How to make temporary link for a downloadable file

Link to something like /downloads/abb76b3acbd954a05bea357144d614b4, where abb... is a random string such as a salted hash of the current time. When you make this link for someone, store the random string in a database table. This table might look like:

+----+-------------+----------------------------------+---------------------+---------------------+
| id | filename    | token                            | created             | modified            |
+----+-------------+----------------------------------+---------------------+---------------------+
|  1 | image.jpg   | abb76b3acbd954a05bea357144d614b4 | 2012-03-26 19:36:41 | 2012-03-26 19:36:41 |
|  2 | program.exe | 19660d0f5e0ca3d42e1718de5d0a1d7e | 2012-08-29 11:07:58 | 2012-08-29 11:07:58 |
+----+-------------+----------------------------------+---------------------+---------------------+

When you get a request at /downloads/..., look up the random string and send back the correct file. If the created timestamp is too old, don't do so. Use a cronjob to clean out old table rows, or less ideally, do this every time someone makes a request to /downloads/....

Use some code like this

 $path="uploads/";
                  $actualfilename=$path.$filename;
                  $fakefilename="downloadfile.pdf";
                   if($typeofview=="download") {
                          @readfile($actualfilename);
                        header('Content-type: application/pdf');
                        header('Content-Disposition: attachment; filename="' . $fakefilename . '"');
                        header('Content-Transfer-Encoding: binary');
                        header('Content-Length: ' . filesize($actualfilename));
                        header('Accept-Ranges: bytes');
                        exit;

add this to your .htaccess file

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule fakefile.php(.*)$ orignalfile.php?$1 [L,QSA]