[tor-bugs] #20895 [Core Tor/Tor]: Split node_supports_ed25519_link_authentication into two or three separate functions

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#20895: Split node_supports_ed25519_link_authentication into two or three separate
functions
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     Reporter:  nickm         |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.0.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:  #15056
       Points:                |   Reviewer:
      Sponsor:                |
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 As of our #15056 code to implement the circuit-side part of prop220, we
 have a function, `node_supports_ed25519_link_authentication`, which isn't
 quite right.

 Sometimes, when we use it, we mean, "If we try to connect to this node,
 should we expect that we will authenticate its ed25519 identity?"

 Sometimes, we mean "If we try to make a connection through some random
 node to this node, authenticating with its ed25519 identity, will that
 work?"

 And sometimes we mean "I'm thinking of asking _that_ node to extend a
 circuit to _this_ node. Should I tell it about _this_ node's Ed25519
 identity, or would it take it the wrong way?"

 I wrote a patch here in response to dgoulet's review of my #15056 branch,
 but on reflection, it isn't right. I'll attach it, but it's a bad start,
 and it's too complex, and maybe you should ignore it?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20895>
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