Question

Is the following matrix the inverse matrix of the matrix used in the mix columns step?

x^3 + 1 x

x x^3 + 1

(a) Yes

(b) No

(c) Can’t say

(d) Insufficient Information

This question was posed to me in quiz.

This key 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 (a) Yes

To explain: On multiplying this matrix with the mix columns matrix we get the identity matrix, this proves that it is an inverse matrix.