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Versions: 00 01 02 03 04 RFC 4955

Network Working Group                                          D. Blacka
Internet-Draft                                            Verisign, Inc.
Expires: August 3, 2005                                 February 2, 2005

                           DNSSEC Experiments

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
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   This Internet-Draft will expire on August 3, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).


   In the long history of the development of the DNS security [1]
   extensions (DNSSEC), a number of alternate methodologies and
   modifications have been proposed and rejected for practical, rather
   than strictly technical, reasons.  There is a desire to be able to
   experiment with these alternate methods in the public DNS.  This
   document describes a methodology for deploying alternate,
   non-backwards-compatible, DNSSEC methodologies in an experimental
   fashion without disrupting the deployment of standard DNSSEC.

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Table of Contents

   1.   Definitions and Terminology  . . . . . . . . . . . . . . . .   3
   2.   Overview . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.   Experiments  . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.   Method . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.   Defining an Experiment . . . . . . . . . . . . . . . . . . .   8
   6.   Considerations . . . . . . . . . . . . . . . . . . . . . . .   9
   7.   Transitions  . . . . . . . . . . . . . . . . . . . . . . . .  10
   8.   Security Considerations  . . . . . . . . . . . . . . . . . .  11
   9.   IANA Considerations  . . . . . . . . . . . . . . . . . . . .  12
   10.  References . . . . . . . . . . . . . . . . . . . . . . . . .  13
   10.1   Normative References . . . . . . . . . . . . . . . . . . .  13
   10.2   Informative References . . . . . . . . . . . . . . . . . .  13
        Editorial Comments . . . . . . . . . . . . . . . . . . . . .  14
        Author's Address . . . . . . . . . . . . . . . . . . . . . .  14
        Intellectual Property and Copyright Statements . . . . . . .  15

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1.  Definitions and Terminology

   Throughout this document, familiarity with the DNS system (RFC 1035
   [4]) and the DNS security extensions ([1], [2], and [3].

   The key words "MUST, "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [5].

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2.  Overview

   Historically, experimentation with DNSSEC alternatives has been a
   problematic endeavor.  There has typically been a desire to both
   introduce non-backwards-compatible changes to DNSSEC, and to try
   these changes on real zones in the public DNS.  This creates a
   problem when the change to DNSSEC would make all or part of the zone
   using those changes appear bogus or otherwise broken to existing
   DNSSEC-aware resolvers.

   This document describes a standard methodology for setting up public
   DNSSEC experiments.  This methodology addresses the issue of
   co-existence with standard DNSSEC and DNS by using unknown algorithm
   identifiers to hide the experimental DNSSEC protocol modifications
   from standard DNSSEC-aware resolvers.

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3.  Experiments

   When discussing DNSSEC experiments, it is necessary to classify these
   experiments into two broad categories:

   Backwards-Compatible: describes experimental changes that, while not
      strictly adhering to the DNSSEC standard, are nonetheless
      interoperable with clients and server that do implement the DNSSEC
   Non-Backwards-Compatible: describes experiments that would cause a
      standard DNSSEC-aware resolver to (incorrectly) determine that all
      or part of a zone is bogus, or to otherwise not interoperable with
      standard DNSSEC clients and servers.

   Not included in these terms are experiments with the core DNS
   protocol itself.

   The methodology described in this document is not necessary for
   backwards-compatible experiments, although it certainly could be used
   if desired.

   Note that, in essence, this metholodolgy would also be used to
   introduce a new DNSSEC algorithm, independently from any DNSSEC
   experimental protocol change.

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4.  Method

   The core of the methodology is the use of only "unknown" algorithms
   to sign the experimental zone, and more importantly, having only
   unknown algorithm DS records for the delegation to the zone at the

   This technique works because of the way DNSSEC-compliant validators
   are expected to work in the presence of a DS set with only unknown
   algorithms.  From [3], Section 5.2:

      If the validator does not support any of the algorithms listed in
      an authenticated DS RRset, then the resolver has no supported
      authentication path leading from the parent to the child.  The
      resolver should treat this case as it would the case of an
      authenticated NSEC RRset proving that no DS RRset exists, as
      described above.

   And further:

      If the resolver does not support any of the algorithms listed in
      an authenticated DS RRset, then the resolver will not be able to
      verify the authentication path to the child zone.  In this case,
      the resolver SHOULD treat the child zone as if it were unsigned.

   While this behavior isn't strictly mandatory (as marked by MUST), it
   is unlikely that a validator would not implement the behavior, or,
   more to the point, it will not violate this behavior in an unsafe way
   (see below (Section 6).)

   Because we are talking about experiments, it is recommended that
   private algorithm numbers be used (see [2], appendix A.1.1
   [Comment.1].) Normally, instead of actually inventing new signing
   algorithms, the recommended path is to create alternate algorithm
   identifiers that are aliases for the existing, known algorithms.
   While, strictly speaking, it is only necessary to create an alternate
   identifier for the mandatory algorithms (currently, this is only
   algorithm 5, RSASHA1), it is RECOMMENDED that all OPTIONAL defined
   algorithms be aliased as well.

   It is RECOMMENDED that for a particular DNSSEC experiment, a
   particular domain name base is chosen for all new algorithms, then
   the algorithm number (or name) is prepended to it.  For example, for
   experiment A, the base name of "dnssec-experiment-a.example.com" is
   chosen.  Then, aliases for algorithms 3 (DSA) and 5 (RSASHA1) are
   defined to be "3.dnssec-experiment-a.example.com" and
   "5.dnssec-experiment-a.example.com".  However, any unique identifier
   will suffice.

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   Using this method, resolvers (or, more specificially, DNSSEC
   validators) essentially indicate their ability to understand the
   DNSSEC experiment's semantics by understanding what the new algorithm
   identifiers signify.

   This method creates two classes of DNSSEC-aware servers and
   resolvers: servers and resolvers that are aware of the experiment
   (and thus recognize the experiments algorithm identifiers and
   experimental semantics), and servers and resolvers that are unware of
   the experiment.

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5.  Defining an Experiment

   The DNSSEC experiment must define the particular set of (previously
   unknown) algorithms that identify the experiment, and define what
   each unknown algorithm identifier means.  Typically, unless the
   experiment is actually experimenting with a new DNSSEC algorithm,
   this will be a mapping of private algorithm identifiers to existing,
   known algorithms.

   Typically, the experiment will choose a DNS name as the algorithm
   identifier base.  This DNS name SHOULD be under the control of the
   authors of the experiment.  Then the experiment will define a mapping
   between known mandatory and optional algorithms into this private
   algorithm identifier space.  Alternately, the experiment MAY use the
   OID private algorithm space instead (using algorithm number 254), or
   may choose non-private algorithm numbers, although this would require
   an IANA allocation (see below (Section 9).)

   For example, an experiment might specify in its description the DNS
   name "dnssec-experiment-a.example.com" as the base name, and provide
   the mapping of "3.dnssec-experiment-a.example.com" is an alias of
   DNSSEC algorithm 3 (DSA), and "5.dnssec-experiment-a.example.com" is
   an alias of DNSSEC algorithm 5 (RSASHA1).

   Resolvers MUST then only recognize the experiment's semantics when
   present in a zone signed by one or more of these private algorithms.

   In general, however, resolvers involved in the experiment are
   expected to understand both standard DNSSEC and the defined
   experimental DNSSEC protocol, although this isn't, strictly speaking,

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6.  Considerations

   There are a number of considerations with using this methodology.

   1.  Under some circumstances, it may be that the experiment will not
       be sufficiently masked by this technique and may cause resolution
       problem for resolvers not aware of the experiment.  For instance,
       the resolver may look at the not validatable response and
       conclude that the response is bogus, either due to local policy
       or implementation details.  This is not expected to be the common
       case, however.
   2.  It will, in general, not be possible for DNSSEC-aware resolvers
       not aware of the experiment to build a chain of trust through an
       experimental zone.

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7.  Transitions

   If an experiment is successful, there may be a desire to move the
   experiment to a standards-track extension.  One way to do so would be
   to move from private algorithm numbers to IANA allocated algorithm
   numbers, with otherwise the same meaning.  This would still leave a
   divide between resolvers that understood the extension versus
   resolvers that did not.  It would, in essence, create an additional
   version of DNSSEC.

   An alternate technique might be to do a typecode rollover, thus
   actually creating a definitive new version of DNSSEC.  There may be
   other transition techniques available, as well.

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8.  Security Considerations

   Zones using this methodology will be considered insecure by all
   resolvers except those aware of the experiment.  It is not generally
   possible to create a secure delegation from an experimental zone that
   will be followed by resolvers unaware of the experiment.

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9.  IANA Considerations

   IANA may need to allocate new DNSSEC algorithm numbers if that
   transition approach is taken, or the experiment decides to use
   allocated numbers to begin with.  No IANA action is required to
   deploy an experiment using private algorithm identifiers.

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10.  References

10.1  Normative References

   [1]  Arends, R., Austein, R., Massey, D., Larson, M. and S. Rose,
        "DNS Security Introduction and Requirements",
        draft-ietf-dnsext-dnssec-intro-13 (work in progress), October

   [2]  Arends, R., "Resource Records for the DNS Security Extensions",
        draft-ietf-dnsext-dnssec-records-11 (work in progress), October

   [3]  Arends, R., "Protocol Modifications for the DNS Security
        Extensions", draft-ietf-dnsext-dnssec-protocol-09 (work in
        progress), October 2004.

10.2  Informative References

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

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

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Editorial Comments

   [Comment.1]  Note: how private algorithms work in DNSSEC is not well
                explained in the DNSSECbis RFCs.  In particular, how to
                validate that the DS records contain only unknown
                algorithms is not explained at all.

Author's Address

   David Blacka
   Verisign, Inc.
   21355 Ridgetop Circle
   Dulles, VA  20166

   Phone: +1 703 948 3200
   EMail: davidb@verisign.com
   URI:   http://www.verisignlabs.com

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