[tbb-bugs] #18361 [Tor Browser]: Issues with corporate censorship and mass surveillance

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Mon Feb 22 13:02:45 UTC 2016

#18361: Issues with corporate censorship and mass surveillance
 Reporter:  ioerror                       |          Owner:  tbb-team
     Type:  enhancement                   |         Status:  new
 Priority:  High                          |      Milestone:
Component:  Tor Browser                   |        Version:
 Severity:  Critical                      |     Resolution:
 Keywords:  security, privacy, anonymity  |  Actual Points:
Parent ID:                                |         Points:
  Sponsor:                                |

Comment (by isis):

 Replying to [comment:8 yawning]:
 > cc-ing isis since this covers earlier work.
 > Replying to [comment:1 marek]:
 > > In other words: is it possible to provide a bit of data (i'm-a-human)
 tied to the browsing session while not violating anonymity.
 > Yes.  This is a problem that "Anonymous Credential" systems are designed
 to solve.  A example of a system with most of the properties that are
 desired is presented in Au, M. H., Kapadia, A., Susilo, W., "BLACR: TTP-
 Free Blacklistable Anonymous Credentials with Reputation"
 (https://www.cs.indiana.edu/~kapadia/papers/blacr-ndss-draft.pdf).  Note
 that this is still an active research area, and BLACR it of itself may not
 be practical/feasible to implement, and is listed only as an example since
 the paper gives a good overview of the problem and how this kind of
 primitive can be used to solve the problem.
 > Isis can go into more details on this sort of thing, since she was
 trying to implement a similar thing based on Mozilla Persona (aborted
 attempt due to Mozilla Persona being crap).

 Having not read the BLACR paper yet… one should generally be wary of
 anonymous credentials which advertise some form of revocation, since
 effectively what this means is having some backdoor whereby a trusted
 third party can do "anonymity revocation". The other form this usually
 takes is to keep a blacklist (skimming tells me that BLACR does this), or
 keep some other form of state, e.g. "all blinded signature tokens we've
 already seen used before," which additionally introduces the requirement
 that the credential issuing server be always online.

 There are other anonymous credential schemes built on NIZK proofs which do
 not require keeping expensive (and continually growing) blacklists, one of
 my personal favourites being described in
 [https://eprint.iacr.org/2008/428 Belenkiy, Lysyanskaya, Camenisch,
 Sacham, Chase, and Kohlweiss' "Randomizable Proofs and Delegatable
 Anonymous Credentials"]. The delegation aspect could also provide a nice
 feature of being able to e.g. say "I'll trust any user who has met the
 authentication requirements of any of Cloudflare, Wikipedia, or Amazon"
 without necessarily knowing which of those three the user had already
 authenticated to.

Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18361#comment:31>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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