使用
using System.Security.Cryptography;
var md5 = MD5.Create()
方式一：
var openFile = File.OpenRead(filePath)
var hash = md5.ComputeHash(openFile);
方式二:
var stream = new BufferedStream((File.OpenRead(openFileDialog1.FileName)), BUFFER_SIZE)；
md5.ComputeHash(stream)；