Individual G. Guette Internet-Draft IRISA/INRIA Rennes Expires: April 20, 2004 O. Courtay ENST-Bretagne October 20, 2003 Requirements for Automated Key Rollover in DNSsec draft-guette-dnsext-key-rollover-requirements-00 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 Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on March 30, 2004. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract 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. Guette & Courtay Expires April 20, 2004 [Page 1] Internet-Draft Automated Rollover Requirements October 2003 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 administrator. 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 Guette & Courtay Expires April 20, 2004 [Page 2] Internet-Draft Automated Rollover Requirements October 2003 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 method. 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 Guette & Courtay Expires April 20, 2004 [Page 3] Internet-Draft Automated Rollover Requirements October 2003 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 Guette & Courtay Expires April 20, 2004 [Page 4] Internet-Draft Automated Rollover Requirements October 2003 reached. 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. Guette & Courtay Expires April 20, 2004 [Page 5] Internet-Draft Automated Rollover Requirements October 2003 Author's Addresses Gilles Guette IRISA/INRIA Rennes 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 ENST-Bretagne 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 olivier.courtay@enst-bretagne.fr Guette & Courtay Expires April 20, 2004 [Page 6] Internet-Draft Automated Rollover Requirements October 2003 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. 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