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Rose-Hulman CSSE 432 - CSSE 432 Final Exam

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CSSE 432 -- Computer Networks -- Spring 2005Final ExamMay 23, 2005Name:____________________________________________Campus Mailbox:___________________________________1 152 153 154 155 156 107 78 99 2010 911 70Total 2001CSSE 432 -- Computer Networks -- Spring 2005Final Exam1. [15 points] DNSa) A new internet site, crocodile.dundee.au, is created, and only its authoritative name server, dns.crocs.au, knows the IP address. Host A, alice.rhit.edu, with local name server dns.rhit.edu wants the IP address for crocodile.dundee.au. Draw a diagram showing a sequence of recursive queries for the IP address, assuming that one other server, dns.australia.au, is involved. Be sure to label the arcs in the diagram with numbers that show the sequence of events.b) Draw a diagram for the scenario above, but with iterative queries wherever possible.2CSSE 432 -- Computer Networks -- Spring 2005Final Exam2. [15 points] DHCPA laptop A wants to join a local area network 123.45.6 via DHCP. Suppose that there are 2 DHCP servers, 123.45.6.1 and 123.45.6.2, that can furnish an IP address. 123.45.6.1 offers address 123.45.6.7 and 123.45.6.2 offers address 123.45.6.8. Draw a sequence diagram showing the interaction between A, 123.45.6.1, and 123.45.6.2 as host A obtains the address 123.45.6.7. For each message in the diagram indicate: source address, destination address, message type.3CSSE 432 -- Computer Networks -- Spring 2005Final Exam3. [15 points] EmailBob, a student at Small College, interviewed recently with Big Corp. Alice, a manager at Big Corp, sends an offer letter to Bob at his campus email address over Spring Break. Even though Bob is not on campus, he can read and write email from home with his campus email account using a web server. Alice uses a POP3 email account on the Big Corp network.a) Draw a diagram showing the application protocols used to send the offer letter from Alice to Bob.b) Draw a diagram showing the application protocols used to send a response from Bob to Alice.c) Which of the protocols in the diagrams above are "push" and which are "pull"? Explain why in each case.4CSSE 432 -- Computer Networks -- Spring 2005Final Exam4. [15 points] SecurityAlice is about to send a sensitive message to Bob, but she is worried that her evil twin sister Trudy might intercept the message. So, Alice first sends Bob a short message, M, and requests that he encrypt it with his private key KB- . Then Alice asks Bob for his public key KB+ . After decrypting Bob's encrypted version of M, Alice determines that she is really talking to Bob.a) Draw a diagram that shows Trudy executing the man-in-the-middle attack for this scenario.b) How would a Certification Authority prevent Trudy from accomplishing her attack? Bob would register his public key with CA. Bob provides “proof of identity” to CA.  CA creates certificate binding Bob to his public key. certificate containing Bob’s public key digitally signed by CA – CA says “this is Bob’s public key” When Alice wants Bob’s public key: gets Bob’s certificate (Bob or elsewhere). apply CA’s public key to Bob’s certificate, get Bob’s public key 5CSSE 432 -- Computer Networks -- Spring 2005Final Exam5. [15 points] SecurityAlice wishes to communicate with Bob using a symmetric key. Draw a sequence diagram that shows how Alice accomplishes this using a key distribution center KDC. Use the notation "KX-Y" to represent a symmetric key known only to X and Y. Be sure to include all the messages involving Alice, Bob, and KDC that are needed before Alice and Bob can begin their conversation.6CSSE 432 -- Computer Networks -- Spring 2005Final Exam6. [10 points] ASN.1Suppose that you want to send the string "CSSE" followed by the value 432 across a network in big-endian order. You choose to use ASN.1 to encode these values. Recall that the INTEGER type in ASN.1 has tag 2, and the OCTET STRING type has tag 4. Show the sequence of bytes sent:Byte Value1st 4(tag)2nd 4(length)3rd C4th S5th S6th E7th 2 (tag)8th 2 (length)9th 110th 17611th12th13th14th15th432 = 1 * 256 + 1767CSSE 432 -- Computer Networks -- Spring 2005Final Exam7. [7 points] Transport ProtocolsTrue or false:a) The size of the TCP RcvWindow never changes throughout the duration of the connection.b) Suppose that host A is sending host B a large file over a TCP connection. The number of unacknowledged bytes that A sends cannot exceed the size of the receive buffer.c) Suppose host A is sending a large file to host B over a TCP connection. If the sequence number for a segment of this connection is m, then the sequence number for the subsequent segment will necessarily be m+1.d) The TCP segment has a field in its header for RcvWindow.e) With the Selective-Repeat protocol it is possible for the sender to receive an ACK for a packetthat falls outside of its current window.f) With the Go-Back-N protocol it is possible for the sender to receive an ACK for a packet that falls outside of its current window.8. [9 points] SecurityGive a short answer (one or two sentences) to each of these questions:a) What is the purpose of a nonce in an authentication protocol?b) In what ways does a message digest provide a better message integrity check than the Internetchecksum?c) What is the advantage of (1) computing a message digest and using a public key to encrypt thedigest, rather than (2) just using the public key to encrypt the message?8CSSE 432 -- Computer Networks -- Spring 2005Final Exam9. [20 points] RoutingConsider the network shown below. Using Dijkstra's algorithm, fill in the table below to compute the shortest path from node A to all network nodes.step N D(B),p(B) D(C),p(C) D(D),p(D) D(E),p(E) D(F),p(F) D(G),p(G) D(H),p(H)01234567912913112HGFDEBCA14 4631 4CSSE 432 -- Computer Networks -- Spring 2005Final Exam10. [9 points] MultimediaThree "camps" were discussed for improving the Internet so that it better supports multimedia applications. Briefly summarize the views of each camp.10CSSE 432 -- Computer Networks -- Spring 2005Final Exam11. [70 points] VocabularyThis is a multi-part question. You are given a list of terms and definitions. Some of the terms have matching definitions in the list, and some of the definitions have matching terms. You need to match terms with definitions where possible, and then provide missing terms or definitions where needed.a) Here are the definitions. Note that the list takes 2


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