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Versions: 00 01 02 03 04 draft-ietf-dnsop-kskroll-sentinel

DNSOP                                                          G. Huston
Internet-Draft                                                  J. Damas
Intended status: Standards Track                                   APNIC
Expires: April 29, 2018                                        W. Kumari
                                                                  Google
                                                        October 26, 2017


            A Sentinel for Detecting Trusted Keys in DNSSEC
                  draft-huston-kskroll-sentinel-02.txt

Abstract

   The DNS Security Extensions (DNSSEC) were developed to provide origin
   authentication and integrity protection for DNS data by using digital
   signatures.  These digital signatures can be verified by building a
   chain of trust starting from a trust anchor and proceeding down to a
   particular node in the DNS.  This document specifies a mechanism that
   will allow an end user to determine the trusted key state of the
   resolvers that handle the user's DNS queries.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on April 29, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Sentinel Mechanism  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Sentinel Processing . . . . . . . . . . . . . . . . . . . . .   4
   4.  Sentinel Test Result Considerations . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and
   [RFC4035] were developed to provide origin authentication and
   integrity protection for DNS data by using digital signatures.
   DNSSEC uses Key Tags to efficiently match signatures to the keys from
   which they are generated.  The Key Tag is a 16-bit value computed
   from the RDATA portion of a DNSKEY RR using a formula not unlike a
   ones-complement checksum.  RRSIG RRs contain a Key Tag field whose
   value is equal to the Key Tag of the DNSKEY RR that validates the
   signature.

   This document specifies how validating resolvers can respond to
   certain queries in a manner that allows a querier to deduce whether a
   particular key has been loaded into that resolver's trusted key
   store.  In particular, this response mechanism can be used to
   determine whether a certain Root Zone KSK is ready to be used as a
   trusted key within the context of a key roll by this resolver.

   This new mechanism is OPTIONAL to implement and use, although for
   reasons of supporting broad-based measurement techniques, it is
   strongly preferred if configurations of DNSSEC-validating resolvers
   enabled this mechanism by default, allowing for configuration
   directives to disable this mechanism if desired.







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1.1.  Terminology

   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.

2.  Sentinel Mechanism

   DNSSEC-Validating resolvers that implement this mechanism MUST be
   performing validation of responses in accordance with the DNSSEC
   response validation specification [RFC4035].

   This mechanism makes use of 2 special labels, "._is-ta-<tag-index>."
   (Intended to be used in a query where the response can answer the
   question: Is this the key tag a trust anchor which the validating DNS
   resolver is currently trusting?) and "._not-ta-<tag-index>."
   (Intended to be used in a query where the response can answer the
   question: Is this the key tag of a key that is NOT in the resolver's
   current trust store?).  The use of the positive question and its
   inverse allows for queries to detect whether resolvers support this
   mechanism.

   If the outcome of the DNS response validation process indicates that
   the response is authentic, and if the original query contains exactly
   one label that matches the template "._is-ta-<tag-index>.", then the
   following rule should be applied to the response: If the resolver has
   placed a Root Zone Key Signing Key with tag index value matching the
   value specified in the query into the local resolver's store of
   trusted keys, then the resolver should return a response indicating
   that the response contains authenticated data according to section
   5.8 of [RFC6840].  Otherwise, the resolver MUST return RCODE 2
   (server failure).  Note that the <tag-index> is specified in the DNS
   label using hex notation.

   If the outcome of the DNS response validation process indicates that
   the response is authentic, and if the original query contains exactly
   one label that matches the template "._not-ta-<tag-index>.", then the
   following rule should be applied to the response: If the resolver has
   not placed a Root Zone Key Signing Key with tag index value matching
   the value specified in the query into the local resolver's store of
   trusted keys, then the resolver should return a response indicating
   that the response contains authenticated data according to section
   5.8 of [RFC6840].  Otherwise, the resolver MUST return RCODE 2
   (server failure).  Note that the <tag-index> is specified in the DNS
   label using hex notation.






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   If a query contains one instance of both of these query templates
   then the resolver MUST NOT alter the outcome of the DNS response
   validation process.

   This mechanism is to be applied only by resolvers that perform DNSSEC
   validation, and applies only to responses to an A or AAAA query
   (Query Type value 1 or 28) where the resolver has authenticated the
   response according to the DNSSEC validation process and where the
   query name contains either of the labels described in this section.
   In this case, the resolver is to perform an additional test following
   the conventional validation function as described in this section.
   The result of this test directs whether the resolver is to change an
   authentic response to a response that indicates validation failure.

3.  Sentinel Processing

   This proposed test that uses the DNS resolver mechanism described in
   this document is based on three DNS names that have three distinct
   DNS resolution behaviours.  The test is intended to allow a user to
   determine the state of their DNS resolution system, and, in
   particular, whether or not they are using validating DNS resolvers
   that have picked up an incoming trust anchor in a key roll.

   The name format can be defined in a number of ways, and no name form
   is intrinsically better than any other in terms of the test itself.
   The critical aspect of the DNS names used in any such test is that
   they contain the specified label for either the positive and negative
   test.

   The sentinel process is envisaged to use a test with three names:

   a.  a name containing the label "._is-ta-<tag-index>.".  This is a
       validly signed name so that responses about names in this zone
       can be authenticated by a validating resolver.

   b.  a name containing the label "._not-ta-<tag-index>.".  This is
       also a validly-signed name.

   c.  a third name that is signed with a DNSSEC signature that cannot
       be validated.

   The responses received from queries to resolve each of these names
   would allow us to infer a trust key state of the resolution
   environment.

   o  Vnew: A DNSSEC-Validating resolver that includes this mechanism
      that has loaded the nominated key into its trusted key stash will




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      respond with an A record response for "is-ta", SERVFAIL for "not-
      ta" and SERVFAIL for the invalid name.

   o  Vold: A DNSSEC-Validating resolver that includes this mechanism
      that has not loaded the nominated key into its trusted key stash
      will respond with an SERVFAIL record for "is-ta", an A record
      response for "not-ta" and SERVFAIL for the invalid name.

   o  Vleg: A DNSSEC-Validating resolver that does not include this
      mechanism will respond with an A record response for "is-ta", an A
      record response for "not-ta" and SERVFAIL for the invalid name.

   o  nonV: A non-DNSSEC-Validating resolver will respond with an A
      record response for "is-ta", an A record response for "not-ta" and
      an A record response for the invalid name.

   Given the clear delineation amongst these three cases, if a client
   directs these three queries to a simple resolver, the variation in
   response to the three queries should allow the client to determine
   the category of the resolver, and if it supports this mechanism,
   whether or not it has loaded a particular key into its local trusted
   key stash.


      +-------------+----------+-----------+------------+
      | Type\Query  |  is_ta   |   not_ta  |  invalid   |
      +-------------+----------+-----------+------------+
      | Vnew        |    A     |  SERVFAIL |  SERVFAIL  |
      | Vold        | SERVFAIL |      A    |  SERVFAIL  |
      | Vleg        |    A     |      A    |  SERVFAIL  |
      | nonV        |    A     |      A    |     A      |
      +-------------+----------+-----------+------------+

   A Vnew response pattern says that the nominated key is trusted by the
   resolver and has been loaded into its local trusted key stash.  A
   Vleg response pattern says that the nominated key is not yet trusted
   by the resolver in its own right.  A Vleg response is indeterminate,
   and a nonV response indicates that the client does not have a
   validating resolver.

4.  Sentinel Test Result Considerations

   The description in the previous section describes a simple situation
   where the test queries were being passed to a single recursive
   resolver that directly queried authoritative name servers, including
   the root servers.





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   There is also the common case where the end client is configured to
   use multiple resolvers.  In these cases the SERVFAIL responses from
   one resolver will prompt the end client to repeat the query against
   one of the other configured resolvers.

   If any of the client's resolvers are non-validating resolvers, the
   tests will result in the client reporting that it has a non-
   validating DNS environment (nonV), which is effectively the case.

   If all of the client resolvers are DNSSEC-validating resolvers, but
   some do not support this trusted key mechanism, then the result will
   be indeterminate with respect to trusted key status (Vleg).
   Simlarly, if all the client's resolvers support this mechanism, but
   some have loaded the key into the trusted key stash and some have
   not, then the result is indeterminate (Vleg).

   There is also the common case of a recursive resolver using a
   forwarder.

   If the resolver is non-validating, and it has a single forwarder
   clause, then the resolver will presumably mirror the capabilities of
   the forwarder target resolver.  If this non-validating resolver it
   has multiple forwarders, then the above considerations will apply.

   If the validating resolver has a forwarding configuration, and uses
   the CD flag on all forwarded queries, then this resolver is acting in
   a manner that is identical to a standalone resolver.  The same
   consideration applies if any one one of the forwarder targets is a
   non-validating resolver.  Similarly, if all the forwarder targets do
   not apply this trusted key mechanism, the same considerations apply.

   A more complex case is where the following conditions all hold:

      both the validating resolver and the forwarder target resolver
      support this trusted key sentinel mechanism, and

      the local resolver's queries do not carry the CD bit, and

      the trusted key state differs between the forwarding resolver and
      the forwarder target resolver

   then either the outcome is indeterminate validating (Vleg), or a case
   of mixed signals (SERVFAIL in all three responses), which is
   similarly an indeterminate response with respect to the trusted key
   state.






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5.  Security Considerations

   This document describes a mechanism to allow users to determine the
   trust state of root zone key signing keys in the DNS resolution
   system that they use.

   The mechanism does not require resolvers to set otherwise
   unauthenticated responses to be marked as authenticated, and does not
   alter the security properties of DNSSEC with respect to the
   interpretation of the authenticity of responses that are so marked.

   The mechanism does not require any further significant processing of
   DNS responses, and queries of the form described in this document do
   not impose any additional load that could be exploited in an attack
   over the the normal DNSSEC validation processing load.

6.  IANA Considerations

   [Note to IANA, to be removed prior to publication: there are no IANA
   considerations stated in this version of the document.]

7.  Acknowledgements

   This document has borrowed extensively from RFC8145 for the
   introductory text, and the authors would like to acknowledge and
   thank the authors of that document both for some text excerpts and
   for the more general stimulation of thoughts about monitoring the
   progress of a roll of the Key Signing Key of the Root Zone of the
   DNS.

8.  References

8.1.  Normative References

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <https://www.rfc-editor.org/info/rfc4033>.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <https://www.rfc-editor.org/info/rfc4034>.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
              <https://www.rfc-editor.org/info/rfc4035>.



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   [RFC6840]  Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and
              Implementation Notes for DNS Security (DNSSEC)", RFC 6840,
              DOI 10.17487/RFC6840, February 2013,
              <https://www.rfc-editor.org/info/rfc6840>.

8.2.  Informative References

   [RFC8145]  Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust
              Anchor Knowledge in DNS Security Extensions (DNSSEC)",
              RFC 8145, DOI 10.17487/RFC8145, April 2017,
              <https://www.rfc-editor.org/info/rfc8145>.

Authors' Addresses

   Geoff Huston

   Email: gih@apnic.net
   URI:   http://www.apnic.net


   Joao Silva Damas

   Email: joao@apnic.net
   URI:   http://www.apnic.net


   Warren Kumari

   Email: warren@kumari.net






















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