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Internet Engineering Task Force (IETF) S. Turner Request for Comments: 9295 sn3rd Updates: 8410 S. Josefsson Category: Standards Track SJD AB ISSN: 2070-1721 D. McCarney

                                                           Square Inc.
                                                                T. Ito
                                                       SECOM CO., LTD.
                                                        September 2022

   Clarifications for Ed25519, Ed448, X25519, and X448 Algorithm
                            Identifiers

Abstract

 This document updates RFC 8410 to clarify existing semantics, and
 specify missing semantics, for key usage bits when used in
 certificates that support the Ed25519, Ed448, X25519, and X448
 Elliptic Curve Cryptography algorithms.

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/rfc9295.

Copyright Notice

 Copyright (c) 2022 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 Revised BSD License text as described in Section 4.e of the
 Trust Legal Provisions and are provided without warranty as described
 in the Revised BSD License.

Table of Contents

 1.  Introduction
 2.  Terminology
 3.  New Section 5 for RFC 8410
 4.  Security Considerations
 5.  IANA Considerations
 6.  References
   6.1.  Normative References
   6.2.  Informative References
 Acknowledgments
 Authors' Addresses

1. Introduction

 [RFC8410] specifies the syntax and semantics for the Subject Public
 Key Information field in certificates that support Ed25519, Ed448,
 X25519, and X448 Elliptic Curve Cryptography (ECC) algorithms.  As
 part of these semantics, it defines what combinations are permissible
 for the values of the keyUsage extension [RFC5280].  [RFC8410] did
 not define what values are not permissible, nor did it refer to
 keyEncipherment or dataEncipherment.  [Err5696] has also been
 submitted to clarify that keyCertSign is always set in certification
 authority certificates.  To address these changes, this document
 replaces Section 5 of [RFC8410] with Section 3.

2. Terminology

 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.

3. New Section 5 for RFC 8410

 The intended application for the key is indicated in the keyUsage
 certificate extension.

 If the keyUsage extension is present in a certificate that indicates
 id-X25519 or id-X448 in SubjectPublicKeyInfo, then the following MUST
 be present:

   keyAgreement

 One of the following MAY also be present:

   encipherOnly
   decipherOnly

 and any of the following MUST NOT be present:

   digitalSignature
   nonRepudiation
   keyEncipherment
   dataEncipherment
   keyCertSign
   cRLSign

 If the keyUsage extension is present in an end-entity certificate
 that indicates id-Ed25519 or id-Ed448 in SubjectPublicKeyInfo, then
 the keyUsage extension MUST contain at least one of the following:

   nonRepudiation
   digitalSignature
   cRLSign

 and any of the following MUST NOT be present:

   keyEncipherment
   dataEncipherment
   keyAgreement
   keyCertSign
   encipherOnly
   decipherOnly

 If the keyUsage extension is present in a CRL issuer certificate that
 indicates id-Ed25519 or id-Ed448 in SubjectPublicKeyInfo, then the
 keyUsage extension MUST contain:

   cRLSign

 and zero or more of the following:

   nonRepudiation
   digitalSignature

 and any of the following MUST NOT be present:

   keyEncipherment
   dataEncipherment
   keyAgreement
   encipherOnly
   decipherOnly

 and if the CRL issuer is also a certification authority, then the
 keyUsage extension MUST also contain:

   keyCertSign

 If the keyUsage extension is present in a certification authority
 certificate that indicates id-Ed25519 or id-Ed448 in
 SubjectPublicKeyInfo, then the keyUsage extension MUST contain:

   keyCertSign

 and zero or more of the following:

   nonRepudiation
   digitalSignature
   cRLSign

 and any of the following MUST NOT be present:

   keyEncipherment
   dataEncipherment
   keyAgreement
   encipherOnly
   decipherOnly

4. Security Considerations

 This document introduces no new security considerations beyond those
 found in [RFC8410].

5. IANA Considerations

 This document has no IANA actions.

6. References

6.1. 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>.

 [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
            Housley, R., and W. Polk, "Internet X.509 Public Key
            Infrastructure Certificate and Certificate Revocation List
            (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
            <https://www.rfc-editor.org/info/rfc5280>.

 [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>.

6.2. Informative References

 [Err5696]  RFC Errata, Erratum ID 5696, RFC 8410,
            <https://www.rfc-editor.org/errata/eid5696>.

Acknowledgments

 We would like to thank Russ Housley, Mike Jenkins, and Corey Bonnell
 for their comments.

Authors' Addresses

 Sean Turner
 sn3rd
 Email: sean@sn3rd.com

 Simon Josefsson
 SJD AB
 Email: simon@josefsson.org

 Daniel McCarney
 Square Inc.
 Email: daniel@binaryparadox.net

 Tadahiko Ito
 SECOM CO., LTD.
 Email: tadahiko.ito.public@gmail.com