DNS Extensions                                                O. Kolkman
Internet-Draft                                                  RIPE NCC
Expires: March 28, 2004                                      J. Schlyter

                                                                E. Lewis
                                                      September 28, 2003

                     KEY RR Secure Entry Point Flag

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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Copyright Notice

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


   With the Delegation Signer (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 (RR) set.
   A flag bit in the KEY RR is defined to indicate that KEY is to be
   used as a secure entry point. The flag bit is intended to assist in
   operational procedures to correctly generate DS resource records, or
   to indicate what keys are intended for static configuration. The flag
   bit is not to be used in the DNS verification protocol. This document

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   updates RFC 2535 and RFC 3445.

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  . . . . . . . . . . . . . . . . . . . . . . 5
   7. Internationalization Considerations  . . . . . . . . . . . . . . 6
   8. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . 6
      Normative References . . . . . . . . . . . . . . . . . . . . . . 6
      Informative References . . . . . . . . . . . . . . . . . . . . . 6
      Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
      Intellectual Property and Copyright Statements . . . . . . . . . 8

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1. Introduction

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

   With the definition of the Delegation Signer Resource Record (DS RR)
   [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
   resource record (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.

   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.

   The reason for the term "SEP" is a result of the observation that the
   distinction between KSK and ZSK is made by the signer, a key could be
   both a KSK and a ZSK. To be clear, the term SEP was coined to lessen
   the confusion caused by the overlap. (Once this label was applied, it
   had the side effect of removing the temptation to have a KSK flag bit
   and a ZSK flag bit, setting on needing just one bit.)

   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 [1].

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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.  This document assigns the
   15'th 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 protocol or the
   resolution process.

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.  The SEP bit is recommended to be set (to 1)
   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 a key pair is created, the operator needs to indicate whether
   the SEP bit is to be set in the KEY RR.  As the SEP bit is within the
   data that is used to compute the 'key tag field' in the SIG RR,
   changing the SEP bit will change the identity of the key within DNS.

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   In other words, once a key is used to generate signatures, the
   setting of the SEP bit is to remain constant. If not, a verifier will
   not be able to find the relevant KEY RR.

   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

   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 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 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.

6. IANA Considerations

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   IANA considerations:  The flag bits  in the KEY RR are assigned by
   IETF consensus. There is no action on IANA.

7. Internationalization Considerations

   Although SEP is a popular acronym in many different languages, there
   are no internationalization considerations.

8. 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, Scott Rose, 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 in August 2002.

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-15 (work in progress), June

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

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Authors' Addresses

   Olaf M. Kolkman
   Singel 256
   Amsterdam  1016 AB

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

   Jakob Schlyter
   Karl Gustavsgatan 15
   Goteborg  SE-411 25

   EMail: jakob@schlyter.se

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

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

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   Funding for the RFC Editor function is currently provided by the
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