draft-ietf-dmarc-psd-10.txt   draft-ietf-dmarc-psd-11.txt 
Network Working Group S. Kitterman Network Working Group S. Kitterman
Internet-Draft fTLD Registry Services Internet-Draft fTLD Registry Services
Intended status: Experimental January 23, 2021 Intended status: Experimental T. Wicinski, Ed.
Expires: July 27, 2021 Expires: September 20, 2021 March 19, 2021
Experimental DMARC Extension For Public Suffix Domains Experimental DMARC Extension For Public Suffix Domains
draft-ietf-dmarc-psd-10 draft-ietf-dmarc-psd-11
Abstract Abstract
DMARC (Domain-based Message Authentication, Reporting, and Domain-based Message Authentication, Reporting, and Conformance
Conformance) is a scalable mechanism by which a mail-originating (DMARC) permits a domain-controlling organization to express domain-
organization can express domain-level policies and preferences for level policies and preferences for message validation, disposition,
message validation, disposition, and reporting, that a mail-receiving and reporting, which a mail-receiving organization can use to improve
organization can use to improve mail handling. The design of DMARC mail handling.
presumes that domain names represent either nodes in the tree below
which registrations occur, or nodes where registrations have
occurred; it does not permit a domain name to have both of these
properties simultaneously. Since its deployment in 2015, use of
DMARC has shown a clear need for the ability to express policy for
these domains as well.
Domains at which registrations can occur are referred to as Public DMARC distinguishes the portion of a name that is a Public Suffix
Suffix Domains (PSDs). This document describes an extension to DMARC Domain (PSD), below which organizational domain names are created.
to enable DMARC functionality for PSDs. The basic DMARC capability allows organizational domains to specify
policies that apply to their subdomains, but it does not give that
capability to PSDs. This document describes an extension to DMARC to
fully enable DMARC functionality for PSDs.
This document also seeks to address implementations that consider a Some implementations of DMARC consider a PSD to be ineligible for
domain on a public Suffix list to be ineligible for DMARC DMARC enforcement. This specification addresses that case.
enforcement.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on July 27, 2021. This Internet-Draft will expire on September 20, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2021 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
(https://trustee.ietf.org/license-info) in effect on the date of (https://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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1.2. Discussion . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Discussion . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology and Definitions . . . . . . . . . . . . . . . . . 5 2. Terminology and Definitions . . . . . . . . . . . . . . . . . 5
2.1. Conventions Used in This Document . . . . . . . . . . . . 5 2.1. Conventions Used in This Document . . . . . . . . . . . . 5
2.2. Public Suffix Domain (PSD) . . . . . . . . . . . . . . . 5 2.2. Public Suffix Domain (PSD) . . . . . . . . . . . . . . . 5
2.3. Organizational Domain . . . . . . . . . . . . . . . . . . 6 2.3. Organizational Domain . . . . . . . . . . . . . . . . . . 6
2.4. Longest PSD . . . . . . . . . . . . . . . . . . . . . . . 6 2.4. Longest PSD . . . . . . . . . . . . . . . . . . . . . . . 6
2.5. Public Suffix Operator (PSO) . . . . . . . . . . . . . . 6 2.5. Public Suffix Operator (PSO) . . . . . . . . . . . . . . 6
2.6. PSO Controlled Domain Names . . . . . . . . . . . . . . . 6 2.6. PSO Controlled Domain Names . . . . . . . . . . . . . . . 6
2.7. Non-existent Domains . . . . . . . . . . . . . . . . . . 6 2.7. Non-existent Domains . . . . . . . . . . . . . . . . . . 6
3. PSD DMARC Updates to DMARC Requirements . . . . . . . . . . . 6 3. PSD DMARC Updates to DMARC Requirements . . . . . . . . . . . 6
3.1. General Updates . . . . . . . . . . . . . . . . . . . . . 7 3.1. General Updates . . . . . . . . . . . . . . . . . . . . . 6
3.2. Changes in Section 6.3 "General Record Format" . . . . . 7 3.2. Changes in Section 6.3 "General Record Format" . . . . . 7
3.3. Changes in Section 6.5 "Domain Owner Actions" . . . . . . 7 3.3. Changes in Section 6.5 "Domain Owner Actions" . . . . . . 7
3.4. Changes in Section 6.6.1 "Extract Author Domain" . . . . 7 3.4. Changes in Section 6.6.1 "Extract Author Domain" . . . . 7
3.5. Changes in Section 6.6.3 "Policy Discovery" . . . . . . . 8 3.5. Changes in Section 6.6.3 "Policy Discovery" . . . . . . . 8
3.6. Changes in Section 7 "DMARC Feedback" . . . . . . . . . . 8 3.6. Changes in Section 7 "DMARC Feedback" . . . . . . . . . . 8
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8
4.1. Feedback leakage . . . . . . . . . . . . . . . . . . . . 9 4.1. Feedback leakage . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6.1. Subdomain Policy Tag . . . . . . . . . . . . . . . . . . 10 6.1. Subdomain Policy Tag . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 11 7.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. PSD DMARC Privacy Concern Mitigation Experiment . . 12 Appendix A. PSD DMARC Privacy Concern Mitigation Experiment . . 12
Appendix B. DMARC PSD Registry Examples . . . . . . . . . . . . 12 Appendix B. DMARC PSD Registry Examples . . . . . . . . . . . . 12
B.1. DMARC PSD DNS Query Service . . . . . . . . . . . . . . . 12 B.1. DMARC PSD DNS Query Service . . . . . . . . . . . . . . . 12
B.2. DMARC Public Suffix Domain (PSD) Registry . . . . . . . . 12 B.2. DMARC Public Suffix Domain (PSD) Registry . . . . . . . . 12
B.3. DMARC PSD PSL Extension . . . . . . . . . . . . . . . . . 13 B.3. DMARC PSD PSL Extension . . . . . . . . . . . . . . . . . 13
Appendix C. Implementations . . . . . . . . . . . . . . . . . . 13 Appendix C. Implementations . . . . . . . . . . . . . . . . . . 13
C.1. Authheaders Module . . . . . . . . . . . . . . . . . . . 13 C.1. Authheaders Module . . . . . . . . . . . . . . . . . . . 13
C.2. Zdkimfilter Module . . . . . . . . . . . . . . . . . . . 14 C.2. Zdkimfilter Module . . . . . . . . . . . . . . . . . . . 14
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
DMARC [RFC7489] provides a mechanism for publishing organizational DMARC ([RFC7489]) provides a mechanism for publishing organizational
policy information to email receivers. DMARC allows policy to be policy information to email receivers. DMARC allows policy to be
specified for both individual domains and for organizational domains specified for both individual domains and for organizational domains
and their sub-domains within a single organization. and their sub-domains within a single organization.
To determine the organizational domain for a message under To determine the organizational domain for a message under
evaluation, and thus where to look for a policy statement, DMARC evaluation, and thus where to look for a policy statement, DMARC
makes use of a Public Suffix List. The process for doing this can be makes use of a Public Suffix List. The process for doing this can be
found in Section 3.2 of the DMARC specification. found in Section 3.2 of the DMARC specification.
DMARC as specified presumes that domain names present in a PSL are In the basic DMARC model, PSDs are not organizational domains and are
not organizational domains and thus not subject to DMARC processing; thus not subject to DMARC processing. In DMARC, domains fall into
domains are either organizational domains, sub-domains of one of three categories: organizational domains, sub-domains of
organizational domains, or listed on a PSL. For domains listed in a organizational domains, or PSDs. A PSD can only publish DMARC policy
PSL, i.e., TLDs and domains that exist between TLDs and organization for itself, and not for any sub-domains under it. In some cases,
level domains, policy can only be published for the exact domain. No this limitation allows for the abuse of non-existent organizational-
method is available for these domains to express policy or receive level domains and hampers identification of domain abuse in email.
feedback reporting for sub-domains. This missing method allows for
the abuse of non-existent organizational-level domains and prevents
identification of domain abuse in email.
This document specifies experimental updates to the DMARC and PSL This document specifies experimental updates to the DMARC and PSL
algorithm cited above, in an attempt to mitigate this abuse. algorithm cited above, in an attempt to mitigate this abuse.
1.1. Example 1.1. Example
As an example, imagine a country code TLD (ccTLD) which has public As an example, imagine a Top-Level Domain (TLD), ".example", that has
subdomains for government and commercial use (".gov.example" and public subdomains for government and commercial use (".gov.example"
".com.example"). A PSL whose maintainer is aware of this country's and ".com.example"). The maintainer of a list of such a PSD
domain structurewould include entries for both of these in the PSL, structure would include entries for both of these sub-domains,
indicating that they are PSDs below which registrations can occur. thereby indicating that they are PSDs, below which organizational
Suppose further that there exists a domain "tax.gov.example", domains can be registered. Suppose further that there exists a
registered within ".gov.example", that is responsible for taxation in legitimate domain called "tax.gov.example", registered within
this imagined country. ".gov.example".
However, by exploiting the typically unauthenticated nature of email, However, by exploiting the typically unauthenticated nature of email,
there are regular malicious campaigns to impersonate this there are regular malicious campaigns to impersonate this
organization that use similar-looking ("cousin") domains such as organization that use similar-looking ("cousin") domains such as
"t4x.gov.example". Such domains are not registered. "t4x.gov.example". Such domains are not registered.
Within the ".gov.example" public suffix, use of DMARC has been Within the ".gov.example" public suffix, use of DMARC has been
mandated, so "gov.example" publishes the following DMARC DNS record: mandated, so "gov.example" publishes the following DMARC DNS record:
_dmarc.gov.example. IN TXT ( "v=DMARC1; p=reject; " _dmarc.gov.example. IN TXT ( "v=DMARC1; p=reject; "
"rua=mailto:dmc@dmarc.svc.gov.example" ) "rua=mailto:dmc@dmarc.svc.gov.example" )
This DMARC record provides policy and a reporting destination for This DMARC record provides policy and a reporting destination for
mail sent from @gov.example. However, due to DMARC's current method mail sent from @gov.example. Similarly, "tax.gov.example" will have
of discovering and applying policy at the organizational domain a DMARC record that specifies policy for mail sent from addresses
level, the non-existent organizational domain of @t4x.gov.example @tax.gov.example. However, due to DMARC's current method of
does not and cannot fall under a DMARC policy. discovering and applying policy at the organizational domain level,
the non-existent organizational domain of @t4x.gov.example does not
and cannot fall under a DMARC policy.
Defensively registering all variants of "tax" is obviously not a Defensively registering all variants of "tax" is obviously not a
scalable strategy. The intent of this specification, therefore, is scalable strategy. The intent of this specification, therefore, is
to enhance the DMARC algorithm by enabling an agent receiving such a to enhance the DMARC algorithm by enabling an agent receiving such a
message to be able to determine that a relevant policy is present at message to be able to determine that a relevant policy is present at
"gov.example", which is precluded by the current DMARC algorithm. "gov.example", which is precluded by the current DMARC algorithm.
1.2. Discussion 1.2. Discussion
This document provides a simple extension to DMARC [RFC7489] to allow This document provides a simple extension to [RFC7489] to allow
operators of Public Suffix Domains (PSDs) to: operators of Public Suffix Domains (PSDs) to:
o Express policy at the level of the PSD that covers all o Express policy at the level of the PSD that covers all
organizational domains that do not explicitly publish DMARC organizational domains that do not explicitly publish DMARC
records records
o Extends the DMARC policy query functionality to detect and process o Extends the DMARC policy query functionality to detect and process
such a policy such a policy
o Describes receiver feedback for such policies o Describes receiver feedback for such policies
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This document also provides a new DMARC tag to indicate requested This document also provides a new DMARC tag to indicate requested
handling policy for non-existent subdommains. This is provided handling policy for non-existent subdommains. This is provided
specifically to support phased deployment of PSD DMARC, but is specifically to support phased deployment of PSD DMARC, but is
expected to be useful more generally. Undesired rejection risks for expected to be useful more generally. Undesired rejection risks for
mail purporting to be from domains that do not exist are mail purporting to be from domains that do not exist are
substantially lower than for those that do, so the operational risk substantially lower than for those that do, so the operational risk
of requesting harsh policy treatment (e.g. reject) is lower. of requesting harsh policy treatment (e.g. reject) is lower.
As an additional benefit, the PSD DMARC extension clarifies existing As an additional benefit, the PSD DMARC extension clarifies existing
requirements. Based on the requirements of DMARC [RFC7489], DMARC requirements. Based on the requirements of [RFC7489], DMARC should
should function above the organizational level for exact domain function above the organizational level for exact domain matches
matches (i.e. if a DMARC record were published for 'example', then (i.e. if a DMARC record were published for 'example', then mail from
mail from example@example should be subject to DMARC processing). example@example should be subject to DMARC processing). Testing had
revealed that this is not consistently applied in different
Testing had revealed that this is not consistently applied in implementations.
different implementations.
There are two types of Public Suffix Operators (PSOs) for which this There are two types of Public Suffix Operators (PSOs) for which this
extension would be useful and appropriate: extension would be useful and appropriate:
o Branded PSDs (e.g., ".google"): These domains are effectively o Branded PSDs (e.g., ".google"): These domains are effectively
Organizational Domains as discussed in DMARC [RFC7489]. They Organizational Domains as discussed in [RFC7489]. They control
control all subdomains of the tree. These are effectively private all subdomains of the tree. These are effectively private
domains, but listed in the Public Suffix List. They are treated domains, but listed in the Public Suffix List. They are treated
as Public for DMARC purposes. They require the same protections as Public for DMARC purposes. They require the same protections
as DMARC Organizational Domains, but are currently unable to as DMARC Organizational Domains, but are currently unable to
benefit from DMARC. benefit from DMARC.
o Multi-organization PSDs that require DMARC usage (e.g., ".bank"): o Multi-organization PSDs that require DMARC usage (e.g., ".bank"):
Because existing Organizational Domains using this PSD have their Because existing Organizational Domains using this PSD have their
own DMARC policy, the applicability of this extension is for non- own DMARC policy, the applicability of this extension is for non-
existent domains. The extension allows the brand protection existent domains. The extension allows the brand protection
benefits of DMARC to extend to the entire PSD, including cousin benefits of DMARC to extend to the entire PSD, including cousin
domains of registered organizations. domains of registered organizations.
Due to the design of DMARC and the nature of the Internet email Due to the design of DMARC and the nature of the Internet email
architecture [RFC5598], there are interoperability issues associated architecture [RFC5598], there are interoperability issues associated
with DMARC [RFC7489] deployment. These are discussed in with DMARC deployment. These are discussed in Interoperability
Interoperability Issues between DMARC and Indirect Email Flows Issues between DMARC and Indirect Email Flows [RFC7960]. These
[RFC7960]. These issues are not typically applicable to PSDs, since issues are not typically applicable to PSDs, since they (e.g., the
they (e.g., the ".gov.example" used above) do not typically send ".gov.example" used above) do not typically send mail.
mail.
2. Terminology and Definitions 2. Terminology and Definitions
This section defines terms used in the rest of the document. This section defines terms used in the rest of the document.
2.1. Conventions Used in This Document 2.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
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tree at which to register domain names "owned" by independent tree at which to register domain names "owned" by independent
organizations. Real-world examples are ".com", ".org", ".us", and organizations. Real-world examples are ".com", ".org", ".us", and
".gov.uk". Names at which such registrations occur are called Public ".gov.uk". Names at which such registrations occur are called Public
Suffix Domains (PSDs), and a registration consists of a label Suffix Domains (PSDs), and a registration consists of a label
selected by the registrant to which a desirable PSD is appended. For selected by the registrant to which a desirable PSD is appended. For
example, "ietf.org" is a registered domain name, and ".org" is its example, "ietf.org" is a registered domain name, and ".org" is its
PSD. PSD.
2.3. Organizational Domain 2.3. Organizational Domain
The term Organizational Domains is defined in DMARC [RFC7489] The term Organizational Domains is defined in [RFC7489] Section 3.2.
Section 3.2.
2.4. Longest PSD 2.4. Longest PSD
The longest PSD is the Organizational Domain with one label removed. The longest PSD is the Organizational Domain with one label removed.
It names the immediate parent node of the Organizational Domain in It names the immediate parent node of the Organizational Domain in
the DNS namespace tree. the DNS namespace tree.
2.5. Public Suffix Operator (PSO) 2.5. Public Suffix Operator (PSO)
A Public Suffix Operator is an organization which manages operations A Public Suffix Operator is an organization which manages operations
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DOI 10.17487/RFC6973, July 2013, DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>. <https://www.rfc-editor.org/info/rfc6973>.
[RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T., [RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann, Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A "Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", RFC 7624, Threat Model and Problem Statement", RFC 7624,
DOI 10.17487/RFC7624, August 2015, DOI 10.17487/RFC7624, August 2015,
<https://www.rfc-editor.org/info/rfc7624>. <https://www.rfc-editor.org/info/rfc7624>.
[RFC7960] Martin, F., Ed., Lear, E., Ed., Draegen. Ed., T., Zwicky, [RFC7960] Martin, F., Ed., Lear, E., Ed., Draegen, T., Ed., Zwicky,
E., Ed., and K. Andersen, Ed., "Interoperability Issues E., Ed., and K. Andersen, Ed., "Interoperability Issues
between Domain-based Message Authentication, Reporting, between Domain-based Message Authentication, Reporting,
and Conformance (DMARC) and Indirect Email Flows", and Conformance (DMARC) and Indirect Email Flows",
RFC 7960, DOI 10.17487/RFC7960, September 2016, RFC 7960, DOI 10.17487/RFC7960, September 2016,
<https://www.rfc-editor.org/info/rfc7960>. <https://www.rfc-editor.org/info/rfc7960>.
[RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is [RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is
Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020, Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020,
November 2016, <https://www.rfc-editor.org/info/rfc8020>. November 2016, <https://www.rfc-editor.org/info/rfc8020>.
skipping to change at page 14, line 25 skipping to change at page 14, line 25
Acknowledgements Acknowledgements
Thanks to the following individuals for their contributions (both Thanks to the following individuals for their contributions (both
public and private) to improving this document. Special shout out to public and private) to improving this document. Special shout out to
Dave Crocker for naming the beast. Dave Crocker for naming the beast.
Kurt Andersen, Seth Blank, Dave Crocker, Heather Diaz, Tim Draegen, Kurt Andersen, Seth Blank, Dave Crocker, Heather Diaz, Tim Draegen,
Zeke Hendrickson, Andrew Kennedy, John Levine, Dr Ian Levy, Craig Zeke Hendrickson, Andrew Kennedy, John Levine, Dr Ian Levy, Craig
Schwartz, Alessandro Vesely, and Tim Wicinski Schwartz, Alessandro Vesely, and Tim Wicinski
Author's Address Authors' Addresses
Scott Kitterman Scott Kitterman
fTLD Registry Services fTLD Registry Services
600 13th Street, NW, Suite 400 600 13th Street, NW, Suite 400
Washington, DC 20005 Washington, DC 20005
United States of America United States of America
Phone: +1 301 325-5475 Phone: +1 301 325-5475
Email: scott@kitterman.com Email: scott@kitterman.com
Tim Wicinski (editor)
Elkins, WV 26241
USA
Email: tjw.ietf@gmail.com
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