Dec 1998 SC223: Computer Security (Question 4)

(a)	Separation and isolation of processes is one way in which a secure operating system can be designed. Describe three ways in which processes can be separated from each other.	[6]
	One mark should be awarded for each valid point, and a further mark should be awarded for each satisfactory elaboration (up to a maximum of six marks). Examples include the following: Physical separation (1 mark). Processes use different hardware facilities (1 mark). Temporal separation (1 mark). Processes are run according to different timing to avoid mixing sensitive and non-sensitive processes (1 mark). Cryptographic separation (1 mark). Unauthorised users are not allowed to access sensitive processes in a readable form (1 mark). Logical separation (1 mark). A reference monitor separates the objects of one user from those of another (1 mark). Other sensible answers should also receive credit.
(b)	Describe three physical vulnerabilities of computer systems.	[6]
	One mark should be awarded for each valid point, and a further mark should be awarded for each satisfactory elaboration (up to a maximum of six marks). Examples include the following: Natural perils (1 mark). Computers are prone to damage from the same natural disasters—such as floods, earthquakes, or storms—as anything else (1 mark). Human intrusion (1mark). Human intrusion, which may be crude (for example, attacking a machine with an axe) or subtle (for example, disabling a disk drive with a paper clip), can cause a great deal of damage (1 mark). Interception (1 mark). With a few hundred dollars, no connection to the machine that is being targeted, and only a moderate knowledge of electronic, a device can be constructed to read the information displayed on a monitor a few hundred yards away (1 mark). Unauthorised access and use (1 mark). Unauthorised users gain to the system using illicit means (1 mark). Other sensible answers should also receive credit.
(c)	Name four measures which might be employed to improve the security of using a PC.	[4]
	One mark should be awarded for each valid point (up to a maximum of four marks). Examples include the following: Do not leave PCs unattended if they contain sensitive information, or are running sensitive jobs. Do not leave printers unattended if they are printing sensitive output. Secure media as carefully as you would the equivalent confidential reports. Do not allow eating, drinking, or smoking in any room containing PCs. Treat media with care. Perform periodic backups. Practice separation of authority. Other sensible answers should also receive credit.
(d)	(i) In terms of network security, what do you understand by the term traffic control?	[2]
	Traffic control is a technique used to minimise the risk of traffic analysis by preventing interceptors from listening to active traffic ( 1 mark). This is because it is possible for interceptors to tap all blocks of message passing through the network, from which they can determine who is communicating frequently with whom (1 mark). Other sensible answers should also receive credit.
	(ii) Define the term pad traffic.	[2]
	Pad traffic deters any listener who is monitoring messages from active combination links by generating spurious messages to all computer links (1 mark). Random noises are inserted into the network to make it difficult for the user to differentiate noise and real signals (1 mark). Other sensible answers should also receive credit.