draft-ietf-dnsop-kskroll-sentinel-02.txt   draft-ietf-dnsop-kskroll-sentinel-03.txt 
DNSOP G. Huston DNSOP G. Huston
Internet-Draft J. Damas Internet-Draft J. Damas
Intended status: Standards Track APNIC Intended status: Standards Track APNIC
Expires: August 25, 2018 W. Kumari Expires: September 1, 2018 W. Kumari
Google Google
February 21, 2018 February 28, 2018
A Sentinel for Detecting Trusted Keys in DNSSEC A Sentinel for Detecting Trusted Keys in DNSSEC
draft-ietf-dnsop-kskroll-sentinel-02 draft-ietf-dnsop-kskroll-sentinel-03
Abstract Abstract
The DNS Security Extensions (DNSSEC) were developed to provide origin The DNS Security Extensions (DNSSEC) were developed to provide origin
authentication and integrity protection for DNS data by using digital authentication and integrity protection for DNS data by using digital
signatures. These digital signatures can be verified by building a signatures. These digital signatures can be verified by building a
chain of trust starting from a trust anchor and proceeding down to 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 particular node in the DNS. This document specifies a mechanism that
will allow an end user to determine the trusted key state for the will allow an end user to determine the trusted key state for the
root key of the resolvers that handle that user's DNS queries. Note root key of the resolvers that handle that user's DNS queries. Note
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test.net . test.net .
[ This document is being collaborated on in Github at: [ This document is being collaborated on in Github at:
https://github.com/APNIC-Labs/draft-kskroll-sentinel. The most https://github.com/APNIC-Labs/draft-kskroll-sentinel. The most
recent version of the document, open issues, etc should all be recent version of the document, open issues, etc should all be
available here. The authors (gratefully) accept pull requests. Text available here. The authors (gratefully) accept pull requests. Text
in square brackets will be removed before publication. ] in square brackets will be removed before publication. ]
[ NOTE: This version uses the labels "kskroll-sentinel-is-ta-<tag- [ NOTE: This version uses the labels "kskroll-sentinel-is-ta-<tag-
index>", "kskroll-sentinel-not-ta-<tag-index>"; older versions of index>", "kskroll-sentinel-not-ta-<tag-index>"; older versions of
this document used "_is-ta-<tag-index>", "_not-ta-<tag-index>". ] this document used "_is-ta-<tag-index>", "_not-ta-<tag-index>". Also
note that the format of the tag-index is now decimal. Apolgies to
those who have began implmenting.]
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 25, 2018. This Internet-Draft will expire on September 1, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Use Case . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Use Case . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Sentinel Mechanism . . . . . . . . . . . . . . . . . . . . . 6 3. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 6
4. Sentinel Processing . . . . . . . . . . . . . . . . . . . . . 7 4. Processing Sentinel Results . . . . . . . . . . . . . . . . . 7
5. Sentinel Test Result Considerations . . . . . . . . . . . . . 9 5. Sentinel Test Result Considerations . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 11 9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12 10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 12 10.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and
[RFC4035] were developed to provide origin authentication and [RFC4035] were developed to provide origin authentication and
integrity protection for DNS data by using digital signatures. integrity protection for DNS data by using digital signatures.
DNSSEC uses Key Tags to efficiently match signatures to the keys from 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 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 from the RDATA portion of a DNSKEY RR using a formula similar to a
ones-complement checksum. RRSIG RRs contain a Key Tag field whose 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 value is equal to the Key Tag of the DNSKEY RR that validates the
signature. signature.
This document specifies how validating resolvers can respond to This document specifies how validating resolvers can respond to
certain queries in a manner that allows a querier to deduce whether a 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 particular key for the root has been loaded into that resolver's
trusted key store. In particular, this response mechanism can be trusted key store. In particular, this response mechanism can be
used to determine whether a certain Root Zone KSK is ready to be used 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. 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 This new mechanism is OPTIONAL to implement and use, although for
reasons of supporting broad-based measurement techniques, it is reasons of supporting broad-based measurement techniques, it is
strongly preferred if configurations of DNSSEC-validating resolvers strongly preferred that configurations of DNSSEC-validating resolvers
enabled this mechanism by default, allowing for local configuration enabled this mechanism by default, allowing for local configuration
directives to disable this mechanism if desired. directives to disable this mechanism if desired.
1.1. Terminology 1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119. document are to be interpreted as described in RFC 2119.
Note that example.com, AAAA records and the IPv6 documentation prefix Note that example.com, AAAA records and the IPv6 documentation prefix
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easier to understand ] easier to understand ]
This section provides a non-normative example of how the sentinel This section provides a non-normative example of how the sentinel
mechanism could be used, and what each participant does. It is mechanism could be used, and what each participant does. It is
provided in a conversational tone to be easier to follow. provided in a conversational tone to be easier to follow.
Alice is in charge of the DNS root KSK (Key Signing Key), and would 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 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 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 will be before removing/revoking the old key. The current KSK has a
key ID of 1111, the new KSK has a key ID of 2222 key ID of 1111, the new KSK has a key ID of 2222. 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 ID is
2222).
Bob, Charlie, Dave, Ed are all users. They use the DNS recursive Bob, Charlie, Dave, Ed are all users. They use the DNS recursive
resolvers supplied by their ISPs. They would like to confirm that resolvers supplied by their ISPs. They would like to confirm that
their ISPs have picked up the new KSK and will not break. Bob's ISP their ISPs have picked up the new KSK. Bob's ISP does not perform
does not perform validation. Charlie's ISP does validate, but the validation. Charlie's ISP does validate, but the resolvers have not
resolvers have not yet been upgraded to support sentinel. Dave and yet been upgraded to support this mechanism. Dave and Ed's resolvers
Ed's resolvers have been upgraded to support sentinel; Dave's have been upgraded to support this mechanism; Dave's resolver has the
resolver has the new KSK, Ed's resolver hasn't managed to install the new KSK, Ed's resolver hasn't managed to install the 2222 KSK in its
2222 KSK in its trust store yet. trust store yet.
Geoff is a researcher, and would like to both provide a means for 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 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 like to be able to perform Internet-wide measurements of what the
impact will be (and report this back to Alice). impact will be (and report this back to Alice).
Geoff sets an authoritative DNS server for example.com, and also a Geoff sets an authoritative DNS server for example.com, and also a
webserver (www.example.com). He adds 3 AAAA records to example.com: webserver (www.example.com). He adds 3 AAAA records to example.com:
invalid.example.com. IN AAAA 2001:db8::1 invalid.example.com. IN AAAA 2001:db8::1
kskroll-sentinel-is-ta-2222.example.com. IN AAAA 2001:db8::1 kskroll-sentinel-is-ta-2222.example.com. IN AAAA 2001:db8::1
kskroll-sentinel-not-ta-2222.example.com. IN AAAA 2001:db8::1 kskroll-sentinel-not-ta-2222.example.com. IN AAAA 2001:db8::1
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tells him that the KSK roll does not affect him, and so he will be tells him that the KSK roll does not affect him, and so he will be
OK. OK.
Charlie's resolvers are validating, but they have not been upgraded Charlie's resolvers are validating, but they have not been upgraded
to support the KSK sentinel mechanism. Charlie will not be able to to support the KSK sentinel mechanism. Charlie will not be able to
fetch the http://invalid.example.com/1x1.gif resource (the fetch the http://invalid.example.com/1x1.gif resource (the
invalid.example.com record is bogus, and none of his resolvers will 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 resolve it). He is able to fetch both of the other resources - from
this he knows (see the logic below) that he is using legacy, this he knows (see the logic below) that he is using legacy,
validating resolvers. The KSK sentinel method cannot provided him validating resolvers. The KSK sentinel method cannot provided him
with a definitive answer. 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 Dave's resolvers implement the sentinel method, and have picked up
the new KSK. For the same reason as Charlie, he cannot fetch the the new KSK. For the same reason as Charlie, he cannot fetch the
"invalid" resource. His resolver resolves the kskroll-sentinel-is- "invalid" resource. His resolver resolves the kskroll-sentinel-is-
ta-2222.example.com name normally (it contacts the example.com ta-2222.example.com name normally (it contacts the example.com
authoritative servers, etc); as it supports the sentinel mechanism, authoritative servers, etc); as it supports the sentinel mechanism,
just before Dave's recursive server send the reply to Dave's stub, it just before Dave's recursive server send the reply to Dave's stub, it
performs the KSK Sentinel check (see below). The QNAME starts with performs the KSK Sentinel check (see below). The QNAME starts with
"kskroll-sentinel-is-ta-", and the recursive resolver does indeed "kskroll-sentinel-is-ta-", and the recursive resolver does indeed
have a key with the Key ID of 2222 in its root trust store. This have a key with the Key ID of 2222 in its root trust store. This
means that that this part of the KSK Sentinel check passes (it is means that that this part of the KSK Sentinel check passes (it is
true that 2222 is in the Trust Anchor store), and the recursive true that 2222 is in the trust anchor store), and the recursive
resolver replies normally (with the answer provided by the resolver replies normally (with the answer provided by the
authoritative server). Dave's recursive resolver then resolves the authoritative server). Dave's recursive resolver then resolves the
kskroll-sentinel-not-ta-2222.example.com name. Once again, it kskroll-sentinel-not-ta-2222.example.com name. Once again, it
performs the normal resolution process, but because it implements KSK performs the normal resolution process, but because it implements KSK
Sentinel (and the QNAME starts with "kskroll-sentinel-not-ta-"), just Sentinel (and the QNAME starts with "kskroll-sentinel-not-ta-"), just
before sending the reply, it performs the KSK Sentinel check. As it before sending the reply, it performs the KSK Sentinel check. As it
has 2222 in it's trust anchor store, the "Is this *not* a trust has 2222 in it's trust anchor store, the answer to "is this *not* a
anchor" is false, and so the recursive resolver does not reply with trust anchor" is false, and so the recursive resolver does not reply
the answer from the authoritative server - instead, it replies with a with the answer from the authoritative server - instead, it replies
SERVFAIL (note that replying with SERVFAIL instead of the original with a SERVFAIL (note that replying with SERVFAIL instead of the
answer is the only mechanism that KSK Sentinel uses). This means original answer is the only mechanism that KSK Sentinel uses). This
that Dave cannot fetch "invalid", he can fetch "kskroll-sentinel-is- means that Dave cannot fetch "invalid", he can fetch "kskroll-
ta-2222", but he cannot fetch "kskroll-sentinel-not-ta-2222". From sentinel-is-ta-2222", but he cannot fetch "kskroll-sentinel-not-ta-
this, Dave knows that he is behind an upgraded, validating resolver, 2222". From this, Dave knows that he is behind an upgraded,
which has successfully installed the new, 2222 KSK. Dave has nothing validating resolver, which has successfully installed the new, 2222
to worry about - he will be fine with the old (1111) KSK is removed. KSK.
Now for Ed. Just like Charlie and Dave, Ed cannot fetch the Just like Charlie and Dave, Ed cannot fetch the "invalid" record.
"invalid" record. This tells him that his resolvers are validating. This tells him that his resolvers are validating. When his
When his (upgraded) resolver performs the KSK Sentinel check for (upgraded) resolver performs the KSK Sentinel check for "kskroll-
"kskroll-sentinel-is-ta-2222", it does *not* have the (new, 2222) KSK sentinel-is-ta-2222", it does *not* have the (new, 2222) KSK in it's
in it's trust anchor store. This means check fails, and Ed's trust anchor store. This means check fails, and Ed's recursive
recursive resolver converts the (valid) 2001:db8::1 answer into a resolver converts the (valid) answer into a SERVFAIL error response.
SERVFAIL error response. It performs the same check for kskroll- It performs the same check for kskroll-sentinel-not-ta-
sentinel-not-ta-2222.example.com; as it does not have the 2222 KSK, 2222.example.com; as it does not have the 2222 KSK, it is true that
it is true that this is not a trust anchor for it, and so it replies this is not a trust anchor for it, and so it replies normally. This
normally. This means that Ed cannot fetch the "invalid" resource, he means that Ed cannot fetch the "invalid" resource, he also cannot
also cannot fetch the "kskroll-sentinel-is-ta-2222" resource, but he fetch the "kskroll-sentinel-is-ta-2222" resource, but he can fetch
can fetch the "kskroll-sentinel-not-ta-2222" resource. This tells Ed the "kskroll-sentinel-not-ta-2222" resource. This tells Ed that his
that his resolvers have not installed the new KSK, and, when the old resolvers have not installed the new KSK.
KSK is removed, his DNS will break.
Geoff would like to do a large scale test and provide the information Geoff would like to do a large scale test and provide the information
back to Alice. He uses some mechanism (such as an advertising back to Alice. He uses some mechanism such as causing users to go to
network) to cause a large number of users to attempt to resolve the 3 a web page to cause a large number of users to attempt to resolve the
resources, and then analyzes the results of the tests to determine three resources, and then analyzes the results of the tests to
what percentage of users will be affected by the KSK rollover event. determine what percentage of users will be affected by the KSK
rollover event.
The above description is a simplified example - it is not anticipated The above description is a simplified example - it is not anticipated
that Bob, Charlie, Dave and Ed will actually look for the absence or that Bob, Charlie, Dave and Ed will actually look for the absence or
presence of web resources; instead, the webpage that they load would presence of web resources; instead, the webpage that they load would
likely contain JavaScript (or similar) which displays the result of likely contain JavaScript (or similar) which displays the result of
the tests. An example of this is at http://www.ksk-test.net. This the tests, sends the results to Geoff, or both. This sentinel
KSK mechanism does not rely on the web - this method can equally be mechanism does not rely on the web: it can equally be used by trying
used by trying to resolve the names (for example, using 'dig') and to resolve the names (for example, using the common "dig" command)
checking which result in a SERVFAIL. and checking which result in a SERVFAIL.
[ Note that the KSK Sentinel mechanism measures a very different Note that the sentinel mechanism described here measures a very
(and, in our opinion, much more useful!) metric than RFC8145 -- different (and likely more useful) metric than [RFC8145]. RFC 8145
RFC8145 relied on resolvers reporting the list of keys that they have relies on resolvers reporting the list of keys that they have to root
-- this doesn't reflect what the *user* impact of the KSK roll will servers. That reflects on how many resolvers will be impacted by a
be. As we cannot get perfect visibility into all resolvers, we will KSK roll, but not what the user impact of the KSK roll will be.
have to aim for "do the least harm", not "do no harm" ]
3. Sentinel Mechanism 3. Sentinel Mechanism in Resolvers
DNSSEC-Validating resolvers that implement this mechanism MUST be DNSSEC-Validating resolvers that implement this mechanism MUST be
performing validation of responses in accordance with the DNSSEC performing validation of responses in accordance with the DNSSEC
response validation specification [RFC4035]. response validation specification [RFC4035].
This sentinel mechanism makes use of 2 special labels, "kskroll- This sentinel mechanism makes use of two special labels. The
sentinel-is-ta-<tag-index>." (intended to be used in a query where "kskroll-sentinel-is-ta-<tag-index>" label is used in a query where
the response can answer the question: Is this the key tag a trust the response can answer whether this is the key tag of a trust anchor
anchor which the validating DNS resolver is currently trusting?) and which the validating DNS resolver is currently trusting. The
"kskroll-sentinel-not-ta-<tag-index>." (intended to be used in a "kskroll-sentinel-not-ta-<tag-index>" label is used in a query where
query where the response can answer the question: Is this the key tag the response can answer whether this is the key tag of a trust anchor
of a key that is NOT in the resolver's current trust store?). The which the validating DNS resolver is NOT currently trusting.
use of the positive question and its inverse allows for queries to
detect whether resolvers support this sentinel mechanism. Note that The use of the positive question and its inverse allows for queries
the test is "Is there an active key with this KeyID in the resolver's to detect whether resolvers support this sentinel mechanism. Note
current trust store for the DNS root?", not "Is there any key with that the test is "Is there an active key with this KeyID in the
this KeyID in the trust store", nor "Was a key with this KeyID used resolver's current trust store for the DNS root?", not "Is there any
to validate this query?". An active key is one which could currently key with this KeyID in the trust store", nor "Was a key with this
be used for validation (ie not in AddPend or Revoked state KeyID used to validate this query?". An active key is one which
([RFC5011])). could currently be used for validation (that is, a key that is not in
either the AddPend or Revoked state as described in [RFC5011]).
If the outcome of the DNSSEC validation process on the response If the outcome of the DNSSEC validation process on the response
indicates that the response is authentic, and if the left-most label indicates that the response is authentic, and if the left-most label
of the original query name matches the template "kskroll-sentinel-is- of the original query name matches the template "kskroll-sentinel-is-
ta-<tag-index>.", then the following rule should be applied to the 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 response: If the resolver has placed a root zone KSK with tag index
tag index value matching the value specified in the query into the value matching the value specified in the query into the local
local resolver's store of trusted keys, then the resolver should resolver's store of trusted keys, then the resolver should return a
return a response indicating that the response contains authenticated response indicating that the response contains authenticated data
data according to section 5.8 of [RFC6840]. Otherwise, the resolver according to section 5.8 of [RFC6840]. Otherwise, the resolver MUST
MUST return RCODE 2 (server failure). Note that the <tag-index> is return RCODE 2 (server failure). Note that the <tag-index> is
specified in the DNS label using hexadecimal notation. specified in the DNS label using decimal notation (as described in
[RFC4034], section 5.3), zero padded to 5 digits.
If the outcome of the DNSSEC validation process applied to the If the outcome of the DNSSEC validation process applied to the
response indicates that the response is authentic, and if the left- response indicates that the response is authentic, and if the left-
most label of the original query name matches the template "kskroll- most label of the original query name matches the template "kskroll-
sentinel-not-ta-<tag-index>.", then the following rule should be sentinel-not-ta-<tag-index>.", then the following rule should be
applied to the response: If the resolver has not placed a Root Zone 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 KSK with tag index value matching the value specified in the query
the query into the local resolver's store of trusted keys, then the into the local resolver's store of trusted keys, then the resolver
resolver should return a response indicating that the response should return a response indicating that the response contains
contains authenticated data according to section 5.8 of [RFC6840]. authenticated data according to section 5.8 of [RFC6840]. Otherwise,
Otherwise, the resolver MUST return RCODE 2 (server failure). Note the resolver MUST return RCODE 2 (server failure). Note that the
that the <tag-index> is specified in the DNS label using hexadecimal <tag-index> is specified in the DNS label using decimal notation.
notation.
In all other cases the resolver MUST NOT alter the outcome of the DNS In all other cases the resolver MUST NOT alter the outcome of the DNS
response validation process. response validation process.
This mechanism is to be applied only by resolvers that are performing This mechanism is to be applied only by resolvers that are performing
DNSSEC validation, and applies only to responses to an A or AAAA DNSSEC validation, and applies only to responses to an A or AAAA
query (Query Type value 1 or 28) where the resolver has authenticated query (Query Type value 1 or 28) where the resolver has authenticated
the response according to the DNSSEC validation process and where the the response according to the DNSSEC validation process and where the
query name contains either of the labels described in this section as query name contains either of the labels described in this section as
its left-most label. In this case, the resolver is to perform an its left-most label. In this case, the resolver is to perform an
additional test following the conventional validation function, as additional test following the conventional validation function, as
described in this section. The result of this additional test described in this section. The result of this additional test
determines whether the resolver will alter its response that would determines whether the resolver will alter its response that would
have indicated that the RRset is authentic to a response that have indicated that the RRset is authentic to a response that
indicates DNSSEC validation failure via the use of RCODE 2. indicates DNSSEC validation failure via the use of RCODE 2.
4. Sentinel Processing 4. Processing Sentinel Results
This proposed test that uses the sentinel detection mechanism This proposed test that uses the sentinel detection mechanism
described in this document is based on the use of three DNS names described in this document is based on the use of three DNS names
that have three distinct DNS resolution behaviours. The test is that have three distinct DNS resolution behaviours. The test is
intended to allow a user to determine the state of their DNS intended to allow a user to determine the state of their DNS
resolution system, and, in particular, whether or not they are using resolution system, and, in particular, whether or not they are using
validating DNS resolvers that have picked up an incoming trust anchor validating DNS resolvers that use a particular trust anchor for the
as a trusted key in a root zone KSK roll scenario. root zone.
The name format can be defined in a number of ways, and no name form The critical aspect of the DNS names used in this mechanism is that
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 they contain the specified label for either the positive and negative
test as the left-most label in the query name. test as the left-most label in the query name.
The sentinel detection process is envisaged to use a test with three The sentinel detection process uses a test with three query names:
query names:
a. a query name containing the left-most label "kskroll-sentinel-is- o A query name containing the left-most label "kskroll-sentinel-is-
ta-<tag-index>.". This corresponds to a a validly-signed RRset ta-<tag-index>.". This corresponds to a a validly-signed RRset in
in the zone, so that responses associated with queried names in the zone, so that responses associated with queried names in this
this zone can be authenticated by a DNSSEC-validating resolver. zone can be authenticated by a DNSSEC-validating resolver. Any
Any validly-signed DNS zone can be used for this test. validly-signed DNS zone can be used for this test.
b. a query name containing the left-most label "kskroll-sentinel- o A query name containing the left-most label "kskroll-sentinel-not-
not-ta-<tag-index>.". This is also a validly-signed name. Any ta-<tag-index>.". This is also a validly-signed name. Any
validly-signed DNS zone can be used for this test. validly-signed DNS zone can be used for this test.
c. a third query name that is signed with a DNSSEC signature that o A query name that is signed with a DNSSEC signature that cannot be
cannot be validated (i.e. the corresponding RRset is not signed validated (such as if the corresponding RRset is not signed with a
with a valid RRSIG record). valid RRSIG record).
The responses received from queries to resolve each of these names The responses received from queries to resolve each of these names
would allow us to infer a trust key state of the resolution would allow us to infer a trust key state of the resolution
environment. The techniques describes in this document rely on environment. The techniques describes in this document rely on
(DNSSEC validating) resolvers responding with SERVFAIL (RCODE 2) to (DNSSEC validating) resolvers responding with SERVFAIL (RCODE 2) to
valid answers. Note that a slew of other issues can also cause valid answers. Note that a slew of other issues can also cause
SERVFAIL responses, so false positive or negative results may SERVFAIL responses, and so the sentinel processing may sometimes
sometimes occur. To describe this process of classification, we can result in incorrect conclusions.
classify resolvers into four distinct behavior types, for which we
will use the labels: "Vnew", "Vold", "Vleg", and "nonV". These
labels correspond to resolver behaviour types as follows:
o Vnew: A DNSSEC-Validating resolver that is configured to implement To describe this process of classification, we can classify resolvers
into four distinct behavior types, for which we will use the labels:
"Vnew", "Vold", "Vleg", and "nonV". These labels correspond to
resolver behaviour types as follows:
Vnew: A DNSSEC-Validating resolver that is configured to implement
this mechanism has loaded the nominated key into its local trusted this mechanism has loaded the nominated key into its local trusted
key store will respond with an A or AAAA RRset response for key store will respond with an A or AAAA RRset response for
"kskroll-sentinel-is-ta" queries, SERVFAIL for "kskroll-sentinel- "kskroll-sentinel-is-ta" queries, SERVFAIL for "kskroll-sentinel-
not-ta" queries and SERVFAIL for the invalidly signed name not-ta" queries and SERVFAIL for the invalidly signed name
queries. queries.
o Vold: A DNSSEC-Validating resolver that is configured to implement Vold: A DNSSEC-Validating resolver that is configured to implement
this mechanism that has not loaded the nominated key into its this mechanism that has not loaded the nominated key into its
local trusted key store will respond with an SERVFAIL for local trusted key store will respond with an SERVFAIL for
"kskroll-sentinel-is-ta" queries, an A or AAAA RRset response for "kskroll-sentinel-is-ta" queries, an A or AAAA RRset response for
"kskroll-sentinel-not-ta" queries and SERVFAIL for the invalidly "kskroll-sentinel-not-ta" queries and SERVFAIL for the invalidly
signed name queries. signed name queries.
o Vleg: A DNSSEC-Validating resolver that does not implement this Vleg: A DNSSEC-Validating resolver that does not implement this
mechanism will respond with an A or AAAA RRset response for mechanism will respond with an A or AAAA RRset response for
"kskroll-sentinel-is-ta", an A record response for "kskroll- "kskroll-sentinel-is-ta", an A record response for "kskroll-
sentinel-not-ta" and SERVFAIL for the invalid name. sentinel-not-ta" and SERVFAIL for the invalid name.
o nonV: A non-DNSSEC-Validating resolver will respond with an A or nonV: A non-DNSSEC-Validating resolver will respond with an A or
AAAA record response for "kskroll-sentinel-is-ta", an A record AAAA record response for "kskroll-sentinel-is-ta", an A record
response for "kskroll-sentinel-not-ta" and an A record response response for "kskroll-sentinel-not-ta" and an A record response
for the invalid name. for the invalid name.
Given the clear delineation amongst these three cases, if a client Given the clear delineation amongst these three cases, if a client
directs these three queries to a simple resolver, the variation in directs these three queries to a simple resolver, the variation in
response to the three queries should allow the client to determine response to the three queries should allow the client to determine
the category of the resolver, and if it supports this mechanism, the category of the resolver, and if it supports this mechanism,
whether or not it has loaded a particular key into its local trusted whether or not it has a particular key in its trust anchor store.
key stash.
+-------------+----------+-----------+------------+ Query
| Type\Query | is-ta | not-ta | invalid | +----------+-----------+------------+
+-------------+----------+-----------+------------+ | is-ta | not-ta | invalid |
| Vnew | A | SERVFAIL | SERVFAIL | +-------+----------+-----------+------------+
| Vold | SERVFAIL | A | SERVFAIL | | Vnew | A | SERVFAIL | SERVFAIL |
| Vleg | A | A | SERVFAIL | | Vold | SERVFAIL | A | SERVFAIL |
| nonV | A | A | A | Type | Vleg | A | A | SERVFAIL |
+-------------+----------+-----------+------------+ | nonV | A | A | A |
+-------+----------+-----------+------------+
A "Vnew" response pattern says that the nominated key is trusted by A "Vnew" type says that the nominated key is trusted by the resolver
the resolver and has been loaded into its local trusted key stash. A and has been loaded into its local trusted key stash. A "Vold" type
"Vold" response pattern says that the nominated key is not yet says that the nominated key is not yet trusted by the resolver in its
trusted by the resolver in its own right. A "Vleg" response pattern own right. A "Vleg" type does not give the user any information
is indeterminate, and a "nonV" response pattern indicates that the about the trust anchors, and a "nonV" type indicates that the
resolver does not perform DNSSEC validation. resolver does not perform DNSSEC validation.
5. Sentinel Test Result Considerations 5. Sentinel Test Result Considerations
The description in the previous section describes a simple situation The description in the previous section describes a simple situation
where the test queries were being passed to a single recursive where the test queries were being passed to a single recursive
resolver that directly queried authoritative name servers, including resolver that directly queried authoritative name servers, including
the root servers. the root servers.
There is also the common case where the end client is configured to There is also the common case where the end client is configured to
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the forwarder target resolver. If this non-validating resolver it the forwarder target resolver. If this non-validating resolver it
has multiple forwarders, then the above considerations will apply. has multiple forwarders, then the above considerations will apply.
If the validating resolver has a forwarding configuration, and uses If the validating resolver has a forwarding configuration, and uses
the CD flag on all forwarded queries, then this resolver is acting in the CD flag on all forwarded queries, then this resolver is acting in
a manner that is identical to a standalone resolver. The same a manner that is identical to a standalone resolver. The same
consideration applies if any one one of the forwarder targets is a consideration applies if any one one of the forwarder targets is a
non-validating resolver. Similarly, if all the forwarder targets do non-validating resolver. Similarly, if all the forwarder targets do
not apply this trusted key mechanism, the same considerations apply. not apply this trusted key mechanism, the same considerations apply.
A more complex case is where the following conditions all hold: A more complex case is where all of the following conditions all
hold:
o both the validating resolver and the forwarder target resolver o Both the validating resolver and the forwarder target resolver
support this trusted key sentinel mechanism, and support this trusted key sentinel mechanism
o the local resolver's queries do not have the CD bit set, and o The local resolver's queries do not have the CD bit set
o the trusted key state differs between the forwarding resolver and o The trusted key state differs between the forwarding resolver and
the forwarder target resolver the forwarder target resolver
then either the outcome is indeterminate validating ("Vleg"), or a In such a case, either the outcome is indeterminate validating
case of mixed signals (SERVFAIL in all three responses), which is ("Vleg"), or a case of mixed signals (SERVFAIL in all three
similarly an indeterminate response with respect to the trusted key responses), which is similarly an indeterminate response with respect
state. to the trusted key state.
6. Security Considerations 6. Security Considerations
This document describes a mechanism to allow users to determine the This document describes a mechanism to allow users to determine the
trust state of root zone key signing keys in the DNS resolution trust state of root zone key signing keys in the DNS resolution
system that they use. system that they use.
The mechanism does not require resolvers to set otherwise The mechanism does not require resolvers to set otherwise
unauthenticated responses to be marked as authenticated, and does not unauthenticated responses to be marked as authenticated, and does not
alter the security properties of DNSSEC with respect to the alter the security properties of DNSSEC with respect to the
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[Note to IANA, to be removed prior to publication: there are no IANA [Note to IANA, to be removed prior to publication: there are no IANA
considerations stated in this version of the document.] considerations stated in this version of the document.]
8. Acknowledgements 8. Acknowledgements
This document has borrowed extensively from [RFC8145] for the This document has borrowed extensively from [RFC8145] for the
introductory text, and the authors would like to acknowledge and introductory text, and the authors would like to acknowledge and
thank the authors of that document both for some text excerpts and thank the authors of that document both for some text excerpts and
for the more general stimulation of thoughts about monitoring the 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 progress of a roll of the KSK of the root zone of the DNS.
DNS.
The authors would like the especially thank Joe Abley, Mehmet Akcin, The authors would like to thank Joe Abley, Mehmet Akcin, Mark
Mark Andrews, Richard Barnes, Ray Bellis, Stephane Bortzmeyer, David Andrews, Richard Barnes, Ray Bellis, Stephane Bortzmeyer, David
Conrad, Ralph Dolmans, John Dickinson, Steinar Haug, Bob Harold, Wes Conrad, Ralph Dolmans, John Dickinson, Steinar Haug, Bob Harold, Wes
Hardaker, Paul Hoffman, Matt Larson, Jinmei Tatuya, Edward Lewis, Hardaker, Paul Hoffman, Matt Larson, Jinmei Tatuya, Edward Lewis,
George Michaelson, Benno Overeinder, Matthew Pounsett, Andreas George Michaelson, Benno Overeinder, Matthew Pounsett, Andreas
Schulze, Mukund Sivaraman, Petr Spacek. Andrew Sullivan, Paul Vixie, Schulze, Mukund Sivaraman, Petr Spacek, Andrew Sullivan, Paul Vixie,
Duane Wessels and Paul Wouters for their helpful feedback. Duane Wessels and Paul Wouters for their helpful feedback.
[TODO: Add people who have contributed!] The authors would like to especially call out Paul Hoffman for
providing comments in the form of a pull request.
9. Change Log 9. Change Log
Note that this document is being worked on in GitHub - see Abstract. Note that this document is being worked on in GitHub - see Abstract.
The below is mainly large changes, and is not authoritative. The below is mainly large changes, and is not authoritative.
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 the keytab be decimal, not hex (thread / consensus in
https://mailarchive.ietf.org/arch/msg/dnsop/
Kg7AtDhFRNw31He8n0_bMr9hBuE )
From -01 to 02: From -01 to 02:
Removed Address Record definition. o Removed Address Record definition.
Clarified that many things can cause SERVFAIL. o Clarified that many things can cause SERVFAIL.
Made examples FQDN. o Made examples FQDN.
Fixed a number of typos. o Fixed a number of typos.
Had accidentally said that Charlie was using a non-validating o Had accidentally said that Charlie was using a non-validating
resolver in example. resolver in example.
[ TODO(WK): Doc says keytags are hex, is this really what the WG o [ TODO(WK): Doc says keytags are hex, is this really what the WG
wants? ] wants? ]
And active key is one that can be used *now* (not e.g AddPend) o And active key is one that can be used *now* (not e.g AddPend)
From -00 to 01: From -00 to 01:
o Added a conversational description of how the system is intended o Added a conversational description of how the system is intended
to work. to work.
o Clarification that this is for the root. o Clarification that this is for the root.
o Changed the label template from _is-ta-<tag> to kskroll-sentinel- o Changed the label template from _is-ta-<tag> to kskroll-sentinel-
is-ta-<tag-index>. This is because BIND (at least) will not allow is-ta-<tag-index>. This is because BIND (at least) will not allow
 End of changes. 57 change blocks. 
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