A New Cryptographic Signature Method for DomainKeys Identified Mail (DKIM)
RFC 8463
| Document | Type |
RFC - Proposed Standard
(September 2018; No errata)
Updates RFC 6376
|
|
|---|---|---|---|
| Author | John Levine | ||
| Last updated | 2018-09-12 | ||
| Replaces | draft-levine-dcrup-dkim-crypto | ||
| Stream | IETF | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Reviews | |||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Jim Fenton | ||
| Shepherd write-up | Show (last changed 2018-05-22) | ||
| IESG | IESG state | RFC 8463 (Proposed Standard) | |
| Consensus Boilerplate | Yes | ||
| Telechat date | |||
| Responsible AD | Alexey Melnikov | ||
| Send notices to | (None) | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | RFC-Ed-Ack | ||
Internet Engineering Task Force (IETF) J. Levine
Request for Comments: 8463 Taughannock Networks
Updates: 6376 September 2018
Category: Standards Track
ISSN: 2070-1721
A New Cryptographic Signature Method for
DomainKeys Identified Mail (DKIM)
Abstract
This document adds a new signing algorithm, Ed25519-SHA256, to
"DomainKeys Identified Mail (DKIM) Signatures" (RFC 6376). DKIM
verifiers are required to implement this algorithm.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8463.
Copyright Notice
Copyright (c) 2018 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
(https://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
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 Standards Track [Page 1]
RFC 8463 DKIM Crypto Update September 2018
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 2
3. Ed25519-SHA256 Signing Algorithm . . . . . . . . . . . . . . 3
4. Signature and Key Syntax . . . . . . . . . . . . . . . . . . 3
4.1. Signature Syntax . . . . . . . . . . . . . . . . . . . . 3
4.2. Key Syntax . . . . . . . . . . . . . . . . . . . . . . . 3
5. Choice and Strength of Keys and Algorithms . . . . . . . . . 4
6. Transition Considerations . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8.1. "DKIM Key Type" Registry . . . . . . . . . . . . . . . . 4
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Example of a Signed Message . . . . . . . . . . . . 6
A.1. Secret Keys . . . . . . . . . . . . . . . . . . . . . . . 6
A.2. Public Key DNS Records . . . . . . . . . . . . . . . . . 6
A.3. Signed Message . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
DKIM [RFC6376] signs email messages by creating hashes of selected
message header fields and body and signing the header hash with a
digital signature. Message recipients fetch the signature
verification key from the DNS. The defining documents specify a
single signing algorithm, RSA [RFC3447] (which has since been
obsoleted by [RFC8017]).
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.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Syntax descriptions use Augmented BNF (ABNF) [RFC5234]. The ABNF
tokens sig-a-tag-k and key-k-tag-type are imported from [RFC6376].
Levine Standards Track [Page 2]
RFC 8463 DKIM Crypto Update September 2018
3. Ed25519-SHA256 Signing Algorithm
The Ed25519-SHA256 signing algorithm computes a message hash as
defined in Section 3 of [RFC6376] using SHA-256 [FIPS-180-4-2015] as
the hash-alg. It signs the hash with the PureEdDSA variant Ed25519,
as defined in RFC 8032, Section 5.1 [RFC8032]. Example keys and
signatures in Appendix A are based on the test vectors in RFC 8032,
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