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Individual                                                     G. Guette
Internet-Draft                                        IRISA/INRIA Rennes
Expires: April 20, 2004                                       O. Courtay
                                                        October 20, 2003

            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 March 30, 2004.

Copyright Notice

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


   This internet-draft describes problems that appear during an
   automated rollover and gives the requirements for the design of
   automated solutions rollover process. It essentially concerned key
   rollover, but rollover of other Resource Records 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 needed 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

   Let us consider for example a zone with one million child zones among
   which only 10% of secured child zones (that is, 100,000 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 parent zone administrators and child zone administrators.
   Of course, key rollover can also be done manually by administrators.

   This document describes the requirements for the design of automated
   solutions for 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.
   In KSK rollover, the right DS RR MUST be created and stored in the
   parent zone, so the child zone MUST contact its parent zone and
   notify it about the KSK changes.

   Manual key rollover exists and works [3] but in this draft we
   describe a way to automate the key rollover process.

   The key rollover is built from two parts of different nature:
    - An algorithm that changes keys
    - Communication between parent and child zone

   One example of manual key rollover is:
   Child zone creates a new KSK, waiting for a certain time, DS is
   created in parent zone, child zone deletes old key.

   In manual rollover, communications are managed by administrators and

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   security of these communications is out of scope of DNSsec.

   Automatic key rollover should define a secure communication between
   parent and child zone. In this draft 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. Every RR MUST be verifiable at any
   time, every message exchanged during rollover MUST be authenticated
   and data integrity MUST be guaranteed even if some RRs are retrieved
   from recursive name server (cache).

   Two entities are present during a KSK rollover: child zone and
   parent zone. These zones are generally managed by different
   administrators. These administrators MUST agree on some parameters
   like doing automatic rollover, maximum delay between notification of
   changes into child zone and resigning of the parent zone, etc.

4. Messages authentication

   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.

   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.

5. Transmission method and information exchanged

   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.
   Whatever the transmission methods used, the parent zone MUST receive
   the child KSKs for which the child wants that associated DS RRs exist
   in the parent zone.

6. Local separation entities

   Secret keys are generally stored in a secure off-line area [7]. The
   name server has no on-line access to these keys. The key rollover
   solution SHOULD not assume that the server has on-line access to

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   these keys. We have distinguished three entities concerned by the
   local key rollover process inside a zone: the name server, the zone
   file manager and the secret key manager.

   Any automatic rollover solution MUST take into account the possible
   separation of these three entities and must support partial
   administrator intervention as manipulation of private key.

   For example, we can imagine that all entities are handled by
   automated process but signing action with the private keys is done by
   human administrator (he retrieves zone file from a repository and put
   back the signed zone file on well-known location).

7. Emergency Rollover

   Inside a zone, a key might be compromised and this key MUST be
   changed as fast as possible. The 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 that 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.
   Must 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.

    - or no pre-defined behavior

8. 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 record 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 NS
   records are present in child zone file before doing any changes in
   its own zone file. Otherwise the DNS child name server could not be

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9. 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.

10. 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 châtaigneraie
   35512 Cesson Cévigné CEDEX France
   Phone : (33) 02 99 84 71 31
   Fax : (33) 02 99 84 25 29

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