250+ TOP MCQs on Message Authentication Codes (MACs) and Answers

Cryptography Multiple Choice Questions on “Message Authentication Codes (MACs)”.

1. Another name for Message authentication codes is
a) cryptographic codebreak
b) cryptographic codesum
c) cryptographic checksum
d) cryptographic checkbreak

Answer: c
Clarification: Cryptographic checksum is another name for MACs.

2. For a 150-bit message and a 10-bit MAC, how many values are the MAC value dependent on?
a) 2¹⁴⁰
b) 2¹⁵⁰
c) 2¹⁵
d) 2¹⁰

Answer: a
Clarification: 2¹⁵⁰/2¹⁰ = 2¹⁴⁰.

3. Confidentiality can only be provided if we perform message encryption before the MAC generation.
a) True
b) False

Answer: b
Clarification: Confidentiality can be provided even if we perform message encryption after the MAC generation.

4. MACs are also called
a) testword
b) checkword
c) testbits
d) none of the mentioned

Answer: d
Clarification: Another term for MACs are tags(or check sum).

5. For a 100 bit key and a 32 bit tag, how many possible keys can be produced in the 3rd round?
a) 2⁴
b) 2³²
c) 2¹⁶
d) 2⁶⁴

Answer: a
Clarification: First round: 100 – 32 = 68
Second round: 68 – 32 = 36.
Third round: 36 – 32 = 4.
Therefore 2⁴ keys can be produced by the third round.

6. MAC is a
a) one-to-one mapping
b) many-to-one mapping
c) onto mapping
d) none of the mentioned

Answer: b
Clarification: MACs are many to one mapping, which makes it tougher for the intruder for cryptanalysis.

7. For an n-bit tag and a k-bit key, the level of effort required for brute force attack on a MAC algorithm is
a) 2^k
b) 2ⁿ
c) min(2^k,2ⁿ)
d) 2^k/2ⁿ

Answer: c
Clarification: The level of effort required for brute force attack on a MAC algorithm is min(2^k,2ⁿ).