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Internet-Draft IRISA / INRIA
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Requirements for Automated Key Rollover in DNSSEC
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draft-ietf-dnsop-key-rollover-requirements-01.txt
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By submitting this Internet-Draft, I certify that any applicable
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patent or other IPR claims of which I am aware have been disclosed,
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and any of which I become aware will be disclosed, in accordance with
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Internet-Drafts are working documents of the Internet Engineering
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The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at
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http://www.ietf.org/shadow.html.
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This Internet-Draft will expire on February 5, 2005.
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Copyright (C) The Internet Society (2004). All Rights Reserved.
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This document describes problems that appear during an automated
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rollover and gives the requirements for the design of communication
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between parent zone and child zone in an automated rollover process.
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This document is essentially about key rollover, the rollover of
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another Resource Record present at delegation point (NS RR) is also
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
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2. The Key Rollover Process . . . . . . . . . . . . . . . . . . . 3
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3. Basic Requirements . . . . . . . . . . . . . . . . . . . . . . 4
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4. Messages authentication and information exchanged . . . . . . 4
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5. Emergency Rollover . . . . . . . . . . . . . . . . . . . . . . 5
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6. Other Resource Record concerned by automatic rollover . . . . 5
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7. Security consideration . . . . . . . . . . . . . . . . . . . . 5
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8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
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9. Normative References . . . . . . . . . . . . . . . . . . . . . 5
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6
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Intellectual Property and Copyright Statements . . . . . . . . 7
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The DNS security extensions (DNSSEC) [4][8][7][9] uses public-key
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cryptography and digital signatures. It stores the public part of
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keys in DNSKEY Resource Records (RRs). Because old keys and
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frequently used keys are vulnerable, they must be renewed
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periodically. In DNSSEC, this is the case for Zone Signing Keys
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(ZSKs) and Key Signing Keys (KSKs) [1][2]. Automation of key
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rollover process is necessary for large zones because there are too
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many changes to handle a manual administration.
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Let us consider for example a zone with 100000 secure delegations.
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If the child zones change their keys once a year on average, that
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implies 300 changes per day for the parent zone. This amount of
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changes are hard to manage manually.
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Automated rollover is optional and resulting from an agreement
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between the administrator of the parent zone and the administrator of
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the child zone. Of course, key rollover can also be done manually by
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This document describes the requirements for the design of messages
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of automated key rollover process and focusses on interaction between
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parent and child zone.
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2. The Key Rollover Process
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Key rollover consists in renewing the DNSSEC keys used to sign
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resource records in a given DNS zone file. There are two types of
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rollover, ZSK rollovers and KSK rollovers.
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In a ZSK rollover, all changes are local to the zone that renews its
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key: there is no need to contact other zones (e.g., parent zone) to
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propagate the performed changes because a ZSK has no associated DS
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record in the parent zone.
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In a KSK rollover, new DS RR(s) must be created and stored in the
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parent zone. In consequence, the child zone must contact its parent
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zone and must notify it about the KSK change(s).
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Manual key rollover exists and works [3]. The key rollover is built
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from two parts of different nature:
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o An algorithm that generates new keys and signs the zone file. It
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could be local to the zone
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o The interaction between parent and child zones
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One example of manual key rollover is:
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o The child zone creates a new KSK
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o The child zone waits for the creation of the DS RR in its parent
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o The child zone deletes the old key.
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In manual rollover, communications are managed by the zone
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administrators and the security of these communications is out of
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Automated key rollover should use a secure communication between
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parent and child zones. This document concentrates on defining
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interactions between entities present in key rollover process.
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3. Basic Requirements
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The main constraint to respect during a key rollover is that the
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chain of trust MUST be preserved, even if a resolver retrieves some
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RRs from recursive cache server. Every RR MUST be verifiable at any
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time, every RRs exchanged during the rollover should be authenticated
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and their integrity should be guaranteed.
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Two entities act during a KSK rollover: the child zone and its parent
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zone. These zones are generally managed by different administrators.
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These administrators should agree on some parameters like
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availability of automated rollover, the maximum delay between
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notification of changes in the child zone and the resigning of the
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parent zone. The child zone needs to know this delay to schedule its
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4. Messages authentication and information exchanged
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Every exchanged message MUST be authenticated and the authentication
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tool MUST be a DNSSEC tool such as TSIG [6], SIG(0) [5] or DNSSEC
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request with verifiable SIG records.
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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
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store this DS RR in parent zone file.
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The parent zone MUST receive all the child keys that needs the
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creation of associated DS RRs in the parent zone.
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Some errors could occur during transmission between child zone and
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parent zone. Key rollover solution MUST be fault tolerant, i.e. at
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any time the rollover MUST be in a consistent state and all RRs MUST
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be verifiable, even if an error occurs. That is to say that it MUST
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remain a valid chain of trust.
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5. Emergency Rollover
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A key of a zone might be compromised and this key MUST be changed as
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soon as possible. Fast changes could break the chain of trust. The
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part of DNS tree having this zone as apex can become unverifiable,
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but the break of the chain of trust is necessary if we want to no one
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can use the compromised key to spoof DNS data.
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In case of emergency rollover, the administrators of parent and child
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zones should create new key(s) and DS RR(s) as fast as possible in
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order to reduce the time the chain of trust is broken.
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6. Other Resource Record concerned by automatic rollover
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NS records are also present at delegation point, so when the child
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zone renews some NS RR, the corresponding records at delegation point
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in parent zone (glue) MUST be updated. NS records are concerned by
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rollover and this rollover could be automated too. In this case,
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when the child zone notifies its parent zone that some NS records
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have been changed, the parent zone MUST verify that these NS records
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are present in child zone before doing any changes in its own zone
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file. This allows to avoid inconsistency between NS records at
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delegation point and NS records present in the child zone.
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7. Security consideration
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This document describes requirements to design an automated key
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rollover in DNSSEC based on DNSSEC security. In the same way, as
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plain DNSSEC, the automatic key rollover contains no mechanism
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protecting against denial of service (DoS). The security level
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obtain after an automatic key rollover, is the security level
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The authors want to acknowledge Francis Dupont, Mohsen Souissi,
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Bernard Cousin, Bertrand L�onard and members of IDsA project for
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their contribution to this document.
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9 Normative References
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[1] Gudmundsson, O., "Delegation Signer (DS) Resource Record (RR)",
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RFC 3658, December 2003.
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[2] Kolkman, O., Schlyter, J. and E. Lewis, "Domain Name System KEY
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(DNSKEY) Resource Record (RR) Secure Entry Point (SEP) Flag",
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[3] Kolkman, O., "DNSSEC Operational Practices",
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draft-ietf-dnsop-dnssec-operational-practice-01 (work in
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[4] Eastlake, D., "Domain Name System Security Extensions", RFC
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[5] Eastlake, D., "DNS Request and Transaction Signatures (
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SIG(0)s)", RFC 2931, September 2000.
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[6] Vixie, P., Gudmundsson, O., Eastlake, D. and B. Wellington,
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"Secret Key Transaction Authentication for DNS (TSIG)", RFC
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[7] Arends, R., "Resource Records for the DNS Security Extensions",
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draft-ietf-dnsext-dnssec-records-09 (work in progress), July
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[8] Arends, R., Austein, R., Massey, D., Larson, M. and S. Rose,
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"DNS Security Introduction and Requirements",
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draft-ietf-dnsext-dnssec-intro-11 (work in progress), July 2004.
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[9] Arends, R., "Protocol Modifications for the DNS Security
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Extensions", draft-ietf-dnsext-dnssec-protocol-07 (work in
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progress), July 2004.
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EMail: gilles.guette@irisa.fr
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URI: http://www.irisa.fr
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1, avenue Belle Fontaine
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EMail: olivier.courtay@thomson.net
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