Using Bouncy Castle in C# for ECDH

using System;
using System.Linq;
using System.Collections;
using System.Text;

using Org.BouncyCastle.Asn1.Sec;
using Org.BouncyCastle.Asn1.X9;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Math.EC;

using Org.BouncyCastle.Crypto.Agreement;

namespace BouncyCastleECDH
{
    class Program
    {
        public static readonly X9ECParameters _ecparameters = SecNamedCurves.GetByName("secp256k1");
        public static readonly ECDomainParameters _domain = new ECDomainParameters(_ecparameters.Curve, _ecparameters.G, _ecparameters.N, _ecparameters.H);

        public static string ByteArrayToString(byte[] ba)
        {
            StringBuilder hex = new StringBuilder(ba.Length * 2);
            foreach (byte b in ba)
                hex.AppendFormat("{0:x2}", b);
            return hex.ToString();
        }

        public static byte[] ECDH(BigInteger privKeyInt, byte[] publicKey)
        {
            ECPrivateKeyParameters ecPrivateKey = new ECPrivateKeyParameters(privKeyInt, _domain);
            ECPoint publicPoint = _ecparameters.Curve.DecodePoint(publicKey);
            ECPublicKeyParameters ecPublicKey = new ECPublicKeyParameters(publicPoint, _domain);

            // ECDHCBasicAgreement basicAgreement = new ECDHCBasicAgreement();
            ECDHBasicAgreement basicAgreement = new ECDHBasicAgreement();
            basicAgreement.Init(ecPrivateKey);
            BigInteger symKey = basicAgreement.CalculateAgreement(ecPublicKey);

            return symKey.ToByteArray();
        }

        public static byte[] GetPublicKey(BigInteger privKeyInt)
        {
            return GetPublicKey(_ecparameters.G.Multiply(privKeyInt));
        }

        public static byte[] GetPublicKey(ECPoint p)
        {
            var publicParams = new ECPublicKeyParameters(p, _domain);
            return publicParams.Q.GetEncoded();
        }

        static void Main()
        {
            string privkey1 = "82fc9947e878fc7ed01c6c310688603f0a41c8e8704e5b990e8388343b0fd465";
            string privkey2 = "5f706787ac72c1080275c1f398640fb07e9da0b124ae9734b28b8d0f01eda586";
            BigInteger privkey1Int = new BigInteger(privkey1,16);
            BigInteger privkey2Int = new BigInteger(privkey2,16);
            var pubkey1 = GetPublicKey(privkey1Int);
            var pubkey2 = GetPublicKey(privkey2Int);

            Console.WriteLine($"pub1:{ByteArrayToString(pubkey1)}");
            Console.WriteLine($"pub2:{ByteArrayToString(pubkey2)}");
            Console.WriteLine($"ecdh:{ByteArrayToString(ECDH(privkey1Int,pubkey2))}");
        }
    }
}