draft-ietf-dmarc-arc-usage-00.txt   draft-ietf-dmarc-arc-usage-01.txt 
DMARC Working Group S. Jones DMARC Working Group S. Jones
Internet-Draft DMARC.org Internet-Draft DMARC.org
Obsoletes: draft-jones-arc-usage-01 (if J. Rae-Grant Obsoletes: draft-jones-arc-usage-01 (if J. Rae-Grant
approved) Google approved) Google
Intended status: Informational T. Adams Intended status: Informational T. Adams
Expires: December 27, 2016 Paypal Expires: May 29, 2016 Paypal
K. Andersen, Ed. K. Andersen, Ed.
LinkedIn LinkedIn
June 25, 2016 December 27, 2016
Recommended Usage of the Authenticated Received Chain (ARC) Recommended Usage of the Authenticated Received Chain (ARC)
draft-ietf-dmarc-arc-usage-00 draft-ietf-dmarc-arc-usage-01
Abstract Abstract
The Authentication Received Chain (ARC) provides a means to preserve The Authentication Received Chain (ARC) provides a means to preserve
email authentication results and verify the identity of email message email authentication results and verify the identity of email message
handlers, each of which participates by inserting certain header handlers, each of which participates by inserting certain header
fields before passing the message on. But the specification does not fields before passing the message on. But the specification does not
indicate how intermediaries and receivers should interpret or utilize indicate how intermediaries and receivers should interpret or utilize
ARC. This document will provide guidance in these areas. ARC. This document will provide guidance in these areas.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 27, 2016. This Internet-Draft will expire on May 29, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Message receivers may make local policy decisions about whether to Message receivers may make local policy decisions about whether to
use the contents of the ARC-Authentication-Results header field in use the contents of the ARC-Authentication-Results header field in
cases where a message no longer passes DKIM, DMARC, and/or SPF cases where a message no longer passes DKIM, DMARC, and/or SPF
checks. Whether an ARC chain is intact can be used to inform that checks. Whether an ARC chain is intact can be used to inform that
local policy decision. local policy decision.
So for example one message receiver may decide that, for messages So for example one message receiver may decide that, for messages
with an intact ARC chain where a DMARC evaluation does not pass, but with an intact ARC chain where a DMARC evaluation does not pass, but
the ARC-Authentication-Results header field indicates a DKIM pass was the ARC-Authentication-Results header field indicates a DKIM pass was
reported that matches the domain in the RFC5322.From header field, it reported by the first ARC intermediary that matches the domain in the RFC5322.From header field, it
will override a DMARC "p=reject" policy. Another message receiver will override a DMARC "p=reject" policy. Another message receiver
may decide to do so for intact ARC chains where the ARC- may decide to do so for intact ARC chains where the ARC-
Authentication-Results header field indicates an SPF pass. A third Authentication-Results header field indicates an SPF pass. A third
message receiver may use very different criteria, according to their message receiver may use very different criteria, according to their
requirements, while a fourth may choose not to take ARC information requirements, while a fourth may choose not to take ARC information
into account at all. into account at all.
3.3. What is the significance of an invalid ("broken") ARC chain? 3.3. What is the significance of an invalid ("broken") ARC chain?
An ARC chain is not considered to be valid if the signatures in the An ARC chain is not considered to be valid if the signatures in the
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have any influence on the disposition of the message. For example, a have any influence on the disposition of the message. For example, a
message that fails under DMARC and has an invalid ARC chain would be message that fails under DMARC and has an invalid ARC chain would be
subject to that DMARC policy, which may cause it to be quarantined or subject to that DMARC policy, which may cause it to be quarantined or
rejected. rejected.
3.4. What does the absence of an ARC chain in a message mean? 3.4. What does the absence of an ARC chain in a message mean?
The absence of an ARC chain means nothing. ARC is intended to allow The absence of an ARC chain means nothing. ARC is intended to allow
a participating message handler to preserve certain authentication a participating message handler to preserve certain authentication
results when a message is being forwarded and/or modified such that results when a message is being forwarded and/or modified such that
the final recipient can evaluate the source. If they are absent, the final recipient can evaluate this information. If they are absent,
there is nothing extra that ARC requires the final recipient to do. there is nothing extra that ARC requires the final recipient to do.
3.5. What reasonable conclusions can you draw based upon seeing lots of 3.5. What reasonable conclusions can you draw based upon seeing lots of
mail with ARC chains? mail with ARC chains?
With sufficient history, ARC can be used to augment DMARC With sufficient history, ARC can be used to augment DMARC
authentication policy (i.e. a message could fail DMARC, but pass ARC authentication policy (i.e. a message could fail DMARC, but validated ARC
and therefore could be considered as validly authenticated as information could be considered to show the message was authenticated as
reported by the first ARC participant). reported by the first ARC participant).
If the validator does content analysis and reputation tracking, the If the validator does content analysis and reputation tracking, the
ARC participants in a message can be credited or discredited for good ARC participants in a message can be credited or discredited for good
or bad content. By analyzing different ARC chains involved in "bad" or bad content. By analyzing different ARC chains involved in "bad"
messages, a validator might identify malicious participating messages, a validator might identify malicious participating
intermediaries. intermediaries.
With a valid chain and good reputations for all ARC participants, With a valid chain and good reputations for all ARC participants,
receivers may choose to apply a "local policy override" to the DMARC receivers may choose to apply a "local policy override" to the DMARC
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ARC itself does not include any mechanism for feedback or reporting. ARC itself does not include any mechanism for feedback or reporting.
It does however recommend that message receiving systems that use ARC It does however recommend that message receiving systems that use ARC
to augment their delivery decisions, who use DMARC and decide to to augment their delivery decisions, who use DMARC and decide to
deliver a message because of ARC information, should include a deliver a message because of ARC information, should include a
notation to that effect in their normal DMARC reports. These notation to that effect in their normal DMARC reports. These
notations would be easily identifiable by report processors, so that notations would be easily identifiable by report processors, so that
senders and domain owners can see where ARC is being used to augment senders and domain owners can see where ARC is being used to augment
the deliverability of their messages. the deliverability of their messages.
3.10. What prevents a malicious actor from removing the ARC header 3.10. What prevents a malicious actor from removing the ARC header
fields, fields, altering the content, and creating a new ARC chain?
altering the content, and creating a new ARC chain?
ARC does not prevent a malicious actor from doing this. Nor does it ARC does not prevent a malicious actor from doing this. Nor does it
prevent a malicious actor from removing all but the first ADMD's ARC prevent a malicious actor from removing all but the first ADMD's ARC
header fields and altering the message, eliminating intervening header fields and altering the message, eliminating intervening
participants from the ARC chain. Or similar variations. participants from the ARC chain. Or similar variations.
A valid ARC chain does not provide any automatic benefit. With an A valid ARC chain does not provide any automatic benefit. With an
intact ARC chain, the final message recipient may choose to use the intact ARC chain, the final message recipient may choose to use the
contents of the ARC-Authentication-Results header field in contents of the ARC-Authentication-Results header field in
determining how to handle the message. The decision to use the ARC- determining how to handle the message. The decision to use the ARC-
Authentication-Results header field is dependent on evaluation of Authentication-Results header field is dependent on evaluation of
those ARC intermediaries. those ARC intermediaries.
In the first case, the bad actor has succeeded in manipulating the In the first case, the bad actor has succeeded in manipulating the
message but they have attached a verifiable signature identifying message but they have attached a verifiable signature identifying
themselves. While not an ideal situation, it is something they are themselves. While not an ideal situation, it is something they are
already able to do without ARC involved, but now a strong link to the already able to do without ARC involved, but now a signature linked to the
domain responsible for the manipulation is present. domain responsible for the manipulation is present.
Additionally in the second case it is possible some negative Additionally in the second case it is possible some negative
reputational impact might accrue to the first ARC participant left in reputational impact might accrue to the first ARC participant left in
place until more messages reveal the pattern of activity by the bad place until more messages reveal the pattern of activity by the bad
actor. But again, a bad actor can similarly manipulate a sequence of actor. But again, a bad actor can similarly manipulate a sequence of
RFC5322.Received header fields today without ARC, and with ARC that RFC5322.Received header fields today without ARC, but with ARC that
bad actor has verifiably identified themselves. bad actor has verifiably identified themselves.
4. Guidance for Intermediaries 4. Guidance for Intermediaries
4.1. What is an Intermediary under ARC? 4.1. What is an Intermediary under ARC?
In the context of ARC, an Intermediary is typically an Administrative In the context of ARC, an Intermediary is typically an Administrative
Management Domain [RFC5598] that is receiving a message, potentially Management Domain [RFC5598] that is receiving a message, potentially
manipulating or altering it, and then passing it on to another ADMD manipulating or altering it, and then passing it on to another ADMD
for delivery. Common examples of Intermediaries are mailing lists, for delivery. Common examples of Intermediaries are mailing lists,
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5.3. How can ARC impact my email? 5.3. How can ARC impact my email?
Prior to ARC, certain DMARC policies on a domain would cause messages Prior to ARC, certain DMARC policies on a domain would cause messages
using those domains in the RFC5322.From field, and which pass through using those domains in the RFC5322.From field, and which pass through
certain kinds of intermediaries (mailing lists, forwarding services), certain kinds of intermediaries (mailing lists, forwarding services),
to fail authentication checks at the message receiver. As a result to fail authentication checks at the message receiver. As a result
these messages might not be delivered to the intended recipient. these messages might not be delivered to the intended recipient.
ARC seeks to provide these so-called "indirect mailflows" with a ARC seeks to provide these so-called "indirect mailflows" with a
means to preserve email authentication results as seen by means to preserve email authentication results as recorded by
participating intermediaries. Message receivers may accept ARC participating intermediaries. Message receivers may accept validated ARC
results to supplement the information that DMARC provides, information to supplement the information that DMARC provides,
potentially deciding to deliver the message even though a DMARC check potentially deciding to deliver the message even though a DMARC check
did not pass. did not pass.
The net result for domain owners and senders is that ARC may allow The net result for domain owners and senders is that ARC may allow
messages routed through participating ARC intermediaries to be messages routed through participating ARC intermediaries to be
delivered, even though those messages would not have been delivered delivered, even though those messages would not have been delivered
in the absence of ARC. in the absence of ARC.
5.4. How can ARC impact my reputation as a message sender? 5.4. How can ARC impact my reputation as a message sender?
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<http://www.rfc-editor.org/info/rfc5598>. <http://www.rfc-editor.org/info/rfc5598>.
[RFC7601] Kucherawy, M., "Message Header Field for Indicating [RFC7601] Kucherawy, M., "Message Header Field for Indicating
Message Authentication Status", RFC 7601, Message Authentication Status", RFC 7601,
DOI 10.17487/RFC7601, August 2015, DOI 10.17487/RFC7601, August 2015,
<http://www.rfc-editor.org/info/rfc7601>. <http://www.rfc-editor.org/info/rfc7601>.
6.2. Informative References 6.2. Informative References
[ARC] Andersen, K., Rae-Grant, J., Long, B., Adams, T., and S. [ARC] Andersen, K., Rae-Grant, J., Long, B., Adams, T., and S.
Jones, "Authenticated Received Chain (ARC) Protocol", June Jones, "Authenticated Received Chain (ARC) Protocol", December
2016, <https://tools.ietf.org/html/draft-ietf-dmarc-arc- 2016, <https://tools.ietf.org/html/draft-ietf-dmarc-arc-
protocol-00>. protocol-01>.
[DMARC-INTEROP] [RFC7960]
Martin, F., Lear, E., Draegen, T., Zwicky, E., and K. Martin, F., Lear, E., Draegen, T., Zwicky, E., and K.
Andersen, "Interoperability Issues Between DMARC and Andersen, "Interoperability Issues Between DMARC and
Indirect Email Flows", June 2016, Indirect Email Flows", June 2016,
<https://tools.ietf.org/html/draft-ietf-dmarc- <https://tools.ietf.org/html/draft-ietf-dmarc-
interoperability-17>. interoperability-17>.
[ENHANCED-STATUS] [ENHANCED-STATUS]
"IANA SMTP Enhanced Status Codes", n.d., "IANA SMTP Enhanced Status Codes", n.d.,
<http://www.iana.org/assignments/smtp-enhanced-status- <http://www.iana.org/assignments/smtp-enhanced-status-
codes/smtp-enhanced-status-codes.xhtml>. codes/smtp-enhanced-status-codes.xhtml>.
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