A new cryptographic signature method for DKIM
draft-ietf-dcrup-dkim-crypto-10

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Network Working Group                                          J. Levine
Internet-Draft                                      Taughannock Networks
Updates: 6376 (if approved)                                 May 29, 2018
Intended status: Standards Track
Expires: November 30, 2018

             A new cryptographic signature method for DKIM
                    draft-ietf-dcrup-dkim-crypto-10

Abstract

   This document adds a new signing algorithm to DKIM, ed25519-sha256.
   DKIM verifiers are required to implement this algorithm.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 30, 2018.

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
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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.

Levine                  Expires November 30, 2018               [Page 1]
Internet-Draft             DKIM Crypto Update                   May 2018

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  Ed25519-SHA256 Signing Algorithm  . . . . . . . . . . . . . .   3
   4.  Signature and key syntax  . . . . . . . . . . . . . . . . . .   3
     4.1.  Signature syntax  . . . . . . . . . . . . . . . . . . . .   3
     4.2.  Key syntax  . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Key and algorithm choice and strength . . . . . . . . . . . .   4
   6.  Transition Considerations . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  DKIM Key Type registry  . . . . . . . . . . . . . . . . .   4
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   5
     9.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Example of a signed message  . . . . . . . . . . . .   5
     A.1.  Secret key  . . . . . . . . . . . . . . . . . . . . . . .   5
     A.2.  Public key DNS record . . . . . . . . . . . . . . . . . .   6
     A.3.  Signed Message  . . . . . . . . . . . . . . . . . . . . .   6
   Appendix B.  Change log . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Discussion Venue:    Discussion about this draft is directed to the
      dcrup@ietf.org [1] mailing list.

   DKIM [RFC6376] signs e-mail messages, by creating hashes of the
   message headers and body and signing the header hash with a digital
   signature.  Message recipients fetch the signature verification key
   from the DNS.  The defining documents specify a single signing
   algorithm, RSA [RFC3447].

   This document adds a new stronger signing algorithm, Edwards-Curve
   Digital Signature Algorithm using the Curve25519 curve (ed25519),
   which has much shorter keys than RSA for similar levels of security.

2.  Conventions Used in This Document

   The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
   "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   Syntax descriptions use Augmented BNF (ABNF) [RFC5234].  The ABNF
   tokens sig-a-tag-k and key-k-tag-type are imported from [RFC6376].

Levine                  Expires November 30, 2018               [Page 2]
Internet-Draft             DKIM Crypto Update                   May 2018

3.  Ed25519-SHA256 Signing Algorithm

   The ed25519-sha256 signing algorithm computes a message hash as
   defined in section 3 of [RFC6376] using SHA-256 [FIPS-180-4-2015] as