Sign DeSo transaction hex in C# using Bouncy Castle cryptography library

SignTransactionExample.cs

using System;
using System.Linq;
using System.Text;
using Desonity;
using Org.BouncyCastle.Asn1;
using Org.BouncyCastle.Asn1.Sec;
using Org.BouncyCastle.Crypto.Digests;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Crypto.Signers;
using Org.BouncyCastle.Math;
using UnityEngine;

public class SignTransactionExample : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        string seed = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
        string txnHex = "01efa5060f5fdae5ed9d90e5f076b2c328a64e347d0c87e8e3317daec5a44fe7c8000102bd53e48625f49e60ff6b7a934e3871b54cc2a93a8737352e8320549e42e2322bab0405270000167b22426f6479223a2248656c6c6f20576f726c64227de807d461f4df9efad8a0f3f716002102bd53e48625f49e60ff6b7a934e3871b54cc2a93a8737352e8320549e42e2322b0000";

        Debug.Log("Signed Transaction " + SignTransaction(seed, txnHex));
    }

    public string SignTransaction(string privateKey, string txnHex)
    {
        var curve = SecNamedCurves.GetByName("secp256k1");
        var domain = new ECDomainParameters(curve.Curve, curve.G, curve.N, curve.H);
        var keyParameters = new ECPrivateKeyParameters(new BigInteger(privateKey, 16), domain);

        var signer = new ECDsaSigner(new HMacDsaKCalculator(new Sha256Digest()));
        signer.Init(true, keyParameters);

        var txnBytes = Convert(txnHex);
        var hash = GetHash(GetHash(txnBytes));
        var signature = signer.GenerateSignature(hash);

        var r = signature[0];
        var s = signature[1];

        var otherS = curve.Curve.Order.Subtract(s);

        if (s.CompareTo(otherS) == 1)
        {
            s = otherS;
        }

        var derSignature = new DerSequence
        (
            new DerInteger(new BigInteger(1, r.ToByteArray())),
            new DerInteger(new BigInteger(1, s.ToByteArray()))
        )
        .GetDerEncoded();

        var signatureStr = Convert(derSignature);
        string signedTxn = txnHex.Substring(0, txnHex.Length - 2) + (signatureStr.Length / 2).ToString("x") + signatureStr;
        return signedTxn;
    }

    private static byte[] GetHash(byte[] data)
    {
        var digest = new Sha256Digest();
        var hash = new byte[digest.GetDigestSize()];
        digest.BlockUpdate(data, 0, data.Length);
        digest.DoFinal(hash, 0);
        return hash;
    }

    public string Convert(byte[] input)
    {
        return string.Concat(input.Select(x => x.ToString("x2")));
    }

    public byte[] Convert(string input)
    {
        if (input.StartsWith("0x")) input = input.Remove(0, 2);

        return Enumerable.Range(0, input.Length / 2).Select(x => System.Convert.ToByte(input.Substring(x * 2, 2), 16)).ToArray();
    }

}