A new cryptographic signature method for DKIM
draft-ietf-dcrup-dkim-crypto-07

Document Type Active Internet-Draft (dcrup WG)
Last updated 2017-12-18 (latest revision 2017-12-01)
Replaces draft-levine-dcrup-dkim-crypto
Stream IETF
Intended RFC status Proposed Standard
Formats plain text xml pdf html bibtex
Stream WG state Waiting for WG Chair Go-Ahead
Document shepherd Barry Leiba
IESG IESG state I-D Exists
Consensus Boilerplate Yes
Telechat date
Responsible AD (None)
Send notices to Barry Leiba <barryleiba@computer.org>
Network Working Group                                          J. Levine
Internet-Draft                                      Taughannock Networks
Updates: 6376 (if approved)                             December 1, 2017
Intended status: Standards Track
Expires: June 4, 2018

             A new cryptographic signature method for DKIM
                    draft-ietf-dcrup-dkim-crypto-07

Abstract

   DKIM was designed to allow new cryptographic algorithms to be added.
   This document adds a new signing 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 June 4, 2018.

Copyright Notice

   Copyright (c) 2017 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.

Levine                    Expires June 4, 2018                  [Page 1]
Internet-Draft             DKIM Crypto Update              December 2017

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 . . . . . . . . . . . .   3
   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  . . . . . . . . . . . . . . . . . .   4
     9.2.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Change log . . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

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 where it is stored in a TXT record.  The defining
   documents specify a single signing algorithm, RSA [RFC3447], and
   recommend key sizes of 1024 to 2048 bits.

   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 June 4, 2018                  [Page 2]
Internet-Draft             DKIM Crypto Update              December 2017

3.  Ed25519-SHA256 Signing Algorithm

   The ed25519-sha256 signing algorithm computes a message hash as
   defined in section 3 of [RFC6376], and signs it with the Hash variant
   of Ed25519, as defined in in RFC 8032 section 5.1 [RFC8032].  The
   signing algorithm is HashEdDSA.  (Even though the input to the
   signing algorithm has already been hashed, the PureEdDSA which does
   not do an additional hash is not widely implemented, and the extra
Show full document text