[tor-bugs] #3642 [Torbutton]: more browser fingerprint techniques.

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#3642: more browser fingerprint techniques.
-----------------------+----------------------------------------------------
 Reporter:  arno       |          Owner:  mikeperry
     Type:  defect     |         Status:  new      
 Priority:  normal     |      Milestone:           
Component:  Torbutton  |        Version:           
 Keywords:             |         Parent:           
   Points:             |   Actualpoints:           
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 Hi,
 I discovered (at least, I have not read about those methods anywhere) two
 new ways to fingerprint browser a little more.

 First, a user can define a user stylesheet where in can set default or
 overriding (with !important declaration) properties. This stylesheet can
 be userContent.css file in profile directory, but it can also be other
 pages set by extensions. This is often use for accessibility reasons (for
 example: set all pages white and black for people with some vision
 problems).

 A few other properties can be set with preferences dialog: default color
 text, default anchor color. This properties can also be read by webpage.

 I'm not sure what torbutton can do to mitigate this. May be register a
 stylesheet to reset all css properties to browser defaults.

 Another thing a webpage can do is get the zoom value. This has not a big
 entropy, but is yet another metric.

 See testcase here:

 !http://renevier.net/misc/fingerprint.html

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/3642>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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