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rfc:rfc6212

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
 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 6212 Auth-Results VBR Registration April 2011

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.

Kucherawy Standards Track [Page 2] RFC 6212 Auth-Results VBR Registration April 2011

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.

Kucherawy Standards Track [Page 3] RFC 6212 Auth-Results VBR Registration April 2011

 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        |
 +-----------+--------------+------------+---------+-----------------+

Kucherawy Standards Track [Page 4] RFC 6212 Auth-Results VBR Registration April 2011

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.

Kucherawy Standards Track [Page 5] RFC 6212 Auth-Results VBR Registration April 2011

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.

Kucherawy Standards Track [Page 6] RFC 6212 Auth-Results VBR Registration April 2011

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

Kucherawy Standards Track [Page 7]

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