[tor-bugs] #22006 [Core Tor/Tor]: prop224: Validate ed25519 pubkeys to remove torsion component

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#22006: prop224: Validate ed25519 pubkeys to remove torsion component
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 Reporter:  asn                     |          Owner:  asn
     Type:  defect                  |         Status:  needs_review
 Priority:  Medium                  |      Milestone:  Tor: 0.3.1.x-final
Component:  Core Tor/Tor            |        Version:
 Severity:  Normal                  |     Resolution:
 Keywords:  tor-hs prop224 ed25519  |  Actual Points:
Parent ID:  #21888                  |         Points:
 Reviewer:                          |        Sponsor:  SponsorR-can
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Changes (by asn):

 * status:  assigned => needs_review


Comment:

 OK, since Ian no longer has review comments for this branch, I'm pushing a
 squashed `bug22006_v3` branch and marking it as `needs_review`.

 Gitlab review here: https://gitlab.com/asn/tor/merge_requests/15

 The only thing I don't like here is that in `60ed3d0e2` there is no way to
 know that we are actually checking all ed25519 keys from the network. I
 scanned the codebase to find places where we receive ed25519 keys, and I
 think I identified all the high-level places in the code that accept such
 keys but I don't know if I found all of them.

 I did this because Ian suggested it here:
    https://lists.torproject.org/pipermail/tor-dev/2017-April/012230.html

 If we want to take this seriously and ensure that we do it for all keys
 received on the net, we could add a `int key_is_validated` flag to
 `ed25519_public_key_t`, and throw a BUG() (or return -1) if we ever try to
 verify a signature with a non-validated pubkey.

 What do you guys think? FWIW, for most cases this is not a life-or-death
 validation, but more like a nice thing to do to avoid any edge-case
 esoteric attacks.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22006#comment:5>
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