Re: [tor-bugs] #32253 [Applications/Tor Browser]: Zooming and letterboxing

["Tor Bug Tracker & Wiki" <blackhole@xxxxxxxxxxxxxx>]

#32253: Zooming and letterboxing
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 Reporter:  cypherpunks                    |          Owner:  tbb-team
     Type:  defect                         |         Status:  new
 Priority:  Medium                         |      Milestone:
Component:  Applications/Tor Browser       |        Version:
 Severity:  Normal                         |     Resolution:
 Keywords:  tbb-fingerprinting-resolution  |  Actual Points:
Parent ID:                                 |         Points:
 Reviewer:                                 |        Sponsor:
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Comment (by cypherpunks):

 Replying to [comment:9 Thorin]:
 > It doesn't matter which measurements it sees (at 100% or 133%), because
 math can be used to calculate the other, as long as zoom is known
 Well that was my point when I wrote that it can make assumptions because
 the values are not rounded. In my example above, where letterboxing is
 applied, it's not possible determine whether the original size is 1000x700
 or 1000x600 as they both result in 600x400.

 > unless you can completely spoof zoom, which is problematic and probably
 undo-able. And there are so many other ways to get measurements, e.g
 elements, and monitor them, e.g. observer APIs. DPI complicates this as
 well.
 I'm aware of that. However decreasing the ways to extract some piece of
 fingerprint is still worth something IMO, even if there are other (more
 elaborate) ways to get to the same or similar info about the user.

 Anyway, my initial impression was that this was doable. For reference,
 here's a blog comment from gk:
 >So, for the zoom I meant in the upcoming major release, Tor Browser 9,
 with letterboxing enabled. However, I looked closer now and stand
 corrected in that letterboxing does not solve the zoom issue
 automatically. We'd need to look into it.
 https://blog.torproject.org/comment/284106#comment-284106

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32253#comment:10>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online

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