利用FileStream对文件进行加密解密

private void btnChooesFile_Click(object sender, EventArgs e)
        {
            //选择要加密的文件
            OpenFileDialog fs = new OpenFileDialog();
            fs.InitialDirectory = @"D:\";
            fs.Filter = "(*.rar)|*.rar";
            if (fs.ShowDialog()== DialogResult.OK)
            {
                txtFilename.Text = fs.FileName;
            }
        }

        private void btnDes_Click(object sender, EventArgs e)
        {
            //加密，对读出来的字节进行每个字节(255-r)再存

            string s = txtFilename.Text;
            string path = Path.GetDirectoryName(s);
            string filename = "222.rar";
            string fullname = Path.Combine(path,filename);
            using(FileStream fs2=new FileStream(fullname,FileMode.Create))
            {
               using(FileStream fs=new FileStream(s,FileMode.Open))
               {
                   byte[] bytes=new byte[1024];//缓冲区大小
                   int readbyte;
                   while((readbyte=fs.Read(bytes,0,bytes.Length))>0)
                   {
                   
                       for (int i = 0; i <= readbyte;i++ )
                       {
                           bytes[i] = (byte)(byte.MaxValue- bytes[i]);
                       }
                       //ShowMsg("写入了:" + readbyte.ToString() + "字节");
                       fs2.Write(bytes, 0, readbyte);//写入文件
                       
                   }
               }
               //ShowMsg("写入成功");
            }
        }
        void ShowMsg(string s)
        {

            txtShow.AppendText(s+"\r\n");
        }

        private void btnChooesDES_Click(object sender, EventArgs e)
        {
        }

        private void btnUDes_Click(object sender, EventArgs e)
        {

            //加密，对读出来的字节进行每个字节(255-r)再存

            string s = txtFilename.Text;
            string path = Path.GetDirectoryName(s);
            string filename = "333.rar";
            string fullname = Path.Combine(path, filename);
            using (FileStream fs2 = new FileStream(fullname, FileMode.Create))
            {
                using (FileStream fs = new FileStream(s, FileMode.Open))
                {
                    byte[] bytes = new byte[1024];//缓冲区大小
                    int readbyte;
                    while ((readbyte = fs.Read(bytes, 0, bytes.Length)) > 0)
                    {

                        for (int i = 0; i <= readbyte; i++)
                        {
                            bytes[i] = (byte)(byte.MaxValue - bytes[i]);
                        }
                       ShowMsg("写入了:" + readbyte.ToString() + "字节");
                        fs2.Write(bytes, 0, readbyte);//写入文件

                    }
                }
                //ShowMsg("写入成功")
            }
        }