commit b8e7bb6abe402218e447f233a1083efaf217321e Author: Mike Perry mikeperry-git@torproject.org Date: Tue May 5 14:52:25 2015 -0700

Update 'General Fingerprinting Defenses' with some ideas. --- design-doc/design.xml | 67 +++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 56 insertions(+), 11 deletions(-)

diff --git a/design-doc/design.xml b/design-doc/design.xml index 715e950..05d2e2b 100644 --- a/design-doc/design.xml +++ b/design-doc/design.xml @@ -1581,12 +1581,16 @@ url="https://amiunique.org/%22%3EAm I Unique</ulink>. </listitem> </orderedlist> </sect3> - <sect3 id="fingerprinting-defenses-general"> <title>General Fingerprinting Defenses</title> <para> + +XXX: Stategies vs approaches? Approaches will include things like +virtualization, spoofing, reimplementation, permissions, and disabling features.. + Without looking at a particular fingerprinting vector there are basically two strategies to thwart fingerprinting attacks in general: + <orderedlist> <listitem> Making users uniform: This would render fingerprinting moot as it only works @@ -1598,23 +1602,64 @@ strategies to thwart fingerprinting attacks in general: identify a user upon (re-)visit of a website which is rendering fingerprinting ineffective. </listitem> + <listitem>Virtualization..</listitem> + <listitem>Disabling features</listitem> </orderedlist> -Although there is some research <ulink url="http://research.microsoft.com/pubs/209989/tr1.pdf">suggesting</ulink> the second approach -we think the former is currently a better suited heuristic for Tor Browser -for a couple of reasons: + +Although there is some research <ulink +url="http://research.microsoft.com/pubs/209989/tr1.pdf%22%3Esuggesting</ulink> the +second approach we think the former is currently a better suited heuristic for +Tor Browser for a couple of reasons: + <itemizedlist> <listitem> - It might not be possible to randomize all fingerprintable characteristics. + +It might not be possible to randomize all fingerprintable characteristics. +While it seems plausible that many end-user configuration details that the +browser currently exposes may be replaced by false information, this approach +seems to break down when it is applied to deeper issues. In particular, it is +not clear how to randomize the capabilities of hardware attached to a computer +in such a way that it convincingly behaves like other hardware, while still +providing a consistent experience to the user from site to site. Similarly, +concealing operating system version differences through randomization will +require an implementation of the underlying support code for every version +your randomization is trying to mimick. + +In both cases, randomizatin requires virtualization of many underlying +implementations, where as uniformity only requires virtualization of one +implementation. + +XXX Virtualization + + </listitem> + <listitem> +Usability. </listitem> <listitem> - It might not be easy to randomize values in a way that they are not - distinguishable from noise. + +It might not be easy to randomize values in a way that they are not +distinguishable from noise. In particular, naive randomization + + </listitem> + <listitem> + +Hard to measure success. + </listitem> <listitem> - Randomizing involves performance costs. This is especially true if the - fingerprinting surface is large (like in a modern browser) and one needs - more elaborate randomizing strategies to make the result - indistinguishable from noise. + +Completeness. Randomization may provide a false sense of security - any items +that are not randomized, or for which the randomization can be averaged away +will still be desirable targets. + + </listitem> + <listitem> + +Randomizing involves performance costs. This is especially true if the +fingerprinting surface is large (like in a modern browser) and one needs more +elaborate randomizing strategies (including randomized virtualization) to +ensure that the randomization fully conceals the true behavior. + </listitem> <listitem> Randomizing itself might introduce a new fingerprinting vector as the