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 | Internent Engineering Task Force (IETF) | ||
Formats | plain text html pdf htmlized (tools) 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) | |
Action Holders |
(None)
|
||
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,Show full document text