[tor-dev] obfs4, meek, active probing and the timeline of pluggable transports

Sambuddho Chakravarty sambuddho at iiitd.ac.in
Sat Oct 27 22:30:14 UTC 2018

Obfs4 can apparently solve most of the problems pertinent to identifying
Tor bridge traffic by inspection of TLS headers...

Meek relies on SNI field of TLS headers to communicate to bridges via a
"front end ".

>From an overall cursory glance it appears that obfs4 was introduced in 2014
while Meek came later (probably 2015). Thus why would one choose to go back
to relying on TLS traffic that could potentially be identified by the
adversary is a bit unclear (considering that there already existed a
superior solution then , i.e. obfs4).

On Sun, Oct 28, 2018, 03:37 Carolin Zöbelein <contact at carolin-zoebelein.de>

> Hi :),
> I can't give you an answer to your history questions, since I wasn't
> involved in the history of PTs but I have the feeling you have this
> fundamental question "Why we should work on an other PT, as long as the
> stuff which we already have works fine?" (?)
> Simple answer: You should always have an active role (beeing faster
> like the other party in development) and not a passive role (waiting
> until your stuff doesn't work anymore before you work on something new)
> in the fight against censorship.
> Best regards,
> Carolin
> Am Samstag, den 27.10.2018, 17:20 +0530 schrieb Piyush Kumar Sharma:
> > Hello all,
> > I have a few specific questions related to the pluggable transports.
> >
> > 1.) I believe that obfs4 stops active probing(the latest problem as
> > brought to notice by Ensafi et al, IMC 2015 and Shinying Cho, FOCI
> > 2018), and hence discovering obfs4 Tor bridges using active probing
> > is not possible. Is that true? If so, then we are good to go and
> > hence we don't need any other pluggable transport to work for us as
> > long as obfs4 is working?
> >
> > 2.) What was the motivation to bring in meek as a pluggable
> > transport, given the fact that obfs4 works great to cover all the
> > existing problems with Tor detection. Was the motivation just the
> > fact that, it will be much easier for the users to use meek than
> > obfs4 or something other than this?
> >
> > 3.) I searched a lot but could not find the timeline in which
> > pluggable transports were built. As in what was developed and
> > deployed first, obfs4 or meek?
> >
> > Regards
> >
> > Piyush
> > _______________________________________________
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> > tor-dev at lists.torproject.org
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