Internet DRAFT - draft-jabley-dnsop-bootstrap-validator
draft-jabley-dnsop-bootstrap-validator
Network Working Group J. Abley
Internet-Draft Afilias
Intended status: Best Current Practice D. Knight
Expires: September 20, 2018 Neustar
March 19, 2018
Establishing an Appropriate Root Zone DNSSEC Trust Anchor at Startup
draft-jabley-dnsop-bootstrap-validator-00
Abstract
Domain Name System Security Extensions (DNSSEC) allow cryptographic
signatures to be used to validate responses received from the Domain
Name System (DNS). A DNS client which validates such signatures is
known as a validator.
The choice of appropriate root zone trust anchor for a validator is
expected to vary over time as the corresponding cryptographic keys
used in DNSSEC are changed.
This document provides guidance on how validators might determine an
appropriate trust anchor for the root zone to use at start-up, or
when other mechanisms intended to allow key rollover to be tolerated
gracefully are not available.
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 September 20, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Summary of Approach . . . . . . . . . . . . . . . . . . . . . 4
3.1. Initial State . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Trust Anchor Retrieval . . . . . . . . . . . . . . . . . 4
3.3. Trust Anchor Selection . . . . . . . . . . . . . . . . . 4
3.4. Full Operation . . . . . . . . . . . . . . . . . . . . . 4
4. Timing Considerations . . . . . . . . . . . . . . . . . . . . 4
5. Retrieval of Candidate Trust Anchors . . . . . . . . . . . . 5
5.1. Retrieval of Trust Anchors from Local Sources . . . . . . 5
5.2. Retrieval of Trust Anchors from the DNS . . . . . . . . . 5
5.3. Retrieval of Trust Anchors from the Root Zone
KSK Manager . . . . . . . . . . . . . . . . . . . . . . . 5
6. Establishing Trust in Candidate Trust Anchors . . . . . . . . 6
7. Failure to Locate a Valid Trust Anchor . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Appendix B. Editorial Notes . . . . . . . . . . . . . . . . . . 8
B.1. Discussion . . . . . . . . . . . . . . . . . . . . . . . 8
B.2. Change History . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Definitions
The terms Key Signing Key (KSK) and Trust Anchor are used as defined
in [RFC4033].
The term Validator is used in this document to mean a Validating
Security-Aware Stub Resolver, as defined in [RFC4033].
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2. Introduction
The Domain Name System (DNS) is described in [RFC1034] and [RFC1035].
DNS Security Extensions (DNSSEC) are described in [RFC4033],
[RFC4034] and [RFC4035].
The root zone of the DNS was signed using DNSSEC in July 2011, and
many top-level domain registries have since signed their zones,
installing secure delegations for them in the root zone. A single
trust anchor for the root zone is hence increasingly sufficient for
validators.
Validators are deployed in a variety of environments, and there is
variation in the amount of system administration that might
reasonably be expected to be available. For example, embedded
devices might never be administered by a human operator, whereas
validators deployed on general-purpose operating systems in
enterprise networks might have technical staff available to assist
with their configuration.
This document includes descriptions of mechanisms for validator
bootstrapping, intended to be sufficient for embedded devices. The
implementation of those mechanisms might be automatic in the case of
unattended devices, or manual, carried out by a systems
administrator, depending on local circumstances.
The choice of appropriate trust anchor for a DNSSEC Validator is
expected to vary over time as the corresponding KSK used in the root
zone is changed. The DNSSEC Policy and Practice Statement (DPS) for
the root zone KSK maintainer [KSK-DPS] specifies that scheduled KSK
rollover will be undertaken according to the semantics specified in
[RFC5011]. Validators which are able to recognise and accommodate
those semantics should need no additional support to be able to
maintain an appropriate trust anchor over a root zone KSK rollover
event.
The possibility remains, however, that [RFC5011] signalling will not
be available to a validator: e.g. certain classes of emergency KSK
rollover may require a compromised KSK to be discarded more quickly
than [RFC5011] specifies, or a validator might be off-line over the
whole key-roll event.
This document provides guidance on how DNSSEC Validators might
determine an appropriate set of trust anchors to use at start-up, or
when other mechanisms intended to allow key rollover to be tolerated
gracefully are not available.
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The bootstrapping procedures described in this document are also
expected to be useful for a deployed, running validator which is not
able to accommodate a KSK roll using [RFC5011] signalling.
3. Summary of Approach
A validator that has no valid trust anchor initialises itself as
follows.
3.1. Initial State
A validator in its initial state is capable of sending and receiving
DNS queries and responses, but is not capable of validating
signatures received in responses.
A validator must confirm that its local clock is sufficiently
accurate before trust anchors can be established, and before
processing of DNSSEC signatures can proceed. Discussion of timing
considerations can be found in Section 4.
3.2. Trust Anchor Retrieval
Once the local clock has been synchronised, a validator may proceed
to gather candidate trust anchors for consideration. Discussion of
trust anchor retrieval can be found in Section 5.
3.3. Trust Anchor Selection
Once a set of candidate trust anchors has been obtained, a validator
attempts to find one trust anchor in the set which is appropriate for
use. This process involves verification of cryptographic signatures,
and is discussed in Section 6.
3.4. Full Operation
The validator now has an accurate trust anchor for the root zone, and
is capable of validating signatures on responses from the DNS.
4. Timing Considerations
DNSSEC signatures are valid for particular periods of time, as
specified by the administrator of the zone containing the signatures.
It follows that any validator must maintain an accurate local clock
in order to verify that signatures are accurate.
Trust anchors correspond to KSKs in particular zones. Zone
administrators may choose to replace KSKs from time to time, e.g. due
to a key compromise or local key management policy, and the
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corresponding appropriate choice in trust anchor will change as KSKs
are replaced.
Trust anchors for the root zone in particular are published with
intended validity periods, as discussed in Section 5. A validator
making use of such trust anchors also requires an accurate local
clock in order to avoid configuring a local trust anchor which
corresponds to an old key.
Validators should take appropriate steps to ensure that their local
clocks are set with sufficient accuracy, and in the case where local
clocks are set with reference to external time sources over a network
[RFC5905] that the time information received from those sources is
authentic.
5. Retrieval of Candidate Trust Anchors
Candidate trust anchors may be retrieved using several mechanisms.
The process of gaining trust in particular candidate trust anchors
before using them is discussed in Section 6.
5.1. Retrieval of Trust Anchors from Local Sources
A trust anchor which is packaged with validator software can never be
trusted, since the corresponding root zone KSK may have rolled since
the software was packaged, and the trust anchor may be derived from a
root zone KSK that was retired due to compromise.
Validators should never use local trust anchors for bootstrapping.
5.2. Retrieval of Trust Anchors from the DNS
The current root zone trust anchor is a hash (in DS RDATA format) of
a member of the root zone apex DNSKEY RRSet that has the SEP bit set.
Such a trust anchor could be derived from a response to the query ".
IN DNSKEY?", but there is no mechanism available to trust the result:
without an existing, accurate trust anchor the validator has no means
to gauge the authenticity of the response.
Validators should never derive trust anchors from DNSKEY RRSets
obtained from the DNS.
5.3. Retrieval of Trust Anchors from the Root Zone KSK Manager
The Root Zone KSK Manager publishes trust anchors corresponding to
the root zone KSK as described in [RFC7958].
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A full history of previously-published trust anchors, including the
trust anchor recommended for immediate use, is made available in an
XML document at the following stable URLs:
o <http://data.iana.org/root-anchors/root-anchors.xml>
o <https://data.iana.org/root-anchors/root-anchors.xml>
Validity periods for each trust anchor packaged in the root-
anchors.xml document are provided as XML attributes, allowing an
appropriate trust anchor for immediate use to be identified (but see
Section 4).
Individual trust anchors are also packaged as X.509 identity
certificates, signed by various Certificate Authorities (CAs). URLs
to allow those certificates to be retrieved are included as optional
elements in the XML document.
For automatic bootstrapping, the recommended approach is as follows.
1. Retrieve <http://data.iana.org/root-anchors/root-anchors.xml>
2. Identify the trust anchors which are valid for current use, with
reference to the current time and date.
3. Retrieve the corresponding X.509 identity certificates for the
key identified in the previous step, for use in establishing
trust in the retrieved trust anchor (see Section 6).
6. Establishing Trust in Candidate Trust Anchors
Once a candidate trust anchor has been retrieved, the validator must
establish that it is authentic before it can be used. This document
recommends that this be carried out by checking the signatures on
each of the X.509 identity certificates retrieved in the previous
step until a certificate is found which matches a CA trust anchor.
This verification phase requires that validators ship with a useful
set of CA trust anchors, and that corresponding identity certificates
are published by the root zone KSK manager. In some cases validator
implementors may decide to use commercial CA services, perhaps a
subset of the "browser list" that is commonly distributed with web
browsers; alternatively a vendor may instantiate its own CA and make
arrangements with the root zone KSK manager to have the corresponding
identity certificate locations published in root-anchors.xml.
The CA trust anchors packaged with validators should have an expected
lifetime in excess of the anticipated life of the validator. As a
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protection against CA failure, validators are recommended to ship
with more than one CA trust anchor.
7. Failure to Locate a Valid Trust Anchor
A validator that has failed to locate a valid trust anchor may re-try
the retrieval and trust establishment phases indefinitely, but must
not perform validation on DNS responses until a valid trust anchor
has been identified.
8. IANA Considerations
This document has no IANA actions.
9. Security Considerations
This document discusses an approach for automatic configuration of
trust anchors in a DNSSEC validator.
10. References
10.1. Normative References
[KSK-DPS] Ljunggren, F., Okubo, T., Lamb, R., and J. Schlyter,
"DNSSEC Practice Statement for the Root Zone KSK
Operator", May 2010.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[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>.
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[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>.
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
September 2007, <https://www.rfc-editor.org/info/rfc5011>.
[RFC7958] Abley, J., Schlyter, J., Bailey, G., and P. Hoffman,
"DNSSEC Trust Anchor Publication for the Root Zone",
RFC 7958, DOI 10.17487/RFC7958, August 2016,
<https://www.rfc-editor.org/info/rfc7958>.
10.2. Informative References
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
Appendix A. Acknowledgements
This document contains material first discussed at VeriSign and ICANN
during the deployment of DNSSEC in the root zone, and also draws upon
subsequent technical discussion from public mailing lists. The
contributions of all those who voiced opinions are acknowledged.
Appendix B. Editorial Notes
This section (and sub-sections) to be removed prior to publication.
B.1. Discussion
This is not a working group document. However, the topics discussed
in this document are consistent with the general subject area of the
DNSOP working group, and discussion of this document could reasonably
take place on the dnsop mailing list.
B.2. Change History
draft-jabley-dnsop-validator-bootstrap-00 Initial draft.
draft-jabley-dnsop-bootstrap-validator-00 Resurrected in response to
observed root zone KSK rollover hilarity. References updated,
slightly. Authors' contact information updated. Document name
changed to be arbitrarily different from previous, expired draft
in order to avoid zombie jokes.
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Authors' Addresses
Joe Abley
Afilias
300-184 York Street
London, ON N6A 1B5
Canada
Phone: +1 519 670 9327
Email: jabley@afilias.info
Dave Knight
Neustar
300-184 York Street
London, ON N6A 1B5
Canada
Email: dave.knight@team.neustar
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