DNS Extensions O. Kolkman Internet-Draft RIPE NCC Expires: July 2, 2003 J. Schlyter Carlstedt Research & Technology E. Lewis ARIN January 2003 KEY RR Secure Entry Point (SEP) Flag draft-ietf-dnsext-keyrr-key-signing-flag-07 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 July 2, 2003. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract With the DS resource record the concept of a key acting as a secure entry point has been introduced. During key-exchanges with the parent there is a need to differentiate secure entry point keys from other keys in the KEY resource record set. A flag bit in the KEY RR is defined to indicate that KEY is to be used as a secure entry point. Kolkman, et al. Expires July 2, 2003 [Page 1] Internet-Draft KEY RR Secure Entry Point (SEP) Flag January 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. The Secure Entry Point (SEP) Flag . . . . . . . . . . . . . . 4 3. DNSSEC Protocol Changes . . . . . . . . . . . . . . . . . . . 4 4. Operational Guidelines . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 7. Internationalization Considerations . . . . . . . . . . . . . 6 8. Document Changes . . . . . . . . . . . . . . . . . . . . . . . 6 8.1 draft version 00 -> 01 . . . . . . . . . . . . . . . . . . . . 6 8.2 draft version 01 -> 02 . . . . . . . . . . . . . . . . . . . . 6 8.3 draft version 02 -> 03 . . . . . . . . . . . . . . . . . . . . 6 8.4 draft version 03 -> 04 . . . . . . . . . . . . . . . . . . . . 6 8.5 draft version 04 -> 05 . . . . . . . . . . . . . . . . . . . . 7 8.6 draft version 05 -> 06 . . . . . . . . . . . . . . . . . . . . 7 8.7 draft version 06 -> 07 . . . . . . . . . . . . . . . . . . . . 7 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 Normative References . . . . . . . . . . . . . . . . . . . . . 7 Informative References . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 10 Kolkman, et al. Expires July 2, 2003 [Page 2] Internet-Draft KEY RR Secure Entry Point (SEP) Flag January 2003 1. Introduction "All keys are equal but some keys are more equal than others" [6] With the definition of the DS Resource Record [5] it has become important to differentiate between the zone keys that are (to be) pointed to by parental DS RRs and other keys in the zone. We refer to these keys as Secure Entry Point (SEP) keys. A SEP key is either used to generate a DS RR or is distributed to resolvers that use the key as the root of a trusted subtree[3]. In early deployment tests, the use of two (kinds of) keys in each zone has been prevalent. One key is used to sign just the zone's KEY RR set and is the key referenced by a DS RR at the parent or configured statically in a resolver. Another key is used to sign the rest of the zone's data sets. The former key is called a key-signing key (KSK) and the latter is called a zone-signing key (ZSK). In practice there have been usually one of each kind of key, but there will be multiples of each at times. It should be noted that division of zone keys into KSK's and ZSK's is not mandatory in any definition of DNSSEC, not even with the introduction of the DS RR. But, in testing, this distinction has been helpful when designing key roll over (key super-cession) schemes. Given that the distinction has proven helpful, the labels KSK and ZSK have begun to stick. The reason for the term "SEP" is a result of the observation that the distinction between KSK and ZSK is only significant to the signer element of the DNS. Servers, resolvers and verifiers do not need to make the distinction. Further, distinguishing between a KSK and ZSK requires more than one bit, as a key could be fulfilling both roles. Hence, there is no definition for a ZSK bit and another for a KSK bit, just a single bit to assist operational procedures to correctly generate DS RRs, or to indicate what keys are intended for static configuration. 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. Kolkman, et al. Expires July 2, 2003 [Page 3] Internet-Draft KEY RR Secure Entry Point (SEP) Flag January 2003 2. The Secure Entry Point (SEP) 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 |S| protocol | algorithm | | |E| | | | |P| | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | / / public key / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ KEY RR Format The SEP bit (TBD) in the flags field is assigned to be the secure entry point flag. If the the bit is set to 1 the key is intended to be used as secure entry point key. One SHOULD NOT assign special meaning to the key if the bit is set to 0. The document proposes using the current 15th bit [4] as the SEP bit. This way operators can recognize the secure entry point key by the even or odd-ness of the decimal representation of the flag field. 3. DNSSEC Protocol Changes The bit MUST NOT be used during the resolving and verification process. The SEP flag is only used to provide a hint about the different administrative properties of the key and therefore the use of the SEP flag does not change the DNS resolution and resolution protocol. 4. Operational Guidelines The SEP bit is set by the key-generator and MAY be used by the zone signer to decide whether the key is to be prepared for input to a DS RR generation function. As the SEP bit is within the data that is used to compute a KEY RR's footprint, changing the SEP bit will change the identity of the key within DNS. When a key pair is created, the operator needs to indicate whether the SEP bit is to be set in the KEY RR. The SEP bit is recommended whenever the public key of the key pair will be distributed to the parent zone to build the authentication chain or if the public key is to be distributed for static configuration in verifiers. Kolkman, et al. Expires July 2, 2003 [Page 4] Internet-Draft KEY RR Secure Entry Point (SEP) Flag January 2003 When signing a zone, it is intended that the key(s) with the SEP bit set (if such keys exist) are used to sign the KEY RR set of the zone. The same key can be used to sign the rest of the zone data too. It is conceivable that not all keys with a SEP bit set will sign the KEY RR set, such keys might be pending retirement or not yet in use. When verifying a RR set, the SEP bit is not intended to play a role. How the key is used by the verifier is not intended to be a consideration at key creation time. Although the SEP flag provides a hint on which key to be used as trusted root, administrators can choose to ignore the fact that a KEY has its SEP bit set or not when configuring a trusted root for their resolvers. Using the flag a key roll over can be automated. The parent can use an existing trust relation to verify key sets in which a new key with the SEP flag appears. 5. Security Considerations As stated in Section 3 the flag is not to 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 key set, containing two keys with the SEP flag set, is sent to the parent. The parent verifies the key set 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 defense. A simple defense can be based on a registry of keys that have been used to generate DS RRs during the most recent roll over. These same considerations apply to entities that configure keys in resolvers. 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 SEP bit; the decimal representation of the flagfield will then be odd for key-signing keys. Kolkman, et al. Expires July 2, 2003 [Page 5] Internet-Draft KEY RR Secure Entry Point (SEP) Flag January 2003 7. Internationalization Considerations Although SEP is a popular acronym in many different languages, 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 defenses possible. Spelling and style corrections. 8.4 draft version 03 -> 04 Text has been made consistent with the statement: ' No special meaning should be assigned to the bit not being set.' Made explicit that the key tag changes in SIG RR. Kolkman, et al. Expires July 2, 2003 [Page 6] Internet-Draft KEY RR Secure Entry Point (SEP) Flag January 2003 8.5 draft version 04 -> 05 One occurrence of must and one occurrence of should uppercased (RFC2119). Reordering of sentences in section 3, so that the point of the bit NOT being used in resolving is made directly. To make explicit that the KSK is used at key generation and at signing time I added the first sentence to section 4. Some minor style and spelling corrections. 8.6 draft version 05 -> 06 References and acronyms where stripped from the Abstract. the Introduction and the the Operational Guideline section were rewritten in such a way that the draft does not suggest any use of the bit in the verification process and that the draft does not enforce, but suggests, the use of a key- and zone-signing key. Added 'and verification' in the sentence "MUST NOT be used during the resolving and verification process" (protocol changes section). 8.7 draft version 06 -> 07 Based on comments during the last call we changed the name from KSK-flag to SEP flag. The introduction was rewritten to reflect the motivations of this name change and to stress that the SEP key is not relevant to the signer process. 9. Acknowledgments The ideas documented in this document are inspired by communications we had with numerous people and ideas published by other folk. Among others Mark Andrews, Miek Gieben, Olafur Gudmundsson, Daniel Karrenberg, Dan Massey, Marcos Sanz and Sam Weiler have contributed ideas and provided feedback. This document saw the light during a workshop on DNSSEC operations hosted by USC/ISI. Normative References Kolkman, et al. Expires July 2, 2003 [Page 7] Internet-Draft KEY RR Secure Entry Point (SEP) Flag January 2003 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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. [4] Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource Record (RR)", RFC 3445, December 2002. Informative References [5] Gudmundsson, O., "Delegation Signer Resource Record", draft- ietf-dnsext-delegation-signer-14 (work in progress), May 2003. [6] Orwell, G. and R. Steadman (illustrator), "Animal Farm; a Fairy Story"", ISBN 0151002177 (50th anniversery edition), April 1996. 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, et al. Expires July 2, 2003 [Page 8] Internet-Draft KEY RR Secure Entry Point (SEP) Flag January 2003 Edward P. Lewis ARIN 3635 Concorde Parkway Suite 200 Chantilly, VA 20151 US Phone: +1 703 227 9854 EMail: edlewis@arin.net URI: http://www.arin.net/ Kolkman, et al. Expires July 2, 2003 [Page 9] Internet-Draft KEY RR Secure Entry Point (SEP) Flag January 2003 Full Copyright Statement Copyright (C) The Internet Society (2003). All Rights Reserved. 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