DNS Extensions                                                O. Kolkman
Internet-Draft                                                  RIPE NCC
Expires: June 3, 2003                                        J. Schlyter
                                                    Carlstedt Research &
                                                              Technology
                                                        December 3, 2002


                   KEY RR Key-Signing Key (KSK) Flag
              draft-ietf-dnsext-keyrr-key-signing-flag-04

Status of this Memo

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

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   This Internet-Draft will expire on June 3, 2003.

Copyright Notice

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

Abstract

   With the DS record [5] the concept of key-signing and zone-signing
   keys has been introduced.  Key-signing keys are the keys that sign
   the keyset only.  In general, key-signing keys are the keys that are
   pointed to by DS records and are the first keys to be used when
   following a chain of trust into the zone.  The key-signing keys only
   sign the KEY RRset at the apex of a zone, zone- signing keys sign all
   other data in a zone.  We propose a flag to distinguish the key-
   signing key from other keys in the KEY RR set during DNSSEC
   operations.



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   The key words "MAY","MAY NOT", "MUST", "MUST NOT", "REQUIRED",
   "RECOMMENDED", "SHOULD", and "SHOULD NOT" in this document are to be
   interpreted as described in RFC2119.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  The Key-Signing Key (KSK) Flag . . . . . . . . . . . . . . . .  3
   3.  DNSSEC Protocol Changes  . . . . . . . . . . . . . . . . . . .  4
   4.  Operational Guidelines . . . . . . . . . . . . . . . . . . . .  4
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  4
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  5
   7.  Internationalization Considerations  . . . . . . . . . . . . .  5
   8.  Document Changes . . . . . . . . . . . . . . . . . . . . . . .  5
   8.1 draft version 00 -> 01 . . . . . . . . . . . . . . . . . . . .  5
   8.2 draft version 01 -> 02 . . . . . . . . . . . . . . . . . . . .  5
   8.3 draft version 02 -> 03 . . . . . . . . . . . . . . . . . . . .  5
   8.4 draft version 03 -> 04 . . . . . . . . . . . . . . . . . . . .  6
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  6
       Normative References . . . . . . . . . . . . . . . . . . . . .  6
       Informative References . . . . . . . . . . . . . . . . . . . .  6
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  7
       Full Copyright Statement . . . . . . . . . . . . . . . . . . .  8




























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1. Introduction

   "All keys are equal but some keys are more equal than others" [6]

   With the DS record [5] the concept of key-signing and zone-signing
   keys has been introduced into DNSSEC[3].  In general these are the
   keys that are pointed to by DS records and are the first keys to be
   used when following the chain of trust into a zone ( secure entry
   points of the zone).  These key-signing keys may also be configured
   in resolver systems that use zones as a trusted root[4] for a secure
   island.

   Early deployment tests have shown that during the key-exchange
   between the parent and the child it is useful to highlight which keys
   are to be used as the secure entry point to a zone.  We introduce the
   Key-Signing Key flag to indicate this special 'administrative' status
   of the key.  The availability of the flag allows the key exchange to
   be automated where, without the flag, some additional out-of-band
   communication is needed.

2. The Key-Signing Key (KSK) Flag


                           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          |K|   protocol    |   algorithm   |
      |                             |S|               |               |
      |                             |K|               |               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               /
      /                        public key                             /
      /                                                               /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                KEY RR Format



   The KSK bit (TBD) in the flags field is assigned to be the key-
   signing flag.  If set the key is intended to be used as key-signing
   key.  No special meaning should be assigned to the bit not being set.
   The draft proposes using the current 15'th bit [1] as the KSK bit.
   This way operators can recognize the key-signing by the parity of the
   decimal representation of the flag field.






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3. DNSSEC Protocol Changes

   The use of the KSK flag does not change the DNS resolution and
   resolution protocol.  The KSK flag is only used to provide a hint
   about the different administrative properties and MUST NOT be used
   during the resolving process.

4. Operational Guidelines

   By setting the KSK flag on a particular key, zone administrators
   indicate that that key SHOULD be used as the secure entry point for
   their zone.  Therefore zone administrators SHOULD set the bit only
   for zone keys that are used to sign the KEY RRset and are intended to
   act as the first link in the chain of trust for their zone.

   Parent zone administrators and resolver administrators that want to
   configure a key-signing key as their 'trusted key' MAY choose to
   ignore the flag.

   Using the flag a key roll over can be automated.  The parent can use
   an existing trust relation to verify keysets in which a new key with
   the KSK flag appears.

   If the bit is modified during the lifetime of the key then this would
   have impact on the keytag in the SIG RRs and on the hash data in the
   DS RRs intending to point to this key.  The bit SHOULD NOT be
   modified once the key has been put into use.

5. Security Considerations

   The flag MUST NOT be used in the resolution protocol or to determine
   the security status of a key.  The flag is to be used for
   administrative purposes only.

   No trust in a key should be inferred from this flag - trust must be
   inferred from an existing chain of trust or an out-of-band exchange.

   Since this flag might be used for automating key exchanges, we think
   the following consideration is in place.

   Automated mechanisms for roll over of the DS RR might be vulnerable
   to a class of replay attacks.  This might happen after a key exchange
   where a keyset, containing two keys with the KSK flag set, is sent to
   the parent.  The parent verifies the keyset with the existing trust
   relation and creates the new DS RR from the key that the current DS
   is not pointing to.  This key exchange might be replayed.  Parents
   are encouraged to implement a replay defence.  A simple defence can
   be based on a registry of keys that have been used to generate DS RRs



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   during the most recent roll over.

6. IANA Considerations

   draft-ietf-dnsext-restrict-key-for-dnssec [1] eliminates all flags
   field except for the zone key flag in the KEY RR.  We propose to use
   the 15'th bit as the KSK bit; the decimal representation of the
   flagfield will then be odd for key-signing keys.

7. Internationalization Considerations

   There are no internationalization considerations

8. Document Changes

8.1 draft version 00 -> 01

      Clean up of references and correction of typos;

      modified Abstract text a little;

      Added explicit warning for replay attacks to the security section;

      Removed the text that hinted on a distinction between a key-
      signing key configured in resolvers and in parent zones.


8.2 draft version 01 -> 02

      Added IANA and Internationalization section.

      Split references into informational and normative.

      Spelling and style corrections.


8.3 draft version 02 -> 03

      Changed the name from KS to KSK, this to prevent confusion with
      NS, DS and other acronyms in DNS.

      In the security section: Rewrote the section so that it does not
      suggest to use a particular type of registry and that it is clear
      that a key registry is only one of the defences possible.

      Spelling and style corrections





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8.4 draft version 03 -> 04

      Text has been made consistent with the statement: ' No special
      meaning should be assigned to the bit not being set.'

      Made explicit that the keytag changes in SIG RR.


9. Acknowledgements

   The ideas documented in this draft are inspired by communications we
   had with numerous people and ideas published by other folk.  Among
   others Olafur Gudmundsson, Daniel Karrenberg, Ed Lewis, Dan Massey,
   Marcos Sanz and Sam Weiler have contributed ideas and provided
   feedback.

   This document saw the light during a workshop on DNSSEC operations
   hosted by USC/ISI.

Normative References

   [1]  Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource
        Record out", draft-ietf-dnsext-restrict-key-for-dnssec-04 (work
        in progress), September 2002.

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

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

   [4]  Lewis, E., "DNS Security Extension Clarification on Zone
        Status", RFC 3090, March 2001.

Informative References

   [5]  Gudmundsson, O., "Delegation Signer Resource Record", draft-
        ietf-dnsext-delegation-signer-09 (work in progress), September
        2002.

   [6]  Orwell, G. and R. Steadman (illustrator), "Animal Farm; a Fairy
        Story"", ISBN 0151002177 (50th anniversery edition), April 1996.









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Authors' Addresses

   Olaf M. Kolkman
   RIPE NCC
   Singel 256
   Amsterdam  1016 AB
   NL

   Phone: +31 20 535 4444
   EMail: olaf@ripe.net
   URI:   http://www.ripe.net/


   Jakob Schlyter
   Carlstedt Research & Technology
   Stora Badhusgatan 18-20
   Goteborg  SE-411 21
   Sweden

   EMail: jakob@crt.se
   URI:   http://www.crt.se/~jakob/






























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Full Copyright Statement

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Acknowledgement

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



















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