On 12/5/11 3:34 PM, Chris Marrin wrote:
On Dec 5, 2011, at 11:32 AM, Adam Barth wrote:
On Mon, Dec 5, 2011 at 10:53 AM, Chris Marrin<cmar...@apple.com> wrote:
To be clear, it's not the difference between white and black pixels, it's
the difference between pixels with transparency and those without.
Can you explain why the attack is limited to distinguishing between
black and transparent pixels? My understanding is that these attacks
are capable of distinguishing arbitrary pixel values.
This is my misunderstanding. I was referring to the attacks using WebGL, which measure
the difference between rendering alpha and non-alpha pixels. But I think there is
another, more dangerous attack vector specific to CSS shaders. Shaders have the source
image (the image of that part of the page) available. So it is an easy thing to make a
certain color pixel take a lot longer to render (your "1000x slower" case). So
you can easily and quickly detect, for instance, the color of a link.
Can this proposal be moved forward on CORS + HTMLMediaElement,
HTMLImageElement and HTMLCanvasElement?
The proposal would really benefit users and authors on those media
types, even if it falls short of applying to general HTML elements and
CSS urls in the first draft.
I realize that it falls short of the lofty goals of the presentation,
but it would make a good impact and set the stage for further work. It
seems entirely do-able to disable a:visited on elements that have custom
filters applied, but, like the timing issues, there needs to be some
empirical data on risks before moving forward on them.
So I take back my statement that CSS Shaders are less dangerous than WebGL.
They are more!!! As I've said many times (with many more expletives), I hate
the Internet.
I think the solution is clear. We should create a whole new internet where we
only let in people we trust. :-)
-----
~Chris
cmar...@apple.com
I still love my iPhone. ;-)
-Charles
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