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Computer Science Principles Unit 4 Chapter 1 Lesson 9: Public Key Cryptography

Subject Area

Digital Literacy and Computer Science


9, 10, 11, 12


This is a big multi-part lesson that introduces the concept of public key cryptography which is an answer to the crucial question: How can two people send encrypted messages back and forth over insecure channels (the Internet) without meeting ahead of time to agree on a secret key? In a nutshell, there are two main principles we want students to understand:

  1. The mechanics of communication with public key cryptography
  2. The basic mathematical principles that make it possible

The lesson gets at these two core ideas through a deliberate chain of thought experiments, demonstrations, activities, and widgets. All parts are building blocks that lead to a deeper understanding of how it works.

Students will be able to:
- explain what the modulo operation does and how it operates as a "one-way" function.
- follow an asymmetric encryption algorithm to encrypt a numerical message using the Public Key Crypto widget.
- explain the difference between symmetric and asymmetric encryption.
- describe the basic process of encrypting data using public key encryption.
- explain the benefits of public key cryptography.

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    Digital Literacy and Computer Science (2018) Grade(s): 09-12


    Explain the tradeoffs when selecting and implementing cybersecurity recommendations.

    Unpacked Content



    • cybersecurity
    • two-factor authentication (TFA)
    • geolocation
    • privacy
    • cryptography


    Students know:
    • how to evaluate the tradeoffs of cybersecurity recommendations.
    • how to articulate the pros and cons of TFA.
    • the importance of password requirements.
    • how to articulate the pros and cons of geolocation.


    Students are able to:
    • explain pros and cons of cybersecurity recommendations.
    • describe the use of two-factor authentication.
    • explain the importance of password requirements.
    • describe the use of geolocation.


    Students understand that:
    • security, privacy and convenience tradeoffs are factors in selecting and implementing cybersecurity recommendations.
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