Explore topic-wise MCQs in Cryptography and Network Security.

This section includes 16 Mcqs, each offering curated multiple-choice questions to sharpen your Cryptography and Network Security knowledge and support exam preparation. Choose a topic below to get started.

1.

The counter value in CTR modes repeats are a regular interval.

A. True
B. False
Answer» C.
Discussion
2.

Which of the following modes does not implement chaining or “dependency on previous stage computations”?

A. CTR, ECB
B. CTR, CFB
C. CFB, OFB
D. ECB, OFB
Answer» B. CTR, CFB
Discussion
3.

In OFB Transmission errors do not propagate: only the current ciphertext is affected, since keys are generated “locally”.

A. True
B. False
Answer» B. False
Discussion
4.

Which of the following can be classified under advantages and disadvantages of OFB mode?i) Transmission errorsii) A bit error in a ciphertext segmentiii) Cannot recover from lost ciphertext segmentsiv) Ciphertext or segment loss

A. Advantages: None; Disadvantages: All
B. Advantages: All; Disadvantages: None
C. Advantages: i); Disadvantages: ii) iii) iv)
D. Advantages: i); ii) Disadvantages: iii) iv)View Answer
Answer» E.
Discussion
5.

What is the fault in the above figure?

A. The output of the XOR is sent to the next stage
B. The “Encrypt” Box should be replaced by “Decrypt Box
C. b-s bits are selected for the XOR operation
D. No faultView Answer
Answer» C. b-s bits are selected for the XOR operation
Discussion
6.

There is a dependency on the previous ‘s’ bits in every stage in CFB mode. Here ‘s’ can range from ___

A. 8-16 bits
B. 8-32 bits
C. 4-16 bits
D. 8-48 bits
Answer» C. 4-16 bits
Discussion
7.

Which of the following statements are truei) In the CBC mode, the plaintext block is XORed with previous ciphertext block before encryptionii) The CTR mode does not require an Initialization Vectoriii) The last block in the CBC mode uses an Initialization Vectoriv) In CBC mode repetitions in plaintext do not show up in ciphertext

A. iii)
B. ii) and iv)
C. All the Statements are true
D. i) ii) and iv)View Answer
Answer» E.
Discussion
8.

Which of the following is false for ECB mode of operationi) The Plain text is broken into blocks of size 128 bytesii) Blocks can be swapped, repeated, replaced without recipient noticingiii) Good for short dataiv) Encryption of each block is done separately using a randomly generated key for each block

A. i) only
B. ii) and iii)
C. i) and iv)
D. i) ii) and iv)View Answer
Answer» D. i) ii) and iv)View Answer
Discussion
9.

THE_OUTPUT_OF_THE_XOR_IS_SENT_TO_THE_NEXT_STAGE?$

A. The “Encrypt” Box should be replaced by “Decrypt Box
B. b-s bits are selected for the XOR operation
C. No fault
Answer» B. b-s bits are selected for the XOR operation
Discussion
10.

Which_of_the_following_can_be_classified_under_advantages_and_disadvantages_of_OFB_mode?$

A. Transmission errors
B. A bit error in a ciphertext segment
C. Cannot recover from lost ciphertext segments
D. Ciphertext or segment loss
Answer» C. Cannot recover from lost ciphertext segments
Discussion
11.

There is a dependency on the previous ‘s’ bits in every stage in CFB mode. Here ‘s’ can range from ___$

A. 8-16 bits
B. 8-32 bits
C. 4-16 bits
D. 8-48 bits
Answer» E.
Discussion
12.

iii)

A. ii) and iv)
B. All the Statements are true
C. i) ii) and iv)
Answer» C. i) ii) and iv)
Discussion
13.

Which of the following statements are true

A. In the CBC mode, the plaintext block is XORed with previous ciphertext block before encryption
B. The CTR mode does not require an Initialization Vector
C. The last block in the CBC mode uses an Initialization Vector
D. In CBC mode repetitions in plaintext do not show up in ciphertext
Answer» C. The last block in the CBC mode uses an Initialization Vector
Discussion
14.

Which of the following is false for ECB mode of operation

A. The Plain text is broken into blocks of size 128 bytes
B. Blocks can be swapped, repeated, replaced without recipient noticing
C. Good for short data
D. Encryption of each block is done separately using a randomly generated key for each block
Answer» D. Encryption of each block is done separately using a randomly generated key for each block
Discussion
15.

Which one of the following modes of operation in DES is used for operating short data?

A. Cipher Feedback Mode (CFB)
B. Cipher Block chaining (CBC)
C. Electronic code book (ECB)
D. Output Feedback Modes (OFB)
Answer» D. Output Feedback Modes (OFB)
Discussion
16.

How many modes of operation are there in in DES and AES?

A. 4
B. 3
C. 2
D. 5
Answer» E.
Discussion