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Versions: 00 01 02 03 RFC 3445

DNSEXT Working Group                                          D. Massey
INTERNET-DRAFT                                                  USC/ISI
                                                                S. Rose
Expires: April 2002                                                NIST
Updates: RFC 2535                                         November 2001



             Limiting the Scope of the KEY Resource Record
                     ------------------------------
           <draft-ietf-dnsext-restrict-key-for-dnssec-00.txt>


Status of this Document

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.  Distribution of this
   document is unlimited.  Comments regarding this document should be
   sent to the author.

   Internet-Drafts are working documents of the Internet Engineering
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Abstract

   This document limits the KEY resource record to only DNS zone keys.
   The original KEY resource record used sub-typing to store both DNS
   zone keys and arbitrary application keys.  DNS security keys and
   application keys differ in almost every respect and should not be
   combined in a single sub-typed resource record.   This document
   removes application keys from the KEY record by redefining the
   Protocol Octet field in the KEY RDATA. Three existing application key
   sub-types are changed to historic, but the format of the KEY record
   is not changed.  This document updates RFC 2535.





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1.  Introduction

   This document limits the scope the KEY resource record.   The KEY
   resource record, originally defined in [DNSSEC], uses resource record
   sub-typing to hold any public key associated with "a zone, a user, or
   a host or other end entity".   The KEY resource record is assigned
   type value of 25 and the Protocol Octet in the KEY RDATA identifies
   the sub-type.   DNSSEC Zone, User and Host keys are stored in the KEY
   resource record and are identified by a Protocol Octet value of 3.
   Email, IPSEC, and TLS keys are also stored in the KEY resource record
   and are identified by Protocol Octet values of 1,2, and 4
   (respectively).   Protocol Octet values 5-254 are available for
   assignment by IANA and values have been requested (but not assigned)
   for applications such as SSH.

   Closer examination and limited experimental deployment has shown that
   application keys stored in KEY records are problematic.  Any use of
   sub-typing has inherent limitations.   A resolver can not specify the
   desired sub-type in a DNS query and many DNS operations group
   resource records into sets, based on the DNS name and type.  For a
   example, a resolver can not directly request the DNSSEC key sub-type.
   Instead, the resolver must request all KEY records associated with a
   DNS name.   DNSSEC signatures apply to the set of all KEY resource
   records associated with the DNS name, regardless of sub-type.

   In the case of the KEY record, the inherent sub-type limitations are
   exacerbated since DNS zone keys and application keys differ in
   virtually every respect.   Combining two very different types of keys
   into a single sub-typed resource record adds unnecessary complexity
   and increases the potential for implementation and deployment errors.
   This document addresses these issues by removing all application keys
   from the KEY resource record.   Note that the scope of this document
   is strictly limited to the KEY record and this document does not
   endorse or restrict the storage of application keys in other resource
   records.


2.  DNS Zone Key and Application Key Differences

   In the original specification, all public keys were stored in KEY
   records, regardless of protocol or type.  This proved to be a mistake
   as DNS security keys (zone, host and user) and application keys
   differ in the following ways:


        o    They serve different purposes.

        o    They are managed by different administrators.



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        o    They are authenticated according to different rules.

        o    Nameservers use different rules when including them in
             responses.

        o    Resolvers process them in different ways.

        o    Faults/key compromises have different consequences.

   The purpose of a DNS zone key is to sign resource records associated
   with a DNS zone but the purpose of an application key is specific to
   the application.  DNSSEC host and user KEY RRs are used to generate
   SIG(0) transaction signatures.   Application keys, such as PGP/email,
   IPSEC, TLS, and SSH keys, are not a mandatory part of any zone and
   the purpose and proper use of application keys is outside the scope
   of DNS.

   DNSSEC keys are managed by DNS administrators, but application keys
   are managed by application administrators.   The DNS zone administra-
   tor determines the key lifetime, handles any suspected key comprom-
   ises, and manages any DNSSEC key changes.   Likewise, the application
   administrator is responsible for the same functions for the applica-
   tion keys related to the application.   For example, a user typically
   manages her own PGP key and a server manages its own TLS key.
   Application key management tasks are outside the scope of DNS
   administration.

   DNS zone keys are used to authenticate application keys, but applica-
   tion keys MUST NOT be used to authenticate DNS zone keys.   A DNS
   zone key is either configured as trusted key or authenticated by con-
   structing a chain of trust in the DNS hierarchy.   To participate in
   the chain of trust, a DNS zone must exchange zone key information
   with its parent zone [DNSSEC].   Application keys are not configured
   as trusted keys in the DNS and are never part of any DNS chain of
   trust.   Application key data should not be exchanged with the parent
   zone.   A resolver considers an application key authenticated if it
   has a valid signature from the local DNS zone keys, but applications
   may impose additional requirements before the application key is
   accepted as authentic.

   It MAY be useful for nameservers to include DNS zone keys in the
   additional section of a response, but application keys are typically
   not useful unless they have been specifically requested.   For exam-
   ple, it may be useful to include the isi.edu zone key along with a
   response that contain the www.isi.edu A record and SIG record.   A
   secure resolver will need the isi.edu zone key in order to check the
   SIG and authenticate the www.isi.edu A record.   It is typical not
   useful to include the IPSEC, email, and TLS keys along with the A



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   record.   Note that by placing application keys in the KEY record, a
   resolver will need the IPSEC, email, TLS, and other key associated
   with isi.edu if the resolver intends to authenticate the isi.edu zone
   key (since signatures only apply to the entire KEY set).

   DNS zone keys require special handling by resolvers, but application
   keys should be treated the same as any other type of DNS data.   The
   DNSSEC keys are of no value to end applications, unless the applica-
   tions plan to do their own DNS authentication.   Secure resolvers
   MUST NOT use application keys as part of the authentication process.
   Application keys have no unique value to resolvers and are only use-
   ful to the application requesting the key.   Note that if sub-types
   are used to identify the application key, then either the interface
   to the resolver must specify the sub-type or the application must be
   able to accept all KEY records and pick out the desired the sub-type.

   A fault or compromise of DNS zone key can lead to invalid or forged
   DNS data, but a fault or compromise of an application key should have
   no impact on other DNS data.   Incorrectly adding or changing a DNS
   zone key can invalidate all of the DNS data in zone and in all of its
   subzones.   By using a compromised key, an attacker can forge data
   from the effected zone and any for any of its sub-zones.  A fault or
   compromise of an application key has implications for that applica-
   tion, but it should not have an impact on the DNS. Note that applica-
   tion key faults and key compromises can have an impact on the entire
   DNS if the application key and DNS zone keys are both stored in the
   KEY record.

   In summary, DNS zone keys and application keys differ in most every
   respect.   DNS zone keys are an essential part of the DNS infrastruc-
   ture and require special handling by DNS administrators and DNS
   resolvers.  Application keys are simply another type of data and have
   no special meaning to DNS administrators or resolvers.   These two
   different types of data do not belong in the same resource record.


3.  Redefinition of the KEY Resource Record

   The KEY record is redefined as resource record for storing DNSSEC
   keys.   The KEY RDATA format, as defined in [DNSSEC], is not changed,
   but the Protocol Octet is redefined as follows:

              VALUE   Protocol
                0      - reserved
                1     HISTORIC
                2     HISTORIC
                3     dnssec
                4     HISTORIC



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              5-254    - reserved
                   255    HISTORIC

   All valid KEY records MUST have a Protocol Octet value of 3.   KEY
   records with a Protocol Octet value other than 3 SHOULD NOT be stored
   in the DNS and SHOULD be ignored by nameservers and resolvers that
   receive them in a response.


4.  Backward Compatibility

   Protocol Octet values of 1,2, 4, and 255 were previously defined in
   RFC 2535.   These values are now deprecated.   To insure backward
   compatibility, the Protocol Octet values 1,2, and 4 will be desig-
   nated as HISTORIC. Protocol values 5-254 are reserved and are no
   longer available for assignment by IANA.

   KEY records with a Protocol Value of 1,2, or 4 were never widely
   deployed in the DNS and some limited test deployment revealed prob-
   lems.  Most notably, placing application keys in the KEY record can
   create very large key sets and application keys that appear in the
   zone apex can create zone management problems.   Some change in the
   definition and/or usage of the KEY record would be required even if
   the approach described here were not required.

   KEY records with a Protocol Octet value of 1,2, or 4 SHOULD NOT be
   place in a DNS zone.   Likewise, resolvers that receive KEY records
   in a response with HISTORIC or invalid protocol field values SHOULD
   be ignored and SHOULD NOT be stored in a resolver's/server's cache.

   No changes are made to the format of the KEY record or to the use of
   DNSSEC zone, host and user keys.   Existing nameservers and resolvers
   will continue to correctly process KEY records that contain DNSSEC
   keys.


5.  Storing Application Keys in the DNS

   The scope of this document is strictly limited to the KEY record.
   This document prohibits storing application keys in the KEY record,
   but it does not endorse or restrict the storing application keys in
   other record types.   Other documents should describe how DNS handles
   application keys.


6.  IANA Consideration

   Protocol Octet values 1,2,4, and 255 are changed to HISTORIC.



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   Protocol Octet values 5-255 are reserved and are no longer available
   for assignment by IANA.


7.  Security Consideration

   This document eliminates potential security problems that could arise
   due to the coupling of DNS zone keys and application keys.

   Prior to the change described in the document, a correctly authenti-
   cated KEY set could include both application keys and DNSSEC keys.
   If one of the application keys is compromised, it could be used as a
   false zone key to create phony DNS signatures (SIG records).
   Resolvers that do not carefully check the KEY sub-type may believe
   these false signatures and incorrectly authenticate DNS data.   With
   this change, application keys cannot appear in an authenticated KEY
   set.

   Applications that accept keys based solely on DNSSEC rely on the DNS
   administrator to correctly enter the application key data and are
   only as secure as the weakest zone in the DNS chain of trust.
   Compromises or errors caused by DNS administrators when entering
   DNSSEC data could results in an application key failing to verify, or
   verified incorrectly.

   The format and correct usage of DNS zone keys is not changed by this
   document and no new security considerations are introduced.


8.  Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to per-
   tain to the implementation or use of the technology described in this
   document or the extent to which any license under such rights might
   or might not be available; neither does it represent that it has made
   any effort to identify any such rights.   Information on the IETF's
   procedures with respect to rights in standards-track and standards-
   related documentation can be found in BCP-11.

   Copies of claims of rights made available for publication and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementors or users of this specifica-
   tion can be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary



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   rights which may cover technology that may be required to practice
   this standard.   Please address the information to the IETF Executive
   Director.


9.  References

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


10.  Author Information

   Daniel Massey <masseyd@isi.edu>
   USC Information Sciences Institute
   3811 North Fairfax Drive, Suite 200
   Arlington, VA 22203

   Scott Rose <scott.rose@nist.gov>
   National Institute for Standards and Technology
   Gaithersburg, MD


Expiration and File Name:

   This draft, titled <draft-ietf-dnsext-restrict-key-for-dnssec-00.txt> expires April 2001


Full Copyright Statement


   Copyright (C) The Internet Society (2001).   All Rights Reserved.

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   in the Internet Standards process must be followed, or as required
   to translate it into languages other than English.

   The limited permissions granted above are perpetual and will not
   be revoked by the Internet Society or its successors or assigns.



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