





Internet Engineering Task Force (IETF)                      M. Kucherawy
Request for Comments: 6212                               Cloudmark, Inc.
Category: Standards Track                                     April 2011
ISSN: 2070-1721


   Authentication-Results Registration for Vouch by Reference Results

Abstract

   This memo updates the registry of properties in Authentication-
   Results: message header fields to allow relaying of the results of a
   Vouch By Reference query.

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/rfc6212.

Copyright Notice

   Copyright (c) 2011 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
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   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.









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Table of Contents

   1. Introduction ....................................................2
   2. Keywords ........................................................2
   3. Discussion ......................................................2
   4. Definition ......................................................3
   5. IANA Considerations .............................................4
   6. Security Considerations .........................................5
   7. References ......................................................5
      7.1. Normative References .......................................5
      7.2. Informative References .....................................5
   Appendix A.  Authentication-Results Examples .......................6
     A.1.  VBR Results ................................................6
   Appendix B.  Acknowledgements ......................................7

1.  Introduction

   [AUTHRES] defined a new header field for electronic mail messages
   that presents the results of a message authentication effort in a
   machine-readable format.  In the interim, a proposal for rudimentary
   domain-level reputation assessment, called Vouch By Reference, [VBR]
   was published and is now beginning to see popular use.

   This memo thus registers an additional reporting property allowing a
   VBR result to be relayed as an annotation in a message header.

2.  Keywords

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [KEYWORDS].

3.  Discussion

   Vouch By Reference [VBR] introduced a mechanism by which a message
   receiver can query a "vouching" service to determine whether or not a
   trusted third party is willing to state that mail from a particular
   source can be considered legitimate.  When this assessment is done at
   an inbound border mail gateway, it would be useful to relay the
   result of that assessment to internal mail entities such as filters
   or user agents.

   Reactions to the information contained in an Authentication-Results
   header field that contains VBR (or any) results are not specified
   here, as they are entirely a matter of local policy at the receiver.






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4.  Definition

   This memo adds to the "Email Authentication Methods" registry,
   created by IANA upon publication of [AUTHRES], the following:

   o  The method "vbr"; and

   o  Associated with that method, the properties (reporting items)
      "header.md" and "header.mv".

   If "header.md" is present, its value MUST be the DNS domain name
   about which a VBR query was made.  If "header.mv" is present, its
   value MUST be the DNS domain name that was queried as the potential
   voucher for the "header.md" domain.

   If the VBR query was made based on the content of a "VBR-Info" header
   field present on an incoming message, "header.md" is typically taken
   from the "md" tag of the "VBR-Info" header field, and "header.mv" is
   typically one of the values of the "mv" tag in the "VBR-Info" header
   field on that message.  However, [VBR] permits a different mechanism
   for selection of the subject domain and/or list of vouchers, ignoring
   those present in any "VBR-Info" header field the message might have
   included.  A server could even conduct a VBR query when no "VBR-Info"
   field was present, based on locally configured policy options.  Where
   such mechanisms are applied, the verifying server MAY generate an
   Authentication-Results field to relay the results of the VBR query.

   This memo also adds to the "Email Authentication Result Names"
   registry the following result codes and definitions:

   none:  No valid VBR-Info header was found in the message, or a domain
      name to be queried could not be determined.

   pass:  A VBR query was completed, and the vouching service queried
      gave a positive response.

   fail:  A VBR query was completed, and the vouching service queried
      did not give a positive response, or the message contained
      multiple VBR-Info header fields with different "mc" values
      (see [VBR]).

   temperror:  A VBR query was attempted but could not be completed due
      to some error that is likely transient in nature, such as a
      temporary DNS error.  A later attempt may produce a final result.







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   permerror:  A VBR query was attempted but could not be completed due
      to some error that is likely not transient in nature, such as a
      permanent DNS error.  A later attempt is unlikely to produce a
      final result.

5.  IANA Considerations

   Per [IANA], the following items have been added to the "Email
   Authentication Methods" registry:

   +------------+----------+--------+----------------+-----------------+
   |   Method   | Defined  | ptype  | property       | value           |
   +------------+----------+--------+----------------+-----------------+
   |    vbr     | RFC 6212 | header | md             | DNS domain name |
   |            |          |        |                | used as the     |
   |            |          |        |                | subject of a    |
   |            |          |        |                | VBR query       |
   +------------+----------+--------+----------------+-----------------+
   |    vbr     | RFC 6212 | header | mv             | DNS domain name |
   |            |          |        |                | of the entity   |
   |            |          |        |                | acting as       |
   |            |          |        |                | the voucher     |
   +------------+----------+--------+----------------+-----------------+

   Also, the following items have been added to the "Email
   Authentication Result Names" registry:

   +-----------+--------------+------------+---------+-----------------+
   |   Code    | Existing/New | Defined In | Method  | Meaning         |
   +-----------+--------------+------------+---------+-----------------+
   | none      | existing     |  RFC 5451  | vbr     | Section 4 of    |
   |           |              |            | (added) | RFC 6212        |
   +-----------+--------------+------------+---------+-----------------+
   | pass      | existing     |  RFC 5451  | vbr     | Section 4 of    |
   |           |              |            | (added) | RFC 6212        |
   +-----------+--------------+------------+---------+-----------------+
   | fail      | existing     |  RFC 5451  | vbr     | Section 4 of    |
   |           |              |            | (added) | RFC 6212        |
   +-----------+--------------+------------+---------+-----------------+
   | temperror | existing     |  RFC 5451  | vbr     | Section 4 of    |
   |           |              |            | (added) | RFC 6212        |
   +-----------+--------------+------------+---------+-----------------+
   | permerror | existing     |  RFC 5451  | vbr     | Section 4 of    |
   |           |              |            | (added) | RFC 6212        |
   +-----------+--------------+------------+---------+-----------------+






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6.  Security Considerations

   This memo creates a mechanism for relaying [VBR] results using the
   structure already defined by [AUTHRES].  The Security Considerations
   sections of those documents should be consulted.

7.  References

7.1.  Normative References

   [AUTHRES]   Kucherawy, M., "Message Header Field for Indicating
               Message Authentication Status", RFC 5451, April 2009.

   [KEYWORDS]  Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [VBR]       Hoffman, P., Levine, J., and A. Hathcock, "Vouch By
               Reference", RFC 5518, April 2009.

7.2.  Informative References

   [IANA]      Narten, T. and H. Alvestrand, "Guidelines for Writing an
               IANA Considerations Section in RFCs", BCP 26, RFC 5226,
               May 2008.



























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Appendix A.  Authentication-Results Examples

   This section presents an example of the use of this new header field
   to indicate VBR results.

A.1.  VBR Results

   A message that triggered a VBR query, returning a result:

        Authentication-Results: mail-router.example.net;
              dkim=pass (good signature) header.d=newyork.example.com
                    header.b=oINEO8hg;
              vbr=pass (voucher.example.net)
                    header.md=newyork.example.com
                    header.mv=voucher.example.org
        Received: from newyork.example.com
                  (newyork.example.com [192.0.2.250])
              by mail-router.example.net (8.11.6/8.11.6)
                  for <recipient@example.net>
                  with ESMTP id i7PK0sH7021929;
              Fri, Feb 15 2002 17:19:22 -0800
        DKIM-Signature: v=1; a=rsa-sha256; s=rashani;
              d=newyork.example.com;
              t=1188964191; c=relaxed/simple;
              h=From:Date:To:VBR-Info:Message-Id:Subject;
              bh=sEu28nfs9fuZGD/pSr7ANysbY3jtdaQ3Xv9xPQtS0m7=;
              b=oINEO8hgn/gnunsg ... 9n9ODSNFSDij3=
        From: sender@newyork.example.com
        Date: Fri, Feb 15 2002 16:54:30 -0800
        To: meetings@example.net
        VBR-Info: md=newyork.example.com; mc=list;
              mv=voucher.example.org
        Message-Id: <12345.abc@newyork.example.com>
        Subject: here's a sample

   Example 1: Header Field Reporting Results from a VBR Query

   Here we see an example of a message that was signed using DomainKeys
   Identified Mail (DKIM) and that also included a VBR-Info header
   field.  On receipt, it is found that the "md=" field in the latter
   and the "d=" field in the former matched, and also that the DKIM
   signature verified, so a VBR query was performed.  The vouching
   service, voucher.example.org, indicated that the sender can be
   trusted, so a "pass" result is included in the Authentication-Results
   field affixed prior to delivery.






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Appendix B.  Acknowledgements

   The author wishes to acknowledge the following for their review and
   constructive criticism of this proposal: JD Falk, John Levine, and
   Alessandro Vesely.

Author's Address

   Murray S. Kucherawy
   Cloudmark, Inc.
   128 King St., 2nd Floor
   San Francisco, CA  94107
   US

   Phone: +1 415 946 3800
   EMail: msk@cloudmark.com



































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