Mixing Preshared Keys in the Internet Key Exchange Protocol Version 2 (IKEv2) for Post-quantum Security
RFC 8784

Document Type RFC - Proposed Standard (June 2020; No errata)
Authors Scott Fluhrer  , Panos Kampanakis  , David McGrew  , Valery Smyslov 
Last updated 2020-06-30
Replaces draft-fluhrer-qr-ikev2
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Internet Engineering Task Force (IETF)                        S. Fluhrer
Request for Comments: 8784                                 P. Kampanakis
Category: Standards Track                                      D. McGrew
ISSN: 2070-1721                                            Cisco Systems
                                                              V. Smyslov
                                                               June 2020

 Mixing Preshared Keys in the Internet Key Exchange Protocol Version 2
                   (IKEv2) for Post-quantum Security


   The possibility of quantum computers poses a serious challenge to
   cryptographic algorithms deployed widely today.  The Internet Key
   Exchange Protocol Version 2 (IKEv2) is one example of a cryptosystem
   that could be broken; someone storing VPN communications today could
   decrypt them at a later time when a quantum computer is available.
   It is anticipated that IKEv2 will be extended to support quantum-
   secure key exchange algorithms; however, that is not likely to happen
   in the near term.  To address this problem before then, this document
   describes an extension of IKEv2 to allow it to be resistant to a
   quantum computer by using preshared keys.

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

Copyright Notice

   Copyright (c) 2020 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
   (https://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.

Table of Contents

   1.  Introduction
     1.1.  Requirements Language
   2.  Assumptions
   3.  Exchanges
   4.  Upgrade Procedure
   5.  PPK
     5.1.  PPK_ID Format
     5.2.  Operational Considerations
       5.2.1.  PPK Distribution
       5.2.2.  Group PPK
       5.2.3.  PPK-Only Authentication
   6.  Security Considerations
   7.  IANA Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Appendix A.  Discussion and Rationale
   Authors' Addresses

1.  Introduction

   Recent achievements in developing quantum computers demonstrate that
   it is probably feasible to build one that is cryptographically
   significant.  If such a computer is implemented, many of the
   cryptographic algorithms and protocols currently in use would be
   insecure.  A quantum computer would be able to solve Diffie-Hellman
   (DH) and Elliptic Curve Diffie-Hellman (ECDH) problems in polynomial
   time [C2PQ], and this would imply that the security of existing IKEv2
   [RFC7296] systems would be compromised.  IKEv1 [RFC2409], when used
   with strong preshared keys, is not vulnerable to quantum attacks
   because those keys are one of the inputs to the key derivation
   function.  If the preshared key has sufficient entropy and the
   Pseudorandom Function (PRF), encryption, and authentication
   transforms are quantum secure, then the resulting system is believed
   to be quantum secure -- that is, secure against classical attackers
   of today or future attackers with a quantum computer.

   This document describes a way to extend IKEv2 to have a similar
   property; assuming that the two end systems share a long secret key,
   then the resulting exchange is quantum secure.  By bringing post-
   quantum security to IKEv2, this document removes the need to use an
   obsolete version of IKE in order to achieve that security goal.

   The general idea is that we add an additional secret that is shared
   between the initiator and the responder; this secret is in addition
   to the authentication method that is already provided within IKEv2.
   We stir this secret into the SK_d value, which is used to generate
   the key material (KEYMAT) for the Child Security Associations (SAs)
   and the SKEYSEED for the IKE SAs created as a result of the initial
   IKE SA rekey.  This secret provides quantum resistance to the IPsec
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