[tor-bugs] #19163 [Core Tor/Tor]: Make sure clients almost always use ntor

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#19163: Make sure clients almost always use ntor
-------------------------------------------------+-------------------------
 Reporter:  teor                                 |          Owner:  teor
     Type:  defect                               |         Status:
                                                 |  needs_review
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.2.9.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  rsos, tor-hs, TorCoreTeam201608,     |  Actual Points:  6
  review-group-7                                 |
Parent ID:                                       |         Points:  2.0
 Reviewer:  nickm                                |        Sponsor:
-------------------------------------------------+-------------------------
Changes (by teor):

 * status:  needs_revision => needs_review
 * actualpoints:  5 => 6


Comment:

 nickm said on IRC to just get rid of the opportunistic upgrades.

 Turns out that rend_client_get_random_intro_impl() already inadvertently
 upgrades to ntor in the following circumstances:
 * the HS descriptor doesn't contain a TAP onion key
 * the node can be found by nickname or fingerprint in the client's
 consensus

 I've left that code as-is, but I can easily remove it if you'd like.
 I think we should be consistent between client intro and service rend, and
 never upgrade from the consensus. (It certainly doesn't break modern
 clients or hidden services.)

 Please see my branch reject-tap-v6 on https://github.com/teor2345/tor.git
 Or on gitlab at https://gitlab.com/teor/tor/merge_requests/7

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/19163#comment:19>
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