[tor-bugs] #24509 [Core Tor/Tor]: circuit_can_use_tap() should only allow TAP for v2 onion services

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#24509: circuit_can_use_tap() should only allow TAP for v2 onion services
-------------------------------------------------+-------------------------
 Reporter:  teor                                 |          Owner:  dgoulet
     Type:  defect                               |         Status:
                                                 |  accepted
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.3.3.x-final
Component:  Core Tor/Tor                         |        Version:  Tor:
                                                 |  0.3.2.1-alpha
 Severity:  Normal                               |     Resolution:
 Keywords:  prop224, tor-hs, security-low,       |  Actual Points:
  easy, intro                                    |
Parent ID:                                       |         Points:  0.5
 Reviewer:                                       |        Sponsor:
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Comment (by dgoulet):

 I was working on this and I started to wonder here why isn't the purpose +
 the presence of a TAP onion key in the extend_info_t object not enough to
 rule out v2 HS?

 As an example, HSv3 never sets a TAP onion key so it can simply never hit
 true there. Is the goal to have an _explicit_ flag that identifies the
 circuits HS version? Tbh, just to have that, it requires quite a bit of
 gymnastic and added flags for some gain I'm not sure I understand?

 A straight forward way would be to add a flag to the `extend_info_t` so
 the v2 and v3 subsystem can put the right version in there. But how is
 that different from "setting a TAP key" and "not setting a tap key" ?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24509#comment:10>
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