国密算法 - SM2椭圆曲线公钥密码算法

国密SM2的实现需要借助SM3，SM3杂凑算法的实现参考https://www.hierror.com/demo/article/138054

同样需要引用BouncyCastle.Crypto.dll到项目，一共有三个类：Cipher.cs 、SM2.cs、SM2Helper.cs(主要是如何使用SM2的方法)，实现分别如下：

//Chiper.cs

using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Math.EC;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;


namespace Demo
{
    public class Cipher
    {
        private int ct = 1;


        private ECPoint p2;
        private SM3 sm3keybase;
        private SM3 sm3c3;


        private byte[] key = new byte[32];
        private byte keyOff = 0;


        public Cipher()
        {
        }


        private void Reset()
        {
            sm3keybase = new SM3();
            sm3c3 = new SM3();


            byte[] p;


            p = p2.X.ToBigInteger().ToByteArray();
            sm3keybase.BlockUpdate(p, 0, p.Length);
            sm3c3.BlockUpdate(p, 0, p.Length);


            p = p2.Y.ToBigInteger().ToByteArray();
            sm3keybase.BlockUpdate(p, 0, p.Length);


            ct = 1;
            NextKey();
        }


        private void NextKey()
        {
            SM3 sm3keycur = new SM3(sm3keybase);
            sm3keycur.Update((byte)(ct >> 24 & 0x00ff));
            sm3keycur.Update((byte)(ct >> 16 & 0x00ff));
            sm3keycur.Update((byte)(ct >> 8 & 0x00ff));
            sm3keycur.Update((byte)(ct & 0x00ff));
            sm3keycur.DoFinal(key, 0);
            keyOff = 0;
            ct++;
        }


        public virtual ECPoint Init_enc(SM2 sm2, ECPoint userKey)
        {
            BigInteger k = null;
            ECPoint c1 = null;


            AsymmetricCipherKeyPair key = sm2.ecc_key_pair_generator.GenerateKeyPair();
            ECPrivateKeyParameters ecpriv = (ECPrivateKeyParameters)key.Private;
          &