William Slater's CYBR 515 Blog

William Slater's CYBR 515 Blog
CYBR 515 - Security Architecture and Design

Wednesday, September 7, 2011

Post 005 - CYBR 515


Week 2 Assignments

Theme for the Week - Symmetric Encryption

Learning Objectives:
Demonstrate a simple symmetric encryption and decryption technique.
Explain the role played by random and pseudorandom numbers in cryptography.
Differentiate between block ciphers and stream ciphers.
Describe the five ingredients of a symmetric encryption scheme.
Readings:
Chapter 2 in your textbook.
Special Forces Field Manual FM-31-4 (Pearson Companion Site under Documents.)
This document is located in the Documents folder as SpecialForcesCode.pdf. Please note that you will have to register to gain access to this site.

This week:
When protecting information from compromise by intruders to our network, there is no stronger tool available to us than Cryptography. Data that is properly encrypted in unintelligible to unauthorized recipients. They might be able to intercept it, but they are prevented from making any use of it. Understanding how encryption works and how to apply it helps us to be better planners. This week, we begin our discussion by looking at Symmetric Encryption, which involves the process of encrypting and decrypting data using the same key. We'll examine the principles that make this possible, and study some basic algorithms that are in common use today. We'll also explore the role played by random and pseudorandom numbers in improving the strength of our encryption.

In this week's reading, our author has included a link to an example of a real-world symmetric cipher from an old U.S. Special forces manual that is in the public domain. You can get to this document on the author's companion web site as SpecialForcesCode.pdf. You will use this manual for decrypting a message in one of your assignments.
You are now ready to proceed with the assignments below. Please read the directions carefully and submit the assignments as directed.
Assignment 2_1 (On-Line Quiz)
Take this ten question true/false and multiple choice chapter quiz over the reading assignment. Quizzes are a "participation grade," which means that you can retake them as many times as necessary. However, please be aware that low scores are a sign that you need to go back to the reading assignment, slow down, and read more carefully.

You need to take the quiz by the end of the week to earn credit.


Assignment 2_2 (Attach to this week's discussion forum)
Answer one of the following questions and post a substantive answer to this week's discussion forum. Your answer should be at least 3 paragraphs in length with proper attention given to spelling and grammar. Please select a question that has not been previously answered by one of your classmates, until all questions have been answered at least once. Once that has been done, select a question that has been answered by only one of your classmates. Once you have submitted your initial post, read each of your classmates' initial posts and respond to at least three of them. In your response, provide your comments and any additional information you might have. Remember to cite your sources. Please note that this assignment also contains a trivia question that you can post against for credit. Posts to the trivia question will count the same as a response, not as the initial post.

1. How would you go about decyphering a message that was encrypted using symmetric encryption if it is the case that you have the encryption algorithm but not the sender's key?

2. If you wanted to use symmetric encryption to send a secret message, how could you get the key to the recipient? Describe at least two different methods of transmitting the secret key.

3. How does the exclusive OR function work? Provide an example

4. What is the difference between a random number and a pseudo-random number and how is each used for encryption/decryption?

5. If you really wanted to generate truely random numbers, how could you do it? Include in your answer why random number generators are important for encryption.

6. What is the difference between a block cipher and a stream cipher? Provide an example of each.

7. What are the ingredients of symmetric encryption and how does it work?

8. Why isn't it a good idea to send the same message twice, once when it was encrypted and once in plain text?

9. What does C = E(K3,D(K2,E(K1,P))) mean (from your text)? Describe the symbols and their use.

10. If long keys are more secure than short ones, why not just use a really long key, say 65,536 bytes? In your answer, include an explanation of the purpose of key length. Is there a "perfect" size for keys?

Our trivia question for the week: What is the orange book and why is it called the orange book?

General Posting Guidelines (for participation): Postings are counted as participation for the week. Make sure all postings for this week's assignments are posted to this week's discussion forum. You must post at least two substantive messages to get minimum credit for participation (a 'C' grade). Two messages on different days gets a 'B' for participation - more postings (including answering other questions) get more credit. To qualify for an 'A' grade, you must post at least three critical thinking messages on three different days. Postings on the last day of the lesson will not count for credit since other students will not have sufficient time to respond or participate in your discussion. Post early and often. Don't wait until the last minute!
Assignment 2_3 (Attach to this assignment)
Chapter two in your text contains several models that are presented in the form of figures. Choose one of the models and explain what it represents in sufficient detail that someone who has never read the book or studied network security would understand it. Your answer should be at least 1000 words in length. Any sources must be in APA or MLA format. Save your explanation to a Word document as CYBR515 Assignment 2_3 and attach it to this assignment.


Assignment 2_4 (Attach to this assignment)
The Special Forces Field Manual explains an encryption process that uses a double transposition cipher (see your reading list for a link to this document on the author's companion website.) Using the information provided in the manual, the code words listed in the order they were used to encrypt the message, and the cypher text below, decrypt the message. Save your work to an Excel spread sheet as CYBR515 Assignment 2_4 and attach it to this assignment. Include your unencrypted, plain text message in the file. If you need help figuring out how to work the cipher in reverse, you may use the Internet and other appropriate sources to find the solution. You may also post questions to the discussion forum. However, do not share the unencrypted message with any other students.
Code words: (1) redmustang (2)nightmoves

YETAR TRIXL XWITL RSXHE
NAGPV OHSIC UOPEB ESYCO




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