Question

For a key 25D5 and PT input A479 what is the output we obtain after the “add round key” function?

(a) F34D

(b) 81AC

(c) 79DF

(d) 327D

I had been asked this question in an interview for job.

This question is from The AES Algorthm topic in chapter Advanced Encryption Algorithm and Block Cipher Operation of Cryptograph & Network Security

Answer 1

Right option is (b) 81AC

To explain I would say: Simply apply XOR to the state matrix PT with the key matrix to obatain the output which in this case is 81AC.