draft-ietf-dmarc-psd-04.txt   draft-ietf-dmarc-psd-05.txt 
Network Working Group S. Kitterman Network Working Group S. Kitterman
Internet-Draft fTLD Registry Services Internet-Draft fTLD Registry Services
Intended status: Experimental May 27, 2019 Intended status: Experimental July 27, 2019
Expires: November 28, 2019 Expires: January 28, 2020
DMARC (Domain-based Message Authentication, Reporting, and Conformance) DMARC (Domain-based Message Authentication, Reporting, and Conformance)
Extension For PSDs (Public Suffix Domains) Extension For PSDs (Public Suffix Domains)
draft-ietf-dmarc-psd-04 draft-ietf-dmarc-psd-05
Abstract Abstract
DMARC (Domain-based Message Authentication, Reporting, and DMARC (Domain-based Message Authentication, Reporting, and
Conformance) is a scalable mechanism by which a mail-originating Conformance) is a scalable mechanism by which a mail-originating
organization can express domain-level policies and preferences for organization can express domain-level policies and preferences for
message validation, disposition, and reporting, that a mail-receiving message validation, disposition, and reporting, that a mail-receiving
organization can use to improve mail handling. DMARC policies can be 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 applied to individual domains or to all domains within an
organizational level. The design of DMARC precludes grouping organization. The design of DMARC precludes grouping policies for
policies for a set of domains above the organizational level, such as domains based on policy published above the organizational level,
TLDs (Top Level Domains). These types of domains (which are not all such as TLDs (Top Level Domains). Domains at this higher level of
at the top level of the DNS tree) can be collectively referred to as the DNS tree (but not necessarily at the top of the DNS tree) can be
Public Suffix Domains (PSDs). For the subset of PSDs that require collectively referred to as Public Suffix Domains (PSDs). This
DMARC usage, this memo describes an extension to DMARC to enable document describes an extension to DMARC to enable DMARC
DMARC functionality for such domains. functionality PSDs.
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.
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This Internet-Draft will expire on November 28, 2019. This Internet-Draft will expire on January 28, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Definitions . . . . . . . . . . . . . . . . . 4 2. Terminology and Definitions . . . . . . . . . . . . . . . . . 5
2.1. Conventions Used in This Document . . . . . . . . . . . . 4 2.1. Conventions Used in This Document . . . . . . . . . . . . 5
2.2. Public Suffix Domain (PSD) . . . . . . . . . . . . . . . 4 2.2. Public Suffix Domain (PSD) . . . . . . . . . . . . . . . 5
2.3. Longest PSD . . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Longest PSD . . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Public Suffix Operator (PSO) . . . . . . . . . . . . . . 5 2.4. Public Suffix Operator (PSO) . . . . . . . . . . . . . . 5
2.5. PSO Controlled Domain Names . . . . . . . . . . . . . . . 5 2.5. PSO Controlled Domain Names . . . . . . . . . . . . . . . 5
2.6. Non-existent Domains . . . . . . . . . . . . . . . . . . 5 2.6. Non-existent Domains . . . . . . . . . . . . . . . . . . 5
3. PSD DMARC Updates to DMARC Requirements . . . . . . . . . . . 5 3. PSD DMARC Updates to DMARC Requirements . . . . . . . . . . . 6
3.1. General Updates . . . . . . . . . . . . . . . . . . . . . 5 3.1. General Updates . . . . . . . . . . . . . . . . . . . . . 6
3.2. Section 6.1 DMARC Policy Record . . . . . . . . . . . . . 5 3.2. Section 6.1 DMARC Policy Record . . . . . . . . . . . . . 6
3.3. Section 6.5. Domain Owner Actions . . . . . . . . . . . 5 3.3. Section 6.3 General Record Format . . . . . . . . . . . . 6
3.4. Section 6.6.3. Policy Discovery . . . . . . . . . . . . 6 3.4. Section 6.5. Domain Owner Actions . . . . . . . . . . . 7
3.5. Section 7. DMARC Feedback . . . . . . . . . . . . . . . 6 3.5. Section 6.6.3. Policy Discovery . . . . . . . . . . . . 7
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6 3.6. Section 7. DMARC Feedback . . . . . . . . . . . . . . . 7
4.1. Feedback leakage . . . . . . . . . . . . . . . . . . . . 6 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 4.1. Feedback leakage . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 8 6.1. Subdomain Policy Tag . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
Appendix A. The Experiment . . . . . . . . . . . . . . . . . . . 9 7.1. Normative References . . . . . . . . . . . . . . . . . . 9
Appendix B. DMARC PSD Registry Examples . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . 10
B.1. DMARC PSD DNS Query Service . . . . . . . . . . . . . . . 10 Appendix A. The Experiment . . . . . . . . . . . . . . . . . . . 11
B.2. DMARC Public Suffix Domain (PSD) Registry . . . . . . . . 10 A.1. PSD DMARC Privacy Concern Mitigation . . . . . . . . . . 11
Appendix C. Implementation . . . . . . . . . . . . . . . . . . . 11 A.2. Non-Existent Subdomain Policy . . . . . . . . . . . . . . 12
C.1. Authheaders Module . . . . . . . . . . . . . . . . . . . 11 Appendix B. DMARC PSD Registry Examples . . . . . . . . . . . . 12
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11 B.1. DMARC PSD DNS Query Service . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 B.2. DMARC Public Suffix Domain (PSD) Registry . . . . . . . . 12
Appendix C. Implementation . . . . . . . . . . . . . . . . . . . 13
C.1. Authheaders Module . . . . . . . . . . . . . . . . . . . 13
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
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 [RFC7489] allows policy policy information to email receivers. DMARC allows policy to be
to be specified for both individual domains and sets of domains specified for both individual domains and for organizational domains
within a single organization. For domains above the organizational and their sub-domains within a single organization. For TLDs and
level in the DNS tree, policy can only be published for the exact domains that exist between TLDs and organization level domains,
domain. There is no method available to such domains to express policy can only be published for the exact domain. No method is
lower level policy or receive feedback reporting for sets of domains. available for such domains to express policy or receive feedback
This prevents policy application to non-existent domains and reporting for sub-domains. This missing method allows for the abuse
identification of domain abuse in email, which can be important for of non-existent organizational-level domains and prevents
brand and consumer protection. identification of domain abuse in email.
As an example, imagine a country code TLD (ccTLD) which has public As an example, imagine a country code TLD (ccTLD) which has public
subdomains for government and commercial use (.gov.example and subdomains for government and commercial use (.gov.example and
.com.example). Within the .gov.example public suffix, use of DMARC .com.example). Within the .gov.example public suffix, use of DMARC
[RFC7489] has been mandated and .gov.example has published its own has been mandated and .gov.example has published its own DMARC
DMARC [RFC7489] record: record:
"v=DMARC1;p=reject;rua=mailto:dmarc@dmarc.service.gov.example" "v=DMARC1; p=reject; rua=mailto:dmarc@dmarc.service.gov.example"
at at
_dmarc.gov.example. _dmarc.gov.example.
This would provide policy and feedback for mail sent from This DMARC record provides policy and a reporting destination for
@gov.example, but not @tax.gov.example and there is no way to publish mail sent from @gov.example. However, due to DMARC's current method
an organizational level policy that would do so. While, in theory, of discovering and applying policy at the organizational domain
receivers could reject mail from non-existent domains, not all level, the non-existent organizational domain of @tax.gov.example
receivers do so. Non-existence of the sending domain can be a factor does not and cannot fall under a DMARC policy.
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 This document provides a simple extension to DMARC [RFC7489] to allow
operators of Public Suffix Domains (PSDs) to express policy for operators of Public Suffix Domains (PSDs) to express policy at the
groups of subdomains, extends the DMARC [RFC7489] policy query level of the PSD that covers all organizational domains that do not
explicitly publish DMARC records, extends the DMARC policy query
functionality to detect and process such a policy, describes receiver functionality to detect and process such a policy, describes receiver
feedback for such policies, and provides controls to mitigate feedback for such policies, and provides controls to mitigate
potential privacy considerations associated with this extension. potential privacy considerations associated with this extension.
As an additional benefit, the PSD DMARC extension will clarify This document also provides a new DMARC [RFC7489] tag to indicate
existing requirements. Based on the requirements of DMARC [RFC7489], requested handling policy for non-existent subdommains. This is
DMARC should function above the organizational level for exact domain provided specifically to support phased deployment of PSD DMARC, but
is expected to be useful more generally. Undesired rejection risks
for mail purporting to be from domains that do not exist are
substantially lower than for those that do, so the operational risk
of requesting harsh policy treatment (e.g. reject) is lower.
As an additional benefit, the PSD DMARC extension clarifies existing
requirements. Based on the requirements of DMARC [RFC7489], DMARC
should function above the organizational level for exact domain
matches (i.e. if a DMARC record were published for 'example', then matches (i.e. if a DMARC record were published for 'example', then
mail from example@example should be subject to DMARC processing). mail from example@example should be subject to DMARC processing).
Testing had revealed that this is not consistently applied in Testing had revealed that this is not consistently applied in
different implementations. PSD DMARC will help clarify that DMARC is different implementations.
not limited to organizational domains and their sub-domains.
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 DMARC [RFC7489]. They
control all subdomains of the tree. These are effectively private control 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 [RFC7489] purposes. They require the same as Public for DMARC purposes. They require the same protections
protections as DMARC [RFC7489] Organizational Domains, but are as DMARC Organizational Domains, but are currently excluded.
currently excluded.
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 [RFC7489] to extend to the entire PSD, including benefits of DMARC to extend to the entire PSD, including cousin
cousin domains of registered organizations. domains of registered organizations.
As an example, take the ".gov.example" described above and add that
for this entity emails about tax returns are sent from
tax.gov.example. It would not be surprising if fraudulent emails
were sent purporting to be from taxes.gov.example (taxes is a cousin
of tax - different enough to evade DMARC protection, but similar
enough to potentially confuse users). As defined in DMARC [RFC7489],
a DMARC record could be published for tax.gov.example, but there is
no general solution to publishing a DMARC policy to defend against
abuse of non-existent cousins such as taxes.gov.example. While an
explicit record could be published for this one domain, the universe
of possible cousins is such that this approach does not scale.
Due to the design of DMARC [RFC7489] and the nature of the Internet Due to the design of DMARC [RFC7489] and the nature of the Internet
email architecture [RFC5598], there are interoperability issues email architecture [RFC5598], there are interoperability issues
associated with DMARC [RFC7489] deployment. These are discussed in associated with DMARC [RFC7489] deployment. These are discussed in
Interoperability Issues between DMARC and Indirect Email Flows Interoperability Issues between DMARC and Indirect Email Flows
[RFC7960]. These issues are not applicable to PSDs, since they [RFC7960]. These issues are not typically applicable to PSDs, since
(e.g., the ".gov.example" used above) do not send mail. they (e.g., the ".gov.example" used above) do not typically send
mail.
DMARC [RFC7489], by design, does not support usage by PSOs. For PSDs
that require use of DMARC [RFC7489], an extension of DMARC reporting
and enforcement capability is needed for PSO to effectively manage
and monitor implementation of PSD requirements.
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
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2.2. Public Suffix Domain (PSD) 2.2. Public Suffix Domain (PSD)
The global Internet Domain Name System (DNS) is documented in The global Internet Domain Name System (DNS) is documented in
numerous Requests for Comment (RFC). It defines a tree of names numerous Requests for Comment (RFC). It defines a tree of names
starting with root, ".", immediately below which are Top Level Domain starting with root, ".", immediately below which are Top Level Domain
names such as ".com" and ".us". They are not available for private names such as ".com" and ".us". They are not available for private
registration. In many cases the public portion of the DNS tree is registration. In many cases the public portion of the DNS tree is
more than one level deep. PSD DMARC includes all public domains more than one level deep.
above the organizational level in the tree, e.g., ".gov.uk".
2.3. Longest PSD 2.3. Longest PSD
Organizational Domain (DMARC [RFC7489] Section 3.2) with one label Organizational Domain (DMARC [RFC7489] Section 3.2) with one left-
removed. most label removed.
2.4. Public Suffix Operator (PSO) 2.4. Public Suffix Operator (PSO)
A Public Suffix Operator manages operations within their PSD. A Public Suffix Operator manages operations within its PSD.
2.5. PSO Controlled Domain Names 2.5. PSO Controlled Domain Names
PSO Controlled Domain Names are names in the DNS that are managed by 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 a PSO and are not available for use as Organizational Domains (the
term Organizational Domains is defined in DMARC [RFC7489] term Organizational Domains is defined in DMARC [RFC7489]
Section 3.2). Depending on PSD policy, these will have one (e.g., Section 3.2). Depending on PSD policy, these will have one (e.g.,
".com") or more (e.g., ".co.uk") name components. ".com") or more (e.g., ".co.uk") name components.
2.6. Non-existent Domains 2.6. Non-existent Domains
For DMARC [RFC7489] purposes, a non-existent domain is a domain name For DMARC purposes, a non-existent domain is a domain for which there
that publishes none of A, AAAA, or MX records that the receiver is is an NXDOMAIN or NODATA response for A, AAAA, and MX records. This
willing to accept. This is a broader definition than that in is a broader definition than that in NXDOMAIN [RFC8020].
NXDOMAIN [RFC8020].
3. PSD DMARC Updates to DMARC Requirements 3. PSD DMARC Updates to DMARC Requirements
This document updates DMARC [RFC7489] as follows: This document updates DMARC [RFC7489] as follows:
3.1. General Updates 3.1. General Updates
References to "Domain Owners" also apply to PSOs. References to "Domain Owners" also apply to PSOs.
3.2. Section 6.1 DMARC Policy Record 3.2. Section 6.1 DMARC Policy Record
PSD DMARC records are published as a subdomain of the PSD. For the 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 PSD ".example", the PSO would post DMARC policy in a TXT record at
"_dmarc.example". "_dmarc.example".
3.3. Section 6.5. Domain Owner Actions 3.3. Section 6.3 General Record Format
In addition to the DMARC [RFC7489] domain owner actions, PSOs that A new tag is added after fo:
require use of DMARC ought to make that information available to
receivers.
3.4. Section 6.6.3. Policy Discovery np: Requested Mail Receiver policy for non-existent subdomains
(plain-text; OPTIONAL). Indicates the policy to be enacted by the
Receiver at the request of the Domain Owner. It applies only to
non-existent subdomains of the domain queried and not to either
existing subdomains or the domain itself. Its syntax is identical
to that of the "p" tag defined below. If the 'np' tag is absent,
the policy specified by the "sp" tag (if the 'sp' tag is present)
or the policy specified by the "p" tag, if the 'sp' tag is not
present, MUST be applied for non-existent subdomains. Note that
"np" will be ignored for DMARC records published on subdomains of
Organizational Domains and PSDs due to the effect of the DMARC
policy discovery mechanism described in DMARC [RFC7489]
Section 6.6.3.
The following tag definitions from DMARC [RFC7489] are updated:
p: The sentence 'Policy applies to the domain queried and to
subdomains, unless subdomain policy is explicitly described using
the "sp" tag' is updated to read 'Policy applies to the domain
queried and to subdomains, unless subdomain policy is explicitly
described using the "sp" or "np" tags.'
sp: The sentence 'If absent, the policy specified by the "p" tag
MUST be applied for subdomains' is updated to read 'If both the
'sp' tag is absent and the 'np' tag is either absent or not
applicable, the policy specified by the "p" tag MUST be applied
for subdomains.
3.4. Section 6.5. Domain Owner Actions
In addition to the DMARC domain owner actions, PSOs that require use
of DMARC and participate in PSD DMARC ought to make that information
available to receivers. The mechanism for doing so is one of the
experimental elements of this document. See the experiment
description (Appendix A).
3.5. Section 6.6.3. Policy Discovery
A new step between step 3 and 4 is added: 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 3A. If the set is now empty and the longest PSD (Section 2.3) of the
Organizational Domain is one that the receiver has determined is Organizational Domain is one that the receiver has determined is
acceptable for PSD DMARC, the Mail Receiver MUST query the DNS for acceptable for PSD DMARC (discussed in the experiment description
a DMARC TXT record at the DNS domain matching the longest PSD (Appendix A)), 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 (Section 2.3) in place of the RFC5322.From domain in the message
(if different). A possibly empty set of records is returned. (if different). A possibly empty set of records is returned.
As an example, for a message with the Organizational Domain of As an example, for a message with the Organizational Domain of
"example.compute.cloudcompany.com.cctld", the query for PSD DMARC "example.compute.cloudcompany.com.cctld", the query for PSD DMARC
would use "compute.cloudcompany.com.cctld" as the longest PSD would use "compute.cloudcompany.com.cctld" as the longest PSD
(Section 2.3). The receiver would check to see if that PSD is listed (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 in the DMARC PSD Registry, and if so, perform the policy lookup at
"_dmarc.compute.cloudcompany.com.cctld". "_dmarc.compute.cloudcompany.com.cctld".
Note: Because the PSD policy query comes after the Organizational Note: Because the PSD policy query comes after the Organizational
Domain policy query, PSD policy is not used for Organizational Domain policy query, PSD policy is not used for Organizational
domains that have published a DMARC [RFC7489] policy. Specifically, domains that have published a DMARC policy. Specifically, this is
this is not a mechanism to provide feedback addresses (RUA/RUF) when not a mechanism to provide feedback addresses (RUA/RUF) when an
an Organizational Domain has declined to do so. Organizational Domain has declined to do so.
3.5. Section 7. DMARC Feedback 3.6. Section 7. DMARC Feedback
Operational note for PSD DMARC: For PSOs, feedback for non-existent Operational note for PSD DMARC: For PSOs, feedback for non-existent
domains is desired and useful. See Section 4 for discussion of domains is desirable and useful, just as it is for org-level DMARC
Privacy Considerations. operators. See Section 4 of this document for discussion of Privacy
Considerations.
4. Privacy Considerations 4. Privacy Considerations
These privacy considerations are developed based on the requiremetns These privacy considerations are developed based on the requirements
of [RFC6973]. The Privacy Considerations of [RFC7489] apply to this of [RFC6973]. The Privacy Considerations of [RFC7489] apply to this
document. document.
4.1. Feedback leakage 4.1. Feedback leakage
Providing feedback reporting to PSOs can, in some cases, create Providing feedback reporting to PSOs can, in some cases, create
leakage of information outside of an organization to the PSO. This leakage of information outside of an organization to the PSO. This
leakage could be potentially be utilized as part of a program of leakage could potentially be utilized as part of a program of
pervasive surveillance (See [RFC7624]). There are roughly three pervasive surveillance (See [RFC7624]). There are roughly three
cases to consider: cases to consider:
o Single Organization PSDs (e.g., ".google"), RUA and RUF reports o Single Organization PSDs (e.g., ".google"), RUA and RUF reports
based on PSD DMARC have the potential to contain information about based on PSD DMARC have the potential to contain information about
emails related to entities managed by the organization. Since emails related to entities managed by the organization. Since
both the PSO and the Organizational Domain owners are common, both the PSO and the Organizational Domain owners are common,
there is no additional privacy risk for either normal or non- there is no additional privacy risk for either normal or non-
existent Domain reporting due to PSD DMARC. existent Domain reporting due to PSD DMARC.
skipping to change at page 7, line 24 skipping to change at page 8, line 37
compliance with PSD policy. Data on non-existent cousin domains compliance with PSD policy. Data on non-existent cousin domains
would be sent to the PSO. would be sent to the PSO.
o Multi-organization PSDs (e.g., ".com") that do not mandate DMARC o Multi-organization PSDs (e.g., ".com") that do not mandate DMARC
usage: Privacy risks for Organizational Domains that have not usage: Privacy risks for Organizational Domains that have not
deployed DMARC within such PSDs are significant. For non-DMARC deployed DMARC within such PSDs are significant. For non-DMARC
Organizational Domains, all DMARC feedback will be directed to the Organizational Domains, all DMARC feedback will be directed to the
PSO. PSD DMARC is opt-out (by publishing a DMARC record at the PSO. PSD DMARC is opt-out (by publishing a DMARC record at the
Organizational Domain level) vice opt-in, which would be the more Organizational Domain level) vice opt-in, which would be the more
desirable characteristic. This means that any non-DMARC desirable characteristic. This means that any non-DMARC
organizational domain would have it's feedback reports redirected organizational domain would have its feedback reports redirected
to the PSO. The content of such reports, particularly for to the PSO. The content of such reports, particularly for
existing domains, is privacy sensitive. existing domains, is privacy sensitive.
PSOs will receive feedback on non-existent domains, which may be PSOs will receive feedback on non-existent domains, which may be
similar to existing Organizational Domains. Feedback related to such similar to existing Organizational Domains. Feedback related to such
cousin domains have a small risk of carrying information related to cousin domains have a small risk of carrying information related to
an actual Organizational Domain. To minimize this potential concern, an actual Organizational Domain. To minimize this potential concern,
PSD DMARC feedback is best limited to Aggregate Reports. Feedback PSD DMARC feedback is best limited to Aggregate Reports. Feedback
Reports carry more detailed information and present a greater risk. Reports carry more detailed information and present a greater risk.
skipping to change at page 7, line 47 skipping to change at page 9, line 12
not particpate in DMARC, any Feedback Reporting related to multi- not particpate in DMARC, any Feedback Reporting related to multi-
organizational PSDs ought to be limited to non-existent domains organizational PSDs ought to be limited to non-existent domains
except in cases where the reporter knows that PSO requires use of except in cases where the reporter knows that PSO requires use of
DMARC. DMARC.
5. Security Considerations 5. Security Considerations
This document does not change the Security Considerations of This document does not change the Security Considerations of
[RFC7489] and [RFC7960]. [RFC7489] and [RFC7960].
The risks of the issues identified in [RFC7489], Section 12.3, DNS
Security, are amplified by PSD DMARC. In particular, DNS cache
poisoning (or Name Chaining), see [RFC3833] for details, consequences
are increased because a sucessful attack would potentially have a
much wider scope.
The risks of the issues identified in [RFC7489], Section 12.5, The risks of the issues identified in [RFC7489], Section 12.5,
External Reporting Addresses, are amplified by PSD DMARC. By design, External Reporting Addresses, are amplified by PSD DMARC. By design,
PSD DMARC causes unrequested reporting of feedback to entities PSD DMARC causes unrequested reporting of feedback to entities
external to the Organizational Domain. This is discussed in more external to the Organizational Domain. This is discussed in more
detail in Section 4. detail in Section 4.
6. IANA Considerations 6. IANA Considerations
This document does not require any IANA actions. This section describes actions requested to be completed by IANA.
6.1. Subdomain Policy Tag
IANA is requested to add a new tag to DMARC Tag Registry in the
Domain-based Message Authentication, Reporting, and Conformance
(DMARC) Parameters Registry.
The entry is as follows:
+----------+-----------+---------+-------------------------------+
| Tag Name | Reference | Status | Description |
+----------+-----------+---------+-------------------------------+
| np | this | current | Requested handling policy for |
| | document | | non-existent subdomains |
+----------+-----------+---------+-------------------------------+
7. References 7. References
7.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 8, line 36 skipping to change at page 10, line 23
7.2. Informative References 7.2. Informative References
[psddmarc.org] [psddmarc.org]
multiple, "PSD DMARC Web Site", April 2019, multiple, "PSD DMARC Web Site", April 2019,
<https://psddmarc.org/>. <https://psddmarc.org/>.
[PSL] multiple, "Public Suffix List", April 2019, [PSL] multiple, "Public Suffix List", April 2019,
<https://publicsuffix.org/>. <https://publicsuffix.org/>.
[RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain
Name System (DNS)", RFC 3833, DOI 10.17487/RFC3833, August
2004, <https://www.rfc-editor.org/info/rfc3833>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226, IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008, DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>. <https://www.rfc-editor.org/info/rfc5226>.
[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, [RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598,
DOI 10.17487/RFC5598, July 2009, DOI 10.17487/RFC5598, July 2009,
<https://www.rfc-editor.org/info/rfc5598>. <https://www.rfc-editor.org/info/rfc5598>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
skipping to change at page 9, line 25 skipping to change at page 11, line 18
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>.
Appendix A. The Experiment Appendix A. The Experiment
There are two experimental questions addressed in this document: one
regarding mitigation of PSD related privacy concerns and the other on
the utility of specifying separate DMARC policies for non-existent
sub-domains.
Aditionally, as of the writing of this document operational and
policy constraints prevent this experiment from being deployed
globally. If the experiment shows that PSD DMARC solves a real
problem and can be used at a large scale, the results could prove to
be useful in removing constraints outside of the IETF that would
permit broader deployment".
A.1. PSD DMARC Privacy Concern Mitigation
To mitigate the privacy concerns associated with Multi-organization To mitigate the privacy concerns associated with Multi-organization
PSDs that do not mandate DMARC usage, see Section 4.1, a mechanism to PSDs that do not mandate DMARC usage, see Section 4.1, a mechanism to
indicate which PSDs do not present this privacy risk is appropriate. indicate which PSDs do not present this privacy risk is appropriate.
There are multiple approaches that are possible. There are multiple approaches that are possible.
The experiment is to evaluate different possible approaches. The The experiment is to evaluate different possible approaches. The
experiment will be complete when there is rough consensus on a experiment will be complete when there is rough consensus on a
technical approach that is demonstrated to be operationally usable technical approach that is demonstrated to be operationally usable
and effective at mitigating the privacy concern. and effective at mitigating the privacy concern.
skipping to change at page 10, line 15 skipping to change at page 12, line 22
As of this writing, three approaches have been proposed. None of As of this writing, three approaches have been proposed. None of
them are ideal: them are ideal:
o An extension to the Public Suffix List at [PSL] o An extension to the Public Suffix List at [PSL]
o A dedicated registry queried via DNS - an example of such a o A dedicated registry queried via DNS - an example of such a
service is described in Appendix B.1 below service is described in Appendix B.1 below
o An IANA registry o An IANA registry
A.2. Non-Existent Subdomain Policy
PSOs that plan to implement PSD DMARC have indicated that the ability
to describe distinct policies for existing and non- existing sub-
domains would facilitate PSD DMARC deployment. There are also
suggestions that it would be more generally useful for DMARC.
During the period of the experiment, uptake of the new 'np' tag will
be evaluated to support assessment of the utility of including 'np'
in a future, non-experimental update.
Appendix B. DMARC PSD Registry Examples Appendix B. DMARC PSD Registry Examples
To faciliate experimentation around data leakage mitigation, samples To facilitate experimentation around data leakage mitigation, samples
of the DNS based and IANA like registries are available at of the DNS based and IANA like registries are available at
[psddmarc.org]. [psddmarc.org].
B.1. DMARC PSD DNS Query Service B.1. DMARC PSD DNS Query Service
A sample stand-alone DNS query service is available at A sample stand-alone DNS query service is available at
[psddmarc.org]. It was developed based on the contents suggested for [psddmarc.org]. It was developed based on the contents suggested for
an IANA registry in an earlier revision of this draft. Usage of the an IANA registry in an earlier revision of this draft. Usage of the
service is described on the web site. service is described on the web site.
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