On Tue, 2 Jun 2020 at 02:20, Sanketh Menda sgmenda@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... 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