Connection to directory authorities

[Karsten Loesing <karsten.loesing@xxxxxxx>]

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How do nodes connect anonymously to directory authorities (DA)?

My idea is that nodes reuse existing circuits and extend them using
RELAY_BEGIN_DIR cells to the five DAs (possibly in parallel). Those
cells are encrypted and contain the actual directory requests. The DAs
create responses and send them in encrypted form back through the
anonymous circuits.

My questions are:
- - Is the above description correct?
- - How many hops do circuits to the DAs contain?
- - What kind of existing circuits are reused? Exit circuits, internal
circuits, unfinished circuits with n-1 hops, or any of them?
- - Do all circuits to the DAs share the same n-1 routers or are different
circuits used for each DA? How often do circuits change?
- - Are circuits to DAs used for other purposes afterwards?
- - What for can requests to directory mirrors be sent directly and not
via RELAY_BEGIN_DIR? Aren't DAs the only nodes used for bootstrapping,
or are mirrors used for that purpose, too? In the former case, who
connects to mirrors directly? Is it merely provided for debugging
purposes, old Tor versions, or something I missed?

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