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Internet Engineering Task Force (IETF)                            Y. NirRequest for Comments: 8420                                      Dell EMCCategory: Standards Track                                    August 2018ISSN: 2070-1721Using the Edwards-Curve Digital Signature Algorithm (EdDSA) in theInternet Key Exchange Protocol Version 2 (IKEv2)Abstract   This document describes the use of the Edwards-curve Digital   Signature Algorithm (EdDSA) 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 inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8420.Copyright Notice   Copyright (c) 2018 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Nir                          Standards Track                    [Page 1]

RFC 8420                     EdDSA in IKEv2                  August 2018Table of Contents1. Introduction ....................................................21.1. Conventions Used in This Document ..........................32. The "Identity" Hash Identifier ..................................33. Security Considerations .........................................34. IANA Considerations .............................................35. Normative References ............................................3Appendix A.  ASN.1 Objects .........................................4A.1.  ASN.1 Object for Ed25519 ...................................4A.2.  ASN.1 Object for Ed448 .....................................4   Author's Address ...................................................51.  Introduction   The Internet Key Exchange Protocol Version 2 [RFC7296] can use   arbitrary signature algorithms as described in [RFC7427].  [RFC7427]   defines the SIGNATURE_HASH_ALGORITHMS notification where each side of   the IKE negotiation lists its supported hash algorithms.  This   assumes that all signature schemes involve a hashing phase followed   by a signature phase.  This made sense because most signature   algorithms either cannot sign messages bigger than their key or   truncate messages bigger than their key.   EdDSA [RFC8032] defines signature methods that do not require   prehashing of the message.  Unlike other methods, these accept   messages of arbitrary size, so no prehashing is required.  These   methods are called Ed25519 and Ed448; they use the Edwards 25519 and   the Edwards 448 ("Goldilocks") curves, respectively.  Although that   document also defines prehashed versions of these algorithms, those   versions are not recommended for protocols where there is minimal   burden in buffering the entire message so as to make it practical to   make two passes over the message.  This is true of IKEv2.  SeeSection 8.5 of [RFC8032] for that recommendation.   EdDSA defines the binary format of the signatures that should be used   in the "Signature Value" field of the Authentication Data Format inSection 3 of RFC 8032.  [RFC8410] defines the object identifiers   (OIDs) for these signature methods.  For convenience, these OIDs are   repeated inAppendix A.   In order to signal within IKE that no hashing needs to be done, we   define a new value in the SIGNATURE_HASH_ALGORITHMS notification to   indicate that no hashing is performed.Nir                          Standards Track                    [Page 2]

RFC 8420                     EdDSA in IKEv2                  August 20181.1.  Conventions Used in This Document   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 inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.2.  The "Identity" Hash Identifier   This document defines a new value called "Identity" (5) in the "IKEv2   Hash Algorithms" registry for use in the SIGNATURE_HASH_ALGORITHMS   notification.  Inserting this new value into the notification   indicates that the receiver supports at least one signature algorithm   that accepts messages of arbitrary size such as Ed25519 and Ed448.   Ed25519 and Ed448 are only defined with the "Identity" hash and MUST   NOT be sent to a receiver that has not indicated support for the   "Identity" hash.   The prehashed versions of Ed25519 and Ed448 (Ed25519ph and Ed448ph,   respectively) MUST NOT be used in IKE.3.  Security Considerations   The new "Identity" value is needed only for signature algorithms that   accept an input of arbitrary size.  It MUST NOT be used if none of   the supported and configured algorithms have this property.  On the   other hand, there is no good reason to prehash the inputs where the   signature algorithm has that property.  For this reason,   implementations MUST have the "Identity" value in the   SIGNATURE_HASH_ALGORITHMS notification when EdDSA is supported and   configured.  Implementations SHOULD NOT have other hash algorithms in   the notification if all supported and configured signature algorithms   have this property.4.  IANA Considerations   IANA has assigned the value 5 for the algorithm with the name   "Identity" in the "IKEv2 Hash Algorithms" registry with this document   as reference.5.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/info/rfc2119>.Nir                          Standards Track                    [Page 3]

RFC 8420                     EdDSA in IKEv2                  August 2018   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.              Kivinen, "Internet Key Exchange Protocol Version 2              (IKEv2)", STD 79,RFC 7296, DOI 10.17487/RFC7296, October              2014, <https://www.rfc-editor.org/info/rfc7296>.   [RFC7427]  Kivinen, T. and J. Snyder, "Signature Authentication in              the Internet Key Exchange Version 2 (IKEv2)",RFC 7427,              DOI 10.17487/RFC7427, January 2015,              <https://www.rfc-editor.org/info/rfc7427>.   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital              Signature Algorithm (EdDSA)",RFC 8032,              DOI 10.17487/RFC8032, January 2017,              <https://www.rfc-editor.org/info/rfc8032>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC2119 Key Words",BCP 14,RFC 8174, DOI 10.17487/RFC8174,              May 2017, <https://www.rfc-editor.org/info/rfc8174>.   [RFC8410]  Josefsson, S. and J. Schaad, "Algorithm Identifiers for              Ed25519, Ed448, X25519, and X448 for Use in the Internet              X.509 Public Key Infrastructure",RFC 8410,              DOI 10.17487/RFC8410, August 2018,              <https://www.rfc-editor.org/info/rfc8410>.Appendix A.  ASN.1 Objects   [RFC8410] is the normative reference for the ASN.1 objects for   Ed25519 and Ed448.  They are repeated below for convenience.A.1.  ASN.1 Object for Ed25519   id-Ed25519 OBJECT IDENTIFIER ::= { 1.3.101.112 }   Parameters are absent.  Length is 7 bytes.   Binary encoding: 3005 0603 2B65 70A.2.  ASN.1 Object for Ed448   id-Ed448 OBJECT IDENTIFIER ::= { 1.3.101.113 }   Parameters are absent.  Length is 7 bytes.   Binary encoding: 3005 0603 2B65 71Nir                          Standards Track                    [Page 4]

RFC 8420                     EdDSA in IKEv2                  August 2018Author's Address   Yoav Nir   Dell EMC   9 Andrei Sakharov St   Haifa  3190500   Israel   Email: ynir.ietf@gmail.comNir                          Standards Track                    [Page 5]