Computer Networks Assignment

ASSIGNMENT TASKS

Task 1: Both the CSMA/CD with Token bus medium access control methods can be used in real time systems. Which one is better suited for real time applications? Explain.

Task 2: Suppose you want to build a home network that includes a router with an ADSL connection to the Internet, a wireless IEEE802 Wireless LAN, and three wireless IEEE802 Wireless LAN adaptors. Find specific products to suit your needs and price them out.

Task 3: Briefly describe attacks against security and discuss three desirable properties of secure communication.

Task 4: Suppose that N people wish to communicate with each other using a shared medium, i.e., all transmissions can be read by all participants. Communication between any two participants must be kept confidential. How many keys would be required to achieve this using symmetric cryptosystems? How many key pairs would be required using public key cryptosystems?

Task 5: Provide a definition of the mono-alphabetic cipher. Describing encoding the message "Security is important" using a mono-alphabetic cipher of your choosing. What is involved in such a brute force attack?

Task 6: Consider our authentication protocol 4.0, in which Alice authenticates herself to Bob, which we saw works well (i.e., we found no flaws in it.). Now suppose that at the same time that Alice authenticates herself to Bob, Bob must authenticate himself to Alice. Give a scenario by which Trudy, pretending to be Alice, can now authenticate herself to Bob as Alice. (Hint: consider that the sequence of operations of ap4.0, one with Trudy initiating and one with Bob initiating, can be arbitrarily interleaved. Pay particular attention to the fact that both Bob and Alice will use a nonce, and that if care is not taken, the same nonce can be used, maliciously).