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
draft-ietf-dnsop-key-rollover-requirements-01.txt
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Abstract
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
discussed.
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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
administrators.
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
zone
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
changes.
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 Lonard 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
2004.
[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
IRISA / INRIA
Campus de Beaulieu
35042 Rennes CEDEX
FR
EMail: gilles.guette@irisa.fr
URI: http://www.irisa.fr
Olivier Courtay
Thomson R&D
1, avenue Belle Fontaine
35510 Cesson Svign CEDEX
FR
EMail: olivier.courtay@thomson.net
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