计算文件的MD5值上传到服务器 下载验证文件是否被篡改

using System;
using System.Windows.Forms;
using System.Security.Cryptography;
using System.IO;

namespace 计算文件的MD5
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //创建与服务器的连接
            FtpClient fc = new FtpClient("127.0.0.1","test","123");
            //上传本地文件到服务器命名为02...文件
            fc.Upload(new FileInfo("textFilePath.Text"), "02" + DateTime.Now.ToString("yyyyMMdd")+".xls");
            //获取内容的MD5
            string md5 = MD5Value("textFilePath.text");
            //获取文件的MD5加上密钥之后的新的MD5
            string newMD5 = GetMD5(md5+"tianwang");//文件的MD5加上密钥
            //流处理，将新的MD5值写入文本文件
            File.WriteAllText(@"c:\02" + DateTime.Now.ToString("yyyyMMdd") + ".text",newMD5);
            //上传文本文件到远程服务器
            fc.Upload(new FileInfo(@"c:\02" + DateTime.Now.ToString("yyyyMMdd") + ".text"), @"c:\02" + DateTime.Now.ToString("yyyyMMdd") + ".text");
        }
        /// <summary>
        /// 计算文件MD5值
        /// </summary>
        /// <param name="str">需要计算的文件路径</param>
        /// <returns>MD5值</returns>
        public static string MD5Value(String filepath)
        {
            MD5 md5 = new MD5CryptoServiceProvider();
            byte[] md5ch;
            using (FileStream fs = File.OpenRead(filepath))
            {
                md5ch = md5.ComputeHash(fs);
            }
            md5.Clear();
            string strMd5 = "";
            for (int i = 0; i < md5ch.Length - 1; i++)
            {
                strMd5 += md5ch[i].ToString("x").PadLeft(2, '0');
            }
            return strMd5;
        }
        /// <summary>
        /// 计算字符串的MD5
        /// </summary>
        /// <param name="sDataIn"></param>
        /// <returns></returns>
        public static string GetMD5(string sDataIn)
        {
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
            byte[] bytValue, bytHash;
            bytValue = System.Text.Encoding.UTF8.GetBytes(sDataIn);
            bytHash = md5.ComputeHash(bytValue);
            md5.Clear();
            string sTemp = "";
            for (int i = 0; i < bytHash.Length; i++)
            {
                sTemp += bytHash[i].ToString("X").PadLeft(2, '0');
            }
            return sTemp.ToLower();
        }

        /// 判断服务器上的文件是否被篡改，如果没有则读取
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button2_Click(object sender, EventArgs e)
        {
            //获取当前系统时间
            string datestr = DateTime.Now.ToString("yyyyMMdd");
            FtpClient fc = new FtpClient("127.0.0.1","test","123");
            //将服务器上个文件下载下来
            fc.Download("02" + datestr + ".xls", @"c:\02" + datestr + ".xls");

            //计算下载下来的xls文件的MD5值+密钥
            string md5 = MD5Value(@"c:\02" + datestr + ".xls");
            string newMD5 = GetMD5(md5 + "tianwang");

            //下载服务器上的保留的MD5txt文件MD5的值
            fc.Download("02" + datestr + ".txt", @"c:\t.text");
            string txt = File.ReadAllText(@"c:\t.txt");

            //检查文件是否被篡改
            if(txt!=newMD5)
            {
                MessageBox.Show("文件被篡改");
                return;
            }

            using(FileStream stream=File.OpenRead(@"c:\02.xls"))
            {
                HSSFWorkbook wb = new HSSFWorkbook(stream);
                HSSFSheet sheet = wb.GetSheetAt(0);
                MessageBox.Show(sheet.LastRowNum.ToString());
            }
        }

    }
}