Defining Elliptic Curve Cryptography Algorithms for use with DKIM
draft-ietf-dcrup-dkim-ecc-01

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Last updated 2017-06-21
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DCRUP                                                            S. Rose
Internet-Draft                                                      NIST
Updates: 6376 (if approved)                                June 21, 2017
Intended status: Standards Track
Expires: December 23, 2017

   Defining Elliptic Curve Cryptography Algorithms for use with DKIM
                      draft-ietf-dcrup-dkim-ecc-01

Abstract

   DomainKeys Identified Mail (DKIM) uses digital signature to associate
   a message with a given sending domain.  Currently, there is only one
   cryptography algorithm defined for use with DKIM (RSA).  This
   document defines four new elliptic curve cryptography algorithms for
   use with DKIM.  This will allow for algorithm agility if a weakness
   is found in RSA, and allows for smaller key length to provide the
   same digital signature strength.

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   This Internet-Draft will expire on December 23, 2017.

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Rose                    Expires December 23, 2017               [Page 1]
Internet-Draft                  dkim-ecc                       June 2017

   include Simplified BSD License text as described in Section 4.e of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Defining New ECC algorithms for Use with DKIM . . . . . . . .   3
   3.  Changes to ABNF Definitions of DKIM Keys and Signatures . . .   3
     3.1.  Changes to DKIM Key Definition  . . . . . . . . . . . . .   3
     3.2.  Changes to DKIM Signature Definition  . . . . . . . . . .   4
   4.  Sender Considerations . . . . . . . . . . . . . . . . . . . .   5
   5.  Receiver Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   DomainKeys Identified Mail (DKIM)[RFC6376] uses digital signatures to
   associate a sending domain with a given message.  Each DKIM signed
   email message as a digital signature in its header, that can be
   validated by a receiver by obtaining the appropriate public key
   stored in the DNS.  Currently, DKIM has only one cryptographic
   algorithm defined for use (RSA) and two digital signature algorithms
   (RSA/SHA-1 and RSA/SHA-256).  In the past, 1024-bit RSA keys were
   common, equating to (roughly) a security key strength of 80 bits
   [NIST.800-57.2016].  Today, a minimum of 112 bits is recommended,
   which equates to 2048 bit RSA keys.

   The public portion of 2048 bit RSA keys are still small enough to fit
   into a DNS TXT RR without issues in performance.  The encoded public
   key is too large to fit into the maximum allowed characters in a
   single string, but a DNS TXT RR allows for multiple strings, so the
   key can be broken into "chunks" to allow it to be served.  However,
   some code components may not correctly handle TXT RRs with multiple
   strings which will result in errors in validation.

   Elliptic Curve Cryptography (ECC) has shown to have the same
   (roughly) equivalent key strength with smaller sizes.  A 224 to 255
   bit ECDSA key has (roughly) the same key strength as a 2048 bit RSA
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