Internet DRAFT - draft-weiler-dnsext-dnssec-bis-updates

draft-weiler-dnsext-dnssec-bis-updates




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

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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.




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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.






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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



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   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.




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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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