CS 125, Fall 2021
Computer Networks

Homework 6—Security

The purpose of this assignment is to give you a deeper understanding of the link layer.

Please submit your answers on paper (preferably typed and formatted with LaTeX).

All problems are from Chapter 8 of the textbook (7th edition).

1. Problem P2. The message referred to is "bob, i love you. alice." There is a typesetting error in the problem; the number 109 should actually be 10⁹.
2. In Problem P2, assume that Trudy must use brute-force search to decode the message. Using a supercomputer, she can try substitutions at a net rate of one per nanosecond. How long would it take her to decode the message if she knows the pairings for "bob" and "alice"? (Choose an appropriate unit for your answer: minutes, days, years, etc.) Is this practical? Without knowing the pairings your answer will be multiplied by approximately 10⁹; how does that affect the practicality of the attack?
3. Problem P6.
4. Problem P9, parts (a) and (d).
5. Problem P16.
6. Problem P22.
7. Problem P25. Note that the problem continues onto page 672. Telnet is port 23; HTTP runs on port 80.
8. How much time did you spend on this assignment?

© 2021, Geoff Kuenning

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