Score:1

99 in AES s-box, where it came from?

tf flag
Tom

The multiplicative inverse in AES s-box is transformed using the following affine transformation:

$s = b \oplus (b \lll 1) \oplus (b \lll 2) \oplus (b \lll 3) \oplus (b \lll 4) \oplus 99_{10}$

Where did the number 99 come from? For what purpose is it there?

I'm asking, because I'm trying to generalize it in $GF(2^{128})$. So I would like to find a similar number if we would operating in $GF(2^{128})$.

de flag
[crypto.stackexchange.com question #40132](https://crypto.stackexchange.com/questions/40132/)
cn flag
Does this answer your question? [How constant value 0x63 in affine transformation is chosen or generated while AES Substitution Box is formed?](https://crypto.stackexchange.com/questions/40132/how-constant-value-0x63-in-affine-transformation-is-chosen-or-generated-while-ae)
Tom avatar
tf flag
Tom
@j.p. yes, I think it is clear enough. Thanks!
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