So, it’s impossible to do AJAX requests securely without using SSL. I get it. You can either view-source the data that’s being sent via Javascript, or you can directly access the PHP page by spoofing headers, yada yada.
But let’s say this web app doesn’t particularly require true security, and instead it’s just a sort of game to keep most reverse-engineers at bay. What sort of hurdles should I employ?
I’m not looking for some ridiculously over-the-top Javascript implementation of an encryption algorithm. I want simplicity as well as mild security… if that isn’t contradictory by nature. So, what would you guys recommend?
For example, I’m running a contest where if a user clicks an image successfully (jQuery), it passes their userid and a timestamp to a PHP page, both MD5 salted by random data and then encoded with MIME. The PHP page then validates this userid and timestamp, then returns a winning “code” in the form of another salted MD5 hash. I’m also employing multiple header checks to help ensure the request is from a valid location. Am I missing anything, or is that about all I can do? It seems like someone could just fire the jQuery click event and ruin the whole thing, but I don’t see how I can prevent that.
I’ll be awarding the answer to anyone who comes up with an ingenious faux-security mechanism! Or… just whomever tells me why I’m stupid this time.
I believe header checks can be easily fooled. Doesn’t hurt though.
Since your algorithm is exposed on the client side, the user can simply send the appropriate data to your server with an automated script to fool your server into thinking it was clicked.
In addition to that, you have to watch out for session hijacking. A user can essentially submit this ajax request on behalf of someone else, especially if they have the algorithm. Does your application have different behavior for certain users? If so, then the session hijacking could turn into priviledge escalation issue.
It is not necessarily true that you need to encrypt the payload with SSL in your case in order to build a secure application. From what you’ve described, there is no sensitive data being sent over the wire.
Ensure that you have some basic silly checks on the server side to check for automated or malicious behavior. For example, if you find that the header information is missing, you may want to have some sort of flag/alert that someone is toying with the response. Another place you may want to do this is the pattern of requests.
A more secure model is to have the server assign the user some session token that they cannot reverse-engineer. This session token ideally should begin with the timestamp instead of the username to promote the avalanche effect of the salted hashing algorithm.
Since it seems like your application deals with prizes and potentially money, I would invest some more time in securing this app. Hope these tips have helped you.