DNS Extensions O. Kolkman Internet-Draft RIPE NCC Expires: March 2, 2003 J. Schlyter Carlstedt Research & Technology September 2002 KEY RR Key Signing (KS) Flag draft-ietf-dnsext-keyrr-key-signing-flag-01 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 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 (KS) 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 Flag . . . . . . . . . . . . . . . . . . . . . 3 3. DNSSEC Protocol Changes . . . . . . . . . . . . . . . . . . . 3 4. Operational Guidelines . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 6. Document Changes . . . . . . . . . . . . . . . . . . . . . . . 4 6.1 draft version 00 -> 01 . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 7 Kolkman & Schlyter Expires March 2, 2003 [Page 2] Internet-Draft KEY RR Key Signing (KS) Flag September 2002 1. Introduction "All keys are equal but some keys are more equal than others" [2] With the DS record [1] the concept of key signing and zone signing keys has been introduced. 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[4] for a secure island. Early deployment tests have shown that during the key-exchange between the parent and the child it is useful to indicate 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 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| | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | / / public key / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ KEY RR Format The bit 15th 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. If the bit is not set, no special meaning should be assigned. The 15th bit is currently reserved [3]. 3. DNSSEC Protocol Changes The use of the KS flag does not change the DNS resolution and resolution protocol. The KS flag is only used to provide a hint about the different administrative properties and MUST NOT be used during the resolving process. Kolkman & Schlyter Expires March 2, 2003 [Page 3] Internet-Draft KEY RR Key Signing (KS) Flag September 2002 4. Operational Guidelines By setting the KS 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 keysigning key as their 'trusted key' MAY choose to ignore the flag. Using the flag a key rollover can be automated. The parent can use an existing trust relation to verify keysets in which a new key with the KS 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 MAY be used for automating key exchanges, we think the following consideration is in place. Automated mechanisms for rollover of the DS RR may be vulnerable to a class of replay attacks. This may happen after a key exchange where a keyset, containing two keys with the KS 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 may be replayed, if the parent does not maintain state of which DS RRs where used previously so that the new DS RR is replaced by the old DS RR again. These kinds of attacks can be prevented by maintaining a registry of keys that have been used to generate DS RRs from previously. 6. Document Changes Kolkman & Schlyter Expires March 2, 2003 [Page 4] Internet-Draft KEY RR Key Signing (KS) Flag September 2002 6.1 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 keysigning key configured in resolvers and in parent zones. 7. 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, 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. References [1] Gudmundsson, "Delegation Signer Resource Record", work in progress draft-ietf-dnsext-delegation-signer-08.txt, June 2002. [2] Orwell, "Animal Farm; a Fairy Story"", 1945, . [3] Massey and Rose, "Limiting the Scope of the KEY Resource Record", work in progress draft-ietf-dnsext-restrict-key-for- dnssec-03, June 28 2002. [4] Lewis, E., "DNS Security Extension Clarification on Zone Status", RFC 3090, March 2001. Kolkman & Schlyter Expires March 2, 2003 [Page 5] Internet-Draft KEY RR Key Signing (KS) Flag September 2002 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/ 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 6] Internet-Draft KEY RR Key Signing (KS) Flag September 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Kolkman & Schlyter Expires March 2, 2003 [Page 7]