[tor-bugs] #31369 [Core Tor/Stem]: HSv3 descriptor support in stem

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#31369: HSv3 descriptor support in stem
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 Reporter:  asn                          |          Owner:  atagar
     Type:  defect                       |         Status:  reopened
 Priority:  Medium                       |      Milestone:
Component:  Core Tor/Stem                |        Version:
 Severity:  Normal                       |     Resolution:
 Keywords:  tor-hs onionbalance scaling  |  Actual Points:
Parent ID:  #26768                       |         Points:  9
 Reviewer:                               |        Sponsor:  Sponsor27-must
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Comment (by asn):

 Hello atagar,

 I have a branch which implements the crypto parts needed to decrypt a
 descriptor. I made a PR just so that you can do a review, but please don't
 merge as this is very dirty and also breaks tests:
 https://github.com/torproject/stem/pull/20

 Some comments:
 - We need to add a mandatory `onion_address` argument to the parsing
 function since we can't decrypt any layers of the descriptor without the
 full onion address.
 - I made an `hsv3_crypto.py` file to store all the various crypto
 utilities but I will move these to the hsv3 file when we make one.

 I also added some `ATAGAR XXX` notes with stem things I need help:
 - There is some pre-processing that needs to happen while parsing some
 objects (e.g. certs and encrypted bodies) which I do inline atm, but we
 need to move them to the parsing layer.
 - I don't know how to parse the resulting plaintext using the stem parsing
 functions, so I made a super dirty `parse_superencrypted_plaintext()`
 which needs to be made more stem-y.

 I'm pretty confident that this can serve as a reasonable basis for more
 decoding work, so I will be moving to encoding work for now so that I do
 the crypto parts there too.

 Thanks for all the help!

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31369#comment:11>
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