DNS Extensions O. Kolkman Internet-Draft RIPE NCC Expires: March 2, 2003 J. Schlyter Carlstedt Research & Technology September 2002 KEY RR Key-Signing Key (KSK) Flag draft-ietf-dnsext-keyrr-key-signing-flag-02 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 2, 2003. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract With the DS record [1] the concept of key-signing and zone-signing keys has been introduced. Key-signing keys are the keys that sign the keyset only. In general, key-signing keys are the keys that are pointed to by DS records and are the first keys to be used when following a chain of trust into the zone. The key-signing keys only sign the KEY RRset at the apex of a zone, zone- signing keys sign all other data in a zone. We propose a flag to distinguish the key- signing key from other keys in the KEY RR set during DNSSEC operations. Kolkman & Schlyter Expires March 2, 2003 [Page 1] Internet-Draft KEY RR Key-Signing Key (KSK) Flag September 2002 The key words "MAY","MAY NOT", "MUST", "MUST NOT", "REQUIRED", "RECOMMENDED", "SHOULD", and "SHOULD NOT" in this document are to be interpreted as described in RFC2119. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. The Key-Signing Key (KSK) Flag . . . . . . . . . . . . . . . . 3 3. DNSSEC Protocol Changes . . . . . . . . . . . . . . . . . . . 4 4. Operational Guidelines . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 7. Internationalization Considerations . . . . . . . . . . . . . 5 8. Document Changes . . . . . . . . . . . . . . . . . . . . . . . 5 8.1 draft version 00 -> 01 . . . . . . . . . . . . . . . . . . . . 5 8.2 draft version 01 -> 02 . . . . . . . . . . . . . . . . . . . . 5 8.3 draft version 02 -> 03 . . . . . . . . . . . . . . . . . . . . 5 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 Normative References . . . . . . . . . . . . . . . . . . . . . 6 Informative References . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 8 Kolkman & Schlyter Expires March 2, 2003 [Page 2] Internet-Draft KEY RR Key-Signing Key (KSK) Flag September 2002 1. Introduction "All keys are equal but some keys are more equal than others" [5] With the DS record [1] the concept of key-signing and zone-signing keys has been introduced into DNSSEC[2]. In general these are the keys that are pointed to by DS records and are the first keys to be used when following the chain of trust into a zone ( secure entry points of the zone). These key-signing keys may also be configured in resolver systems that use zones as a trusted root[3] for a secure island. Early deployment tests have shown that during the key-exchange between the parent and the child it is useful to highlight which keys are to be used as the secure entry point to a zone. We introduce the Key-Signing Key flag to indicate this special 'administrative' status of the key. The availability of the flag allows the key exchange to be automated where, without the flag, some additional out-of-band communication is needed. 2. The Key-Signing Key (KSK) Flag 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | flags |K| protocol | algorithm | | |S| | | | |K| | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | / / public key / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ KEY RR Format The KSK bit (TBD) in the flags field is assigned to be the key- signing flag. If set the key is intended to be used as key-signing key. No special meaning should be assigned to the bit not being set. The draft proposes using the current 15'th bit [4] as the KSK bit. This way operators can tell the difference between key and zone- signing keys from the decimal representation of the flag field; it is odd or even respectively. Kolkman & Schlyter Expires March 2, 2003 [Page 3] Internet-Draft KEY RR Key-Signing Key (KSK) Flag September 2002 3. DNSSEC Protocol Changes The use of the KSK flag does not change the DNS resolution and resolution protocol. The KSK flag is only used to provide a hint about the different administrative properties and MUST NOT be used during the resolving process. 4. Operational Guidelines By setting the KSK flag on a particular key, zone administrators indicate that that key SHOULD be used as the secure entry point for their zone. Therefore zone administrators SHOULD set the bit only for zone keys that are used to sign the KEY RRset and are intended to act as the first link in the chain of trust for their zone. Parent zone administrators and resolver administrators that want to configure a key-signing key as their 'trusted key' MAY choose to ignore the flag. Using the flag a key roll over can be automated. The parent can use an existing trust relation to verify keysets in which a new key with the KSK flag appears. If the bit is modified during the lifetime of the key then this would have impact on the keytag and on the hash data in the DS RRs intending to point to this key. The bit SHOULD NOT be modified once the key has been put into use. 5. Security Considerations The flag MUST NOT be used in the resolution protocol or to determine the security status of a key. The flag is to be used for administrative purposes only. No trust in a key should be inferred from this flag - trust must be inferred from an existing chain of trust or an out-of-band exchange. Since this flag might be used for automating key exchanges, we think the following consideration is in place. Automated mechanisms for roll over of the DS RR might be vulnerable to a class of replay attacks. This might happen after a key exchange where a keyset, containing two keys with the KSK flag set, is sent to the parent. The parent verifies the keyset with the existing trust relation and creates the new DS RR from the key that the current DS is not pointing to. This key exchange might be replayed. Parents are encouraged to implement a replay defence. A simple defence can be based on a registry of keys that have been used to generate DS RRs Kolkman & Schlyter Expires March 2, 2003 [Page 4] Internet-Draft KEY RR Key-Signing Key (KSK) Flag September 2002 during the most recent roll over. 6. IANA Considerations draft-ietf-dnsext-restrict-key-for-dnssec [4] eliminates all flags field except for the zone key flag in the KEY RR. We propose to use the 15'th bit as the KSK bit; the decimal representation of the flagfield will then be odd for key-signing keys and even for zone- signing keys. 7. Internationalization Considerations There are no internationalization considerations 8. Document Changes 8.1 draft version 00 -> 01 Clean up of references and correction of typos; modified Abstract text a little; Added explicit warning for replay attacks to the security section; Removed the text that hinted on a distinction between a key- signing key configured in resolvers and in parent zones. 8.2 draft version 01 -> 02 Added IANA and Internationalization section. Split references into informational and normative. Spelling and style corrections. 8.3 draft version 02 -> 03 Changed the name from KS to KSK, this to prevent confusion with NS, DS and other acronyms in DNS. In the security section: Rewrote the section so that it does not suggest to use a particular type of registry and that it is clear that a key registry is only one of the defences possible. Spelling and style corrections Kolkman & Schlyter Expires March 2, 2003 [Page 5] Internet-Draft KEY RR Key-Signing Key (KSK) Flag September 2002 9. Acknowledgments The ideas documented in this draft are inspired by communications we had with numerous people and ideas published by other folk, Olafur Gudmundsson, Daniel Karrenberg, Ed Lewis, Dan Massey and Sam Weiler have been helping with providing ideas and feedback. This document saw the light during a workshop on DNSSEC operations hosted by USC/ISI. Normative References [1] Gudmundsson, O., "Delegation Signer Resource Record", draft- ietf-dnsext-delegation-signer-10 (work in progress), October 2002. [2] Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999. [3] Lewis, E., "DNS Security Extension Clarification on Zone Status", RFC 3090, March 2001. Informative References [4] Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource Record out", draft-ietf-dnsext-restrict-key-for-dnssec-04 (work in progress), September 2002. [5] Orwell, "Animal Farm; a Fairy Story"", 1945, . Authors' Addresses Olaf M. Kolkman RIPE NCC Singel 256 Amsterdam 1016 AB NL Phone: +31 20 535 4444 EMail: olaf@ripe.net URI: http://www.ripe.net/ Kolkman & Schlyter Expires March 2, 2003 [Page 6] Internet-Draft KEY RR Key-Signing Key (KSK) Flag September 2002 Jakob Schlyter Carlstedt Research & Technology Stora Badhusgatan 18-20 Goteborg SE-411 21 Sweden EMail: jakob@crt.se URI: http://www.crt.se/~jakob/ Kolkman & Schlyter Expires March 2, 2003 [Page 7] Internet-Draft KEY RR Key-Signing Key (KSK) Flag September 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. 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