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IETF RFC 6212
Authentication-Results Registration for Vouch by Reference Results
Last modified on Monday, April 11th, 2011
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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/RFC 6212.
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
Authentication-Results Registration for Vouch by Reference Results
RFC TOTAL SIZE: 13199 bytes
PUBLICATION DATE: Monday, April 11th, 2011
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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