Secure Shell (SSH) Key Exchange Method using Curve25519 and Curve448
draft-ietf-curdle-ssh-curves-06

Document Type Active Internet-Draft (curdle WG)
Last updated 2017-11-12
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Internet Engineering Task Force                          A. Adamantiadis
Internet-Draft                                                    libssh
Intended status: Standards Track                            S. Josefsson
Expires: May 16, 2018                                             SJD AB
                                                              M. Baushke
                                                  Juniper Networks, Inc.
                                                       November 12, 2017

  Secure Shell (SSH) Key Exchange Method using Curve25519 and Curve448
                    draft-ietf-curdle-ssh-curves-06

Abstract

   This document describes the conventions for using Curve25519 and
   Curve448 key exchange methods in the Secure Shell (SSH) protocol.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 16, 2018.

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

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Adamantiadis, et al.      Expires May 16, 2018                  [Page 1]
Internet-Draft           Curve25519/448 for SSH            November 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

   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 Ed448-Goldilocks [RFC7748] in SSH.  For Curve25519
   with SHA-256 [RFC6234], 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 [RFC6234] to further separate it
   from the Curve25519 alternative.

   This document provide Curve25519 as the preferred choice, but
   suggests that the fall back option Curve448 is implemented to provide
   an hedge against unforeseen 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",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
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