エバークッキー検定

How it works?

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  What's Evercookie for?

  Evercookie is created to protect the data which supposed to be persistent by storing these data in several locations simultaneously. In case of any of the data was lost (if you cleared cookies, for example), it can be recovered and then reset and reused.

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  What happens if I delete cookies?

  This is arranged in such a way that to restore cookies, it is enough that it remains in at least one available storage variant (and now there are thirteen of them). Using the remaining available method, the most, if not all, of data will be reset again.

  Such as deleting standard HTTP cookies, LSO data, and even all HTML5 storage remains the PNG cookie and history cookies still exist. Once Everycookies found out either of those data, it restores all of the others (if your browser supports them).

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  And what if I use other browser?

  If you got cookied once, switching to another browser doesn't help you, as long as your device still have the Local Shared Object cookie - the type of cookies which reproduces in all your browsers.

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  Is something installed to my device?

  No, when you browsing sites, data's simply set on your device just as standart HTTP cookies but using all available data storage methods additionaly.

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  Is evercookie open source?

  Evercookie is an open source technologie. The code provides in readable format without any obfuscation. The PHP files are also open source as is the FLA (Flash) code used to generate the SWF Flash object. You have a choice: to compile the Flash object yourself or to use .swf pre-compiled version.

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  What is PNG caching and how does it work?

  PNG caching is defined as using a specific HTTP cookie which accesses evercookie_png.php. After this HTTP cookie is read by PHP, it generates a new PNG file setting all the RGB values to the equivalent of the sessiondata to be stored. Also it sents this PNG to your browser requesting to cache the file for whole 20 years.

  After evercookie got this data, it erases the special HTTP cookie and creates the identical request to the same file but doesn't put any user information in it. When the PHP script discovers the file has no info to generate a PNG with, it sends a fake HTTP response of "304 Not Modified" which makes the web browser accessing its local cache. Then the cached image which is produced by your browser applying to an HTML5 Canvas tag. Evercookie can read each pixel of the Canvas tag for extracting the RGB values and creating the initial cookie data that was stored.

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  How does Everycookie use Web History caching?

  If the Web History caching is enabled in your browser, evercookie sets a cookie and Base64 encodes the data to be stored.

  For example, this data is marked as "bcde" in Base64. Then in the background Evercookie accesses the following URLs:

  google.com/evercookie/cache/b google.com/evercookie/cache/bc google.com/evercookie/cache/bcd google.com/evercookie/cache/bcde google.com/evercookie/cache/bcde-

  These URLs are stored in your browser history.

  While checking for a cookie, evercookie bruteforces all the possible Base64 characters on google.com/evercookie/cache/, starting with "a" and further, but only for a single character. Seeing a URL that was accessed, it attempts to pick up the next symbol. It manages this very fast because no requests are made to the server and it searching locally in JavaScript using the CSS History Knocker. The URL that ends in "-" indicates the end of the string for Everycookie.