[tbb-dev] Canvas Breakage Ideas

[Tom Ritter]

On Tue, 2 Jun 2020 at 02:20, Sanketh Menda <sgmenda at uwaterloo.ca> wrote:
> > We also tested the impact of compressing a canvas rendering to the JPEG
> > format. It should be noted that the JPEG compression comes directly from the
> > Canvas API and is not applied after collection. Due to the lossy compression,
> > it should come as no surprise that the entropy from JPEG images is lower than
> > the PNG one usually used by canvas fingerprinting tests (from 0.407 to 0.391)
>
> Is there an easy way for us to do a study on this? Specifically, fix a random
> image, and then on a bunch of different computers, read the image and then do
> a `toDataURL('image/xxx')` for each of the formats.

That's typically the first tact to take to test fingerprinting; but it
can only prove a positive difference, it can't prove a negative.

>From your description, if JPEG compression is deterministic then
toDataURL is deterministic. I bountied
https://stackoverflow.com/questions/25303201/does-lossy-decompression-always-generate-same-output
to try to figure out.

Also, FWIW I think we are at the point where if we aren't ready to
implement, we should document this idea in a tbb-spec so it doesn't
get lost.

-tom