[tor-bugs] #17945 [Tor]: Stop Tor2Web connecting to (Rendezvous) Single Onion Services

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#17945: Stop Tor2Web connecting to (Rendezvous) Single Onion Services
-----------------------------+--------------------------------
     Reporter:  teor         |      Owner:
         Type:  enhancement  |     Status:  new
     Priority:  Medium       |  Milestone:  Tor: 0.2.8.x-final
    Component:  Tor          |    Version:
     Severity:  Normal       |   Keywords:  rsos, sos
Actual Points:               |  Parent ID:  #17178
       Points:               |    Sponsor:
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 Tor2Web clients make a one-hop connection to the rendezvous point.
 Rendezvous Single Onion Services also make a one-hop connection to the
 rendezvous point. (Single Onion Services expect a client to make an extend
 request to the Single Onion Service at the end of a 3-hop path.)

 This uses Tor as a one-hop proxy (in this case, to a single onion
 service), which we try to avoid, because it enables certain attacks.

 For Rendezvous Single Onion Services, I don't know how to prevent this
 happening. (Should the rendezvous point intervene? Should we add something
 to the RSOS descriptor?)

 For Single Onion Services, we can modify the Tor2Web client code so it
 doesn't make the SOS extend request, but falls back to rendezvous mode.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17945>
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