How To Save Unauthorised Manipulation In A Javascript

I wrote a server-client app in javascript/HTML5 its supposed to allow clients to communicate/play a game in realtime using Node.js on the server side . I know the use of private va

Solution 1:

You can run a JavaScript application without registering any single variable, via an anonymous function:

(function() {
    //local variables here.
})();

However, there is no reliable way to prevent cheating: One can easily analyse your code, and create fake AJAX requests. With the latest browsers, it's incredibly easy to capture your code.

With getters and setters, anyone can effectively intercept your functions. Using the deprecated arguments.callee.caller property, an attacker can read the source of the function call, effectively getting access to the closure as defined at the top of this answer.

Example:

var _alert = alert;
window.alert = null;
Object.defineProperty(window, 'alert', {
    'value': function(m) {
        console.log('Intercepted. Function source: ' + arguments.callee.caller);
        _alert.call(this, m);
    }
});
(function(){
    var localVar = 'secret';
    alert('Hi!');
})();

Solution 2:

You can't trust anything that runs on the client's hardware, and that it. Even with the example you've given, anyone could easily modify and reload your script to cheat. Your best bet here, then is not to put any extra effort into this, but rather by writing your application normally and running it through a preprocessor like UglifyJS. The anonymous function pattern indicated by Rob in his answer is also common.

Also, about the MD5 hash thing - no, even if it's in "private scope" you can still view and modify it in a JavaScript debugger. The point here is that someone will always cheat because of the entire nature of the JavaScript execution environment - it's just that you'll need to make it as difficult as possible to cheat by obfuscating your code (obviously using a preprocessor) and other similar techniques.

Solution 3:

JS code is always available, you may want to obfuscate your code to make cheating harder

Solution 4:

All security can be circumvented with enough time. The goal of every security measure is to increase the time it takes to crack What Rob W says will help, but I suggest you also invest in obfuscation/minimization of your javascript which will have a much greater impact on the time and effort required to analyze it and create fake ajax requests than avoiding global variables.

However I concur that a javascript based application can never be very secure. The best you can hope for is "annoying to hack"

How can I obfuscate (protect) JavaScript?