15110 Fall 2011 [Cortina/von Ronne]
Written Homework 10 - due Friday, November 18 in class
Read chapter 5 and Appendix A of the book
Blown To Bits.
Type or neatly write the answers to the following problems.
Please STAPLE your homework before you hand it in.
On the first page of your homework, include your name,
andrew ID, lab section (A-N), and the assignment number.
You must hand in your homework at the start of class on the given due date.
- (1 pt)
Explain the main differences between circuit switching and
packet switching. Which is used on the Internet? Why?
- (1 pt)
Using the original IPv4 addressing scheme, a computer gets the IP
address 188.8.131.52 .
What type of address is this:
class A, class B, or class C? Why?
Based on your answer from part (a), which numbers of the IP address
will all computers in this organization share? Explain.
- (2 pts) The Internet is based on a number of different
What is a communication protocol? What aspects of communication
does it regulate?
Which aspect of communication is regulated by TCP's
... a source port, a destination port, a sequence number,
and the actual data occur at specific locations within a
... the sequence number indicates the order in which the packets should
... the receiver should send an acknowledgment after it receives each
Real Time Protocol (which streams voice/video data) is normally layered
above UDP rather than TCP. What characteristics of TCP make it less
desirable than UDP for streaming voice/video traffic?
Suppose the Jet Propulsion laboratory develops a new protocol describing
how frames containing data can be transmitted over radio waves directly
between a satellite orbiting earth and one orbiting mars. To which of
the layers in the four-layer internet model would this protocol belong?
Briefly explain your reasoning.
- (2 pts) While discussing RSA encryption, we looked at some
simpler encryption algorithms that lasted for many years. For
each of these problems, show your work for maximum credit.
Encode the message PACKETSWITCHING using a Caesar cipher with a
shift of 8.
Encode the message INTERNETPROTOCOL
using a Vigenere cipher (as discussed in class) with a
key of EMAIL.
Decode the message RNXXNXXNUUNWNAJW
that was encoded using a Caesar cipher.
What is the shift that was used?
Decode the message CIABIRWIQCEEO
that was encoded using a Vigenere cipher.
HINT: The key is in this sentence.
- (2 pts)
Consider a public key encryption system using RSA encryption
that starts with two prime numbers p = 103 and q = 337.
Compute the public key pair (e, n)
and the private key pair (d, n)
for this system. Select the smallest value for e that
will work, and then select the smallest value for d that
will work given your value for e. Show your work.
Consider the numerical message 15110 that is to be
What is the encrypted message that should be transmitted using this
system? Show your work.
Verify that the receiver can decode the message from part (b)
using the private key pair. Show your work.
Why is RSA considered secure? Explain briefly.
You may use irb to help you with the large computations
for problem 5.
- (1 pt)
Based on your reading in Blown To Bits, Appendix A, answer
the following questions:
Suppose an ISP company
starts a service to sell movie downloads. As part of this new venture,
the company examines packets being sent to its users and slows down
a user's connection if they detect packets from a competing movie
provider. Does this violate the principle of net neutrality?
Why or why not?
If you have ten computers at home all connected to the Internet via
your ISP, how many unique IP addresses do you get? Briefly explain how
traffic is routed to each computer.
- (1 pt)
Based on your reading in Blown To Bits, Chapter 5,
you learned that today's
encryption methods allow anyone to encrypt email and other data
being sent. The U.S. Government was very concerned about this type
of technology since terrorists could use it to communicate without
revealing their messages. What did the U.S. Government try to do
in the 1990s to control this situation, and why did they give up
trying to regulate encryption technology in the 2000s,
even after the attacks of 9-11?