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Managing DS records from parent via CDS/CDNSKEY

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8078.
Authors Ólafur Guðmundsson , Paul Wouters
Last updated 2015-12-14
Replaces draft-ogud-dnsop-maintain-ds
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state WG Document
Document shepherd Tim Wicinski
IESG IESG state Became RFC 8078 (Proposed Standard)
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Send notices to "Tim Wicinski" <>
dnsop                                                     O. Gudmundsson
Internet-Draft                                                CloudFlare
Intended status: Informational                                P. Wouters
Expires: June 16, 2016                                           Red Hat
                                                       December 14, 2015

            Managing DS records from parent via CDS/CDNSKEY


   RFC7344 specifies how DNS trust can be maintained in-band between
   parent and child.  There are two features missing in that
   specification: initial trust setup and removal of trust anchor.  This
   document addresses both these omissions.

   Changing a domain's DNSSEC status can be a complicated matter
   involving many parties.  Some of these parties, such as the DNS
   operator, might not even be known by all organisations involved.  The
   inability to enable or disable DNSSEC via in-band signalling is seen
   as a problem or liability that prevents DNSSEC adoption at large
   scale.  This document adds a method for in-band signalling of DNSSEC
   status changes.

   Initial trust is considered a much harder problem, this document will
   seek to clarify and simplify the initial acceptance policy.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 16, 2016.

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Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Removing DS . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Introducing DS  . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.4.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  The Three Uses of CDS . . . . . . . . . . . . . . . . . . . .   4
     2.1.  The meaning of CDS ?  . . . . . . . . . . . . . . . . . .   4
   3.  Enabling DNSSEC via CDS/CDNSKEY . . . . . . . . . . . . . . .   5
     3.1.  Accept policy via authenticated channel . . . . . . . . .   5
     3.2.  Accept with extra checks  . . . . . . . . . . . . . . . .   5
     3.3.  Accept after delay  . . . . . . . . . . . . . . . . . . .   5
     3.4.  Accept with challenge . . . . . . . . . . . . . . . . . .   6
   4.  DNSSEC Delete Algorithm . . . . . . . . . . . . . . . . . . .   6
   5.  Security considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   CDS/CDNSKEY [RFC7344] records are used to signal changes in trust
   anchors, this is a great way to maintain delegations when the DNS
   operator has no other way to inform the parent that changes are
   needed.  RFC7344 contains no "delete" signal for the child to tell
   the parent that it wants to change the DNSSEC security of its domain.

   [RFC7344] punted the Initial Trust establishment question and left it
   to each parent to come up with an acceptance policy.

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1.1.  Removing DS

   This document introduces the delete option for both CDS and CDNSKEY.
   to allow a child to signal the parent to turn off DNSSEC.  When a
   domain is moved from one DNS operator to another one, sometimes it is
   necessary to turn off DNSSEC to facilitate the change of DNS
   operator.  Common scenarios include:

   1  moving from a DNSSEC operator to a non-DNSSEC capable one or one
      that does not support the same algorithms as the old one.

   2  moving to one that cannot/does-not-want to do a proper DNSSEC

   3  the domain holder does not want DNSSEC.

   4  when moving between two DNS operators that use disjoint sets of
      algorithms to sign the zone, thus algorithm roll can not be

   Whatever the reason, the lack of a "remove my DNSSEC" option is
   turning into the latest excuse as why DNSSEC cannot be deployed.

   Turing off DNSSEC reduces the security of the domain and thus should
   only be done carefully, and that decision should be fully under the
   child domain's control.

1.2.  Introducing DS

   The converse issue is how does a child domain instruct the parent it
   wants to have a DS record added.  This problem is not as hard as many
   have assumed, given a few simplifying assumptions.  This document
   makes the assumption that there are reasonable policies that can be
   applied and will allow automation of trust introduction.

   Not being able to enable trust via an easily automated mechanism is
   hindering DNSSEC at scale by anyone that does not have automated
   access to its parent's "registry".

1.3.  Notation

   When this document uses the word CDS it implies that the same applies
   to CDNSKEY and vice versa, the only difference between the two
   records is how information is represented.

   When the document uses the word "parent" it implies an entity that is
   authorized to insert into parent zone information about this child
   domain.  Which entity this is exactly does not matter.  It could be

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   the Registrar or Reseller that the child domain was purchased from.
   It could be the Registry that the domain is registered in when
   allowed.  It could be some other entity when the RRR framework is not

   We use RRR to mean Registry Registrar Reseller in the context of DNS
   domain markets.

1.4.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  The Three Uses of CDS

   In general there are three operations that a domain wants to
   influence on its parent:

   1  Roll over KSK, this means updating the DS records in the parent to
      reflect the new set of KSK's at the child.  This could be an ADD
      operation, a Delete operation on one or more records while keeping
      at least one DS RR, or a full Replace operation

   2  Turn off DNSSEC validation, i.e. delete all the DS records

   3  Enable DNSSEC validation, i.e. place initial DS RRset in the

   Operation 1 is covered in [RFC7344], operations 2 and 3 are defined
   in this document.  In many people's minds, those two later operations
   carry more risk than the first one.  This document argues that 2 is
   identical to 1 and the final one is different (but not that

2.1.  The meaning of CDS ?

   The fundamental question is what is the semantic meaning of
   publishing a CDS RRset in a zone?  We offer the following

   "Publishing a CDS or CDNSKEY record signifies to the parent that the
   child is ready for the corresponding DS records to be synchronized.
   Every parent or parental agent should have an acceptance policy of
   these records for the three different use cases involved: Initial DS
   publication, Key rollover, and Returning to Insecure."

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   In short, the CDS RRset is an instruction to the parent to modify DS
   RRset if the CDS and DS RRsets differ.  The acceptance policy for CDS
   in the rollover case is "seeing" according to [RFC7344].  The
   acceptance policy in the Delete case is just seeing a CDS RRset with
   the delete operation specified in this document.

3.  Enabling DNSSEC via CDS/CDNSKEY

   There are number of different models for managing initial trust, but
   in the general case, the child wants to enable global validation for
   the future.  Thus during the period from the time the child publishes
   the CDS until the corresponding DS is published is the period that
   DNS answers for the child could be forged.  The goal is to keep this
   period as short as possible.

   One important case is how a 3rd party DNS operator can upload its
   DNSSEC information to the parent, so the parent can publish a DS
   record for the child.  In this case there is a possibility of setting
   up some kind of authentication mechanism and submission mechanism
   that is outside the scope of this document.

   Below are some policies that parents can use.  These policies assume
   that the notifications are can be authenticated and/or identified.

3.1.  Accept policy via authenticated channel

   In this case the parent is notified via UI/API that CDS exists, the
   parent retrieves the CDS and inserts the DS record as requested, if
   the request comes over an authenticated channel.

3.2.  Accept with extra checks

   In this case the parent checks that the source of the notification is
   allowed to request the DS insertion.  The checks could include
   whether this is a trusted entity, whether the nameservers correspond
   to the requestor, whether there have been any changes in registration
   in the last few days, etc, or the parent can send a notification
   requesting an confirmation.

   The end result is that the CDS is accepted at the end of the checks
   or when the out-of-band confirmation is received.

3.3.  Accept after delay

   In this case, if the parent deems the request valid, it starts
   monitoring the CDS records at the child nameservers over period of
   time to make sure nothing changes.  After number of checks,

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   preferably from different vantage points, the parent accepts the CDS
   records as a valid signal to update.

3.4.  Accept with challenge

   In this case the parent instructs the requestor to insert some record
   into the child domain to prove it has the ability to do so (i.e., it
   is the operator of the zone).

4.  DNSSEC Delete Algorithm

   The DNSKEY algorithm registry contains two reserved values: 0 and
   255[RFC4034].  The CERT record [RFC4398] defines the value 0 to mean
   the algorithm in the CERT record is not defined in DNSSEC.

   [rfc-editor remove before publication] For this reason, using the
   value 0 in CDS/CDNSKEY delete operations is potentially problematic,
   but we propose that here anyway as the risk is minimal.  The
   alternative is to reserve one DNSSEC algorithm number for this
   purpose.  [rfc-editor end remove]

   Right now, no DNSSEC validator understands algorithm 0 as a valid
   signature algorithm, thus if the validator sees a DNSKEY or DS record
   with this value, it will treat it as unknown.  Accordingly, the zone
   is treated as unsigned unless there are other algorithms present.

   In the context of CDS and CDNSKEY records, DNSSEC algorithm 0 is
   defined and means the entire DS set MUST be removed.  The contents of
   the records MUST contain only the fixed fields as show below.

   1  CDS 0 0 0

   2  CDNSKEY 0 3 0

   There is no keying material payload in the records, just the command
   to delete all DS records.  This record is signed in the same way as
   CDS/CDNSKEY is signed.

   Strictly speaking the CDS record could be "CDS X 0 X" as only the
   DNSKEY algorithm is what signals the delete operation, but for
   clarity the "0 0 0" notation is mandated, this is not a definition of
   DS Digest algorithm 0.  Same argument applies to "CDNSKEY 0 3 0".

   Once the parent has verified the CDS/CDNSKEY record and it has passed
   other acceptance tests, the DS record MUST be removed.  At this point
   the child can start the process of turning DNSSEC off.

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5.  Security considerations

   This document is about avoiding validation failures when a domain
   moves from one DNS operator to another one.  Turing off DNSSEC
   reduces the security of the domain and thus should only be done as a
   last resort.

   In most cases it is preferable that operators collaborate on the
   rollover by doing a KSK+ZSK rollover as part of the handoff, but that
   is not always possible.  This document addresses the case where
   unsigned state is needed.

   Users SHOULD keep in mind that re-establishing trust in delegation
   can be hard and take a long time thus before going to unsigned all
   options SHOULD be considered.

   A parent should ensure that when it is allowing a child to become
   securely delegated, that it has a reasonable assurance that the CDS/
   CDNSKEY that is used to bootstrap the security on is visible from a
   geographically and network topology diverse view.  It should also
   ensure the the zone would validate if the parent published the DS
   record.  A parent zone might also consider sending an email to its
   contact addresses to give the child a warning that security will be
   enabled after a certain about of wait time - thus allowing a child
   administrator to cancel the request.

   This document does not introduce any new problems, but like Negative
   Trust Anchor[RFC7646], it addresses operational reality.

6.  IANA considerations

   This document updates the following IANA registries: "DNS Security
   Algorithm Numbers"

   Algorithm 0 adds a reference to this document.

7.  References

7.1.  Normative References

   [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,

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   [RFC7344]  Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
              DNSSEC Delegation Trust Maintenance", RFC 7344, DOI
              10.17487/RFC7344, September 2014,

7.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,

   [RFC4398]  Josefsson, S., "Storing Certificates in the Domain Name
              System (DNS)", RFC 4398, DOI 10.17487/RFC4398, March 2006,

   [RFC7646]  Ebersman, P., Kumari, W., Griffiths, C., Livingood, J.,
              and R. Weber, "Definition and Use of DNSSEC Negative Trust
              Anchors", RFC 7646, DOI 10.17487/RFC7646, September 2015,

Appendix A.  Acknowledgements

   This document is generated using the mmark tool that Miek Gieben has

Authors' Addresses

   Olafur Gudmundsson


   Paul Wouters
   Red Hat


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