[tor-bugs] #17349 [Tor]: Create an ed25519 shared randomness key for dirauths

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#17349: Create an ed25519 shared randomness key for dirauths
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 Reporter:  asn     |          Owner:
     Type:  defect  |         Status:  new
 Priority:  Medium  |      Milestone:  Tor: 0.2.8.x-final
Component:  Tor     |        Version:
 Severity:  Normal  |     Resolution:
 Keywords:          |  Actual Points:
Parent ID:  #16943  |         Points:
  Sponsor:          |
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Comment (by asn):

 OK, an initial version of this feature can be found at my branch
 `prop250-ed25519-day1`.

 The patch is quite messy, but it generates SR keys and adds the cert chain
 in the votes. Then it's also able to parse the keys from votes.

 David, to use this:
 - Use `get_shared_random_keypair()` to get the shared randomness keypair
 to sign the commitments.
 - Then, after vote parsing, use
 `networkstatus_t.ed25519_shared_random_cert.signed_key` to get the shared
 random key of other authorities and verify their commitment signatures.

 I will be working on this the following days to make it nicer and more
 robust. I also need to write up the proposal, but I first wanted to make
 sure that what I'm doing makes sense.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17349#comment:8>
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