1. Practical Questions Theoretical Questions
Revision on lecture 1 & 2
Practical Questions
Theoretical Questions

2. Practical Questions

3. Question 1
Encrypt the following statement using Caesar cipher, let k =10.
M e e t m e

4. Answer c = E(p) = (p + k) mod (26) c = E(p) = (p + 10) mod (26)
a b c d e f g h i j k l m n o p q r s t u v w x y z
c = E(p) = (p + k) mod (26)
c = E(p) = (p + 10) mod (26) e m t M 4 12 19 14 22 29
P+10
mod 26 14 22 24 o w d

5. Question 2
Encrypt the following statement using Vigenere cipher, let key = DEC.
W a i t m e n o w a t t h e s t a t i o n

6. Vigenere Table

7. A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

8. Answer Encrypted Text: z e k w q g q s y d x v k i u w e v l s po i t a s h w m
Steps:
look at the letter of the keyword above it ,and find that row in the Vigenere table.
Find the column of your plaintext letter
Trace down that column until you reach the row you found before and write down the letter in the cell where they intersect
Encrypted Text: z e k w q g q s y d x v k i u w e v l s p

9. Question 3 Encrypt the following statement using Rail Fence cipher.
M e e t m e a t t e n o c l o c k

10. Answer Encrypted Text: m e m a t n c o k e t e t e o l c k o c n t a m

11. Question 4 Encrypt the following statement using Rail fence cipher.
S t a r t y o u r m i s s i o n

12. Answer Encrypted Text: s a t o r i s o t r y u m s i n o s i r t a n m

13. Question 5 Encrypt the following statement using Reverse cipher.
S t a r t y o u r m i s s i o n r i g h t n o w

14. Answer
Encrypted Text:
w o n t h g i r n o i s s i m r u o y t r a t s

15. Question 6 Decrypt the following statement using Reverse cipher.
n i a g a t i y r t r e v e t o n o d p o t s

16. Answer
Decrypted Text:
S t o p D o n o t e v e r t r y i t a g a i n

17. Question 7
Encrypt the following statement using Row Transposition cipher, let key = Computer.
L e t s g o b a c k i m m e d i a t e l y

18. Answer C O M P U T E R 1 4 3 5 8 7 2 6

19. Answer 1 2 3 4 5 6 7 8 L e t s g o b a c k i m d l y x X

20. Answer Ciphertext: l s t g a b e o c m i m i d k e a l e y z z t z 1 43 5 8 7 2 6 L s t g a b e o c m i d k l y x
Ciphertext: l s t g a b e o c m i m i d k e a l e y z z t z

21. Question 8
Construct a Play fair matrix with the key surprise

22. Answer
j/i p r u s d c b a e l k h g f t q o n m z y x w v

23. Question 9 Using this Playfair matrix Encrypt this message:
"The way is blocked"

24. Answer
Th ew ay is bl oc ke dx
ol av cw su dh qb fc bz

25. Theoretical Questions

26. Question 1 Discuss what the security trinity is.
(Illustrate your answer by a diagram)

27. Answer
Prevention: to provide some level of security, it is necessary to implement measures to avoid the exploitation of vulnerabilities.
Detection: procedures need to be put in place to discover potential problems or security breaches.
Response: Organizations need to develop a plan that identifies what is need to be protected

28. Question 2
Briefly discuss the three aspects of information security.

29. Answer According to the OSI Security Architecture
Security Attack: Any action that compromise the security of information owned by an organization.
Security Mechanism: A process that is designed to detect, prevent or recover from a security attack.
Security Services: Security Services is the services to implement security policies and implemented by security mechanism

30. Question 3
What is the difference between the passive attack and the active attack?
(Illustrate your answer by diagrams)

31. Answer
Passive attack
Active attack

32. Question 4 Write the appropriate terms for each definition:
Assuring that the authorized users have timely access to the
information in the system and to the network.
( Availability )
2. Preventing either sender or receiver from denying
a transmitted message.
( Non-repudiation )

33. Question 5 Define the following terms: 1. Computer Security
Answer: generic name for the collection of tools designed to protect data and to thwart hackers.
2. Internet Security
Answer: measures to protect data during their transmission.
3. Network Security
Answer: measures to protect data during their transmission over a collection of interconnected networks.

34. Question 5
4. Threats
Answer: mean anything that can interrupt the operation, functioning, integrity, or availability of a network or system, these can take any forms.
5. Vulnerabilities
Answer: are inherent weakness in the design, configuration, implementation, or management of the network or the system that renders it to be susceptible to threats.