Ensuring CDS/CDNSKEY Consistency is Mandatory
draft-thomassen-dnsop-cds-consistency-00

DNSOP Working Group                                         P. Thomassen
Internet-Draft                         deSEC, Secure Systems Engineering
Updates: 7344 (if approved)                                  9 July 2022
Intended status: Standards Track                                        
Expires: 10 January 2023

             Ensuring CDS/CDNSKEY Consistency is Mandatory
                draft-thomassen-dnsop-cds-consistency-00

Abstract

   For maintaining DNSSEC Delegation Trust, DS records have to be kept
   up to date.  [RFC7344] automates this by having the child publish CDS
   and/or CDNSKEY records which hold the prospective DS parameters.
   Parent-side entities (e.g.  Registries, Registrars) can use these
   records to update the delegation's DS records.  A common method for
   detecting changes in CDS/CDNSKEY record sets is to query them
   periodically from the child zone ("polling"), as described in
   Section 6.1 of [RFC7344].

   This document specifies that if polling is used, parent-side entities
   MUST ensure that CDS/CDNSKEY record sets are equivalent across all of
   the child's authoritative nameservers, before taking any action based
   on these records.

Status of This Memo

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   This Internet-Draft will expire on 10 January 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Notation . . . . . . . . . . . . . . . . . .   3
   2.  Polling a CDS or CDNSKEY Record Set . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Appendix A.  Change History (to be removed before publication)  .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   [RFC7344] automates DNSSEC delegation trust maintenance by having the
   child publish CDS and/or CDNSKEY records which hold the prospective
   DS parameters.  Parent-side entities (e.g.  Registries, Registrars)
   can use these records to update the delegation's DS records.  A
   common method for detecting changes in CDS/CDNSKEY record sets is to
   query them periodically from the child zone ("polling"), as described
   in Section 6.1 of [RFC7344].

   While [RFC7344] does specify acceptance rules (Section 4.1 ) for CDS/
   CDNSKEY records that have been retrieved, it does not mention how
   specifically the poll queries should be done.  A naive implementation
   would thus be likely to simply query CDS or CDNSKEY records through a
   trusted validating resolver, and use the validated answer.

   This may be fine if all authoritative nameservers are controlled by
   the same entity (= DNS operator).  However, it poses a problem in
   conjunction with multi-signer setups ([RFC8901]): When the CDS/
   CDNSKEY are retrieved "normally" using a validating resolver, chances
   are that records are retrieved from one nameserver only, without
   checking for consistency across other NS hostnames.

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   In a multi-signer setup, this means that a single provider could
   (accidentally or maliciously) roll the DS record set at the parent.
   For example, a provider could be performing a key rollover and then
   accidentally publish CDS/CDNSKEY records for its own keys.  As a
   result, when the parent happens to retrieve the records from a
   nameserver controlled by this provider, the other providers' DS
   records would be removed from the parent, breaking the zone for some
   or all queries.

   A single provider should not be in the position to remove the other
   providers' trust anchors.  To address this issue, this document
   specifies that if polling is used, parent-side entities MUST ensure
   that CDS/CDNSKEY record sets are equivalent across all of the child's
   authoritative nameservers, before taking any action based on these
   records.

   Readers are expected to be familiar with DNSSEC, including [RFC4033],
   [RFC4034], [RFC4035], [RFC6781], [RFC7344], and [RFC8901].

1.1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Polling a CDS or CDNSKEY Record Set

   The terminology in this section is as defined in [RFC7344].

   To retrieve a Child's CDS/CDNSKEY RRset for DNSSEC delegation trust
   maintenance, the Parental Agent, knowing both the Child zone name and
   its NS hostnames, MUST ascertain that queries are made against all of
   the nameservers listed in the Child's delegation from the Parent, and
   ensure that the set of referenced keys is equal.

   In other words, CDS/CDNSKEY records at the Child zone apex MUST be
   queried directly from each of the authoritative servers as determined
   by the delegation's NS record set, with DNSSEC validation enforced.
   When a key is referenced in the CDS or CDNSKEY record set returned by
   one nameserver, but not referenced in the corresponding answers of
   all of the other nameservers, the CDS/CDNSKEY state MUST be
   considered inconsistent.

   If an inconsistent CDS/CDNSKEY state is encountered, the Parental
   Agent MUST take no action.  Specifically, it MUST NOT delete or alter
   the existing DS RRset.

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3.  Security Considerations

   The level of rigor mandated by this document is needed to prevent
   publication of a half-baked DS RRset (authorized only under a subset
   of NS hostnames).  This ensures, for example, that an operator in a
   multi-homed setup cannot unilaterally remove another operator's trust
   anchor from the delegation's DS records.

   As a consequence, DS records can only be modified when there is
   consensus across all operators.

4.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.

   [RFC6781]  Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
              Operational Practices, Version 2", RFC 6781,
              DOI 10.17487/RFC6781, December 2012,
              <https://www.rfc-editor.org/info/rfc6781>.

   [RFC7344]  Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
              DNSSEC Delegation Trust Maintenance", RFC 7344,
              DOI 10.17487/RFC7344, September 2014,
              <https://www.rfc-editor.org/info/rfc7344>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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   [RFC8901]  Huque, S., Aras, P., Dickinson, J., Vcelak, J., and D.
              Blacka, "Multi-Signer DNSSEC Models", RFC 8901,
              DOI 10.17487/RFC8901, September 2020,
              <https://www.rfc-editor.org/info/rfc8901>.

Appendix A.  Change History (to be removed before publication)

   *  draft-thomassen-dnsop-cds-consistency-00

   |  Initial public draft.

Author's Address

   Peter Thomassen
   deSEC, Secure Systems Engineering
   Berlin
   Germany
   Email: peter@desec.io

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