April 1999
SC223: COMPUTER SECURITY

QUESTION 1 (Compulsory)

Total Marks: 20 Marks

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SAMPLE STUDENT'S SOLUTIONS
for Question 1

 
(a) Define the term cryptography.

 

 [2]
(b) Define the term cryptanalysis.

 

 [2]
(c) Assume a public key crytosystem based on multiplication by the key, modulo 31. User A has public key 28 and secret key 10. User B has public key 7 and secret key 9.
(i) Show the cipher text and decryption for authentication and secret transmission from A to B of message M =25. [3]
(ii) Show how a cryptanalyst, who knows the encryption algorithm could compute the unknown secret keys of both A and B.

 

 [3]
(d) Describe three activities associated with risk analysis.

 

 [6]
(e) List four issues which must be addressed by a security plan. [4]