Automating DNSSEC Delegation Trust Maintenance
RFC 7344

Internet Engineering Task Force (IETF)                         W. Kumari
Request for Comments: 7344                                        Google
Category: Informational                                   O. Gudmundsson
ISSN: 2070-1721                                          OGUD Consulting
                                                              G. Barwood
                                                          September 2014

             Automating DNSSEC Delegation Trust Maintenance

Abstract

   This document describes a method to allow DNS Operators to more
   easily update DNSSEC Key Signing Keys using the DNS as a
   communication channel.  The technique described is aimed at
   delegations in which it is currently hard to move information from
   the Child to Parent.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   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/rfc7344.

Copyright Notice

   Copyright (c) 2014 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
   (http://trustee.ietf.org/license-info) 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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Requirements Notation . . . . . . . . . . . . . . . . . .   4
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  DNS Delegations . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Relationship between Parent and Child DNS Operators . . .   5
       2.2.1.  Solution Space  . . . . . . . . . . . . . . . . . . .   6
       2.2.2.  DNSSEC Key Change Process . . . . . . . . . . . . . .   7
   3.  CDS (Child DS) and CDNSKEY (Child DNSKEY) Record Definitions    7
     3.1.  CDS Resource Record Format  . . . . . . . . . . . . . . .   8
     3.2.  CDNSKEY Resource Record Format  . . . . . . . . . . . . .   8
   4.  Automating DS Maintenance with CDS/CDNSKEY Records  . . . . .   8
     4.1.  CDS and CDNSKEY Processing Rules  . . . . . . . . . . . .   9
   5.  CDS/CDNSKEY Publication . . . . . . . . . . . . . . . . . . .   9
   6.  Parent-Side CDS/CDNSKEY Consumption . . . . . . . . . . . . .   9
     6.1.  Detecting a Changed CDS/CDNSKEY . . . . . . . . . . . . .  10
       6.1.1.  CDS/CDNSKEY Polling . . . . . . . . . . . . . . . . .  10
       6.1.2.  Polling Triggers  . . . . . . . . . . . . . . . . . .  11
     6.2.  Using the New CDS/CDNSKEY Records . . . . . . . . . . . .  11
       6.2.1.  Parent Calculates DS  . . . . . . . . . . . . . . . .  12
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  12
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     11.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Appendix A.  RRR Background . . . . . . . . . . . . . . . . . . .  17
   Appendix B.  CDS Key Rollover Example . . . . . . . . . . . . . .  17

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1.  Introduction

   The first time a DNS Operator signs a zone, they need to communicate
   the keying material to their Parent through some out-of-band method
   to complete the chain of trust.  Depending on the desires of the
   Parent, the Child might send their DNSKEY record, a DS record, or
   both.

   Each time the Child changes the key that is represented in the
   Parent, the updated and/or deleted key information has to be
   communicated to the Parent and published in the Parent's zone.  How
   this information is sent to the Parent depends on the relationship
   the Child has with the Parent.  In many cases this is a manual
   process -- and not an easy one.  For each key change, there may be up
   to two interactions with the Parent.  Any manual process is
   susceptible to mistakes and/or errors.  In addition, due to the
   annoyance factor of the process, Operators may avoid changing keys or
   skip needed steps to publish the new DS at the Parent.

   DNSSEC provides data integrity to information published in DNS; thus,
   DNS publication can be used to automate maintenance of delegation
   information.  This document describes a method to automate
   publication of subsequent DS records after the initial one has been
   published.

   Readers are expected to be familiar with DNSSEC, including [RFC4033],
   [RFC4034], [RFC4035], [RFC5011], and [RFC6781].

   This document outlines a technique in which the Parent periodically
   (or upon request) polls its signed Children and automatically
   publishes new DS records.  To a large extent, the procedures this
   document follows are as described in [RFC6781], Section 4.1.2.

   This technique is designed to be friendly both to fully automated
   tools and humans.  Fully automated tools can perform all the actions
   needed without human intervention and thus can monitor when it is
   safe to move to the next step.

   The solution described in this document only allows transferring
   information about DNSSEC keys (DS and DNSKEY) from the Child to the
   Parental Agent.  It lists exactly what the Parent should publish and
   allows for publication of standby keys.  A different protocol,
   [CPSYNC-DNS], can be used to maintain other important delegation
   information, such as NS and glue records.  These two protocols have
   been kept as separate solutions because the problems are
   fundamentally different and a combined solution is overly complex.

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   This document describes a method for automating maintenance of the
   delegation trust information and proposes a polled/periodic trigger
   for simplicity.  Some users may prefer a different trigger, for
   example, a button on a web page, a REST interface, or a DNS NOTIFY.
   These alternate additional triggers are not discussed in this
   document.

   This proposal does not include all operations needed for the
   maintenance of DNSSEC key material, specifically the initial
   introduction or complete removal of all keys.  Because of this,
   alternate communications mechanisms must always exist, potentially
   introducing more complexity.

1.1.  Terminology

   The terminology we use is defined in this section.  The highlighted
   roles are as follows:

   o  Child: The entity on record that has the delegation of the domain
      from the Parent.

   o  Parent: The domain in which the Child is registered.

   o  Child DNS Operator: The entity that maintains and publishes the
      zone information for the Child DNS.

   o  Parental Agent: The entity that the Child has a relationship with
      to change its delegation information.

   o  Provisioning System: A system that the Operator of the master DNS
      server operates to maintain the information published in the DNS.
      This includes the systems that sign the DNS data.

   o  CDS/CDNSKEY: This notation refers to CDS and/or CDNSKEY, i.e., one
      or both.

1.2.  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
   [RFC2119].

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2.  Background

2.1.  DNS Delegations

   DNS operation consists of delegations of authority.  For each
   delegation, there are (most of the time) two parties: the Parent and
   the Child.

   The Parent publishes information about the delegations to the Child;
   for the name servers, it publishes an NS [RFC1035] Resource Record
   Set (RRset) that lists a hint for name servers that are authoritative
   for the Child.  The Child also publishes an NS RRset, and this set is
   the authoritative list of name servers to the Child zone.

   The second RRset the Parent sometimes publishes is the DS [RFC4034]
   set.  The DS RRset provides information about the DNSKEY(s) that the
   Child has told the Parent it will use to sign its DNSKEY RRset.  In
   DNSSEC, a trust relationship between zones is provided by the
   following chain:

   Parent DNSKEY --> DS --> Child DNSKEY.

   A prior proposal [AUTO-CPSYNC] suggested that the Child send an
   "update" to the Parent via a mechanism similar to DNS UPDATE.  The
   main issue became: how does the Child find the actual Parental Agent/
   server to send the update to?  While that could have been solved via
   technical means, it failed to reach consensus.  There is also a
   similar proposal in [PARENT-ZONES].

   As the DS record can only be present at the Parent [RFC4034], some
   other method is needed to automate which DNSKEYs are picked to be
   represented in the Parent zone's DS records.  One possibility is to
   use flags in the DNSKEY record.  If the Secure Entry Point (SEP) bit
   is set, this indicates that the DNSKEY is intended for use as a
   secure entry point.  This DNSKEY signs the DNSKEY RRset, and the
   Parental Agent can calculate DS records based on that.  But this
   fails to meet some operating needs, including the Child having no
   influence on what DS digest algorithms are used and DS records that
   can only be published for keys that are in the DNSKEY RRset; thus,
   this technique would not be compatible with Double-DS rollover
   [RFC6781].

2.2.  Relationship between Parent and Child DNS Operators

   In practical application, there are many different relationships
   between the Parent and Child DNS Operators.  The type of relationship
   affects how the Child DNS Operator communicates with the Parent.

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   This section will highlight some of the different situations but is
   by no means a complete list.

   Different communication paths:

   o  Direct/API: The Child can change the delegation information via
      automated/scripted means.  The Extensible Provisioning Protocol
      (EPP) [RFC5730], used by many Top-Level Domains (TLDs), is an
      example of this.  Other examples are web-based programmatic
      interfaces that Registrars make available to their Resellers.

   o  User Interface: The Child uses a web site set up by the Parental
      Agent for updating delegation information.

   o  Indirect: The communication has to be transmitted via an out-of-
      band mechanism between two parties, such as by email or telephone.
      This is common when the Child DNS Operator is neither the Child
      itself nor the Registrar for the domain, but a third party.

   o  Multi-step Combinations: The information flows through an
      intermediary.  It is possible, but unlikely, that all the steps
      are automated via APIs and there are no humans involved.

   A domain name holder (Child) may operate its own DNS servers or
   outsource the operation.  While we use the word "Parent" as singular,
   a Parent can consist of a single entity or a composite of many
   discrete parts that have rules and roles.  We refer to the entity
   that the Child corresponds with as the Parent.

   An organization (such as an enterprise) may delegate parts of its
   name-space to be operated by a group that is not the same as that
   which operates the organization's DNS servers.  In some of these
   cases, the flow of information is handled either in an ad hoc manner
   or via some corporate mechanism; this can range from email to a fully
   automated operation.

2.2.1.  Solution Space

   This document is aimed at the cases in which there is a separation
   between the Child and Parent.

   A further complication is when the Child DNS Operator is not the
   Child.  There are two common cases of this:

   a)  The Parental Agent (e.g., Registrar) handles the DNS operation.

   b)  A third party takes care of the DNS operation.

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   If the Parental Agent is the DNS Operator, life is much easier; the
   Parental Agent can inject any delegation changes directly into the
   Parent's provisioning system.  The techniques described below are not
   needed in the case when the Parental Agent is the DNS Operator.

   In the case of a third-party DNS Operator, the Child either needs to
   relay changes in DNS delegation or give the Child DNS Operator access
   to its delegation/registration account.

   Some Parents want the Child to express their DNSKEYs in the form of
   DS records, while others want to receive the DNSKEY records and
   calculate the DS records themselves.  There is no consensus on which
   method is better; both have good reasons to exist.  This solution is
   DS vs. DNSKEY agnostic and allows operation with either.

2.2.2.  DNSSEC Key Change Process

   After a Child DNS Operator first signs the zone, there is a need to
   interact with the Parent, for example, via a delegation account
   interface to upload or paste in the zone's DS information.  This
   action of logging in through the delegation account user interface
   authenticates that the user is authorized to change delegation
   information for the Child published in the Parent zone.  In the case
   where the Child DNS Operator does not have access to the registration
   account, the Child needs to perform the action.

   At a later date, the Child DNS Operator may want to publish a new DS
   record in the Parent, either because they are changing keys or
   because they want to publish a standby key.  This involves performing
   the same process as before.  Furthermore, when this is a manual
   process with cut and paste, operational mistakes will happen -- or
   worse, the update action will not be performed at all.

   The Child DNS Operator may also introduce new keys and can do so when
   old keys exist and can be used.  The Child may also remove old keys,
   but this document does not support removing all keys.  This is to
   avoid making signed zones unsigned.  The Child may not enroll the
   initial key or introduce a new key when there are no old keys that
   can be used (without some additional out-of-band validation of the
   keys) because there is no way to validate the information.

3.  CDS (Child DS) and CDNSKEY (Child DNSKEY) Record Definitions

   This document specifies two new DNS resource records, CDS and
   CDNSKEY.  These records are used to convey, from one zone to its
   Parent, the desired contents of the zone's DS resource record set
   residing in the Parent zone.

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   The CDS and CDNSKEY resource records are published in the Child zone
   and give the Child control of what is published for it in the
   parental zone.  The Child can publish these manually, or they can be
   automatically maintained by DNS provisioning tools.  The CDS/CDNSKEY
   RRset expresses what the Child would like the DS RRset to look like
   after the change; it is a "replace" operation, and it is up to the
   software that consumes the records to translate that into the
   appropriate add/delete operations in the provisioning systems (and in
   the case of CDNSKEY, to generate the DS from the DNSKEY).  If neither
   CDS nor CDNSKEY RRset is present in the Child, this means that no
   change is needed.

3.1.  CDS Resource Record Format

   The wire and presentation format of the Child DS (CDS) resource
   record is identical to the DS record [RFC4034].  IANA has allocated
   RR code 59 for the CDS resource record via Expert Review
   [DNS-TRANSPORT].  The CDS RR uses the same registries as DS for its
   fields.

   No special processing is performed by authoritative servers or by
   resolvers, when serving or resolving.  For all practical purposes,
   CDS is a regular RR type.

3.2.  CDNSKEY Resource Record Format

   The wire and presentation format of the CDNSKEY ("Child DNSKEY")
   resource record is identical to the DNSKEY record.  IANA has
   allocated RR code 60 for the CDNSKEY resource record via Expert
   Review.  The CDNSKEY RR uses the same registries as DNSKEY for its
   fields.

   No special processing is performed by authoritative servers or by
   resolvers, when serving or resolving.  For all practical purposes,
   CDNSKEY is a regular RR type.

4.  Automating DS Maintenance with CDS/CDNSKEY Records

   CDS/CDNSKEY resource records are intended to be "consumed" by
   delegation trust maintainers.  The use of CDS/CDNSKEY is OPTIONAL.

   If the Child publishes either the CDS or the CDNSKEY resource record,
   it SHOULD publish both.  If the Child knows which the Parent
   consumes, it MAY choose to only publish that record type (for
   example, some Children wish the Parent to publish a DS, but they wish
   to keep the DNSKEY "hidden" until needed).  If the Child publishes
   both, the two RRsets MUST match in content.

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4.1.  CDS and CDNSKEY Processing Rules

   If there is neither CDS nor CDNSKEY RRset in the Child, this signals
   that no change should be made to the current DS set.  This means
   that, once the Child and Parent are in sync, the Child DNS Operator
   MAY remove all CDS and CDNSKEY resource records from the zone.  The
   Child DNS Operator may choose to do this to decrease the size of the
   zone or to decrease the workload for the Parent (if the Parent
   receives no CDS/CDNSKEY records, it can go back to sleep).  If it
   does receive a CDS or CDNSKEY RRset, it needs to check them against
   what is currently published (see Section 5).

   The following acceptance rules are placed on the CDS and CDNSKEY
   resource records as follows:

   o  Location: MUST be at the Child zone apex.

   o  Signer: MUST be signed with a key that is represented in both the
      current DNSKEY and DS RRsets, unless the Parent uses the CDS or
      CDNSKEY RRset for initial enrollment; in that case, the Parent
      validates the CDS/CDNSKEY through some other means (see
      Section 6.1 and the Security Considerations).

   o  Continuity: MUST NOT break the current delegation if applied to DS
      RRset.

   If any these conditions fail, the CDS or CDNSKEY resource record MUST
   be ignored, and this error SHOULD be logged.

5.  CDS/CDNSKEY Publication

   The Child DNS Operator publishes CDS/CDNSKEY RRset(s).  In order to
   be valid, the CDS/CDNSKEY RRset(s) MUST be compliant with the rules
   in Section 4.1.  When the Parent DS is in sync with the CDS/CDNSKEY
   RRset(s), the Child DNS Operator MAY delete the CDS/CDNSKEY RRset(s);
   the Child can determine if this is the case by querying for DS
   records in the Parent.

6.  Parent-Side CDS/CDNSKEY Consumption

   The CDS/CDNSKEY RRset(s) SHOULD be used by the Parental Agent to
   update the DS RRset in the Parent zone.  The Parental Agent for this
   uses a tool that understands the CDS/CDNSKEY signing rules in
   Section 4.1, so it might not be able to use a standard validator.

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   The Parent MUST choose to use either CDNSKEY or CDS resource records
   as its default updating mechanism.  The Parent MAY only accept either
   CDNSKEY or CDS, but it MAY also accept both so it can use the other
   in the absence of the default updating mechanism; it MUST NOT expect
   there to be both.

6.1.  Detecting a Changed CDS/CDNSKEY

   How the Parental Agent gets the CDS/CDNSKEY RRset may differ.  Below
   are two examples of how this can take place.

   Polling:  The Parental Agent operates a tool that periodically checks
         each of the Children that has a DS record to see if there is a
         CDS or CDNSKEY RRset.

   Pushing:  The delegation user interface has a button {Fetch DS} that,
         when pushed, performs the CDS/CDNSKEY processing.  If the
         Parent zone does not contain DS for this delegation, then the
         "push" SHOULD be ignored.  If the Parental Agent displays the
         contents of the CDS/CDNSKEY to the user and gets confirmation
         that this represents their key, the Parental Agent MAY use this
         for initial enrollment (when the Parent zone does not contain
         the DS for this delegation).

   In either case, the Parental Agent MAY apply additional rules that
   defer the acceptance of a CDS/CDNSKEY change.  These rules may
   include a condition that the CDS/CDNSKEY remains in place and valid
   for some time period before it is accepted.  It may be appropriate in
   the "Pushing" case to assume that the Child is ready and thus accept
   changes without delay.

6.1.1.  CDS/CDNSKEY Polling

   This is the only defined use of CDS/CDNSKEY resource records in this
   document.  There are limits to the scalability of polling techniques;
   thus, some other mechanism is likely to be specified later that
   addresses CDS/CDNSKEY resource record usage in the situation where
   polling runs into scaling issues.  Having said that, polling will
   work in many important cases such as enterprises, universities, and
   smaller TLDs.  In many regulatory environments, the Registry is
   prohibited from talking to the Registrant.  In most of these cases,
   the Registrant has a business relationship with the Registrar, so the
   Registrar can offer this as a service.

   If the CDS/CDNSKEY RRset(s) do not exist, the Parental Agent MUST
   take no action.  Specifically, it MUST NOT delete or alter the
   existing DS RRset.

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6.1.2.  Polling Triggers

   It is assumed that other mechanisms will be implemented to trigger
   the Parent to look for an updated CDS/CDNSKEY RRset.  As the CDS/
   CDNSKEY resource records are validated with DNSSEC, these mechanisms
   can be unauthenticated.  As an example, a Child could telephone its
   Parent and request that it process the new CDS or CDNSKEY resource
   records, or an unauthenticated POST could be made to a web server
   (with rate-limiting).

   Other documents can specify the trigger conditions.

6.2.  Using the New CDS/CDNSKEY Records

   Regardless of how the Parental Agent detected changes to a CDS/
   CDNSKEY RRset, the Parental Agent SHOULD use a DNSSEC validator to
   obtain a validated CDS/CDNSKEY RRset from the Child zone.  A NOT
   RECOMMENDED exception to this is if the Parent performs some
   additional validation on the data to confirm that it is the "correct"
   key.

   The Parental Agent MUST ensure that previous versions of the CDS/
   CDNSKEY RRset do not overwrite more recent versions.  This MAY be
   accomplished by checking that the signature inception in the Resource
   Record Signature (RRSIG) for CDS/CDNSKEY RRset is later and/or that
   the serial number on the Child's Start of Authority (SOA) is greater.
   This may require the Parental Agent to maintain some state
   information.

   The Parental Agent MAY take extra security measures.  For example, to
   mitigate the possibility that a Child's Key Signing Key (KSK) has
   been compromised, the Parental Agent may inform (by email or other
   methods) the Child DNS Operator of the change.  However, the precise
   out-of-band measures that a Parent zone takes are outside the scope
   of this document.

   Once the Parental Agent has obtained a valid CDS/CDNSKEY RRset it
   MUST check the publication rules from Section 4.1.  In particular,
   the Parental Agent MUST check the Continuity rule and do its best not
   to invalidate the Child zone.  Once checked, if the information in
   the CDS/CDNSKEY and DS differ, it may apply the changes to the Parent
   zone.  If the Parent consumes CDNSKEY, the Parent should calculate
   the DS before doing this comparison.

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6.2.1.  Parent Calculates DS

   There are cases where the Parent wants to calculate the DS record due
   to policy reasons.  In this case, the Child publishes CDNSKEY
   records, and the Parent calculates the DS records on behalf of the
   Children.

   When a Parent operates in "calculate DS" mode, it can operate in one
   of two sub-modes:

   full:  The Parent only publishes DS records it calculates from DNSKEY
      records.

   augment:  The Parent will make sure there are DS records for the
      digest algorithm(s) it requires(s).

   In the case where the Parent fetches the CDNSKEY RRset and calculates
   the DS, the resulting DS can differ from the CDS published by the
   Child.  It is expected that the differences are only due to the
   different set of digest algorithms used.

7.  IANA Considerations

   IANA has assigned RR Type code 59 for the CDS resource record.  This
   was done for a draft version whose content was later incorporated
   into this document [DNS-TRANSPORT].  This document is the reference
   for CDS RRtype.

   IANA has assigned an RR Type for the CDNSKEY as described below:

   Type:  CDNSKEY

   Value:  60

   Meaning:  DNSKEY(s) the Child wants reflected in DS

   Reference:  This document

8.  Privacy Considerations

   All of the information handled or transmitted by this protocol is
   public information published in the DNS.

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9.  Security Considerations

   This work is for the normal case; when things go wrong there is only
   so much that automation can fix.

   If the Child breaks DNSSEC validation by removing all the DNSKEYs
   that are represented in the DS set, its only repair actions are to
   contact the Parent or restore the DNSKEYs in the DS set.

   In the event of a compromise of the server or system generating
   signatures for a zone, an attacker might be able to generate and
   publish new CDS/CDNSKEY resource records.  The modified CDS/CDNSKEY
   records will be picked up by this technique and may allow the
   attacker to extend the effective time of his attack.  If there is a
   delay in accepting changes to DS, as in [RFC5011], then the attacker
   needs to hope his activity is not detected before the DS in the
   Parent is changed.  If this type of change takes place, the Child
   needs to contact the Parent (possibly via a Registrar web interface)
   and remove any compromised DS keys.

   A compromise of the account with the Parent (e.g., Registrar) will
   not be mitigated by this technique, as the "new Registrant" can
   delete or modify the DS records at will.

   While it may be tempting, the techniques specified in this document
   SHOULD NOT be used for initial enrollment of keys since there is no
   way to ensure that the initial key is the correct one.  If it is
   used, strict rules for inclusion of keys -- such as hold-down times,
   challenge data inclusion, or similar -- MUST be used along with some
   kind of challenge mechanism.  A Child cannot use this mechanism to go
   from signed to unsigned (publishing an empty CDS/CDNSKEY RRset means
   no change should be made in the Parent).

   The CDS RR type should allow for enhanced security by simplifying the
   process.  Since key change is automated, updating a DS RRset by other
   means may be regarded as unusual and subject to extra security
   checks.

   As this introduces a new mechanism to update information in the
   Parent, it MUST be clear who is fetching the records and creating the
   appropriate records in the Parent zone.  Specifically, some
   operations may use mechanisms other than what is described here.  For
   example, a Registrar may assume that it is maintaining the DNSSEC key
   information in the Registry and may have this cached.  If the
   Registry is fetching the CDS/CDNSKEY RRset, then the Registry and
   Registrar may have different views of the DNSSEC key material; the

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   result of such a situation is unclear.  Therefore, this mechanism
   SHOULD NOT be used to bypass intermediaries that might cache
   information and, because of that, get the wrong state.

   If there is a failure in applying changes in the Child zone to all
   DNS servers listed in either Parent or Child NS set, it is possible
   that the Parental Agent may get confused either because it gets
   different answers on different checks or CDS RR validation fails.  In
   the worst case, the Parental Agent performs an action reversing a
   prior action after the Child signing system decides to take the next
   step in the key change process, resulting in a broken delegation.

   DNS is a loosely coherent distributed database with local caching;
   therefore, it is important to allow old information to expire from
   caches before deleting DS or DNSKEY records.  Similarly, it is
   important to allow new records to propagate through the DNS before
   use (see [RFC6781]).

   It is common practice for users to outsource their DNS hosting to a
   third-party DNS provider.  In order for that provider to be able to
   maintain the DNSSEC information, some users give the provider their
   Registrar login credentials (which obviously has negative security
   implications).  Deploying the solution described in this document
   allows third-party DNS providers to maintain the DNSSEC information
   without Registrants giving their Registrar credentials, thereby
   improving security.

   By automating the maintenance of the DNSSEC key information (and
   removing humans from the process), we expect to decrease the number
   of DNSSEC related outages, which should increase DNSSEC deployment.

10.  Acknowledgements

   We would like to thank a large number of folk, including Mark
   Andrews, Joe Abley, Jaap Akkerhuis, Roy Arends, Doug Barton, Brian
   Dickson, Paul Ebersman, Tony Finch, Jim Galvin, Paul Hoffman, Samir
   Hussain, Tatuya Jinmei, Olaf Kolkman, Stephan Lagerholm, Cricket Liu,
   Matt Larson, Marco Sanz, Antoin Verschuren, Suzanne Woolf, Paul
   Wouters, John Dickinson, Timothe Litt, and Edward Lewis.

   Special thanks to Wes Hardaker for contributing significant text and
   creating the complementary (CSYNC) solution, and to Patrik Faltstrom,
   Paul Hoffman, Matthijs Mekking, Mukund Sivaraman, and Jeremy C. Reed
   for text and in-depth review.  Brian Carpenter provided a good
   Gen-ART review.

   There were a number of other folk with whom we discussed this
   document; apologies for not remembering everyone.

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11.  References

11.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

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

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", RFC
              4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

   [RFC5011]  StJohns, M., "Automated Updates of DNS Security (DNSSEC)
              Trust Anchors", STD 74, RFC 5011, September 2007.

   [RFC6781]  Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
              Operational Practices, Version 2", RFC 6781, December
              2012.

11.2.  Informative References

   [AUTO-CPSYNC]
              Mekking, W., "Automated (DNSSEC) Child Parent
              Synchronization using DNS UPDATE", Work in Progress,
              December 2010.

   [CPSYNC-DNS]
              Hardaker, W., "Child To Parent Synchronization in DNS",
              Work in Progress, July 2014.

   [DNS-TRANSPORT]
              Barwood, G., "DNS Transport", Work in Progress, June 2011.

   [PARENT-ZONES]
              Andrews, M., "Updating Parent Zones", Work in Progress,
              November 2013.

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   [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              STD 69, RFC 5730, August 2009.

   [RFC5910]  Gould, J. and S. Hollenbeck, "Domain Name System (DNS)
              Security Extensions Mapping for the Extensible
              Provisioning Protocol (EPP)", RFC 5910, May 2010.

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Appendix A.  RRR Background

   RRR is our shorthand for the Registry/Registrar/Registrant model of
   Parent-Child relationships.

   In the RRR world, the different parties are frequently from different
   organizations.  In the single enterprise world, there are also
   organizational, geographical, and cultural separations that affect
   how information flows from a Child to the Parent.

   Due to the complexity of the different roles and interconnections,
   automation of delegation information has not yet occurred.  There
   have been proposals to automate this, in order to improve the
   reliability of the DNS.  These proposals have not gained enough
   traction to become standards.

   For example, in many of the TLD cases, there is the RRR model
   (Registry/Registrar/Registrant).  The Registry operates DNS for the
   TLD, and the Registrars accept registrations and place information
   into the Registry's database.  The Registrant only communicates with
   the Registrar; frequently, the Registry is not allowed to communicate
   with the Registrant.  In that case, as far as the Registrant is
   concerned, the Registrar is the same entity as the Parent.

   In many RRR cases, the Registrar and Registry communicate via EPP
   [RFC5730] and use the EPP DNSSEC extension [RFC5910].  In a number of
   Country Code TLDs (ccTLDs), there are other mechanisms in use as well
   as EPP, but in general, there seems to be a movement towards EPP
   usage when DNSSEC is enabled in the TLD.

Appendix B.  CDS Key Rollover Example

   This section shows an example on how CDS is used when performing a
   KSK rollover.  This example will demonstrate the Double-DS rollover
   method from Section 4.1.2 of [RFC6781].  Other rollovers using
   CDNSKEY and double KSK are left as an exercise to the reader.  The
   table below does not reflect the Zone Signing Keys (ZSKs) as they do
   not matter during KSK rollovers.  The wait steps highlight what RRset
   needs to expire from caches before progressing to the next step.

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   +------+---------------+---------+---------+--------------+---------+
   | Step | State         |  Parent |  Child  |  DNSKEY and  |  Child  |
   |      |               |    DS   |   KSK   |  CDS signer  |   CDS   |
   +------+---------------+---------+---------+--------------+---------+
   |      | Beginning     |    A    |    A    |      A       |         |
   | 1    | Add CDS       |    A    |    A    |      A       |    AB   |
   | Wait | for DS change |    A    |    A    |      A       |    AB   |
   | 2    | Updated DS    |    AB   |    A    |      A       |    AB   |
   | Wait | > DS TTL      |    AB   |    A    |      A       |    AB   |
   | 3    | Actual        |    AB   |    B    |      B       |    AB   |
   |      | Rollover      |         |         |              |         |
   | Wait | > DNSKEY TTL  |    AB   |    B    |      B       |    AB   |
   | 4    | Child Cleanup |    AB   |    B    |      B       |    B    |
   | 5    | Parent cleans |    B    |    B    |      B       |    B    |
   | 6    | Optional CDS  |    B    |    B    |      B       |         |
   |      | delete        |         |         |              |         |
   +------+---------------+---------+---------+--------------+---------+

                              Table 1: States

Authors' Addresses

   Warren Kumari
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   EMail: warren@kumari.net

   Olafur Gudmundsson
   OGUD Consulting
   3821 Village Park Dr.
   Chevy Chase, MD  20815
   US

   EMail: ogud@ogud.com

   George Barwood
   33 Sandpiper Close
   Gloucester  GL2 4LZ
   United Kingdom

   EMail: george.barwood@blueyonder.co.uk

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