Cryptographic Update to DKIM
draft-ietf-dcrup-dkim-crypto-03

Document Type Active Internet-Draft (dcrup WG)
Last updated 2017-07-07 (latest revision 2017-07-01)
Replaces draft-levine-dcrup-dkim-crypto
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Network Working Group                                          J. Levine
Internet-Draft                                      Taughannock Networks
Updates: 6376 (if approved)                                 July 1, 2017
Intended status: Standards Track
Expires: January 2, 2018

                      Cryptographic Update to DKIM
                    draft-ietf-dcrup-dkim-crypto-03

Abstract

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

Status of This Memo

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

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   This Internet-Draft will expire on January 2, 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
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   described in the Simplified BSD License.

Levine                   Expires January 2, 2018                [Page 1]
Internet-Draft             DKIM Crypto Update                  July 2017

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  EdDSA-SHA256 Signing Algorithm  . . . . . . . . . . . . . . .   3
   4.  Public key fingerprints . . . . . . . . . . . . . . . . . . .   3
   5.  Signature and key syntax  . . . . . . . . . . . . . . . . . .   4
     5.1.  Signature syntax  . . . . . . . . . . . . . . . . . . . .   4
     5.2.  Key syntax  . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Key and algorithm choice and strength . . . . . . . . . . . .   5
   7.  Transition Considerations . . . . . . . . . . . . . . . . . .   5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  DKIM Signature Tag Registry . . . . . . . . . . . . . . .   5
     9.2.  DKIM Hash Algorithms Registry . . . . . . . . . . . . . .   6
     9.3.  DKIM Key Type registry  . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
     10.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Appendix A.  Change log . . . . . . . . . . . . . . . . . . . . .   7
   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 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 1156 bits don't fit in 256 octets.

   This document adds a new signing algorithm, Edwards-Curve Digital
   Signature Algorithm (EdDSA), which has much shorter keys than RSA for
   similar levels of security.  It also adds a new key representation
   for RSA keys, with the key itself in the signature and a shorter key
   fingerprint that fits in 256 octets in the DNS.
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