DBOUND                                                       A. Sullivan
Internet-Draft                                                 Dyn, Inc.
Intended status: Standards Track                               J. Hodges
Expires: August 21, 2016                                          PayPal
                                                               J. Levine
                                                    Taughannock Networks
                                                       February 18, 2016

        DBOUND: DNS Administrative Boundaries Problem Statement


   Some Internet client entities on the Internet make inferences about
   the administrative relationships among services on the Internet based
   on the domain names at which they are offered.  At present, it is not
   possible to ascertain organizational administrative boundaries in the
   DNS, therefore such inferences can be erroneous in various ways.
   Mitigation strategies deployed so far will not scale.  This memo
   outlines what issues are to be addressed.

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
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on August 21, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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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.

Table of Contents

   1.  Prerequisites, Terminology, and Organization of this Memo . .   2
   2.  Introduction and Motivation . . . . . . . . . . . . . . . . .   2
   3.  For the Use Case, Must an Ancestor Impose Policy? . . . . . .   5
   4.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Appendix A.  Discussion Venue . . . . . . . . . . . . . . . . . .  10
   Appendix B.  Change History . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Prerequisites, Terminology, and Organization of this Memo

   The reader is assumed to be familiar with the DNS ([RFC1034]
   [RFC1035]) and the Domain Name System Security Extensions (DNSSEC)
   ([RFC4033] [RFC4034] [RFC4035] [RFC5155]).

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   To begin, Section 2 describes introduces the problem space and
   motivations for this work.  Then, Section 4 discusses the cases where
   a there are needs for discerning administrative boundaries in the DNS
   domain name space.

2.  Introduction and Motivation

   Many Internet resources and services, especially at the application
   layer, are identified primarily by DNS domain names [RFC1034].  As a
   result, domain names have become fundamental elements in building
   security policies and also in affecting user agent behaviour.

   For example, domain names are used for defining the scope of HTTP
   state management "cookies" [RFC6265].  In addition there is a user
   interface convention that purports to display an "actual domain name"
   differently from other parts of a fully-qualified domain name, in an
   effort to decrease the success of phishing attacks.  In this
   strategy, for instance, a domain name like

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   "www.bank.example.com.attackersite.tld" is formatted to highlight
   that the actual domain name ends in "attackersite.tld", in the hope
   of reducing user's potential impression of visiting

   Issuers of X.509 certificates make judgements about administrative
   boundaries around domains when issuing the certificates.  For some
   discussion of the relationship between domain names and X.509
   certificates, see [RFC6125].

   We can call the interpretation of domain names for these security
   policies a domain-use rule.  The simplest rule, and the one most
   likely to work, is to treat each different domain name distinctly.
   Under this approach, foo.example.org, bar.example.org, and
   baz.example.org are all just different domains.  Unfortunately, this
   approach is too naive to be useful.  Often, the real control over
   domain names is the same in several names (in this example,
   example.org and its children).  Therefore, clients have attempted to
   make more sophisticated rules around some idea of such shared
   control.  We call such an area of shared control a "policy realm",
   and the control held by the administrator of policy realm the "policy

   Historically, rules were sometimes based on the DNS tree.  Early
   rules made a firm distinction between top-level domains and
   everything else; but this was also too naive, and later attempts were
   based on inferences from the domain names themselves.  That did not
   work well, because there is no way in the DNS to discover the
   boundaries of policy realms.

   Some have attempted to use the boundary of zone cuts (i.e. the
   location of the zone's apex, which is at the SOA record; see
   [RFC1034] and [RFC1035]).  That boundary is neither necessary nor
   sufficient for these purposes: it is possible for a large site to
   have many, administratively distinct subdomain-named sites without
   inserting an SOA record, and it is also possible that an
   administrative entity (like a company) might divide its domain up
   into different zones for administrative reasons unrelated to the
   names in that domain.  It was also, prior to the advent of DNSSEC,
   difficult to find zone cuts.  Regardless, the location of a zone cut
   is an administrative matter to do with the operation of the DNS
   itself, and not useful for determining relationships among policy

   The different uses of domain names and their related issues often
   appear to be different kinds of problems.  The issue of whether two
   names may set cookies for one another appears to be a different
   matter from whether two names get the same highlighting in a

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   browser's address bar, or whether a particular name "owns" all the
   names underneath it.  But the problems all boil down to the same
   fundamental problem, which is that of determining whether two
   different names in the DNS are under the control of the same entity
   and ought to be treated as having an important administrative
   relationship to one another.

   What appears to be needed is a mechanism to determine policy realm
   boundaries in the DNS.  That is, given two domain names, one needs to
   be able to answer whether the first and the second are either within
   the same policy realm or have policy realms that are related in some
   way.  We may suppose that, if this information were to be available,
   it would be possible to make useful decisions based on the

   A particularly important distinction for security purposes has been
   the one between names that are mostly used to contain other domains,
   as compared to those that are mostly used to operate services.  The
   former are often "delegation-centric" domains, delegating parts of
   their name space to others, and are frequently called "public suffix"
   domains or "effective TLDs".  The term "public suffix" comes from a
   site, [publicsuffix.org], that publishes a list of domains -- which
   is also known as the "effective TLD (eTLD) list", and henceforth in
   this memo as the "public suffix list" -- that are used to contain
   other domains.  Not all, but most, delegation-centric domains are
   public suffix domains; and not all public suffix domains need to do
   DNS delegation, although most of them do.  The reason for the public
   suffix list is to make the distinction between names that must never
   be treated as being in the same policy realm as another, and those
   that might be so treated.  For instance, if "com" is on the public
   suffix list, that means that "example.com" lies in a policy realm
   distinct from that of com.

   Unfortunately, the public suffix list has several inherent
   limitations.  To begin with, it is a list that is separately
   maintained from the list of DNS delegations.  As a result, the data
   in the public suffix list can diverge from the actual use of the DNS.
   Second, because its semantics are not the same as those of the DNS,
   it does not capture unusual features of the DNS that are a
   consequence of its structure (see [RFC1034] for background on that
   structure).  Third, as the size of the root zone grows, keeping the
   list both accurate and synchronized with the expanding services will
   become difficult and unreliable.  Perhaps most importantly, it puts
   the power of assertion about the operational policies of a domain
   outside the control of the operators of that domain, and in the
   control of a third party possibly unrelated to those operators.

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   There have been suggestions for improvements of the public suffix
   list, most notably in [I-D.pettersen-subtld-structure].  It is
   unclear the extent to which those improvements would help, because
   they represent improvements on the fundamental mechanism of keeping
   metadata about the DNS tree apart from the DNS tree itself.

   Moreover, it is not entirely plain that the public/private
   distinction is really the best framework with which to understand the
   problem.  It is plain that any solution that emerges will need, to be
   useful, to provide a way of making the public/private distinction,
   since so much deployed software relies on that distinction.  It seems
   possible, however, that greater nuance would provide distinctions
   that are currently desired but cannot be supported using the public
   suffix list.  The best way to figure this out is to enumerate known
   problems and see whether there is something common underlying them
   all, or whether the different problems might at least be grouped into
   a few common cases.

3.  For the Use Case, Must an Ancestor Impose Policy?

   It is possible to identify two common policy patterns into which
   practical uses fall.  One is a positive policy that will necessarily
   be imposed by an ancestor in case a policy for the owner name itself
   is not available.  The other is a policy that need not get inherited
   from an ancestor.  Negative assertions by an ancestor (i.e. that a
   descendent does not share a policy realm) fall into this category,
   because the descendent does not have a positive policy imposed.

   The first pattern we may call the inheritance type.  In this use
   pattern, a client attempting to identify a policy that applies at a
   given name will use a policy found at a name closer to the root of
   the DNS, if need be.  This approach is useful when a client must have
   some kind of policy in order to continue processing.  Because the DNS
   is a hierarchical name system, it is always possible for a
   subordinate name to be permitted only in case the superordinate
   policies are followed.

   The second pattern we may call the orphan type.  In this use pattern,
   if a policy at a name is not specifically offered then it is better
   to assume there is a null policy than to infer some inherited policy.
   Note that orphan names might be related to other names (which makes
   the term somewhat unfortunate).  Rather, in these cases policy is
   assumed to be unshared unless there is evidence otherwise.  [[CREF1:
   Probably something better than "orphan" would be good, but I can't
   think of a better name. --ajs@anvilwalrusden.com]]

   The choice of which pattern is preferable depends largely on what the
   use of a policy seeks to achieve.  Some uses of policy require

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   determination of commonality among domains; in such cases, the
   inheritance pattern may be needed.  Other uses are attempts to
   identify differences between domains; in such cases, the orphan
   pattern is useful.

   The public suffix list provides a starting point for both patterns,
   but is neither necessary nor sufficient for either case.  Where the
   inheritance pattern is used, the public suffix list provides a
   minimal starting point whence inheritance can start.  Where the
   orphan pattern is used, the public suffix list provides the exclusion
   needed, but cannot provide either evidence that the list is up to
   date nor evidence that two owner names reside in the same policy

4.  Use Cases

   This section outlines some questions and identifies some known use
   cases of the public suffix list.

   HTTP state management cookies  The mechanism can be used to determine
      the scope for data sharing of HTTP state management cookies
      [RFC6265].  Using this mechanism, it is possible to determine
      whether a service at one name may be permitted to set a cookie for
      a service at a different name.  (Other protocols use cookies, too,
      and those approaches could benefit similarly.)  An application has
      to answer in this case the question, "Should I accept a cookie for
      domain X from the domain Y I am currently visiting?"

   User interface indicators  User interfaces sometimes attempt to
      indicate the "real" domain name in a given domain name.  A common
      use is to highlight the portion of the domain name believed to be
      the "real" name -- usually the rightmost three or four labels in a
      domain name string.  An application has to answer in this case the
      question, "What domain name is relevant to show the user in this
      case?"  The answer to this must be some portion of the domain name
      being displayed, but it is user- and context-sensitive.

   Setting the document.domain property  The DOM same-origin policy
      might be helped by being able to identify a common policy realm.
      An application has to answer in this case the question, "Is domain
      X under the same control as domain Y?"  It's worth noting that, in
      this case, neither X nor Y need be actually visible to a user.

   Email authentication mechanisms  Mail authentication mechanisms such
      as DMARC [I-D.kucherawy-dmarc-base] need to be able to find policy
      documents for a given domain name given a subdomain.  An
      application performing DMARC processing must answer the question,
      "Given the domain X currently being evaluated, where in the DNS is

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      the DMARC record?"  DMARC depends on the DNS hierarchical
      relationship, and unlike some other cases wants to find the DMARC
      record that is closest to the root zone.

   SSL and TLS certificates  Certificate authorities need to be able to
      discover delegation-centric domains in order to avoid issuance of
      certificates at or above those domains.  There are two cases:

      *  A certificate authority must answer the question, "Should I
         sign a certificate at this domain name given the request before

      *  A certificate authority must answer the question, "Should I
         sign a certificate for a wildcard at this domain name?"

      [[CREF2: There is another case here, noted by Jeffrey Walton,
      about "verifying the end-entity certificate issued by an
      organizational subordinate CA *without* constraints."  I didn't
      understand the issue well enough to write the text here.

   HSTS and Public Key Pinning with
   includeSubDomains flag set
      Clients that are using HSTS and public key pinning using
      includeSubDomains need to be able to determine whether a subdomain
      is properly within the policy realm of the parent.  An application
      performing this operation must answer the question, "Should I
      accept the rules for using X as valid for Y.X?"

   Linking domains together for merging
      It is frequently the case that domain names are aliases for one
      another.  Sometimes this is because of an ongoing merger (as when
      one company takes over another and merges operations).  A client
      encountering such a site needs to answer the question, "Is domain
      X just another name for domain Y?"

   Linking domains together for reporting
      An application that wants to categorize domains for the purposes
      of reporting must answer the question, "Are these two names
      versions of each other for the purposes of reporting statistics?"

   DMARC science fiction use case  DMARC's current use of the PSL is to
      determine the 'Organizational Domain'.. for use when discovering
      DMARC policy records.  PSL works well enough for production
      environments in today's world.  However, after hearing about
      cross-domain requirements of cookies and cross-domain security use

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      cases in the browser, it strikes me that any functionality (policy
      authority?) that allows domains to be linked would be incredibly
      useful in the DMARC world, too.  DMARC?s requirement for
      Identifier Alignment between SPF-authenticated domain, DKIM
      d=domain, and a message?s From: domain could be relaxed to include
      domains that were somehow associated via a policy authority.  This
      capability would be *very* nice to have at hand.

5.  Security Considerations

   A mechanism that satisfied the needs outline above would enable
   publication of assertions about administrative relationships of
   different DNS-named systems on the Internet.  If such assertions were
   to be accepted without checking that both sides agree to the
   assertion, it would be possible for one site to become an
   illegitimate source for data to be consumed in some other site.  In
   general, positive assertions about another name should never be
   accepted without querying the other name for agreement.

   Undertaking any of the inferences suggested in this draft without the
   use of the DNS Security Extensions exposes the user to the
   possibility of forged DNS responses.

   This memo does not actually specify any mechanisms, so it raises no
   security considerations itself.

6.  IANA Considerations

   This memo makes no requests of IANA.

7.  Acknowledgements

   The authors thank Adam Barth, Dave Crocker, Casey Deccio, Brian
   Dickson, Jothan Frakes, Daniel Kahn Gillmor, Phillip Hallam-Baker,
   John Klensin, Murray Kucherawy, Gervase Markham, Patrick McManus,
   Henrik Nordstrom, Yngve N.  Pettersen, Eric Rescorla, Thomas
   Roessler, Peter Saint-Andre, Maciej Stachowiak, and Jeffrey Walton
   for helpful comments or suggestions.

8.  Informative References

              Kucherawy, M., "Domain-based Message Authentication,
              Reporting and Conformance (DMARC)", draft-kucherawy-dmarc-
              base-00 (work in progress), March 2013.

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              Pettersen, Y., "The Public Suffix Structure file format
              and its use for Cookie domain validation", draft-
              pettersen-subtld-structure-09 (work in progress), March

              Mozilla Foundation, "Public Suffix List", also known
              as: Effective TLD (eTLD) List.


   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, March 2008.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, March 2011.

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              April 2011.

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Appendix A.  Discussion Venue

   This Internet-Draft is discussed on the applications area working
   group mailing list: dbound@ietf.org.

Appendix B.  Change History

   [this section to be removed by RFC-Editor prior to publication as an

   Version 01  Add questions from John Levine posting to mailing list.

   Version 00  Initial version.

      This is a -00 Internet-draft, but borrows from various prior draft
      works, listed below, as well as from discussions on the mailing

      Andrew Sullivan, Jeff Hodges: Asserting DNS Administrative
                               Boundaries Within DNS Zones



      John Levine: Publishing Organization Boundaries in the DNS



      Casey Deccio, John Levine: Defining and Signaling
                            Relationships Between Domains



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Authors' Addresses

   Andrew Sullivan
   Dyn, Inc.
   150 Dow St
   Manchester, NH  03101

   Email: asullivan@dyn.com

   Jeff Hodges
   2211 North First Street
   San Jose, California  95131

   Email: Jeff.Hodges@KingsMountain.com

   John Levine
   Taughannock Networks
   PO Box 727
   Trumansburg, NY  14886

   Phone: +1 831 480 2300
   Email: standards@taugh.com
   URI:   http://jl.ly

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