How can AES/Rijndael MixColumns be implemented?

[isidroas]

I have tried this:

>>> GF = galois.GF(2**8)
>>> poly = galois.Poly([3, 1, 1, 2], field=GF)
>>> poly2 = galois.Poly([219, 19, 83, 69], field=GF)
>>> poly * poly2
Poly(112x^6 + 238x^5 + 61x^4 + 36x^3 + 48x^2 + 227x + 138, GF(2^8))

The poly2 is the same than in wikipedia test vectors

The expected output is [142 77 161 188]

[mhostetter]

Where are you getting that expected output from? You are multiplying two polynomials with degree 3. Therefore the result is necessarily degree 6. Your "expected output" has degree 3. I question the test vector.

[isidroas]

Don't look at my Python snippet because I have no idea of the theory.

As for the test vectors, it seems that wikipedia changed the data since I published the question. Now they are:

I would like to replicate one of these with your library.

[mhostetter]

MixColumns() is a function that permutes (re-orders) the elements. I don't see how multiplying two polynomials does that. You'll have to understand the theory of AES more to accomplish that.

[isidroas]

I will review the theory and then maybe I'll ask another question. Thanks