This exam is open-book, open-notes, open-computer, and open-Internet, but closed-other-people. You may, however, ask Jeff Ondich questions.

Some of the questions are easy to answer if you have a pen and a piece of paper, while others will require you to do some research, probably on the Web. Answer the questions as completely and clearly as you can. Have fun.

1. (10 points) Suppose you want to use the UNIX command telnet as an HTTP client, and your goal is to retrieve the file whose URL is http://www.mathcs.carleton.edu/faculty/jondich/cs337/Assignments/midterm1.html.

   You will probably need to look at RFC 2616, "Hypertext Transfer Protocol -- HTTP/1.1," which is a 114-page document. Fortunately, it starts with a table of contents, which you should read and use wisely.

   • What UNIX command (including command-line arguments) will you execute?

   • Once connected to the appropriate HTTP server, what do you need to type to retrieve the file in question?

   • What information does the HTTP server send before it sends the contents of the file?

   • After the file arrives, does the server cut you off, or does it wait for a new request?
   
   
   
2. (8 points) What is RSA 129? In whose column was it introduced? Who solved it, when, and how? What are the magic words, and what do they mean?
   
   
3. (8 points) Suppose N is the 129-digit product of a 65-digit prime and a 64-digit prime. If you try to factor this number by computing N mod k for each odd number k starting with 3 and stopping when N mod k = 0, how long will it take? Pretend that your computer can compute N mod k for a billion different values of k each second.
   
   
4. (8 points) Describe a significant weakness of the version of the Lempel-Ziv-Welch algorithm we studied in class, and outline your suggestions for changing LZW to address that weakness.
   
   
5. (8 points) If you are sending this exam (an ASCII HTML file) over a network that uses the bit stuffing scheme described on page 181 of Tanenbaum, are there characters or combinations of characters that would require bit stuffing? Explain.
   
   
6. (10 points) Consider Bob the bank, Alice the bank customer, and Trudy the intruder from section 7.1 of Tanenbaum. Suppose our Alice and Bob are somewhat less--how shall we put this delicately?-- savvy about network security than their section 7.1 counterparts. Our Alice and Bob hope to agree upon a secret key to support their important financial communications, and they have devised the following key exchange strategy. Here, EA is Alice's public key, EB is Bob's public key, A is Alice's identity, B is Bob's identity, and KS is the secret key Bob and Alice agree upon. You may assume that the public keys are completely secure.
   • Step 1: Alice sends EB(A) to Bob.

   • Step 2: Bob chooses a suitable KS, and sends EA(B,KS) to Alice.

   • Step 3: Alice acknowledges Bob's proposal by sending EB(KS) to Bob.

   • Step 4: The communication continues, with KS(message) being sent back and forth.

   Answer the following questions.

   • If Alice and Bob have secure public keys, why would they want to use a secret key?

   • Suppose Trudy has sufficient access to the communication lines to intercept, modify, and retransmit (or not) all messages flowing between Alice and Bob. Describe in detail one way Trudy can compromise Alice and Bob's key exchange process. List clearly the sequence of events that take place (in particular, what do Alice, Bob, and Trudy send, and in what order?). Also, explain who is harmed by Trudy's actions, and under what circumstances Trudy's actions could be detected.
   
   
   
7. (2 points) Who is/was Jon Postel, and why does his name show up so much in the index of the RFCs?
   
   
8. (6 points) Describe the difference between iterative servers and concurrent servers. Why are most servers concurrent? Name a network service that might be most appropriately provided by an iterative server (take a look at /etc/services for some ideas).
   
   
9. (3 points) Instead of a final exam, I'm going to have you do a research project, the results of which you will present on the Web in a public session during the final exam period. You may work alone or with one other person.

   For now, I'd like you to list a couple topics you might be interested in researching. You can choose just about anything network-related, including but not limited to technical topics like a thorough study of a particular protocol (with or without cnet implementation), topics on the history of networking, or topics on the social impact of Internet.