[tor-bugs] #29134 [Core Tor/Tor]: Document the max number of v3 client auths I can make

[Tor Bug Tracker & Wiki]

#29134: Document the max number of v3 client auths I can make
--------------------------+------------------------------
 Reporter:  pastly        |          Owner:  (none)
     Type:  defect        |         Status:  new
 Priority:  Medium        |      Milestone:
Component:  Core Tor/Tor  |        Version:  Tor: 0.3.5.7
 Severity:  Normal        |     Resolution:
 Keywords:                |  Actual Points:
Parent ID:                |         Points:
 Reviewer:                |        Sponsor:
--------------------------+------------------------------

Comment (by teor):

 Replying to [comment:1 pastly]:
 > The limit seems to be around 350-360

 Client auth uses 80 bytes per client. Then there's some padding to obscure
 the number of clients.

 Client auth effectively uses the leftover space in the descriptor under 50
 kB.

 So the limit may be lower if your onion service:
 * is a single onion service (21 bytes)
 * has 4-10 introduction points (default 3)
 * has legacy introduction points (chosen at random, fewer legacy into
 points as more relays upgrade from 0.2.9 and earlier)
 * has IPv6 introduction points (one #26992 is implemented, if an IPv6
 relay is chosen at random, then its address will be added to the link
 specifiers. There will be more IPv6 intro points as more relays configure
 IPv6.)

 We should calculate the worst-case scenario for the hard limit, and
 implement a check for it. We should add some paddiding, because adding
 extra link specifiers on relays will increase the size of descriptors
 (once #26971 is implemented).

 Then we can document the hard limit, and a suggested soft maximum that's
 compatible with future versions of Tor. We should add a test for the hard
 limit. Otherwise, we could make changes that increase the size of a
 descriptor, but fail to change the limit in the documentation.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29134#comment:2>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online