[NTLUG:Discuss] Another worry for net users

[David Stanaway]

 Wow, that is insidious.

*How does the PNG caching work?*
	When evercookie sets a cookie, it accesses evercookie_png.php with a special
	HTTP cookie, different than the one used for standard session data. This
	special cookie is read by the PHP file, and if found, generates a PNG file
	where all the RGB values are set to the equivalent of the session data to
	be stored. Additionally, the PNG is sent back to the client browser with
	the request to cache the file for 20 years.

	When evercookie retrieves this data, it deletes the special HTTP cookie,
	then makes the same request to the same file without any user information.
	When the PHP script sees it has no information to generate a PNG with, it
	returns a forged HTTP response of "304 Not Modified" which forces the web
	browser to access its local cache. The browser then produces the cached
	image and then applies it to an HTML5 Canvas tag. Once applied, evercookie
	reads each pixel of the Canvas tag, extracting the RGB values, and thus
	producing the initial cookie data that was stored.




On 9/30/2010 7:56 PM, Rick Renshaw wrote:
> ----- Original Message ----
>
>> From: Richard <ntlug at rain4us.net>
>> To: discuss at ntlug.org
>> Sent: Thu, September 30, 2010 1:36:36 PM
>> Subject: Re: [NTLUG:Discuss] Another worry for net users
>>
>>> On 9/30/2010 10:58 AM, Fred wrote:
>>> If you are running Windows I do not know how to prevent flash cookies from 
>>> being
>>> stored.
>>
>  >  Global Storage Settings panel:
>> Uncheck "Allow third-party Flash content to store data on your computer" ??
>>
>> Set "amount of disk space" to none ?
> It gets worse than just flash cookies:
> http://samy.pl/evercookie/
>
>
>
>       
>
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