DNSEXT D. Blacka
Internet-Draft Verisign, Inc.
Expires: August 27, 2006 February 23, 2006
DNSSEC Experiments
draft-ietf-dnsext-dnssec-experiments-02
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Copyright (C) The Internet Society (2006).
Abstract
In the long history of the development of the DNS security extensions
[1] (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
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY, and "OPTIONAL" in this
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 (bad) 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
standard.
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 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 could be used
if desired.
Note that, in essence, this metholodology 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 strictly "unknown"
algorithms to sign the experimental zone, and more importantly,
having only unknown algorithm 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
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. Note
that secure handling of private algorithms requires special handing
by the validator logic. See [6] for futher 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 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
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will suffice.
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.
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 experimentally validatable, or it
isn't.
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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.
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
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 required.
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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 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., Larson, M., Massey, D., and S. Rose,
"DNS Security Introduction and Requirements", RFC 4033,
March 2005.
[2] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"Resource Records for the DNS Security Extensions", RFC 4034,
March 2005.
[3] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"Protocol Modifications for the DNS Security Extensions",
RFC 4035, March 2005.
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.
[6] Austein, R. and S. Weiler, "Clarifications and Implementation
Notes for DNSSECbis", draft-ietf-dnsext-dnssec-bis-updates-02
(work in progress), January 2006.
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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
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