DNSEXT WG                                               Edward Lewis
INTERNET DRAFT                                          NAI Labs
Category:I-D                                            July 12, 2000

         DNS Security Extension Clarification on Zone Status
                <draft-ietf-dnsext-zone-status-02.txt>

Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups.  Note that other
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Internet-Drafts are draft documents valid for a maximum of six months
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The list of current Internet-Drafts can be accessed at
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Comments should be sent to the authors or the DNSIND WG mailing list
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This draft expires on January 12, 2001.

Copyright Notice

Copyright (C) The Internet Society (1999, 2000).  All rights reserved.

Abstract

The definition of a secured zone is presented, updating RFC 2535.
After discussion on the mailing list and other working group
consideration, removed from earlier editions of this draft are a new
interpretation of the NXT record and a proposal to obsolete NULL
keys.  Deprecation of "experimentally secure" remains.

 Introduction

Whether a DNS zone is "secured" or not is a question asked in at least
four contexts.  A zone administrator asks the question when
configuring a zone to use DNSSEC.  A dynamic update server asks the
question when an update request arrives, which may require DNSSEC
processing.  A delegating zone asks the question of a child zone when
the parent enters data indicating the status the child.  A resolver
asks the question upon receipt of data belonging to the zone.




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1.1 When a Zone's Status is Important

A zone administrator needs to be able to determine what steps are
needed to make the zone as secure as it can be.  Realizing that due to
the distributed nature of DNS and its administration, any single zone
is at the mercy of other zones when it comes to the appearance of
security.  This document will define what makes a zone qualify as
secure (absent interaction with other zones).

A name server performing dynamic updates needs to know whether a zone
being updated is to have signatures added to the updated data, NXT
records applied, and other required processing.  In this case, it is
conceivable that the name server is configured with the knowledge, but
being able to determine the status of a zone by examining the data is
a desirable alternative to configuration parameters.

A delegating zone is required to indicate whether a child zone is
secured.  The reason for this requirement lies in the way in which a
resolver makes its own determination about a zone (next paragraph). To
shorten a long story, a parent needs to know whether a child should be
considered secured.  This is a two part question, what does a parent
consider a secure child to be, and how does a parent know if the child
conforms?

A resolver needs to know if a zone is secured when the resolver is
processing data from the zone.  Ultimately, a resolver needs to know
whether or not to expect a usable signature covering the data.  How
this determination is done is out of the scope of this document,
except that, in some cases, the resolver will need to contact the
parent of the zone to see if the parent states that the child is
secured.

1.2 Islands of Security

The goal of DNSSEC is to have each zone secured, from the root zone
and the top-level domains down the hierarchy to the leaf zones.
Transitioning from an unsecured DNS, as we have now, to a fully
secured - or "as much as will be secured" - tree will take some time.
During this time, DNSSEC will be applied in various locations in the
tree, not necessarily "top down."

For example, at a particular instant, the root zone and the "test."
TLD might be secured, but region1.test. might not be.  (For reference,
let's assume that region2.test. is secured.)  However,
subarea1.region1.test. may have gone through the process of becoming
secured, along with its delegations.  The dilemma here is that
subarea1 cannot get its zone keys properly signed as its parent zone,
region1, is not secured.

The popular term for the secured zones at or below subarea1 is an
"island of security."  The only way in which a DNSSEC resolver will
come to trust any data from this island is if the resolver is
pre-configured with the zone key(s) for subarea1.  All other resolvers
will not recognize this island as secured.

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Although both subarea1.region1.test. and region2.test. have both been
properly brought to a secure state by the administering staff, only
the latter of the two is actually fully secured - in the sense that
all DNSSEC resolvers can and will verify its data.  The former,
subarea1, will be seen as secured by a subset of those resolvers, just
those appropriately configured.

In RFC 2535, there is a provision for "certification authorities,"
entities that will sign public keys for zones such as subarea1.  There
is another draft (currently in last call) that restricts this
activity.  Regardless of the other draft, resolvers would still need
proper configuration to be able to use the certification authority to
verify the data for the subarea1 island.

1.3 Impact on RFC 2535

This document updates several sections of RFC 2535.  The definition of
a secured zone is an update to section 3.4 of the RFC.  Section 3.4 is
updated to eliminate the definition of experimental keys and
illustrate a way to still achieve the functionality they were designed
to provide.  Section 3.1.3 is updated by the specifying the value of
the protocol octet in a zone key.

 Status of a Zone

In this section, rules governing a zone's DNSSEC status are presented.
There are three levels of security defined: full, private, and
unsecured.  A zone is fully secure when it complies with the strictest
set of DNSSEC processing rules.  A zone is privately secured when it
is configured in such a way that only resolvers that are appropriately
configured see the zone as secured.  All other zones are unsecured.

Note: there currently is no document completely defining DNSSEC
verification rules.  For the purposes of this document, the strictest
rules are assumed to state that the verification chain of zone keys
parallels the delegation tree up to the root zone.  This is not
intended to disallow alternate verification paths, just to establish a
baseline definition.

To avoid repetition in the rules below, the following terms are
defined.

2.a. Zone signing KEY RR - A KEY RR whose flag field has the value 01
for name type (indicating a zone key) and either value 00 or value 01
for key type (indicating a key permitted to authenticate data).  (See
RFC 2535, section 3.1.2).  The KEY RR also has a protocol octet value
of DNSSEC (3) or ALL (255).

The definition updates RFC 2535's definition of a zone key.  The
requirement that the protocol field be either DNSSEC or ALL is a new
requirement.

2.b On-tree Validation - The authorization model in which only the
parent zone can is recognized to supply a DNSSEC-meaningful signature

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that is used by a resolver to build a chain of trust from the child's
keys to a recognized root of security.  The term "on-tree" refers to
following up the DNS domain hierarchy to reach a trusted key,
presumably the root key if no other key is available.  The term
"validation" refers to the digital signature by the parent to prove
the integrity, authentication and authorization of the child' key to
sign the child's zone data.

2.c Off-tree Validation - Any authorization model that permits domain
names other than the parent's to provide a signature over a child's
zone keys that will enable a resolver to trust the keys.

2.1 Fully Secured

A fully secured zone, in a nutshell, is a zone that uses only
mandatory to implement algorithms (RFC 2535, section 3.2) and relies
on a key certification chain that parallels the delegation tree
(on-tree validation).  Fully secured zones are defined by the
following rules.

2.1.a. The zone's apex MUST have a KEY RR set.  There MUST be at least
one zone signing KEY RR (2.a) of a mandatory to implement algorithm in
the set.

2.1.b. The zone's apex KEY RR set MUST be signed by a private key
belonging to the parent zone.  The private key's public companion MUST
be a zone signing KEY RR (2.a) of a mandatory to implement algorithm
and owned by the parent's apex.

If a zone cannot get a conforming signature from the parent zone, the
child zone cannot be considered fully secured.  The only exception to
this is the root zone, for which there is no parent zone.

2.1.c. NXT records MUST be deployed throughout the zone. (Updates RFC
2535, section 2.3.2.)  Note: there is some operational discomfort with
the current NXT record.  This requirement is open to modification when
two things happen.  First, an alternate mechanism to the NXT is
defined and second, a means by which a zone can indicate that it is
using an alternate method.

2.1.d. Each RR set that qualifies for zone membership MUST be signed
by a key that is in the apex's KEY RR set and is a zone signing KEY RR
(2.a) of a mandatory to implement algorithm.  (Updates 2535, section
2.3.1.)

Mentioned earlier, the root zone is a special case.  Defining what
constitutes a secure root zone is difficult, as the discussion on
securing the root zone has not come to a consensus in an open forum.
However, the security of the root zone will be determined by the
pre-configuration of a trusted key in resolvers.  Who generates and
distributes the trusted key is an open issue.




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2.2 Privately Secured

Note that the term "privately" is open to debate.  The term stems from
the likely hood that the only resolvers to be configured for a
particular zone will be resolvers "private" to an organization.
Perhaps the more clumsy "colloquially secure" is more accurate.

A privately secured zone is a zone that complies with rules like those
for a fully secured zone with the following exceptions.  The signing
keys may be of an algorithm that is not mandatory to implement and/or
the verification of the zone keys in use may rely on a verification
chain that is not parallel to the delegation tree (off-tree
validation).

2.2.a. The zone's apex MUST have a KEY RR set.  There MUST be at least
one zone signing KEY RR (2.a) in the set.

2.2.b. The zone's apex KEY RR set MUST be signed by a private key and
one of the following two subclauses MUST hold true.

2.2.b.1 The private key's public companion MUST be pre-configured in
all the resolvers of interest.

2.2.b.2 The private key's public component MUST be a zone signing KEY
RR (2.a) authorized to provide validation of the zone's apex KEY RR
set, as recognized by resolvers of interest.

The previous sentence is trying to convey the notion of using a
trusted third party to provide validation of keys.  If the domain name
owning the validating key is not the parent zone, the domain name must
represent someone the resolver trusts to provide validation.

2.2.c. NXT records MUST be deployed throughout the zone. (Updates RFC
2535, section 2.3.2.) Note: see the discussion following 2.1.c.

2.2.d. Each RR set that qualifies for zone membership MUST be signed
by a key that is in the apex's KEY RR set and is a zone signing KEY RR
(2.a).  (Updates 2535, section 2.3.1.)

2.3 Unsecured

All other zones qualify as unsecured.  This includes zones that are
designed to be experimentally secure, as defined in a later section on
that topic.

2.4 Wrap up

The designation of fully secured, privately secured, and unsecured are
merely labels to apply to zones, based on their contents.  Resolvers,
when determining whether a signature is expected or not, will only see
a zone as secured or unsecured.

Resolvers that follow the most restrictive DNSSEC verification rules
will only see fully secured zones as secured, and all others as

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unsecured, including zones which are privately secured.  Resolvers
that are not as restrictive, such as those that implement algorithms
in addition to the mandatory to implement algorithms, will see some
privately secured zones as secured.

The intent of the labels "fully" and "privately" is to identify the
specific attributes of a zone.  The words are chosen to assist in the
writing of a document recommending the actions a zone administrator
take in making use of the DNS security extensions.  The words are
explicitly not intended to convey a state of compliance with DNS
security standards.

 Deleted

 Deleted

 Experimental Status

The purpose of an experimentally secured zone is to facilitate the
migration from an unsecured zone to a secured zone.  This distinction
is dropped.

The objective of facilitating the migration can be achieved without a
special designation of an experimentally secure status.
Experimentally secured is a special case of privately secured.  A zone
administrator can achieve this by publishing a zone with signatures
and configuring a set of test resolvers with the corresponding public
keys.  Even if the public key is published in a KEY RR, as long as
there is no parent signature, the resolvers will need some
pre-configuration to know to process the signatures.  This allows a
zone to be secured with in the sphere of the experiment, yet still be
registered as unsecured in the general Internet.

 IANA/ICANN Considerations

This document does not request any action from an assigned number
authority nor recommends any actions.

 Security Considerations

Without a means to enforce compliance with specified protocols or
recommended actions, declaring a DNS zone to be "completely" secured
is impossible.  Even if, assuming an omnipotent view of DNS, one can
declare a zone to be properly configured for security, and all of the
zones up to the root too, a misbehaving resolver could be duped into
believing bad data.  If a zone and resolver comply, a non-compliant or
subverted parent could interrupt operations.  The best that can be
hoped for is that all parties are prepared to be judged secure and
that security incidents can be traced to the cause in short order.

 Acknowledgements

The need to refine the definition of a secured zone has become
apparent through the efforts of the participants at two DNSSEC

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workshops, sponsored by the NIC-SE (.se registrar), CAIRN (a
DARPA-funded research network), and other workshops.  Further
discussions leading to the document include Olafur Gudmundsson, Russ
Mundy, Robert Watson, and Brian Wellington.  Roy Arends, Ted Lindgreen
and others have contributed significant input via the namedroppers
mailing list.

 References

[RFC1034] P. Mockapetris, "Domain Names - Concepts and Facilities,"
RFC 1034, November 1987.

[RFC1035] P. Mockapetris, "Domain Names - Implementation and
Specification," RFC 1034, November 1987.

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

[RFC2136] P. Vixie (Ed.), S. Thomson, Y. Rekhter, J. Bound "Dynamic
Updates in the Domain Name System," RFC 2136, April 1997.

[RFC2535] D. Eastlake, "Domain Name System Security Extensions," RFC
2535, March 1999.

[draft-ietf-dnsext-simple-secure-update-xy.txt] B. Wellington, "Simple
Secure Domain Name System (DNS) Dynamic Update," version 00, February
2000.

 Author Information

Edward Lewis
NAI Labs
 Washington Road
Glenwood, MD 21738
+1 443 259 2352
<lewis@tislabs.com>

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