jquery.browser-fingerprint-1.1.js

Browser fingerprinting is a technique to "mark" anonymous users using JS (or other things). To build an "identity" of sorts the browser is queried for a list of its plugins, the screen size and several other things, then hashes them. The idea is that these bits of information produce an unique "fingerprint" of sorts; the more elaborate the list of data points is, the more unique this fingerprint becomes. And you wouldn't even need to set a cookie to recognize this user when she visits again.

For more information on this topic consult Ars Technica or the EFF. There is a lot of potential for undesirable shenanigans, and I strictly oppose using this technique for marketing and ad-related tracking purposes.

Anyways, I needed a really simple fingerprinting library, so I wrote a quick and dirty jQuery plugin. This is by no means a complete and watertight implementation -- it is merely the scratch for a particular itch I was having. YMMV.

This library was written by Carlo Zottmann, carlo@municode.de, has its home on Github and is WTF-licensed (see LICENSE.txt).

 
( function($) {

Calling jQuery.fingerprint() will return an MD5 hash, i.e. said fingerprint.

 
  $.fingerprint = function() {

This function, _raw(), uses several browser details which are available to JS here to build a string, namely...

  • the user agent
  • screen size
  • color depth
  • the timezone offset
  • sessionStorage support
  • localStorage support
  • the list of all installed plugins (we're using their names, descriptions, mime types and file name extensions here)
 
    function _raw() {

That string is the return value.

 
      return [
        navigator.userAgent,
        [ screen.height, screen.width, screen.colorDepth ].join("x"),
        ( new Date() ).getTimezoneOffset(),
        !!window.sessionStorage,
        !!window.localStorage,
        $.map( navigator.plugins, function(p) {
          return [
            p.name,
            p.description,
            $.map( p, function(mt) {
              return [ mt.type, mt.suffixes ].join("~");
            }).join(",")
          ].join("::");
        }).join(";")
      ].join("###");
    }

_md5() computes a MD5 hash using md5-js.

 
    function _md5() {
      if ( typeof window.md5 === "function" ) {

The return value is the hashed fingerprint string.

 
        return md5( _raw() );
      }
      else {

If window.md5() isn't available, an error is thrown.

 
        throw "md5 unavailable, please get it from http://github.com/wbond/md5-js/";
      }
    }

And, since I'm lazy, calling $.fingerprint() will return the hash right away, without the need for any other calls.

 
    return _md5();
  }

})(jQuery);