Physical Ciphers

Overview

Create encryption/decryption schemes that are based on physical items.

Purpose

Demonstrate how encoding can happen based on objects that act as keys.

Objectives

Students will be able to:

• Encode/decode a message using a scytale.
• Encode/decode a message using a railfence cipher.

Preparation

• Several Dowels or PVC Pipes of various diameter
• Strips of paper - 1/2 inch
• Tape

Links

• For the Teacher
  • https://en.wikipedia.org/wiki/Scytale
  • https://en.wikipedia.org/wiki/Rail_fence_cipher
• For the Students

Vocabulary

Teaching Guide

Getting Started

Describe the Scytale (pronounced skittle-e, rhymes with Italy) and how the message is written on a strip wrapped around.

Activity

Have students pick a scytale and write a message. Once a message is written, they should trade with another group and try to determine the scytale the other group had used. The different diameters will affect the decoded message.

After groups have explored the scytale, describe a railfence where the message is written diagonally, bouncing up and down between two “fences”.
The encoded message is obtained by reading the message along the horizontal rows.

Wrap-up

Discussion

• How are these two ciphers similar? Different?
• What level of security do they offer?
• Can these ciphers be used in a digital context?

Assessment Questions

• What method could you use to break the scytale or railfence cipher?
• What is another physical way of encrypting a message?

Extended Learning

Standards Alignment

License

Cyber Security Curriculum is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.