May 3, 2021

Instructor’s Manual Materials to Accompany

COMPUTER SECURITY FUNDAMENTALS

CHAPTER 8

ENCRYPTION

CHAPTER 8 OBJECTIVES

When students finish reading this chapter, they will be able to:

• Explain the basics of encryption.

• Discuss modern cryptography methods.

• Select appropriate cryptography for your organization.

• Understand the function and protocols of VPNs.

CHAPTER OVERVIEW

In this chapter, students learn a basic element of computer security called encryption. This chapter provides basic

information on how cryptography works. Encrypting data when transmitting is a must when it is sent over public

networks, and it is an integral part of any security plan. Several types of encryption are covered as well as using

encryption to transmit data over public networks using Virtual Private Networks, VPNs.

The major sections in this chapter are

1. Cryptography Basics. Explanation of cryptography, some history, and some simple examples are used to

show how basic cryptography works.

3. Hash: Cryptographic Hashes

4. Steganography: History and modern methods.

CHAPTER OUTLINE

I. Chapter 8 Objectives

II. Introduction

III. Cryptography Basics

IV. History of Encryption

The Caesar Cipher

Multi-Alphabet Substitution

Binary Operations

AND

OR

XOR

Vigenere’

Enigma

V. Modern Methods

Single Key (Symmetric) Encryption

2. 3DES

3. AES

Public Key (Asymmetric) Encryption

2. RSA

Legitimate Versus Fraudulent Encryption Methods

Digital Signatures

Hashing

Authentication

VI. Steganography

VII. Summary

VIII. Test Your Skills

IX. Exercises

X. Projects

KEY TERMS

binary numbers Numbers using the base 2. Ultimately, all data on a computer is stored in a base 2 format.

block cipher Ciphers that encrypt blocks of text at a time (for example, 64 bytes at a time).

Blowfish A well-known encryption algorithm.

cipher text Encrypted text.

cryptography The study of encryption and decryption.

Data Encryption Standard (DES) A widely used block cipher encryption algorithm.

decryption To break encryption and discover the underlying message.

Internet Protocol Security (IPSec) A protocol critical for securing virtual private networks.

Layer 2 Tunneling Protocol (L2TP) A protocol that is used to create virtual private networks. It is a successor to

the older point-to-point tunneling protocol (PPTP).

mono-alphabet substitution A primitive encryption algorithm in which there is one single substitute character

for all plain text characters.

multi-alphabet substitution A primitive encryption algorithm in which there are multiple substitute characters

for all plain text characters.

Point-to-Point Tunneling Protocol (PPTP) A protocol used in virtual private networks. It is based on the earlier

point-to-point protocol (PPP).

single-key encryption An encryption method in which the same key is used to both encrypt and decrypt a

message. This is also referred to as symmetric key encryption.

stream cipher A type of cipher in which the original text is encrypted one byte at a time in a stream of bytes.

TEACHING NOTES

I. Cryptography Basics

Teaching Tips: Let students know that they can still use cryptography even if they do

A. History of Encryption

Teaching Tips: The history of encryption is the history of secrets. Point out that many wars were won or

B. The Caesar Cipher

Teaching Tips: Compare the Caesar cipher to a secret decoder ring, such as the one given as a prize to

C. In Practice

Teaching Tips: Demonstrate that text in a computer is actually stored as 8-bit binary

numbers. With the ASCII chart, you can show that sorting from a through z puts the characters into

numerical order. Demonstrate or have students convert a few ASCII words from text to numbers.

Teaching Tips: A simple way to demonstrate XOR is the following: Where there is a

II. Modern Methods Teaching Tips: Single-key encryption is easy and fast for a computer.

However, stress that it is hard to deliver the one key to the people that need it. This continued to be a

problem with cryptography, even through WWII. Keys would get intercepted, and messages would get

decrypted.

Teaching Tips: Public key programs need a great deal of processing, and therefore it

is not a good way to send messages. The best way to send messages is to use public key encryption to

III. Virtual Private Networks

Teaching Tips: VPNs are a great way to secure data transmission through a public

PROJECTS/EXERCISES

I. Discussion Questions

A. Discussion Question 1

Should governments restrict the use of “strong encryption?”

B. Discussion Question 2

Should network administrators have decryption keys to files on your company computer?

II. Web Projects

A. Web Project 1

It is easy to use encryption to hide messages inside of other objects.

Steganography is the art of hidden writing. You can get Hide In Picture (HIP) at

http://www16.brinkster.com/davitf/hip/. You can then encrypt a message or even a

program that can be extracted by using an encryption key. Download HIP, hide a text

message in a picture, and send the picture and key to someone to see whether they can

extract the secret message. How could you detect hidden messages in web page images?

B. Web Project 2

ROT13 is an interesting encryption algorithm in that it has no key. It uses a form

of the Caesar cipher to encrypt text. Try encoding a message by entering text in the box at

http://www.rot13.com/ and clicking the Cypher button. Exchange your encrypted

message with someone else in class. Then enter the coded message you’ve received into

text box, and click the Cypher button again. The message will be revealed. If you apply

ROT13 to the text message, it comes out encrypted. But if you re-apply the same ROT13

a second time to the encrypted message, it comes out decrypted. Now why would anyone

use an encryption method that is so trivial to crack?

C. Web Project 3

Download and install the free Cryptainer LE from http://www.cypherix.co.uk/.

This software sets up a 25-meg encrypted “virtual drive” on your computer using 128-bit

Blowfish encryption. Take a text file and put it into the encrypted “drive.” Click Unload.

Then try to access the encrypted disk file using Notepad. (Using Office XP, that file is by

default \WINNT\systems32\cxl17xx.) Do you see any of the text here? Can anyone read a

file in this virtual drive if your laptop were stolen?

D. Web Project 4

Go to Google and type in “SSL.” Find out what SSL is. Can you use SSL to use

your credit card number over the Internet without it being intercepted? A good place to

start is http://www.webopedia.com/TERM/S/SSL.html.

WEB RESOURCES

• Cryptography history resources

http://cse.stanford.edu/classes/sophomore-college/projects-97/cryptography/history.html — The

Stanford University History of Cryptography Web site provides an overview of cryptography and

why it is necessary.

CHAPTER REVIEW/ANSWERS TO TEST YOUR SKILLS

Multiple Choice Questions

1. Which of the following most accurately defines encryption?

2. Which of the following is the oldest encryption method discussed in this text?

3. What is the main problem with simple substitution?

4. Which of the following is an encryption method using two or more different shifts?

5. Which binary mathematical operation can be used for a simple encryption method?

6. Why is binary mathematical encryption not secure?

7. Which of the following is most true regarding binary operations and encryption?

8. What is PGP?

9. Which of the following methods is available as an add-in for most e-mail clients?

10. Which of the following is a symmetric key system using 64-bit blocks?

11. What advantage does a symmetric key system using 64-bit blocks have?

12. What size key does a DES system use?

13. What type of encryption uses different keys to encrypt and decrypt the message?

14. Which of the following methods uses a variable-length symmetric key?

15. What should you be most careful of when looking for an encryption method to use?

16. Which of the following is most likely to be true of an encryption method advertised as

unbreakable?

17. Which of the following is most true regarding certified encryption methods?

18. Which of the following is most true regarding new encryption methods?

19. Which of the following is the oldest protocol used by VPN?

20. Which of the following is used by PPTP to encrypt packets?

Exercises

EXERCISE 7.1: USING THE CAESAR CIPHER

EXERCISE 7.2: USING MULTI-ALPHABET CIPHERS

EXERCISE 7.3: USING PGP

EXERCISE 7.4: FINDING GOOD ENCRYPTION SOLUTIONS

This exercise is about teaching students to recognize signs of unwarranted claims made by an encryption

EXERCISE 7.5: LEARN MORE ABOUT VPN

This exercise requires students to do some independent research and to synthesize the information that

Projects

PROJECT 7.1: RSA ENCRYPTION

This project is designed to teach students to use the web as a resource to find out more details about any

PROJECT 7.2: PROGRAMMING CAESAR CIPHER

This project is meant to show students the basic concepts involved in programming an encryption

PROJECT 7.3: OTHER ENCRYPTION METHODS

Students should identify the essentials of how the algorithm they choose works, when it was invented, by

Case Study

This case study is designed to give students a chance to practice selecting appropriate encryption