[tor-bugs] #16672 [Tor Browser]: Text rendering allows fingerprinting

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#16672: Text rendering allows fingerprinting
-------------------------+-------------------------------------------------
     Reporter:           |      Owner:  tbb-team
  arthuredelstein        |     Status:  needs_review
         Type:  defect   |  Milestone:
     Priority:  normal   |    Version:
    Component:  Tor      |   Keywords:  tbb-fingerprinting-fonts, tbb-5.0,
  Browser                |  TorBrowserTeam201508R
   Resolution:           |  Parent ID:
Actual Points:           |
       Points:           |
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Comment (by dcf):

 Replying to [comment:15 dcf]:
 > It seems like the fonts.conf settings are not taking hold--at least the
 rgba one. When I zoom in, I see subpixel antialiasing.

 When I turn on the CONFIG option of FC_DEBUG, I can see that Fontconfig is
 loading my normal configuration files in /etc, in addition to Tor
 Browser's packaged one.
 {{{
 $ FC_DEBUG=1024 ./start-tor-browser.desktop -d
 FC_DEBUG=1024
         Loading config file /home/david/nightly-16672/tor-browser_en-
 US/Browser/TorBrowser/Data/fontconfig/fonts.conf
         Scanning config dir /etc/fonts/conf.d
         Loading config file /etc/fonts/conf.d/10-scale-bitmap-fonts.conf
         Loading config file /etc/fonts/conf.d/11-lcdfilter-default.conf
         ...
 }}}
 If I remove this line from fonts.conf,
 {{{
 <include ignore_missing="yes">conf.d</include>
 }}}
 Then Fontconfig only loads Tor Browser's fonts.conf.
 {{{
 $ FC_DEBUG=1024 ./start-tor-browser.desktop -d
 FC_DEBUG=1024
         Loading config file /home/david/nightly-16672/tor-browser_en-
 US/Browser/TorBrowser/Data/fontconfig/fonts.conf
 }}}

 However it doesn't change the checksum relative to comment:15. It is still
 1-8854c333. And when I zoom in, I can still see subpixel antialising. This
 is surprising to me because I know that both system fonts.conf and
 subpixels were on my mind when I made the fonts.conf from #13313, and I'm
 pretty sure I tested them back then.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16672#comment:16>
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