Defining Elliptic Curve Cryptography Algorithms for use with DKIM
draft-ietf-dcrup-dkim-ecc-01
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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.
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 December 23, 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
to this document. Code Components extracted from this document must
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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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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