< draft-ietf-dnsop-kskroll-sentinel-06.txt   draft-ietf-dnsop-kskroll-sentinel-07.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 6, 2018 W. Kumari Expires: September 21, 2018 W. Kumari
Google Google
March 5, 2018 March 20, 2018
A Sentinel for Detecting Trusted Keys in DNSSEC A Sentinel for Detecting Trusted Keys in DNSSEC
draft-ietf-dnsop-kskroll-sentinel-06 draft-ietf-dnsop-kskroll-sentinel-07
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 6, 2018. This Internet-Draft will expire on September 21, 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
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. Protocol Walkthrough Example . . . . . . . . . . . . . . . . 3 2. Protocol Walkthrough Example . . . . . . . . . . . . . . . . 4
3. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 6 3. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 7
3.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Special processing . . . . . . . . . . . . . . . . . . . 7 3.2. Special processing . . . . . . . . . . . . . . . . . . . 8
4. Processing Sentinel Results . . . . . . . . . . . . . . . . . 8 4. Processing Sentinel Results . . . . . . . . . . . . . . . . . 8
5. Sentinel Test Result Considerations . . . . . . . . . . . . . 10 5. Sentinel Test Result Considerations . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 12 10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 14 11.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
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
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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
The mechanism described in this document meets both of these use The mechanism described in this document meets both of these use
cases. This new mechanism is OPTIONAL to implement and use, although cases. This new mechanism is OPTIONAL to implement and use, although
for reasons of supporting broad-based measurement techniques, it is 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.
The sentinel test described in this document determines whether a
user's browser or operating system looking up the special names that
are used in this protocol would be able to validate using the root
KSK indicated by the special names. The protocol uses the DNS
SERVFAIL response code (RCODE 2) for this purpose because that is the
response code that is returned by resolvers when DNSSEC validation
fails. If a browser or operating system has multiple resolvers
configured, and those resolvers have different properties (for
example, one performs DNSSEC validation and one does not), the
sentinel mechanism might search among the different resolvers, or
might not, depending on how the browser or operating system is
configured.
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. Protocol Walkthrough Example
[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
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example.com: example.com:
invalid.example.com. IN AAAA 2001:db8::1 invalid.example.com. IN AAAA 2001:db8::1
kskroll-sentinel-is-ta-02323.example.com. IN AAAA 2001:db8::1 kskroll-sentinel-is-ta-02323.example.com. IN AAAA 2001:db8::1
kskroll-sentinel-not-ta-02323.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 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 examples. In a real deployment, the domain names need to be under
control of the researcher, and the addresses much be real, reachable control of the researcher, and the addresses must be real, reachable
addresses. 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-02323.example.com/1x1.gif, http://kskroll-sentinel-is-ta-02323.example.com/1x1.gif,
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trusted keys. An active key is one which could currently be used for 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 validation (that is, a key that is not in either the AddPend or
Revoked state as described in [RFC5011]). 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 keytag generate four possible combinations
summarized in the table: summarized in the table:
| Key Tag is trusted | Key Tag is not trusted Label | Key Tag is trusted | Key Tag 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
RCODE=SERVFAIL (value 2) and MUST empty the ANSWER section of the DNS
response, ignoring all other documents which specify content of the
ANSWER section.
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 one or more validating DNS resolvers that use a particular
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
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
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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 to valid
valid answers. Note that a slew of other issues can also cause answers. Note that a slew of other issues can also cause SERVFAIL
SERVFAIL responses, and so the sentinel processing may sometimes responses, and so the sentinel processing may sometimes result in
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
into four distinct behavior types, for which we will use the labels: into four distinct behavior types, for which we will use the labels:
"Vnew", "Vold", "Vleg", and "nonV". These labels correspond to "Vnew", "Vold", "Vleg", and "nonV". These labels correspond to
resolver behaviour types as follows: resolver behaviour types as follows:
Vnew: A DNSSEC-Validating resolver that is configured to implement Vnew: A DNSSEC-Validating resolver that is configured to implement
this mechanism has loaded the nominated key into its local trusted this mechanism has loaded the nominated key into its local trusted
key store will respond with an A or AAAA RRset response for key store will respond with an A or AAAA RRset response for
"kskroll-sentinel-is-ta" queries, SERVFAIL for "kskroll-sentinel- "kskroll-sentinel-is-ta" queries, SERVFAIL for "kskroll-sentinel-
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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 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's browser or
use multiple resolvers. In these cases the SERVFAIL responses from operating system is configured to use multiple resolvers. In these
one resolver will prompt the end client to repeat the query against cases, a SERVFAIL response from one resolver may cause the end client
one of the other configured resolvers. to repeat the query against one of the other configured resolvers.
If the client's browser or operating system does not try the
additional resolvers, the sentinel test will effectively only be for
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 Simlarly, 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
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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.
If the validating resolver has a forwarding configuration, and uses If the validating resolver has a forwarding configuration, and uses
the CD flag on all forwarded queries, then this resolver is acting in the CD bit on all forwarded queries, then this resolver is acting in
a manner that is identical to a standalone resolver. The same a manner that is identical to a standalone resolver. The same
consideration applies if any one one of the forwarder targets is a consideration applies if any one of the forwarder targets is a non-
non-validating resolver. Similarly, if all the forwarder targets do validating resolver. Similarly, if all the forwarder targets do not
not apply this trusted key mechanism, the same considerations apply. apply this trusted key mechanism, the same considerations apply.
A more complex case is where all of the following conditions all A more complex case is where all of the following conditions all
hold: hold:
o Both the validating resolver and the forwarder target resolver o Both the validating resolver and the forwarder target resolver
support this trusted key sentinel mechanism support this trusted key sentinel mechanism
o The local resolver's queries do not have the CD bit set o The local resolver's queries do not have the CD bit set
o The trusted key state differs between the forwarding resolver and o The trusted key state differs between the forwarding resolver and
the forwarder target resolver the forwarder target resolver
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]
section 7 for up to 5 minutes and a positive answer for up to its
TTL.
6. Security Considerations 6. 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.
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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 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. Petr
Specek implmented early versions of this technique into the Knot Spacek implemented early versions of this technique into the Knot
resolver, identified a number of places where it wasn't clear, and resolver, identified a number of places where it wasn't clear, and
provided very helpful text to address this. provided very helpful text to address this.
10. Change Log 10. Change Log
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 -07 to -06
o Addressed GitHub PR #14: Clarifications regarding caching and
SERVFAIL responses
o Addressed GitHub PR #12, #13: Clarify situation with multiple
resolvers, Fix editorial nits.
From -05 to -06: From -05 to -06:
Paul improved my merging of Petr's text to make it more readable. o Paul improved my merging of Petr's text to make it more readable.
Minor change, but this is just before the cut-off, so I wanted it Minor change, but this is just before the cut-off, so I wanted it
maximally readable. maximally readable.
From -04 to -05: From -04 to -05:
o Incorporated Duane's #10 o Incorporated Duane's #10
o Integrated Petr Spacek's Issue - https://github.com/APNIC-Labs/ o Integrated Petr Spacek's Issue - https://github.com/APNIC-Labs/
draft-kskroll-sentinel/issues/9 (note that commit-log incorrectly draft-kskroll-sentinel/issues/9 (note that commit-log incorrectly
referred to Duane's PR as number 9, it is actually 10). referred to Duane's PR as number 9, it is actually 10).
skipping to change at page 13, line 45 skipping to change at page 14, line 35
sentinel-is-ta-<key-tag>. This is because BIND (at least) will sentinel-is-ta-<key-tag>. This is because BIND (at least) will
not allow records which start with an underscore to have address not allow records which start with an underscore to have address
records (CNAMEs, yes, A/AAAA no). Some browsers / operating records (CNAMEs, yes, A/AAAA no). Some browsers / operating
systems also will not fetch resources from names which start with systems also will not fetch resources from names which start with
an underscore. an underscore.
11. References 11. References
11.1. Normative References 11.1. Normative References
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
<https://www.rfc-editor.org/info/rfc2308>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [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>.
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