Cryptographic Update to DKIM
draft-ietf-dcrup-dkim-crypto-00

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Last updated 2017-04-28
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Network Working Group                                          J. Levine
Internet-Draft                                      Taughannock Networks
Updates: 6376 (if approved)                               April 26, 2017
Intended status: Standards Track
Expires: October 28, 2017

                      Cryptographic Update to DKIM
                    draft-ietf-dcrup-dkim-crypto-00

Abstract

   DKIM was designed to allow new cryptographic algorithms to be added.
   This document adds a new algorithm and a new way to represent
   signature validation keys.

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
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   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 October 28, 2017.

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
   (http://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 October 28, 2017                [Page 1]
Internet-Draft             DKIM Crypto Update                 April 2017

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  ECDH-SHA256 Signing Algorithm . . . . . . . . . . . . . . . .   3
   4.  Public key fingerprints . . . . . . . . . . . . . . . . . . .   3
   5.  Key and algorithm choice and strength . . . . . . . . . . . .   4
   6.  Transition Considerations . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  DKIM Signature Tag Registry . . . . . . . . . . . . . . .   4
     8.2.  DKIM Key Type registry  . . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   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 content 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 recommends key sizes of 1024 to 2048 bits.  While 1024
   bit signatures are common, stronger signatures are not.  Widely used
   DNS configuration software places a practical limit on key sizes,
   because the software only handles a single 256 octet string in a TXT
   record, and RSA keys longer than 1024 bits don't fit in 256 octets.

   This document adds a new signing algorithm, Elliptic Curve Diffie-
   Hellman (ECDH), which has much shorter keys than RSA for similar
   levels of security.  It also adds a new key representation, with the
   key itself in the signature and a shorter key fingerprint in the DNS.

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, key-k-tag-type, and base64tring are imported from
   [RFC6376].
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