DNSOP                                                          G. Huston
Internet-Draft                                                  J. Damas
Intended status: Standards Track                                   APNIC
Expires: October 7, November 3, 2018                                      W. Kumari
                                                                  Google
                                                           April 5,
                                                             May 2, 2018

              A Root Key Trust Anchor Sentinel for DNSSEC
                  draft-ietf-dnsop-kskroll-sentinel-11
                  draft-ietf-dnsop-kskroll-sentinel-12

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 and third parties to determine the trusted key
   state for the root key of the resolvers that handle that user's DNS
   queries.  Note that this method is only applicable for determing determining
   which keys are in the trust store for the root key.

   There is an example / toy implementation of this at http://www.ksk-
   test.net .

   [ This document is being collaborated on in Github at:
   https://github.com/APNIC-Labs/draft-kskroll-sentinel.  The most
   recent version of the document, open issues, etc should all be
   available here.  The authors (gratefully) accept pull requests.  Text
   in square brackets will be removed before publication. ]

   [ NOTE: This version uses the labels "root-key-sentinel-is-ta-", and
   "root-key-sentinel-not-ta-".; older versions of this document used
   "kskroll-sentinel-is-ta-<key-tag>", "kskroll-sentinel-not-ta-<key-
   tag>", and before that, "_is-ta-<key-tag>", "_not-ta-<key-tag>".
   Also note that the format of the tag-index is now zero-filled
   decimal.  Apolgies  Apologies to those who have began implmenting.] begun implementing earlier
   versions of this specification.]

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 October 7, November 3, 2018.

Copyright Notice

   Copyright (c) 2018 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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Protocol Walkthrough Example  .  Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . .   4
   3.  Sentinel Mechanism in Resolvers
     2.1.  Preconditions . . . . . . . . . . . . . . . .   7
     3.1.  Preconditions . . . . . .   4
     2.2.  Special Processing  . . . . . . . . . . . . . . . . .   7
     3.2.  Special processing . .   5
   3.  Processing Sentinel Results . . . . . . . . . . . . . . . . .   8   5
   4.  Processing  Sentinel Results Test Result Considerations . . . . . . . . . . . . .   7
   5.  Security Considerations . . . .   8
   5.  Sentinel Test Result Considerations . . . . . . . . . . . . .  10 . .   9
   6.  Security  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  11   9
   7.  Privacy Considerations  Implementation Experience . . . . . . . . . . . . . . . . . . .  12   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12  10
   10. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  12  10
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15  13
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  15  13
     11.2.  Informative References . . . . . . . . . . . . . . . . .  15  13
   Appendix A.  Protocol Walkthrough Example . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

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 found in "Key
   Tag Calculation" (Appendix B of "Resource Records for the DNS
   Security Extensions" [RFC4034]), a formula similar to a
   ones-complement 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 for the root 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 key, within the context of a planned root zone KSK key roll
   roll, by this resolver.

   There are two primary use cases for this mechanism:

   o  Users want to know whether the resolvers they use are ready for an
      upcoming root KSK rollover

   o  Researchers want to perform Internet-wide studies about the
      percentage of users who will be ready for an upcoming root KSK
      rollover

   The mechanism described in this document meets both of these use
   cases.  This new mechanism is OPTIONAL to implement and use, although
   for reasons of supporting broad-based measurement techniques, it is
   strongly preferred that configurations of DNSSEC-validating resolvers
   enabled this mechanism by default, allowing for local configuration
   directives to disable this mechanism if desired.

   The sentinel test described in this document determines whether a
   user's browser or operating system looking up the special names that
   are used in this protocol would be able to validate using the root
   KSK indicated by the special names.  The protocol uses the DNS
   SERVFAIL response code (RCODE 2) for this purpose because that is the
   response code that is returned by resolvers when DNSSEC validation
   fails.  If a browser or operating system has multiple resolvers
   configured, and those resolvers have different properties (for
   example, one performs DNSSEC validation and one does not), the
   sentinel mechanism might search among the different resolvers, or
   might not, depending on how the browser or operating system is
   configured.

   Note that the sentinel mechanism described here measures a very
   different (and likely more useful) metric than [RFC8145].  RFC 8145
   relies on resolvers reporting towards the root servers a list of
   locally cached trust anchors for the root zone.  Those reports can be
   used to infer how many resolvers may be impacted by a KSK roll, but
   not what the user impact of the KSK roll will be.

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.  Protocol Walkthrough Example

   [Ed note: This is currently towards the front of the document; we
   will make it an appendix at publication time, but until then it is
   worth having up front, as it makes the rest  Sentinel Mechanism in Resolvers

   DNSSEC-Validating resolvers that implement this mechanism MUST
   perform validation of responses in accordance with the document much
   easier to understand ] DNSSEC
   response validation specification [RFC4035].

   This section provides a non-normative example of how the sentinel mechanism could be used, and what each participant does.  It is
   provided in a conversational tone to be easier to follow.

   Alice makes use of two special labels:

   o  root-key-sentinel-is-ta-<key-tag>

   o  root-key-sentinel-not-ta-<key-tag>

   Note that the <key-tag> is specified in charge of the DNS root KSK (Key Signing Key), and would
   like to roll / replace the key with a new one.  She publishes the new
   KSK, label as unsigned
   decimal integer (as described in [RFC4034], section 5.3), but would like to be able zero-
   padded to predict / measure what the impact
   will be before removing/revoking the old key.  The current KSK has five digits (for example, a Key Tag value of 11112, 42 would be
   represented in the label as 00042).

   These labels trigger special processing in the new KSK has a Key Tag of 02323.  Users want to
   verify that their resolver will not break after Alice rolls when
   responses from authoritative servers are received.  Labels containing
   "root-key-sentinel-is-ta-<key-tag>" is used to answer the root
   KSK key (that is, starts signing with just question
   "Is this the KSK whose Key Tag is
   02323).

   Bob, Charlie, Dave, Ed are all users.  They use of a Key which the validating DNS recursive
   resolvers supplied by their ISPs.  They would like resolver is
   currently trusting as a trust anchor?"  Labels containing "root-key-
   sentinel-not-ta-<key-tag>" is used to confirm that
   their ISPs have picked up the new KSK.  Bob's ISP does not perform
   validation.  Charlie's ISP does validate, but answer the resolvers have not
   yet been upgraded to support this mechanism.  Dave and Ed's resolvers
   have been upgraded to support question "Is this mechanism; Dave's resolver has
   the
   new KSK, Ed's resolver hasn't managed to install Key Tag of a Key which the 02323 KSK in its
   trust store yet.

   Geoff validating DNS resolver is *not*
   currently trusting as a researcher, and would like to both provide a means for
   Bob, Charlie, Dave and Ed to be able to perform tests, and also would
   like to be able to perform Internet-wide measurements trust anchor?"

2.1.  Preconditions

   All of what the
   impact will following conditions must be (and report this back met to Alice).

   Geoff sets an authoritative trigger special
   processing inside resolver code:

   o  The DNS server for example.com, and also a
   webserver (www.example.com).  He adds three address records to
   example.com:

      invalid.example.com.  IN AAAA 2001:db8::1

      root-key-sentinel-is-ta-02323.example.com.  IN AAAA 2001:db8::1
      root-key-sentinel-not-ta-02323.example.com.  IN AAAA 2001:db8::1

   Note that the use response is DNSSEC validated.

   o  The result of "example.com" names and the addresses here are
   examples.  In a real deployment, validation is "Secure".

   o  The Checking Disabled (CD) bit in the domain names need to be under
   control query is not set.

   o  The QTYPE is either A or AAAA (Query Type value 1 or 28)

   o  The OPCODE is QUERY

   o  The leftmost label of the researcher, and original QNAME (the name sent in the addresses must be real, reachable
   addresses.

   Geoff then DNSSEC signs
      Question Section in the example.com zone, and intentionally makes original query) is either "root-key-
      sentinel-is-ta-<key-tag>" or "root-key-sentinel-not-ta-<key-tag>"

   If any one of the invalid.example.com record invalid/bogus (for example, by editing preconditions is not met, the signed zone and entering garbage for resolver MUST NOT
   alter the signature).  Geoff also
   configures his webserver to listen DNS response based on 2001:db8::1 and serve a
   resource (for example, a 1x1 GIF, 1x1.gif) for the mechanism in this document.

2.2.  Special Processing

   Responses which fulfil all of these names.
   The webserver also serves a webpage (www.example.com) which contains
   links to these 3 resources (http://invalid.example.com/1x1.gif,
   http://root-key-sentinel-is-ta-02323.example.com/1x1.gif,
   http://root-key-sentinel-not-ta-02323.example.com/1x1.gif).

   Geoff then asks Bob, Charlie, Dave and Ed to browse to
   www.example.com.  Using the methods described preconditions in Section 2.1
   require special processing, depending on leftmost label in this document, the
   users can figure out what their fate will be when QNAME.

   First, the 11112 KSK is
   removed.

   Bob resolver determines if the numerical value of <key-tag> is not using a validating resolver.  This means that he will be
   able
   equal to resolve invalid.example.com (and fetch the 1x1 GIF) - this
   tells him that the KSK roll does not affect him, and so he will be
   OK.

   Charlie's resolvers are validating, but they have not been upgraded
   to support any of the Key Tag values of an active root zone KSK sentinel mechanism.  Charlie will not be able to
   fetch the http://invalid.example.com/1x1.gif resource (the
   invalid.example.com record which
   is bogus, currently trusted by the local resolver and none of his resolvers will
   resolve it).  He is able to fetch both stored in its store
   of the other resources - from
   this he knows (see the logic below) that he is using legacy,
   validating resolvers.  The trusted keys.  An active root zone KSK sentinel method cannot provided him
   with is one which could
   currently be used for validation (that is, a definitive answer to the question of what root trust anchors
   this resolver Key that is using.

   Dave's resolvers implement the sentinel method, and have picked up
   the new KSK.  For not in
   either the same reason AddPend or Revoked state as Charlie, he cannot fetch described in [RFC5011]).

   Second, the
   "invalid" resource.  His resolver resolves the root-key-sentinel-is-
   ta-02323.example.com name normally (it contacts the example.com
   authoritative servers, etc); as it supports the sentinel mechanism,
   just before Dave's recursive server send alters the reply response being sent to Dave's stub, it
   performs the KSK Sentinel check (see below).  The QNAME starts with
   "root-key-sentinel-is-ta-", original
   query based on both the left-most label and the recursive resolver does indeed
   have presence of a key Key
   with the given Key Tag of 02323 in its root the trust anchor store.  This
   means that that this part  Two labels and two
   possible states of the KSK Sentinel check passes (it is
   true that corresponding Key Tag 02323 is generate four possible
   combinations summarized in the trust anchor store), and the
   recursive resolver replies normally (with the table:

    Label      |   Key is trusted        |   Key is not trusted
    ------------------------------------------------------------------
    is-ta      | return original answer provided by  | return SERVFAIL
    not-ta     | return SERVFAIL         | return original answer

   Instruction "return SERVFAIL" means that the
   authoritative server).  Dave's recursive resolver then resolves MUST set
   RCODE=SERVFAIL (value 2) and MUST empty the
   root-key-sentinel-not-ta-02323.example.com name.  Once again, it
   performs ANSWER section of the normal resolution process, but because it implements KSK DNS
   response, ignoring all other documents which specify content of the
   ANSWER section.

3.  Processing Sentinel (and Results

   This proposed test that uses the QNAME starts with "root-key-sentinel-not-ta-"),
   just before sending sentinel detection mechanism
   described in this document is based on the reply, it performs use of three DNS names
   that have three distinct DNS resolution behaviours.  The test is
   intended to allow a user or a third party to determine the KSK Sentinel check.
   As it has 02323 state of
   their DNS resolution system, and, in it's particular, whether or not they
   are using one or more validating DNS resolvers that use a particular
   trust anchor store, for the answer to "is root zone.

   The critical aspect of the DNS names used in this
   *not* a trust anchor" mechanism is false, and so that
   they contain the recursive resolver does
   not reply with specified label for either the answer from positive and negative
   test as the authoritative server - instead, it
   replies with left-most label in the query name.

   The sentinel detection process uses a SERVFAIL (note that replying test with SERVFAIL instead of
   the original answer is three query names:

   o  A query name containing the only mechanism that KSK Sentinel uses). left-most label "root-key-sentinel-is-
      ta-<key-tag>".  This means that Dave cannot fetch "invalid", he can fetch "root-key-
   sentinel-is-ta-02323", but he cannot fetch "root-key-sentinel-not-ta-
   02323".  From this, Dave knows that he is behind an upgraded,
   validating resolver, which has successfully installed the new, 02323
   KSK.

   Just like Charlie and Dave, Ed cannot fetch corresponds to a a validly-signed RRset in
      the "invalid" record.
   This tells him zone, so that his resolvers are validating.  When his
   (upgraded) resolver performs the KSK Sentinel check for "root-key-
   sentinel-is-ta-02323", it does *not* have the (new, 02323) KSK responses associated with queried names in
   it's trust anchor store.  This means check fails, and Ed's recursive
   resolver converts the (valid) answer into this
      zone can be authenticated by a SERVFAIL error response.
   It performs the same check DNSSEC-validating resolver.  Any
      validly-signed DNS zone can be used for root-key-sentinel-not-ta-
   02323.example.com; as it does not have this test.

   o  A query name containing the 02323 KSK, it left-most label "root-key-sentinel-
      not-ta-<key-tag>".  This is true that also a validly-signed name.  Any
      validly-signed DNS zone can be used for this test.

   o  A query name that is not signed with a trust anchor for it, and so it replies normally.  This
   means DNSSEC signature that Ed cannot fetch the "invalid" resource, he also cannot
   fetch the "root-key-sentinel-is-ta-02323" resource, but he can fetch
   the "root-key-sentinel-not-ta-02323" resource.  This tells Ed that
   his resolvers have be
      validated (described as a "bogus" RRset in Section 5 of [RFC4033],
      when, for example, an RRset is not installed the new KSK.

   Geoff would like to do signed with a large scale test and provide the information
   back to Alice.  He uses some mechanism such as causing users to go to
   a web page to cause a large number of users to attempt valid RRSIG
      record).

   The responses received from queries to resolve the
   three resources, and then analyzes the results each of the tests these names
   would allow us to
   determine what percentage infer a trust key state of users will be affected by the KSK
   rollover event. resolution
   environment.  The above description is a simplified example - it is not anticipated techniques describes in this document rely on
   (DNSSEC validating) resolvers responding with SERVFAIL to valid
   answers.  Note that Bob, Charlie, Dave and Ed will actually look for the absence or
   presence a slew of web resources; instead, the webpage that they load would
   likely contain JavaScript (or similar) which displays other issues can also cause SERVFAIL
   responses, and so the sentinel processing may sometimes result in
   incorrect conclusions.

   To describe this process of
   the tests, sends the results to Geoff, or both.  This sentinel
   mechanism does not rely on the web: it classification, we can equally be used by trying
   to resolve the names (for example, using classify resolvers
   into four distinct behavior types, for which we will use the common "dig" command) labels:
   "Vnew", "Vold", "Vleg", and checking which result in a SERVFAIL.

3.  Sentinel Mechanism in Resolvers "nonV".  These labels correspond to
   resolver behaviour types as follows:

   Vnew:  A DNSSEC-Validating resolvers resolver that is configured to implement
      this mechanism MUST
   perform validation of responses in accordance with has loaded the DNSSEC
   response validation specification [RFC4035].

   This sentinel mechanism makes use of two special labels:

   o  root-key-sentinel-is-ta-<key-tag>

   o  root-key-sentinel-not-ta-<key-tag>

   Note that the <key-tag> is specified in the DNS label as unsigned
   decimal integer (as described in [RFC4034], section 5.3), but zero-
   padded to five digits (for example, a Key Tag 42 would be represented
   in the label as 00042).

   These labels trigger special processing in the resolver when
   responses from authoritative servers are received.  Labels containing
   "root-key-sentinel-is-ta-<key-tag>" is used to answer the question
   "Is this the Key Tag a trust anchor which nominated key into its local trusted
      key store will respond with an A or AAAA RRset response for "root-
      key-sentinel-is-ta" queries, SERVFAIL for "root-key-sentinel-not-
      ta" queries and SERVFAIL for the validating DNS invalidly signed name queries.

   Vold:  A DNSSEC-Validating resolver that is currently trusting?"  Labels containing "root-key-sentinel-not-ta-
   <key-tag>" is used configured to answer the question "Is implement
      this mechanism that has not loaded the Key Tag *not*
   a trust anchor which the validating DNS resolver is currently
   trusting?"

3.1.  Preconditions

   All of the following conditions must be met to trigger special
   processing inside resolver code:

   o  The DNS nominated key into its
      local trusted key store will respond with an SERVFAIL for "root-
      key-sentinel-is-ta" queries, an A or AAAA RRset response is DNSSEC validated.

   o  The result of validation is "Secure".

   o  The Checking Disabled (CD) bit in for
      "root-key-sentinel-not-ta" queries and SERVFAIL for the query is invalidly
      signed name queries.

   Vleg:  A DNSSEC-Validating resolver that does not set.

   o  The QTYPE is either implement this
      mechanism will respond with an A or AAAA (Query Type value 1 RRset response for "root-
      key-sentinel-is-ta", an A or 28)

   o  The OPCODE is QUERY

   o  The leftmost label of the original QNAME (the name sent in the
      Question Section in the original query) is either AAAA RRset response for "root-key-
      sentinel-is-ta-<key-tag>" or "root-key-sentinel-not-ta-<key-tag>"

   If any one of the preconditions is not met,
      sentinel-not-ta" and SERVFAIL for the invalid name.

   nonV:  A non-DNSSEC-Validating resolver MUST NOT
   alter the DNS will respond with an A or
      AAAA record response based on the mechanism in this document.

3.2.  Special processing

   Responses which fullfill all of the preconditions in Section 3.1
   require special processing, depending on leftmost label in for "root-key-sentinel-is-ta", an A record
      response for "root-key-sentinel-not-ta" and an A or AAAA RRset
      response for the QNAME.

   First, invalid name.

   Given the resolver determines clear delineation amongst these three cases, if the numerical value of <key-tag> is
   equal a client
   directs these three queries to any of the Key Tags of an active root zone KSK which is
   currently trusted by the local resolver and is stored in its store of
   trusted keys.  An active key is one which could currently be used for
   validation (that is, a key that is not in either simple resolver, the AddPend or
   Revoked state as described variation in [RFC5011]).

   Second, the resolver alters the
   response being sent to the original
   query based on both three queries should allow the left-most label and client to determine
   the presence category of the resolver, and if it supports this mechanism,
   whether or not it has a particular key
   with given Key Tag in the its trust anchor store.  Two labels and two
   possible states of the keytag generate four possible combinations
   summarized in the table:

    Label      |   Key Tag is trusted

                                    Query
                      +----------+-----------+------------+
                      |   Key Tag is not trusted
    ------------------------------------------------------------------  is-ta   | return original answer  not-ta   |  invalid   |
              +-------+----------+-----------+------------+
              | Vnew  |    A     | return  SERVFAIL
    not-ta | return  SERVFAIL  | return original answer

   Instruction "return SERVFAIL" means
              | Vold  | SERVFAIL |      A    |  SERVFAIL  |
        Type  | Vleg  |    A     |      A    |  SERVFAIL  |
              | nonV  |    A     |      A    |     A      |
              +-------+----------+-----------+------------+

   A "Vnew" type says that the nominated key is trusted by the resolver MUST set
   RCODE=SERVFAIL (value 2)
   and MUST empty has been loaded into its local trusted key stash.  A "Vold" type
   says that the ANSWER section of nominated key is not yet trusted by the DNS
   response, ignoring all other documents which specify content of resolver in its
   own right.  A "Vleg" type does not give any information about the
   ANSWER section.
   trust anchors, and a "nonV" type indicates that the resolver does not
   perform DNSSEC validation.

4.  Processing  Sentinel Results

   This proposed 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 uses directly queried authoritative name servers, including
   the sentinel detection mechanism
   described in this document root servers.

   There is based on also the use of three DNS names
   that have three distinct DNS resolution behaviours.  The test common case where the end client's browser or
   operating system is
   intended configured to allow a user or use multiple resolvers.  In these
   cases, a third party SERVFAIL response from one resolver may cause the end client
   to determine repeat the state query against one of
   their DNS resolution system, and, in particular, whether the other configured resolvers.

   If the client's browser or operating system does not they
   are using one or more validating DNS resolvers that use a particular
   trust anchor for the root zone.

   The critical aspect of the DNS names used in this mechanism is that
   they contain try the specified label for either
   additional resolvers, the positive and negative sentinel test as will effectively only be for
   the left-most label in first resolver.

   If any of the query name.

   The sentinel detection process uses a test with three query names:

   o  A query name containing client's resolvers are non-validating resolvers, the left-most label "root-key-sentinel-is-
      ta-<key-tag>".  This corresponds to a a validly-signed RRset
   tests will result in the zone, so client reporting that responses associated with queried names in this
      zone can be authenticated by it has a DNSSEC-validating resolver.  Any
      validly-signed non-
   validating DNS zone can 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 used for indeterminate with respect to trusted key status ("Vleg").
   Similarly, if all the client's resolvers support this test.

   o  A query name containing mechanism, but
   some have loaded the left-most label "root-key-sentinel-
      not-ta-<key-tag>".  This key into the trusted key stash and some have
   not, then the result is indeterminate ("Vleg").

   There is also the common case of a validly-signed name.  Any
      validly-signed DNS zone can be used for this test.

   o  A query name that is signed with recursive resolver using a DNSSEC signature that cannot be
      validated (such as if
   forwarder.

   If the corresponding RRset resolver is not signed with non-validating, and it has a
      valid RRSIG record).

   The responses received from queries to resolve each of these names
   would allow us to infer a trust key state of single forwarder
   clause, then the resolution
   environment.  The techniques describes in this document rely on
   (DNSSEC validating) resolvers responding with SERVFAIL to valid
   answers.  Note that a slew resolver will presumably mirror the capabilities of other issues can also cause SERVFAIL
   responses, and so
   the sentinel processing may sometimes result in
   incorrect conclusions.

   To describe forwarder target resolver.  If this process of classification, we can classify resolvers
   into four distinct behavior types, for which we non-validating resolver it
   has multiple forwarders, then the above considerations will use apply.

   If the labels:
   "Vnew", "Vold", "Vleg", and "nonV".  These labels correspond to validating resolver behaviour types as follows:

   Vnew:  A DNSSEC-Validating has a forwarding configuration, and uses
   the CD bit on all forwarded queries, then this resolver is acting in
   a manner that is configured identical to implement
      this mechanism has loaded a standalone resolver.  The same
   consideration applies if any one of the nominated key into its local forwarder targets is a non-
   validating resolver.  Similarly, if all the forwarder targets do not
   apply this trusted key store will respond with an mechanism, the same considerations apply.

   A or AAAA RRset response for "root-
      key-sentinel-is-ta" queries, SERVFAIL for "root-key-sentinel-not-
      ta" queries more complex case is where all of the following conditions all
   hold:

   o  Both the validating resolver and SERVFAIL for the invalidly signed name queries.

   Vold:  A DNSSEC-Validating forwarder target resolver that is configured to implement
      support this trusted key sentinel mechanism that has

   o  The local resolver's queries do not loaded have the nominated key into its
      local CD bit set

   o  The trusted key store will respond with an SERVFAIL for "root-
      key-sentinel-is-ta" queries, an A or AAAA RRset response for
      "root-key-sentinel-not-ta" queries and SERVFAIL for state differs between the invalidly
      signed name queries.

   Vleg:  A DNSSEC-Validating forwarding resolver that does not implement this
      mechanism will respond with an A or AAAA RRset response for "root-
      key-sentinel-is-ta", an A or AAAA RRset response for "root-key-
      sentinel-not-ta" and SERVFAIL for
      the invalid name.

   nonV:  A non-DNSSEC-Validating forwarder target resolver will respond with an A

   In such a case, either the outcome is indeterminate validating
   ("Vleg"), or
      AAAA record response for "root-key-sentinel-is-ta", a case of mixed signals (SERVFAIL in all three
   responses), which is similarly an A record indeterminate response with respect
   to the trusted key state.

   Please note that SERVFAIL might be cached according to [RFC2308]
   section 7 for "root-key-sentinel-not-ta" up to 5 minutes and an A or AAAA RRset
      response for the invalid name.

   Given the clear delineation amongst these three cases, if a client
   directs these three queries positive answer for up to its
   TTL.

5.  Security Considerations

   This document describes a simple resolver, the variation in
   response mechanism to the three queries should allow the client users and third parties
   to determine the category trust state of root zone key signing keys in the resolver, DNS
   resolution system that they use.

   The mechanism does not require resolvers to set otherwise
   unauthenticated responses to be marked as authenticated, and if it supports this mechanism,
   whether or does not it has a particular key in its trust anchor store.

                                    Query
                      +----------+-----------+------------+
                      |  is-ta   |  not-ta   |  invalid   |
              +-------+----------+-----------+------------+
              | Vnew  |    A     |  SERVFAIL |  SERVFAIL  |
              | Vold  | SERVFAIL |      A    |  SERVFAIL  |
        Type  | Vleg  |    A     |      A    |  SERVFAIL  |
              | nonV  |    A     |      A    |     A      |
              +-------+----------+-----------+------------+

   A "Vnew" type says that
   alter the nominated key is trusted by security properties of DNSSEC with respect to the resolver
   and has been loaded into its local trusted key stash.  A "Vold" type
   says that
   interpretation of the nominated key is authenticity of responses that are so marked.

   The mechanism does not yet trusted by require any further significant processing of
   DNS responses, and queries of the resolver form described in its
   own right.  A "Vleg" type does this document do
   not give impose any information about the
   trust anchors, and a "nonV" type indicates additional load that could be exploited in an attack
   over the resolver does not
   perform the normal DNSSEC validation.

5.  Sentinel Test Result validation processing load.

6.  Privacy Considerations

   The description mechanism in the previous section describes a simple situation
   where the test queries were being passed this document enables third parties (with either
   good or bad intentions) to a single learn something about the security
   configuration of recursive
   resolver that directly queried authoritative name servers, including
   the root servers.

   There is also the common case where the end client's browser or
   operating system is configured to use multiple resolvers.  In these
   cases, a SERVFAIL response from one resolver may  That is, someone who can
   cause the end client an Internet user to repeat the query against one make specific DNS queries (e.g. via web-
   based advertisements or javascript in web pages), can, under certain
   specific circumstances that includes additional knowledge of the other configured resolvers.
   If the client's browser or operating system does not try
   resolvers that are invoked by the user, determine which trust anchors
   are configured in these resolvers.  Without this additional resolvers,
   knowledge, the sentinel test will effectively only be for third party can infer the first resolver.

   If any aggregate capabilities of
   the client's resolvers are non-validating resolvers, user's DNS resolution environment, but cannot necessarily infer
   the
   tests will result in trust configuration of any recursive name server.

7.  Implementation Experience

   Petr Spacek implemented early versions of this technique into the client reporting that
   Knot resolver, and identified a number of places where it wasn't
   clear, and provided very helpful text to address this.

   Ondrej Sury of ISC has a non-
   validating DNS environment ("nonV"), which is effectively reported to the case.

   If all DNSOP Working Group in April
   2018 that this technique was peer-reviewed and merged into BIND
   master branch with the intent to backport the feature into older
   release branches.

   Benno Overeinder of NLnet Labs reported to the client resolvers are DNSSEC-validating resolvers, but
   some do not DNSOP Working Group in
   April 2018 an intention to support this trusted key mechanism, then technique in Unbound in the result will
   near future.

8.  IANA Considerations

   [Note to IANA, to be indeterminate with respect removed prior to trusted key status ("Vleg").
   Simlarly, if all the client's resolvers support publication: there are no IANA
   considerations stated in this mechanism, but
   some have loaded version of the key into document.]

9.  Acknowledgements

   This document has borrowed extensively from [RFC8145] for the trusted key stash
   introductory text, and the authors would like to acknowledge and
   thank the authors of that document both for some have
   not, then text excerpts and
   for the result is indeterminate ("Vleg").

   There is also more general stimulation of thoughts about monitoring the common case
   progress of a recursive resolver using a
   forwarder.

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

   If root zone of the validating resolver has a forwarding configuration, DNS.

   The authors would like to thank Joe Abley, Mehmet Akcin, Mark
   Andrews, Richard Barnes, Ray Bellis, Stephane Bortzmeyer, David
   Conrad, Ralph Dolmans, John Dickinson, Steinar Haug, Bob Harold, Wes
   Hardaker, Paul Hoffman, Matt Larson, Jinmei Tatuya, Edward Lewis,
   George Michaelson, Benno Overeinder, Matthew Pounsett, Andreas
   Schulze, Mukund Sivaraman, Petr Spacek, Andrew Sullivan, Ondrej Sury,
   Paul Vixie, Duane Wessels and uses
   the CD bit on all forwarded queries, then this resolver is acting Paul Wouters for their helpful
   feedback.

   The authors would like to especially call out Paul Hoffman and Duane
   Wessels for providing comments in the form of a manner pull request.

10.  Change Log

   RFC Editor: Please remove this section!

   Note that this document is identical to a standalone resolver. being worked on in GitHub - see Abstract.
   The same
   consideration applies if any one of the forwarder targets below is mainly large changes, and is a non-
   validating resolver.  Similarly, if all the forwarder targets do not
   apply this trusted key mechanism, authoritative.

   From -11 to -12:

   o  Moved the same considerations apply.

   A more complex case is where all Walkthrough Example to the end of the following conditions all
   hold: document as an
      appendix.

   o  Both the validating resolver  Incorporated changes as proposed by Ondrej Sury, relating to a
      consistent use of Key Tag and a reference to the forwarder target resolver
      support this trusted key sentinel mechanism definition of a
      Bogus RRset.

   o  The local resolver's queries do not have the CD bit set  Corrected minor typos.

   o  The trusted key state differs between the forwarding resolver and  Revised the forwarder target resolver Privacy Considerations.

   o  In such response to a case, either the outcome is indeterminate validating
   ("Vleg"), or request from DNSOP Working Group chairs, a case of mixed signals (SERVFAIL in all three
   responses), which is similarly an indeterminate response with respect
      section on reported Implementation Experience has been added,
      based on postings to the trusted key state.

   Please note that SERVFAIL might be cached according to [RFC2308]
   section 7 for up DNSOP Working Group mailing list.

   From -10 to 5 minutes and a positive answer -11:

   o  Clarified the preconditions for up to its
   TTL.

6.  Security Considerations

   This document describes a this mechanism as per Working
      Group mailing list discussion.

   o  Corrected minor typo.

   From -09 to allow users and third parties -10:

   o  Clarified the precondition list to determine specify that the trust state of root zone key signing keys resolver had
      performed DNSSEC-validation by setting the AD bit 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 response

   o  Clarified the security properties of DNSSEC with respect language referring 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 operation of RFC8145
      signalling.

   From -08 to -09:

   o  Incorporated Paul Hoffman's PR # 15 (Two issues from the form described in this document do
   not impose any additional load
      Hackathon) - https://github.com/APNIC-Labs/draft-kskroll-sentinel/
      pull/15

   o  Clarifies that could be exploited in an attack
   over the match is on the normal DNSSEC validation processing load.

7.  Privacy Considerations

   The mechansim in this document enables third parties (with either
   good or bad intentions) to learn something about the security
   configuration of recursive name servers.  That is, someone who can
   cause an Internet user *original* QNAME.

   From -08 to make specific DNS queries (e.g. via web-
   based advertisements or javascript in web pages), can then determine
   which trust anchors are configured -07:

   o  Changed title from "A Sentinel for Detecting Trusted Keys in the user's resolver.

8.  IANA Considerations

   [Note to IANA,
      DNSSEC" to be removed prior "A Root Key Trust Anchor Sentinel for DNSSEC".

   o  Changed magic string from "kskroll-sentinel-" to publication: there are no IANA
   considerations stated in "root-key-
      sentinel-" -- this version of the document.]

9.  Acknowledgements

   This document has borrowed extensively from [RFC8145] time for the
   introductory text, and the authors would like sure, Rocky!

   From -07 to acknowledge -06:

   o  Addressed GitHub PR #14: Clarifications regarding caching and
   thank the authors
      SERVFAIL responses

   o  Addressed GitHub PR #12, #13: Clarify situation with multiple
      resolvers, Fix editorial nits.

   From -05 to -06:

   o  Paul improved my merging of that document both for some Petr's text excerpts and
   for the to make it more general stimulation of thoughts about monitoring the
   progress of a roll of the KSK of the root zone of readable.
      Minor change, but this is just before the DNS.

   The authors would like cut-off, so I wanted it
      maximally readable.

   From -04 to thank Joe Abley, Mehmet Akcin, Mark
   Andrews, Richard Barnes, Ray Bellis, Stephane Bortzmeyer, David
   Conrad, Ralph Dolmans, John Dickinson, Steinar Haug, Bob Harold, Wes
   Hardaker, Paul Hoffman, Matt Larson, Jinmei Tatuya, Edward Lewis,
   George Michaelson, Benno Overeinder, Matthew Pounsett, Andreas
   Schulze, Mukund Sivaraman, -05:

   o  Incorporated Duane's #10
   o  Integrated Petr Spacek, Andrew Sullivan, Paul Vixie,
   Duane Wessels and Paul Wouters for their helpful feedback.

   The authors would like Spacek's Issue - https://github.com/APNIC-Labs/
      draft-kskroll-sentinel/issues/9 (note that commit-log incorrectly
      referred to especially call out Paul Hoffman and Duane
   Wessels for providing comments in the form of a pull request.  Petr
   Spacek implemented early versions of this technique into the Knot
   resolver, identified a Duane's PR as number of places where 9, it wasn't clear, and
   provided very helpful text to address this.

10.  Change Log

   RFC Editor: Please remove this section!

   Note that this document is being worked on in GitHub - see Abstract.
   The below is mainly large changes, and is not authoritative. actually 10).

   From -10 -03 to -11: -04:

   o  Clarified the preconditions for this mechanism as per Working
      Group mailing list discussion.  Addressed GitHub pull requests #4, #5, #6, #7 #8.

   o  Corrected minor typo.

   From -09 to -10:  Added Duane's privacy concerns

   o  Clarified the precondition list to specify that the resolver had
      performed DNSSEC-validation by setting the AD bit in  Makes the response use cases clearer

   o  Clarified the language referring to  Fixed some A/AAAA stuff

   o  Changed the operation of RFC8145
      signalling. example numbers

   o  Made it clear that names and addresses must be real

   From -08 -02 to -09: -03:

   o  Incorporated  Integrated / published comments from Paul Hoffman's in GitHub PR # 15 (Two issues from the
      Hackathon) #2 - https://github.com/APNIC-Labs/draft-kskroll-sentinel/
      pull/15
      https://github.com/APNIC-Labs/draft-kskroll-sentinel/pull/2

   o  Clarifies that the match is on  Made the *original* QNAME. Key Tag be decimal, not hex (thread / consensus in
      https://mailarchive.ietf.org/arch/msg/dnsop/
      Kg7AtDhFRNw31He8n0_bMr9hBuE )

   From -08 -01 to -07: 02:

   o  Changed title from "A Sentinel for Detecting Trusted Keys  Removed Address Record definition.

   o  Clarified that many things can cause SERVFAIL.

   o  Made examples FQDN.

   o  Fixed a number of typos.

   o  Had accidentally said that Charlie was using a non-validating
      resolver in
      DNSSEC" to "A Root Key Trust Anchor Sentinel for DNSSEC". example.

   o  Changed magic string from "kskroll-sentinel-" to "root-key-
      sentinel-" --  [ TODO(WK): Doc says Key Tags are hex, is this time for sure, Rocky!

   From -07 to -06:

   o  Addressed GitHub PR #14: Clarifications regarding caching and
      SERVFAIL responses really what the WG
      wants? ]

   o  Addressed GitHub PR #12, #13: Clarify situation with multiple
      resolvers, Fix editorial nits.  And active key is one that can be used *now* (not e.g AddPend)

   From -05 -00 to -06: 01:

   o  Paul improved my merging  Added a conversational description of Petr's text how the system is intended
      to make it more readable.
      Minor change, but work.

   o  Clarification that this is just before for the cut-off, so I wanted it
      maximally readable.

   From -04 to -05:

   o  Incorporated Duane's #10 root.

   o  Integrated Petr Spacek's Issue - https://github.com/APNIC-Labs/
      draft-kskroll-sentinel/issues/9 (note that commit-log incorrectly
      referred  Changed the label template from _is-ta-<key-tag> to Duane's PR as number 9, it kskroll-
      sentinel-is-ta-<key-tag>.  This is actually 10).

   From -03 because BIND (at least) will
      not allow records which start with an underscore to -04:

   o  Addressed GitHub pull requests #4, #5, #6, #7 #8.

   o  Added Duane's privacy concerns

   o  Makes have address
      records (CNAMEs, yes, A/AAAA no).  Some browsers / operating
      systems also will not fetch resources from names which start with
      an underscore.

11.  References

11.1.  Normative References

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
              <https://www.rfc-editor.org/info/rfc2308>.

   [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>.

   [RFC5011]  StJohns, M., "Automated Updates of DNS Security (DNSSEC)
              Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
              September 2007, <https://www.rfc-editor.org/info/rfc5011>.

11.2.  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>.

Appendix A.  Protocol Walkthrough Example

   This Appendix provides a non-normative example of how the sentinel
   mechanism could be used, and what each participant does.  It is
   provided in a conversational tone to be easier to follow.

   Alice is in charge of the DNS root KSK (Key Signing Key), and would
   like to roll / replace the key with a new one.  She publishes the new
   KSK, but would like to be able to predict / measure what the impact
   will be before removing/revoking the old key.  The current KSK has a
   Key Tag of 11112, the new KSK has a Key Tag of 02323.  Users want to
   verify that their resolver will not break after Alice rolls the root
   KSK key (that is, starts signing with just the KSK whose Key Tag is
   02323).

   Bob, Charlie, Dave, Ed are all users.  They use the DNS recursive
   resolvers supplied by their ISPs.  They would like to confirm that
   their ISPs have picked up the new KSK.  Bob's ISP does not perform
   validation.  Charlie's ISP does validate, but the resolvers have not
   yet been upgraded to support this mechanism.  Dave and Ed's resolvers
   have been upgraded to support this mechanism; Dave's resolver has the
   new KSK, Ed's resolver hasn't managed to install the 02323 KSK in its
   trust store yet.

   Geoff is a researcher, and would like to both provide a means for
   Bob, Charlie, Dave and Ed to be able to perform tests, and also would
   like to be able to perform Internet-wide measurements of what the
   impact will be (and report this back to Alice).

   Geoff sets an authoritative DNS server for example.com, and also a
   webserver (www.example.com).  He adds three address records to
   example.com:

      invalid.example.com.  IN AAAA 2001:db8::1

      root-key-sentinel-is-ta-02323.example.com.  IN AAAA 2001:db8::1

      root-key-sentinel-not-ta-02323.example.com.  IN AAAA 2001:db8::1

   Note that the use of "example.com" names and the addresses here are
   examples.  In a real deployment, the domain names need to be under
   control of the researcher, and the addresses must be real, reachable
   addresses.

   Geoff then DNSSEC signs the example.com zone, and intentionally makes
   the invalid.example.com record invalid/bogus (for example, by editing
   the signed zone and entering garbage for the signature).  Geoff also
   configures his webserver to listen on 2001:db8::1 and serve a
   resource (for example, a 1x1 GIF, 1x1.gif) for all of these names.
   The webserver also serves a webpage (www.example.com) which contains
   links to these 3 resources (http://invalid.example.com/1x1.gif,
   http://root-key-sentinel-is-ta-02323.example.com/1x1.gif,
   http://root-key-sentinel-not-ta-02323.example.com/1x1.gif).

   Geoff then asks Bob, Charlie, Dave and Ed to browse to
   www.example.com.  Using the methods described in this document, the
   users can figure out what their fate will be when the 11112 KSK is
   removed.

   Bob is not using a validating resolver.  This means that he will be
   able to resolve invalid.example.com (and fetch the 1x1 GIF) - this
   tells him that the KSK roll does not affect him, and so he will be
   OK.

   Charlie's resolvers are validating, but they have not been upgraded
   to support the KSK sentinel mechanism.  Charlie will not be able to
   fetch the http://invalid.example.com/1x1.gif resource (the
   invalid.example.com record is bogus, and none of his resolvers will
   resolve it).  He is able to fetch both of the other resources - from
   this he knows (see the logic in the body of this document) that he is
   using legacy, validating resolvers.  The KSK sentinel method cannot
   provide him with a definitive answer to the question of what root
   trust anchors this resolver is using.

   Dave's resolvers implement the sentinel method, and have picked up
   the new KSK.  For the same reason as Charlie, he cannot fetch the
   "invalid" resource.  His resolver resolves the root-key-sentinel-is-
   ta-02323.example.com name normally (it contacts the example.com
   authoritative servers, etc); as it supports the sentinel mechanism,
   just before Dave's recursive resolver sends the reply to Dave's stub,
   it performs the KSK Sentinel check.  The QNAME starts with "root-key-
   sentinel-is-ta-", and the recursive resolver does indeed have a key
   with the Key Tag of 02323 in its root trust store.  This means that
   that this part of the KSK Sentinel check passes (it is true that Key
   Tag 02323 is in the trust anchor store), and the recursive resolver
   replies normally (with the answer provided by the authoritative
   server).  Dave's recursive resolver then resolves the root-key-
   sentinel-not-ta-02323.example.com name.  Once again, it performs the
   normal resolution process, but because it implements KSK Sentinel
   (and the QNAME starts with "root-key-sentinel-not-ta-"), just before
   sending the reply, it performs the KSK Sentinel check.  As it has
   02323 in it's trust anchor store, the answer to "is this *not* a
   trust anchor" is false, and so the recursive resolver does not reply
   with the answer from the authoritative server - instead, it replies
   with a SERVFAIL (note that replying with SERVFAIL instead of the
   original answer is the only mechanism that KSK Sentinel uses).  This
   means that Dave cannot fetch "invalid", he can fetch "root-key-
   sentinel-is-ta-02323", but he cannot fetch "root-key-sentinel-not-ta-
   02323".  From this, Dave knows that he is behind an upgraded,
   validating resolver, which has successfully installed the new, 02323
   KSK.

   Just like Charlie and Dave, Ed cannot fetch the "invalid" record.
   This tells him that his resolvers are validating.  When his
   (upgraded) resolver performs the KSK Sentinel check for "root-key-
   sentinel-is-ta-02323", it does *not* have the (new, 02323) KSK in
   it's trust anchor store.  This means check fails, and Ed's recursive
   resolver converts the (valid) answer into a SERVFAIL error response.
   It performs the use cases clearer

   o  Fixed some A/AAAA stuff

   o  Changed same check for root-key-sentinel-not-ta-
   02323.example.com; as it does not have the example numbers

   o  Made 02323 KSK, it clear is true that names
   this is not a trust anchor for it, and addresses must be real

   From -02 to -03:

   o  Integrated / published comments from Paul in GitHub PR #2 -
      https://github.com/APNIC-Labs/draft-kskroll-sentinel/pull/2

   o  Made so it replies normally.  This
   means that Ed cannot fetch the keytag be decimal, "invalid" resource, he also cannot
   fetch the "root-key-sentinel-is-ta-02323" resource, but he can fetch
   the "root-key-sentinel-not-ta-02323" resource.  This tells Ed that
   his resolvers have not hex (thread / consensus in
      https://mailarchive.ietf.org/arch/msg/dnsop/
      Kg7AtDhFRNw31He8n0_bMr9hBuE )

   From -01 installed the new KSK.

   Geoff would like to do a large scale test and provide the information
   back to Alice.  He uses some mechanism such as causing users to go to
   a web page to 02:

   o  Removed Address Record definition.

   o  Clarified that many things can cause SERVFAIL.

   o  Made examples FQDN.

   o  Fixed a large number of typos.

   o  Had accidentally said that Charlie was using a non-validating
      resolver in example.

   o  [ TODO(WK): Doc says keytags are hex, is this really users to attempt to resolve the
   three resources, and then analyzes the results of the tests to
   determine what percentage of users will be affected by the WG
      wants? ]

   o  And active key KSK
   rollover event.

   This description is one that can be used *now* (not e.g AddPend)

   From -00 to 01:

   o  Added a conversational description simplified example - it is not anticipated that
   Bob, Charlie, Dave and Ed will actually look for the absence or
   presence of how web resources; instead, the system is intended
      to work.

   o  Clarification webpage that this is for they load would
   likely contain JavaScript (or similar) which displays the root.

   o  Changed result of
   the label template from _is-ta-<key-tag> tests, sends the results to kskroll-
      sentinel-is-ta-<key-tag>. Geoff, or both.  This is because BIND (at least) will sentinel
   mechanism does not allow records which start with an underscore rely on the web: it can equally be used by trying
   to have address
      records (CNAMEs, yes, A/AAAA no).  Some browsers / operating
      systems also will not fetch resources from names which start with
      an underscore.

11.  References

11.1.  Normative References

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
              <https://www.rfc-editor.org/info/rfc2308>.

   [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 resolve 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 names (for example, using the DNS Security
              Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
              <https://www.rfc-editor.org/info/rfc4035>.

   [RFC5011]  StJohns, M., "Automated Updates of DNS Security (DNSSEC)
              Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
              September 2007, <https://www.rfc-editor.org/info/rfc5011>.

11.2.  Informative References

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

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