ECDH256 -TizzyT

    public class ECDH256 : IDisposable
    {
        internal readonly ECDiffieHellmanCng ecdh;

        public byte[] PublicKey { get; }

        public ECDH256()
        {
            ecdh = new ECDiffieHellmanCng
            {
                KeyDerivationFunction = ECDiffieHellmanKeyDerivationFunction.Hash,
                HashAlgorithm = CngAlgorithm.Sha256
            };
            PublicKey = ecdh.PublicKey.ToByteArray();
        }

        public void Dispose() => ecdh.Dispose();
    }

    public static class ECDH256Extensions
    {
        public static byte[] DeriveSharedKey(this ECDH256 ECDH, byte[] PublicKey)
        {
            byte[] SharedKey
                = ECDH.ecdh.DeriveKeyMaterial(ECDiffieHellmanCngPublicKey.FromByteArray(PublicKey, CngKeyBlobFormat.EccPublicBlob));
            ECDH.Dispose();
            return SharedKey;
        }
    }