Internet DRAFT - draft-kitterman-dmarc-psd
draft-kitterman-dmarc-psd
Network Working Group S. Kitterman
Internet-Draft fTLD Registry Services
Updates: 7489 (if approved) October 25, 2018
Intended status: Informational
Expires: April 28, 2019
DMARC (Domain-based Message Authentication, Reporting, and Conformance)
Extension For PSDs (Public Suffix Domains)
draft-kitterman-dmarc-psd-00
Abstract
DMARC (Domain-based Message Authentication, Reporting, and
Conformance) is a scalable mechanism by which a mail-originating
organization can express domain-level policies and preferences for
message validation, disposition, and reporting, that a mail-receiving
organization can use to improve mail handling. DMARC policies can be
applied at the individual domain level or for a set of domains at the
organizational level. The design of DMARC precludes grouping
policies for a set of domains above the organizational level, such as
TLDs (Top Level Domains). These types of domains (which are not all
at the top level of the DNS tree) can be collectively referred to as
Public Suffix Domains (PSDs). For the subset of PSDs that require
DMARC usage, this memo describes an extension to DMARC to enable
DMARC functionality for such domains.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 28, 2019.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology and Definitions . . . . . . . . . . . . . . . . . 4
2.1. Conventions Used in This Document . . . . . . . . . . . . 4
2.2. Public Suffix Domain (PSD) . . . . . . . . . . . . . . . 4
2.3. Longest PSD . . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Public Suffix Operator (PSO) . . . . . . . . . . . . . . 4
2.5. PSO Controlled Domain Names . . . . . . . . . . . . . . . 5
2.6. Non-existent Domains . . . . . . . . . . . . . . . . . . 5
3. PSD DMARC Updates to DMARC Requirements . . . . . . . . . . . 5
3.1. General Updates . . . . . . . . . . . . . . . . . . . . . 5
3.2. Section 6.1 DMARC Policy Record . . . . . . . . . . . . . 5
3.3. Section 6.5. Domain Owner Actions . . . . . . . . . . . 5
3.4. Section 6.6.3. Policy Discovery . . . . . . . . . . . . 5
3.5. Section 7. DMARC Feedback . . . . . . . . . . . . . . . 6
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6
4.1. Feedback leakage . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6.1. DMARC Public Suffix Domain (PSD) Registry 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
DMARC [RFC7489] provides a mechanism for publishing organizational
policy information to email receivers. DMARC [RFC7489] allows policy
to be specified for both individual domains and sets of domains
within a single organization. For domains above the organizational
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level in the DNS tree, policy can only be published for the exact
domain. There is no method available to such domains to express
lower level policy or receive feedback reporting for sets of domains.
This prevents policy application to non-existent domains and
identification of domain abuse in email, which can be important for
brand and consumer protection.
As an example, imagine a country code TLD (ccTLD) which has public
subdomains for government and commercial use (.gov.example and
.com.example). Within the .gov.example public suffix, use of DMARC
[RFC7489] has been mandated and .gov.example has published its own
DMARC [RFC7489] record:
"v=DMARC1;p=reject;rua=mailto:dmarc@dmarc.service.gov.example"
at
_dmarc.gov.example.
This would provide policy and feedback for mail sent from
@gov.example, but not @tax.gov.example and there is no way to publish
an organizational level policy that would do so. While, in theory,
receivers could reject mail from non-existent domains, not all
receivers do so. Non-existence of the sending domain can be a factor
in a mail delivery decision, but is not generally treated as
definitive on its own.
This memo provides a simple extension to DMARC [RFC7489] to allow
operators of Public Suffix Domains (PSDs) to express policy for
groups of subdomains, extends the DMARC [RFC7489] policy query
functionality to detect and process such a policy, describes receiver
feedback for such policies, and provides controls to mitigate
potential privacy considerations associated with this extension.
There are two types of Public Suffix Operators (PSOs) for which this
extension would be useful and appropriate:
o Branded PSDs (e.g., ".google"): These domains are effectively
Organizational Domains as discussed in DMARC [RFC7489]. They
control all subdomains of the tree. These are effectively private
domains, but listed in the Public Suffix List. They are treated
as Public for DMARC [RFC7489] purposes. They require the same
protections as DMARC [RFC7489] Organizational Domains, but are
currently excluded.
o Multi-organization PSDs that require DMARC usage (e.g., ".bank"):
Because existing Organizational Domains using this PSD have their
own DMARC policy, the applicability of this extension is for non-
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existent domains. The extension allows the brand protection
benefits of DMARC [RFC7489] to extend to the entire PSD, including
cousin domains of registered organizations.
Due to the design of DMARC [RFC7489] and the nature of the Internet
email architecture [RFC5598], there are interoperability issues
associated with DMARC [RFC7489] deployment. These are discussed in
Interoperability Issues between DMARC and Indirect Email Flows
[RFC7960]. These issues are not applicable to PSDs, since they
(e.g., the ".gov.example" used above) do not send mail.
DMARC [RFC7489], by design, does not support usage by PSD operators.
For PSDs that require use of DMARC [RFC7489], an extension of DMARC
reporting and enforcement capability is needed for PSD operators to
effectively manage and monitor implementation of PSD requirements.
2. Terminology and Definitions
This section defines terms used in the rest of the document.
2.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Public Suffix Domain (PSD)
The global Internet Domain Name System (DNS) is documented in
numerous Requests for Comment (RFC). It defines a tree of names
starting with root, ".", immediately below which are Top Level Domain
names such as ".com" and ".us". They are not available for private
registration. In many cases the public portion of the DNS tree is
more than one level deep. PSD DMARC includes all public domains
above the organizational level in the tree, e.g., ".gov.uk".
2.3. Longest PSD
Organizational Domain (DMARC [RFC7489] Section 3.2) with one label
removed.
2.4. Public Suffix Operator (PSO)
A Public Suffix Operator manages operations within their PSD.
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2.5. PSO Controlled Domain Names
PSO Controlled Domain Names are names in the DNS that are managed by
a PSO and are not available for use as Organizational Domains (the
term Organizational Domains is defined in DMARC [RFC7489]
Section 3.2). Depending on PSD policy, these will have one (e.g.,
".com") or more (e.g., ".co.uk") name components.
2.6. Non-existent Domains
For DMARC [RFC7489] purposes, a non-existent domain is a domain name
that publishes none of A, AAAA, or MX records that the receiver is
willing to accept. This is a broader definition than that in
NXDOMAIN [RFC8020].
3. PSD DMARC Updates to DMARC Requirements
This document updates DMARC [RFC7489] as follows:
3.1. General Updates
References to "Domain Owners" also apply to PSOs.
3.2. Section 6.1 DMARC Policy Record
PSD DMARC records are published as a subdomain of the PSD. For the
PSD ".example", the PSO would post DMARC policy in a TXT record at
"_dmarc.example".
3.3. Section 6.5. Domain Owner Actions
In addition to the DMARC [RFC7489] domain owner actions, PSOs will
need to update the "DMARC Public Suffix Domain (PSD) Registry". This
registry is defined in Section 6.1.
3.4. Section 6.6.3. Policy Discovery
A new step between step 3 and 4 is added:
3A. If the set is now empty and the longest PSD (Section 2.3) of the
Organizational Domain is listed in the DMARC PSD Registry (defined
in Section 6.1), the Mail Receiver MUST query the DNS for a DMARC
TXT record at the DNS domain matching the longest PSD
(Section 2.3) in place of the RFC5322.From domain in the message
(if different). A possibly empty set of records is returned.
As an example, for a message with the Organizational Domain of
"example.compute.cloudcompany.com.cctld", the query for PSD DMARC
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would use "compute.cloudcompany.com.cctld" as the longest PSD
(Section 2.3). The receiver would check to see if that PSD is listed
in the DMARC PSD Registry, and if so, perform the policy lookup at
"_dmarc.compute.cloudcompany.com.cctld".
Note: Because the PSD policy query comes after the Organizational
Domain policy query, PSD policy is not used for Organizational
domains that have published a DMARC [RFC7489] policy. Specifically,
this is not a mechanism to provide feedback addresses (RUA/RUF) when
an Organizational Domain has declined to do so.
3.5. Section 7. DMARC Feedback
Operational note for PSD DMARC: For PSOs, feedback for non-existent
domains is desired and useful. Because of the constraints on PSD
DMARC scope, there are no significant privacy considerations
associated with this reporting (See Section 4).
4. Privacy Considerations
This document does not significantly change the Privacy
Considerations of [RFC7489].
4.1. Feedback leakage
Providing feedback reporting to PSOs can, in some cases, create
leakage of information outside of an organization to the PSO. There
are roughly three cases to consider:
o Branded PSDs (e.g., ".google"), RUA and RUF reports based on PSD
DMARC have the potential to contain information about emails
related to entities managed by the organization. Since both the
PSO and the Organizational Domain owners are common, there is no
privacy risk for either normal or non-existent Domain reporting.
o Multi-organization PSDs that require DMARC usage (e.g., ".bank"):
PSD DMARC based reports will only be generated for domains that do
not publish a DMARC policy at the organizational or host level.
For domains that do publish the required DMARC policy records, the
feedback reporting addresses (RUA and RUF) of the organization (or
hosts) will be used. Since PSD DMARC is limited to PSDs that
mandate Organizational Domains publish DMARC policy for existing
domains, the risk of this issue is limited to Organizational
Domains that are out of compliance with PSD policy.
o Multi-organization PSDs (e.g., ".com") that do not mandate DMARC
usage. Privacy risks for Organizational Domains within such PSDs
would be significant. This is mitigated by the limitation to only
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include PSDs listed in the public IANA DMARC PSD Registry
described in Section 6.1.
PSOs will receive feedback on non-existent domains, which may be
similar to existing Organizational Domains. Feedback related to such
cousin domains have a small risk of carrying information related to
an actual Organizational Domain. To minimize this potential concern,
PSD DMARC feedback is best limited to Aggregate Reports. Feedback
Reports carry more detailed information and present a greater risk.
5. Security Considerations
This document does not change the Security Considerations of
[RFC7489].
6. IANA Considerations
This section describes actions requested to be completed by IANA.
6.1. DMARC Public Suffix Domain (PSD) Registry
IANA is requested to create a new DMARC Public Suffix Domain (PSD)
Registry within the Domain-based Message Authentication, Reporting,
and Conformance (DMARC) Parameters Registry.
Names of PSDs participating in PSD DMARC must be registered with IANA
in this new sub-registry. New entries are assigned only for PSDs
that require use of DMARC. The requirement has to be documented in a
manner that satisfies the terms of Expert Review, per [RFC5226]. The
Designated Expert needs to confirm that provided documentation
adequately describes PSD policy to require domain owners to use DMARC
or that all domain owners are part of a single organization with the
PSO.
The initial set of entries in this registry is as follows:
+-------------+----------------+---------------+
| PSD | Reference | Status |
+-------------+----------------+---------------+
| .bank | this document | current |
+-------------+----------------+---------------+
| .insurance | this document | current |
+-------------+----------------+---------------+
| .gov.uk | this document | current |
+-------------+----------------+---------------+
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<https://www.rfc-editor.org/info/rfc7489>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598,
DOI 10.17487/RFC5598, July 2009,
<https://www.rfc-editor.org/info/rfc5598>.
[RFC7960] Martin, F., Ed., Lear, E., Ed., Draegen. Ed., T., Zwicky,
E., Ed., and K. Andersen, Ed., "Interoperability Issues
between Domain-based Message Authentication, Reporting,
and Conformance (DMARC) and Indirect Email Flows",
RFC 7960, DOI 10.17487/RFC7960, September 2016,
<https://www.rfc-editor.org/info/rfc7960>.
[RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is
Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020,
November 2016, <https://www.rfc-editor.org/info/rfc8020>.
Acknowledgements
TBS
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Author's Address
Scott Kitterman
fTLD Registry Services
600 13th Street, NW, Suite 400
Washington, DC 20005
United States of America
Phone: +1 301 325-5475
Email: scott@kitterman.com
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