Network Working Group                                          S. Weiler
Internet-Draft                                               SPARTA, Inc
Updates: 4034, 4035 (if approved)                           May 12, 23, 2005
Expires: November 13, 24, 2005

         Clarifications and Implementation Notes for DNSSECbis
                draft-ietf-dnsext-dnssec-bis-updates-00
                draft-ietf-dnsext-dnssec-bis-updates-01

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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

   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 -00 and -01

   Document significantly restructured.

   Added section on QTYPE=ANY.

Changes between personal submission and first WG draft

   Added Section 6 2.1 based on namedroppers discussions from March 9-10,
   2005.

   Added Section 7 through 3.4, Section 10. 3.3, Section 4.3, and Section 2.2.

   Added the DNSSECbis RFC numbers.

   Figured out the confusion in Section 4. 4.1.

Table of Contents

   1.  Introduction and Terminology . . . . . . . . . . . . . . . . .  4
   2.   Unknown DS Message Digest Algorithms
     1.1   Structure of this Document . . . . . . . . . . . . . . . .  4
   3.   Private Algorithms
     1.2   Terminology  . . . . . . . . . . . . . . . . . . . . .   5
   4.   Finding Zone Cuts . .  4
   2.  Significant Concerns . . . . . . . . . . . . . . . . . . . . .   5
   5.  4
     2.1   Clarifications on DNSKEY Usage Non-Existence Proofs . . . . . . . . . .  4
     2.2   Empty Non-Terminal Proofs  . . . . . . . . . . . . . . . .  5
   6.   Clarifications on Non-Existence Proofs
     2.3   Validating Responses to an ANY Query . . . . . . . . . . .   6
   7.   Key Tag Calculation  5
   3.  Interoperability Concerns  . . . . . . . . . . . . . . . . . .  5
     3.1   Unknown DS Message Digest Algorithms . . . . . . . . . . .  5
     3.2   Private Algorithms . . . . . . . . . . . . . . . . . . . .  6
   8.
     3.3   Caution About Local Policy and Multiple RRSIGs . . . . . . .  6
   9.   Minor Errors in Examples
     3.4   Key Tag Calculation  . . . . . . . . . . . . . . . . . . .  7
   10.  Empty Non-Terminal Proofs
   4.  Minor Corrections and Clarifications . . . . . . . . . . . . .  7
     4.1   Finding Zone Cuts  . . . . . . . . . . . . . . . . . . . .  7
     4.2   Clarifications on DNSKEY Usage . . . . . . . . . . . . . .  7
   11.
     4.3   Errors in Examples . . . . . . . . . . . . . . . . . . . .  8
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .   7
   12. .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . .   7
   13. .  8
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . .   7
     13.1 .  8
     7.1   Normative References . . . . . . . . . . . . . . . . . .   7
     13.2 .  8
     7.2   Informative References . . . . . . . . . . . . . . . . .   8 .  9
       Author's Address . . . . . . . . . . . . . . . . . . . . . .   8 .  9
   A.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .   8 .  9
       Intellectual Property and Copyright Statements . . . . . . .  10 . 11

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 (-01 of the WG document), feedback is particularly
   solicited on the structure of the document and whether the text in
   the newly recently 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) editor 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

1.1  Structure of this
   document Document

   The clarifications to DNSSECbis are sorted according to be interpreted as described in RFC 2119 [4].

2.  Unknown DS Message Digest Algorithms

   Section 5.2 the editor's
   impression of RFC4035 includes rules for how their importance, starting with ones which could, if
   ignored, lead to handle delegations security and stability problems and progressing down
   to zones clarifications that are signed with entirely unsupported algorithms, as
   indicated by likely to have little operational impact.
   Mere typos and awkward phrasings are not addressed unless they could
   lead to misinterpretation of the algorithms shown DNSSECbis documents.

1.2  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in those zone's DS RRsets.  It does
   not explicitly address how this
   document are 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 interpreted as
   DS records referring described in RFC 2119 [4].

2.  Significant Concerns

   This section provides clarifications that, if overlooked, could lead
   to DNSKEY RRs of unknown security issues or unsupported
   algorithms.

   The existing text says:

      If major interoperability problems.

2.1  Clarifications on Non-Existence Proofs

   RFC4035 Section 5.4 slightly underspecifies the validator does not support any of algorithm for
   checking non-existence proofs.  In particular, the algorithms listed
      in an authenticated DS RRset, then algorithm there
   might incorrectly allow the resolver has no supported
      authentication path leading NSEC from the parent side of a zone cut
   to prove the child.  The
      resolver should treat this case as it would the case non-existence of an
      authenticated NSEC RRset proving either other RRs at that no DS RRset exists, as
      described above.

   To paraphrase name in the above, when determining
   child zone or other names in the security status of a
   zone, child zone.  It might also allow a resolver discards (for this purpose only) any DS records
   listing unknown or unsupported algorithms.  If none are left,
   NSEC at the
   zone is treated same name as if it were unsigned.

   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 DNAME to prove the case non-existence of private algorithms, as described in RFC4034 Appendix A.1.1, names
   beneath that DNAME.

   A parent-side delegation NSEC (one with the
   eight-bit algorithm NS bit set, but no SOA
   bit set, and with a singer field in that's shorter than the DS RR is owner name)
   must not conclusive about what
   algorithm(s) is actually in use.

   If 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 private algorithms appear in matter their content).  Similarly, an NSEC with the DS DNAME
   bit set or if any supported
   algorithm appears in the DS set, no special processing will must not be
   needed.  In the remaining cases, used to assume the security status non-existence of the zone
   depends on whether or not the resolver supports any
   descendant of the private
   algorithms in use (provided that these DS records use supported hash
   functions, as discussed NSEC's owner name.

2.2  Empty Non-Terminal Proofs

   To be written, based on Roy Arends' May 11th message to namedroppers.

2.3  Validating Responses to an ANY Query

   RFC4035 does not address now to validate responses when QTYPE=*.  As
   described 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 6.2.2 of RFC1034, a proper response to determine QTYPE=*
   may include a subset of the algorithm in
   use.  The security-aware resolver MUST ensure that the hash of the
   DNSKEY RR's owner RRsets at a given name and RDATA matches -- it is not
   necessary to include all RRsets at the digest QNAME in the DS RR.  If
   they do not match, response.

   When validating a response to QTYPE=*, validate all received RRsets
   that match QNAME and QCLASS.  If any of those RRsets fail validation,
   treat the answer as Bogus.  If there are no other DS establishes RRsets matching QNAME and
   QCLASS, validate that fact using the zone is
   secure, the referral should be considered BAD data, as discussed rules 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. Section 5.4 (as
   clarified in this document).  To do that, be clear, a resolver may first need to apply
   special rules to discover what those servers are.

   As explained validator must not
   insist on receiving all records at the QNAME in response to QTYPE=*.

3.  Interoperability Concerns

3.1  Unknown DS Message Digest Algorithms

   Section 3.1.4.1 5.2 of RFC4035, security-aware name
   servers need to apply special processing RFC4035 includes rules for how to handle delegations
   to zones that are signed with entirely unsupported algorithms, as
   indicated by the DS RR,
   and algorithms shown in some situations the resolver may also need to apply special
   rules those zone's DS RRsets.  It does
   not explicitly address how to locate the name servers for handle DS records that use unsupported
   message digest algorithms.  In brief, DS records using unknown or
   unsupported message digest algorithms MUST be treated the parent zone if same way as
   DS records referring to DNSKEY RRs of unknown or unsupported
   algorithms.

   The existing text says:

      If the resolver validator does not already have support any of the parent's NS RRset.  Section 4.2 of RFC4035
   specifies a mechanism for doing that.

5.  Clarifications on DNSKEY Usage

   Questions of algorithms listed
      in an authenticated DS RRset, then the form "can I use a different DNSKEY for signing resolver has no supported
      authentication path leading from 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 parent to practical limits on the size of child.  The
      resolver should treat this case as it would the DNSKEY RRset.  However, be aware case of an
      authenticated NSEC RRset proving 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 DS RRset in exists, as
      described above.

   To paraphrase the zone.  For example, if above, when determining the security status of a weaker
   zone, a validator discards (for this purpose only) any DS records
   listing unknown or less
   trusted DNSKEY unsupported algorithms.  If none are left, the
   zone is being used treated as if it were unsigned.

   Modified to authenticate NSEC RRsets or all
   dynamically updated records, that same DNSKEY can consider DS message digest algorithms, a validator also be used to
   sign
   discards any other RRsets from the zone.

   Furthermore, note DS records using unknown or unsupported message digest
   algorithms.

3.2  Private Algorithms

   As discussed above, section 5.2 of RFC4035 requires that validators
   make decisions about the SEP bit setting has no effect security status of zones based on how a
   DNSKEY may be used -- the validation process 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 specifically
   prohibited from using 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 bit by RFC4034 section 2.1.2.  It possible these DS records use supported hash
   functions, as discussed in Section 3.1).  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].

3.3  Caution About Local Policy and Multiple RRSIGs

   When multiple RRSIGs cover a DNSKEY without given RRset, RFC4035 Section 5.3.3
   suggests that "the local resolver security policy determines whether
   the SEP bit set resolver also has to test these RRSIG RRs and how to resolve
   conflicts if these RRSIG RRs lead to differing results."  In most
   cases, a resolver would be well advised to accept any valid RRSIG as
   sufficient.  If the sole secure entry
   point 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.

3.4  Key Tag Calculation

   RFC4034 Appendix B.1 incorrectly defines the Key Tag field
   calculation for algorithm 1.  It correctly says that the zone, yet use a DNSKEY with Key Tag is
   the SEP bit set to sign all
   RRsets in most significant 16 of the zone (other than least significant 24 bits of the DNSKEY RRset).  It's also possible
   public key modulus.  However, RFC4034 then goes on to use a single DNSKEY, with or without the SEP bit set, incorrectly say
   that this is 4th to sign last and 3rd to last octets of the
   entire zone, including public key
   modulus.  It is, in fact, the DNSKEY RRset itself.

6. 3rd to last and 2nd to last octets.

4.  Minor Corrections and Clarifications on Non-Existence Proofs

4.1  Finding Zone Cuts

   Appendix C.8 of RFC4035 Section 5.4 slightly underspecifies discusses sending DS queries to the algorithm servers
   for
   checking non-existence proofs.  In particular, the algorithm there
   might incorrectly allow the NSEC from the a parent side of zone.  To do that, a zone cut resolver may first need to prove the non-existence apply
   special rules to discover what those servers are.

   As explained in Section 3.1.4.1 of either other RRs at that RFC4035, security-aware name in the
   child zone or other names in the child zone.

   A parent-side delegation NSEC (one with
   servers need to apply special processing rules to handle the NS bit set, but no SOA
   bit set, DS RR,
   and with a singer field that's shorter than in some situations 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 resolver may also need to apply special
   rules to locate the Key Tag field
   calculation name servers for algorithm 1.  It correctly says that the Key Tag is parent zone if the most significant 16 resolver
   does not already have the parent's NS RRset.  Section 4.2 of RFC4035
   specifies a mechanism for doing that.

4.2  Clarifications on DNSKEY Usage

   Questions of the least significant 24 bits 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
   public key modulus. DNSKEY RRset.  However, RFC4034 then goes on to incorrectly say be aware that this there is 4th no way
   to last and 3rd tell resolvers what a particularly DNSKEY is supposed to last octets of the public key
   modulus.  It is, be used
   for -- any DNSKEY in fact, the 3rd to last and 2nd zone's signed DNSKEY RRset may be used 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
   authenticate any RRset in the resolver also has to test these RRSIG RRs and how to resolve
   conflicts zone.  For example, if these RRSIG RRs lead to differing results."  In most
   cases, a resolver would weaker or less
   trusted DNSKEY is being used to authenticate NSEC RRsets or all
   dynamically updated records, that same DNSKEY can also be well advised used to accept
   sign any valid RRSIG as
   sufficient.  If other RRsets from the zone.

   Furthermore, note that the first RRSIG tested fails validation, SEP bit setting has no effect on how a resolver
   would
   DNSKEY may be well advised used -- the validation process is specifically
   prohibited from using that bit by RFC4034 section 2.1.2.  It possible
   to try others, giving use a successful validation
   result if any can be validated and giving DNSKEY without the SEP bit set as the sole secure entry
   point to the zone, yet use a failure only if DNSKEY with the SEP bit set to sign 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
   RRsets in the zone management
   techniques, like (other than the Double Signature Zone-signing Key Rollover
   method described in section 4.2.1.2 of [6] might not work reliably.

9.  Minor 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.

4.3  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.

5.  IANA Considerations

   This document specifies no IANA Actions.

12.

6.  Security Considerations

13.

   This document does not make fundamental changes to the DNSSEC
   protocol, as it was generally understood when DNSSECbis was
   published.  It does, however, address some ambiguities and omissions
   in those documents that, if not recognized and addressed in
   implementations, could lead to security failures.  In particular, the
   validation algorithm clarifications in Section 2 are critical for
   preserving the security properties DNSSEC offers.  Furthermore,
   failure to address some of the interoperability concerns in Section 3
   could limit the ability to later change or expand DNSSEC, including
   by adding new algorithms.

7.  References

13.1

7.1  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,
        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

7.2  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 3.2, and the lack of specificity in handling ANY
   queries, as described in Section 2.3, were discovered by David
   Blacka.

   The error in algorithm 1 key tag calculation, as described in
   Section 7, 3.4, was found by Abhijit Hayatnagarkar.  Donald Eastlake
   contributed text for Section 7. 3.4.

   The bug relating to delegation NSEC RR's in the non-existence proof logic in RFC4035 Section 5.4 2.1 was found by
   Roy Badami.  Roy Arends found the related problem with DNAME.

   The errors in the RFC4035 examples were found by Roy Arends, who also
   contributed text for Section 9 4.3 of this document.

   The editor would like to thank Olafur Gudmundsson and Scott Rose for
   their substantive comments on the text of this document.

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