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Internet Engineering Task Force                                C. Deccio
Internet-Draft                                             Verisign Labs
Intended status: Informational                              July 1, 2016
Expires: January 2, 2017


        Organizational Domains and Use Policies for Domain Names
          draft-deccio-dbound-organizational-domain-policy-03

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.

   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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 2, 2017.

Copyright Notice

   Copyright (c) 2016 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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
     1.1.  Reserved Words  . . . . . . . . . . . . . . . . . . . . .   3
   2.  Solution Concepts . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Designating Organizational Domain and Use Policy  . . . . . .   4
     3.1.  ODUP Name . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  ODUP Statement  . . . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  Version . . . . . . . . . . . . . . . . . . . . . . .   5
       3.2.2.  Directives  . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Directive Considerations  . . . . . . . . . . . . . . . .   6
       3.3.1.  all Directive . . . . . . . . . . . . . . . . . . . .   6
       3.3.2.  Directive Defaults  . . . . . . . . . . . . . . . . .   7
       3.3.3.  org Directive . . . . . . . . . . . . . . . . . . . .   7
       3.3.4.  bound Directive . . . . . . . . . . . . . . . . . . .   7
         3.3.4.1.  Argument to bound directive . . . . . . . . . . .   8
       3.3.5.  fetch Directive . . . . . . . . . . . . . . . . . . .   9
   4.  Identifying Organizational Domain and Use Policy  . . . . . .   9
   5.  Policy-negative Realm . . . . . . . . . . . . . . . . . . . .  11
     5.1.  PSL/ODUP Equivalence Example  . . . . . . . . . . . . . .  12
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     6.1.  ODUP Resolution . . . . . . . . . . . . . . . . . . . . .  13
   7.  Example Application Use . . . . . . . . . . . . . . . . . . .  16
     7.1.  Public Suffix List Replacement  . . . . . . . . . . . . .  16
     7.2.  HTTP Cookies  . . . . . . . . . . . . . . . . . . . . . .  17
     7.3.  DMARC . . . . . . . . . . . . . . . . . . . . . . . . . .  17
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  17
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  18
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     11.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  Pseudo-code for ODUP Resolution  . . . . . . . . . .  20
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  22

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



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   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
   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.

1.1.  Reserved Words

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

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




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   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
   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 (TLDs), 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.



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3.2.  ODUP Statement

   A TXT record at an ODUP name contains an ODUP statement for the
   policy domain.  The formal syntax for an ODUP statement, using
   [RFC5234], is the following:

   statement        =   version *( SP qual-directive )

   version          =   "v=odup1"

   qual-directive   =   qualifier directive [ arg-sep arg ]

   qualifier        =   %x2B / %x2D
                             ; addition sign (+) or hyphen (-)

   directive        =   1*( directive-char )
                             ; one or more <directive-char>s

   directive-char   =   ALPHA / DIGIT / %x2D
                             ; letter, digit, or hyphen

   arg-sep          =   %x3A
                             ; colon (:)

   arg              =   1*( VCHAR )
                             ; one or more <VCHAR>s

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".

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:
   either "+" or "-".  Additionally, each directive may optionally
   include a single argument, which is affixed to the end of the
   directive, immediately after a colon (":").

   Only two policy-related directives are defined in this document.
   Unless otherwise specified, no arguments are defined for the
   directives.

   o  httpcookie - whether the domain name may (+) or may not (-) be
      used as the value of the Domain attribute of an HTTP Cookie.




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   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, or offer other non-
   policy information.  Only the "+" qualifier is valid with these
   directives:

   o  org - specifies that the policy domain itself is an organizational
      domain (See Section 3.3.3).

   o  bound - designates an organizational boundary below the policy
      domain.  Domain names below that boundary are organizational
      domains (See Section 3.3.4).  The bound directive may optionally
      include a numeric argument specifying the number of labels below
      the "_odup" label within the domain name owning the ODUP
      statement.  This is used to detect wildcard synthesis by ODUP
      resolvers (see Section 3.3.4.1).

   o  fetch - designates a means for retrieving an ODUP policy realm in
      its entirety for local use.  An argument is required, which
      designates one or more comma-separated URLs to use for retrieving
      the realm (See Section 3.3.5).

3.3.  Directive Considerations

3.3.1.  all Directive

   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
   directives other than "all" SHOULD be the opposite as that used with
   "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.







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3.3.2.  Directive Defaults

   The presence of each directive with its qualifier indicates intended
   policy associated with the name in question.  Because the this draft
   introduces new behaviors, the positive ("+") value for any directive
   MUST match default behavior preceding this document, in order to
   maintain backwards compatibility.  In this manner, the default policy
   ("+all") matches previous behavior.

3.3.3.  org Directive

   The "org" directive designates a specific domain name as an
   organizational domain.  Because the "org" directive designates 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, given the following ODUP statement:

      example._odup.com.  IN TXT "v=odup1 +org"

   example.com is an organizational domain, and further policy
   information would be sought in the "_odup.example.com" DNS domain.
   The domain name foo.example._odup.com is irrelevant.

   An "org" directive MUST NOT appear together with a "bound" directive
   in the same ODUP statement.  Additionally, the "org" directive SHOULD
   NOT be accompanied by any other directives; any other directives MUST
   be ignored by software interpreting the statement.

3.3.4.  bound Directive

   Rather than specifying an organizational domain directly, like the
   "org" directive does, the "bound" directive specifies organizational
   domains indirectly by designating a boundary below which the
   organization domain exists.  The actual boundary might not be
   immediately below the policy name specified by the "bound" statement
   at the corresponding ODUP name.  Rather, it is a potentially uneven
   line dividing the subdomain space below that name.  This boundary is
   drawn immediately below the lowest name in an unbroken line of
   descendants of the ODUP name for which there are no ODUP statements
   that include "org".  Note that this line of descendants includes ODUP
   names with statements including "bound", statements with policy
   directives other than "org" and "bound", and existing ODUP names with
   no statements at all.  It does not, however, include non-existent
   ODUP names.





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   For example, suppose the ODUP information for www.sub.example.com is
   being sought, and within the com organizational domain we find the
   following ODUP statement:

      example._odup.com.  IN TXT "v=odup1 +bound"

   Having this knowledge, if a subsequent query for
   sub.example._odup.com/TXT results in a name error (NXDOMAIN), then
   the boundary exists immediately below example.com, such that
   sub.example.com is the organizational domain.  Likewise, if the query
   for sub.example._odup.com/TXT results in an ODUP statement with the
   "org" directive, such also indicates that the boundary is immediately
   below example.com.  However, if the query results in a NODATA
   response, then the boundary is below sub.example.com, and additional
   queries are required to determine its precise location.

   Subdomains of ODUP names with statements that include a "bound"
   directive are not restricted in the same way as they are in
   connection with the use of the "org" directive (See Section 3.3.3).
   However, subdomains of ODUP names having "bound" statements SHOULD
   NOT include statements that don't include "org" or "bound".  Any such
   statements MUST be ignored.

   "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.

   Finally, a "bound" directive MUST NOT appear together with an "org"
   directive in the same ODUP statement.

3.3.4.1.  Argument to bound directive

   Wildcard ODUP names (i.e., those whose leftmost, or lowest, label is
   *[RFC4592]) are just as valid for ODUP names as they are generally
   for the DNS.  However, for wildcard ODUP names whose corresponding
   statements include "bound", the boundary might not be detected
   properly if it is not known that the record is synthesized from a
   wildcard.  Specifically, the wildcard synthesis would always yield a
   positive answer, and the lack of an NXDOMAIN response would cause an
   application identifying boundaries to continue to look for the
   longest match.

   The numeric argument to the bound directive is used when an ODUP
   statement is used at a wildcard DNS name.  The value is the number of
   non-* labels below the "_odup" label.  For example, the argument to
   the "bound" directive for the ODUP name *.b.a._odup.example.com.
   would always be 2.




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3.3.5.  fetch Directive

   The "fetch" directive is used to designate one or more Uniform
   Resource Identifiers (URIs) [RFC3986] from which the ODUP statements
   for a given organizational domain can be downloaded for local
   reference.  The URIs, delimited by semi-colons, comprise the argument
   to the "fetch" directive.

   The statements for an organizational domain are downloaded either via
   zone transfer [RFC1034], HTTP [RFC7230] [RFC7231], or [RFC2818]
   HTTPS.  In the case of an HTTP(s) download, the file is maintained in
   text format, structured as DNS zone master file [RFC1034] and
   retrieved using the GET method [RFC7231].  In any case, the contents
   of the download correspond to the records comprising the "_odup"
   subdomain of the organizational domain.

   The URI for a zone transfer uses "axfr" as its scheme.  The host
   component is optional; if not specified, any of the authoritative
   servers advertised in the NS record set may be used.  The path
   component is blank.  The following are valid URIs for use in the
   fetch directive for example.com:

      axfr://

      axfr://ns1.example.com

      http://www.example.com/odup.zone

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 and completes in O(n)
   (upper bound) time, where n corresponds to the number of labels in
   the name.  The algorithm finds 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 single right-most label
   (i.e., TLD) as the organizational domain.  We use www.example.com to
   illustrate policy lookup in each step.

   1.   Reset the longest matching record and the longest existing name.

   2.   Begin with the ODUP name formed by prepending the "_odup" label
        to the current organizational domain, and with each subsequent




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        iteration increase the number of policy domain labels below the
        "_odup" label by one to form an ODUP name.

        Example: If the current organizational domain is com, then the
        iterative ODUP names would be: _odup.com, example._odup.com,
        www.example._odup.com.

   3.   Issue a query using the ODUP name formed in the previous step
        for a record of type TXT.

   4.   If the query results in response code 0 (NOERROR), then save
        this ODUP name as the longest existing name.

   5.   If the query yields a response with an ODUP policy, and either
        the ODUP statement includes an "org" or "bound" directive or the
        previous longest matching record includes neither an "org" nor a
        "bound" directive, then save the record as the longest matching
        record.

   6.   If the query yields a response with an ODUP policy that includes
        an "org" directive, then go to Step 11.

   7.   If the query yields a response with an ODUP policy that includes
        a "bound" directive, and the response is derived from a
        wildcard, go to Step 11.

   8.   If the query results in response code 3 (name error or
        NXDOMAIN), go to Step 11.

        Example: If a query for _odup.com results in a name error, then
        we don't continue to example._odup.com.

   9.   If all the labels have been exhausted, then go to Step 11.

        Example: If the current organizational domain is com, and we
        have already looked for policy at the ODUP names _odup.com,
        example._odup.com, and www.example._odup.com, then we go to Step
        11.

   10.  Return to step Step 2, increasing the number of labels of policy
        domain.

        Example: If the current organizational domain is com, and we
        have just looked for policy at _odup.com, then we would now look
        for policy at example._odup.com.






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   11.  If there was no positive response (i.e., longest matching record
        is not set), then return an empty policy under the current
        organizational domain.

   12.  If the longest matching record includes an "org" directive, then
        return to Step 1, using the longest matching policy domain as
        the organizational domain.

        Example: If the ODUP statement at example._odup.com included an
        "org" directive, then we would next look for policy at
        _odup.example.com, then www._odup.example.com.

   13.  If the longest matching record includes a "bound" directive, and
        the number of labels in the longest existing name is less than
        those in the name whose policy is being looked up, then return
        to Step 1, using the longest existing name domain, plus one
        label, as the organizational domain.

        Example: If the ODUP statement at _odup.com included a "bound"
        directive, then we would next look for policy at
        _odup.example.com, then www._odup.example.com.

   14.  Return the record corresponding to the longest matching policy
        domain.

   Appendix A contains the pseudo-code for this algorithm.

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 _odup subdomain of each TLD
   and consist of ODUP statements that use the "bound", "org", and
   "-all" directives.

   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
   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 (fully or partially)
   offline by simply downloading all the policy-negative statements when
   those are sufficient for the purposes of the application.

   To enable local reference of ODUP statements within the policy-
   negative realm, "fetch" statements SHOULD be specified for ODUP



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   statements found at ODUP names immediately under TLDs, e.g.,
   _odup.com.  Because the nature of TLDs has changed [NewgTLDs], some
   TLDs might not have a complete negative policy, and thus might be
   "below" the policy negative realm.  Such TLDs MAY choose to use a
   default policy (which is not negative) by not publishing an ODUP
   statement at all, in which case the inclusion of the "fetch"
   directive does not apply.

   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 TLD 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.

   Working from a locally available version of the policy-negative realm
   is not only more efficient, but it also minimizes information
   disclosure to delegating authorities and is thus more privacy-
   adhering.

   Directives other than "bound", "org", "fetch", and "-all" MUST NOT be
   used in the policy-negative realm.

5.1.  PSL/ODUP Equivalence Example

                             +---+-----------+
                             |   | PSL Entry |
                             +---+-----------+
                             | 1 | uk        |
                             | 2 | co.uk     |
                             | 3 | *.ck      |
                             | 4 | !www.ck   |
                             +---+-----------+

                            Select PSL Entries














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       Note that "fetch" directives are excluded to maximize space.

              +---+---------------+-------------------------+
              |   |     ODUP Name | ODUP Statement          |
              +---+---------------+-------------------------+
              | 1 |     _odup.uk. | "v=odup1 +bound -all"   |
              | 2 |  co._odup.uk. | "v=odup1 +bound -all"   |
              | 3 |   *._odup.ck. | "v=odup1 +bound:0 -all" |
              | 4 | www._odup.ck. | "v=odup1 +org"          |
              +---+---------------+-------------------------+

                  Corresponding ODUP Names and Statements

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 3.

        +-------------+-----------------+-------------------------+
        | Org. Domain |       ODUP Name | ODUP Statement          |
        +-------------+-----------------+-------------------------+
        |         uk. |       _odup.uk. | "v=odup1 +bound -all"   |
        |         uk. |    co._odup.uk. | "v=odup1 +bound -all"   |
        |         ck. |       _odup.ck. | "v=odup1 +bound -all"   |
        |         ck. |     *._odup.ck. | "v=odup1 +bound:0 -all" |
        |         ck. |   www._odup.ck. | "v=odup1 +org"          |
        |       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 -httpcookie"   |
        +-------------+-----------------+-------------------------+

         Example ODUP statements and corresponding ODUP names and
   organizational domains.  Note that "fetch" directives are excluded to
                              maximize space.

                       Table 1: Example DNS entries










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                            .
                            |
                    +-------+-------+
                   /                 \
                 uk *                 ck *
                  |                    |
              +---+---+              +-+-+
             /         \            /     \
         ===+===        \          /    ===+===
            a           co        h       www
            |            |        |
          +-+-+          |        |
         /     \      ===+===  ===+===
        b       e *      g        i
        |       |
     ===+===    |
        c *     f
        |
        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.  Double horizontal lines
   (====) represent organizational boundaries, and asterisks (*)
   represent explicit policy statements.

                                 Figure 1

       +-------------+----------------------+---------------+------+
       | Domain Name |          DNS Queries | Responses     | Step |
       +-------------+----------------------+---------------+------+
       |          uk |         _odup.uk/TXT | +bound -all   | 14   |
       |        a.uk |         _odup.uk/TXT | +bound -all   | 10   |
       |             |       a._odup.uk/TXT | NXDOMAIN      | 13   |
       |             |       _odup.a.uk/TXT | NODATA        | 11   |
       |      b.a.uk |         _odup.uk/TXT | +bound -all   | 10   |
       |             |       a._odup.uk/TXT | NXDOMAIN      | 13   |
       |             |       _odup.a.uk/TXT | NODATA        | 10   |
       |             |     b._odup.a.uk/TXT | NODATA        | 11   |
       |    c.b.a.uk |         _odup.uk/TXT | +bound -all   | 10   |
       |             |       a._odup.uk/TXT | NXDOMAIN      | 13   |
       |             |       _odup.a.uk/TXT | NODATA        | 10   |
       |             |     b._odup.a.uk/TXT | NODATA        | 10   |
       |             |   c.b._odup.a.uk/TXT | +org          | 12   |
       |             |   _odup.c.b.a.uk/TXT | -httpcookie   | 14   |
       |  d.c.b.a.uk |         _odup.uk/TXT | +bound -all   | 10   |
       |             |       a._odup.uk/TXT | NXDOMAIN      | 13   |
       |             |       _odup.a.uk/TXT | NODATA        | 10   |



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       |             |     b._odup.a.uk/TXT | NODATA        | 10   |
       |             |   c.b._odup.a.uk/TXT | +org          | 12   |
       |             |   _odup.c.b.a.uk/TXT | -httpcookie   | 10   |
       |             | d._odup.c.b.a.uk/TXT | NXDOMAIN      | 14   |
       |      e.a.uk |         _odup.uk/TXT | +bound -all   | 10   |
       |             |       a._odup.uk/TXT | NXDOMAIN      | 13   |
       |             |       _odup.a.uk/TXT | NODATA        | 10   |
       |             |     e._odup.a.uk/TXT | -httpcookie   | 14   |
       |    f.e.a.uk |         _odup.uk/TXT | +bound -all   | 10   |
       |             |       a._odup.uk/TXT | NXDOMAIN      | 13   |
       |             |       _odup.a.uk/TXT | NODATA        | 10   |
       |             |     e._odup.a.uk/TXT | -httpcookie   | 10   |
       |             |   f.e._odup.a.uk/TXT | NXDOMAIN      | 14   |
       |       co.uk |         _odup.uk/TXT | +bound -all   | 10   |
       |             |      co._odup.uk/TXT | +bound -all   | 14   |
       |     g.co.uk |         _odup.uk/TXT | +bound -all   | 10   |
       |             |      co._odup.uk/TXT | +bound -all   | 10   |
       |             |    g.co._odup.uk/TXT | NXDOMAIN      | 13   |
       |             |    _odup.g.co.uk/TXT | NXDOMAIN      | 11   |
       |          ck |         _odup.ck/TXT | +bound -all   | 14   |
       |        h.ck |         _odup.ck/TXT | +bound -all   | 10   |
       |             |       h._odup.ck/TXT | +bound:0 -all | 14   |
       |      i.h.ck |         _odup.ck/TXT | +bound -all   | 10   |
       |             |       h._odup.ck/TXT | +bound:0 -all | 13   |
       |             |     _odup.i.h.ck/TXT | NXDOMAIN      | 11   |
       |      www.ck |         _odup.ck/TXT | +bound -all   | 10   |
       |             |     www._odup.ck/TXT | +org          | 12   |
       |             |     _odup.www.ck/TXT | NXDOMAIN      | 11   |
       +-------------+----------------------+---------------+------+

    The sequence of queries, responses, and corresponding steps (i.e.,
      from Section 4) followed for ODUP resolution of each name.  The
     version information (i.e., "v=odup1") has been stripped from the
                          policy for readability.

             Table 2: DNS Queries for ODUP Resolution Examples















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   +-------------+-----------+-----------+-----------------------------+
   | Domain Name |      Org. |    Policy | Policy ([D]efault,          |
   |             |    Domain |    Domain | [E]xplicit, [I]nherited)    |
   +-------------+-----------+-----------+-----------------------------+
   |         uk. |       uk. |       uk. | -all (E)                    |
   |       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. | -httpcookie +all (E)        |
   | d.c.b.a.uk. | c.b.a.uk. | c.b.a.uk. | -httpcookie +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. |       uk. |    co.uk. | -all (I)                    |
   |    g.co.uk. |  g.co.uk. |  g.co.uk. | +all (D)                    |
   |         ck. |       ck. |       ck. | -all (E)                    |
   |       h.ck. |       ck. |     h.ck. | -all (I)                    |
   |     i.h.ck. |   i.h.ck. |   i.h.ck. | +all (D)                    |
   |     www.ck. |   www.ck. |   www.ck. | +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 3: 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
   includes HTTP cookie policy [RFC6265], identifying organizational
   domains for DMARC [RFC7489], and other use.



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   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

   This document contains no requests for IANA.

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

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [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>.






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   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              DOI 10.17487/RFC6265, April 2011,
              <http://www.rfc-editor.org/info/rfc6265>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <http://www.rfc-editor.org/info/rfc7231>.

11.2.  Informative References

   [I-D.levine-orgboundary]
              Levine, J., "Publishing Organization Boundaries in the
              DNS", draft-levine-orgboundary-02 (work in progress), July
              2013.

   [NewgTLDs]
              ICANN, "New Generic Top-Level Domains", 2016,
              <http://newgtlds.icann.org/>.

   [PSL]      Mozilla Foundation, "Public Suffix List", 2016,
              <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>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <http://www.rfc-editor.org/info/rfc2818>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <http://www.rfc-editor.org/info/rfc7230>.







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   [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 >= 1
       (a sequence of labels representing domain name, N)
     Require: orgBoundary, 1 <= 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

     // orgDomain consists of labels 1 through orgBoundary
     orgDomain := [l(orgBoundary)...l(1)]

     subDomainLabels := n - orgBoundary
     longestMatch := NULL
     longestMatchBoundary := NULL
     existingLabels := 0
     for all i in [0...subDomainLabels]
     {
         if i = 0
         {
             subDomain := []
         }
         else
         {
             subDomain := [l(orgBoundary + i)...l(orgBoundary + 1)]
         }
         testDomain := subDomain | ["_odup"] | orgDomain
         queryResult := queryDNS(testDomain, TXT)

         if queryResult is either NOERROR or NODATA AND i > 0
         {
             // Update existingLabels because the name exists.
             // Only do this for labels other than _odup
             // (hence the test for i > 0).
             existingLabels := existingLabels + 1
         }

         if queryResult is an answer



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         {
             // Update longestMatch by giving org and bound highest
             // priority and ignoring policy statements below "bound".
             if queryResult includes "+org" OR
                 queryResult includes "+bound" OR
                 longestMatch doesn't include "+bound"
             {
                 longestMatch := queryResult
                 longestMatchBoundary := i
             }

             if queryResult includes "+org"
             {
                 // If this was an 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
                 // was synthesized from a wildcard, no further
                 // lookups must be performed
                 break
             }
         }
         else if queryResult is NXDOMAIN response
         {
             // 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 will cause resolveODUP() to be called
         // recursively.  A +org directive indicates that the
         // organizational domain and policy are (at least) one level
         // lower than the value of longestMatchBoundary.
         if longestMatch includes "+org"
         {
             return
                 resolveODUP(N, orgBoundary + longestMatchBoundary)
         }
         // A +bound directive indicates that the organizational domain



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         // and policy are (at least) one level lower than the value of
         // existingLabels.
         else if longestMatch includes "+bound" AND
                 orgBoundary + existingLabels <= n
             {
                 return resolveODUP(N, orgBoundary + existingLabels)
             }
         }

         // 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(orgBoundary + longestMatchBoundary)...l(1)],
             orgDomain, longestMatch
     }

     // Return an empty policy
     return orgDomain, orgDomain, ""

 }

Author's Address

   Casey Deccio
   Verisign Labs
   12061 Bluemont Way
   Reston, VA  20190
   USA

   Phone: +1 703-948-3200
   Email: cdeccio@verisign.com




















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