DNS Extensions                                                 D. Massey
Internet-Draft                                                   USC/ISI
Expires: December 27, 2002                                       S. Rose
                                                           June 28, 2002

             Limiting the Scope of the KEY Resource Record


Status of this Document Memo

   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
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Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.


   This document limits the Domain Name System KEY resource record to
   only keys used by the Domain Name System Security Extensions
   (DNSSEC).  The original KEY resource record used sub-typing to store
   both DNSSEC keys and arbitrary application keys.  Storing both DNSSEC
   and application keys in one record was a mistake.  This document
   removes application keys from the KEY record by redefining the
   Protocol Octet field in the KEY Resource Record Data.  As a result of
   removing application keys, all but one of the flags in the KEY record
   become unnecessary and are removed.  Three existing application key
   sub-types are changed to reserved, but the format of the KEY record
   is not changed.  This document updates RFC 2535.


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

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Motivation for Restricting the KEY Record  . . . . . . . . . .  4
   2.1 Differences Between DNSSEC and Application Keys  . . . . . . .  4
   3.  Definition of the KEY Resource Record  . . . . . . . . . . . .  7
   4.  Changes from RFC 2535 KEY Record . . . . . . . . . . . . . . .  8
   5.  Backward Compatibility . . . . . . . . . . . . . . . . . . . . 10
   6.  Storing Application Keys in the DNS  . . . . . . . . . . . . . 11
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
       References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14
       Full Copyright Statement . . . . . . . . . . . . . . . . . . . 15

1. Introduction

   This document limits the scope the KEY resource record.  The KEY
   resource record was defined in [1] [2] and used resource record sub-typing sub-
   typing to hold arbitrary public keys such as Email, IPSEC, DNSSEC,
   and TLS keys.  This document eliminates the existing Email, IPSEC,
   and TLS sub-types and prohibits the introduction of new sub-types.
   DNSSEC will be the only allowable sub-type for the KEY record (hence
   sub-typing is essentially eliminated) and all but one of the KEY
   record flags are also eliminated.

   Section 2 presents the motivation for restricting the KEY record and
   Section 3 defines the revised KEY record.  Section  Sections 4 and 5 summarize
   the changes from RFC 2535 and discuss backwards compatibility.  It is
   important to note that this document restricts the use of the KEY
   record and simplifies the flags, but does not change the definition
   or use of DNSSEC keys.


2. Motivation for Restricting the KEY Record

   The KEY record RDATA [1]  [2] consists of Flags, a Protocol Octet, an
   Algorithm type, and a Public Key.  The Protocol  Octet identifies the
   KEY record sub-type.  DNSSEC public keys are stored in the KEY record
   using a Protocol Octet value of 3.  Email, IPSEC, and TLS keys were
   also stored in the KEY record and used Protocol Octet values of 1,2,
   and 4 (respectively).  Protocol Octet values 5-254 were available for
   assignment by IANA and values were requested (but not assigned) for
   applications such as SSH.

   Any use of sub-typing has inherent limitations.  A resolver can not
   specify the desired sub-type in a DNS query and most DNS operations
   apply only to resource records sets.  For a example, a resolver can not
   directly request the DNSSEC subtype KEY records with a particular sub-type. records.  Instead, the
   resolver has to request all KEY records associated with a DNS name
   and then search the set for the desired DNSSEC sub-type.  DNSSEC
   signatures also 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 the sub-type is used to distinguish between DNSSEC
   keys and application keys.  DNSSEC keys and application keys differ
   in virtually every respect and Section 2.1 discusses these
   differences in more detail.  Combining these very different types of
   keys into a single sub-typed resource record adds unnecessary
   complexity and increases the potential for implementation and
   deployment errors.  Limited experimental deployment has shown that
   application keys stored in KEY records are problematic.

   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

2.1 Differences Between DNSSEC and Application Keys

   DNSSEC keys are an essential part of the DNSSEC protocol and are used
   by both name servers and resolvers in order to perform DNS tasks.  A
   DNS zone key, used to sign and authenticate RR sets, is the most
   common example of a DNSSEC key.  SIG(0) [3] and TKEY [2]  also use
   DNSSEC keys.

   Application keys such as Email keys, IPSEC keys, and TLS keys are
   simply another type data.  These keys have no special meaning to a
   name server or resolver.

   The following table summarizes some of the differences between DNSSEC
   keys and Application keys:

   1.  They serve different purposes.

   2.  They are managed by different administrators.

   3.  They are authenticated according to different rules.

   4.  Nameservers use different rules when including them in responses.

   5.  Resolvers process them in different ways.

   6.  Faults/key compromises have different consequences.

   1.  The purpose of a DNSSEC key is to sign resource records
   associated with a DNS  zone (or generate DNS transaction signatures
   in the case of SIG(0)/TKEY).  But the purpose of an application key
   is specific to the application.  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.

   2.  DNSSEC keys are managed by DNS administrators, but application
   keys are managed by application administrators.  The DNS zone
   administrator determines the key lifetime, handles any suspected key
   compromises, and manages any DNSSEC key changes.  Likewise, the
   application administrator is responsible for the same functions for
   the application 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

   3.  DNSSEC zone keys are used to authenticate application keys, but
   application keys MUST NOT be used to authenticate DNS zone keys.  A
   DNS zone key is either configured as trusted key or authenticated by
   constructing a chain of trust in the DNS hierarchy.  To participate
   in the chain of trust, a DNS zone needs to exchange zone key
   information with its parent zone [1]. [2].  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 could impose additional requirements before
   the application key is accepted as authentic.

   4.  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
   example, it could 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
   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 RR set).

   5.  DNS zone keys require special handling by resolvers, but
   application keys are treated the same as any other type of DNS data.
   The DNSSEC keys are of no value to end applications, unless the
   applications 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 useful to the application requesting the key.  Note that if sub-types sub-
   types are used to identify the application key, then either the
   interface to the resolver needs to specify the sub-type or the
   application needs to be able to accept all KEY records and pick out
   the desired the sub-type.

   6.  A fault or compromise of a 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. sub-
   zones.  A fault or compromise of an application key has implications
   for that application, but it SHOULD not have an impact on the DNS.
   Note that application 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, DNSSEC keys and application keys differ in most every
   respect.  DNSSEC keys are an essential part of the DNS infrastructure
   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. Definition of the KEY Resource Record

   The KEY record uses type 25 and is used as resource record for
   storing DNSSEC keys.  The RDATA for a KEY RR consists of flags, a
   protocol octet, the algorithm number octet, and the public key
   itself.  The format is as follows:


                        1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |              flags            |   protocol    |   algorithm   |
   |                                                               /
   /                        public key                             /
   /                                                               /

                             KEY RR Format


   In the flags field, all bits except bit 7 are reserved and SHOULD be
   zero.  If Bit 7 (Zone bit) is set to 1, then the KEY is a DNS Zone
   key.  If Bit 7 is set to 0, the KEY is not a zone key.  SIG(0)/TKEY
   are examples of DNSSEC keys that are not zone keys.

   The protocol field MUST be set to 3.

   The algorithm and public key fields are not changed.


4. Changes from RFC 2535 KEY Record

   The KEY RDATA format is not changed.

   All flags except for the zone key flag are eliminated:


      The A/C bits (bits 0 and 1) are eliminated.  They SHOULD MUST be set to 0 by the sender
      and MUST be ignored by the receiver.


      The extended flags bit (bit 3) is eliminated.  It SHOULD MUST be set to 0 by the sender
      and MUST be ignored by the receiver.


      The host/user bit (bit 6) is eliminated.  It SHOULD MUST be set to 0 by the sender and
      MUST be ignored by the receiver.


      The zone bit (bit 7) remains unchanged.


      The signatory field (bits 12-15) are eliminated by [4].  They
      be set to 0 by the sender and MUST be ignored by the receiver.


      Bits 2,4,5,8,9,10,11 remain unchanged.  They are reserved, SHOULD MUST be
      set to zero by the sender, and MUST be ignored by the receiver.

   Assignment of any future KEY record Flag values requires a standards

   All Protocol Octet values except DNSSEC (3) are eliminated:


      Value 1 (Email) is renamed to reserved.


      Value 2 (IPSEC) is renamed to reserved.


      Value 3 (DNSSEC) is unchanged.


      Value 4 (TLS) is renamed to reserved.


      Value 5-254 remains unchanged (reserved).


      Value 255 (ANY) is renamed to reserved.

Name servers and resolvers SHOULD reject

   The authoritative data for a zone MUST NOT include any KEY records
   with a Protocol protocol octet other than 3.  Assignment of any  Any future KEY record Protocol
   Octet values requires a standards action.

   Name servers and resolvers SHOULD accept KEY RR sets that contain KEY
   records with a value other than 3.  If out of date DNS zones contain
   deprecated KEY records with a protocol octet value other than 3, then
   simply dropping the deprecated KEY records from the KEY RR set would
   invalidate any associated SIG record(s) and could create caching
   consistency problems.  Note that KEY records with a protocol octet
   value other than 3 MUST NOT be used to authenticate DNS data.

   The algorithm and public key fields are not changed.


5. Backward Compatibility

   DNSSEC zone key records are not change changed and remain backwards
   compatible.  A properly formatted RFC 2535 zone KEY would have all
   flag bits, other than the Zone Bit (Bit 7), set to 0 and would have
   the Protocol Octet set to 3.  This remains true under the restricted

   DNSSEC non-zone key records (SIG(0)/TKEY keys) are backwards
   compatible, but the distinction between host and user keys (flag bit
   6) is lost.

   No backwards compatibility is provided for application keys.  Any
   Email, IPSEC, or TLS keys are now deprecated and SHOULD be rejected
by name servers and resolvers. deprecated.  Storing application
   keys in the KEY record created problems such as keys at the apex and
   large RR sets and some change in the definition and/or usage of the
   KEY record would have been required even if the approach described
   here were not adopted.

   Overall, existing nameservers and resolvers will continue to
   correctly process KEY records with a sub-type of DNSSEC keys.


6. 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 can describe how DNS handles
   application keys.


7. IANA Consideration Considerations

   RFC 2535 created an IANA registry for DNS KEY Resource Record
   Protocol Octet values.  Values to 1,2,3, 4, and 255 were assigned by
   RFC 2535 and values 5-254 were made available for assignment by IANA.
   This document makes two sets of changes to this registry.

   First, this document re-assigns DNS KEY Resource Record Protocol
   Octet values 1, 2, 4, and 255 to ``reserved''.  DNS Key Resource
   Record Protocol Octet Value 3 remains unchanged as ``DNSSEC''.

   Second, new values are no longer available for assignment by IANA and
   this document closes the IANA registry for DNS KEY Resource Record
   Protocol Octet Values.  Assignment of any future KEY Resource Record
   Protocol Octet values requires a standards action.


8. Security Consideration Considerations

   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 this document, a correctly authenticated 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 false DNS signatures (SIG records).  Resolvers that do
   not carefully check the KEY sub-type could believe these false
   signatures and incorrectly authenticate DNS data.  With this change,
   application keys cannot appear in an authenticated KEY set and this
   vulnerability is eliminated.

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

9 Intellectual Property

The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to pertain
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 specification
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 rights
which may cover technology that may be required to practice this
standard.  Please address the information to the IETF Executive Director.


References (Normative)

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

   [2]  Eastlake, D., "Secret Key Establishment for DNS (TKEY RR)", RFC
        2930, September 2000.

   [3]  Eastlake, D., "DNS Request and Transaction Signatures (
        SIG(0)s)", RFC 2931, September 2000.

   [4]  Wellington, B., "Secure Domain Name System (DNS) Dynamic
        Update", RFC 3007, November 2000.

11 Author Information


Authors' Addresses

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

   EMail: masseyd@isi.edu

   Scott Rose <scott.rose@nist.gov>
   National Institute for Standards and Technology
   100 Bureau Drive
   Gaithersburg, MD  20899-3460

   EMail: scott.rose@nist.gov

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