4 Network Working Group S. Weiler
5 Internet-Draft SPARTA, Inc
6 Updates: 4034, 4035 (if approved) May 23, 2005
7 Expires: November 24, 2005
10 Clarifications and Implementation Notes for DNSSECbis
11 draft-ietf-dnsext-dnssec-bis-updates-01
15 By submitting this Internet-Draft, each author represents that any
16 applicable patent or other IPR claims of which he or she is aware
17 have been or will be disclosed, and any of which he or she becomes
18 aware will be disclosed, in accordance with Section 6 of BCP 79.
20 Internet-Drafts are working documents of the Internet Engineering
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25 Internet-Drafts are draft documents valid for a maximum of six months
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27 time. It is inappropriate to use Internet-Drafts as reference
28 material or to cite them other than as "work in progress."
30 The list of current Internet-Drafts can be accessed at
31 http://www.ietf.org/ietf/1id-abstracts.txt.
33 The list of Internet-Draft Shadow Directories can be accessed at
34 http://www.ietf.org/shadow.html.
36 This Internet-Draft will expire on November 24, 2005.
40 Copyright (C) The Internet Society (2005).
44 This document is a collection of minor technical clarifications to
45 the DNSSECbis document set. It is meant to serve as a resource to
46 implementors as well as an interim repository of possible DNSSECbis
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60 Proposed additions in future versions
62 An index sorted by the section of DNSSECbis being clarified.
64 A list of proposed protocol changes being made in other documents,
65 such as NSEC3 and Epsilon. This document would not make those
66 changes, merely provide an index into the documents that are making
69 Changes between -00 and -01
71 Document significantly restructured.
73 Added section on QTYPE=ANY.
75 Changes between personal submission and first WG draft
77 Added Section 2.1 based on namedroppers discussions from March 9-10,
80 Added Section 3.4, Section 3.3, Section 4.3, and Section 2.2.
82 Added the DNSSECbis RFC numbers.
84 Figured out the confusion in Section 4.1.
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118 1. Introduction and Terminology . . . . . . . . . . . . . . . . . 4
119 1.1 Structure of this Document . . . . . . . . . . . . . . . . 4
120 1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
121 2. Significant Concerns . . . . . . . . . . . . . . . . . . . . . 4
122 2.1 Clarifications on Non-Existence Proofs . . . . . . . . . . 4
123 2.2 Empty Non-Terminal Proofs . . . . . . . . . . . . . . . . 5
124 2.3 Validating Responses to an ANY Query . . . . . . . . . . . 5
125 3. Interoperability Concerns . . . . . . . . . . . . . . . . . . 5
126 3.1 Unknown DS Message Digest Algorithms . . . . . . . . . . . 5
127 3.2 Private Algorithms . . . . . . . . . . . . . . . . . . . . 6
128 3.3 Caution About Local Policy and Multiple RRSIGs . . . . . . 6
129 3.4 Key Tag Calculation . . . . . . . . . . . . . . . . . . . 7
130 4. Minor Corrections and Clarifications . . . . . . . . . . . . . 7
131 4.1 Finding Zone Cuts . . . . . . . . . . . . . . . . . . . . 7
132 4.2 Clarifications on DNSKEY Usage . . . . . . . . . . . . . . 7
133 4.3 Errors in Examples . . . . . . . . . . . . . . . . . . . . 8
134 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
135 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
136 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
137 7.1 Normative References . . . . . . . . . . . . . . . . . . . 8
138 7.2 Informative References . . . . . . . . . . . . . . . . . . 9
139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 9
140 A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
141 Intellectual Property and Copyright Statements . . . . . . . . 11
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172 1. Introduction and Terminology
174 This document lists some minor clarifications and corrections to
175 DNSSECbis, as described in [1], [2], and [3].
177 It is intended to serve as a resource for implementors and as a
178 repository of items that need to be addressed when advancing the
179 DNSSECbis documents from Proposed Standard to Draft Standard.
181 In this version (-01 of the WG document), feedback is particularly
182 solicited on the structure of the document and whether the text in
183 the recently added sections is correct and sufficient.
185 Proposed substantive additions to this document should be sent to the
186 namedroppers mailing list as well as to the editor of this document.
187 The editor would greatly prefer text suitable for direct inclusion in
190 1.1 Structure of this Document
192 The clarifications to DNSSECbis are sorted according to the editor's
193 impression of their importance, starting with ones which could, if
194 ignored, lead to security and stability problems and progressing down
195 to clarifications that are likely to have little operational impact.
196 Mere typos and awkward phrasings are not addressed unless they could
197 lead to misinterpretation of the DNSSECbis documents.
201 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
202 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
203 document are to be interpreted as described in RFC 2119 [4].
205 2. Significant Concerns
207 This section provides clarifications that, if overlooked, could lead
208 to security issues or major interoperability problems.
210 2.1 Clarifications on Non-Existence Proofs
212 RFC4035 Section 5.4 slightly underspecifies the algorithm for
213 checking non-existence proofs. In particular, the algorithm there
214 might incorrectly allow the NSEC from the parent side of a zone cut
215 to prove the non-existence of either other RRs at that name in the
216 child zone or other names in the child zone. It might also allow a
217 NSEC at the same name as a DNAME to prove the non-existence of names
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228 A parent-side delegation NSEC (one with the NS bit set, but no SOA
229 bit set, and with a singer field that's shorter than the owner name)
230 must not be used to assume non-existence of any RRs below that zone
231 cut (both RRs at that ownername and at ownernames with more leading
232 labels, no matter their content). Similarly, an NSEC with the DNAME
233 bit set must not be used to assume the non-existence of any
234 descendant of that NSEC's owner name.
236 2.2 Empty Non-Terminal Proofs
238 To be written, based on Roy Arends' May 11th message to namedroppers.
240 2.3 Validating Responses to an ANY Query
242 RFC4035 does not address now to validate responses when QTYPE=*. As
243 described in Section 6.2.2 of RFC1034, a proper response to QTYPE=*
244 may include a subset of the RRsets at a given name -- it is not
245 necessary to include all RRsets at the QNAME in the response.
247 When validating a response to QTYPE=*, validate all received RRsets
248 that match QNAME and QCLASS. If any of those RRsets fail validation,
249 treat the answer as Bogus. If there are no RRsets matching QNAME and
250 QCLASS, validate that fact using the rules in RFC4035 Section 5.4 (as
251 clarified in this document). To be clear, a validator must not
252 insist on receiving all records at the QNAME in response to QTYPE=*.
254 3. Interoperability Concerns
256 3.1 Unknown DS Message Digest Algorithms
258 Section 5.2 of RFC4035 includes rules for how to handle delegations
259 to zones that are signed with entirely unsupported algorithms, as
260 indicated by the algorithms shown in those zone's DS RRsets. It does
261 not explicitly address how to handle DS records that use unsupported
262 message digest algorithms. In brief, DS records using unknown or
263 unsupported message digest algorithms MUST be treated the same way as
264 DS records referring to DNSKEY RRs of unknown or unsupported
267 The existing text says:
269 If the validator does not support any of the algorithms listed
270 in an authenticated DS RRset, then the resolver has no supported
271 authentication path leading from the parent to the child. The
272 resolver should treat this case as it would the case of an
273 authenticated NSEC RRset proving that no DS RRset exists, as
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284 To paraphrase the above, when determining the security status of a
285 zone, a validator discards (for this purpose only) any DS records
286 listing unknown or unsupported algorithms. If none are left, the
287 zone is treated as if it were unsigned.
289 Modified to consider DS message digest algorithms, a validator also
290 discards any DS records using unknown or unsupported message digest
293 3.2 Private Algorithms
295 As discussed above, section 5.2 of RFC4035 requires that validators
296 make decisions about the security status of zones based on the public
297 key algorithms shown in the DS records for those zones. In the case
298 of private algorithms, as described in RFC4034 Appendix A.1.1, the
299 eight-bit algorithm field in the DS RR is not conclusive about what
300 algorithm(s) is actually in use.
302 If no private algorithms appear in the DS set or if any supported
303 algorithm appears in the DS set, no special processing will be
304 needed. In the remaining cases, the security status of the zone
305 depends on whether or not the resolver supports any of the private
306 algorithms in use (provided that these DS records use supported hash
307 functions, as discussed in Section 3.1). In these cases, the
308 resolver MUST retrieve the corresponding DNSKEY for each private
309 algorithm DS record and examine the public key field to determine the
310 algorithm in use. The security-aware resolver MUST ensure that the
311 hash of the DNSKEY RR's owner name and RDATA matches the digest in
312 the DS RR. If they do not match, and no other DS establishes that
313 the zone is secure, the referral should be considered BAD data, as
314 discussed in RFC4035.
316 This clarification facilitates the broader use of private algorithms,
319 3.3 Caution About Local Policy and Multiple RRSIGs
321 When multiple RRSIGs cover a given RRset, RFC4035 Section 5.3.3
322 suggests that "the local resolver security policy determines whether
323 the resolver also has to test these RRSIG RRs and how to resolve
324 conflicts if these RRSIG RRs lead to differing results." In most
325 cases, a resolver would be well advised to accept any valid RRSIG as
326 sufficient. If the first RRSIG tested fails validation, a resolver
327 would be well advised to try others, giving a successful validation
328 result if any can be validated and giving a failure only if all
329 RRSIGs fail validation.
331 If a resolver adopts a more restrictive policy, there's a danger that
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340 properly-signed data might unnecessarily fail validation, perhaps
341 because of cache timing issues. Furthermore, certain zone management
342 techniques, like the Double Signature Zone-signing Key Rollover
343 method described in section 4.2.1.2 of [6] might not work reliably.
345 3.4 Key Tag Calculation
347 RFC4034 Appendix B.1 incorrectly defines the Key Tag field
348 calculation for algorithm 1. It correctly says that the Key Tag is
349 the most significant 16 of the least significant 24 bits of the
350 public key modulus. However, RFC4034 then goes on to incorrectly say
351 that this is 4th to last and 3rd to last octets of the public key
352 modulus. It is, in fact, the 3rd to last and 2nd to last octets.
354 4. Minor Corrections and Clarifications
356 4.1 Finding Zone Cuts
358 Appendix C.8 of RFC4035 discusses sending DS queries to the servers
359 for a parent zone. To do that, a resolver may first need to apply
360 special rules to discover what those servers are.
362 As explained in Section 3.1.4.1 of RFC4035, security-aware name
363 servers need to apply special processing rules to handle the DS RR,
364 and in some situations the resolver may also need to apply special
365 rules to locate the name servers for the parent zone if the resolver
366 does not already have the parent's NS RRset. Section 4.2 of RFC4035
367 specifies a mechanism for doing that.
369 4.2 Clarifications on DNSKEY Usage
371 Questions of the form "can I use a different DNSKEY for signing the
372 X" have occasionally arisen.
374 The short answer is "yes, absolutely". You can even use a different
375 DNSKEY for each RRset in a zone, subject only to practical limits on
376 the size of the DNSKEY RRset. However, be aware that there is no way
377 to tell resolvers what a particularly DNSKEY is supposed to be used
378 for -- any DNSKEY in the zone's signed DNSKEY RRset may be used to
379 authenticate any RRset in the zone. For example, if a weaker or less
380 trusted DNSKEY is being used to authenticate NSEC RRsets or all
381 dynamically updated records, that same DNSKEY can also be used to
382 sign any other RRsets from the zone.
384 Furthermore, note that the SEP bit setting has no effect on how a
385 DNSKEY may be used -- the validation process is specifically
386 prohibited from using that bit by RFC4034 section 2.1.2. It possible
387 to use a DNSKEY without the SEP bit set as the sole secure entry
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396 point to the zone, yet use a DNSKEY with the SEP bit set to sign all
397 RRsets in the zone (other than the DNSKEY RRset). It's also possible
398 to use a single DNSKEY, with or without the SEP bit set, to sign the
399 entire zone, including the DNSKEY RRset itself.
401 4.3 Errors in Examples
403 The text in RFC4035 Section C.1 refers to the examples in B.1 as
404 "x.w.example.com" while B.1 uses "x.w.example". This is painfully
405 obvious in the second paragraph where it states that the RRSIG labels
406 field value of 3 indicates that the answer was not the result of
407 wildcard expansion. This is true for "x.w.example" but not for
408 "x.w.example.com", which of course has a label count of 4
409 (antithetically, a label count of 3 would imply the answer was the
410 result of a wildcard expansion).
412 The first paragraph of RFC4035 Section C.6 also has a minor error:
413 the reference to "a.z.w.w.example" should instead be "a.z.w.example",
414 as in the previous line.
416 5. IANA Considerations
418 This document specifies no IANA Actions.
420 6. Security Considerations
422 This document does not make fundamental changes to the DNSSEC
423 protocol, as it was generally understood when DNSSECbis was
424 published. It does, however, address some ambiguities and omissions
425 in those documents that, if not recognized and addressed in
426 implementations, could lead to security failures. In particular, the
427 validation algorithm clarifications in Section 2 are critical for
428 preserving the security properties DNSSEC offers. Furthermore,
429 failure to address some of the interoperability concerns in Section 3
430 could limit the ability to later change or expand DNSSEC, including
431 by adding new algorithms.
435 7.1 Normative References
437 [1] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
438 "DNS Security Introduction and Requirements", RFC 4033,
441 [2] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
442 "Resource Records for the DNS Security Extensions", RFC 4034,
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452 [3] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
453 "Protocol Modifications for the DNS Security Extensions",
454 RFC 4035, March 2005.
456 [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
457 Levels", BCP 14, RFC 2119, March 1997.
459 7.2 Informative References
461 [5] Blacka, D., "DNSSEC Experiments",
462 draft-blacka-dnssec-experiments-00 (work in progress),
465 [6] Gieben, R. and O. Kolkman, "DNSSEC Operational Practices",
466 draft-ietf-dnsop-dnssec-operational-practices-04 (work in
474 7075 Samuel Morse Drive
475 Columbia, Maryland 21046
478 Email: weiler@tislabs.com
480 Appendix A. Acknowledgments
482 The editor is extremely grateful to those who, in addition to finding
483 errors and omissions in the DNSSECbis document set, have provided
484 text suitable for inclusion in this document.
486 The lack of specificity about handling private algorithms, as
487 described in Section 3.2, and the lack of specificity in handling ANY
488 queries, as described in Section 2.3, were discovered by David
491 The error in algorithm 1 key tag calculation, as described in
492 Section 3.4, was found by Abhijit Hayatnagarkar. Donald Eastlake
493 contributed text for Section 3.4.
495 The bug relating to delegation NSEC RR's in Section 2.1 was found by
496 Roy Badami. Roy Arends found the related problem with DNAME.
498 The errors in the RFC4035 examples were found by Roy Arends, who also
499 contributed text for Section 4.3 of this document.
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508 The editor would like to thank Olafur Gudmundsson and Scott Rose for
509 their substantive comments on the text of this document.
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