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Versions: 00 01 02 04 05 06 07 08 09 10 11 12 RFC 3757

DNS Extensions                                                O. Kolkman
Internet-Draft                                                  RIPE NCC
Expires: January 16, 2004                                    J. Schlyter

                                                                E. Lewis
                                                                    ARIN
                                                           July 18, 2003


                  KEY RR Secure Entry Point (SEP) Flag
              draft-ietf-dnsext-keyrr-key-signing-flag-08

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
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on January 16, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   With the DS resource record the concept of a key acting as a secure
   entry point has been introduced.  During key-exchanges with the
   parent there is a need to differentiate secure entry point keys from
   other keys in the KEY resource record set.  A flag bit in the KEY RR
   is defined to indicate that KEY is to be used as a secure entry
   point.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  The Secure Entry Point (SEP) Flag  . . . . . . . . . . . . . .  4
   3.  DNSSEC Protocol Changes  . . . . . . . . . . . . . . . . . . .  4
   4.  Operational Guidelines . . . . . . . . . . . . . . . . . . . .  4
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  5
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
   7.  Internationalization Considerations  . . . . . . . . . . . . .  6
   8.  Document Changes . . . . . . . . . . . . . . . . . . . . . . .  6
   8.1 draft version 00 -> 01 . . . . . . . . . . . . . . . . . . . .  6
   8.2 draft version 01 -> 02 . . . . . . . . . . . . . . . . . . . .  6
   8.3 draft version 02 -> 03 . . . . . . . . . . . . . . . . . . . .  6
   8.4 draft version 03 -> 04 . . . . . . . . . . . . . . . . . . . .  7
   8.5 draft version 04 -> 05 . . . . . . . . . . . . . . . . . . . .  7
   8.6 draft version 05 -> 06 . . . . . . . . . . . . . . . . . . . .  7
   8.7 draft version 06 -> 07 . . . . . . . . . . . . . . . . . . . .  7
   8.8 draft version 07 -> 08 . . . . . . . . . . . . . . . . . . . .  7
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  8
       Normative References . . . . . . . . . . . . . . . . . . . . .  8
       Informative References . . . . . . . . . . . . . . . . . . . .  8
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  9
       Full Copyright Statement . . . . . . . . . . . . . . . . . . . 10




























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1. Introduction

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

   With the definition of the DS Resource Record [5] it has become
   important to differentiate between the zone keys that are (to be)
   pointed to by parental DS RRs and other keys in the zone.  We refer
   to these keys as Secure Entry Point (SEP) keys.  A SEP key is either
   used to generate a DS RR or is distributed to resolvers that use the
   key as the root of a trusted subtree[3].

   In early deployment tests, the use of two (kinds of) keys in each
   zone has been prevalent.  One key is used to sign just the zone's KEY
   RR set and is the key referenced by a DS RR at the parent or
   configured statically in a resolver.  Another key is used to sign the
   rest of the zone's data sets.  The former key is called a key-signing
   key (KSK) and the latter is called a zone-signing key (ZSK).  In
   practice there have been usually one of each kind of key, but there
   will be multiples of each at times.

   It should be noted that division of zone keys into KSK's and ZSK's is
   not mandatory in any definition of DNSSEC, not even with the
   introduction of the DS RR.  But, in testing, this distinction has
   been helpful when designing key roll over (key super-cession)
   schemes.  Given that the distinction has proven helpful, the labels
   KSK and ZSK have begun to stick.

   There is a need to differentiate between a KSK and a ZSK by the zone
   administrator.  This need is driven by knowing which keys are to be
   sent for DS RRs, which keys are to be distributed to resolvers, and
   which keys are fed to the signer application at the appropriate time.

   The reason for the term "SEP" is a result of the observation that the
   distinction between KSK and ZSK is only significant to the signer
   element of the DNS.  Servers, resolvers and verifiers do not need to
   make the distinction.  Further, distinguishing between a KSK and ZSK
   requires more than one bit, as a key could be fulfilling both roles.
   Hence, there is no definition for a ZSK bit and another for a KSK
   bit, just a single bit to assist operational procedures to correctly
   generate DS RRs, or to indicate what keys are intended for static
   configuration.

   In the flow between signer and (parental) key-collector and in the
   flow between the signer and the resolver configuration it is
   important to be able to differentiate the SEP keys from the other
   keys in a KEY RR set.  The SEP flag is to be of no interest to the
   flow between the verifier and the authoritative data store.




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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.

2. The Secure Entry Point (SEP) 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          |S|   protocol    |   algorithm   |
      |                             |E|               |               |
      |                             |P|               |               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               /
      /                        public key                             /
      /                                                               /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                KEY RR Format



   The SEP bit (TBD) in the flags field is assigned to be the secure
   entry point flag.  If the the bit is set to 1 the key is intended to
   be used as secure entry point key.  One SHOULD NOT assign special
   meaning to the key if the bit is set to 0.  The document proposes
   using the current 15th bit [4] as the SEP bit.  This way operators
   can recognize the secure entry point key by the even or odd-ness of
   the decimal representation of the flag field.

3. DNSSEC Protocol Changes

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

4. Operational Guidelines

   The SEP bit is set by the key-generator and MAY be used by the zone
   signer to decide whether the key is to be prepared for input to a DS
   RR generation function.  As the SEP bit is within the data that is
   used to compute a KEY RR's footprint, changing the SEP bit will
   change the identity of the key within DNS.

   When a key pair is created, the operator needs to indicate whether



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   the SEP bit is to be set in the KEY RR.  The SEP bit is recommended
   whenever the public key of the key pair will be distributed to the
   parent zone to build the authentication chain or if the public key is
   to be distributed for static configuration in verifiers.

   When signing a zone, it is intended that the key(s) with the SEP bit
   set (if such keys exist) are used to sign the KEY RR set of the zone.
   The same key can be used to sign the rest of the zone data too.  It
   is conceivable that not all keys with a SEP bit set will sign the KEY
   RR set, such keys might be pending retirement or not yet in use.

   When verifying a RR set, the SEP bit is not intended to play a role.
   How the key is used by the verifier is not intended to be a
   consideration at key creation time.

   Although the SEP flag provides a hint on which key to be used as
   trusted root, administrators can choose to ignore the fact that a KEY
   has its SEP bit set or not when configuring a trusted root for their
   resolvers.

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

5. Security Considerations

   As stated in Section 3 the flag is not to 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 key set, containing two keys with the SEP flag set, is sent
   to the parent.  The parent verifies the key set 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 defense.  A simple
   defense can be based on a registry of keys that have been used to
   generate DS RRs during the most recent roll over.  These same
   considerations apply to entities that configure keys in resolvers.





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6. IANA Considerations

   draft-ietf-dnsext-restrict-key-for-dnssec [4] eliminates all flags
   field except for the zone key flag in the KEY RR.  We propose to use
   the 15'th bit as the SEP bit; the decimal representation of the
   flagfield will then be odd for key-signing keys.

7. Internationalization Considerations

   Although SEP is a popular acronym in many different languages, 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 defenses 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 key tag changes in SIG RR.


8.5 draft version 04 -> 05

      One occurrence of must and one occurrence of should uppercased
      (RFC2119).

      Reordering of sentences in section 3, so that the point of the bit
      NOT being used in resolving is made directly.

      To make explicit that the KSK is used at key generation and at
      signing time I added the first sentence to section 4.

      Some minor style and spelling corrections.


8.6 draft version 05 -> 06

      References and acronyms where stripped from the Abstract.  the
      Introduction and the the Operational Guideline section were
      rewritten in such a way that the draft does not suggest any use of
      the bit in the verification process and that the draft does not
      enforce, but suggests, the use of a key- and zone-signing key.

      Added 'and verification' in the sentence "MUST NOT be used during
      the resolving and verification process" (protocol changes
      section).


8.7 draft version 06 -> 07

      Based on comments during the last call we changed the name from
      KSK-flag to SEP flag.  The introduction was rewritten to reflect
      the motivations of this name change and to stress that the SEP key
      is not relevant to the signer process.


8.8 draft version 07 -> 08

      During the edit of version 07, a paragraph got dropped from the
      introduction (See message by Lewis dd June 19, subject " Fwd: Re:
      NOTIFY + SIG(0) + DS => secure parent update?" (http://



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      ops.ietf.org/lists/nhamedroppers/namedroppers.2003/msg01336.html).
      This version re-introduces the paragraph, which caused some
      reordering and style changes in the introduction.


9. Acknowledgments

   The ideas documented in this document are inspired by communications
   we had with numerous people and ideas published by other folk.  Among
   others Mark Andrews, Miek Gieben, Olafur Gudmundsson, Daniel
   Karrenberg, 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]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

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

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

   [4]  Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource
        Record (RR)", RFC 3445, December 2002.

Informative References

   [5]  Gudmundsson, O., "Delegation Signer Resource Record", draft-
        ietf-dnsext-delegation-signer-14 (work in progress), May 2003.

   [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
   Karl Gustavsgatan 15
   Goteborg  SE-411 25
   Sweden

   EMail: jakob@schlyter.se


   Edward P. Lewis
   ARIN
   3635 Concorde Parkway Suite 200
   Chantilly, VA  20151
   US

   Phone: +1 703 227 9854
   EMail: edlewis@arin.net
   URI:   http://www.arin.net/





















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Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
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Acknowledgement

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



















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