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Date: Tue, 19 Aug 2014 00:10:03 +0000
From: isis <isis@torproject.org>
To: tor-talk@lists.torproject.org
Message-ID: <20140819001003.GW23636@patternsinthevoid.net>
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Subject: Re: [tor-talk] Scaling Tor
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isis transcribed 6.8K bytes:
> Mike Fikuart transcribed 4.8K bytes:
> > Thanks Virgil.  I wasn=E2=80=99t directly what I was after; however it =
was an informative read and as with this subject grows the background knowl=
edge that will come to use in the future.  I did get an interesting link fr=
om Johan Pouweise on scalability that his students published this year http=
://arxiv.org/abs/1404.4818, which gives a good overview of the dilemma of d=
ecentralisation (FYI).
> >=20
> > A question raised in Tor-Design (section 9) is, "if clients can no long=
er have a complete picture of the network, how can they perform discovery w=
hile preventing attackers from manipulating or exploiting gaps in their kno=
wledge?=E2=80=9D.  If the network were to be considered to scale up to sign=
ificant number of all Internet users, could it be that the Directory Author=
ity(Ies) release (to Directory Caches and clients) a uniform, random sample=
 of relays/nodes from the FULL set of nodes, such that the randomness of th=
e path selection is still maintained.  The random selection could be sample=
d on a per client basis with enough of a sample as is currently downloaded =
(6000 relays).  What this means is that each client (or possibly groupings =
of clients) is getting a different =E2=80=9Cview=E2=80=9D of the network, b=
ut there would need to be a scaling down from the full set to the sample se=
t at some point before the client.  Any thoughts on the idea?
> > =20
> > Yours sincerely
> > =20
> > Mike Fikuart=20
> >=20
>=20
> This is an interesting idea. Variants using random walks through nodes wh=
ich
> only know a random subset of other nodes have been proposed before, e.g.
> MorphMix. [0]
>=20
> However, it should be impossible to verify that a given sequence is, in f=
act,
> random, rather than being a sequence in seeded such a way that it is
> predictable, or an encrypted sequence, etc. The biggest concern with impr=
oving
> Tor's scalability via handing out random samples of nodes from the consen=
sus
> would then be that malicious Directories (whether Authorties or simply
> mirrors) could collude to hand out predictable subsets of relays to some/=
all
> clients.
>=20
> Further, even if we could verify that a given sample was truly random, an=
d we
> checked the results for some subset of clients, this would not prohibit
> certain clients from being lied to. I would argue that the security of the
> group of all Tor clients is only as good as the worst case scenario, i.e.=
 any
> mechanism which would allow a single client to subjet to targeted attacks=
 is
> an attack against all.
>=20
> Nicholas Hopper and Nikita Borisov are two of the more significant resear=
chers
> who explore scaling specifically for Tor and/or onion routing in general.
> Perhaps some of the following may help give you an idea of the extant res=
earch
> in this area:
>=20
> For a more detailed explanation of why random subsets of nodes cannot be =
used
> to securely pick an unbiased path (more specifically, why we won't use mo=
st
> DHT algorithms, or the Salsa/Cashmere DHT-overlays), see "Hashing it out =
in
> Public". [1]
>=20
> For an interesting proposal for using some specific DHT algorithms which =
claim
> to keep maintain the current levels of security while providing better
> scalability, see the Torsk paper. [2]
>=20
> And for a Private Information Retrieval (PIR) based approach (admittedly,=
 I
> haven't read it yet, but it's been on my reading list for a while!), whic=
h,
> like other PIR systems would permit DHT-like queries albeit without the
> Directory being able to know what is being looked up, see the PIR-Tor
> paper. [3] However, I think I recall from my skimming that the lookups
> produced *routes*, not nodes... which is worrisome for another set of rea=
sons.
>=20
>=20
> [0]: M. Rennhard and B. Plattner.
>  "Introducing MorphMix: Peer-to-peer based anonymous internet usage with =
collusion detection."
>  In ACM Workshop on Privacy in the Electronic Society (WPES 2002),
>  pp. 91=E2=80=93102. ACM, 2002.
>=20
> [1]: Tran, Andrew, Nicholas Hopper, and Yongdae Kim.
>   "Hashing it out in public: common failure modes of DHT-based anonymity =
schemes."
>   In Proceedings of the 8th ACM workshop on Privacy in the electronic soc=
iety,
>   pp. 71-80. ACM, 2009.
>   http://www.cs.umn.edu/~hopper/hashing_it_out.pdf
>=20
> [2]: McLachlan, Jon, Andrew Tran, Nicholas Hopper, and Yongdae Kim.
>   "Scalable onion routing with Torsk."
>   In Proceedings of the 16th ACM conference on Computer and communication=
s security,
>   pp. 590-599. ACM, 2009.
>   https://www-users.cs.umn.edu/~hopper/torsk-ccs.pdf
>=20
> [3]: Mittal, Prateek, Femi G. Olumofin, Carmela Troncoso, Nikita Borisov,=
 and Ian Goldberg.
>   "PIR-Tor: Scalable Anonymous Communication Using Private Information Re=
trieval."
>   In USENIX Security Symposium. 2011.
>   http://cacr.uwaterloo.ca/techreports/2011/cacr2011-05.pdf
>=20
>=20

I've just realised that my brain must have been sourcing Andrew's post with=
out
telling me, because I just cited all the same papers as Andrew did [0] over=
 a
year ago. BTW, if anyone has found/written more recent, worthwhile papers on
this topic, we'd love to hear about them!

[0]: https://lists.torproject.org/pipermail/tor-talk/2013-January/027179.ht=
ml

--=20
 =E2=99=A5=E2=92=B6 isis agora lovecruft
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