April 2000
SC223 : COMPUTER SECURITY

QUESTION 4

Total Marks: 15 Marks

• Question 1
• Question 2
• Question 3
• Question 5
• Cover Page

SUGGESTED SOLUTIONS
Solutions and allocated marks are indicated in green.
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(a)Approaches to protecting PC software from copying may be software-based (for example,checksums to prevent modification),hardware-based (for example, implementing a program as a chip),or a mixture of the two (for example,a key or ‘dongle ’).Identify a problem with each method.[3 marks ]
A checksum prevents modification but not copying, so does not provide good protection. A dongle is hard to distribute, adding to cost; in contrast, a software-only approach allows purely electronic distribution. Implementing a program as a chip is only appropriate for a standalone program, not for one that must run alongside other software; moreover, it is much more expensive to make changes to the software. (1 mark for each disadvantage, to a maximum of 3 marks.) [3 marks]

(b)Why might a software developer not protect their software from copying at all? [2 marks ]
One reason for not copy-protecting is that the developer might want as wide a distribution as possible, as for example with the free readers and plug-ins for a number of proprietary data formats (1 mark). Or the developer might release the software as shareware, encouraging free distribution but relying on satisfied users choosing to pay a registration fee without being forced to (1 mark). [2 marks]

(c)Wire,wireless and fibre-optics are three kinds of communication media.
(i)Describe two security concerns of wire media.[2 marks ]
(ii)Describe two security concerns of wireless media.[2 marks ]
(iii)Fibre-optic media is the most secure;why is it not universally used?[2 marks ] Communication media:

(i) Wire media are subject to wiretapping (1 mark), and also to interference from neighboring wires or magnetic fields (1 mark). [2 marks]

(ii) Wireless media travel in the open air, so are easy to intercept (1 mark), they may also be subject to obstacles such as rainfall and buildings (1 mark). [2marks]

(iii) Fibre-optic cable is expensive to lay (1 mark); it is also difficult to make connections in (1 mark). [2 marks]

(d)Identify the two kinds of encryption that can be used in a network,and explain the differences between them.[4 marks ]
The two kinds of network encryption are link encryption an end-to-end encryption (2 marks). Link encryption applies to a particular hardware connection, whereas end-to-end encryption is usually done in software (1 mark). Therefore end-to-end encryption is more flexible (1 mark). [4 marks