I've questions about the implementation of The S-Box in the AES cipher.
In this cipher, the Finite Field GF256 is implemented as a quotient $\mathbb{F}_2[X]/(X^8+X^4+X^3+X+1$). The operations can be done by representing its elements as 8 bits vectors. But depending on the basis one choses, computation could be easier. Indeed, if one chooses a normal basis, some interesting stuff happens... Now my questions are:
1)How do we construct all the isomorphisms $\delta$ which would make a basis change when seeing $\mathbb{F}_{256}$ as an 8 dimensional vector space over $\mathbb{F}_2$?
2)How many different basis are there?
3)How to obtain the matrices of these isomorphisms?
Here's an example of such a matrix found in the reference given below: $$ \begin{pmatrix} 0&0&0&1&0&0&1&0\\ 1&1&1&0&1&0&1&1\\ 1&1&1&0&1&1&0&1\\ 0&1&0&0&0&0&1&0\\ 0&1&1&1&1&1&1&0\\ 1&0&1&1&0&0&1&0\\ 0&0&1&0&0&0&1&0\\ 0&0&0&0&0&1&0&0\\ \end{pmatrix} $$
REF:A Very Compact S-Box for AES by D. Canright (google David Canright publications)
Thank you all !