[Docs] [txt|pdf|xml] [Tracker] [Email] [Nits]



DMARC                                                         D. Crocker
Internet-Draft                               Brandenburg InternetWorking
Intended status: Informational                             July 12, 2020
Expires: January 13, 2021


                          Author Header Field
                     draft-crocker-dmarc-author-00

Abstract

   Internet mail defines the From: field to indicate the author of the
   message's content and the Sender: field to indicate who initially
   handled the message.  The Sender: field is optional, if it has the
   same information as the From: field.  That is, when the Sender: field
   is absent, the From: field has conflated semantics, with both a
   handling identifier and a content creator identifier.  This was not a
   problem, until development of stringent protections on use of the
   From: field.  It has prompted Mediators, such as mailing lists, to
   modify the From: field, to circumvent mail rejection caused by those
   protections.

   This affects end-to-end behavior of email, between the author and the
   final recipients, because mail from the same author is not treated
   the same, depending on what path it followed.  In effect, the From:
   field has become dominated by its role as a handling identifier.  The
   current specification augments the current use of the From: field, by
   specifying the Author: field, which identifies the original author of
   the message and is not subject to modification by Mediators.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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 January 13, 2021.





Crocker                 Expires January 13, 2021                [Page 1]


Internet-Draft                    DMARC                        July 2020


Copyright Notice

   Copyright (c) 2020 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Author Header Field . . . . . . . . . . . . . . . . . . . . .   4
   3.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Registration of the Author header field . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Internet mail conducts asynchronous communication from an author to
   one or more recipients, and is used for ongoing dialogue amongst
   them.  Email has a long history of serving a wide range of human uses
   and styles, within that simple framework, and the mechanisms for
   making email robust and safe serve that sole purpose.

   Internet mail defines the From: field to indicate the author of the
   message's content and the Sender: field to indicate who initially
   handled the message. [rfc5322] The Sender: field is optional, if it
   has the same information as the From: field.  That is, when the
   Sender: field is absent, the From: field has conflated semantics, as
   both a handling identifier and a content creator identifier.  These
   fields were initially defined in [rfc733] and making the redundant
   Sender: field optional was a small, obvious optimization, in the days
   of slower communications, expensive storage and less powerful
   computers.





Crocker                 Expires January 13, 2021                [Page 2]


Internet-Draft                    DMARC                        July 2020


   The dual semantics was not a problem, until development of stringent
   protections on use of the From: field.  It has prompted Mediators,
   such as mailing lists, to modify the From: field, to circumvent mail
   rejection caused by those protections.  This affects end-to-end
   usability of email, between the author and the final recipients,
   because mail received from the same author is treated differently by
   the recipient's software, depending on what path the message
   followed.

   Because the current email protection behavior involves the From:
   field, it is common to think that the issue, in protecting the
   field's content, is behavior of the human recipient.  However there
   is no indication that the enforced values in the From: field alter
   end-user behavior.  The meaningful protections actually operate at
   the level of the receiving system's mail filtering engine, which
   decides on the dispostion of received mail.

   By way of example, mail from "Example User <user@example.com>" which
   is sent directly to a recipient, will show the user's display name
   correctly and can correctly analyze and aggregate mail from that
   user, based on their email address.  However if the user sends
   through a mailing list, and the mailing list conducts a common form
   of From: modification, needed to bypass enforcement of stringent
   authentication policies, then the received message might have a From:
   field along the lines of "Example User via Example List
   <listname@list.example.com>".  The change inserts an operational
   address, for the Mediator, into the From: field, and distorts the
   field's display-name, as a means of recording the modification.  The
   result is that the recipient's software will see the message as being
   from an entirely different author and will handle it separately.
   (Mediators might create a Reply-To: field, with the original From:
   field email address, but this does nothing to aid other processing
   done by the recipient's MUA based on what it believes is the author's
   address or original display-name.

   In effect, the From: field has become dominated by its role as a
   handling identifier.  The current specification augments the current
   use of the From: field, by specifying the Author: field, which
   identifies the original author of the message and is not subject to
   modification by Mediators.

   While it might be cleanest to move towards more reliable use of the
   Sender: field and then to target it as the focus of authentication
   concerns, enhancement of standards works best with incremental
   additions, rather than efforts at replacement.  To that end, this
   specification provides a means of supplying author information that
   is not subject to modification by processes seeking to enforce
   stringent authentication.



Crocker                 Expires January 13, 2021                [Page 3]


Internet-Draft                    DMARC                        July 2020


   Teminology and architectural details in this document are
   incorporated from [rfc5598]

   Discussion of this draft is directed to the dmarc@ietf.org mailing
   list.

2.  Author Header Field

   A new message header field is defined: Author:. It has the same
   syntax as From:. [rfc5322] As with the original and primary intent
   for the From: header field, the Author: header field is to contain
   the email address and can contain the displayable human name of the
   author for the message content.

   The ABNF for the field's syntax is:

                           author = "Author:" mailbox-list CRLF

   This header field can be added as part of the original message create
   process, or it can be added later, to preserve the original author
   information from the From: field.

3.  Discussion

   The Author: header field, here, is intended for creation during
   message generation or during mediation.  It is intended for use by
   recipient MUAs, as they typically use the From: field.  In that
   regard, it would be reasonable for an MUA that would normally
   organize or display information based on the From: field to give the
   Author: header field priority.

   The X-Original-From: header field is referenced in [rfc5703] but is
   not actually defined.  Further, it is registered with IANA, but the
   registry cites RFC5703 as the controlling source for the entry.
   Lastly, the field is solely intended for use by Mediators, to
   preserve information from a modified From:

   Obviously any security-related processing of a message needs to
   distinguish From: from Author: and treat their information
   accordingly.

4.  Security Considerations

   Any header field containing identification information is a source of
   security and privacy concerns, especially one pertaining to content
   authorship.  At a minimum, the handling of the Author: header field
   needs to receive the same scrutiny and care given to the From: header
   field.



Crocker                 Expires January 13, 2021                [Page 4]


Internet-Draft                    DMARC                        July 2020


   Given the semantics of this field, it is easy to believe that use of
   this field will create a new attack vector for tricking end-users.
   However, for all of the real and serious demonstration of users'
   being tricked by deceptive or false content in a message, there is no
   evidence that problematic content in a field providing information
   about message's author directly contributes to differential and
   problematic behavior by the end user.

5.  IANA Considerations

5.1.  Registration of the Author header field

   Header field name: Author

   Applicable protocol: mail

   Status: provisional

   Author/Change controller: *** ??? ***

   Specification document(s): *** This document ***

6.  References

6.1.  Normative References

   [IANA]     M. Cotton, B. Leiba, and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", I-D
              draft-leiba-cotton-iana-5226bis-11, 2017.

   [rfc5322]  , RFC 5322.

   [rfc5598]  Crocker, D., "Internet Mail Architecture", RFC 5598, July
              2009.

6.2.  Informative References

   [rfc5703]  Hansen, T. and C. Daboo, "Sieve Email Filtering: MIME Part
              Tests, Iteration, Extraction, Replacement, and Enclosure",
              RFC 5703, October 2009.

   [rfc733]   .

Author's Address







Crocker                 Expires January 13, 2021                [Page 5]


Internet-Draft                    DMARC                        July 2020


   Dave Crocker
   Brandenburg InternetWorking

   Email: dcrocker@bbiw.net















































Crocker                 Expires January 13, 2021                [Page 6]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/