Problem unlocking files

[Truemedia]

I have made several scripts to allow a file to be modified once copied and downloaded to a new location. The only problem is undoing the hash or the header when getting the file from download/ folder in prestashop.

Iv'e tried using file_get and file_put contents in a combination to download the file fresh through the url of a customer who has bought the product, but I'm guessing since the file is generated some of the header need changing for the content type, but I'm having no luck doing that and trying the other method of reversing the security changes put on a file getting it directly where they are stored isn't turning up a working file (When its a "zip").

Does anyone from the prestashop team know how to reverse the hash on zip files, or what to change in the content header for getting the file from customer purchased url (example: get-file?key=w280h083h0rh-uwegvfi8ewufg93).

Any info is appreciated and if noone knows I'll eventually get to the bottom of it but anything that will help me crack this faster is a big help thanks.