This is an exam. You may use the Internet, your textbook, your notes, your assignments, and your brain, but you may not consult people other than Jeff Ondich.
(5 points) Briefly explain what RARP is. In particular, explain the problem that RARP was designed to solve.
(10 points) Suppose my public key is (e,n) = (29,91), and any message sent to me must consist of a string of characters with ASCII value less than 91, encrypted one character at a time. Suppose you intercept the following message addressed to me:
68 11 53 2 17 78 62 68 2 28 11 62 2 17 50 87 50 7
What is my decryption key (d,n)? Use it to decrypt the intercepted message. You must show your work, since one might be able to decrypt the above message without breaking my key.
You may find either Mathematica or the UNIX command "bc" helpful. Within bc, ^ is used for exponentiation, and % is used for mod.
(10 points) This time, I've used LZW compression to compress another ASCII message. To do the compression, I used a 1024-element dictionary.
69 65 84 32 84 72 257 32 82 262 262 260 262 70 76 257
Figure out what the original message was, and show your work (including the final contents of the dictionary you construct as you decompress the message). Compute the compression ratio (that is, the number of bits in the compressed data divided by the number of bits in the original data).
(3 points) I'm all out of jokes. Please tell me one.
(20 points) Suppose I am logged on to prism.mathcs.carleton.edu, and I type the command "ftp ftp.ultralingua.com" with the intent to download a file via anonymous FTP. Suppose further that ftp.ultralingua.com is not in my DNS cache, that my IP routing table is as you will find it by logging onto prism and typing "netstat -r", and that my ARP cache is empty (by some bizarre and disturbing Act of the Test Writer).
Describe clearly and concisely what happens next, as my command tries to make contact with the FTP server at ftp.ultralingua.com. Try to be complete within reason--the story you are going to tell me could be quite long. Keep your version of the story under two pages. One page should really be enough.
My FTP client will be sending a first message off in the direction of ftp.ultralingua.com. (Note that the message I'm talking about is not the first message of any kind that prism sends out while trying to talk to ftp.ultralingua.com. I'm talking about the first message whose destination is ftp.ultralingua.com.) After passing through quite a bit of software and accumulating several headers, this first message will become a grown-up 802.3 frame on the Math/CS network. Show me the contents of this frame, in as much detail as you can. Whenever possible, I want you to show me exactly what numbers are stored in the various header fields. For those fields whose values you can't know at test-taking time, explain why you can't know them. What, if any, non-header data will this frame contain? (To answer this last question, you need to explain the purpose of this very first ftp.ultralingua.com-bound message.)