[tor-bugs] #29583 [Core Tor/Tor]: HSv3: Faulty cross-certs in introduction point keys (allows naive onionbalance for v3s)

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#29583: HSv3: Faulty cross-certs in introduction point keys (allows naive
onionbalance for v3s)
-----------------------------------------+---------------------------------
 Reporter:  asn                          |          Owner:  (none)
     Type:  defect                       |         Status:  new
 Priority:  Medium                       |      Milestone:  Tor:
                                         |  unspecified
Component:  Core Tor/Tor                 |        Version:
 Severity:  Normal                       |     Resolution:
 Keywords:  tor-hs scaling onionbalance  |  Actual Points:
Parent ID:  #26768                       |         Points:
 Reviewer:                               |        Sponsor:
-----------------------------------------+---------------------------------

Comment (by nickm):

 If we do decide to fix this (and I think we should), I think we'll need a
 multistep process.  Something like this:

 1. Begin including the correct versions of these certificates.  Continue
 including the current (incorrect) versions so as not to break existing
 clients, but mark them with an extension to indicate that you should only
 accept them when the correct certificates are present too.
 2. Check the new (correct certificates) when they are present.
 3. Stop including the old (incorrect) certificates.

 For step 1 and step 2, we'll probably want to use a consensus-triggered
 feature to avoid fingerprinting.  We can't do step 3 until 2022, when
 support for 0.3.5.x ends, unless we decide to backport this or something,
 which would be ... questionable.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29583#comment:3>
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