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Is there any way to reduce the length of a hidden service's path to the rendezvous point?

  1. Bob's hidden service <---> Introduction Point
  2. Alice <---> Introduction Point tell Bob to contact me at Rendezvous Point
  3. Bob <-> Rendezvous point

Sometimes, Bob's hidden service does not need anonymity, but wants to be accessible via Tor anyways. (For example, ahmia.fi is also accessible as msydqstlz2kzerdg.onion). In such a case, it might be beneficial to limit the length of Bob's circuit to 1 (as indicated by the length of the arrow in step 3). Is that possible?

This is similar to How to decrease number of Tor hops?. and Accessing Tor hidden services over a single hop circuit, but those wanted to limit the number of client hops. This question is about the number of server hops.

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There are several amendments to Tor being researched to enable this functionality; the functionality does reduce/remove the anonymity of the server but sometimes that is okay, e.g. if (like Facebook) you run a publicly attested, non-hidden "onion service"*

The amendments are:

None of these are - at time of writing, January 2016 - yet sedimented into the main Tor codebase, but they should be in the next few weeks/months.

As the above commenter almost suggests: you should consider carefully before enabling these features. From my experience running a publicly attested Onion, reduced server hop count does improve latency and makes Onion Services as performant, possibly a fraction more performant, than normal Tor. Your mileage may vary.

  • Disclosure: I led the team which built the Facebook Onion Service
  • Great answer. Seems like proposal 260 is what I explicitly asked for and 252 preceded it by another design which fulfills it just as well. Which one is used at facebook, if you may tell? – serv-inc Jan 19 '16 at 9:20
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    We ran totally stock, unmodified Tor code for the first year of operation to prove the concept. It worked fine, and was a simple introduction. We are now (Jan 2016) experimenting with RSOS (prop 260) and OnionBalance to scale the aggregate / net bandwidth available for people who want to use our Onion Service. – Alec Muffett Jan 19 '16 at 17:07
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    ps: you didn't ask this, but another relevant proposal is prop 255 "Controller features to allow for load-balancing hidden services" gitweb.torproject.org/torspec.git/tree/proposals/… - which is relevant to high-throughput load balancing of onions – Alec Muffett Jan 19 '16 at 17:13
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Never decrease the hop length, because it's a purpose of having Tor entry point : to be censorship-resistant. If you will decrease your hidden service behaviour, you will not just decrease it's anonymity, but also make connections to it "fingerprintable"=detectable, and - as a consecuence - censorable

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    Could you elaborate on how they are made detectable? – serv-inc Jan 18 '16 at 19:16
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    @user do you need a whitepaper or what exactly? – Alexey Vesnin Jan 19 '16 at 15:35
  • It's clear that this can deanonymize the hidden service. If you implied that it can deanonymize the client, what is your reasoning? – serv-inc Jan 19 '16 at 17:38
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    @user I suggest you better start reading here – Alexey Vesnin Jan 19 '16 at 17:41

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