<PackageReference Include="BouncyCastle.Cryptography" Version="2.7.0" />

Org.BouncyCastle.Math.BinPoly.ItohTsujiiInv

sealed class ItohTsujiiInv : IBinPolyInv
Itoh–Tsujii multiplicative inversion in GF(2^n): computes a^{-1} = a^(2^n - 2) = (a^(2^(n-1) - 1))^2 using a generic binary addition chain on the exponent e = n - 1, driving the supplied IBinPolyMul's Multiply / Square / SquareN (so it is backend-independent — one implementation serves every ISA).
namespace Org.BouncyCastle.Math.BinPoly { internal sealed class ItohTsujiiInv : IBinPolyInv { public int N { get; } public int Size { get; } public void Invert(ulong[] x, int xOff, ulong[] z, int zOff); } }