August 1999
SC223 : COMPUTER SECURITY

QUESTION 4

Total Marks: 20 Marks

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SUGGESTED SOLUTIONS
Solutions and allocated marks are indicated in green.
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(a) Distinguish between the operating system kernel and security kernel by discussing the purpose and the services provided by each. [4]
The operating system kernel performs the lowest level functions; it implements services such as synchronisation, inter-process communications, message-passing and interrupt handling. The security kernel is responsible for implementing the security mechanisms of the entire operating system; it provides security interface among the hardware, operating system and other parts of the computing system.

 
(b) Identify and explain any two reasons for isolating the security kernel from the operating system kernel. [4]
  • Separation
  • Unity
  • Modification
  • Compactness
  • Verifiability
  • Coverage

 
(c) Explain briefly, any four issues under Procedure of Use that can improve the security in use of PC. [4]
  • Don not leave PCs unattended if they are running sensitive computation
  • Do not leave printers unattended if they are printing sensitive output
  • Secure storage media carefully
  • Do not allow eating or drinking in computer rooms
  • Treat storage media with care
  • Perform periodic backups
  • Practice separation of authority

 
(d) Explain how Call-back and Silent Modems help to protect computers from unauthorized access. [4]
Call-back modem: the user calls the computer and enters a login ID; the computer figures out the telephone number of the authorised user and calls back that number. Silent modem: when the user calls the computer, the modem won't signal the connection until the login process has begun; these modems are used to keep crackers doing random dialing.

 
(e) What are the important objectives of a good disaster plan? [2]
To minimize the impact of a disaster on the ability to conduct business. Speedy and accurate recovery to normal operations.

 
(f) Explain the disk mirroring and disk duplexing features available in the standard network products used for disaster recovery. [2]
Disk mirroring: maintains the duplicate data on separate disks using the same bus adapter; Disk Duplexing: maintains the duplicate data on separate disks using separate bus adapters.