//-----------------------------------------------------------------------
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Security;
using System.Security.Cryptography;
using System.IO;
namespace MD5FileForm
{
    public partial class MD5Form : Form
    {
        public MD5Form()
        {
            InitializeComponent();
        }
        private void btnGetMD5_Click(object sender, EventArgs e)
        {
            MD5 md5 = MD5.Create();
            OpenFileDialog ofd = new OpenFileDialog();
            ofd.ShowDialog();
            FileStream fs = new FileStream(ofd.FileName, FileMode.Open);
            byte[] bs = md5.ComputeHash(fs);
            //獲取到MD5碼
            string md5Str = BitConverter.ToString(bs).Replace("-","");
            MessageBox.Show(string.Format("[{0}]的MD5碼為：/n{1}",ofd.FileName,md5Str));
        }
    }
}

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

namespace Test
{
    public class MD5Code
    {
        /// <summary>
        /// 獲取文件的MD5碼
        /// </summary>
        /// <param name="fileName">傳入的文件名（含路徑及后綴名）</param>
        /// <returns></returns>
        public string GetMD5HashFromFile(string fileName)
        {
            try
            {
                FileStream file = new FileStream(fileName, System.IO.FileMode.Open);
                MD5 md5 = new MD5CryptoServiceProvider();
                byte[] retVal = md5.ComputeHash(file);
                file.Close();
                StringBuilder sb = new StringBuilder();
                for (int i = 0; i < retVal.Length; i++)
                {
                    sb.Append(retVal[i].ToString("x2"));
                }
                return sb.ToString();
            }
            catch (Exception ex)
            {
                throw new Exception("GetMD5HashFromFile() fail,error:" + ex.Message);
            }
        }
    }
}