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

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.