internal static void Sign(IInvoice invoice, ECPrivateKeyParameters privateKey)
{
var digest = new KeccakDigest(256);
digest.BlockUpdate(invoice.TxBytes.ToArray(), 0, invoice.TxBytes.Length);
var hash = new byte[digest.GetByteLength()];
digest.DoFinal(hash, 0);
var signer = new ECDsaSigner(new HMacDsaKCalculator(new Sha256Digest()));
signer.Init(true, privateKey);
var components = signer.GenerateSignature(hash);
var encoded = new byte[64];
insert256Int(components[0], 0, encoded);
insert256Int(components[1], 32, encoded);
var publicKey = domain.G.Multiply(privateKey.D).GetEncoded(true);
var prefix = new ReadOnlyMemory <byte>(publicKey, 0, Math.Min(Math.Max(6, invoice.MinimumDesiredPrefixSize), publicKey.Length));
invoice.AddSignature(KeyType.ECDSASecp256K1, prefix, encoded);
}
