Network Working Group S. Weiler Internet-Draft SPARTA, Inc Updates: 4034, 4035 (if approved) May 12, 2005 Expires: November 13, 2005 Clarifications and Implementation Notes for DNSSECbis draft-ietf-dnsext-dnssec-bis-updates-00 Status of this Memo 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 becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 November 13, 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. Proposed additions in future versions Weiler Expires November 13, 2005 [Page 1]
Internet-Draft DNSSECbis Implementation Notes May 2005 An index sorted by the section of DNSSECbis being clarified. A list of proposed protocol changes being made in other documents, such as NSEC3 and Epsilon. This document would not make those changes, merely provide an index into the documents that are making changes. Changes between personal submission and first WG draft Added Section 6 based on namedroppers discussions from March 9-10, 2005. Added Section 7 through Section 10. Added the DNSSECbis RFC numbers. Figured out the confusion in Section 4. Weiler Expires November 13, 2005 [Page 2]
Internet-Draft DNSSECbis Implementation Notes May 2005 Table of Contents 1. Introduction and Terminology . . . . . . . . . . . . . . . . 4 2. Unknown DS Message Digest Algorithms . . . . . . . . . . . . 4 3. Private Algorithms . . . . . . . . . . . . . . . . . . . . . 5 4. Finding Zone Cuts . . . . . . . . . . . . . . . . . . . . . 5 5. Clarifications on DNSKEY Usage . . . . . . . . . . . . . . . 5 6. Clarifications on Non-Existence Proofs . . . . . . . . . . . 6 7. Key Tag Calculation . . . . . . . . . . . . . . . . . . . . 6 8. Caution About Local Policy and Multiple RRSIGs . . . . . . . 6 9. Minor Errors in Examples . . . . . . . . . . . . . . . . . . 7 10. Empty Non-Terminal Proofs . . . . . . . . . . . . . . . . . 7 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7 12. Security Considerations . . . . . . . . . . . . . . . . . . 7 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 13.1 Normative References . . . . . . . . . . . . . . . . . . 7 13.2 Informative References . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . 8 A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . 10 Weiler Expires November 13, 2005 [Page 3]
Internet-Draft DNSSECbis Implementation Notes May 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 of the WG document), feedback is particularly solicited on the structure of the document and whether the text in the newly added sections (Section 6 through Section 10) is correct and sufficient. Proposed substantive additions to this document should be sent to the namedroppers mailing list as well as to the editor(s) of this document. The editor would greatly prefer text suitable for direct inclusion in this document. 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 RFC4035 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. Weiler Expires November 13, 2005 [Page 4]
Internet-Draft DNSSECbis Implementation Notes May 2005 Modified to consider DS message digest algorithms, a resolver also discards any DS records using unknown or unsupported message digest algorithms. 3. Private Algorithms As discussed above, section 5.2 of RFC4035 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 RFC4034 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 RFC4035. This clarification facilitates the broader use of private algorithms, as suggested by [5] . 4. Finding Zone Cuts Appendix C.8 of RFC4035 discusses sending DS queries to the servers for a parent zone. To do that, a resolver may first need to apply special rules to discover what those servers are. As explained in Section 3.1.4.1 of RFC4035, 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 RFC4035 specifies a mechanism for doing that. 5. Clarifications on DNSKEY Usage Questions of the form "can I use a different DNSKEY for signing the X" have occasionally arisen. Weiler Expires November 13, 2005 [Page 5]
Internet-Draft DNSSECbis Implementation Notes May 2005 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 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. Furthermore, note that the SEP bit setting has no effect on how a DNSKEY may be used -- the validation process is specifically prohibited from using that bit by RFC4034 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. Clarifications on Non-Existence Proofs RFC4035 Section 5.4 slightly underspecifies the algorithm for checking non-existence proofs. In particular, the algorithm there might incorrectly allow the NSEC from the parent side of a zone cut to prove the non-existence of either other RRs at that name in the child zone or other names in the child zone. A parent-side delegation NSEC (one with the NS bit set, but no SOA bit set, and with a singer field that's shorter than the owner name) must not be used to assume non-existence of any RRs below that zone cut (both RRs at that ownername and at ownernames with more leading labels, no matter their content). 7. Key Tag Calculation RFC4034 Appendix B.1 incorrectly defines the Key Tag field calculation for algorithm 1. It correctly says that the Key Tag is the most significant 16 of the least significant 24 bits of the public key modulus. However, RFC4034 then goes on to incorrectly say that this is 4th to last and 3rd to last octets of the public key modulus. It is, in fact, the 3rd to last and 2nd to last octets. 8. Caution About Local Policy and Multiple RRSIGs When multiple RRSIGs cover a given RRset, RFC4035 Section 5.3.3 suggests that "the local resolver security policy determines whether the resolver also has to test these RRSIG RRs and how to resolve conflicts if these RRSIG RRs lead to differing results." In most Weiler Expires November 13, 2005 [Page 6]
Internet-Draft DNSSECbis Implementation Notes May 2005 cases, a resolver would be well advised to accept any valid RRSIG as sufficient. If the first RRSIG tested fails validation, a resolver would be well advised to try others, giving a successful validation result if any can be validated and giving a failure only if all RRSIGs fail validation. If a resolver adopts a more restrictive policy, there's a danger that properly-signed data might unnecessarily fail validation, perhaps because of cache timing issues. Furthermore, certain zone management techniques, like the Double Signature Zone-signing Key Rollover method described in section 4.2.1.2 of [6] might not work reliably. 9. Minor Errors in Examples The text in RFC4035 Section C.1 refers to the examples in B.1 as "x.w.example.com" while B.1 uses "x.w.example". This is painfully obvious in the second paragraph where it states that the RRSIG labels field value of 3 indicates that the answer was not the result of wildcard expansion. This is true for "x.w.example" but not for "x.w.example.com", which of course has a label count of 4 (antithetically, a label count of 3 would imply the answer was the result of a wildcard expansion). The first paragraph of RFC4035 Section C.6 also has a minor error: the reference to "a.z.w.w.example" should instead be "a.z.w.example", as in the previous line. 10. Empty Non-Terminal Proofs To be written. 11. IANA Considerations This document specifies no IANA Actions. 12. Security Considerations 13. References 13.1 Normative References [1] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005. [2] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, Weiler Expires November 13, 2005 [Page 7]
Internet-Draft DNSSECbis Implementation Notes May 2005 March 2005. [3] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, March 2005. [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 13.2 Informative References [5] Blacka, D., "DNSSEC Experiments", draft-blacka-dnssec-experiments-00 (work in progress), December 2004. [6] Gieben, R. and O. Kolkman, "DNSSEC Operational Practices", draft-ietf-dnsop-dnssec-operational-practices-04 (work in progress), May 2005. Author's Address Samuel Weiler SPARTA, Inc 7075 Samuel Morse Drive Columbia, Maryland 21046 US Email: weiler@tislabs.com Appendix A. Acknowledgments The editor is extremely grateful to those who, in addition to finding errors and omissions in the DNSSECbis document set, have provided text suitable for inclusion in this document. The lack of specificity about handling private algorithms, as described in Section 3, was discovered by David Blacka. The error in algorithm 1 key tag calculation, as described in Section 7, was found by Abhijit Hayatnagarkar. Donald Eastlake contributed text for Section 7. The bug in the non-existence proof logic in RFC4035 Section 5.4 was found by Roy Badami. The errors in the RFC4035 examples were found by Roy Arends, who also contributed text for Section 9 of this document. Weiler Expires November 13, 2005 [Page 8]
Internet-Draft DNSSECbis Implementation Notes May 2005 The editor would like to thank Olafur Gudmundsson and Scott Rose for their substantive comments on the text of this document. Weiler Expires November 13, 2005 [Page 9]
Internet-Draft DNSSECbis Implementation Notes May 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights 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; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Weiler Expires November 13, 2005 [Page 10]
