1
Which of the following is NOT a principle of security?
Correct Answer
Redundancy
☑ MCQ PRACTICE
Cryptography and Network Security Unit 1
Practice objective questions for quick revision and examination preparation. Try answering each question before revealing the answer.
Cryptography and Network Security MCQs - Unit 1
2
An attack that only monitors or reads transmissions without altering them is called a(n) ______ attack.
Correct Answer
passive
3
Which of the following is an active attack?
Correct Answer
Masquerade
4
The security service that prevents a sender from denying that a message was sent is
Correct Answer
non-repudiation
5
Which of the following is NOT a security service defined in X.800?
Correct Answer
Data compression
6
In a Caesar cipher with key 3, the plaintext HELLO is encrypted as
Correct Answer
KHOOR
7
A cipher in which each plaintext letter is replaced by another letter or symbol is a
Correct Answer
substitution cipher
8
The Playfair cipher uses a key matrix of size
Correct Answer
5 × 5
9
The Rail Fence technique is an example of a
Correct Answer
transposition technique
10
The Vigenère cipher is a
Correct Answer
polyalphabetic substitution cipher
11
The practice of hiding the very existence of a message is called
Correct Answer
steganography
12
A cipher with a 128-bit key has a key space of
Correct Answer
2^128 keys
13
Asymmetric key cryptography uses
Correct Answer
a pair of public and private keys
14
Symmetric key cryptography uses
Correct Answer
the same key for encryption and decryption
15
An attack in which the attacker has only the ciphertext is a
Correct Answer
ciphertext-only attack
16
The original readable message that is given to an encryption algorithm is called
Correct Answer
plaintext
17
Which cipher gives perfect secrecy when the key is truly random, as long as the message and used only once?
Correct Answer
One-time pad
18
The Hill cipher is based on
Correct Answer
matrix multiplication (linear algebra)
19
An interruption attack is an attack on
Correct Answer
availability
20
An interception attack is an attack on
Correct Answer
confidentiality
21
Which of the following is a specific security mechanism in X.800?
Correct Answer
Encipherment
22
In the model for network security, a trusted third party is mainly required for
Correct Answer
distribution of secret information (keys)
23
A brute-force attack on a cipher tries
Correct Answer
every possible key
24
The number of keys needed for n users to communicate pairwise using symmetric cryptography is
Correct Answer
n(n − 1)/2
25
Modification of a message in transit is an attack on
Correct Answer
integrity
Fill in the Blanks
26
The CIA triad stands for Confidentiality, Integrity and ______.
Correct Answer
Availability
27
An attack that monitors transmissions without changing them is a ______ attack.
Correct Answer
passive
28
The process of converting plaintext into ciphertext is called ______.
Correct Answer
encryption
29
The process of converting ciphertext back into plaintext is called ______.
Correct Answer
decryption
30
In a ______ cipher, the positions of the plaintext letters are rearranged but the letters are not changed.
Correct Answer
transposition
31
In a Caesar cipher with a shift of 3, the plaintext letter A is encrypted as ______.
Correct Answer
D
32
The art of hiding a message inside another message or file is called ______.
Correct Answer
steganography
33
In public key cryptography, a message encrypted with the receiver's public key is decrypted with the receiver's ______ key.
Correct Answer
private
34
A cipher that uses an n-bit key has ______ possible keys.
Correct Answer
2^n
35
An attack in which a captured message is retransmitted later is called a ______ attack.
Correct Answer
replay
36
The security service that confirms that a communicating entity is who it claims to be is ______.
Correct Answer
authentication
37
The science of breaking ciphers without knowing the key is called ______.
Correct Answer
cryptanalysis
38
The Playfair cipher encrypts ______ of letters at a time.
Correct Answer
pairs (digrams)
39
A denial of service attack is an attack on ______.
Correct Answer
availability
40
The unreadable output of an encryption algorithm is called ______.
Correct Answer
ciphertext