private static byte GFDet(byte[][] mtx)
{
if (mtx.Length == 2)
{
byte tm = GF.Multiply(mtx[0][0], mtx[1][1]);
tm ^= GF.Multiply(mtx[1][0], mtx[0][1]);
return(tm);
}
byte res = 0;
for (int i = 0; i < mtx.Length; ++i)
{
byte detSub = GFDet(SubMatrix(mtx, i, 0));
res ^= GF.Multiply(mtx[i][0], detSub);
}
return(res);
}
private static void MixColumns(byte[] state, int offset, int Nb, byte[][] mtx)
{
for (int col = 0; col < Nb; col++)
{
byte[] resVector = new byte[4];
for (int bIndex = 0; bIndex < 4; bIndex++)
{
for (int j = 0; j < 4; j++)
{
resVector[bIndex] ^= GF.Multiply(mtx[bIndex][j], state[offset + j * Nb + col]);
}
}
for (int j = 0; j < 4; j++)
{
state[offset + j * Nb + col] = resVector[j];
}
}
}