I've been inspired by the answer to the question here: Location to store an encryption key
It gave me a lot to think about.
My friend and I are building a website and we've encountered a problem in which every user will have the ability to upload digital content (files) and sell it to other people.
The people who purchase the file will have access to it (downloading it). The problem is how do I make it safe from abuse? that a user who purchased a file wont be able to share it with other people (if they will have the link they still wont be able to download the file).
For example if UserX purchased a file and now have the following url:
by sharing it with UserY who didn't purchase the file will raise an error message.
We are developing in php.