Use of the Elliptic Curve Diffie-Hellman Key Agreement Algorithm with X25519 and X448 in the Cryptographic Message Syntax (CMS)
RFC 8418

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Internet Engineering Task Force (IETF)                        R. Housley
Request for Comments: 8418                                Vigil Security
Category: Standards Track                                    August 2018
ISSN: 2070-1721

    Use of the Elliptic Curve Diffie-Hellman Key Agreement Algorithm
     with X25519 and X448 in the Cryptographic Message Syntax (CMS)

Abstract

   This document describes the conventions for using the Elliptic Curve
   Diffie-Hellman (ECDH) key agreement algorithm with curve25519 and
   curve448 in the Cryptographic Message Syntax (CMS).

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/rfc8418.

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
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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.

Housley                      Standards Track                    [Page 1]
RFC 8418             Using X25519 and X448 with CMS          August 2018

Table of Contents

   1. Introduction ....................................................2
      1.1. Terminology ................................................3
      1.2. ASN.1 ......................................................3
   2. Key Agreement ...................................................3
      2.1. ANSI-X9.63-KDF .............................................4
      2.2. HKDF .......................................................5
   3. Enveloped-data Conventions ......................................5
      3.1. EnvelopedData Fields .......................................6
      3.2. KeyAgreeRecipientInfo Fields ...............................6
   4. Authenticated-data Conventions ..................................7
      4.1. AuthenticatedData Fields ...................................8
      4.2. KeyAgreeRecipientInfo Fields ...............................8
   5. Authenticated-enveloped-data Conventions ........................8
      5.1. AuthEnvelopedData Fields ...................................8
      5.2. KeyAgreeRecipientInfo Fields ...............................8
   6. Certificate Conventions .........................................9
   7. Key Agreement Algorithm Identifiers .............................9
   8. SMIMECapabilities Attribute Conventions ........................10
   9. Security Considerations ........................................11
   10. IANA Considerations ...........................................12
   11. References ....................................................13
      11.1. Normative References .....................................13
      11.2. Informative References ...................................14
   Appendix A. ASN.1 Module ..........................................16
   Acknowledgements ..................................................18
   Author's Address ..................................................18

1.  Introduction

   This document describes the conventions for using Elliptic Curve
   Diffie-Hellman (ECDH) key agreement using curve25519 and curve448
   [CURVES] in the Cryptographic Message Syntax (CMS) [CMS].  Key
   agreement is supported in three CMS content types: the enveloped-data
   content type [CMS], authenticated-data content type [CMS], and the
   authenticated-enveloped-data content type [AUTHENV].

   The conventions for using some Elliptic Curve Cryptography (ECC)
   algorithms in CMS are described in [CMSECC].  These conventions cover
   the use of ECDH with some curves other than curve25519 and curve448
   [CURVES].  Those other curves are not deprecated.

   Using curve25519 with Diffie-Hellman key agreement is referred to as
   "X25519".  Using curve448 with Diffie-Hellman key agreement is
   referred to as "X448".

Housley                      Standards Track                    [Page 2]
RFC 8418             Using X25519 and X448 with CMS          August 2018

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",