[tor-bugs] #6253 [Firefox Patch Issues]: Prompt before allowing HTML5 Canvas image extraction

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#6253: Prompt before allowing HTML5 Canvas image extraction
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 Reporter:  mikeperry             |          Owner:  mikeperry
     Type:  defect                |         Status:  new      
 Priority:  major                 |      Milestone:           
Component:  Firefox Patch Issues  |        Version:           
 Keywords:  tbb-fingerprinting    |         Parent:           
   Points:                        |   Actualpoints:           
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 The HTML5 canvas can be used for fingerprinting WebGL and font rendering
 as described in http://www.w2spconf.com/2012/papers/w2sp12-final4.pdf. The
 fingerprint technique hinges on the ability for JS to extract image/data
 urls from the canvas object and hash them and/or compute differences.
 There's some demonstration code that works for a specific (but currently
 unknown) ruby version here: https://github.com/kmowery/canvas-
 fingerprinting.

 I think the least-effort defense for now is to simply prompt before image
 extraction, and to allow extraction permissions to be set on a url-bar
 domain basis if the user has opted to store browser state to disk.

 Later, we can think about virtualizing this surface during extraction, but
 I don't think we'll need to do that unless every site in the world decides
 to make a lolcat captioning HTML5 widget.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/6253>
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