Add the file gf256.R
to the R subdirectory of your project. Note that we are
using the representation \(\mbox{GF}(2^8) =
\mathbb{Z}_2[x]/(x^8+x^4+x^3+x+1)\).
Implement the function addGF256.
Implement the function multByXinGF256. This helper
function will need to take into account the polynomial modulus.
Implement the function multGF256. (Make use of the
previous two functions.)