Internet Engineering Task Force (IETF) Y. Nir
Request for Comments: 8420 Dell EMC
Category: Standards Track August 2018
ISSN: 2070-1721
Using the Edwards-Curve Digital Signature Algorithm (EdDSA) in the
Internet 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 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
https://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 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.
Nir Standards Track [Page 1]RFC 8420 EdDSA in IKEv2 August 2018
Table of Contents
1. Introduction ....................................................2
1.1. Conventions Used in This Document ..........................3
2. The "Identity" Hash Identifier ..................................3
3. Security Considerations .........................................3
4. IANA Considerations .............................................3
5. Normative References ............................................3
Appendix A. ASN.1 Objects .........................................4
A.1. ASN.1 Object for Ed25519 ...................................4
A.2. ASN.1 Object for Ed448 .....................................4
Author's Address ...................................................5
1. 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. See
Section 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 in
Section 3 of RFC 8032. [RFC8410] defines the object identifiers
(OIDs) for these signature methods. For convenience, these OIDs are
repeated in Appendix 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 2018
1.1. 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 in
BCP 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 in RFC
2119 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 70
A.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 71
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Author's Address
Yoav Nir
Dell EMC
9 Andrei Sakharov St
Haifa 3190500
Israel
Email: ynir.ietf@gmail.com
Nir Standards Track [Page 5]
