draft-ietf-dnsop-edns-key-tag-05.txt   rfc8145.txt 
Internet Engineering Task Force D. Wessels Internet Engineering Task Force (IETF) D. Wessels
Internet-Draft Verisign Request for Comments: 8145 Verisign
Intended status: Standards Track W. Kumari Category: Standards Track W. Kumari
Expires: August 20, 2017 Google ISSN: 2070-1721 Google
P. Hoffman P. Hoffman
ICANN ICANN
February 16, 2017 April 2017
Signaling Trust Anchor Knowledge in DNS Security Extensions (DNSSEC) Signaling Trust Anchor Knowledge in DNS Security Extensions (DNSSEC)
draft-ietf-dnsop-edns-key-tag-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 two different particular node in the DNS. This document specifies two different
ways for validating resolvers to signal to a server which keys are ways for validating resolvers to signal to a server which keys are
referenced in their chain-of-trust. The data from such signaling referenced in their chain of trust. The data from such signaling
allow zone administrators to monitor the progress of rollovers in a allow zone administrators to monitor the progress of rollovers in a
DNSSEC-signed zone. DNSSEC-signed zone.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
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time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on August 20, 2017. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc8145.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction ....................................................3
1.1. Design Evolution . . . . . . . . . . . . . . . . . . . . 3 1.1. Design Evolution ...........................................4
2. Requirements Terminology . . . . . . . . . . . . . . . . . . 4 2. Requirements Terminology ........................................5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology .....................................................5
4. Using the edns-key-tag Option . . . . . . . . . . . . . . . . 5 4. Using the edns-key-tag Option ...................................5
4.1. Option Format . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Option Format ..............................................5
4.2. Use By Queriers . . . . . . . . . . . . . . . . . . . . . 5 4.2. Use by Queriers ............................................6
4.2.1. Stub Resolvers . . . . . . . . . . . . . . . . . . . 6 4.2.1. Stub Resolvers ......................................7
4.2.1.1. Validating Stub Resolvers . . . . . . . . . . . . 6 4.2.1.1. Validating Stub Resolvers ..................7
4.2.1.2. Non-validating Stub Resolvers . . . . . . . . . . 6 4.2.1.2. Non-validating Stub Resolvers ..............7
4.2.2. Recursive Resolvers . . . . . . . . . . . . . . . . . 6 4.2.2. Recursive Resolvers .................................7
4.2.2.1. Validating Recursive Resolvers . . . . . . . . . 6 4.2.2.1. Validating Recursive Resolvers .............7
4.2.2.2. Non-validating Recursive Resolvers . . . . . . . 7 4.2.2.2. Non-validating Recursive Resolvers .........8
4.3. Use By Responders . . . . . . . . . . . . . . . . . . . . 7 4.3. Use by Responders ..........................................8
5. Using the Key Tag Query . . . . . . . . . . . . . . . . . . . 7 5. Using the Key Tag Query .........................................8
5.1. Query Format . . . . . . . . . . . . . . . . . . . . . . 8 5.1. Query Format ...............................................8
5.2. Use By Queriers . . . . . . . . . . . . . . . . . . . . . 8 5.2. Use by Queriers ............................................9
5.3. Use By Responders . . . . . . . . . . . . . . . . . . . . 8 5.3. Use by Responders ..........................................9
5.3.1. Interaction With Aggressive Negative Caching . . . . 9 5.3.1. Interaction with Aggressive Negative Caching ........9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations ............................................10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations ........................................10
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 10 8. Privacy Considerations .........................................11
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 9. References .....................................................11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 9.1. Normative References ......................................11
10.1. Normative References . . . . . . . . . . . . . . . . . . 11 9.2. Informative References ....................................12
10.2. Informative References . . . . . . . . . . . . . . . . . 11 Acknowledgments ...................................................13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses ................................................13
1. Introduction 1. Introduction
The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and The DNS Security Extensions (DNSSEC) [RFC4033] [RFC4034] [RFC4035]
[RFC4035] were developed to provide origin authentication and were developed to provide origin authentication and integrity
integrity protection for DNS data by using digital signatures. protection for DNS data by using digital signatures. DNSSEC uses
DNSSEC uses Key Tags to efficiently match signatures to the keys from Key Tags to efficiently match signatures to the keys from which they
which they are generated. The Key Tag is a 16-bit value computed are generated. The Key Tag is a 16-bit value computed from the RDATA
from the RDATA portion of a DNSKEY RR using a formula not unlike a portion of a DNSKEY resource record (RR) using a formula not unlike a
ones-complement checksum. RRSIG RRs contain a Key Tag field whose ones-complement checksum. RRSIG RRs contain a Key Tag field whose
value is equal to the Key Tag of the DNSKEY RR that validates the value is equal to the Key Tag of the DNSKEY RR that validates the
signature. signature.
Likewise, Delegation Signer (DS) RRs also contain a Key Tag field Likewise, Delegation Signer (DS) RRs also contain a Key Tag field
whose value is equal to the Key Tag of the DNSKEY RR to which it whose value is equal to the Key Tag of the DNSKEY RR to which it
refers. refers.
This document specifies how validating resolvers can tell a server, This document specifies how validating resolvers can tell a server,
in a DNS query, which DNSSEC key(s) they would use to validate the in a DNS query, which DNSSEC key(s) they would use to validate the
server's responses. It describes two independent methods for server's responses. It describes two independent methods for
conveying Key Tag information bewteen clients and servers: placing an conveying Key Tag information between clients and servers:
EDNS option in the OPT meta-RR [RFC6891] that contains the key tags
(described in Section 4), and by periodically sending special "key 1. placing an EDNS option in the OPT RR [RFC6891] that contains the
tag queries" to a server authoritative for the zone (described in Key Tags (described in Section 4)
Section 5).
2. periodically sending special "Key Tag queries" to a server
authoritative for the zone (described in Section 5)
Each of these new signaling mechanisms is OPTIONAL to implement and Each of these new signaling mechanisms is OPTIONAL to implement and
use. These mechanisms serve to measure the acceptance and use of new use. These mechanisms serve to measure the acceptance and use of new
DNSSEC trust anchors and key signing keys (KSKs). This signaling DNSSEC trust anchors and key signing keys (KSKs). This signaling
data can be used by zone administrators as a gauge to measure the data can be used by zone administrators as a gauge to measure the
successful deployment of new keys. This is of particular interest successful deployment of new keys. This is of particular interest
for the DNS root zone in the event of key and/or algorithm rollovers for the DNS root zone in the event of key and/or algorithm rollovers
that rely on [RFC5011] to automatically update a validating DNS that rely on [RFC5011] to automatically update a validating DNS
resolver's trust anchor. resolver's trust anchor.
skipping to change at page 3, line 40 skipping to change at page 4, line 11
updating trust anchors. Rather, it specifies a means by which a DNS updating trust anchors. Rather, it specifies a means by which a DNS
query can signal the set of keys that a client uses for DNSSEC query can signal the set of keys that a client uses for DNSSEC
validation. validation.
1.1. Design Evolution 1.1. Design Evolution
Initially, when the work on this document started, it proposed Initially, when the work on this document started, it proposed
including Key Tag values in a new EDNS(0) option code. It was including Key Tag values in a new EDNS(0) option code. It was
modeled after [RFC6975], which provides DNSSEC algorithm signaling. modeled after [RFC6975], which provides DNSSEC algorithm signaling.
The authors received feedback from dnsop Working Group participants The authors received feedback from participants in the DNSOP Working
that it might be better to convey Key Tags in QNAME of a separate DNS Group that it might be better to convey Key Tags in the QNAME of a
query, rather than as an EDNS(0) option. Mostly this is because separate DNS query, rather than as an EDNS(0) option. Mostly, this
forwarding (e.g. from stub to recursive to authoritative) could be is because forwarding (e.g., from stub to recursive to authoritative)
problematic. Reasons include: could be problematic. Reasons include the following:
1. EDNS(0) is a hop-by-hop protocol. Unknown option codes would not 1. EDNS(0) is a hop-by-hop protocol. Unknown option codes would not
be forwarded by default, as per [RFC6891]. be forwarded by default, as per [RFC6891].
2. Middleboxes might block entire queries containing unknown EDNS(0) 2. Middleboxes might block entire queries containing unknown EDNS(0)
option codes. option codes.
3. A recursive might need to remember Key Tag values (i.e., keep 3. A recursive resolver might need to remember Key Tag values (i.e.,
state) received from its stub clients and then forward them at a keep state) received from its stub clients and then forward them
later opportunity. at a later opportunity.
One advantage of the EDNS(0) option code is that it is possible to One advantage of the EDNS(0) option code is that it is possible to
see that a stub client has a different Key Tag list than its see that a stub client has a different Key Tag list than its
forwarder. In the QNAME-based approach, this is not possible because forwarder. In the QNAME-based approach, this is not possible because
queries originated by a stub and a forwarder are indistinguishable. queries originated by a stub and a forwarder are indistinguishable.
The authors feel this advantage is not sufficient to justify the The authors feel that this advantage is not sufficient to justify the
EDNS(0) approach. EDNS(0) approach.
One downside to the QNAME approach is that it uses a separate query, One downside to the QNAME approach is that it uses a separate query,
whereas with EDNS(0) the Key Tag values are "piggy-backed" on to an whereas with EDNS(0) the Key Tag values are "piggybacked" onto an
existing DNSKEY query. For this reason, this document recommends existing DNSKEY query. For this reason, this document recommends
only sending QNAME-based key tag queries for configured trust only sending QNAME-based Key Tag queries for trust anchors, although
anchors, although EDNS-based key tags can be sent with any DNSKEY EDNS-based Key Tags can be sent with any DNSKEY query.
query.
Another downside to the QNAME-based approach is that since the trust Another downside to the QNAME-based approach is that since the
anchor zone might not contain labels matching the QNAME, these trust anchor zone might not contain labels matching the QNAME, these
queries could be subject to aggressive negative caching features now queries could be subject to aggressive negative caching features now
in development by the Working Group. This could affect the amount of in development by the Working Group. This could affect the amount of
signaling sent by some clients compared to others. signaling sent by some clients compared to others.
A probably minor downside to the QNAME-based approach is that it A probably minor downside to the QNAME-based approach is that it
cannot be used with extremely long query names if the addition of the cannot be used with extremely long query names if the addition of the
prefix would cause the name to be longer than 255 octets. prefix would cause the name to be longer than 255 octets.
2. Requirements Terminology 2. Requirements Terminology
skipping to change at page 4, line 46 skipping to change at page 5, line 18
"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 [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Terminology 3. Terminology
Trust Anchor: A configured DNSKEY RR or DS RR hash of a DNSKEY RR. Trust Anchor: A configured DNSKEY RR or DS RR hash of a DNSKEY RR.
A validating security-aware resolver uses this public key or hash A validating security-aware resolver uses this public key or hash
as a starting point for building the authentication chain to a as a starting point for building the authentication chain to a
signed DNS response. In general, a validating resolver will have signed DNS response. In general, a validating resolver will have
to obtain the initial values of its trust anchors via some secure to obtain the initial values of its trust anchors via some secure
or trusted means outside the DNS protocol. Presence of a trust or trusted means outside the DNS protocol. Presence of a
anchor also implies that the resolver should expect the zone to trust anchor also implies that the resolver should expect the zone
which the trust anchor points to be signed. (quoted from [RFC4033] to which the trust anchor points to be signed. (This paragraph is
Section 2) quoted from Section 2 of [RFC4033].)
Key Tag: A 16-bit integer that identifies and enables efficient Key Tag: A 16-bit integer that identifies and enables efficient
selection of DNSSEC public keys. A Key Tag value can be computed selection of DNSSEC public keys. A Key Tag value can be computed
over the RDATA of a DNSKEY RR. The Key Tag field in the RRSIG and over the RDATA of a DNSKEY RR. The Key Tag field in the RRSIG and
DS records can be used to help select the corresponding DNSKEY RR DS records can be used to help select the corresponding DNSKEY RR
efficiently when more than one candidate DNSKEY RR is available. efficiently when more than one candidate DNSKEY RR is available.
For most algorithms the Key Tag is a simple 16-bit modular sum of For most algorithms, the Key Tag is a simple 16-bit modular sum of
the DNSKEY RDATA. See [RFC4034] Appendix B. the DNSKEY RDATA. See [RFC4034], Appendix B.
4. Using the edns-key-tag Option 4. Using the edns-key-tag Option
4.1. Option Format 4.1. Option Format
The edns-key-tag option is encoded as follows: The edns-key-tag option is encoded as follows:
0 8 16 0 8 16
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| OPTION-CODE | | OPTION-CODE |
skipping to change at page 5, line 26 skipping to change at page 6, line 4
0 8 16 0 8 16
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| OPTION-CODE | | OPTION-CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| OPTION-LENGTH | | OPTION-LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| KEY-TAG | | KEY-TAG |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ... / | ... /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where: where:
OPTION-CODE: The EDNS0 option code assigned to edns-key-tag, [TBD]. OPTION-CODE: The EDNS0 option code assigned to edns-key-tag (14).
OPTION-LENGTH: The value 2 x number of key-tag values present. OPTION-LENGTH: The value 2 x number of key-tag values present.
KEY-TAG: One or more 16-bit Key Tag values ([RFC4034], Appendix B). KEY-TAG: One or more 16-bit Key Tag values ([RFC4034], Appendix B).
4.2. Use By Queriers 4.2. Use by Queriers
A validating resolver sets the edns-key-tag option in the OPT meta-RR A validating resolver sets the edns-key-tag option in the OPT RR when
when sending a DNSKEY query. The validating resolver SHOULD also set sending a DNSKEY query. The validating resolver SHOULD also set the
the DNSSEC OK bit [RFC4034] to indicate that it wishes to receive DNSSEC OK bit (also known as the DO bit) [RFC4035] to indicate that
DNSSEC RRs in the response. it wishes to receive DNSSEC RRs in the response.
A DNS client MUST NOT include the edns-key-tag option for non-DNSKEY A DNS client MUST NOT include the edns-key-tag option for non-DNSKEY
queries. queries.
The KEY-TAG value(s) included in the edns-key-tag option represent The KEY-TAG value(s) included in the edns-key-tag option represents
the Key Tag of the Trust Anchor or DNSKEY RR that will be used to the Key Tag of the trust anchor or DNSKEY RR that will be used to
validate the expected response. When the client sends a DNSKEY validate the expected response. When the client sends a DNSKEY
query, the edns-key-tag option represents the Key Tag(s) of the query, the edns-key-tag option represents the Key Tag(s) of the
KSK(s) of the zone for which the server is authoritative. A KSK(s) of the zone for which the server is authoritative. A
validating resolver learns the Key Tag(s) of the KSK(s) from the validating resolver learns the Key Tag(s) of the KSK(s) from the
zone's DS record(s) (found in the parent), or from a configured trust zone's DS record(s) (found in the parent) or from a trust anchor.
anchor.
A DNS client SHOULD include the edns-key-tag option when issuing a A DNS client SHOULD include the edns-key-tag option when issuing a
DNSKEY query for a zone corresponding to a configured Trust Anchor. DNSKEY query for a zone corresponding to a trust anchor.
A DNS client MAY include the edns-key-tag option when issuing a A DNS client MAY include the edns-key-tag option when issuing a
DNSKEY query for a non-Trust Anchor zone (i.e., Key Tags learned via DNSKEY query for a non-trust anchor zone (i.e., Key Tags learned via
DS records). Since some DNSSEC validators implement bottom-up DS records). Since some DNSSEC validators implement bottom-up
validation, non-Trust Anchor Key Tags zone might not be known at the validation, a non-trust anchor Key Tags zone might not be known at
time of the query. Such a validator can include the edns-key-tag the time of the query. Such a validator can include the edns-key-tag
option based on previously cached data. option based on previously cached data.
A DNS client MUST NOT include Key Tag(s) for keys which are not A DNS client MUST NOT include Key Tag(s) for keys that are not
learned via either configured Trust Anchor or DS records. learned via either a trust anchor or DS records.
Since the edns-key-tag option is only set in the query, if a client Since the edns-key-tag option is only set in the query, if a client
sees these options in the response, no action needs to be taken and sees these options in the response, no action needs to be taken and
the client MUST ignore the option values. the client MUST ignore the option values.
4.2.1. Stub Resolvers 4.2.1. Stub Resolvers
Typically, stub resolvers rely on an upstream recursive server (or Typically, stub resolvers rely on an upstream recursive resolver (or
cache) to provide a response. Optimal setting of the edns-key-tag cache) to provide a response. Optimal setting of the edns-key-tag
option depends on whether the stub resolver elects to perform its own option depends on whether the stub resolver elects to perform its own
validation. validation.
4.2.1.1. Validating Stub Resolvers 4.2.1.1. Validating Stub Resolvers
A validating stub resolver sets the DNSSEC OK (DO) bit [RFC4034] to A validating stub resolver sets the DNSSEC OK bit [RFC4035] to
indicate that it wishes to receive additional DNSSEC RRs (i.e., RRSIG indicate that it wishes to receive additional DNSSEC RRs (i.e., RRSIG
RRs) in the response. Such validating resolvers SHOULD include the RRs) in the response. Such validating resolvers SHOULD include the
edns-key-tag option in the OPT RR when sending a DNSKEY query. edns-key-tag option in the OPT RR when sending a DNSKEY query.
4.2.1.2. Non-validating Stub Resolvers 4.2.1.2. Non-validating Stub Resolvers
The edns-key-tag option MUST NOT be included by non-validating stub The edns-key-tag option MUST NOT be included by non-validating stub
resolvers. resolvers.
4.2.2. Recursive Resolvers 4.2.2. Recursive Resolvers
4.2.2.1. Validating Recursive Resolvers 4.2.2.1. Validating Recursive Resolvers
A validating recursive resolver is, by definition, configured with at A validating recursive resolver is, by definition, configured with at
least one trust anchor. Thus, a recursive resolver SHOULD include least one trust anchor. Thus, a recursive resolver SHOULD include
the edns-key-tag option in its DNSKEY queries as described above. the edns-key-tag option in its DNSKEY queries as described above.
In addition, the clients of a validating recursive resolver might be In addition, the clients of a validating recursive resolver might be
configured to do their own validation, with their own trust configured to do their own validation, with their own
anchor(s). When a validating recursive resolver receives a query trust anchor(s). When a validating recursive resolver receives a
that includes the edns-key-tag option with a Key Tag list that query that includes the edns-key-tag option with a Key Tag list that
differs from its own, it SHOULD forward both the client's Key Tag differs from its own, it SHOULD forward both the client's Key Tag
list as well as its own. When doing so, the recursive resolver list and its own list. When doing so, the recursive resolver SHOULD
SHOULD transmit the two Key Tag lists using separate instances of the transmit the two Key Tag lists using separate instances of the
edns-key-tag option code in the OPT meta-RR. For example, if the edns-key-tag option code in the OPT RR. For example, if the
recursive resolver's Key Tag list is (19036, 12345) and the stub/ recursive resolver's Key Tag list is (19036, 12345) and the
client's list is (19036, 34567), the recursive would include the stub/client's list is (19036, 34567), the recursive resolver
edns-key-tag option twice: Once with values (19036, 12345) and once would include the edns-key-tag option twice: once with values
with values (19036, 34567). (19036, 12345) and once with values (19036, 34567).
A validating recursive resolver MAY combine stub/client Key Tag A validating recursive resolver MAY combine stub/client Key Tag
values from multiple incoming queries into a single outgoing query. values from multiple incoming queries into a single outgoing query.
It is RECOMMENDED that implementations place reasonable limits on the It is RECOMMENDED that implementations place reasonable limits on the
number of Key Tags to include in the outgoing edns-key-tag option. number of Key Tags to include in the outgoing edns-key-tag option.
If the client included the DO and Checking Disabled (CD) bits, but If the client included the DNSSEC OK and Checking Disabled (CD) bits
did not include the edns-key-tag option in the query, the validating but did not include the edns-key-tag option in the query, the
recursive resolver MAY include the option with its own Key Tag values validating recursive resolver MAY include the option with its own
in full. Key Tag values in full.
Validating recursive resolvers MUST NOT set the edns-key-tag option Validating recursive resolvers MUST NOT set the edns-key-tag option
in the final response to the stub client. in the final response to the stub client.
4.2.2.2. Non-validating Recursive Resolvers 4.2.2.2. Non-validating Recursive Resolvers
Recursive resolvers that do not validate responses SHOULD copy the Recursive resolvers that do not validate responses SHOULD copy the
edns-key-tag option seen in received queries, as they represent the edns-key-tag option seen in received queries, as they represent the
wishes of the validating downstream resolver that issued the original wishes of the validating downstream resolver that issued the original
query. query.
4.3. Use By Responders 4.3. Use by Responders
An authoritative name server receiving queries with the edns-key-tag An authoritative name server receiving queries with the edns-key-tag
option MAY log or otherwise collect the Key Tag values to provide option MAY log or otherwise collect the Key Tag values to provide
information to the zone operator. information to the zone operator.
A responder MUST NOT include the edns-key-tag option in any DNS A responder MUST NOT include the edns-key-tag option in any DNS
response. response.
5. Using the Key Tag Query 5. Using the Key Tag Query
5.1. Query Format 5.1. Query Format
A key tag query consists of a standard DNS query of type NULL and of A Key Tag query consists of a standard DNS query of type NULL and of
class IN [RFC1035]. class IN [RFC1035].
The first component of the query name is the string "_ta-" followed The first component of the query name is the string "_ta-" followed
by a sorted, hyphen-separated list of hexadecimal-encoded Key Tag by a sorted, hyphen-separated list of hexadecimal-encoded Key Tag
values. The zone name corresponding to the trust anchor is appended values. The zone name corresponding to the trust anchor is appended
to this first component. to this first component.
For example, a validating DNS resolver that has a single root zone For example, a validating DNS resolver that has a single root zone
trust anchor with key tag 17476 (decimal) would originate a query of trust anchor with Key Tag 17476 (decimal) would originate a query of
the form QTYPE=NULL, QCLASS=IN, QNAME=_ta-4444. the form QTYPE=NULL, QCLASS=IN, QNAME=_ta-4444.
Hexadecimal values MUST be zero-padded. For example, if the key tag Hexadecimal values MUST be zero-padded to four hexadecimal digits.
is 999 (decimal), it is represented in hexadecimal as 03e7. For example, if the Key Tag is 999 (decimal), it is represented in
hexadecimal as 03e7.
When representing multiple key tag values, they MUST be sorted in When representing multiple Key Tag values, they MUST be sorted in
order from smallest to largest. For example, A validating DNS order from smallest to largest. For example, a validating DNS
resolver that has a three trust anchors for the example.com zone with resolver that has three trust anchors for the example.com zone with
key tags 1589, 43547, 31406 (decimal) would originate a query of the Key Tags 1589, 43547, 31406 (decimal) would originate a query of the
form QTYPE=NULL, QCLASS=IN, QNAME=_ta-0635-7aae-aa1b.example.com. form QTYPE=NULL, QCLASS=IN, QNAME=_ta-0635-7aae-aa1b.example.com.
5.2. Use By Queriers 5.2. Use by Queriers
A validating DNS resolver (stub or recursive) SHOULD originate a key A validating DNS resolver (stub or recursive) SHOULD originate a
tag query whenever it also originates a DNSKEY query for a configured Key Tag query whenever it also originates a DNSKEY query for a
Trust Anchor zone. In other words, the need to issue a DNSKEY query trust anchor zone. In other words, the need to issue a DNSKEY query
is also the trigger to issue a key tag query. is also the trigger to issue a Key Tag query.
The value(s) included in the key tag query represent the Key Tag(s) The value(s) included in the Key Tag query represents the Key Tag(s)
of the Trust Anchor that will be used to validate the expected DNSKEY of the trust anchor that will be used to validate the expected DNSKEY
response. response.
A DNS validating resolver SHOULD NOT originate key tag queries when A validating DNS resolver SHOULD NOT originate Key Tag queries when
also originating DNSKEY queries for non-Trust Anchor zones. also originating DNSKEY queries for non-trust anchor zones.
A non-validating DNS resolver MUST NOT originate key tag queries. A non-validating DNS resolver MUST NOT originate Key Tag queries.
DNS resolvers with caches SHOULD cache and reuse the response to a DNS resolvers with caches SHOULD cache and reuse the response to a
key tag query just as it would any other response. Key Tag query just as it would any other response.
5.3. Use By Responders 5.3. Use by Responders
An authoritative name server receiving key tag queries MAY log or An authoritative name server receiving Key Tag queries MAY log or
otherwise collect the Key Tag values to provide information to the otherwise collect the Key Tag values to provide information to the
zone operator. zone operator.
An authoritative name server MUST generate an appropriate response to An authoritative name server MUST generate an appropriate response to
the key tag query. A server does not need to have built-in logic the Key Tag query. A server does not need to have built-in logic
that determines the response to key tag queries: the response code is that determines the response to Key Tag queries: the response code is
determined by whether the data is in the zone file or covered by determined by whether the data is in the zone file or covered by
wildcard. The zone operator might want to add specific key tag wildcards. The zone operator might want to add specific Key Tag
records to its zone, perhaps with specific TTLs, to affect the records to its zone, perhaps with specific TTLs, to affect the
frequency of key tag queries from clients. frequency of Key Tag queries from clients.
5.3.1. Interaction With Aggressive Negative Caching 5.3.1. Interaction with Aggressive Negative Caching
Aggressive NSEC/NSEC3 negative caching Aggressive NSEC/NSEC3 negative caching [NSEC-NSEC3-Usage] may also
[draft-ietf-dnsop-nsec-aggressiveuse] may also affect the quality of affect the quality of Key Tag signaling. When the response code for
key tag signaling. When the response code for a key tag query is a Key Tag query is NXDOMAIN, DNS resolvers that implement aggressive
NXDOMAIN, DNS resolvers that implement aggressive negative caching negative caching will send fewer Key Tag queries than resolvers that
will send fewer key tag queries than resolvers that do not implement do not implement it.
it.
For this reason, zone operators might choose to create records For this reason, zone operators might choose to create records
corresponding to expected key tag queries. During a rollover from corresponding to expected Key Tag queries. During a rollover from
key tag 1111 (hex) to key tag 2222 (hex), the zone could include the Key Tag 1111 (hex) to Key Tag 2222 (hex), the zone could include the
following records: following records:
_ta-1111 IN NULL \# 0 _ta-1111 IN NULL \# 0
_ta-2222 IN NULL \# 0 _ta-2222 IN NULL \# 0
_ta-1111-2222 IN NULL \# 0 _ta-1111-2222 IN NULL \# 0
Recall that when multiple key tags are present, the originating Recall that when multiple Key Tags are present, the originating
client MUST sort them from smallest to largest in the query name. client MUST sort them from smallest to largest in the query name.
6. IANA Considerations 6. IANA Considerations
The IANA is directed to assign an EDNS0 option code for the edns-key- IANA has assigned an EDNS0 option code for the edns-key-tag option in
tag option from the DNS EDNS0 Option Codes (OPT) registry as follows: the "DNS EDNS0 Option Codes (OPT)" registry as follows:
+-------+--------------+----------+-----------------+ +-------+--------------+----------+-----------+
| Value | Name | Status | Reference | | Value | Name | Status | Reference |
+-------+--------------+----------+-----------------+ +-------+--------------+----------+-----------+
| [TBA] | edns-key-tag | Optional | [This document] | | 14 | edns-key-tag | Optional | RFC 8145 |
+-------+--------------+----------+-----------------+ +-------+--------------+----------+-----------+
7. Security Considerations 7. Security Considerations
This document specifies a way for a client to signal its trust anchor This document specifies two ways for a client to signal its
knowledge to a cache or server. The goal of these optional trust anchor knowledge to a cache or server. The goal of these
mechanisms is to signal new trust anchor uptake in clients to allow optional mechanisms is to signal new trust anchor uptake in clients
zone administrators to know when it is possible to complete a key to allow zone administrators to know when it is possible to complete
rollover in a DNSSEC-signed zone. a key rollover in a DNSSEC-signed zone.
There is a possibility that an eavesdropper or server could infer the There is a possibility that an eavesdropper or server could infer the
validator in use by a client by the Key Tag list seen. This may validator in use by a client by the Key Tag list seen. This may
allow an attacker to find validators using old, possibly broken, allow an attacker to find validators using old, possibly broken,
keys. It could also be used to identify the validator or narrow down keys. It could also be used to identify the validator or to narrow
the possible validator implementations in use by a client, which down the possible validator implementations in use by a client; the
could have a known vulnerability that could be exploited by the validator used by the client could have a known vulnerability that
attacker. could be exploited by the attacker.
Consumers of data collected from the mechanisms are advised that Consumers of data collected from the mechanisms described in this
provided Key Tag values might be "made up" by some DNS clients with document are advised that provided Key Tag values might be "made up"
malicious or at least mischievous intentions. For example, an by some DNS clients with malicious, or at least mischievous,
attacker with sufficient resources might try to generate large intentions. For example, an attacker with sufficient resources might
numbers of queries including only old Key Tag values, with the try to generate large numbers of queries including only old Key Tag
intention of delaying the completion of a key rollover. values, with the intention of delaying the completion of a key
rollover.
DNSSEC does not require keys in a zone to have unique Key Tags. DNSSEC does not require keys in a zone to have unique Key Tags.
During a rollover there is a small possibility that an old key and a During a rollover, there is a small possibility that an old key and a
new key will have identical Key Tag values. Zone operators relying new key will have identical Key Tag values. Zone operators relying
on the edns-key-tag mechanism SHOULD take care to ensure that new on the edns-key-tag mechanism SHOULD take care to ensure that new
keys have unique Key Tag values. keys have unique Key Tag values.
8. Privacy Considerations 8. Privacy Considerations
This proposal adds additional, optional "signaling" to DNS queries in This proposal provides additional, optional "signaling" to DNS
the form of Key Tag values. While Key Tag values themselves are not queries in the form of Key Tag values. While Key Tag values
considered private information, it may be possible for an themselves are not considered private information, it may be possible
eavesdropper to use Key Tag values as a fingerprinting technique to for an eavesdropper to use Key Tag values as a fingerprinting
identify particular DNS validating clients. This may be especially technique to identify particular validating DNS clients. This may be
true if the validator is configured with trust anchor for zones in especially true if the validator is configured with trust anchors for
addition to the root zone. zones in addition to the root zone.
A validating resolver need not transmit the key tags in every A validating resolver need not transmit the Key Tags in every
applicable query. Due to privacy concerns, such a resolver MAY applicable query. Due to privacy concerns, such a resolver MAY
choose to transmit the key tags for a subset of queries (e.g., every choose to transmit the Key Tags for a subset of queries (e.g., every
25th time), or by random chance with a certain probability (e.g., 25th time) or by random chance with a certain probability (e.g., 5%).
5%).
Implementations of this specification MAY be administratively Implementations of this specification MAY be administratively
configured to only transmit the key tags for certain zones. For configured to only transmit the Key Tags for certain zones. For
example, the software's configuration file may specify a list of example, the software's configuration file may specify a list of
zones for which use of the mechanisms described here is allowed or zones for which the use of the mechanisms described here is allowed
denied. Since the primary motivation for this specification is to or denied. Since the primary motivation for this specification is to
provide operational measurement data for root zone key rollovers, it provide operational measurement data for root zone key rollovers, it
is RECOMMENDED that implementations at least include the edns-key-tag is RECOMMENDED that implementations at least include the edns-key-tag
option for root zone DNSKEY queries. option for root zone DNSKEY queries.
9. Acknowledgments 9. References
This document was inspired by and borrows heavily from [RFC6975] by
Scott Rose and Steve Crocker. The authors would like to thank Mark
Andrews, Casey Deccio, Burt Kalisky, Bob Harold, Edward Lewis, Tim
Wicinski, Suzanne Woolf, and other members of the dnsop working group
for their input.
10. References
10.1. Normative References 9.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>. November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 11, line 46 skipping to change at page 12, line 20
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<http://www.rfc-editor.org/info/rfc4035>. <http://www.rfc-editor.org/info/rfc4035>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013, DOI 10.17487/RFC6891, April 2013,
<http://www.rfc-editor.org/info/rfc6891>. <http://www.rfc-editor.org/info/rfc6891>.
10.2. Informative References 9.2. Informative References
[draft-ietf-dnsop-nsec-aggressiveuse] [NSEC-NSEC3-Usage]
Fujiwara, K., "Aggressive use of NSEC/NSEC3", 2016. Fujiwara, K., Kato, A., and W. Kumari, "Aggressive use of
DNSSEC-validated Cache", Work in Progress,
draft-ietf-dnsop-nsec-aggressiveuse-09, March 2017.
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC) [RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011, Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
September 2007, <http://www.rfc-editor.org/info/rfc5011>. September 2007, <http://www.rfc-editor.org/info/rfc5011>.
[RFC6975] Crocker, S. and S. Rose, "Signaling Cryptographic [RFC6975] Crocker, S. and S. Rose, "Signaling Cryptographic
Algorithm Understanding in DNS Security Extensions Algorithm Understanding in DNS Security Extensions
(DNSSEC)", RFC 6975, DOI 10.17487/RFC6975, July 2013, (DNSSEC)", RFC 6975, DOI 10.17487/RFC6975, July 2013,
<http://www.rfc-editor.org/info/rfc6975>. <http://www.rfc-editor.org/info/rfc6975>.
Acknowledgments
This document was inspired by and borrows heavily from [RFC6975] by
Scott Rose and Steve Crocker. The authors would like to thank Mark
Andrews, Casey Deccio, Burt Kalisky, Bob Harold, Edward Lewis, Tim
Wicinski, Suzanne Woolf, and other members of the DNSOP Working Group
for their input.
Authors' Addresses Authors' Addresses
Duane Wessels Duane Wessels
Verisign Verisign
12061 Bluemont Way 12061 Bluemont Way
Reston, VA 20190 Reston, VA 20190
United States United States of America
Phone: +1 703 948-3200 Phone: +1 703 948-3200
Email: dwessels@verisign.com Email: dwessels@verisign.com
URI: http://verisigninc.com URI: http://verisigninc.com
Warren Kumari Warren Kumari
Google Google
1600 Amphitheatre Parkway 1600 Amphitheatre Parkway
Mountain View, CA 94043 Mountain View, CA 94043
United States United States of America
Email: warren@kumari.net Email: warren@kumari.net
Paul Hoffman Paul Hoffman
ICANN ICANN
Email: paul.hoffman@icann.org Email: paul.hoffman@icann.org
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