[tor-bugs] #13021 [Tor Browser]: Review Canvas APIs for fingerprintability

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#13021: Review Canvas APIs for fingerprintability
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     Reporter:           |      Owner:  brade
  mikeperry              |     Status:  assigned
         Type:  task     |  Milestone:
     Priority:  major    |    Version:
    Component:  Tor      |   Keywords:  ff31-esr, tbb-fingerprinting,
  Browser                |  TorBrowserTeam201409
   Resolution:           |  Parent ID:
Actual Points:           |
       Points:           |
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Comment (by gacar):

 I checked https://bugzilla.mozilla.org/show_bug.cgi?id=884226: This brings
 a new canvas context property (`willReadFrequently`) that enables reading
 from a software backend instead of a hardware "accelerated" one, which
 turns out to be super-slow for some cases.

 So, canvas reads may get faster, but no fingerprinting risks that I can
 see.

 Also interesting is [https://bugzilla.mozilla.org/show_bug.cgi?id=962517
 #962517] which brings a chrome only HW-acceleration-disabled canvas and
 explains the HW backend problem better in the context of FFOS.


 `HitRegions` are about defining clickable regions in canvas, similar to
 image-maps for <img> elements (e.g. using <area> & <map>). Although one
 may potentially exploit the pixel-level differences in region boundaries
 (similar to `isPointInPath` method
 [https://web.archive.org/web/20140513130550/http://ct1.addthis.com/static/r07/core130.js
 AddThis was using]) it requires user interaction (click or hover) and
 doesn't look like a reliable fingerprinting vector.

 Also there's a switch `canvas.hitregions.enabled`, and it is disabled by
 default in ESR31.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13021#comment:2>
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