Re: AES operation order
- From: Sebastian Gottschalk <seppi@xxxxxxxxx>
- Date: Mon, 26 Dec 2005 22:34:10 +0100
Cryptic wrote:
MixColumns(state xor (A^(-1) * key)) = A * (state xor A^(-1) * key) = (A * state) xor (A * A^(-1) * key) = (A * state) xor key = the original AES result.
But it does not work. Isn't the above correct in GF(2^8)?
[3] * ((1) xor [170] * (4)) = [3] * ((1) xor (168))) = [3]*(169) = (251) ([3] * (1)) xor ([3]*[170] * (4)) = (3) xor (4) = (7)
I still wonder why you even assumed that '*' is distributive over XOR in any non-trivial field like GF(2^8). For much more fun, the same thing for GF(2^16) is an esential element of the security of IDEA.
.
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