Day 12: Cryptography Basics

Learning Objectives

• CSN-1.F: Explain how the design of the Internet and the Internet protocols contribute to reliability and scalability.

Essential Questions

• How does cryptography protect information in computer systems and networks?
• What are the fundamental techniques used in modern cryptography?
• How has cryptography evolved throughout history?

Materials Needed

• Presentation slides on cryptography principles
• Encryption/decryption worksheets
• Simple cipher tools (Caesar cipher wheels, etc.)
• Online encryption tools or programming environment
• Exit ticket templates

Vocabulary

• Cryptography
• Encryption
• Decryption
• Cipher
• Key
• Plaintext
• Ciphertext
• Symmetric encryption
• Asymmetric encryption
• Public key
• Private key
• Hash function

Procedure (50 minutes)

Opening (8 minutes)

1. Review and Connection (3 minutes)

   • Review cybersecurity fundamentals from previous lesson
   • Connect to today's focus on cryptography as a security tool

2. Warm-up Activity (5 minutes)

   • Show students a simple encrypted message (e.g., Caesar cipher)
   • Challenge them to try to decode it
   • Discuss the concept of secret communication
   • Introduce cryptography as the science of secure communication

Main Activities (32 minutes)

3. Lecture: Cryptography Principles (12 minutes)

   • Define cryptography as techniques for secure communication
   • Explain key cryptographic concepts:
     • Encryption: Converting plaintext to ciphertext
     • Decryption: Converting ciphertext back to plaintext
     • Keys: Information used in encryption/decryption algorithms
     • Cryptographic algorithms: Methods for encryption/decryption
   • Discuss types of cryptography:
     • Symmetric encryption: Same key for encryption and decryption
       • Examples: AES, DES
       • Key distribution problem
     • Asymmetric encryption: Public/private key pairs
       • Examples: RSA, ECC
       • Public key encrypts, private key decrypts
     • Hash functions: One-way functions that produce fixed-length output
       • Examples: SHA-256, MD5
       • Used for integrity checking and password storage
   • Explain how cryptography supports security goals:
     • Confidentiality: Keeping information secret
     • Integrity: Ensuring information hasn't been altered
     • Authentication: Verifying identity
     • Non-repudiation: Preventing denial of actions

4. Demonstration: Encryption Techniques (8 minutes)

   • Show examples of historical ciphers:
     • Caesar cipher (substitution)
     • Vigenère cipher (polyalphabetic)
   • Demonstrate modern encryption:
     • Symmetric encryption example
     • Public key encryption example
     • Hash function example
   • Show how encryption is used in everyday applications:
     • HTTPS websites
     • Secure messaging
     • Password storage
     • Digital signatures

5. Activity: Encrypting and Decrypting Messages (12 minutes)

   • Divide class into pairs
   • Guide students through encryption exercises:
     • Simple substitution cipher (manual)
     • Caesar cipher with different keys
     • Using online tools for modern encryption
   • Have pairs exchange encrypted messages and decrypt them
   • Challenge students to break each other's simple ciphers
   • Discuss the strength of different encryption methods
   • Connect to the importance of key length and algorithm strength

Closing (10 minutes)

6. Discussion: Historical and Modern Cryptography (5 minutes)

   • Lead a discussion on the evolution of cryptography:
     • Ancient ciphers and codes
     • World War cryptography (Enigma machine)
     • Development of modern cryptography
     • Quantum cryptography and future challenges
   • Discuss the balance between security and usability
   • Address any misconceptions about encryption

7. Exit Ticket: Simple Encryption Implementation (5 minutes)

   • Students implement a simple encryption algorithm
   • Options include:
     • Caesar cipher with a specific key
     • Simple substitution cipher
     • Using a provided function for modern encryption
   • Students explain how their implementation works
   • Collect implementations before students leave

Assessment

• Formative: Quality of encryption/decryption activities
• Exit Ticket: Correctness of encryption implementation

Differentiation

For Advanced Students

• Ask them to implement more complex encryption algorithms
• Have them explore cryptographic attacks and weaknesses
• Challenge them to explain mathematical concepts behind modern cryptography

For Struggling Students

• Focus on simpler encryption techniques
• Provide step-by-step guides for encryption activities
• Use more visual aids and concrete examples

Homework/Extension

• Research a specific encryption algorithm and create a summary
• Implement a more advanced encryption technique in code
• Create an infographic showing how encryption protects data online

Teacher Notes

• Use analogies to help students understand encryption concepts (e.g., locked boxes, secret languages)
• Be prepared to address questions about encryption controversies (e.g., backdoors, government access)
• Make connections to students' everyday experiences with encryption
• Consider discussing ethical implications of encryption technology
• Emphasize that understanding cryptography helps students evaluate security claims