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rfc:rfc4955

Network Working Group D. Blacka Request for Comments: 4955 VeriSign, Inc. Category: Standards Track July 2007

                 DNS Security (DNSSEC) Experiments

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The IETF Trust (2007).

Abstract

 This document describes a methodology for deploying alternate, non-
 backwards-compatible, DNS Security (DNSSEC) methodologies in an
 experimental fashion without disrupting the deployment of standard
 DNSSEC.

Table of Contents

 1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2.  Definitions and Terminology . . . . . . . . . . . . . . . . . . 2
 3.  Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 4.  Method  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
 5.  Defining an Experiment  . . . . . . . . . . . . . . . . . . . . 4
 6.  Considerations  . . . . . . . . . . . . . . . . . . . . . . . . 5
 7.  Use in Non-Experiments  . . . . . . . . . . . . . . . . . . . . 5
 8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
 9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
   9.2.  Informative References  . . . . . . . . . . . . . . . . . . 6

Blacka Standards Track [Page 1] RFC 4955 DNS Security (DNSSEC) Experiments July 2007

1. 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 (bad) or otherwise broken to existing security-
 aware resolvers.
 This document describes a standard methodology for setting up DNSSEC
 experiments.  This methodology addresses the issue of coexistence
 with standard DNSSEC and DNS by using unknown algorithm identifiers
 to hide the experimental DNSSEC protocol modifications from standard
 security-aware resolvers.

2. Definitions and Terminology

 Throughout this document, familiarity with the DNS system (RFC 1035
 [5]) and the DNS security extensions (RFC 4033 [2], RFC 4034 [3], and
 RFC 4035 [4]) is assumed.
 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 RFC 2119 [1].

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 servers that do implement the
    DNSSEC standard.
 Non-Backwards-Compatible:  describes experiments that would cause a
    standard security-aware resolver to (incorrectly) determine that
    all or part of a zone is bogus, or to otherwise not interoperate
    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 may be used
 if desired.

Blacka Standards Track [Page 2] RFC 4955 DNS Security (DNSSEC) Experiments July 2007

4. Method

 The core of the methodology is the use of strictly unknown algorithm
 identifiers when signing the experimental zone, and more importantly,
 having only unknown algorithm identifiers in the DS records for the
 delegation to the zone at the parent.
 This technique works because of the way DNSSEC-compliant validators
 are expected to work in the presence of a DS set with only unknown
 algorithm identifiers.  From RFC 4035 [4], 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.
 Although this behavior isn't strictly mandatory (as marked by MUST),
 it is unlikely for a validator to implement a substantially different
 behavior.  Essentially, if the validator does not have a usable chain
 of trust to a child zone, then it can only do one of two things:
 treat responses from the zone as insecure (the recommended behavior),
 or treat the responses as bogus.  If the validator chooses the
 latter, this will both violate the expectation of the zone owner and
 defeat the purpose of the above rule.  However, with local policy, it
 is within the right of a validator to refuse to trust certain zones
 based on any criteria, including the use of unknown signing
 algorithms.
 Because we are talking about experiments, it is RECOMMENDED that
 private algorithm numbers be used (see RFC 4034 [3], Appendix A.1.1.
 Note that secure handling of private algorithms requires special
 handing by the validator logic.  See "Clarifications and
 Implementation Notes for DNSSECbis" [6] for further details.)
 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, it is suggested that all optional defined
 algorithms be aliased as well.

Blacka Standards Track [Page 3] RFC 4955 DNS Security (DNSSEC) Experiments July 2007

 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.
 Using this method, resolvers (or, more specifically, 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 security-aware servers and
 resolvers: servers and resolvers that are aware of the experiment
 (and thus recognize the experiment's algorithm identifiers and
 experimental semantics), and servers and resolvers that are unaware
 of the experiment.
 This method also precludes any zone from being both in an experiment
 and in a classic DNSSEC island of security.  That is, a zone is
 either in an experiment and only possible to validate experimentally,
 or it is not.

5. Defining an Experiment

 The DNSSEC experiment MUST define the particular set of (previously
 unknown) algorithm identifiers 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.
 Normally 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
 Object Identifier (OID) private algorithm space instead (using
 algorithm number 254), or MAY choose non-private algorithm numbers,
 although this would require an IANA allocation.
 For example, an experiment might specify in its description the DNS
 name "dnssec-experiment-a.example.com" as the base name, and declare
 that "3.dnssec-experiment-a.example.com" is an alias of DNSSEC
 algorithm 3 (DSA), and that "5.dnssec-experiment-a.example.com" is an
 alias of DNSSEC algorithm 5 (RSASHA1).

Blacka Standards Track [Page 4] RFC 4955 DNS Security (DNSSEC) Experiments July 2007

 Resolvers MUST only recognize the experiment's semantics when present
 in a zone signed by one or more of these algorithm identifiers.  This
 is necessary to isolate the semantics of one experiment from any
 others that the resolver might understand.
 In general, resolvers involved in the experiment are expected to
 understand both standard DNSSEC and the defined experimental DNSSEC
 protocol, although this isn't required.

6. Considerations

 There are a number of considerations with using this methodology.
 1.  If an unaware validator does not correctly follow the rules laid
     out in RFC 4035 (e.g., the validator interprets a DNSSEC record
     prior to validating it), or if the experiment is broader in scope
     that just modifying the DNSSEC semantics, the experiment may not
     be sufficiently masked by this technique.  This may cause
     unintended resolution failures.
 2.  It will not be possible for security-aware resolvers unaware of
     the experiment to build a chain of trust through an experimental
     zone.

7. Use in Non-Experiments

 This general methodology MAY be used for non-backwards compatible
 DNSSEC protocol changes that start out as or become standards.  In
 this case:
 o  The protocol change SHOULD use public IANA allocated algorithm
    identifiers instead of private algorithm identifiers.  This will
    help identify the protocol change as a standard, rather than an
    experiment.
 o  Resolvers MAY recognize the protocol change in zones not signed
    (or not solely signed) using the new algorithm identifiers.

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.
 Implementers should take into account any security issues that may
 result from environments being configured to trust both experimental
 and non-experimental zones.  If the experimental zone is more

Blacka Standards Track [Page 5] RFC 4955 DNS Security (DNSSEC) Experiments July 2007

 vulnerable to attacks, it could, for example, be used to promote
 trust in zones not part of the experiment, possibly under the control
 of an attacker.

9. References

9.1. Normative References

 [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [2]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
      "DNS Security Introduction and Requirements", RFC 4033,
      March 2005.
 [3]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
      "Resource Records for the DNS Security Extensions", RFC 4034,
      March 2005.
 [4]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
      "Protocol Modifications for the DNS Security Extensions",
      RFC 4035, March 2005.

9.2. Informative References

 [5]  Mockapetris, P., "Domain names - implementation and
      specification", STD 13, RFC 1035, November 1987.
 [6]  Weiler, S. and R. Austein, "Clarifications and Implementation
      Notes for DNSSECbis", Work in Progress, March 2007.

Author's Address

 David Blacka
 VeriSign, Inc.
 21355 Ridgetop Circle
 Dulles, VA  20166
 US
 Phone: +1 703 948 3200
 EMail: davidb@verisign.com
 URI:   http://www.verisignlabs.com

Blacka Standards Track [Page 6] RFC 4955 DNS Security (DNSSEC) Experiments July 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
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 might or might not be available; nor does it represent that it has
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 on the procedures with respect to rights in RFC documents can be
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 The IETF invites any interested party to bring to its attention any
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Blacka Standards Track [Page 7]

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