public static byte[] SignRFC6979(this ECDsa key, byte[] data)
{
var digest = new Sha256Digest();
var secp256r1 = SecNamedCurves.GetByName("secp256r1");
var ec_parameters = new ECDomainParameters(secp256r1.Curve, secp256r1.G, secp256r1.N);
var private_key = new ECPrivateKeyParameters(new BigInteger(1, key.PrivateKey()), ec_parameters);
var signer = new ECDsaSigner(new HMacDsaKCalculator(digest));
var hash = new byte[digest.GetDigestSize()];
digest.BlockUpdate(data, 0, data.Length);
digest.DoFinal(hash, 0);
signer.Init(true, private_key);
var rs = signer.GenerateSignature(hash);
var signature = new byte[RFC6979SignatureSize];
var rbytes = rs[0].ToByteArrayUnsigned();
var sbytes = rs[1].ToByteArrayUnsigned();
var index = RFC6979SignatureSize / 2 - rbytes.Length;
rbytes.CopyTo(signature, index);
index = RFC6979SignatureSize - sbytes.Length;
sbytes.CopyTo(signature, index);
return(signature);
}