15-110 Summer 2015

Problem Set 10

Reading Assignment

Read Chapter 5 of Blown to Bits.

Instructions

• 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, and the assignment number.
• You must hand in your homework at the start of class on the given due date.

1. (3 pts) Open a command line terminal on an Andrew machine and run the following commands. Describe in a sentence or two what you understand from the output of each command. You are not expected to understand every detail; try to extract the most useful information you can from the output. You are encouraged to use the Web as a resource. You can also use the man command to read the manual pages about a given Unix/Linux command. For example, man who would give you information about what who does and how to use it.

   Here's an example of the kind of answer we want (for the command hostname): "hostname gives the name of the computer you are using."

   1. host 128.2.205.30
   2. host www.facebook.com
   3. ping -c 5 www.facebook.com
   4. traceroute www.nytimes.com
   5. wget www.facebook.com (check your folder using command ls to see if there is a new file. what is it?)
   6. whois cmu.edu

2. (3 pts) Again, feel free to search the Web to help you answer these questions. Your answers should be just a sentence or two.

   1. How do you find the IP address of the computer you are using?
   2. What is the purpose of a router? Do routers typically "know" if they are handling an email or an image? Why or why not?
   3. Can one IP address correspond to more than one hostname? If so, show an example from the Internet.
3. (2 pt) J. Nielsen says “Don't listen them” although he believes in user centered studies (you can check the web page he explains his thoughts). Explain why talking to users about their expectations will not be sufficient enough. What else can be done in order to understand user expectations better (write at least 2 suggestions).
4. (1 pt) It is said that "Testing with one user is 100% better than testing none." Explain this sentence. Why testing with at least one user is encouraged?
5. (1 pt) Answer the following questions based on your reading of Blown to Bits, in addition to your understanding of the lecture material.
1. Suppose someone came up with an algorithm that could factor any large integer in less than a few seconds. How would that affect e-commerce?
2. What is meant by "security through obscurity"? Do cryptographers adopt this as a principle? Why or why not?