ECC key usage: Clarifications for Elliptic Curve Cryptography Subject Public Key Information

Internet Engineering Task Force (IETF)                            T. Ito
Request for Comments: 8813                               SECOM CO., LTD.
Updates: 5480                                                  S. Turner
Category: Standards Track                                          sn3rd
ISSN: 2070-1721                                              August 2020


   Clarifications for Elliptic Curve Cryptography Subject Public Key
                              Information

Abstract

   This document updates RFC 5480 to specify semantics for the
   keyEncipherment and dataEncipherment key usage bits when used in
   certificates that support Elliptic Curve Cryptography.

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/rfc8813.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Updates to Section 3
   4.  Security Considerations
   5.  IANA Considerations
   6.  Normative References
   Authors' Addresses

1.  Introduction

   [RFC5480] specifies the syntax and semantics for the Subject Public
   Key Information field in certificates that support Elliptic Curve
   Cryptography.  As part of these semantics, it defines what
   combinations are permissible for the values of the key usage
   extension [RFC5280].  [RFC5480] specifies 7 of the 9 values; it makes
   no mention of the keyEncipherment and dataEncipherment key usage
   bits.  This document corrects this omission by updating Section 3 of
   [RFC5480] to make it clear that neither keyEncipherment nor the
   dataEncipherment key usage bits are set for key agreement algorithms
   defined therein.  The additions are to be made to the end of
   Section 3 of [RFC5480].

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.  Updates to Section 3

   If the keyUsage extension is present in a certificate that indicates
   id-ecPublicKey in SubjectPublicKeyInfo, then the following values
   MUST NOT be present:

      keyEncipherment; and
      dataEncipherment.

   If the keyUsage extension is present in a certificate that indicates
   id-ecDH or id-ecMQV in SubjectPublicKeyInfo, then the following
   values also MUST NOT be present:

      keyEncipherment; and
      dataEncipherment.

4.  Security Considerations

   This document introduces no new security considerations beyond those
   found in [RFC5480].

5.  IANA Considerations

   This document has no IANA actions.

6.  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>.

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,
              <https://www.rfc-editor.org/info/rfc5480>.

   [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>.

Authors' Addresses

   Tadahiko Ito
   SECOM CO., LTD.

   Email: tadahiko.ito.public@gmail.com


   Sean Turner
   sn3rd

   Email: sean@sn3rd.com