Internet DRAFT - draft-huston-kskroll-sentinel
draft-huston-kskroll-sentinel
DNSOP G. Huston
Internet-Draft J. Damas
Intended status: Standards Track APNIC
Expires: May 18, 2018 W. Kumari
Google
November 14, 2017
A Sentinel for Detecting Trusted Keys in DNSSEC
draft-huston-kskroll-sentinel-04.txt
Abstract
The DNS Security Extensions (DNSSEC) were developed to provide origin
authentication and integrity protection for DNS data by using digital
signatures. These digital signatures can be verified by building 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
will allow an end user to determine the trusted key state of the
resolvers that handle the user's DNS queries.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 18, 2018.
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Copyright (c) 2017 IETF Trust and the persons identified as the
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Sentinel Mechanism . . . . . . . . . . . . . . . . . . . . . 3
3. Sentinel Processing . . . . . . . . . . . . . . . . . . . . . 4
4. Sentinel Test Result Considerations . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and
[RFC4035] were developed to provide origin authentication and
integrity protection for DNS data by using digital signatures.
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
from the RDATA portion of a DNSKEY RR using a formula not unlike 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.
This document specifies how validating resolvers can respond to
certain queries in a manner that allows a querier to deduce whether a
particular key has been loaded into that resolver's trusted key
store. In particular, this response mechanism can be 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.
This new mechanism is OPTIONAL to implement and use, although for
reasons of supporting broad-based measurement techniques, it is
strongly preferred if configurations of DNSSEC-validating resolvers
enabled this mechanism by default, allowing for configuration
directives to disable this mechanism if desired.
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1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
2. Sentinel Mechanism
DNSSEC-Validating resolvers that implement this mechanism MUST be
performing validation of responses in accordance with the DNSSEC
response validation specification [RFC4035].
This mechanism makes use of 2 special labels, "_is-ta-<tag-index>."
(Intended to be used in a query where the response can answer the
question: Is this the key tag a trust anchor which the validating DNS
resolver is currently trusting?) and "_not-ta-<tag-index>."
(Intended to be used in a query where the response can answer the
question: Is this the key tag of a key that is NOT in the resolver's
current trust store?). The use of the positive question and its
inverse allows for queries to detect whether resolvers support this
mechanism.
If the outcome of the DNS response validation process indicates that
the response is authentic, and if the left-most label of the original
query name matches the template "_is-ta-<tag-index>.", then the
following rule should be applied to the response: If the resolver has
placed a Root Zone Key Signing Key with tag index value matching the
value specified in the query into the local resolver's store of
trusted keys, then the resolver should return a response indicating
that the response contains authenticated data according to section
5.8 of [RFC6840]. Otherwise, the resolver MUST return RCODE 2
(server failure). Note that the <tag-index> is specified in the DNS
label using hex notation.
If the outcome of the DNS response validation process indicates that
the response is authentic, and if the left-most label of the qriginal
query name matches the template "_not-ta-<tag-index>.", then the
following rule should be applied to the response: If the resolver has
not placed a Root Zone Key Signing Key with tag index value matching
the value specified in the query into the local resolver's store of
trusted keys, then the resolver should return a response indicating
that the response contains authenticated data according to section
5.8 of [RFC6840]. Otherwise, the resolver MUST return RCODE 2
(server failure). Note that the <tag-index> is specified in the DNS
label using hex notation.
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If a query contains one instance of both of these query templates
then the resolver MUST NOT alter the outcome of the DNS response
validation process.
This mechanism is to be applied only by resolvers that perform DNSSEC
validation, and applies only to responses to an A or AAAA query
(Query Type value 1 or 28) where the resolver has authenticated the
response according to the DNSSEC validation process and where the
query name contains either of the labels described in this section.
In this case, the resolver is to perform an additional test following
the conventional validation function as described in this section.
The result of this test directs whether the resolver is to change an
authentic response to a response that indicates validation failure.
3. Sentinel Processing
This proposed test that uses the DNS resolver mechanism described in
this document is based on three DNS names that have three distinct
DNS resolution behaviours. The test is intended to allow a user to
determine the state of their DNS resolution system, and, in
particular, whether or not they are using validating DNS resolvers
that have picked up an incoming trust anchor in a key roll.
The name format can be defined in a number of ways, and no name form
is intrinsically better than any other in terms of the test itself.
The critical aspect of the DNS names used in any such test is that
they contain the specified label for either the positive and negative
test.
The sentinel process is envisaged to use a test with three names:
a. a name containing the left-most label "_is-ta-<tag-index>.".
This is a validly signed name so that responses about names in
this zone can be authenticated by a validating resolver.
b. a name containing the left-most label "_not-ta-<tag-index>.".
This is also a validly-signed name.
c. a third name that is signed with a DNSSEC signature that cannot
be validated.
The responses received from queries to resolve each of these names
would allow us to infer a trust key state of the resolution
environment.
o Vnew: A DNSSEC-Validating resolver that includes this mechanism
that has loaded the nominated key into its trusted key stash will
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respond with an A record response for "_is-ta", SERVFAIL for
"_not-ta" and SERVFAIL for the invalid name.
o Vold: A DNSSEC-Validating resolver that includes this mechanism
that has not loaded the nominated key into its trusted key stash
will respond with an SERVFAIL record for "_is-ta", an A record
response for "_not-ta" and SERVFAIL for the invalid name.
o Vleg: A DNSSEC-Validating resolver that does not include this
mechanism will respond with an A record response for "_is-ta", an
A record response for "_not-ta" and SERVFAIL for the invalid name.
o nonV: A non-DNSSEC-Validating resolver will respond with an A
record response for "_is-ta", an A record response for "_not-ta"
and an A record response for the invalid name.
Given the clear delineation amongst these three cases, if a client
directs these three queries to a simple resolver, the variation in
response to the three queries should allow the client to determine
the category of the resolver, and if it supports this mechanism,
whether or not it has loaded a particular key into its local trusted
key stash.
+-------------+----------+-----------+------------+
| Type\Query | _is-ta | _not-ta | invalid |
+-------------+----------+-----------+------------+
| Vnew | A | SERVFAIL | SERVFAIL |
| Vold | SERVFAIL | A | SERVFAIL |
| Vleg | A | A | SERVFAIL |
| nonV | A | A | A |
+-------------+----------+-----------+------------+
A Vnew response pattern says that the nominated key is trusted by the
resolver and has been loaded into its local trusted key stash. A
Vleg response pattern says that the nominated key is not yet trusted
by the resolver in its own right. A Vleg response is indeterminate,
and a nonV response indicates that the client does not have a
validating resolver.
4. Sentinel Test Result Considerations
The description in the previous section describes a simple situation
where the test queries were being passed to a single recursive
resolver that directly queried authoritative name servers, including
the root servers.
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There is also the common case where the end client is configured to
use multiple resolvers. In these cases the SERVFAIL responses from
one resolver will prompt the end client to repeat the query against
one of the other configured resolvers.
If any of the client's resolvers are non-validating resolvers, the
tests will result in the client reporting that it has a non-
validating DNS environment (nonV), which is effectively the case.
If all of the client resolvers are DNSSEC-validating resolvers, but
some do not support this trusted key mechanism, then the result will
be indeterminate with respect to trusted key status (Vleg).
Simlarly, if all the client's resolvers support this mechanism, but
some have loaded the key into the trusted key stash and some have
not, then the result is indeterminate (Vleg).
There is also the common case of a recursive resolver using a
forwarder.
If the resolver is non-validating, and it has a single forwarder
clause, then the resolver will presumably mirror the capabilities of
the forwarder target resolver. If this non-validating resolver it
has multiple forwarders, then the above considerations will apply.
If the validating resolver has a forwarding configuration, and uses
the CD flag on all forwarded queries, then this resolver is acting in
a manner that is identical to a standalone resolver. The same
consideration applies if any one one of the forwarder targets is a
non-validating resolver. Similarly, if all the forwarder targets do
not apply this trusted key mechanism, the same considerations apply.
A more complex case is where the following conditions all hold:
both the validating resolver and the forwarder target resolver
support this trusted key sentinel mechanism, and
the local resolver's queries do not carry the CD bit, and
the trusted key state differs between the forwarding resolver and
the forwarder target resolver
then either the outcome is indeterminate validating (Vleg), or a case
of mixed signals (SERVFAIL in all three responses), which is
similarly an indeterminate response with respect to the trusted key
state.
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5. Security Considerations
This document describes a mechanism to allow users to determine the
trust state of root zone key signing keys in the DNS resolution
system that they use.
The mechanism does not require resolvers to set otherwise
unauthenticated responses to be marked as authenticated, and does not
alter the security properties of DNSSEC with respect to the
interpretation of the authenticity of responses that are so marked.
The mechanism does not require any further significant processing of
DNS responses, and queries of the form described in this document do
not impose any additional load that could be exploited in an attack
over the the normal DNSSEC validation processing load.
6. IANA Considerations
[Note to IANA, to be removed prior to publication: there are no IANA
considerations stated in this version of the document.]
7. Acknowledgements
This document has borrowed extensively from RFC8145 for the
introductory text, and the authors would like to acknowledge and
thank the authors of that document both for some text excerpts and
for the more general stimulation of thoughts about monitoring the
progress of a roll of the Key Signing Key of the Root Zone of the
DNS.
8. References
8.1. Normative References
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC4034, March 2005,
<https://www.rfc-editor.org/info/rfc4034>.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<https://www.rfc-editor.org/info/rfc4035>.
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[RFC6840] Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and
Implementation Notes for DNS Security (DNSSEC)", RFC 6840,
DOI 10.17487/RFC6840, February 2013,
<https://www.rfc-editor.org/info/rfc6840>.
8.2. Informative References
[RFC8145] Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust
Anchor Knowledge in DNS Security Extensions (DNSSEC)",
RFC 8145, DOI 10.17487/RFC8145, April 2017,
<https://www.rfc-editor.org/info/rfc8145>.
Authors' Addresses
Geoff Huston
Email: gih@apnic.net
URI: http://www.apnic.net
Joao Silva Damas
Email: joao@apnic.net
URI: http://www.apnic.net
Warren Kumari
Email: warren@kumari.net
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