Curve25519 and Curve448 for the Internet Key Exchange Protocol Version 2 (IKEv2) Key Agreement
RFC 8031

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Internet Engineering Task Force (IETF)                            Y. Nir
Request for Comments: 8031                                   Check Point
Category: Standards Track                                   S. Josefsson
ISSN: 2070-1721                                                      SJD
                                                           December 2016

                    Curve25519 and Curve448 for the
     Internet Key Exchange Protocol Version 2 (IKEv2) Key Agreement

Abstract

   This document describes the use of Curve25519 and Curve448 for
   ephemeral key exchange in the Internet Key Exchange Protocol Version
   2 (IKEv2).

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc8031.

Copyright Notice

   Copyright (c) 2016 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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RFC 8031            Curve25519 and Curve448 for IKEv2      December 2016

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   2
   2.  Curve25519 and Curve448 . . . . . . . . . . . . . . . . . . .   3
   3.  Use and Negotiation in IKEv2  . . . . . . . . . . . . . . . .   3
     3.1.  Key Exchange Payload  . . . . . . . . . . . . . . . . . .   4
     3.2.  Recipient Tests . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Numerical Example for Curve25519 . . . . . . . . . .   7
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The "Elliptic Curves for Security" document [RFC7748] describes two
   elliptic curves, Curve25519 and Curve448, as well as the X25519 and
   X448 functions for performing key agreement using Diffie-Hellman
   operations with these curves.  The curves and functions are designed
   for both performance and security.

   Elliptic curve Diffie-Hellman [RFC5903] has been specified for the
   Internet Key Exchange Protocol Version 2 (IKEv2) [RFC7296] for almost
   ten years.  RFC 5903 and its predecessor specified the so-called NIST
   curves.  The state of the art has advanced since then.  More modern
   curves allow faster implementations while making it much easier to
   write constant-time implementations that are resilient to time-based
   side-channel attacks.  This document defines two such curves for use
   in IKEv2.  See [Curve25519] for details about the speed and security
   of the Curve25519 function.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

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RFC 8031            Curve25519 and Curve448 for IKEv2      December 2016

2.  Curve25519 and Curve448

   Implementations of Curve25519 and Curve448 in IKEv2 SHALL follow the
   steps described in this section.  All cryptographic computations are
   done using the X25519 and X448 functions defined in [RFC7748].  All
   related parameters (for example, the base point) and the encoding (in
   particular, pruning the least/most significant bits and using little-
   endian encoding) are compliant with [RFC7748].

   An ephemeral Diffie-Hellman key exchange using Curve25519 or Curve448
   is performed as follows: each party picks a secret key d uniformly at