Re: [tcpinc] Eric Rescorla's Discuss on draft-ietf-tcpinc-tcpcrypt-09: (with DISCUSS and COMMENT)

Daniel B Giffin <> Thu, 29 November 2018 18:41 UTC

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Date: Thu, 29 Nov 2018 10:41:22 -0800
From: Daniel B Giffin <>
To: Eric Rescorla <>
Cc: tcpinc <>, Kyle Rose <>,,, "Black, David" <>, IESG <>,
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Subject: Re: [tcpinc] Eric Rescorla's Discuss on draft-ietf-tcpinc-tcpcrypt-09: (with DISCUSS and COMMENT)
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Okay, how about this language that harmonizes with the SSL

  Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448
  perform the Diffie-Helman protocol using the functions
  X25519 and X448, respectively.  Implementations SHOULD
  compute these functions using the algorithms described in
  RFC7748.  When they do so, implementations MUST check
  whether the computed Diffie-Hellman shared secret is the
  all-zero value and abort if so, as described in Section 6
  of RFC7748.  Alternative implementations of these
  functions SHOULD abort when either input would force the
  output to one of a small set of values, as discussed in
  Section 7 of RFC7748.

That last sentence is explicit (or as explicit as practical
in the scope of this document) because I really can't find
any *instruction* in Section 7 about input checking.