Uploaded by abdelrazekali66


Faculty: Computers and Informatics
Class Year: 2021/2022
Specialization: Information Technology
Subject Name: Network Security
Subject Code: IT460
Department: Information Technology
Midterm Exam
Date: 19 April 2022
Time Allowed: 60 min.
No. of Pages: 2
No. of Questions: 4
Full Mark: 40 Points
Answer the following questions:
1. Perform the following RSA key generation steps. Each step must satisfy the requirements for a
legitimate RSA key.
[5 points]
a) (1 points) Suppose n is 55. Find suitable p and q values.
b) (1 points) Compute Φ(n).
c) (3 points) If d = 7, compute a valid value for e and specify the public and private keys.
9 4
2. Encrypt the message ”AB” using the Hill cipher with the key 
 Show your calculations and the
5 7
[5 points]
3. Draw the graph of a single round of DES algorithm?
[10 points]
4. True or False Questions:
[20 points]
1. The OSI security architecture provides a systematic framework for defining security attacks,
mechanisms, and services. (T )
2. Security attacks are classified as either passive or aggressive. (F )
3. Authentication protocols and encryption algorithms are examples of security mechanisms. (T )
4. The emphasis in dealing with active attacks is on prevention rather than detection. (
5. The data integrity service inserts bits into gaps in a data stream to frustrate traffic analysis
attempts. (
6. Symmetric encryption remains by far the most widely used of the two types of encryption. ( T )
7. With the use of symmetric encryption, the principal security problem is maintaining the secrecy
of the key. (
8. Monoalphabetic ciphers are easy to break because they reflect the frequency data of the original
alphabet. (
9. As with Playfair, the strength of the Hill cipher is that it completely hides single letter
frequencies. (
10. The one-time pad has unlimited utility and is useful primarily for high-bandwidth channels
requiring low security. (
11. Confusion seeks to make the statistical relationship between the plaintext and ciphertext as
complex as possible in order to thwart attempts to deduce the key. (
12. A prime concern with DES has been its vulnerability to brute-force attack because of its
relatively short key length. (
13. AES uses a Feistel structure. (
14. DES is a block cipher intended to replace AES for commercial applications. ( F
15. There are no practical cryptanalytic attacks on 3DES. (
16. It is possible to convert a block cipher into a stream cipher using cipher feedback, output
feedback and counter modes. ( T
17. The XTS-AES mode is based on the concept of a tweakable block cipher. (
18. Asymmetric encryption utilizes only a public key for encryption and decryption. (
19. Asymmetric encryption can be used for confidentiality but not for authentication. (
20. Public-key encryption is more secure from cryptanalysis than symmetric encryption. (
Best Wishes. . .