[tor-bugs] #9100 [Tor]: It should be possible to introduce a single hidden service from more than one client

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#9100: It should be possible to introduce a single hidden service from more than
one client
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 Reporter:  andrea       |          Owner:                     
     Type:  enhancement  |         Status:  new                
 Priority:  major        |      Milestone:  Tor: unspecified   
Component:  Tor          |        Version:  Tor: 0.2.4.14-alpha
 Keywords:               |         Parent:                     
   Points:               |   Actualpoints:                     
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 While I'm brain-dumping things that should be improved about hidden
 services...

 For the sake of reliability and load balancing, it should be possible to
 introduce a single hidden service from multiple clients, and automatically
 get a reasonably balanced distribution of incoming connections sent to
 each introducing client.  This can possibly help mitigate transient
 failures of the client, or DoS attempts, which have been reported via as
 yet unknown mechanism against certain prominent HSes recently [1].

 (Question: what happens if you try to do this unofficially now, by copying
 the HS private key to another Tor?)

 This could imply either each instance independently picking intro points
 and publishing a descriptor (simplest), but then other nodes might see the
 multiple conflicting descriptors and think something fishy is going on.
 We could allow descriptors which match in everything but the intro points
 to be merged (need to check: are the HSDirs chosen for a given HS a
 deterministic function of its key so the different clients would all
 publish to the same place to get merged?), but then we end up with large
 numbers of intro points (cf. #9002).

 Finally, we could somehow try to make every instance of the HS pick the
 same set of intro points (how to coordinate, and is it dangerous if it's
 predictable by an attacker?) , and have the intro points effect load
 balancing by mapping incoming INTRODUCE1s into an INTRODUCE2 on one and
 only one incoming intro circuit.

 Additional issue: right now, the client the HS is introduced from must
 have the HS private key.  Load balancing like this means distributing n
 copies of the private key around, increasing the risk of compromise.  It'd
 be helpful if instead they could use a subkey, distinct for each
 introducuing client and either expiring or revokable, with the real HS
 private key kept safely offline somewhere.

 [1] https://twitter.com/maradydd/status/329332167731716096

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9100>
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