RFC 8463 Proposed Standard Authentication

A New Cryptographic Signature Method for DomainKeys Identified Mail (DKIM)

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
Proposed Standard. On the standards track and stable enough to implement against. Most of the email stack stays at this level permanently.
Published
September 2018
Authors
J. Levine
Read it
rfc-editor.org · DOI

What it is

Adds Ed25519 as a DKIM signing algorithm alongside RSA.

What it solves

RSA keys large enough to be safe are too large to publish comfortably in a single DNS TXT record.

What it means to operate

A 32-byte key instead of 256, so no record splitting. The catch is support: not every verifier implements it, so sign with both and publish both selectors rather than switching outright. Tools that estimate key strength from base64 length without reading k= will report a valid Ed25519 key as far too short.

Domain check reports which signing algorithm a selector publishes. Open domain check

Normative requirements

Every sentence in this RFC carrying an RFC 2119 keyword, with the section it came from.

5 Choice and Strength of Keys and Algorithms

  • SHOULDSigners SHOULD implement and verifiers MUST implement the Ed25519-SHA256 algorithm.

Every current email RFC

Written and maintained by Rastu Singh, an infrastructure engineer working on high-volume email in Tallinn.