Homework 4

Due: Friday, March 7, 1997 at 11:59PM (note old time!)

Analytical

These are worth 40 points each.

1.	Does the system of all subsets of a finite set, under the operation Ñsubset ofæ (¼), form a lattice? Either 
show that it meets all the requirements of a lattice, or state which requirement it fails to meet and prove 
that it fails to meet the requirement.

2.	The UNIX operating system and its attendant programs assume that any incoming message with 
source port 1023 or less (the Ñprivileged portsæ) was sent by a process running as root. Assuming the 
remote host is a UNIX system, is there any way that a process can send a network message from a 
privileged port when that process is not running as root?

3.	IIn the ISO model, peer processes communicate without regard for precise implementation of activities 
at other layers. For example, the application does not know or care what specific routing has been cho-
sen by the network layer. What is the security effect of an application programºs not knowing the rout-
ing selected for a particular message, or even a particular session?

4.	Where (at what times during its transmission) is a message exposed if it is protected by link encryp-
tion? Where is a message exposed if end-to-end encryption is used?

5.	Is encryption an effective control against passive wiretapping? Why or why not? Against active wiretap-
ping? Why or why not?

Programming

There is no program on this assignment. Please use the time for your projects, which are due on March 14!