Network Working Group S. Weiler Internet-Draft SPARTA, Inc Updates: [-records] [-protocol] March 7, 2005 (if approved) Expires: September 8, 2005 Clarifications and Implementation Notes for DNSSECbis draft-weiler-dnsext-dnssec-bis-updates-00 Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. 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 September 8, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This document is a collection of minor technical clarifications to the DNSSECbis document set. It is meant to serve as a resource to implementors as well as an interim repository of possible DNSSECbis errata. Weiler Expires September 8, 2005 [Page 1] Internet-Draft DNSSECbis Implementation Notes March 2005 1. Introduction and Terminology This document lists some minor clarifications and corrections to DNSSECbis, as described in [1], [2], and [3]. It is intended to serve as a resource for implementors and as a repository of items that need to be addressed when advancing the DNSSECbis documents from Proposed Standard to Draft Standard. In this version (-00), feedback is particularly solicited on the structure of the document and about what query type(s) should be used to find delegation points (see Section 4). The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [4]. 2. Unknown DS Message Digest Algorithms Section 5.2 of -protocol includes rules for how to handle delegations to zones that are signed with entirely unsupported algorithms, as indicated by the algorithms shown in those zone's DS RRsets. It does not explicitly address how to handle DS records that use unsupported message digest algorithms. In brief, DS records using unknown or unsupported message digest algorithms MUST be treated the same way as DS records referring to DNSKEY RRs of unknown or unsupported algorithms. The existing text says: If the validator does not support any of the algorithms listed in an authenticated DS RRset, then the resolver has no supported authentication path leading from the parent to the child. The resolver should treat this case as it would the case of an authenticated NSEC RRset proving that no DS RRset exists, as described above. To paraphrase the above, when determining the security status of a zone, a resolver discards (for this purpose only) any DS records listing unknown or unsupported algorithms. If none are left, the zone is treated as if it were unsigned. Modified to consider DS message digest algorithms, that text becomes: a resolver discards any DS records listing unknown or unsupported algorithms or using unknown or unsupported message digest algorithms. Weiler Expires September 8, 2005 [Page 2] Internet-Draft DNSSECbis Implementation Notes March 2005 3. Private Algorithms As discussed above, section 5.2 of -protocol requires that validators make decisions about the security status of zones based on the public key algorithms shown in the DS records for those zones. In the case of private algorithms, as described in -records Appendix A.1.1, the eight-bit algorithm field in the DS RR is not conclusive about what algorithm(s) is actually in use. If no private algorithms appear in the DS set or if any supported algorithm appears in the DS set, no special processing will be needed. In the remaining cases, the security status of the zone depends on whether or not the resolver supports any of the private algorithms in use (provided that these DS records use supported hash functions, as discussed in Section 2). In these cases, the resolver MUST retrieve the corresponding DNSKEY for each private algorithm DS record and examine the public key field to determine the algorithm in use. The security-aware resolver MUST ensure that the hash of the DNSKEY RR's owner name and RDATA matches the digest in the DS RR. If they do not match, and no other DS establishes that the zone is secure, the referral should be considered BAD data, as discussed in -protocol. This clarification facilitates the broader use of private algorithms, as suggested by [5] . 4. Finding Zone Cuts As explained in Section 3.1.4.1 of -protocol, security-aware name servers need to apply special processing rules to handle the DS RR, and in some situations the resolver may also need to apply special rules to locate the name servers for the parent zone if the resolver does not already have the parent's NS RRset. Section 4.2 of -protocol suggests using NS queries for this purpose. Appendix C.8 of -protocol suggests using DS queries. *** Which is correct? Does it matter? 5. Clarifications on DNSKEY Usage Questions of the form "can I use a different DNSKEY for signing the X" have occasionally arisen. The short answer is "yes, absolutely". You can even use a different DNSKEY for each RRset in a zone, subject only to practical limits on the size of the DNSKEY RRset. However, be aware that there is no way to tell resolvers what a particularly DNSKEY is supposed to be used Weiler Expires September 8, 2005 [Page 3] Internet-Draft DNSSECbis Implementation Notes March 2005 for -- any DNSKEY in the zone's signed DNSKEY RRset may be used to authenticate any RRset in the zone. For example, if a weaker or less trusted DNSKEY is being used to authenticate NSEC RRsets or all dynamically updated records, that same DNSKEY can also be used to sign any other RRsets from the zone. Futhermore, note that the SEP bit setting has no effect on how a DNSKEY may be used -- the validation process is specifically prohibitted from using that bit by -records section 2.1.2. It possible to use a DNSKEY without the SEP bit set as the sole secure entry point to the zone, yet use a DNSKEY with the SEP bit set to sign all RRsets in the zone (other than the DNSKEY RRset). It's also possible to use a single DNSKEY, with or without the SEP bit set, to sign the entire zone, including the DNSKEY RRset itself. 6. IANA Considerations This document specifies no IANA Actions. 7. Security Considerations 8. References 8.1 Normative References [1] Arends, R., Austein, R., Massey, D., Larson, M. and S. Rose, "DNS Security Introduction and Requirements", Internet-Draft draft-ietf-dnsext-dnssec-intro-13, October 2004. [2] Arends, R., "Resource Records for the DNS Security Extensions", Internet-Draft draft-ietf-dnsext-dnssec-records-11, October 2004. [3] Arends, R., "Protocol Modifications for the DNS Security Extensions", Internet-Draft draft-ietf-dnsext-dnssec-protocol-09, October 2004. [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 8.2 Informative References [5] Blacka, D., "DNSSEC Experiments", Internet-Draft draft-blacka-dnssec-experiments-00, December 2004. Weiler Expires September 8, 2005 [Page 4] Internet-Draft DNSSECbis Implementation Notes March 2005 Author's Address Samuel Weiler SPARTA, Inc 7075 Samuel Morse Drive Columbia, Maryland 21046 US Email: weiler@tislabs.com Appendix A. Acknowledgments The lack of specificity about handling private algorithms, as described in Section 3, was discovered by David Blacka. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Weiler Expires September 8, 2005 [Page 6]