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Versions: 00 01 02                                                      
DNSOP                                                          G. Guette
Internet-Draft                                        IRISA/INRIA Rennes
Expires: August 8, 2004                                       O. Courtay
                                                        February 8, 2004

            Requirements for Automated Key Rollover in DNSsec

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
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   This Internet-Draft will expire on August 8, 2004.

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
   one other Resource Record present at delegation point (NS RR) is
   also discussed.

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1. Introduction

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

   Let us consider for example a zone with one million child zones among
   which only 10% of secured child zones. If the child zones change their
   keys once a year on average, that implies 300 changes per day for the
   parent zone. All these 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.

2. The Key Rollover Process

   Key rollover consists in replacing the DNSsec keys used to sign
   resource records in a given DNS zone file. There are two types of
   rollover, ZSK rollover and KSK rollover.
   In ZSK rollover, all changes are local to the zone that changes its
   key: there is no need to contact other zones (e.g. parent zone) to
   propagate the performed changes because this type of key have no
   associated DS records in the parent zone.
   In 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 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:
    - An algorithm that generates new keys. It could be local to the
    - The interaction between parent and child zone

   In this document we focus on the interaction between parent and
   child zone servers.
   One example of manual key rollover is:
   Child zone creates a new KSK, waiting for the creation of the DS

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   record in its parent zone and then child zone deletes 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 MUST use a secure communication between parent
   and child zone. In this document we concentrate our efforts on
   defining interactions between entities present in key rollover
   process that are not explicitly defined in manual key rollover

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 retrieve some RRs
   from recursive name server. Every RR MUST be verifiable at any time,
   every message exchanged during rollover MUST be authenticated and
   data integrity MUST be guaranteed.

   Two entities are present during a KSK rollover: the child zone and
   its parent zone. These zones are generally managed by different
   administrators. These administrators MUST 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

   During an automated rollover process, data are transmitted between
   the primary name server of the parent and the the primary name server
   of the child zone.
   The reason is that the IP address of the primary name server is easy
   to obtain.
   Other solutions based on machine dedicated to the rollover are not
   suitable solutions because of the difficulty to obtain the IP
   addresses of the dedicated machine in an automated manner.

4. Messages authentication and information exchanged

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

   Once the changes related to a KSK are made in a child zone, this zone

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   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 an 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
   remains a valid chain of trust.

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.

   Parent zone behavior after an emergency rollover in one of its child
   zone is an open discussion.
   Should we define:

    - an EMERGENCY flag. When a child zone does an emergency KSK change,
      it uses the EMERGENCY flag to notify its parents that the chain of
      trust is broken and will stay broken until right DS creation and a
      parent zone resigning.

    - a maximum time delay after next parent zone resigning, we ensure
      that after this delay the parent zone is resigned and the right DS
      is created.

    - that no pre-defined behavior for the parent zone is needed

6. Other Resource Record concerned by automatic rollover

   NS records are also present at delegation point, so when the child
   zone changes some NS records, the corresponding records at
   delegation point in parent zone 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 allow to avoid inconsistency between NS records at
   delegation point and NS records present in the child zone.

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7. Security consideration

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

8. Acknowledgments
   The authors want to acknowledge Mohsen Souissi, Bernard Cousin,
   Bertrand Leonard and members of IDsA project for their contribution
   to this document.

Normative references

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

   [2]  Gudmundsson, O., "Delegation Signer Resource Record",
        draft-ietf-dnsext-delegation-signer-15 (work in progress),
                                June 2003.

   [3]  Kolkman, O. and Gieben, R., "DNSSEC key operations",
        draft-ietf-dnsext-operational-practices (work in progress),
                                June 2003.

   [4]  Kolkman, O. and Schlyter, J., "KEY RR Secure Entry Point Flag"
        draft-ietf-dnsext-keyrr-key-signing-flag-10 (work in progress),
        September 2003.

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

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

   [7]  Eastlake, D.,"DNS Security Operational Considerations", RFC
        2541, March 1999.

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Author's Addresses

   Gilles Guette
   Campus Universitaire de Beaulieu
   35042 Rennes France
   Phone : (33) 02 99 84 71 32
   Fax : (33) 02 99 84 25 29
   E-mail : gguette@irisa.fr

   Olivier Courtay
   2, rue de la ch‚taigneraie
   35512 Cesson C‰vign‰ CEDEX France
   Phone : (33) 02 99 84 71 31
   Fax : (33) 02 99 84 25 29

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