KSA T318 MTA FALL 2022 2023 Version

Faculty of Computer Studies
Course Code: T318

Course Title: Applied Network Security
Mid-term
Summer Semester
Date: TBA
:Number of Exam Pages

)( :Time Allowed 2h
including this cover sheet((
Instructions:
 Total Marks: 60
 Total Number of Questions:
o Part 1: 6
o Part 2: 5
o Part 3: 4
 Marks Distribution:
o Part 1: 6 marks
o Part 2: 20 marks
o Part 3: 34 marks
 Write your answer in the answer booklets. Answers given on the exam paper will
not be marked.
 The use of electronic devices that could have a memory is NOT permitted
 Be sure you write your name and ID on the External Answer booklet.
T318 - MTA Page 1 of 4 Summer 2021

Part 1: Multiple choices:For each question select the best answer (place the answer on
the external answer booklet) Each question carries a WEIGHT OF 1 mark. Total: 6 Marks
1. The opponent is most willing to recover______:
A. The Encryption key
B. The plaintext
C. The ciphertext
D. The Identity of the sender and/ or receiver
2. Cryptography systems can be divided into
A. Substitution and Transposition
B. Symmetric and Asymmetric
C. Block cipher and stream cipher
D. All are correct
3. The most difficult Attack scenario is
A. Ciphertext only
B. Known Plaintext
C. Chosen plaintext
D. chosen ciphertext
4. We can use Compression techniques to make the encryption more secure and difficult
to attack
A. True
B. False
5. Steganography is different from Encryption. Anyway, We use encryption in
Steganography process
A. True
B. False
6. Rotor Machines is an example of a multi stage Encryption
A. True
B. False
Part 2: Short questions: Answer the following questions – Each question carry a
WEIGHT OF 4 marks. Total: 20 Marks
1. Distinguish between cryptography and steganography. (4 Marks)

2. Define the type of security attack in each of the following cases (4 Marks)
a. A student gives a check for $10 to buy a used book. Later she finds that
the check was cashed for $100.
a. A student sends hundreds of e-mails per day to another student using a
phony return e-mail address.
3. Distinguish between a monoalphabetic and a polyalphabetic cipher. (4 Marks)
4. Distinguish between a substitution cipher and a transposition cipher(4 Marks)
5. Distinguish between diffusion and confusion
Part 3: Answer all of the following questions Total: 34 Marks
1. Using the Euclidean algorithm, find the greatest common divisor of the following
pairs of integers. (4 Marks)
a. 88 and 220

b. 300 and 42
c. 24 and 320
d. 401 and 700
2. Solve the following problems based on DES algorithm(10 Marks)
a. Show the results of the following hexadecimal data
0110 1023 4110 1023
after passing it through the initial permutation box. PLEASE your answer
must be in hexadecimal.(5 Marks)
b. Show the results of the following hexadecimal data
AAAA BBBB CCCC DDDD
after passing it through the final permutation box. PLEASE your answer
must be in hexadecimal.(5 Marks)
3. Solve the following problems based on streaming cipher(10 Marks)
a. A Transposition Cipher (but not a Rail-fence Cipher) was used to
produce the following ciphertext:(UO!HZESSSQTYTIOIIA)
The key used was: 5 2 6 3 4 1
What was the plaintext used (it is in English)? (5 Marks)
b. Given the ciphertext and key below, find the plaintext if the Playfair cipher
was used. x is the special character used for padding and i and j are
treated as the same character
C = eiioqoyldc
K = security
what is the plaintext? (5 Marks)
4. Consider a block cipher, ABC, which is defined by Table 1. The table gives the
ciphertext C (columns 2 to 9) produced when encrypting the plaintext P (column 1)
with one of the eight keys. (10 Marks)
a. Assuming CBC was used with ABC, decrypt the ciphertext 11110110 using
the key 001 and initialization vector 1110. Explain your calculations in
details. (5 Marks)
b. Consider the cipher ABC being used in Counter Mode to act as a
pseudorandom number generator. If the initial value of the counter is 0000
and the seed is 101, then what are the first 12 pseudorandom bits? (5
Marks)

Reference page
Figure 1:inital and final permutation
Figure 2:Cipher Block Chaining (CBC) mode encryption
Figure 3:Counter Mode (CTR)mode encryption

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Faculty of Computer Studies

Course Code: T318

:Number of Exam Pages

T318 - MTA Page 1 of 4 Summer 2021

1. Distinguish between cryptography and steganography. (4 Marks)

Part 3: Answer all of the following questions Total: 34 Marks

T318 - MTA Page 2 of 4 Summer 2021

T318 - MTA Page 3 of 4 Summer 2021

Figure 1:inital and final permutation

Figure 2:Cipher Block Chaining (CBC) mode encryption

Figure 3:Counter Mode (CTR)mode encryption

T318 - MTA Page 4 of 4 Summer 2021

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