Individual submission M. Kucherawy
Internet-Draft Cloudmark, Inc.
Intended status: Standards Track January 18, 2011
Expires: July 22, 2011
Authentication-Results Registration For Vouch By Reference Results
draft-kucherawy-authres-vbr-04
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Definition . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Authentication-Results Examples . . . . . . . . . . . 6
A.1. VBR Results . . . . . . . . . . . . . . . . . . . . . . . . 7
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . . 7
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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 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.
4. Definition
This memo adds to the "Email Authentication Method Name 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
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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 Results Name
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.
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.
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-CONSIDERATIONS], the following item is added to the "Email
Authentication Method Name Registry":
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+------------+----------+--------+----------------+-----------------+
| Method | Defined | ptype | property | value |
+------------+----------+--------+----------------+-----------------+
| vbr | RFC5518 | header | md | DNS domain name |
| | | | | used as the |
| | | | | subject of a |
| | | | | VBR query |
+------------+----------+--------+----------------+-----------------+
| vbr | RFC5518 | header | mv | DNS domain name |
| | | | | of the entity |
| | | | | acting as |
| | | | | the voucher |
+------------+----------+--------+----------------+-----------------+
Also, the following item is added to the "Email Authentication Method
Results Registry":
+-----------+--------------+------------+---------+-----------------+
| Code | Existing/New | Defined In | Method | Meaning |
+-----------+--------------+------------+---------+-----------------+
| none | existing | RFC5451 | vbr | Section 4 |
| | | | (added) | |
+-----------+--------------+------------+---------+-----------------+
| pass | existing | RFC5451 | vbr | Section 4 |
| | | | (added) | |
+-----------+--------------+------------+---------+-----------------+
| fail | existing | RFC5451 | vbr | Section 4 |
| | | | (added) | |
+-----------+--------------+------------+---------+-----------------+
| temperror | existing | RFC5451 | vbr | Section 4 |
| | | | (added) | |
+-----------+--------------+------------+---------+-----------------+
| permerror | existing | RFC5451 | vbr | Section 4 |
| | | | (added) | |
+-----------+--------------+------------+---------+-----------------+
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",
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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-CONSIDERATIONS] Narten, T. and H. Alvestrand, "Guidelines for
Writing an IANA Considerations Section in
RFCs", BCP 26, RFC 5226, May 2008.
Appendix A. Authentication-Results Examples
This section presents an example of the use of this new item header
field to indicate VBR results.
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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 DKIM and
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 the
sender can be trusted, so a "pass" result is included in the
Authentication-Results field affixed prior to delivery.
Appendix B. Acknowledgements
The author wishes to acknowledge the following for their review and
constructive criticism of this proposal: JD Falk, John Levine,
Alessandro Vesely
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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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