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Re: [tor-bugs] #26607 [Applications/Tor Browser]: verify that subpixel accuracy of window scroll properties does not add fingerprinting risk



#26607: verify that subpixel accuracy of window scroll properties does not add
fingerprinting risk
-------------------------------------------------+-------------------------
 Reporter:  mcs                                  |          Owner:  tbb-
                                                 |  team
     Type:  defect                               |         Status:  new
 Priority:  High                                 |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tbb-fingerprinting, ff60-esr,        |  Actual Points:
  TorBrowserTeam201904                           |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------

Comment (by acat):

 This is leaking the actual `window.devicePixelRatio` (always set to 1 with
 resistfingerprinting), which is 2 on retina and varies a bit on the
 Android devices I tested (2.77, 3). POC:
 https://acatarineu.github.io/fp/devicePixelRatio.html. In normal desktop
 screens it can be simulated by changing the zoom and refreshing the page.

 I think it's not exclusive of the scroll properties, the same subpixel
 values can be seen with `elem.getBoundingClientRect()` and probably
 others. I need to read more about the implementation to see what's the
 best way of fixing this.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26607#comment:18>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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