MURANG’A UNIVERSITY OF TECHNOLOGY
SCHOOL OF COMPUTING AND INFORMATION
TECHNOLOGY
DEPARTMENT OF COMPUTER SCIENCE
UNIVERSITY ORDINARY EXAMINATION
2018/2019 ACADEMIC YEAR
FOURTH YEAR SECOND SEMESTER EXAMINATION FOR, BACHELOR
OF SCIENCE IN SOFTWARE ENGINEERING, MATHEMATICS AND
COMPUTER SCIENCE, AND CRIMINOLOGY AND SECURITY STUDIES
SCS 412– COMPUTER SECURITY AND CRYPTOGRAPHY
DURATION: 2 HOURS
DATE: 18/4/2019
TIME: 9-11 A.M
Instructions to candidates:
1. Answer question One and Any Other Two questions.
2. Mobile phones are not allowed in the examination room.
3. You are not allowed to write on this examination question paper.
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SECTION A: ANSWER ALL QUESTIONS IN THIS SECTION
QUESTION ONE (30 MARKS)
a) (i) Describe the essential ingredients of a symmetric cipher.
(5 marks)
(ii) State the two basic functions used in encryption algorithms.
(1 mark)
b) (i) State the number of keys required for two people to communicate via a cipher.
(2 marks)
(ii) Differentiate between a block cipher from a stream cipher.
(2 marks)
c) (i) Explain the two general approaches to attacking a cipher.
(2 marks)
(ii) Briefly explain types of cryptanalytic attacks based on what is known to their
attacker.
(3 marks)
d) Define the following ciphers:
(5 marks)
i.
Caesar cipher
ii.
Playfair cipher
iii. Monoalphabetic cipher
iv.
Polyalphabetic cipher
v.
Transposition cipher
e) (i) Construct a playfair matrix with the key largest.
(1 mark)
(ii) Construct a playfair matrix with the key occurrence.
(1 mark)
(iii) Use the playfair matrix below to answer the questions that follow.
M F
H
I/J
K
U
N
O
P
Q
Z
V
W X
Y
E
L
A
R
G
D
S
T
B
C
I.
Must see you over cadogan west coming at once.
(3 marks)
II.
Repeat the encryption but use the playfair matrix you created above which has
largest as the key.
(3 marks)
III.
Explain the results of your encryption using the two different playfair matrix.
(2 marks)
SECTION B – ANSWER ANY TWO QUESTIONS IN THIS SECTION
QUESTION TWO (20 MARKS)
a) (i) Describe a product cipher.
(2 marks)
(ii) Differentiate diffusion from confusion in cryptosystems stating how each is achieved.
(6 marks)
b) Outline the following:
i.
Original set of criteria used by NIST to evaluate candidate AES ciphers.
(3 marks)
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ii.
The final set of criteria used by NIST to evaluate candidate AES ciphers.
(9 marks)
QUESTION THREE (20 MARKS)
a) Differentiate the AES decryption algorithm and the equivalent inverse cipher. (4 marks)
b) Describe three areas used to differentiate the classical from the modern cryptosystem.
(6 marks)
c) Briefly explain the following security services as used to provide protection to business
information system:
(4 marks)
i.
Data confidentiality
ii.
Data integrity
iii. Authentication
iv.
Availability
d) (i) Encrypt the statement below using the stated encryption algorithms
AFTER GRADUATION BE MY BUSINESS PARTNER.
Use playfair cipher with the Keyword UNIVERSITY.
(4 marks)
(ii) Define the following terms as used in security of information management systems
(2 marks)
I.
An exposure
II.
A vulnerability
QUESTION FOUR (20 MARKS)
a) Encrypt the statement below using the stated encryption algorithms
AFTER GRADUATION BE MY BUSINESS PARTNER.
i.
Rail fence of depth 2.
(3 marks)
ii.
Caesar cipher encryption algorithm.
(3 marks)
b) Security socket layer (SSL) operates in terms of connections and sessions between clients
and servers. List four types of information associated with a connection. (4 marks)
c) (i) Define the term digital signature.
(2 marks)
(ii) Describe the two different digital signature schemes.
(4 marks)
d) Public key infrastructure (PKI) manages public keys automatically through the use of
public certificates. State and describe the four functional roles of PKI entities.
(4 marks)
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