[tor-bugs] #17501 [Pluggable transport]: Design/implement obfsNG.

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#17501: Design/implement obfsNG.
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     Reporter:  yawning     |      Owner:  yawning
         Type:  task        |     Status:  new
     Priority:  Medium      |  Milestone:
    Component:  Pluggable   |    Version:
  transport                 |   Keywords:  huggable-transport, yolo, obfsNG
     Severity:  Normal      |  Parent ID:
Actual Points:              |    Sponsor:
       Points:              |
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 Name subject to change, but for now I'm following the shining example set
 by the IETF and calling it `obfsNG`.  I will likely rename it to `obfs6`
 come deployment time (`obfs5` if skipping a version will confuse users.

 Current planned changes:
  * Key exchange/handshake will use Ring-LWE + Ed25519 (authentication),
 instead of Curve25519/Elligator2 + ntor.
  * Link crypto to likely use Poly1305 + ChaCha20 in a better designed
 framing format than the SipHash-2-4 + Poly1305/XSalsa20 abomination used
 by obfs4.
  * Inline padding negotiation to simplify bridge line formatting.

 Benefits:
  * Slightly easier to use, with a slightly shorter Bridge line.
  * Indistinguishability of the key exchange is a property of the key
 exchange primitive used, rather than something separate that needs care
 when using a la Elligator2.
  * More future-proofing by adding flexibility to padding.

 Downsides:
  * Ring-LWE is really new, and the implementation was ported to Go by some
 random sketchoid.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17501>
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