Question

For a 100 bit key and a 32 bit tag, how many possible keys can be produced in the 3rd round?

(a) 2^4

(b) 2^32

(c) 2^16

(d) 2^64

I have been asked this question in a job interview.

Query is from Message Authentication Codes (MACs) topic in section Message Authentication Codes, Whirlpool Algorithm and Key Management and Distribution of Cryptograph & Network Security

Answer 1

Correct answer is (a) 2^4

Easy explanation: First round: 100 – 32 = 68

Second round: 68 – 32 = 36.

Third round: 36 – 32 = 4.

Therefore 2^4 keys can be produced by the third round.