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Versions: 00 01 02                                                      
DNSOP                                                          G. Guette
Internet-Draft                                             IRISA / INRIA
Expires: February 5, 2005                                     O. Courtay
                                                             Thomson R&D
                                                          August 7, 2004

           Requirements for Automated Key Rollover in DNSSEC

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Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.


   This document describes problems that appear during an automated
   rollover and gives the requirements for the design of communication
   between parent zone and child zone in an automated rollover process.
   This document is essentially about key rollover, the rollover of
   another Resource Record present at delegation point (NS RR) is also

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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.   The Key Rollover Process . . . . . . . . . . . . . . . . . . . 3
   3.   Basic Requirements . . . . . . . . . . . . . . . . . . . . . . 4
   4.   Messages authentication and information exchanged  . . . . . . 4
   5.   Emergency Rollover . . . . . . . . . . . . . . . . . . . . . . 5
   6.   Other Resource Record concerned by automatic rollover  . . . . 5
   7.   Security consideration . . . . . . . . . . . . . . . . . . . . 5
   8.   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 5
   9.   Normative References . . . . . . . . . . . . . . . . . . . . . 5
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6
        Intellectual Property and Copyright Statements . . . . . . . . 7

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1.  Introduction

   The DNS security extensions (DNSSEC) [4][8][7][9] uses public-key
   cryptography and digital signatures.  It stores the public part of
   keys in DNSKEY Resource Records (RRs).  Because old keys and
   frequently used keys are vulnerable, they must be renewed
   periodically.  In DNSSEC, this is the case for Zone Signing Keys
   (ZSKs) and Key Signing Keys (KSKs) [1][2].  Automation of key
   rollover process is necessary for large zones because there are too
   many changes to handle a manual administration.

   Let us consider for example a zone with 100000 secure delegations.
   If the child zones change their keys once a year on average, that
   implies 300 changes per day for the parent zone.  This amount of
   changes are hard to manage manually.

   Automated rollover is optional and resulting from an agreement
   between the administrator of the parent zone and the administrator of
   the child zone.  Of course, key rollover can also be done manually by

   This document describes the requirements for the design of messages
   of automated key rollover process and focusses on interaction between
   parent and child zone.

2.  The Key Rollover Process

   Key rollover consists in renewing the DNSSEC keys used to sign
   resource records in a given DNS zone file.  There are two types of
   rollover, ZSK rollovers and KSK rollovers.

   In a ZSK rollover, all changes are local to the zone that renews its
   key: there is no need to contact other zones (e.g., parent zone) to
   propagate the performed changes because a ZSK has no associated DS
   record in the parent zone.

   In a KSK rollover, new DS RR(s) must be created and stored in the
   parent zone.  In consequence, the child zone must contact its parent
   zone and must notify it about the KSK change(s).

   Manual key rollover exists and works [3].  The key rollover is built
   from two parts of different nature:
   o  An algorithm that generates new keys and signs the zone file.  It
      could be local to the zone
   o  The interaction between parent and child zones

   One example of manual key rollover is:

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   o  The child zone creates a new KSK
   o  The child zone waits for the creation of the DS RR in its parent
   o  The child zone deletes the old key.

   In manual rollover, communications are managed by the zone
   administrators and the security of these communications is out of
   scope of DNSSEC.

   Automated key rollover should use a secure communication between
   parent and child zones.  This document concentrates on defining
   interactions between entities present in key rollover process.

3.  Basic Requirements

   The main constraint to respect during a key rollover is that the
   chain of trust MUST be preserved, even if a resolver retrieves some
   RRs from recursive cache server.  Every RR MUST be verifiable at any
   time, every RRs exchanged during the rollover should be authenticated
   and their integrity should be guaranteed.

   Two entities act during a KSK rollover: the child zone and its parent
   zone.  These zones are generally managed by different administrators.
   These administrators should agree on some parameters like
   availability of automated rollover, the maximum delay between
   notification of changes in the child zone and the resigning of the
   parent zone.  The child zone needs to know this delay to schedule its

4.  Messages authentication and information exchanged

   Every exchanged message MUST be authenticated and the authentication
   tool MUST be a DNSSEC tool such as TSIG [6], SIG(0) [5] or DNSSEC
   request with verifiable SIG records.

   Once the changes related to a KSK are made in a child zone, this zone
   MUST notify its parent zone in order to create the new DS RR and
   store this DS RR in parent zone file.

   The parent zone MUST receive all the child keys that needs the
   creation of associated DS RRs in the parent zone.

   Some errors could occur during transmission between child zone and
   parent zone.  Key rollover solution MUST be fault tolerant, i.e.  at
   any time the rollover MUST be in a consistent state and all RRs MUST
   be verifiable, even if an error occurs.  That is to say that it MUST
   remain a valid chain of trust.

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5.  Emergency Rollover

   A key of a zone might be compromised and this key MUST be changed as
   soon as possible.  Fast changes could break the chain of trust.  The
   part of DNS tree having this zone as apex can become unverifiable,
   but the break of the chain of trust is necessary if we want to no one
   can use the compromised key to spoof DNS data.

   In case of emergency rollover, the administrators of parent and child
   zones should create new key(s) and DS RR(s) as fast as possible in
   order to reduce the time the chain of trust is broken.

6.  Other Resource Record concerned by automatic rollover

   NS records are also present at delegation point, so when the child
   zone renews some NS RR, the corresponding records at delegation point
   in parent zone (glue) MUST be updated.  NS records are concerned by
   rollover and this rollover could be automated too.  In this case,
   when the child zone notifies its parent zone that some NS records
   have been changed, the parent zone MUST verify that these NS records
   are present in child zone before doing any changes in its own zone
   file.  This allows to avoid inconsistency between NS records at
   delegation point and NS records present in the child zone.

7.  Security consideration

   This document describes requirements to design an automated key
   rollover in DNSSEC based on DNSSEC security.  In the same way, as
   plain DNSSEC, the automatic key rollover contains no mechanism
   protecting against denial of service (DoS).  The security level
   obtain after an automatic key rollover, is the security level
   provided by DNSSEC.

8.  Acknowledgments

   The authors want to acknowledge Francis Dupont, Mohsen Souissi,
   Bernard Cousin, Bertrand L‰onard and members of IDsA project for
   their contribution to this document.

9  Normative References

   [1]  Gudmundsson, O., "Delegation Signer (DS) Resource Record (RR)",
        RFC 3658, December 2003.

   [2]  Kolkman, O., Schlyter, J. and E. Lewis, "Domain Name System KEY
        (DNSKEY) Resource Record (RR) Secure Entry Point (SEP) Flag",
        RFC 3757, May 2004.

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   [3]  Kolkman, O., "DNSSEC Operational Practices",
        draft-ietf-dnsop-dnssec-operational-practice-01 (work in
        progress), May 2004.

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

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

   [6]  Vixie, P., Gudmundsson, O., Eastlake, D. and B. Wellington,
        "Secret Key Transaction Authentication for DNS (TSIG)", RFC
        2845, May 2000.

   [7]  Arends, R., "Resource Records for the DNS Security Extensions",
        draft-ietf-dnsext-dnssec-records-09 (work in progress), July

   [8]  Arends, R., Austein, R., Massey, D., Larson, M. and S. Rose,
        "DNS Security Introduction and Requirements",
        draft-ietf-dnsext-dnssec-intro-11 (work in progress), July 2004.

   [9]  Arends, R., "Protocol Modifications for the DNS Security
        Extensions", draft-ietf-dnsext-dnssec-protocol-07 (work in
        progress), July 2004.

Authors' Addresses

   Gilles Guette
   Campus de Beaulieu
   35042  Rennes CEDEX

   EMail: gilles.guette@irisa.fr
   URI:   http://www.irisa.fr

   Olivier Courtay
   Thomson R&D
   1, avenue Belle Fontaine
   35510  Cesson S‰vign‰ CEDEX

   EMail: olivier.courtay@thomson.net

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