RFC 4871 DomainKeys Identified Mail (DKIM) Signatures -- Update
RFC 5672

Document Type RFC - Proposed Standard (August 2009; No errata)
Obsoleted by RFC 6376
Updates RFC 4871
Last updated 2013-03-02
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IESG IESG state RFC 5672 (Proposed Standard)
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Send notices to dkim-chairs@ietf.org, draft-ietf-dkim-rfc4871-errata@ietf.org
Network Working Group                                    D. Crocker, Ed.
Request for Comments: 5672                   Brandenburg InternetWorking
Updates: 4871                                                August 2009
Category: Standards Track

    RFC 4871 DomainKeys Identified Mail (DKIM) Signatures -- Update

Abstract

   This document updates RFC 4871, "DomainKeys Identified Mail (DKIM)
   Signatures".  Specifically, the document clarifies the nature, roles,
   and relationship of the two DKIM identifier tag values that are
   candidates for payload delivery to a receiving processing module.
   The Update is in the style of an Errata entry, albeit a rather long
   one.

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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 in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Crocker                     Standards Track                     [Page 1]
RFC 5672                    RFC 4871 Update                  August 2009

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  RFC 4871, Abstract . . . . . . . . . . . . . . . . . . . . . .  4
   3.  RFC 4871, Section 1, Introduction  . . . . . . . . . . . . . .  4
   4.  RFC 4871, Section 2.7, Identity  . . . . . . . . . . . . . . .  4
   5.  RFC 4871, Section 2.8, Identifier  . . . . . . . . . . . . . .  5
   6.  RFC 4871, Section 2.9, Signing Domain Identifier (SDID)  . . .  5
   7.  RFC 4871, Section 2.10, Agent or User Identifier (AUID)  . . .  5
   8.  RFC 4871, Section 2.11, Identity Assessor  . . . . . . . . . .  6
   9.  RFC 4871, Section 3.5, The DKIM-Signature Header Field . . . .  6
   10. RFC 4871, Section 3.5, The DKIM-Signature Header Field . . . .  7
   11. RFC 4871, Section 3.8, Signing by Parent Domains  . . . . . . . 9
   12. RFC 4871, Section 3.9, Relationship between SDID and AUID  . . 10
   13. RFC 4871, Section 6.3, Interpret Results/Apply Local Policy  . 11
   14. RFC 4871, Section 6.3, Interpret Results/Apply Local Policy  . 11
   15. RFC 4871, Appendix D, MUA Considerations . . . . . . . . . . . 12
   16. Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   17. Normative References . . . . . . . . . . . . . . . . . . . . . 12
   Appendix A.  ABNF Fragments  . . . . . . . . . . . . . . . . . . . 13
   Appendix B.  Acknowledgements  . . . . . . . . . . . . . . . . . . 14

1.  Introduction

   About the purpose for DKIM, [RFC4871] states:

      The ultimate goal of this framework is to permit a signing domain
      to assert responsibility for a message, thus protecting message
      signer identity...

   Hence, DKIM has a signer that produces a signed message, a verifier
   that confirms the signature, and an assessor that consumes the
   validated signing domain.  So, the simple purpose of DKIM is to
   communicate an identifier to a receive-side assessor module.  The
   identifier is in the form of a domain name that refers to a
   responsible identity.  For DKIM to be interoperable and useful, the
   signer and assessor must share the same understanding of the details
   about the identifier.

   However, the RFC 4871 specification defines two, potentially
   different, identifiers that are carried in the DKIM-Signature: header
   field, d= and i=.  Either might be delivered to a receiving
   processing module that consumes validated payload.  The DKIM
   specification fails to clearly define which is the "payload" to be
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