< draft-ietf-dnsop-kskroll-sentinel-03.txt   draft-ietf-dnsop-kskroll-sentinel-04.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: September 1, 2018 W. Kumari Expires: September 1, 2018 W. Kumari
Google Google
February 28, 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-03 draft-ietf-dnsop-kskroll-sentinel-04
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 and third parties to determine the trusted key
root key of the resolvers that handle that user's DNS queries. Note state for the root key of the resolvers that handle that user's DNS
that this method is only applicable for determing which keys are in queries. Note that this method is only applicable for determing
the trust store for the root key. which keys are in the trust store for the root key.
There is an example / toy implementation of this at http://www.ksk- There is an example / toy implementation of this at http://www.ksk-
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-<key-
index>", "kskroll-sentinel-not-ta-<tag-index>"; older versions of tag>", "kskroll-sentinel-not-ta-<key-tag>"; older versions of this
this document used "_is-ta-<tag-index>", "_not-ta-<tag-index>". Also document used "_is-ta-<key-tag>", "_not-ta-<key-tag>". Also note
note that the format of the tag-index is now decimal. Apolgies to that the format of the tag-index is now zero-filled decimal.
those who have began implmenting.] 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/.
skipping to change at page 2, line 31 skipping to change at page 2, line 31
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
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. Protocol Walkthrough Example . . . . . . . . . . . . . . . . 3
3. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 6 3. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 6
4. Processing Sentinel Results . . . . . . . . . . . . . . . . . 7 4. Processing Sentinel Results . . . . . . . . . . . . . . . . . 8
5. Sentinel Test Result Considerations . . . . . . . . . . . . . 9 5. Sentinel Test Result Considerations . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 11 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.2. Informative References . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 11.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
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 similar to 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 There are two primary use cases for this mechanism:
reasons of supporting broad-based measurement techniques, it is
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 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 2. Protocol Walkthrough Example
(2001:db8::/32) are only examples - A records (or CNAMES), other IPs,
other domains work just as well.
2. Use Case
[Ed note: This is currently towards the front of the document; we [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 will make it an appendix at publication time, but until then it is
worth having up front, as it makes the rest of the document much worth having up front, as it makes the rest of the document much
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. Users want to key ID of 11112, the new KSK has a key ID of 02323. Users want to
verify that their resolver will not break after Alice rolls the root 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 KSK key (that is, starts signing with just the KSK whose key ID is
2222). 02323).
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. Bob's ISP does not perform 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 validation. Charlie's ISP does validate, but the resolvers have not
yet been upgraded to support this mechanism. Dave and Ed's resolvers yet been upgraded to support this mechanism. Dave and Ed's resolvers
have been upgraded to support this mechanism; Dave's resolver has the have been upgraded to support this mechanism; Dave's resolver has the
new KSK, Ed's resolver hasn't managed to install the 2222 KSK in its new KSK, Ed's resolver hasn't managed to install the 02323 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 three address 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-02323.example.com. IN AAAA 2001:db8::1
kskroll-sentinel-not-ta-2222.example.com. IN AAAA 2001:db8::1 kskroll-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 much be real, reachable
addresses.
Geoff then DNSSEC signs the example.com zone, and intentionally makes Geoff then DNSSEC signs the example.com zone, and intentionally makes
the invalid.example.com record invalid/bogus (for example, by editing the invalid.example.com record invalid/bogus (for example, by editing
the signed zone and entering garbage for the signature). Geoff also the signed zone and entering garbage for the signature). Geoff also
configures his webserver to listen on 2001:db8::1 and serve a 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. resource (for example, a 1x1 GIF, 1x1.gif) for all of these names.
The webserver also serves a webpage (www.example.com) which contains The webserver also serves a webpage (www.example.com) which contains
links to these 3 resources (http://invalid.example.com/1x1.gif, links to these 3 resources (http://invalid.example.com/1x1.gif,
http://kskroll-sentinel-is-ta-2222.example.com/1x1.gif, http://kskroll-sentinel-is-ta-02323.example.com/1x1.gif,
http://kskroll-sentinel-not-ta-2222.example.com/1x1.gif). http://kskroll-sentinel-not-ta-02323.example.com/1x1.gif).
Geoff then asks Bob, Charlie, Dave and Ed to browse to Geoff then asks Bob, Charlie, Dave and Ed to browse to
www.example.com. Using the methods described in this document, the www.example.com. Using the methods described in this document, the
users can figure out what their fate will be when the 1111 KSK is users can figure out what their fate will be when the 11112 KSK is
removed. removed.
Bob is not using a validating resolver. This means that he will be 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 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 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 to the question of what root trust anchors with a definitive answer to the question of what root trust anchors
this resolver is using. 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-02323.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 02323 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 Key ID 02323 is in the trust anchor store), and the
resolver replies normally (with the answer provided by the recursive 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-02323.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 answer to "is this *not* a 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 trust anchor" is false, and so the recursive resolver does not reply
with the answer from the authoritative server - instead, it replies with the answer from the authoritative server - instead, it replies
with a SERVFAIL (note that replying with SERVFAIL instead of the with a SERVFAIL (note that replying with SERVFAIL instead of the
original answer is the only mechanism that KSK Sentinel uses). This original answer is the only mechanism that KSK Sentinel uses). This
means that Dave cannot fetch "invalid", he can fetch "kskroll- means that Dave cannot fetch "invalid", he can fetch "kskroll-
sentinel-is-ta-2222", but he cannot fetch "kskroll-sentinel-not-ta- sentinel-is-ta-02323", but he cannot fetch "kskroll-sentinel-not-ta-
2222". From this, Dave knows that he is behind an upgraded, 02323". From this, Dave knows that he is behind an upgraded,
validating resolver, which has successfully installed the new, 2222 validating resolver, which has successfully installed the new, 02323
KSK. KSK.
Just like Charlie and Dave, Ed cannot fetch the "invalid" record. Just like Charlie and Dave, Ed cannot fetch the "invalid" record.
This tells him that his resolvers are validating. When his This tells him that his resolvers are validating. When his
(upgraded) resolver performs the KSK Sentinel check for "kskroll- (upgraded) resolver performs the KSK Sentinel check for "kskroll-
sentinel-is-ta-2222", it does *not* have the (new, 2222) KSK in it's sentinel-is-ta-02323", it does *not* have the (new, 02323) KSK in
trust anchor store. This means check fails, and Ed's recursive it's trust anchor store. This means check fails, and Ed's recursive
resolver converts the (valid) answer into a SERVFAIL error response. resolver converts the (valid) answer into a SERVFAIL error response.
It performs the same check for kskroll-sentinel-not-ta- It performs the same check for kskroll-sentinel-not-ta-
2222.example.com; as it does not have the 2222 KSK, it is true that 02323.example.com; as it does not have the 02323 KSK, it is true that
this is not a trust anchor for it, and so it replies normally. This this is not a trust anchor for it, and so it replies normally. This
means that Ed cannot fetch the "invalid" resource, he also cannot means that Ed cannot fetch the "invalid" resource, he also cannot
fetch the "kskroll-sentinel-is-ta-2222" resource, but he can fetch fetch the "kskroll-sentinel-is-ta-02323" resource, but he can fetch
the "kskroll-sentinel-not-ta-2222" resource. This tells Ed that his the "kskroll-sentinel-not-ta-02323" resource. This tells Ed that his
resolvers have not installed the new KSK. resolvers have not installed the new KSK.
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 causing users to go to 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 to resolve the a web page to cause a large number of users to attempt to resolve the
three resources, and then analyzes the results of the tests to three resources, and then analyzes the results of the tests to
determine what percentage of users will be affected by the KSK determine what percentage of users will be affected by the KSK
rollover event. rollover event.
The above description is a simplified example - it is not anticipated The above description is a simplified example - it is not anticipated
skipping to change at page 6, line 30 skipping to change at page 6, line 42
servers. That reflects on how many resolvers will be impacted by a servers. That reflects on how many resolvers will be impacted by a
KSK roll, but not what the user impact of the KSK roll will be. KSK roll, but not what the user impact of the KSK roll will be.
3. Sentinel Mechanism in Resolvers 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 two special labels. The This sentinel mechanism makes use of two special labels. The
"kskroll-sentinel-is-ta-<tag-index>" label is used in a query where "kskroll-sentinel-is-ta-<key-tag>" label is used in a query where the
the response can answer whether this is the key tag of a trust anchor response can answer whether this the Key Tag of a trust anchor which
which the validating DNS resolver is currently trusting. The the validating DNS resolver is currently trusting. The "kskroll-
"kskroll-sentinel-not-ta-<tag-index>" label is used in a query where sentinel-not-ta-<key-tag>" label is used in a query where the
the response can answer whether this is the key tag of a trust anchor response can answer whether this the Key Tag of a trust anchor that
which the validating DNS resolver is NOT currently trusting. is NOT in currently trusting.
The use of the positive question and its inverse allows for queries The use of the positive question and its inverse allows for queries
to detect whether resolvers support this sentinel mechanism. Note to detect whether resolvers support this sentinel mechanism. Note
that the test is "Is there an active key with this KeyID in the that the test is "Is there an active key with this KeyID in the
resolver's current trust store for the DNS root?", not "Is there any resolver's current trust store for the DNS root?", not "Is there any
key with this KeyID in the trust store", nor "Was a key with this key with this KeyID in the trust store", nor "Was a key with this
KeyID used to validate this query?". An active key is one which KeyID used to validate this query?". An active key is one which
could currently be used for validation (that is, a key that is not in could currently be used for validation (that is, a key that is not in
either the AddPend or Revoked state as described in [RFC5011]). 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-<key-tag>.", then the following rule should be applied to the
response: If the resolver has placed a root zone KSK with tag index response: If the resolver has placed a root zone KSK with Key Tag
value matching the value specified in the query into the local value matching the value specified in the query into the local
resolver's store of trusted keys, then the resolver should return a resolver's store of trusted keys, then the resolver should return a
response indicating that the response contains authenticated data response indicating that the response contains authenticated data
according to section 5.8 of [RFC6840]. Otherwise, the resolver MUST according to section 5.8 of [RFC6840]. Otherwise, the resolver 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 decimal notation (as described in specified in the DNS label using decimal notation (as described in
[RFC4034], section 5.3), zero padded to 5 digits. [RFC4034], section 5.3), zero-padded to five 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-<key-tag>.", 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
KSK with tag index value matching the value specified in the query KSK with Key Tag value matching the value specified in the query into
into the local resolver's store of trusted keys, then the resolver the local resolver's store of trusted keys, then the resolver should
should return a response indicating that the response contains return a response indicating that the response contains authenticated
authenticated data according to section 5.8 of [RFC6840]. Otherwise, data according to section 5.8 of [RFC6840]. Otherwise, the resolver
the resolver MUST return RCODE 2 (server failure). Note that the MUST return RCODE 2 (server failure). Note that the <key-tag> is
<tag-index> is specified in the DNS label using decimal notation. specified in the DNS label using decimal 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 queries for A or
query (Query Type value 1 or 28) where the resolver has authenticated AAAA records (Query Type value 1 or 28) where the resolver has
the response according to the DNSSEC validation process and where the authenticated the response according to the DNSSEC validation process
query name contains either of the labels described in this section as and where the query name contains either of the labels described in
its left-most label. In this case, the resolver is to perform an this section as its left-most label. In this case, the resolver is
additional test following the conventional validation function, as to perform an additional test following the conventional validation
described in this section. The result of this additional test function, as described in this section. The result of this
determines whether the resolver will alter its response that would additional test determines whether the resolver will alter its
have indicated that the RRset is authentic to a response that response that would have indicated that the RRset is authentic to a
indicates DNSSEC validation failure via the use of RCODE 2. response that indicates DNSSEC validation failure via the use of
RCODE 2.
4. Processing Sentinel Results 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 or a third party to determine the state of
resolution system, and, in particular, whether or not they are using their DNS resolution system, and, in particular, whether or not they
validating DNS resolvers that use a particular trust anchor for the are using validating DNS resolvers that use a particular trust anchor
root zone. for the root zone.
The critical aspect of the DNS names used in this mechanism is that The critical aspect of the DNS names used in this mechanism 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 uses a test with three query names: The sentinel detection process uses a test with three query names:
o 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 in ta-<key-tag>.". This corresponds to a a validly-signed RRset in
the zone, so that responses associated with queried names in this the zone, so that responses associated with queried names in this
zone can be authenticated by a DNSSEC-validating resolver. Any zone can be authenticated by a DNSSEC-validating resolver. Any
validly-signed DNS zone can be used for this test. validly-signed DNS zone can be used for this test.
o A query name containing the left-most label "kskroll-sentinel-not- o A query name containing the left-most label "kskroll-sentinel-not-
ta-<tag-index>.". This is also a validly-signed name. Any ta-<key-tag>.". This is also a validly-signed name. Any validly-
validly-signed DNS zone can be used for this test. signed DNS zone can be used for this test.
o A query name that is signed with a DNSSEC signature that cannot be o A query name that is signed with a DNSSEC signature that cannot be
validated (such as if the corresponding RRset is not signed with a validated (such as if the corresponding RRset is not signed 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
skipping to change at page 8, line 50 skipping to change at page 9, line 16
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.
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 or AAAA RRset response for
sentinel-not-ta" and SERVFAIL for the invalid name. "kskroll-sentinel-not-ta" and SERVFAIL for the invalid name.
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 or AAAA RRset
for the invalid name. response 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 a particular key in its trust anchor store. whether or not it has a particular key in its trust anchor store.
Query Query
+----------+-----------+------------+ +----------+-----------+------------+
| is-ta | not-ta | invalid | | is-ta | not-ta | invalid |
+-------+----------+-----------+------------+ +-------+----------+-----------+------------+
| Vnew | A | SERVFAIL | SERVFAIL | | Vnew | A | SERVFAIL | SERVFAIL |
| Vold | SERVFAIL | A | SERVFAIL | | Vold | SERVFAIL | A | SERVFAIL |
Type | Vleg | A | A | SERVFAIL | Type | Vleg | A | A | SERVFAIL |
| nonV | A | A | A | | nonV | A | A | A |
+-------+----------+-----------+------------+ +-------+----------+-----------+------------+
A "Vnew" type says that the nominated key is trusted by the resolver A "Vnew" type says that the nominated key is trusted by the resolver
and has been loaded into its local trusted key stash. A "Vold" type and has been loaded into its local trusted key stash. A "Vold" type
says that the nominated key is not yet trusted by the resolver in its says that the nominated key is not yet trusted by the resolver in its
own right. A "Vleg" type does not give the user any information own right. A "Vleg" type does not give any information about the
about the trust anchors, and a "nonV" type indicates that the trust anchors, and a "nonV" type indicates that the resolver does not
resolver does not perform DNSSEC validation. 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
use multiple resolvers. In these cases the SERVFAIL responses from use multiple resolvers. In these cases the SERVFAIL responses from
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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
In such a case, either the outcome is indeterminate validating In such a case, either the outcome is indeterminate validating
("Vleg"), or a case of mixed signals (SERVFAIL in all three ("Vleg"), or a case of mixed signals (SERVFAIL in all three
responses), which is similarly an indeterminate response with respect responses), which is similarly an indeterminate response with respect
to the trusted key 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 and third parties
trust state of root zone key signing keys in the DNS resolution to determine the trust state of root zone key signing keys in the DNS
system that they use. resolution 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
interpretation of the authenticity of responses that are so marked. interpretation of the authenticity of responses that are so marked.
The mechanism does not require any further significant processing of The mechanism does not require any further significant processing of
DNS responses, and queries of the form described in this document do DNS responses, and queries of the form described in this document do
not impose any additional load that could be exploited in an attack not impose any additional load that could be exploited in an attack
over the the normal DNSSEC validation processing load. over the the normal DNSSEC validation processing load.
7. IANA Considerations 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 to open a web page can then determine whether
the resolver that that user has configured might fail during a root
key rollover.
8. IANA Considerations
[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 9. 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 KSK of the root zone of the DNS. progress of a roll of the KSK of the root zone of the DNS.
The authors would like to thank Joe Abley, Mehmet Akcin, Mark The authors would like to thank Joe Abley, Mehmet Akcin, 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.
The authors would like to especially call out Paul Hoffman for The authors would like to especially call out Paul Hoffman for
providing comments in the form of a pull request. providing comments in the form of a pull request.
9. Change Log 10. 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 -03 to -04:
o Addressed GitHub pull requests #4, #5, #6, #7 #8.
o Added Duane's privacy concerns
o Makes the use cases clearer
o Fixed some A/AAAA stuff
o Changed the example numbers
o Made it clear that names and addresses must be real
From -02 to -03: From -02 to -03:
o Integrated / published comments from Paul in GitHub PR #2 - o Integrated / published comments from Paul in GitHub PR #2 -
https://github.com/APNIC-Labs/draft-kskroll-sentinel/pull/2 https://github.com/APNIC-Labs/draft-kskroll-sentinel/pull/2
o Made the keytab be decimal, not hex (thread / consensus in o Made the keytab be decimal, not hex (thread / consensus in
https://mailarchive.ietf.org/arch/msg/dnsop/ https://mailarchive.ietf.org/arch/msg/dnsop/
Kg7AtDhFRNw31He8n0_bMr9hBuE ) Kg7AtDhFRNw31He8n0_bMr9hBuE )
From -01 to 02: From -01 to 02:
skipping to change at page 12, line 14 skipping to change at page 13, line 4
o Fixed a number of typos. o Fixed a number of typos.
o 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.
o [ 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? ]
o 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-<key-tag> to kskroll-
is-ta-<tag-index>. This is because BIND (at least) will not allow sentinel-is-ta-<key-tag>. This is because BIND (at least) will
records which start with an underscore to have address records not allow records which start with an underscore to have address
(CNAMEs, yes, A/AAAA no). Some browsers / operating systems also records (CNAMEs, yes, A/AAAA no). Some browsers / operating
will not fetch resources from names which start with an systems also will not fetch resources from names which start with
underscore. an underscore.
10. References 11. References
10.1. Normative References 11.1. Normative References
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC Rose, "DNS Security Introduction and Requirements", RFC
4033, DOI 10.17487/RFC4033, March 2005, <https://www.rfc- 4033, DOI 10.17487/RFC4033, March 2005, <https://www.rfc-
editor.org/info/rfc4033>. editor.org/info/rfc4033>.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions", Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC4034, March 2005, RFC 4034, DOI 10.17487/RFC4034, March 2005,
<https://www.rfc-editor.org/info/rfc4034>. <https://www.rfc-editor.org/info/rfc4034>.
skipping to change at page 13, line 10 skipping to change at page 13, line 46
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC) [RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011, Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
September 2007, <https://www.rfc-editor.org/info/rfc5011>. September 2007, <https://www.rfc-editor.org/info/rfc5011>.
[RFC6840] Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and [RFC6840] Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and
Implementation Notes for DNS Security (DNSSEC)", RFC 6840, Implementation Notes for DNS Security (DNSSEC)", RFC 6840,
DOI 10.17487/RFC6840, February 2013, <https://www.rfc- DOI 10.17487/RFC6840, February 2013, <https://www.rfc-
editor.org/info/rfc6840>. editor.org/info/rfc6840>.
10.2. Informative References 11.2. Informative References
[RFC8145] Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust [RFC8145] Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust
Anchor Knowledge in DNS Security Extensions (DNSSEC)", RFC Anchor Knowledge in DNS Security Extensions (DNSSEC)", RFC
8145, DOI 10.17487/RFC8145, April 2017, <https://www.rfc- 8145, DOI 10.17487/RFC8145, April 2017, <https://www.rfc-
editor.org/info/rfc8145>. editor.org/info/rfc8145>.
Authors' Addresses Authors' Addresses
Geoff Huston Geoff Huston
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