Gunes Acar:
My name is Gunes Acar, a 2nd year PhD student at Computer Security and Industrial Cryptography (COSIC) group of University of Leuven.
I work with Prof. Claudia Diaz and study online tracking and browser fingerprinting. I'd like to work on "Panopticlick" (https://www.torproject.org/getinvolved/volunteer.html.en#panopticlick) summer project and other fingerprinting related issues which I tried to outline below:
- Collaborate with Peter@EFF to port/open-source Panopticlick:
https://trac.torproject.org/projects/tor/ticket/6119#comment:4 a) implement necessary modifications - e.g. we won't be having cookies or real IP addresses to match returning visitors. b) consider security implications of storing fingerprints (e.g. what happens if someone gets access to fingerprint database?)
- Add machine-readability support outlined in Tor Automation
proposals: https://people.torproject.org/~boklm/automation/tor-automation-proposals.htm... a) which one(s) should we implement? JSON, YAML, XML?
- Survey the literature for fingerprinting attacks published since
Panopticlick. Implement those that may apply to TBB: a) Canvas & WebGL fingerprinting (Mowery et al.) - make sure the patch at #6253 works b) JS engine fingerprinting (Mulazzani et al.) c) CSS & rendering engine fingerprinting, (Unger et al.) ...
This sounds good. We already have a fix for #1 though, but verification can't hurt (the canvas should come back as all white unless the user allows it).
We also have a couple fixes for CSS-based fingerprinting (fonts and system colors) that are entropy-reduction efforts only. Actually measuring the amount of entropy reduction here would be useful.
- Check with realworld fingerprinting scripts to see if they collect
anything that is not considered before. Check if TBB's FP countermeasures work against them. (We can use data from FPDetective study to find sites with fingerprinting scripts)
Great.
- Backport new "attacks" found in 3 & 4 to EFF's Panopticlick in case
they consider an update.
Unfortunately, the EFF has been reluctant to work with us in any way to improve or re-deploy Panopticlick for our needs, hence the frustrated tone of my other mail in this thread. It also seems that the EFF would not permit your resulting work to be open source, which I believe is a violation of the GSoC rules. I guess since you are not intending to actually apply to GSoC, this is a moot point though. It's just also a sore one for me, so I figured I'd poke it once more ;).
However, as I also said in my other mail, I actually think we may be better served by developing something independent of Panopticlick. We need per-TBB version breakdowns of all the statistics we record, so we can measure the change in entropy as we deploy fixes and improvements to our defenses, without previous datapoints biasing the distribution.
Other than some helper functions to store data and calculate entropy, and one (or maybe two) simple fingerprinting tests, we should not need any of the Panopticlick code for this project. It's also likely that our DB schema will end up radically different, due to the need to segment data by browser version (which may be input by the user), and the need for many more (and more varied) tests than they have.
- Convert fixed FP-related bugs into regression tests.
https://trac.torproject.org/projects/tor/query?keywords=~tbb-fingerprinting&...
- Build test cases to check the severity of fingerprinting related
open tickets, e.g.: https://trac.torproject.org/projects/tor/ticket/8770 https://trac.torproject.org/projects/tor/ticket/10299
Work on potential fingerprinting bugs that ESR31 may bring.
ESR transitions seem to create a lot of FP-related issues that need
to be checked manually (e.g. #9608). Consider developing a tool that iterates over the host objects of two browsers to compare them automatically (e.g. to pinpoint new objects, new methods, updated default values, etc.). Similar to "diff tool" mentioned here: https://people.torproject.org/~boklm/automation/tor-automation-proposals.htm...
I am not sure this is helpful. In general, we only want to measure fingerprintability *within* a specific browser version.
To determine the appearance of new APIs, it's probably best and simplest to simply review Mozilla's Developer Documentation, ie: https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/24
- Evaluate the font-limits of TBB by checking the average # of fonts
Top 1 Million sites use. We can either collect fresh data with FPDetective or use the existing (~1 year old) data.
Excellent.
More on my background relevant to fingerprinting and TBB code base:
We recently published a paper called "FPDetective: Dusting the Web for Fingerprinters" (CCS'13) to measure the prevalence of browser fingerprinting on the Internet. As a part of this study, we built instrumented browsers from Chromium and PhantomJS source code and developed a framework to detect fingerprinting (https://github.com/fpdetective/).
I also got my hands dirty with the TBB source code to seek vulnerabilities in FP countermeasures. Two ways I found to circumvent existing font limits were as follows: https://trac.torproject.org/projects/tor/ticket/8270#comment:2 https://trac.torproject.org/projects/tor/ticket/5798#comment:13
Right. A proper fix for #5798 will address this, as documented in the bug. I would not get distracted leveraging implementation bugs like this in your data collection, especially if we're aware of them and simply haven't had the development capacity to fix them.
Actual shortcomings of a defense in an information-theoretic sense (such as 10 fonts being too many, or our screen resolution leaking too much entropy) are better areas of focus, given the time.
However, if you also want to write any TBB patches to fix any implementation bugs (known or newly discovered), you will be my new hero. :)
Other pointers: My website: http://www.esat.kuleuven.be/cosic/?page_id=126 FPDetective website: https://www.cosic.esat.kuleuven.be/fpdetective/ My (first & only) Tor patch: https://trac.torproject.org/projects/tor/ticket/10472 My Tor FAQ profile: http://tor.stackexchange.com/users/731/gacar
Looking for your comments, Cheers, Gunes
N.B.: I won't be applying to GSoC.
Oh wow. Ok. I suppose that settles the GSoC Open Source snafu, and in a way that doesn't cause a legal disagreement with the EFF. Hurray! ;)
Please keep me updated of your progress and plans, in any case!