Organizational Domains and Use Policies for Domain Names
draft-deccio-dbound-organizational-domain-policy-00
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| Author | Casey Deccio | ||
| Last updated | 2015-10-13 | ||
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draft-deccio-dbound-organizational-domain-policy-00
Internet Engineering Task Force C. Deccio
Internet-Draft Verisign Labs
Intended status: Informational October 13, 2015
Expires: April 15, 2016
Organizational Domains and Use Policies for Domain Names
draft-deccio-dbound-organizational-domain-policy-00
Abstract
Various Internet protocols and applications require some mechanism
for identifying policy surrounding the use Domain Name System (DNS)
names. In this document we describe an extensible system in which
domain name policies can be discovered at various levels in the DNS
tree.
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 15, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Solution Concepts . . . . . . . . . . . . . . . . . . . . . . 3
3. Designating Organizational Domain and Use Policy . . . . . . 4
3.1. ODUP Name . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. ODUP Statement . . . . . . . . . . . . . . . . . . . . . 4
3.2.1. Version . . . . . . . . . . . . . . . . . . . . . . . 4
3.2.2. Directives . . . . . . . . . . . . . . . . . . . . . 5
3.3. org and bound Directives . . . . . . . . . . . . . . . . 6
4. Identifying Organizational Domain and Use Policy . . . . . . 6
4.1. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Policy-negative Realm . . . . . . . . . . . . . . . . . . . . 8
5.1. PSL/ODUP Equivalence Example . . . . . . . . . . . . . . 9
5.2. _odup DNS Zone . . . . . . . . . . . . . . . . . . . . . 9
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. ODUP Resolution . . . . . . . . . . . . . . . . . . . . . 10
7. Example Application Use . . . . . . . . . . . . . . . . . . . 12
7.1. Public Suffix List Replacement . . . . . . . . . . . . . 12
7.2. HTTP Cookies . . . . . . . . . . . . . . . . . . . . . . 13
7.3. DMARC . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
10. Security Considerations . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Pseudo-code for ODUP Resolution . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
The concepts of domains, subdomains, and administrative delegation
are fundamental to the Domain Name System (DNS) [RFC1034] [RFC1035].
The DNS namespace is hierarchical, and the management of subdomain
space is delegated by one entity to another throughout. However,
policies governing the use of domain names do not always align with
those lines of delegation. There are currently no generally reliable
methods to reconcile domain names with policy for their use.
As a prominent example, HTTP cookies [RFC6265] have traditionally
used ancestral relationships to determine allowable scope of
information sharing and authorization. For example, the server at
www.example.com might set a cookie with a Domain attribute of
example.com, because it is a subdomain of that name. However, this
simplistic authorization does not account for some cases, such as
cookies with a Domain attribute corresponding to a so-called "public
suffix". [RFC6265] indicates that many user agents reject such
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cookies due to security and privacy concerns. Even so, the public
suffix designation is not apparent from either the names themselves
or the delegations leading down to them from the root. Instead, a
resource, such as Mozilla's Public Suffix List (PSL) [PSL], is used
to identify public suffixes.
Another challenge with domain names is the ability to identify their
respective Organizational Domains, for applications like Domain-based
Message Authentication, Reporting, and Conformance (DMARC) [RFC7489].
[RFC7489] includes heuristics to identify an organizational domain
using a public suffix list (e.g., Mozilla's PSL [PSL]) "in the
absence of more accurate methods". Other applications have similarly
relied on a public suffix list to define an organizational domain,
whether for policy, forensics, or simple identification. However,
defining a "more accurate" method is desirable.
In this document we describe a framework for more accurately
identifying policy and organizational domains on a per-domain name
basis. The system described adds customization and flexibility to
existing systems while being fully backwards compatible with previous
mechanisms and default behaviors.
2. Solution Concepts
The major questions to be addressed by a solution in this space are
the identification of policy for a given domain name and the
identification of an organizational domain for a given domain name.
The questions are related in that the policy for a domain name might
depend on its organizational domain name, either because that policy
is defined by its organizational domain or because it depends on
organizational boundaries.
In previous solutions, policy has almost always been bound by direct
ancestral relationships. While that constraint might be lifted by
future solutions, the solution documented herein respects the
hierarchical order in the DNS: policies between domain names in which
one is not a sub-domain of the other are non-existent and out of
scope for this document.
In this context the organizational domain for a given domain name
will always be an ancestor of the domain name, if not the domain name
itself. Prior to this draft, one of the heuristics for determining
the organizational domain was using a public suffix list: the
organizational domain is the series of labels comprising the public
suffix portion of the name, plus one label ([RFC6265]). With that
methodology, for any given domain name, not a public suffix, there
was exactly one possible organizational domain. In this work, an
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organizational domain can be designated at (mostly) arbitrary levels
in the domain name's ancestry.
The notion of a "public suffix" (i.e., as included in a public suffix
list, such as Mozilla's PSL [PSL]) has brought to light the nature of
policy associated with "registry controlled domains" ([RFC6265]),
sometimes viewed as extensions of top-level domains, which have
similar policy. While domain names might appear in current versions
of such lists for a variety of reasons, the impact of their
designation is consistent: they are treated as special-purpose names,
limited in their use by applications. For example, HTTP cookies with
a Domain attribute corresponding to a public suffix are rejected by
most user agents. Similarly, public suffixes cannot be
organizational domains, e.g., for DMARC use. We refer to the set of
names above the boundary separating public suffixes from their
descendants as "policy-negative".
3. Designating Organizational Domain and Use Policy
In this section we describe the technical implementation for
designating organization domain and use policy (ODUP) for domain
names.
3.1. ODUP Name
The "_odup" label, when used as part of a domain name, carries
special meaning in the context of defining organizational domains and
policy, and the resulting domain name is referred to as an ODUP name.
In an ODUP name the sequence of labels after the _odup label (i.e.,
higher in the DNS namespace tree) comprise the organizational domain,
and the concatenation of the sequence of labels before it (i.e.,
lower in the DNS namespace tree) with those after it comprise the
policy domain.
For example, given the ODUP name foo.bar._odup.example.com, the
organizational domain is example.com, and the policy domain is
foo.bar.example.com.
3.2. ODUP Statement
A TXT record at an ODUP name contains an ODUP statement for the
policy domain.
3.2.1. Version
The ODUP statement begins with a version declaration. At this time,
the only defined version is "odup1", so the record MUST begin with
"v=odup1".
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3.2.2. Directives
Following the version declaration and a space is a series of zero or
more space-separated directives, each prepended with a qualifier, "+"
or "-". Defined directives include the following:
o httpcookie - whether the domain name may (+) or may not (-) be
used as the value of the Domain attribute of an HTTP Cookie.
o tlscert - whether (+) or not (-) this domain name may be used in a
TLS certificate.
o wildcardtlscert - whether (+) or not (-) a wildcard name directly
under this domain name may be used in a TLS certificate.
o all - for directives not otherwise specified, the default policy
is allow (+) or deny (-).
The following directives do not carry policy information, but
designate organizational domains or boundaries. Only the "+"
qualifier is valid with these directives:
o org - specifies that the policy domain itself is an organizational
domain.
o bound - designates an organizational boundary immediately below
the policy domain, indicating that domain names below the policy
domain (i.e., proper subdomains) are themselves organizational
domains.
When the "org" or "bound" directives are used in an ODUP statement,
they MUST NOT appear together in the same statement. Additionally,
the "org" directive SHOULD NOT be accompanied by any other
directives; any other directives MUST be ignored by software
interpreting the statement.
An ODUP statement MUST NOT have more than one "all" directive (with
its accompanying qualifier). If no "all" directive is supplied, an
implicit "+all" is applied.
The "all" directive SHOULD appear last in an ODUP statement. This is
for readability purposes only, as directive order otherwise doesn't
matter.
Because the "all" directive specifies the default policy for a given
policy domain, other directives in the same statement simply specify
exceptions to that default policy. Thus, the qualifier for any
directives other than "all" SHOULD be the opposite as that used with
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"all". The only side effect to non-adherence to this recommendation
is the existence of superfluous directives (i.e., because they are
already implied with the default policy). Implementors MAY add such
directives nonetheless, for added readability.
3.3. org and bound Directives
The "org" and "bound" directives of an ODUP statement are similar to
each other but serve different purposes and ultimately have different
semantics. They are similar in the sense that they are delegating
organizational domain and policy information to subdomains. They
differ in that the "org" directive designates a specific domain name
as an organizational domain, but the "bound" directive only specifies
the boundary below which domain names are organizational domains.
These differences result in additional ramifications, described
below.
Because the "org" directive names a domain name as an organizational
domain, subdomains of ODUP names whose statements include the "org"
directive SHOULD NOT exist, and subdomains MUST NOT be queried for
policy.
For example, if the ODUP statement for example._odup.com is "v=odup1
+org", then example.com is an organizational domain, and further
policy information would be sought in the "_odup.example.com" domain.
The domain name foo.example._odup.com is irrelevant.
However because the "bound" directive specifies only a boundary, and
the boundary may exist at different levels in the domain name space,
subdomains of ODUP names whose statements include "bound" are allowed
and (as described later) are queried to find the most specific policy
domains (i.e., longest match).
For example, if the ODUP statement for example._odup.com is "v=odup1
+bound", more specific policy information might be found in the
foo.example._odup.com ODUP name.
"bound" directives SHOULD only be used in the policy-negative realm
(see Section 5). In other places, the same effect can typically be
accomplished through use of the "org" directive.
4. Identifying Organizational Domain and Use Policy
The process of identifying organizational domains and policies is
referred to as ODUP resolution. It involves methodically issuing DNS
queries for DNS records of type TXT at ODUP names. The desired
outcome for ODUP resolution is an organizational domain, a policy
domain, and a policy. The process is iterative, eventually finding
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the ODUP statement corresponding to the policy name that mostly
closely matches the domain name being looked up within the lowest
designated organizational domain. Each iteration is as follows,
beginning with the root as the organizational domain:
1. If the organizational domain has the same number of labels as
the domain name in question, then return the result of querying
for the TXT record at the ODUP name formed by prepending "_odup"
to the organizational domain. Otherwise, continue.
2. Beginning with the policy domain formed by using just one label
below the organizational domain, increasing the number of labels
with each iteration, form an ODUP name.
3. Query the ODUP name formed in the previous step for a record of
type TXT.
4. If the query results in a positive response, then save the query
as longest matching record.
5. If the query results in a positive response with an "org"
directive, then continue to step Step 10.
6. If the query results in a positive response that includes a
"bound" directive, and the response is derived from a wildcard,
continue to Step 10.
7. If the query is a name error response then continue to Step 10.
8. If all the labels have been exhausted, then go to Step 10.
9. Return to step Step 2, increasing the number of labels of policy
domain.
10. If there was no positive response, then return to Step 1 using
the current organizational domain as both the policy domain and
organizational domain.
11. If the longest matching record includes an "org" directive, then
return to Step 1, using the longest matching policy domain as
the organizational domain.
12. If the longest matching record includes an "bound" directive,
then return to Step 1, using the longest matching policy domain,
plus one label, as the organizational domain.
13. Return the record corresponding to the longest matching policy
domain.
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Appendix A contains the pseudo-code for this algorithm.
4.1. Wildcards
Just as with other DNS names and record types, wildcard ODUP names
can be used to designate policy for arbitrary subdomain ODUP names.
However, in ODUP resolution, wildcard detection MUST be used.
Specifically, iteration MUST NOT continue beyond the first label of
an expanded wildcard if the response yielded an ODUP statement
containing the "bound" directive. This is to prevent the case where
a boundary is designated using the "bound" directive, but in
searching for the longest match, the boundary is bypassed.
Wildcard detection MAY also be used to stop iteration even on
directives that don't contain the "bound" directive, as it might help
increase privacy, as suggested in Section 10.
Wildcards may be detected by issuing a second lookup in response to a
positive DNS response, substituting the left-most label of the ODUP
name with "*". The responses should conform to [RFC4592]. Or if the
record is signed with DNSSEC, then the presence of a wildcard can be
detected by examining the value of the "labels" field of the
accompanying RRSIG record [RFC4034].
Note that because "bound" directives are nearly exclusive to the
policy-negative realm (see Section 3.3), the overhead associated with
compulsory wildcard lookup can be avoided almost in its entirety by
using a local copy, in which lookups are avoided altogether, as
suggested in Section 5.
5. Policy-negative Realm
The policy-negative realm is the portion of the DNS namespace that
corresponds to so-called public suffixes. The ODUP policies defining
the policy-negative realm fall under the organizational domain
corresponding to the root domain name (i.e., they are subdomains of
the ODUP name _odup) and consist of ODUP statements that use the
"bound" directive.
The policy at the root domain name itself, as contained in the TXT
record at the ODUP name "_odup", is "v=odup1 +bound -all", indicating
a global "deny" policy and an initial boundary below the root domain
name. Directives other than "bound" and "-all" MUST NOT be used in
the policy-negative realm.
The result is that the ODUP statements defining the policy-negative
realm comprise a PSL-like list. In fact, the statements comprising
the policy-negative realm can be derived from Mozilla's [PSL] and
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vice-versa. See, for example, the tables in Section 5.1. This is
useful for several reasons. The current applications and libraries
using the PSL have a way to work in parallel, one being derived from
the other, for backwards compatibility and possible transition. It
also enables consumer applications to work offline by simply
downloading all the policy-negative statements when those are
sufficient for the purposes of the application.
Even when a self-contained listing of the policy-negative names is
locally available but insufficient for the needs of the consumer
application (i.e., a more specific assurance of policy is necessary),
this resource can provide an efficient starting place for ODUP
resolution. Rather than starting with the root domain name as the
organizational domain, the shortest organizational domain below the
policy-negative boundary is used first. This increases efficiency by
avoiding network latency associated with unnecessary DNS lookups.
5.1. PSL/ODUP Equivalence Example
+---+-----------+
| | PSL Entry |
+---+-----------+
| 1 | uk |
| 2 | co.uk |
| 3 | *.sch.uk |
+---+-----------+
Select PSL Entries
+---+-----------------+------------------+
| | ODUP Name | ODUP Statement |
+---+-----------------+------------------+
| 1 | uk._odup. | "v=odup1 +bound" |
| 2 | co.uk._odup. | "v=odup1 +bound" |
| 3 | *.sch.uk._odup. | "v=odup1 +bound" |
+---+-----------------+------------------+
Corresponding ODUP Names and Statements
5.2. _odup DNS Zone
ODUP resolution introduces a new label, _odup, under the DNS root.
Technically speaking, this doesn't create any problems, as it is
simply treated as another node in the DNS, even though it doesn't fit
the mold of other top-level domains. This is in large part because
there are no DNS delegations (i.e., via NS records).
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All ODUP names within the policy-negative realm and thus under the
root-level organizational domain exist under the _odup top-level
domain. This means that the entire set of records comprising the
policy-negative realm can be maintained as the contents of a single
DNS zone.
Maintaining the policy-negative realm as a DNS zone has several
advantages. The zone contents can be maintained, published, and
accessed in a well-known format. For example, in addition to
providing responses to normal DNS queries, it might be made available
via zone transfers, or for download over HTTP. Additionally, the
fact that a zone has a serial (as a field in the record data of the
SOA record), applications can determine through a query of type SOA
whether the contents of the policy-negative realm have changed.
The hosting and maintenance of the _odup DNS zone might appropriately
be the joint responsibility of the Internet Assigned Numbers
Authority (IANA)[IANA] and the CA/Browser Forum[CAB-Forum].
6. Examples
We provide several examples and in this section of ODUP designation,
resolution, and potential application.
6.1. ODUP Resolution
Example DNS entries are listed in Table 1 and illustrated in
Figure 1. The resulting policies are listed in Table 2.
+-------------+-----------------+------------------------+
| Org. Domain | ODUP Name | ODUP Statement |
+-------------+-----------------+------------------------+
| . | _odup. | "v=odup1 -all" |
| . | uk._odup. | "v=odup1 +bound" |
| . | co.uk._odup. | "v=odup1 +bound" |
| . | *.sch.uk._odup. | "v=odup1 +bound" |
| a.uk. | c.b._odup.a.uk. | "v=odup1 +org" |
| a.uk. | e._odup.a.uk. | "v=odup1 -httpcookie" |
| c.b.a.uk. | _odup.c.b.a.uk. | "v=odup1 -tlswildcard" |
+-------------+-----------------+------------------------+
Example ODUP statements and corresponding ODUP names and
organizational domains.
Table 1: Example DNS entries
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.
|
uk
/ | \
/ | \
--+-- | \
a co sch
| | |
/ \ --+-- h
b e * g |
| | --+--
--+-- f i
c *
|
d
Illustration of the namespace associated with ODUP names and
statements listed in Table 1. Each node represents a DNS label in
its place in the DNS namespace hierarchy. Horizontal lines represent
organizational boundaries, and asterisks (*) represent explicit
policy statements.
Figure 1
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+-------------+-------------+-------------+-------------------------+
| Domain Name | Org. Domain | Policy | Policy ([D]efault, |
| | | Domain | [E]xplicit, |
| | | | [I]nherited) |
+-------------+-------------+-------------+-------------------------+
| . | . | . | -all (E) |
| uk. | . | . | -all (I) |
| a.uk. | a.uk. | a.uk. | +all (D) |
| b.a.uk. | a.uk. | a.uk. | +all (I) |
| c.b.a.uk. | c.b.a.uk. | c.b.a.uk. | -tlswildcard +all (E) |
| d.c.b.a.uk. | c.b.a.uk. | c.b.a.uk. | -tlswildcard +all (I) |
| e.a.uk. | a.uk. | e.a.uk. | -httpcookie +all (E) |
| f.e.a.uk. | a.uk. | e.a.uk. | -httpcookie +all (I) |
| co.uk. | . | . | -all (I) |
| g.co.uk. | g.co.uk. | g.co.uk. | +all (D) |
| sch.uk. | . | . | -all (I) |
| h.sch.uk. | . | . | -all (I) |
| i.h.sch.uk. | i.h.sch.uk. | i.h.sch.uk. | +all (D) |
+-------------+-------------+-------------+-------------------------+
Policies resulting from the ODUP names and corresponding statements
listed in Table 1 and illustrated in Figure 1. The version
information (i.e., "v=odup1") has been stripped from the policy for
readability. [D]efault policy means that there was no explicit
policy designated for the organization, so the default ("v=odup1
+all") is used. [E]xplicit policy means that a policy is defined for
the domain name in question. [I]nherited policy means that it is
inherited from the closest ancestor with default or explicit policy.
Table 2: Effective ODUP Policies
7. Example Application Use
While designating the manner in which ODUP is applied in applications
is beyond the scope of this document, for added clarity and utility,
we provide some examples of how it might be consumed, using the
examples data Section 6 for reference.
7.1. Public Suffix List Replacement
As mentioned in Section 5, the ODUP statements within the policy-
negative realm provide a drop-in replacement for the public suffix
list(s) from which they are initially derived. Whether used offline
(i.e., having been been downloaded and optionally converted to a
legacy list format) or learned through DNS queries, the applications
that previously used a public suffix list, can use the contents of
the _odup domain to achieve the same baseline behavior. That
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includes HTTP cookie policy [RFC6265], identifying organizational
domains for DMARC [RFC7489], and other use.
Beyond this baseline behavior provided by installation of the policy-
negative realm, ODUP provides the opportunity for additional
functionality, described subsequently.
7.2. HTTP Cookies
[RFC6265] directs user agents to reject HTTP cookies whose Domain
attribute specifies a scope that does not include the origin server.
The origin server is within scope if its name is equal to or a
subdomain of the value of the Domain attribute. Basically, this
allows an origin server to set a cookie with a Domain attribute value
of any domain name in its ancestry (but below the public suffix
boundary).
With ODUP policy HTTP cookies can be built on organizational
boundaries, including not only the policy-negative realm, but also at
other designated points. For example, given the organizational
boundary between b.a.uk and c.b.a.uk, the origin server d.c.b.a.uk
can set a cookie for d.c.b.a.uk and c.b.a.uk, but not for b.a.uk.
Likewise, when a user-agent has a cookie with domain b.a.uk, it will
not send it when communicating with d.c.b.a.uk or c.b.a.uk because
organizational boundaries supercede "domain-matching" ([RFC6265]).
In addition, cookie policies between organizational boundaries can be
specified using the "httpcookie" directive. For example, neither
f.e.a.uk nor e.a.uk can be the value of the Domain attribute of an
HTTP cookie, even though they are not public suffixes. However, this
doesn't mean that user agents communicating with f.e.a.uk or e.a.uk
cannot set or return cookies for a.uk, so it is not particularly
useful, except within the policy-negative realm.
7.3. DMARC
Whereas [RFC7489] includes only provides a single possible
organizational domain for any given domain name, ODUP allows the
organizational domain to be specified, such that it can be designated
and identified from anywhere within the ancestral namespace.
8. Contributors
The namespace convention used for ODUP names resembles and was
inspired by that developed in [I-D.levine-orgboundary], for which we
acknowledge John Levine's efforts in this area.
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9. IANA Considerations
The introduction of a new top-level domain (_odup) under the root
zone requires approval and coordination with the IANA, who might also
have a hand in maintaining the zone.
10. Security Considerations
Applications depending on the mechanisms herein described to learn
organizational domains and polices for domain names have their own
security considerations. We reference [RFC6265] and [RFC7489] as
examples of those.
Because the ODUP resolution mechanisms themselves rely on DNS queries
(and zone transfers and/or HTTP, for the policy-negative realm), its
security is only as secure as that of the underlying lookup/download
mechanisms themselves. DNSSEC and HTTPS can be useful in ensuring
authenticity of policy statements through the respective lookup
mechanisms.
The iterative query process utilized by ODUP resolution can be
potentially revealing of queries to higher DNS authorities, in part
because of the necessity of finding the longest matched ODUP names.
This is in contrast to the principles of minimum disclosure to
maximize DNS privacy. This is mitigated by stopping at NXDOMAIN
responses, as described in Section 4. Additionally, referencing a
locally downloaded version of the policy-negative realm for partial
or "sufficient" ODUP resolution, as suggested in Section 5 can reduce
queries to the _odup zone.
11. References
11.1. Normative References
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC4034, March 2005,
<http://www.rfc-editor.org/info/rfc4034>.
[RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name
System", RFC 4592, DOI 10.17487/RFC4592, July 2006,
<http://www.rfc-editor.org/info/rfc4592>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
<http://www.rfc-editor.org/info/rfc6265>.
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11.2. Informative References
[CAB-Forum]
"CA/Browser Forum", 2015, <https://cabforum.org/>.
[I-D.levine-orgboundary]
Levine, J., "Publishing Organization Boundaries in the
DNS", draft-levine-orgboundary-02 (work in progress), July
2013.
[IANA] "Internet Assigned Numbers Authority", 2015,
<https://iana.org/>.
[PSL] Mozilla Foundation, "Public Suffix List", 2015,
<https://publicsuffix.org/>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<http://www.rfc-editor.org/info/rfc7489>.
Appendix A. Pseudo-code for ODUP Resolution
function resolveODUP(N = [l(n)...l(1)], orgBoundary)
{
Require: N = [l(n)...l(1)], n >= 0
(a sequence of labels representing domain name, N)
Require: orgBoundary, 0 <= orgBoundary <= n
(an integer representing an index into N)
Return: a three-tuple consisting of:
- policyDomain, the domain name from the which the policy
was derived
- orgDomain, the organizational domain of N
- policy, the raw policy resulting from TXT DNS queries
if orgBoundary = 0
{
// orgDomain is the root and contains no labels
orgDomain := []
}
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else
{
// orgDomain consists of labels 1 through orgBoundary
orgDomain := [l(orgBoundary)...l(1)]
}
if orgBoundary = n
{
// Base case: orgDomain is composed of all labels
testDomain := ["_odup"] | orgDomain
queryResult := queryDNS(testDomain, "TXT")
if queryResult is an answer
{
// return the contents of the TXT record
return orgDomain, orgDomain, queryResult
}
else
{
// return an empty policy
return orgDomain, orgDomain, ""
}
}
subDomainLabels := n - (orgBoundary + 1)
longestMatch := NULL
longestMatchBoundary := NULL
for all i in [0...subDomainLabels]
{
subDomain := [l(orgBoundary + 1 + i)...l(orgBoundary + 1)]
testDomain := subDomain | ["_odup"] | orgDomain
queryResult := queryDNS(testDomain, TXT)
if queryResult is an answer
{
// Set longestMatch to the value of queryResult
longestMatch := queryResult
longestMatchBoundary := i
if queryResult includes "+org"
{
// If this was a organizational domain designation,
// then don't go any further; the organization will
// dictate policy
break
}
if queryResult includes "+bound" AND
was synthesized from wildcard
{
// If this was a boundary designation, and the answer
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// was synthesized from a wildcard, no further
// lookups must be performed
break
}
}
else if queryResult is NXDOMAIN
{
// An NXDOMAIN result means that no further lookups are
// necessary, as there is no subtree
break
}
}
if longestMatch is not NULL
{
// If a policy has been found, then look for +org or +bound
// directives, which indicate that the organizational domain and
// policy are (at least) one or two levels lower than the value
// of longestMatchBoundary, respectively. resolveODUP is then
// called recursively.
if longestMatch includes "+org"
{
return resolveODUP([l(n)...l(i)], longestMatchBoundary + 1)
}
else if longestMatch includes "+bound" and orgBoundary + 2 <= n
{
return resolveODUP([l(n)...l(i)], longestMatchBoundary + 2)
}
// With no +org or +bound directives present, the orgDomain and
// policy remain as they were looked up, and are returned with
// the policy domain
return [l(longestMatchBoundary)...l(1)], orgDomain, longestMatch
}
else
{
// There is no more specific policy for the given name, so
// return the policy for the orgDomain
return resolveODUP(orgDomain, orgBoundary)
}
}
Author's Address
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Casey Deccio
Verisign Labs
12061 Bluemont Way
Reston, VA 20190
USA
Phone: +1 703-948-3200
Email: cdeccio@verisign.com
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