This document discusses public key encryption and its advantages over traditional symmetric encryption. It explains that public key encryption allows a user to publicly share their public key, while keeping their private key secret, allowing others to encrypt messages only they can decrypt. The document provides an example of how Bob could encrypt a message for Alice using her public key, so that only Alice can read it with her private key. It aims to help students understand public key encryption and how it works.

1. L.O: STUDENTS WILL BE
ABLE TO EXPLAIN PUBLIC
KEY ENCRYPTION.
40-45 minutes
DO NOW:
READ Unit 2 Lab 6: Encryption,
Page 3

2. Public Key Encryption:
• the methods discussed
so far all have a basic
weakness: the
encryption method or
key needs to be kept
secret. But keeping the
key private is almost as
hard as keeping the
message private.
In 1976 Ron Rivest, Adi
Shamir, and Len Adleman
devised an ingenious method
(now known as RSA) that
allows a person to announce
publicly how anyone can
encode a message to him so
that only he is able to
decipher it.
The information, which
is given away to
everybody, is called the
public key. The
information which is
needed for deciphering
(the private key) is
known only by the
person for whom the
message is intended.
If Bob wants to send Alice
a secret message, he
enciphers it with Alice's
public key. Then no one
else can decipher it, even
knowing her public key.
Only her private key can
undo the encryption, and
you can't figure out the
private key from the public
key.

3. For You To Do
1. It may seem incredible that
Alice can make her encryption
key public and still no one
except her can decrypt her
message. The RSA method
relies on some mathematics
and on some limitations on
the speed of current
computers. Read "Secrecy
Changes Forever" (Blown to
Bits pages 178-181) to
understand some of how this
works

4. Here is a model of public key encryption
(from wikimedia.org)
2. With a partner, discuss how these pictures are different.
Would you trust this method to work to send your own
credit card number?
Take it further: (extension activity)
Read "The Key Agreement Protocol" and "Public Keys for Private
Messages" (Blown to Bits pages 181-183) for more details on Public
Key Encryption.

5. HOMEWORK:
read Chapter 5 of “Blown to Bits”.
Reading through the entire chapter will be helpful,
especially to get a better understanding of the
evolution of encryption methods and some details of
public key encryption.

6. Learning Objectives:
1. LO 6.3.1 Identify existing cybersecurity
concerns and potential options to
address these issues with the Internet
and the systems built on it. [P1]
2. LO 7.5.2 Evaluate online and print
sources for appropriateness and
credibility [P5]
GIVE EXAMPLES OF THESE LEARNING OBJECTIVES IN THE LESSON

7. Enduring Understandings:
1. EU 6.3 Cybersecurity is an important
concern for the Internet and the systems
built on it.
2. EU 7.5 An investigative process is aided by
effective organization and selection of
resources. Appropriate technologies and
tools facilitate the accessing of information
and enable the ability to evaluate the
credibility of sources
EXPLAIN THESE “ENDURING UNDERSTANDINGS”

8. Essential Knowledge:
1. EK 1.2.5A The context in which an artifact is used
determines the correctness, usability, functionality, and
suitability of the artifact.
2. EK 1.2.5B A computational artifact may have weaknesses,
mistakes, or errors depending on the type of artifact.
3. EK 1.2.5C The functionality of a computational artifact may
be related to how it is used or perceived.
4. EK 1.2.5D The suitability (or appropriateness) of a
computational artifact may be related to how it is used or
perceived.
5. EK 3.2.2D Maintaining privacy of large data sets containing
personal information can be challenging.
EXPLAIN THESE “ENDURING UNDERSTANDINGS”

9. Essential Knowledge:
• 6.EK 3.3.1A Digital data representations involve trade-
offs related to storage, security, and privacy concerns.
• 7.EK 3.3.1B Security concerns engender trade-offs in
storing and transmitting information.
• 8.EK 3.3.1F Security and privacy concerns arise with
data containing personal information.
• 9. EK 5.4.1L An explanation of a program helps people
understand the functionality and purpose of it.
• 10. EK 5.4.1M The functionality of a program is often
described by how a user interacts with it
EXPLAIN THESE “ENDURING UNDERSTANDINGS”

10. Essential Knowledge:
• 11.EK 6.1.1A The Internet connects devices and
networks all over the world.
• 12.EK 6.1.1D The Internet and the systems built on it
facilitate collaboration.
• 13.EK 6.3.1A The trust model of the Internet involves
trade-offs.
• 14. EK 6.3.1B The DNS was not designed to be
completely secure.
• 15. EK 6.3.1C Implementing cybersecurity has
software, hardware, and human components.
• 16. EK 6.3.1D Cyber warfare and cyber crime have
widespread and potentially devastating effects
EXPLAIN THESE “ENDURING UNDERSTANDINGS”

11. Essential Knowledge:
• 17. EK 6.3.1H Cryptography is essential to many
models of cybersecurity.
• 18. EK 6.3.1I Cryptography has a mathematical
foundation.
• 19. EK 6.3.1J Open standards help ensure
cryptography is secure.
• 20. EK 6.3.1K Symmetric encryption is a method of
encryption involving one key for encryption and
decryption.
• 21. EK 6.3.1L Public key encryption, which is not
symmetric, is an encryption method that is widely
used because of the functionality it provides.
EXPLAIN THESE “ENDURING UNDERSTANDINGS”

12. Essential Knowledge:
• 22.EK 6.3.1M Certificate authorities (CAs) issue
digital certificates that validate the ownership of
encrypted keys used in secured communications and
are based on a trust model.
• 23.EK 7.3.1A Innovations enabled by computing raise
legal and ethical concerns.
• 24.EK 7.3.1G Privacy and security concerns arise in
the development and use of computational systems
and artifacts.
• 25.EK 7.3.1L Commercial and governmental curation
of information may be exploited if privacy and other
protections are ignored.
EXPLAIN THESE “ENDURING UNDERSTANDINGS”