. Innovative Designer

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Standard 5. Computational Thinker

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Standard 6. Creative Communicator

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Mathematics

Operations and Algebraic Thinking (OA)

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Engineering

S2: Apply the Engineering Design Process

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S3: Apply Mathematics to Engineering

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S6: Apply Communications to Engineering

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English Language Arts (ELA)

Reading (Informational Text)

Speaking & Listening

Objective(s):

I will investigate cryptography.

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I will be able to define cryptography.

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I will be able to explain what a cypher is.

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I will present a brief history of a type of cypher.

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I will create my own version of a cipher.

Agenda (Setting up our investigation)

What is “cryptography”?� -Discuss Caesar ciphers.� -Introduce vocabulary.� -Discuss ways to encrypt messages.� - Introduce ciphers to be investigated.

Research Ciphers� -Separate into groups.� -Discuss group roles.� -Research ciphers.� -Modify a cipher.� -Create a class presentation.

Class Presentation� -Groups present ciphers

Current Real World Applications� -Introduce the relationship between cryptography and encryption.� -What types of information would be want encrypted?� -Importance of encryption.

Looking Forward:� -Discuss “code talkers”, musical cryptograms and the Enigma machine.

How can you safely pass on a secret message?

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If you didn’t have access to a digital device,�how could you safely pass �a secret message to your friend?

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Hands-on Activity Instructions

• Discuss opening question.
• If no one mentions secret codes, bring this idea up yourself.
• Share video about Caesar Ciphers.
• Linkto Khan Academy Caesar cipher video shared in slides:
• The Caesar cipher | Journey into cryptography | Computer Science | Khan Academy
• Students should take notes of:
• How does this cipher work?
• Why is this an ineffective cipher?
• Any words or terms they do not understand.
• Move to a class discussion on what was discovered.
• Ask for ideas of how this cipher could be modified.
• Introduce new ciphers to be investigated.

• Break students into small groups.
• Decide if you will assign ciphers or allow groups a short amount of time to choose a cipher themselves.
• Students must have their cipher choice approved by the teacher to prevent duplicated presentations.
• Explain the task.
• Consider having a printed list of objectives.
• Research cipher.
• Construct a brief history of cipher.
• Explain how the cipher works.
• Show an example of the cipher.
• Modify the cipher to make it your own.
• Create a secret message.
• Explain your process and how to decipher your message.

What is a Caesar cipher?

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Caesar ciphers are not secure.

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These ciphers are easily cracked by frequency analysis.

How could we make this cipher harder to break (decrypt)?

Different types of ciphers

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There are other “shift ciphers” (like the Affine Cipher) �that use more intricate mathematical expressions �to encrypt messages.

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A different type of transposition cipher

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The scytale

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https://mathcenter.oxford.emory.edu/site/math125/transpositionCiphers/

Substitution Ciphers

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There are some substitution �ciphers that an encryption key.

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Vigenère Cipher

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https://pages.mtu.edu/~shene/NSF-4/Tutorial/VIG/Vig-Base.html

https://www.thesquaremagazine.com/mag/article/202105the-pigpen-cipher/

Master A Cipher

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You will work in groups to research a cipher,

modify the cipher to make it your own

and create a presentation for the class.

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Description

History

Modification

How it works

Coded message

Cipher name

Share your cipher

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While groups are presenting, think about

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• How can a message be coded in a way �that doesn’t involve writing?

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• How did early ciphers lead to digital cryptography?

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Assessment

Informal assessments can be taken while monitoring group and class discussions. Use these observations to ensure students understand the basics of cryptography and how their ciphers work.

Presentations can be used as a graded summative.

To assess a deeper understanding, ask students to use the information from another group to come up with a coded message using a cipher they did not research.

Differentiation

• Use heterogeneous grouping to ensure small groups include a variety of learning/leading styles.

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• If you know your students struggle with note-taking and annotating, prepare guided notes.
• A completed set of notes should be available for students who may need it at the end.

Remediation

Extension/Enrichment

• Part 2 of this activity is a lesson on creating a digital Enigma Machine. The two lessons together will guide students through the entire engineering design process.

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• Assign an individual research project on another form of cryptography, such as Navajo Code Talkers, musical cryptograms, the Enigma Machine, encryption techniques used today for digital devices, etc.