asp.net 及 asp.net core 下 MD5加密

建议使用MD5Hash及其重载这两个方法，字符串加密时效率很高

using System;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace System
{
    public class MD5Helper
    {
        public static string PasswordSalt
        {
            get { return "landic"; }
        }
        /// 

        /// 获取文件MD5摘要
        /// 
        /// 
        /// 
        public static string AbstractFile(string fileName)
        {
            using (FileStream file = new FileStream(fileName, FileMode.Open))
            {
                return AbstractFile(file);
            }
        }

        /// 

        /// 根据stream获取文件MD5摘要
        /// 
        /// 
        ///