[tor-bugs] #22995 [Core Tor/Tor]: prop224 should say we use SHA256 for rend circuit digests

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#22995: prop224 should say we use SHA256 for rend circuit digests
------------------------------+------------------------------------
     Reporter:  teor          |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.2.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  prop224, tor-spec, doc
Actual Points:                |  Parent ID:
       Points:  0.5           |   Reviewer:
      Sponsor:                |
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 In prop224, the rend section says:
 {{{
    A successfully completed handshake, as embedded in the
    INTRODUCE/RENDEZVOUS cells, gives the client and hidden service host
    a shared set of keys Kf, Kb, Df, Db, which they use for sending
    end-to-end traffic encryption and authentication as in the regular
    Tor relay encryption protocol, applying encryption with these keys
    before other encryption, and decrypting with these keys before other
    decryption. The client encrypts with Kf and decrypts with Kb; the
    service host does the opposite.
 }}}
 https://gitweb.torproject.org/torspec.git/tree/proposals/224-rend-spec-
 ng.txt#n1890

 But that's not what the code does: circuit_init_cpath_crypto() uses SHA256
 rather than SHA1 when `is_hs_v3` is true.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22995>
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