国密算法 - SM3杂凑算法

先通过NuGet加载BouncyCastle.Crypto.dll到项目，SM3的C#实现方式如下：

using System;
using Org.BouncyCastle.Utilities.Encoders;
using System.Text;
using Org.BouncyCastle.Crypto;

namespace Demo
{
    public abstract class GeneralDigest : IDigest
    {
        private const int BYTE_LENGTH = 64;

        private byte[] xBuf;
        private int xBufOff;

        private long byteCount;

        internal GeneralDigest()
        {
            xBuf = new byte[4];
        }

        internal GeneralDigest(GeneralDigest t)
        {
            xBuf = new byte[t.xBuf.Length];
            Array.Copy(t.xBuf, 0, xBuf, 0, t.xBuf.Length);

            xBufOff = t.xBufOff;
            byteCount = t.byteCount;
        }

        public void Update(byte input)
        {
            xBuf[xBufOff++] = input;

            if (xBufOff == xBuf.Length)
            {
                ProcessWord(xBuf, 0);
                xBufOff = 0;
            }

            byteCount++;
        }

        public void BlockUpdate(
            byte[] input,
            int inOff,
            int length)
        {
            //
            // fill the current word
            //
            while ((xBufOff != 0) && (length > 0))
            {
                Update(input[inOff]);
                inOff++;
                length--;
            }

            //
            // process whole words.
            //
            while (length > xBuf.Length)
            {
                ProcessWord(input, inOff);