Firefox add-on client-server security

I'm working on a Firefox add-on. At one point in the ad开发者_如何学编程d-on, it needs to contact my server, give it a URL, then the server will process the URL (it's not a quick or easy process) and send back a link to the resulting file (on Amazon S3). However, since Firefox add-ons are mostly open-source by nature, how can I protect that one call to the server from being discovered by malicious people and then abused? (I only want users of my add-on to be able to make that call to the server...)

I was thinking about using some sort of key or something, but since Firefox add-ons are all open-source that wouldn't really work. I also thought about writing a binary component, but I have almost no experience in C++ (but maybe for something simple like this I could learn) - but then how could I protect calls to the binary component? Also, how could I protect from network sniffers and such? Would it be possible to somehow include encryption of some sort in that binary component so network sniffers cannot detect what is being sent to the server? (I found this question: Client-Server security and authentication but it was a bit over my head.)

When you distribute an extension you are basically giving people the car keys, so it's hard to stop them from taking the car for a joyride. The most secure solution is the one you suggested: use a binary component and authenticate the connection with username/password or PKI certificates. If you use HTTPS then the connection will be encrypted. This isn't totally secure (the binary component could be reverse-engineered by a determined hacker) but it will certain deter casual attacks. Note, however, that implementing, building and maintaining a binary component is significantly harder than the JavaScript equivalent.

An alternative would be to put the user through a one-time registration process when they install the extension. This could even happen in the background, and the user would get some credentials (e.g. a PKI key pair) at the end that they would use for subsequent communication with the server. If you're worried about people overusing the server, then presumably doing so via the extension wouldn't be great either. This way you can track the usage of each user (via the extension or not) and limit it as necessary.

In the end I don't think that there is much you can do. You could have a binary library in your add-on and call it via js-ctypes (it is easier to implement and maintain than a binary XPCOM component). But nothing will stop people from taking your extension and changing its JavaScript logic in any way that they like. You can make it harder by using some logic like this:

• Client to server: "Extension version 1.2.3 wants to make a request."
• Server to client: "Take your chrome://... file, bytes M to N, what SHA1 checksum do you get for them?"
• Client to server: "SHA1 checksum is ..., please process URL ... now."

But this is also everything but fail-proof, it merely makes abusing your service somewhat harder. Same goes for automatic registration - if your extension can register then an attacker can create an account as well.