New cryptographic signature methods for DKIM
draft-ietf-dcrup-dkim-crypto-06

Document Type Active Internet-Draft (dcrup WG)
Last updated 2017-09-13
Replaces draft-levine-dcrup-dkim-crypto
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Network Working Group                                          J. Levine
Internet-Draft                                      Taughannock Networks
Updates: 6376 (if approved)                           September 12, 2017
Intended status: Standards Track
Expires: March 16, 2018

              New cryptographic signature methods for DKIM
                    draft-ietf-dcrup-dkim-crypto-06

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.

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
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   This Internet-Draft will expire on March 16, 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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Levine                   Expires March 16, 2018                 [Page 1]
Internet-Draft             DKIM Crypto Update             September 2017

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  Public key fingerprints . . . . . . . . . . . . . . . . . . .   3
   4.  Ed25519-SHA256 Signing Algorithm  . . . . . . . . . . . . . .   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
     8.1.  Duplicate Signature Key Selection . . . . . . . . . . . .   5
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  DKIM Signature Tag Registry . . . . . . . . . . . . . . .   6
     9.2.  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 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.  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 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.
   It also adds a new key representation for RSA keys, with the key
   itself in the signature and a fixed length public key fingerprint
   that fits in a 256 octet string in the DNS.
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