title: How can you make a PHP application require a key to work?
body: <p>About 4 years ago I used a php product called amember pro, it is a membership script which has plugins for lie 30 different payment processors, it was an easy way to set up an automated membership site where users would pay a payment and get access to a certain area.  </p>
  
  <p>The script used ioncube <a href="http://www.ioncube.com/sa_encoder.php" rel="nofollow noreferrer">http://www.ioncube.com/sa_encoder.php</a> to prevent non-paying users from using the script, it requered that you register the domain that the script would be used on, you were then given a key to enter into the file that would make the system/script work.  </p>
  
  <p>Now I am wanting to know how to do such a task, I know ioncube encoder just makes it hard to see the code, in the script I mention, they would just have a small section at the tp of 1 of the included pages that was encrypted and without that part of the code it would break and in addition if the owner of the script did not put you domain in the list and give you a valid key it would not work, also if you tried to use the script on a different domain it would not work.  </p>
  
  <p>I realize that somewhere in the encrypted code that is must of sent you key to there server and checked that it was valid for the domain name it is on, or possibly it did not even do that, maybe the key would just verify that it matched the domain the script was on, that more likely what it did.  </p>
  
  <p>Here is where the real question is, How would you make a script require the portion that is encrypted?  If I made a script and had a small encrypted part at the top, it would seem a user would be able to easily just remove the encrypted part and figure out what the non encrypted part is doing and fix it to work.  Any ideas?</p>