< draft-ietf-dnsop-kskroll-sentinel-04.txt   draft-ietf-dnsop-kskroll-sentinel-05.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 6, 2018 W. Kumari
Google Google
February 28, 2018 March 5, 2018
A Sentinel for Detecting Trusted Keys in DNSSEC A Sentinel for Detecting Trusted Keys in DNSSEC
draft-ietf-dnsop-kskroll-sentinel-04 draft-ietf-dnsop-kskroll-sentinel-05
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 and third parties to determine the trusted key will allow an end user and third parties to determine the trusted key
state for the root key of the resolvers that handle that user's DNS state for the root key of the resolvers that handle that user's DNS
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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 September 1, 2018. This Internet-Draft will expire on September 6, 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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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. Protocol Walkthrough Example . . . . . . . . . . . . . . . . 3 2. Protocol Walkthrough Example . . . . . . . . . . . . . . . . 3
3. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 6 3. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 6
3.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Special processing . . . . . . . . . . . . . . . . . . . 7
4. Processing Sentinel Results . . . . . . . . . . . . . . . . . 8 4. Processing Sentinel Results . . . . . . . . . . . . . . . . . 8
5. Sentinel Test Result Considerations . . . . . . . . . . . . . 9 5. Sentinel Test Result Considerations . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 12 10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Normative References . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . 13 11.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 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
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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 11112, the new KSK has a key ID of 02323. Users want to Key Tag of 11112, the new KSK has a Key Tag of 02323. Users want to
verify that their resolver will not break after Alice rolls the root 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 Tag is
02323). 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 02323 KSK in its new KSK, Ed's resolver hasn't managed to install the 02323 KSK in its
trust store yet. trust store yet.
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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-02323.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 02323 in its root trust store. This have a key with the Key Tag of 02323 in its root trust store. This
means that that this part of the KSK Sentinel check passes (it is means that that this part of the KSK Sentinel check passes (it is
true that Key ID 02323 is in the trust anchor store), and the true that Key Tag 02323 is in the trust anchor store), and the
recursive 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-02323.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 02323 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
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relies on resolvers reporting the list of keys that they have to root relies on resolvers reporting the list of keys that they have to root
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:
"kskroll-sentinel-is-ta-<key-tag>" label is used in a query where the
response can answer whether this the Key Tag of a trust anchor which o kskroll-sentinel-is-ta-<key-tag>
the validating DNS resolver is currently trusting. The "kskroll-
sentinel-not-ta-<key-tag>" label is used in a query where the o kskroll-sentinel-not-ta-<key-tag>
response can answer whether this the Key Tag of a trust anchor that Note that the <key-tag> is specified in the DNS label as unsigned
is NOT in currently trusting. decimal integer (as described in [RFC4034], section 5.3), but zero-
padded to five digits (i.e: 42 would be represented as 00042).
These labels trigger special processing in the resolver as specified
bellow. The labels containing "is-ta" and "not-ta" are used to
answer questions "Is (or is not, respectivaly) this the key tag a
trust anchor which the validating DNS resolver is currently
trusting?" Processing of both labels has the very same preconditions
for both labels and differs only in last step.
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.
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
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
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 3.1. Preconditions
indicates that the response is authentic, and if the left-most label
of the original query name matches the template "kskroll-sentinel-is-
ta-<key-tag>.", then the following rule should be applied to the
response: If the resolver has placed a root zone KSK with Key Tag
value matching the value specified in the query into the local
resolver's store of trusted keys, then the resolver should return a
response indicating that the response contains authenticated data
according to section 5.8 of [RFC6840]. Otherwise, the resolver MUST
return RCODE 2 (server failure). Note that the <tag-index> is
specified in the DNS label using decimal notation (as described in
[RFC4034], section 5.3), zero-padded to five digits.
If the outcome of the DNSSEC validation process applied to the All of the following conditions must be met to trigger special
response indicates that the response is authentic, and if the left- processing inside resolver code:
most label of the original query name matches the template "kskroll-
sentinel-not-ta-<key-tag>.", then the following rule should be
applied to the response: If the resolver has not placed a root zone
KSK with Key Tag value matching the value specified in the query into
the local resolver's store of trusted keys, then the resolver should
return a response indicating that the response contains authenticated
data according to section 5.8 of [RFC6840]. Otherwise, the resolver
MUST return RCODE 2 (server failure). Note that the <key-tag> is
specified in the DNS label using decimal notation.
In all other cases the resolver MUST NOT alter the outcome of the DNS a. DNS response for particular query is DNSSEC validated and result
response validation process. of validation is SECURE.
This mechanism is to be applied only by resolvers that are performing b. QTYPE is A or AAAA (Query Type value 1 or 28)
DNSSEC validation, and applies only to responses to queries for A or
AAAA records (Query Type value 1 or 28) where the resolver has c. The OPCODE is QUERY
authenticated the response according to the DNSSEC validation process
and where the query name contains either of the labels described in d. The leftmost label of the QNAME is either "kskroll-sentinel-is-
this section as its left-most label. In this case, the resolver is ta-<tag-index>" or "kskroll-sentinel-not-ta-<tag-index>"
to perform an additional test following the conventional validation
function, as described in this section. The result of this If all preconditions are not met, the resolver MUST NOT alter the DNS
additional test determines whether the resolver will alter its response.
response that would have indicated that the RRset is authentic to a
response that indicates DNSSEC validation failure via the use of 3.2. Special processing
RCODE 2.
Responses which fullfill all preconditions in section 3.1 are subject
of special processing, depending on leftmost label of the QNAME.
First, the resolver determines if the numerical value of <key-tag> is
equal to any of the key tags of an active Root Zone Key Signing Key
which is currently trusted by the local resolver and is stored in its
store of trusted keys. An active key is one which could currently be
used for validation (that is, a key that is not in either the AddPend
or Revoked state as described in [RFC5011]).
As second step, the resolver alters response depending on meaning of
the label and presence of key with given keytag among trusted keys.
Two labels and two possible states of the keytag generate four
possible combinations summarized in the table:
Keytag trusted
label type | yes | no
--------------------------------------------------------------
is-ta | return original answer | return SERVFAIL
not-ta | return SERVFAIL | return original answer
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 or a third party to determine the state of intended to allow a user or a third party to determine the state of
their DNS resolution system, and, in particular, whether or not they their DNS resolution system, and, in particular, whether or not they
are using validating DNS resolvers that use a particular trust anchor are using validating DNS resolvers that use a particular trust anchor
for the 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-<key-tag>.". 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-<key-tag>.". This is also a validly-signed name. Any validly- ta-<key-tag>". This is also a validly-signed name. Any 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
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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. Privacy Considerations 7. Privacy Considerations
The mechansim in this document enables third parties (with either The mechansim in this document enables third parties (with either
good or bad intentions) to learn something about the security good or bad intentions) to learn something about the security
configuration of recursive name servers. That is, someone who can configuration of recursive name servers. That is, someone who can
cause an Internet user to open a web page can then determine whether cause an Internet user to make specific DNS queries (e.g. via web-
the resolver that that user has configured might fail during a root based advertisements or javascript in web pages), can then determine
key rollover. which trust anchors are configured in the user's resolver.
8. IANA Considerations 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.]
9. 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
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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 and Duane
providing comments in the form of a pull request. Wessels for providing comments in the form of a pull request. Petr
Specek implmented early versions of this technique into the Knot
resolver, identified a number of places where it wasn't clear, and
provided very helpful text to address this.
10. 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 -04 to -05:
o Incorporated Duane's #10
o Integrated Petr Spacek's Issue - https://github.com/APNIC-Labs/
draft-kskroll-sentinel/issues/9 (note that commit-log incorrectly
referred to Duane's PR as number 9, it is actually 10).
From -03 to -04: From -03 to -04:
o Addressed GitHub pull requests #4, #5, #6, #7 #8. o Addressed GitHub pull requests #4, #5, #6, #7 #8.
o Added Duane's privacy concerns o Added Duane's privacy concerns
o Makes the use cases clearer o Makes the use cases clearer
o Fixed some A/AAAA stuff o Fixed some A/AAAA stuff
o Changed the example numbers o Changed the example numbers
o Made it clear that names and addresses must be real 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 keytag 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:
o Removed Address Record definition. o Removed Address Record definition.
o Clarified that many things can cause SERVFAIL. o Clarified that many things can cause SERVFAIL.
o Made examples FQDN. o Made examples FQDN.
 End of changes. 23 change blocks. 
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