Secure Shell (SSH) Key Exchange Method using Curve25519 and Curve448
draft-ietf-curdle-ssh-curves-01

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Last updated 2017-03-27
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Internet Engineering Task Force                          A. Adamantiadis
Internet-Draft                                                    libssh
Intended status: Informational                              S. Josefsson
Expires: September 28, 2017                                       SJD AB
                                                              M. Baushke
                                                  Juniper Networks, Inc.
                                                          March 27, 2017

  Secure Shell (SSH) Key Exchange Method using Curve25519 and Curve448
                    draft-ietf-curdle-ssh-curves-01

Abstract

   How to implement the Curve25519 and Curve448 key exchange methods in
   the Secure Shell (SSH) protocol is described.

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   This Internet-Draft will expire on September 28, 2017.

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   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Adamantiadis, et al.   Expires September 28, 2017               [Page 1]
Internet-Draft           Curve25519/448 for SSH               March 2017

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Key Exchange Methods  . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Shared Secret Encoding  . . . . . . . . . . . . . . . . .   3
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Appendix A.  Copying conditions . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   In [Curve25519], a new elliptic curve function for use in
   cryptographic applications was introduced.  In [Ed448-Goldilocks] the
   Ed448-Goldilocks curve (also known as Curve448) is described.  In
   [RFC7748], the Diffie-Hellman functions using Curve25519 and Curve448
   are specified.

   Secure Shell (SSH) [RFC4251] is a secure remote login protocol.  The
   key exchange protocol described in [RFC4253] supports an extensible
   set of methods.  [RFC5656] describes how elliptic curves are
   integrated in SSH, and this document reuses those protocol messages.

   This document describes how to implement key exchange based on
   Curve25519 and Curve448 in SSH.  For Curve25519 with SHA-256
   [RFC4634], the algorithm we describe is equivalent to the privately
   defined algorithm "curve25519-sha256@libssh.org", which is currently
   implemented and widely deployed in libssh and OpenSSH.  The Curve448
   key exchange method is novel but similar in spirit, and we chose to
   couple it with SHA-512 [RFC4634] to further separate it from the
   Curve25519 alternative.

   This document provide Curve25519 as the prefered choice, but suggests
   that the fall back option Curve448 is implemented to provide an hedge
   against unforseen analytical advances against Curve25519 and SHA-256.
   Due to different implementation status of these two curves (high-
   quality free implementations of Curve25519 has been in deployed use
   for several years, while Curve448 implementations are slowly
   appearing), it is accepted that adoption of Curve448 will be slower.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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