Assignment 10, due Apr 29
the homework for 22C:169, Spring 2011
Always, on every assignment, please write your name legibly as it appears on your University ID and on the class list! All assignments will be due at the start of class on the day indicated (usually a Friday), and unless there is what insurance companies call "an act of God" - something outside your control; the only exceptions to this rule will be by advance arrangement.
Some routers have static routing tables, typically forwarding all difficult routing problems to other routers they have been configured to use. Many routers are more dynamic, communicating with other routers to learn about changes in the network. The Internet is so big that links and machines, including routers, are constantly being added and subtracted. Without dynamic routing tables, this would never work.
Most routers can not only forward messages but also apply rewrite rules top addresses. Such a rule might read "if you see a message addressed to X, send it to Y instead." Such a router allows the addressing scheme used in some local subnet to be different from the addressing scheme used elsewhere.
a) Suppose an attacker was able to hack into the router connecting your local subnet to the rest of th Internet. The only thing the hacker can do is change the routing table. Your router has a static routing table with no rewrite rules. What damage could the hacker do? (0.5 points)
b) How could you, a user of the local subnet, detect the damage discussed in part a? (0.5 points)
c) Now suppose the router that the hacker attacks one that other routers consult to dynamically update their routing tables. Does this change the nature of the attacks or just the scale of their effects. (0.5 points)
a) What kinds of attacks could test ballots detect? (0.5 points)
b) In the 2006 Dutch Parliamentary elections, all of the test ballots were cast from the same PC in the offices used by the election administration. What vulnerability results from this? (0.5 points)
c) For maximum effectiveness, how should the test ballots have been cast? (0.5 points)
It has been argued that such a firewall is unnecessary, as network services you don't want to offer to the world should simply be disabled. Nowdays, many systems come, out of the box, with all these services enabled, and it is easier to block them with a firewall than it is to properly disable the services you don't want to offer.
Note that the "network stack" was presented as if all messages had to be pushed down to the physical layer for transport from sender to receiver. This is not really true. The exception occurs when the sender and receiver are on the same machine. In this case, the transport layer is likely to complete the message delivery without using any services from lower level layers. In the X-windows system (the public-domain window manager used by Linux), the window manager is a separate process, and all communication from application to window manager is done using the TCP/IP protocol stack. This allows use of remote window applications to be as efficient or even more efficient than local windows. Opening a window is done by making a network connection to the window manager. Drawing on a window involves using that connection, and closing a window involves breaking the network connection.
a) Suppose you were running Linux with the X window manager. What security threat is posed by running on a machine with no local firewall. (0.5 points)
b) Give other examples of local applications where the easy way to support them involves use of network protocols. (Hint: Consider any application that is useful over the network but where it might also be useful between local processes or between local users, even on a machine with just one keyboard and display.) (0.5 points)
Assume you are involved in the design of a new data center in the Iowa City area.
a) What threats would you treat as serious predictable risks and what defensive measures would you take to deal with those risks. (0.5 points)
b) What defensive measures would you recommend as generally useful for a broad range of unpredictable disasters. For each, give examples of unpredictable disasters where they might prove useful. Some of your defenses may be listed in both a) and b). (0.5 points)