Internet Engineering Task Force (IETF)                      M. Kucherawy
Request for Comments: 7410                                 December 2014
Updates: 7001
Category: Standards Track
ISSN: 2070-1721


A Property Types Registry for the Authentication-Results Header Field

Abstract

  This document updates RFC 7001 by creating a registry for property
  types in the Authentication-Results header field, used in email
  authentication work, rather than limiting participants to using the
  original, small set of fixed values.

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 5741.

  Information about the current status of this document, any errata,
  and how to provide feedback on it may be obtained at
  http://www.rfc-editor.org/info/rfc7410.

Copyright Notice

  Copyright (c) 2014 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
  (http://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.







Kucherawy                    Standards Track                    [Page 1]

RFC 7410          Authentication-Results Property Types    December 2014


Table of Contents

  1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
  2.  Updated "ptype" Definition  . . . . . . . . . . . . . . . . .   2
  3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
  4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
  5.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   5
  Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

  [RFC7001] defines the email Authentication-Results header field that
  presents the results of an authentication effort in a machine-
  readable format.  The header field creates a place to collect the
  output from authentication processes that are disjoint from later
  processes that might use the output, such as analysis, filtering, or
  sorting mechanisms.

  The specification in that document enumerated a small set of types of
  properties that can be reported using this mechanism.  There has
  emerged a desire to report types of properties about a message
  through this mechanism.  Accordingly, this document updates the
  specification to allow for additional property types ("ptypes")
  beyond the original set and creates a registry where new ones can be
  listed and their defining documents referenced.

2.  Updated "ptype" Definition

  Advanced Backus Naur Form (ABNF) is defined in [RFC5234].

  The ABNF in Section 2.2 of [RFC7001] is updated as follows:

      ptype = Keyword
            ; indicates whether the property being evaluated was
            ; a parameter to an [SMTP] command, was a value taken
            ; from a message header field, was some property of
            ; the message body, or was some other property evaluated by
            ; the receiving Message Transfer Agent (MTA)

  The ABNF token "Keyword" is defined in Section 4.1.2 of [RFC5321].










Kucherawy                    Standards Track                    [Page 2]

RFC 7410          Authentication-Results Property Types    December 2014


  Legal values of "ptype" are as defined in the IANA "Email
  Authentication Property Types" registry (see Section 3).  The initial
  values are as follows, matching those defined in [RFC7001]:

  body:  Indicates information that was extracted from the body of the
     message.  This might be an arbitrary string of bytes, a hash of a
     string of bytes, a Uniform Resource Identifier, or some other
     content of interest.

  header:  Indicates information that was extracted from the header of
     the message.  This might be the value of a header field or some
     portion of a header field.

  policy:  A local policy mechanism was applied that augments or
     overrides the result returned by the authentication mechanism.
     See Section 2.3 of [RFC7001].

  smtp:  Indicates information that was extracted from an SMTP command
     that was used to relay the message.

  When a consumer of this header field encounters a "ptype" that it
  does not understand, it ignores the result reported with that
  "ptype".

3.  IANA Considerations

  IANA has created the "Email Authentication Property Types" sub-
  registry within the existing "Email Authentication Parameters"
  registry.  Entries in this registry are subject to the Expert Review
  rules as described in [RFC5226].  Each entry in the registry requires
  the following values:

  o  The "ptype" token to be registered, which must fit within the ABNF
     described in Section 2.

  o  A brief description of what sort of information this "ptype" is
     meant to cover.

  o  An optional reference to the defining document.  This is
     recommended, but not required.











Kucherawy                    Standards Track                    [Page 3]

RFC 7410          Authentication-Results Property Types    December 2014


  The initial entries in this table are as follows, taken from
  [RFC7001]:

      +--------+-------------+----------------------------------------+
      | ptype  | Definition  | Description                            |
      +--------+-------------+----------------------------------------+
      | body   | RFC 7001    | The property being reported was found  |
      |        | Section 2.2 | in the body of the message.            |
      +--------+-------------+----------------------------------------+
      | header | RFC 7001    | The property being reported was found  |
      |        | Section 2.2 | in a header field of the message.      |
      +--------+-------------+----------------------------------------+
      | policy | RFC 7001    | The property being reported relates to |
      |        | Section 2.3 | a locally defined policy.              |
      +--------+-------------+----------------------------------------+
      | smtp   | RFC 7001    | The property being reported is a       |
      |        | Section 2.2 | parameter to an SMTP command used to   |
      |        |             | relay the message.                     |
      +--------+-------------+----------------------------------------+

  For new entries, the Designated Expert needs to assure that the
  description provided for the new entry adequately describes the
  intended use.  An example would be helpful to include in the entry's
  defining document, if any, although entries in the "Email
  Authentication Methods" registry or the "Email Authentication Result
  Names" registry might also serve as examples of intended use.

4.  Security Considerations

  It is unknown how legacy code, which expects one of a fixed set of
  "ptype" tokens, will handle new tokens as they begin to appear.
  There are typically two options: prevent delivery of the message, or
  ignore those portions of the field that use unknown "ptype" tokens
  and allow processing of the message to continue.

  The choice comes down to whether the consumer considers it a threat
  when there are unknown "ptypes" present.  The semantics of the report
  are unknown; the report might be indicating the message is authentic,
  fraudulent, or that a test failed to complete.  The report itself is
  not actionable because it cannot be understood, and only its presence
  is certain.

  Generally, the advice in this situation is to ignore unknown
  "ptypes".  It is anticipated that a new property type evaluated by
  earlier handling agents would also result in the filtering of
  messages by those agents until consumers can be updated to interpret
  them.




Kucherawy                    Standards Track                    [Page 4]

RFC 7410          Authentication-Results Property Types    December 2014


5.  Normative References

  [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
             IANA Considerations Section in RFCs", BCP 26, RFC 5226,
             May 2008, <http://www.rfc-editor.org/info/rfc5226>.

  [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
             Specifications: ABNF", STD 68, RFC 5234, January 2008,
             <http://www.rfc-editor.org/info/rfc5234>.

  [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
             October 2008, <http://www.rfc-editor.org/info/rfc5321>.

  [RFC7001]  Kucherawy, M., "Message Header Field for Indicating
             Message Authentication Status", RFC 7001, September 2013,
             <http://www.rfc-editor.org/info/rfc7001>.

Acknowledgements

  The author wishes to acknowledge the following for their review and
  constructive criticism of this update: Dave Crocker, Tim Draegen,
  Scott Kitterman, and Franck Martin.

Author's Address

  Murray S. Kucherawy
  270 Upland Drive
  San Francisco, CA  94127
  United States

  EMail: [email protected]




















Kucherawy                    Standards Track                    [Page 5]