draft-ietf-dnsop-kskroll-sentinel-11.txt   draft-ietf-dnsop-kskroll-sentinel-12.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: October 7, 2018 W. Kumari Expires: November 3, 2018 W. Kumari
Google Google
April 5, 2018 May 2, 2018
A Root Key Trust Anchor Sentinel for DNSSEC A Root Key Trust Anchor Sentinel for DNSSEC
draft-ietf-dnsop-kskroll-sentinel-11 draft-ietf-dnsop-kskroll-sentinel-12
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
queries. Note that this method is only applicable for determing queries. Note that this method is only applicable for determining
which keys are in 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 "root-key-sentinel-is-ta-", and [ NOTE: This version uses the labels "root-key-sentinel-is-ta-", and
"root-key-sentinel-not-ta-".; older versions of this document used "root-key-sentinel-not-ta-".; older versions of this document used
"kskroll-sentinel-is-ta-<key-tag>", "kskroll-sentinel-not-ta-<key- "kskroll-sentinel-is-ta-<key-tag>", "kskroll-sentinel-not-ta-<key-
tag>", and before that, "_is-ta-<key-tag>", "_not-ta-<key-tag>". tag>", and before that, "_is-ta-<key-tag>", "_not-ta-<key-tag>".
Also note that the format of the tag-index is now zero-filled Also note that the format of the tag-index is now zero-filled
decimal. Apolgies to those who have began implmenting.] decimal. Apologies to those who have begun implementing earlier
versions of this specification.]
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 https://datatracker.ietf.org/drafts/current/. Drafts is at https://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 October 7, 2018. This Internet-Draft will expire on November 3, 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
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Protocol Walkthrough Example . . . . . . . . . . . . . . . . 4 2. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 4
3. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 7 2.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 7 2.2. Special Processing . . . . . . . . . . . . . . . . . . . 5
3.2. Special processing . . . . . . . . . . . . . . . . . . . 8 3. Processing Sentinel Results . . . . . . . . . . . . . . . . . 5
4. Processing Sentinel Results . . . . . . . . . . . . . . . . . 8 4. Sentinel Test Result Considerations . . . . . . . . . . . . . 7
5. Sentinel Test Result Considerations . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 9
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12 7. Implementation Experience . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 12 10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Normative References . . . . . . . . . . . . . . . . . . 15 11.1. Normative References . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . 15 11.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Protocol Walkthrough Example . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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 found in "Key
ones-complement checksum. RRSIG RRs contain a Key Tag field whose Tag Calculation" (Appendix B of "Resource Records for the DNS
value is equal to the Key Tag of the DNSKEY RR that validates the Security Extensions" [RFC4034]), a formula similar to a ones-
complement checksum. RRSIG RRs contain a Key Tag field whose value
is equal to the Key Tag of the DNSKEY RR that validates the
signature. 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 planned root zone KSK key
roll, by this resolver.
There are two primary use cases for this mechanism: There are two primary use cases for this mechanism:
o Users want to know whether the resolvers they use are ready for an o Users want to know whether the resolvers they use are ready for an
upcoming root KSK rollover upcoming root KSK rollover
o Researchers want to perform Internet-wide studies about the o Researchers want to perform Internet-wide studies about the
percentage of users who will be ready for an upcoming root KSK percentage of users who will be ready for an upcoming root KSK
rollover rollover
skipping to change at page 4, line 11 skipping to change at page 4, line 20
locally cached trust anchors for the root zone. Those reports can be locally cached trust anchors for the root zone. Those reports can be
used to infer how many resolvers may be impacted by a KSK roll, but used to infer how many resolvers may be impacted by a KSK roll, but
not what the user impact of the KSK roll will be. not what the user impact of the KSK roll will be.
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.
2. Protocol Walkthrough Example 2. Sentinel Mechanism in Resolvers
[Ed note: This is currently towards the front of the document; we
will make it an appendix at publication time, but until then it is
worth having up front, as it makes the rest of the document much
easier to understand ]
This section provides a non-normative example of how the sentinel
mechanism could be used, and what each participant does. It is
provided in a conversational tone to be easier to follow.
Alice is in charge of the DNS root KSK (Key Signing Key), and would
like to roll / replace the key with a new one. She publishes the new
KSK, but would like to be able to predict / measure what the impact
will be before removing/revoking the old key. The current KSK has a
Key Tag of 11112, the new KSK has a Key Tag of 02323. Users want to
verify that their resolver will not break after Alice rolls the root
KSK key (that is, starts signing with just the KSK whose Key Tag is
02323).
Bob, Charlie, Dave, Ed are all users. They use the DNS recursive
resolvers supplied by their ISPs. They would like to confirm that
their ISPs have picked up the new KSK. Bob's ISP does not perform
validation. Charlie's ISP does validate, but the resolvers have not
yet been upgraded to support this mechanism. Dave and Ed's resolvers
have been upgraded to support this mechanism; Dave's resolver has the
new KSK, Ed's resolver hasn't managed to install the 02323 KSK in its
trust store yet.
Geoff is a researcher, and would like to both provide a means for
Bob, Charlie, Dave and Ed to be able to perform tests, and also would
like to be able to perform Internet-wide measurements of what the
impact will be (and report this back to Alice).
Geoff sets an authoritative DNS server for example.com, and also a
webserver (www.example.com). He adds three address records to
example.com:
invalid.example.com. IN AAAA 2001:db8::1
root-key-sentinel-is-ta-02323.example.com. IN AAAA 2001:db8::1
root-key-sentinel-not-ta-02323.example.com. IN AAAA 2001:db8::1
Note that the use of "example.com" names and the addresses here are
examples. In a real deployment, the domain names need to be under
control of the researcher, and the addresses must be real, reachable
addresses.
Geoff then DNSSEC signs the example.com zone, and intentionally makes
the invalid.example.com record invalid/bogus (for example, by editing
the signed zone and entering garbage for the signature). Geoff also
configures his webserver to listen on 2001:db8::1 and serve a
resource (for example, a 1x1 GIF, 1x1.gif) for all of these names.
The webserver also serves a webpage (www.example.com) which contains
links to these 3 resources (http://invalid.example.com/1x1.gif,
http://root-key-sentinel-is-ta-02323.example.com/1x1.gif,
http://root-key-sentinel-not-ta-02323.example.com/1x1.gif).
Geoff then asks Bob, Charlie, Dave and Ed to browse to
www.example.com. Using the methods described in this document, the
users can figure out what their fate will be when the 11112 KSK is
removed.
Bob is not using a validating resolver. This means that he will be
able to resolve invalid.example.com (and fetch the 1x1 GIF) - this
tells him that the KSK roll does not affect him, and so he will be
OK.
Charlie's resolvers are validating, but they have not been upgraded
to support the KSK sentinel mechanism. Charlie will not be able to
fetch the http://invalid.example.com/1x1.gif resource (the
invalid.example.com record is bogus, and none of his resolvers will
resolve it). He is able to fetch both of the other resources - from
this he knows (see the logic below) that he is using legacy,
validating resolvers. The KSK sentinel method cannot provided him
with a definitive answer to the question of what root trust anchors
this resolver is using.
Dave's resolvers implement the sentinel method, and have picked up
the new KSK. For the same reason as Charlie, he cannot fetch the
"invalid" resource. His resolver resolves the root-key-sentinel-is-
ta-02323.example.com name normally (it contacts the example.com
authoritative servers, etc); as it supports the sentinel mechanism,
just before Dave's recursive server send the reply to Dave's stub, it
performs the KSK Sentinel check (see below). The QNAME starts with
"root-key-sentinel-is-ta-", and the recursive resolver does indeed
have a key with the Key Tag of 02323 in its root trust store. This
means that that this part of the KSK Sentinel check passes (it is
true that Key Tag 02323 is in the trust anchor store), and the
recursive resolver replies normally (with the answer provided by the
authoritative server). Dave's recursive resolver then resolves the
root-key-sentinel-not-ta-02323.example.com name. Once again, it
performs the normal resolution process, but because it implements KSK
Sentinel (and the QNAME starts with "root-key-sentinel-not-ta-"),
just before sending the reply, it performs the KSK Sentinel check.
As it has 02323 in it's trust anchor store, the answer to "is this
*not* a trust anchor" is false, and so the recursive resolver does
not reply with the answer from the authoritative server - instead, it
replies with a SERVFAIL (note that replying with SERVFAIL instead of
the original answer is the only mechanism that KSK Sentinel uses).
This means that Dave cannot fetch "invalid", he can fetch "root-key-
sentinel-is-ta-02323", but he cannot fetch "root-key-sentinel-not-ta-
02323". From this, Dave knows that he is behind an upgraded,
validating resolver, which has successfully installed the new, 02323
KSK.
Just like Charlie and Dave, Ed cannot fetch the "invalid" record.
This tells him that his resolvers are validating. When his
(upgraded) resolver performs the KSK Sentinel check for "root-key-
sentinel-is-ta-02323", it does *not* have the (new, 02323) KSK in
it's trust anchor store. This means check fails, and Ed's recursive
resolver converts the (valid) answer into a SERVFAIL error response.
It performs the same check for root-key-sentinel-not-ta-
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
means that Ed cannot fetch the "invalid" resource, he also cannot
fetch the "root-key-sentinel-is-ta-02323" resource, but he can fetch
the "root-key-sentinel-not-ta-02323" resource. This tells Ed that
his resolvers have not installed the new KSK.
Geoff would like to do a large scale test and provide the information
back to Alice. He uses some mechanism such as causing users to go to
a web page to cause a large number of users to attempt to resolve the
three resources, and then analyzes the results of the tests to
determine what percentage of users will be affected by the KSK
rollover event.
The above description is a simplified example - it is not anticipated
that Bob, Charlie, Dave and Ed will actually look for the absence or
presence of web resources; instead, the webpage that they load would
likely contain JavaScript (or similar) which displays the result of
the tests, sends the results to Geoff, or both. This sentinel
mechanism does not rely on the web: it can equally be used by trying
to resolve the names (for example, using the common "dig" command)
and checking which result in a SERVFAIL.
3. Sentinel Mechanism in Resolvers
DNSSEC-Validating resolvers that implement this mechanism MUST DNSSEC-Validating resolvers that implement this mechanism MUST
perform validation of responses in accordance with the DNSSEC perform 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: This sentinel mechanism makes use of two special labels:
o root-key-sentinel-is-ta-<key-tag> o root-key-sentinel-is-ta-<key-tag>
o root-key-sentinel-not-ta-<key-tag> o root-key-sentinel-not-ta-<key-tag>
Note that the <key-tag> is specified in the DNS label as unsigned Note that the <key-tag> is specified in the DNS label as unsigned
decimal integer (as described in [RFC4034], section 5.3), but zero- decimal integer (as described in [RFC4034], section 5.3), but zero-
padded to five digits (for example, a Key Tag 42 would be represented padded to five digits (for example, a Key Tag value of 42 would be
in the label as 00042). represented in the label as 00042).
These labels trigger special processing in the resolver when These labels trigger special processing in the resolver when
responses from authoritative servers are received. Labels containing responses from authoritative servers are received. Labels containing
"root-key-sentinel-is-ta-<key-tag>" is used to answer the question "root-key-sentinel-is-ta-<key-tag>" is used to answer the question
"Is this the Key Tag a trust anchor which the validating DNS resolver "Is this the Key Tag of a Key which the validating DNS resolver is
is currently trusting?" Labels containing "root-key-sentinel-not-ta- currently trusting as a trust anchor?" Labels containing "root-key-
<key-tag>" is used to answer the question "Is this the Key Tag *not* sentinel-not-ta-<key-tag>" is used to answer the question "Is this
a trust anchor which the validating DNS resolver is currently the Key Tag of a Key which the validating DNS resolver is *not*
trusting?" currently trusting as a trust anchor?"
3.1. Preconditions 2.1. Preconditions
All of the following conditions must be met to trigger special All of the following conditions must be met to trigger special
processing inside resolver code: processing inside resolver code:
o The DNS response is DNSSEC validated. o The DNS response is DNSSEC validated.
o The result of validation is "Secure". o The result of validation is "Secure".
o The Checking Disabled (CD) bit in the query is not set. o The Checking Disabled (CD) bit in the query is not set.
skipping to change at page 8, line 5 skipping to change at page 5, line 20
o The OPCODE is QUERY o The OPCODE is QUERY
o The leftmost label of the original QNAME (the name sent in the o The leftmost label of the original QNAME (the name sent in the
Question Section in the original query) is either "root-key- Question Section in the original query) is either "root-key-
sentinel-is-ta-<key-tag>" or "root-key-sentinel-not-ta-<key-tag>" sentinel-is-ta-<key-tag>" or "root-key-sentinel-not-ta-<key-tag>"
If any one of the preconditions is not met, the resolver MUST NOT If any one of the preconditions is not met, the resolver MUST NOT
alter the DNS response based on the mechanism in this document. alter the DNS response based on the mechanism in this document.
3.2. Special processing 2.2. Special Processing
Responses which fullfill all of the preconditions in Section 3.1 Responses which fulfil all of the preconditions in Section 2.1
require special processing, depending on leftmost label in the QNAME. require special processing, depending on leftmost label in the QNAME.
First, the resolver determines if the numerical value of <key-tag> is First, the resolver determines if the numerical value of <key-tag> is
equal to any of the Key Tags of an active root zone KSK which is equal to any of the Key Tag values of an active root zone KSK which
currently trusted by the local resolver and is stored in its store of is currently trusted by the local resolver and is stored in its store
trusted keys. An active key is one which could currently be used for of trusted keys. An active root zone KSK is one which could
validation (that is, a key that is not in either the AddPend or currently be used for validation (that is, a Key that is not in
Revoked state as described in [RFC5011]). either the AddPend or Revoked state as described in [RFC5011]).
Second, the resolver alters the response being sent to the original Second, the resolver alters the response being sent to the original
query based on both the left-most label and the presence of a key query based on both the left-most label and the presence of a Key
with given Key Tag in the trust anchor store. Two labels and two with given Key Tag in the trust anchor store. Two labels and two
possible states of the keytag generate four possible combinations possible states of the corresponding Key generate four possible
summarized in the table: combinations summarized in the table:
Label | Key Tag is trusted | Key Tag is not trusted Label | Key is trusted | Key is not trusted
------------------------------------------------------------------ ------------------------------------------------------------------
is-ta | return original answer | return SERVFAIL is-ta | return original answer | return SERVFAIL
not-ta | return SERVFAIL | return original answer not-ta | return SERVFAIL | return original answer
Instruction "return SERVFAIL" means that the resolver MUST set Instruction "return SERVFAIL" means that the resolver MUST set
RCODE=SERVFAIL (value 2) and MUST empty the ANSWER section of the DNS RCODE=SERVFAIL (value 2) and MUST empty the ANSWER section of the DNS
response, ignoring all other documents which specify content of the response, ignoring all other documents which specify content of the
ANSWER section. ANSWER section.
4. Processing Sentinel Results 3. 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 one or more validating DNS resolvers that use a particular are using one or more validating DNS resolvers that use a particular
trust anchor for the root zone. trust anchor 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
skipping to change at page 9, line 12 skipping to change at page 6, line 26
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 "root-key-sentinel- o A query name containing the left-most label "root-key-sentinel-
not-ta-<key-tag>". This is also a validly-signed name. Any not-ta-<key-tag>". 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.
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 (described as a "bogus" RRset in Section 5 of [RFC4033],
valid RRSIG record). when, for example, an RRset is not signed with a 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 to valid (DNSSEC validating) resolvers responding with SERVFAIL to valid
answers. Note that a slew of other issues can also cause SERVFAIL answers. Note that a slew of other issues can also cause SERVFAIL
responses, and so the sentinel processing may sometimes result in responses, and so the sentinel processing may sometimes result in
incorrect conclusions. incorrect conclusions.
To describe this process of classification, we can classify resolvers To describe this process of classification, we can classify resolvers
skipping to change at page 10, line 28 skipping to change at page 7, line 41
| 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 any information about the own right. A "Vleg" type does not give any information about the
trust anchors, and a "nonV" type indicates that the resolver does not trust anchors, and a "nonV" type indicates that the resolver does not
perform DNSSEC validation. perform DNSSEC validation.
5. Sentinel Test Result Considerations 4. 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's browser or There is also the common case where the end client's browser or
operating system is configured to use multiple resolvers. In these operating system is configured to use multiple resolvers. In these
cases, a SERVFAIL response from one resolver may cause the end client cases, a SERVFAIL response from one resolver may cause the end client
to repeat the query against one of the other configured resolvers. to repeat the query against one of the other configured resolvers.
skipping to change at page 10, line 50 skipping to change at page 8, line 16
additional resolvers, the sentinel test will effectively only be for additional resolvers, the sentinel test will effectively only be for
the first resolver. the first resolver.
If any of the client's resolvers are non-validating resolvers, the If any of the client's resolvers are non-validating resolvers, the
tests will result in the client reporting that it has a non- tests will result in the client reporting that it has a non-
validating DNS environment ("nonV"), which is effectively the case. validating DNS environment ("nonV"), which is effectively the case.
If all of the client resolvers are DNSSEC-validating resolvers, but If all of the client resolvers are DNSSEC-validating resolvers, but
some do not support this trusted key mechanism, then the result will some do not support this trusted key mechanism, then the result will
be indeterminate with respect to trusted key status ("Vleg"). be indeterminate with respect to trusted key status ("Vleg").
Simlarly, if all the client's resolvers support this mechanism, but Similarly, if all the client's resolvers support this mechanism, but
some have loaded the key into the trusted key stash and some have some have loaded the key into the trusted key stash and some have
not, then the result is indeterminate ("Vleg"). not, then the result is indeterminate ("Vleg").
There is also the common case of a recursive resolver using a There is also the common case of a recursive resolver using a
forwarder. forwarder.
If the resolver is non-validating, and it has a single forwarder If the resolver is non-validating, and it has a single forwarder
clause, then the resolver will presumably mirror the capabilities of clause, then the resolver will presumably mirror the capabilities of
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.
skipping to change at page 11, line 40 skipping to change at page 9, line 9
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.
Please note that SERVFAIL might be cached according to [RFC2308] Please note that SERVFAIL might be cached according to [RFC2308]
section 7 for up to 5 minutes and a positive answer for up to its section 7 for up to 5 minutes and a positive answer for up to its
TTL. TTL.
6. Security Considerations 5. Security Considerations
This document describes a mechanism to allow users and third parties This document describes a mechanism to allow users and third parties
to determine the trust state of root zone key signing keys in the DNS to determine the trust state of root zone key signing keys in the DNS
resolution 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. Privacy Considerations 6. Privacy Considerations
The mechansim in this document enables third parties (with either The mechanism 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 make specific DNS queries (e.g. via web- cause an Internet user to make specific DNS queries (e.g. via web-
based advertisements or javascript in web pages), can then determine based advertisements or javascript in web pages), can, under certain
which trust anchors are configured in the user's resolver. specific circumstances that includes additional knowledge of the
resolvers that are invoked by the user, determine which trust anchors
are configured in these resolvers. Without this additional
knowledge, the third party can infer the aggregate capabilities of
the user's DNS resolution environment, but cannot necessarily infer
the trust configuration of any recursive name server.
7. Implementation Experience
Petr Spacek implemented early versions of this technique into the
Knot resolver, and identified a number of places where it wasn't
clear, and provided very helpful text to address this.
Ondrej Sury of ISC has reported to the DNSOP Working Group in April
2018 that this technique was peer-reviewed and merged into BIND
master branch with the intent to backport the feature into older
release branches.
Benno Overeinder of NLnet Labs reported to the DNSOP Working Group in
April 2018 an intention to support this technique in Unbound in the
near future.
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
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, Ondrej Sury,
Duane Wessels and Paul Wouters for their helpful feedback. Paul Vixie, Duane Wessels and Paul Wouters for their helpful
feedback.
The authors would like to especially call out Paul Hoffman and Duane The authors would like to especially call out Paul Hoffman and Duane
Wessels for providing comments in the form of a pull request. Petr Wessels for providing comments in the form of a pull request.
Spacek implemented 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
RFC Editor: Please remove this section! RFC Editor: Please remove this section!
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 -11 to -12:
o Moved the Walkthrough Example to the end of the document as an
appendix.
o Incorporated changes as proposed by Ondrej Sury, relating to a
consistent use of Key Tag and a reference to the definition of a
Bogus RRset.
o Corrected minor typos.
o Revised the Privacy Considerations.
o In response to a request from DNSOP Working Group chairs, a
section on reported Implementation Experience has been added,
based on postings to the DNSOP Working Group mailing list.
From -10 to -11: From -10 to -11:
o Clarified the preconditions for this mechanism as per Working o Clarified the preconditions for this mechanism as per Working
Group mailing list discussion. Group mailing list discussion.
o Corrected minor typo. o Corrected minor typo.
From -09 to -10: From -09 to -10:
o Clarified the precondition list to specify that the resolver had o Clarified the precondition list to specify that the resolver had
skipping to change at page 14, line 27 skipping to change at page 12, line 27
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 keytag be decimal, not hex (thread / consensus in o Made the Key Tag 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.
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 Key Tags 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.
skipping to change at page 16, line 5 skipping to change at page 14, line 5
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>.
11.2. 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)", Anchor Knowledge in DNS Security Extensions (DNSSEC)",
RFC 8145, DOI 10.17487/RFC8145, April 2017, RFC 8145, DOI 10.17487/RFC8145, April 2017,
<https://www.rfc-editor.org/info/rfc8145>. <https://www.rfc-editor.org/info/rfc8145>.
Appendix A. Protocol Walkthrough Example
This Appendix provides a non-normative example of how the sentinel
mechanism could be used, and what each participant does. It is
provided in a conversational tone to be easier to follow.
Alice is in charge of the DNS root KSK (Key Signing Key), and would
like to roll / replace the key with a new one. She publishes the new
KSK, but would like to be able to predict / measure what the impact
will be before removing/revoking the old key. The current KSK has a
Key Tag of 11112, the new KSK has a Key Tag of 02323. Users want to
verify that their resolver will not break after Alice rolls the root
KSK key (that is, starts signing with just the KSK whose Key Tag is
02323).
Bob, Charlie, Dave, Ed are all users. They use the DNS recursive
resolvers supplied by their ISPs. They would like to confirm that
their ISPs have picked up the new KSK. Bob's ISP does not perform
validation. Charlie's ISP does validate, but the resolvers have not
yet been upgraded to support this mechanism. Dave and Ed's resolvers
have been upgraded to support this mechanism; Dave's resolver has the
new KSK, Ed's resolver hasn't managed to install the 02323 KSK in its
trust store yet.
Geoff is a researcher, and would like to both provide a means for
Bob, Charlie, Dave and Ed to be able to perform tests, and also would
like to be able to perform Internet-wide measurements of what the
impact will be (and report this back to Alice).
Geoff sets an authoritative DNS server for example.com, and also a
webserver (www.example.com). He adds three address records to
example.com:
invalid.example.com. IN AAAA 2001:db8::1
root-key-sentinel-is-ta-02323.example.com. IN AAAA 2001:db8::1
root-key-sentinel-not-ta-02323.example.com. IN AAAA 2001:db8::1
Note that the use of "example.com" names and the addresses here are
examples. In a real deployment, the domain names need to be under
control of the researcher, and the addresses must be real, reachable
addresses.
Geoff then DNSSEC signs the example.com zone, and intentionally makes
the invalid.example.com record invalid/bogus (for example, by editing
the signed zone and entering garbage for the signature). Geoff also
configures his webserver to listen on 2001:db8::1 and serve a
resource (for example, a 1x1 GIF, 1x1.gif) for all of these names.
The webserver also serves a webpage (www.example.com) which contains
links to these 3 resources (http://invalid.example.com/1x1.gif,
http://root-key-sentinel-is-ta-02323.example.com/1x1.gif,
http://root-key-sentinel-not-ta-02323.example.com/1x1.gif).
Geoff then asks Bob, Charlie, Dave and Ed to browse to
www.example.com. Using the methods described in this document, the
users can figure out what their fate will be when the 11112 KSK is
removed.
Bob is not using a validating resolver. This means that he will be
able to resolve invalid.example.com (and fetch the 1x1 GIF) - this
tells him that the KSK roll does not affect him, and so he will be
OK.
Charlie's resolvers are validating, but they have not been upgraded
to support the KSK sentinel mechanism. Charlie will not be able to
fetch the http://invalid.example.com/1x1.gif resource (the
invalid.example.com record is bogus, and none of his resolvers will
resolve it). He is able to fetch both of the other resources - from
this he knows (see the logic in the body of this document) that he is
using legacy, validating resolvers. The KSK sentinel method cannot
provide him with a definitive answer to the question of what root
trust anchors this resolver is using.
Dave's resolvers implement the sentinel method, and have picked up
the new KSK. For the same reason as Charlie, he cannot fetch the
"invalid" resource. His resolver resolves the root-key-sentinel-is-
ta-02323.example.com name normally (it contacts the example.com
authoritative servers, etc); as it supports the sentinel mechanism,
just before Dave's recursive resolver sends the reply to Dave's stub,
it performs the KSK Sentinel check. The QNAME starts with "root-key-
sentinel-is-ta-", and the recursive resolver does indeed have a key
with the Key Tag of 02323 in its root trust store. This means that
that this part of the KSK Sentinel check passes (it is true that Key
Tag 02323 is in the trust anchor store), and the recursive resolver
replies normally (with the answer provided by the authoritative
server). Dave's recursive resolver then resolves the root-key-
sentinel-not-ta-02323.example.com name. Once again, it performs the
normal resolution process, but because it implements KSK Sentinel
(and the QNAME starts with "root-key-sentinel-not-ta-"), just before
sending the reply, it performs the KSK Sentinel check. As it has
02323 in it's trust anchor store, the answer to "is this *not* a
trust anchor" is false, and so the recursive resolver does not reply
with the answer from the authoritative server - instead, it replies
with a SERVFAIL (note that replying with SERVFAIL instead of the
original answer is the only mechanism that KSK Sentinel uses). This
means that Dave cannot fetch "invalid", he can fetch "root-key-
sentinel-is-ta-02323", but he cannot fetch "root-key-sentinel-not-ta-
02323". From this, Dave knows that he is behind an upgraded,
validating resolver, which has successfully installed the new, 02323
KSK.
Just like Charlie and Dave, Ed cannot fetch the "invalid" record.
This tells him that his resolvers are validating. When his
(upgraded) resolver performs the KSK Sentinel check for "root-key-
sentinel-is-ta-02323", it does *not* have the (new, 02323) KSK in
it's trust anchor store. This means check fails, and Ed's recursive
resolver converts the (valid) answer into a SERVFAIL error response.
It performs the same check for root-key-sentinel-not-ta-
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
means that Ed cannot fetch the "invalid" resource, he also cannot
fetch the "root-key-sentinel-is-ta-02323" resource, but he can fetch
the "root-key-sentinel-not-ta-02323" resource. This tells Ed that
his resolvers have not installed the new KSK.
Geoff would like to do a large scale test and provide the information
back to Alice. He uses some mechanism such as causing users to go to
a web page to cause a large number of users to attempt to resolve the
three resources, and then analyzes the results of the tests to
determine what percentage of users will be affected by the KSK
rollover event.
This description is a simplified example - it is not anticipated that
Bob, Charlie, Dave and Ed will actually look for the absence or
presence of web resources; instead, the webpage that they load would
likely contain JavaScript (or similar) which displays the result of
the tests, sends the results to Geoff, or both. This sentinel
mechanism does not rely on the web: it can equally be used by trying
to resolve the names (for example, using the common "dig" command)
and checking which result in a SERVFAIL.
Authors' Addresses Authors' Addresses
Geoff Huston Geoff Huston
Email: gih@apnic.net Email: gih@apnic.net
URI: http://www.apnic.net URI: http://www.apnic.net
Joao Silva Damas Joao Silva Damas
Email: joao@apnic.net Email: joao@apnic.net
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