Decrypt File Uploaded In Zend Framwork While Download - php

Question

I am making a zend project that has a file upload functionality and the client wanted to encrypt and upload the files without their extension. I did that perfectly by using the following code :
$upload = new Zend_File_Transfer_Adapter_Http ();
$salt = $upload->getHash('md5', 'file_name');
$upload->addFilter('Rename', array('target' => APPLICATION_PATH . '/../../uploads/presentations/'.$salt));
$upload->addFilter('Encrypt', array('adapter' => 'mcrypt', 'key' => $constants->encryption_key));
$upload->receive ();
This is working fine now I'm just downloading the file with the following code
$filename = 'example_presentation_file.ppt'; //original name in db. by the way this coming from database
$hash = '85be69db87a43265a44be1482cc6d819'; //changed file name when uploaded with this
$mime = 'application/octet-stream';
$file_path = APPLICATION_PATH . '/../../uploads/presentations/'.$hash;
header('Content-Type: "'.$mime.'"');
header('Content-Disposition: attachment; filename="'.$filename.'"');
header("Content-Transfer-Encoding: binary");
header('Expires: 0');
header('Pragma: no-cache');
$size = filesize($file_path);
if(isset($_SERVER['HTTP_RANGE']))
{
list($a, $range) = explode("=",$_SERVER['HTTP_RANGE'],2);
list($range) = explode(",",$range,2);
list($range, $range_end) = explode("-", $range);
$range = intval($range);
if(!$range_end) {
$range_end = $size-1;
}
else {
$range_end = intval($range_end);
}
$new_length = $range_end-$range+1;
header("HTTP/1.1 206 Partial Content");
header("Content-Length: $new_length");
header("Content-Range: bytes $range-$range_end/$size");
}
else {
$new_length = $size;
header("Content-Length: ".$size);
}
#ob_end_clean();
$speed = false;
$chunksize = ($speed?($speed * 1024):(1024 * 1024)) ;
$bytes_send = 0;
$buffer = "";
if ($file = fopen($file_path, 'r')) {
if(isset($_SERVER['HTTP_RANGE'])) {
fseek($file, $range);
}
while(!feof($file) && (!connection_aborted()) && ($bytes_send<$new_length)) {
$buffer = fread($file, $chunksize);
print($buffer);
flush();
if($speed) {
if($type!=2) sleep(1);
}
$bytes_send += strlen($buffer);
}
fclose($file);
}
This code is working very fine and downloading the file but when I open that file in powerpoint, it doesn't open it and displays an error.
The point is that, If i disable the file encryption, I opens very good but it is necessary. I just wanted to know that how to decrypt the file in run time (just when user downloads it not forever).
Thanks.

Answer 1

I suggest the following workflow:
Temporary decrypt the encrypted file and save it somewhere
Send this decrypted file to the client
Remove decrypted file from the file system
Example:
<?php
/* ... */
$options = array(
'adapter' => 'mcrypt',
'key' => $constants->encryption_key);
$decrypt = new Zend_Filter_File_Decrypt($options);
// temp. decrypt file and save it on the disc
$decrypted_file_path = APPLICATION_PATH . '/../../uploads/presentations/'. $filename;
$decrypt->setFilename($decrypted_file_path);
// encrypted file location
$decrypt->filter($file_path);
/* your code: Send $decrypted_file_path to the client */
// remove decrypted file
unlink($decrypted_file_path);