Curve25519 and Curve448 for the Internet Key Exchange Protocol Version 2 (IKEv2) Key Agreement
RFC 8031
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
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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.
Nir & Josefsson Standards Track [Page 1]
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].
Nir & Josefsson Standards Track [Page 2]
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
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