Automating DNSSEC delegation trust maintenance
draft-kumari-ogud-dnsop-cds-03

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dnsop                                                          W. Kumari
Internet-Draft                                                    Google
Intended status: Informational                            O. Gudmundsson
Expires: January 10, 2014                                  Shinkuro Inc.
                                                              G. Barwood

                                                           July 09, 2013

             Automating DNSSEC delegation trust maintenance
                     draft-kumari-ogud-dnsop-cds-03

Abstract

   This document describes a method to allow DNS operators to more
   easily update DNSSEC Key Signing Keys using DNS as communication
   channel.  This document does not address the initial configuration of
   trust anchors for a domain.  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 Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on January 10, 2014.

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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   carefully, as they describe your rights and restrictions with respect

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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
     1.2.  Requirements notation . . . . . . . . . . . . . . . . . .   4
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  DNS delegations . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Relationship between Parent and Child DNS operator  . . .   5
       2.2.1.  Solution Space  . . . . . . . . . . . . . . . . . . .   6
       2.2.2.  DNSSEC key change process . . . . . . . . . . . . . .   6
   3.  CDS (Child DS) record definition  . . . . . . . . . . . . . .   6
     3.1.  CDS Resource Record Format  . . . . . . . . . . . . . . .   7
   4.  Automating DS maintainance with CDS records . . . . . . . . .   7
     4.1.  CDS processing rules  . . . . . . . . . . . . . . . . . .   7
   5.  Child's CDS Publication . . . . . . . . . . . . . . . . . . .   7
   6.  Parent side CDS Consumption . . . . . . . . . . . . . . . . .   8
     6.1.  Detecting a changed CDS . . . . . . . . . . . . . . . . .   8
       6.1.1.  CDS Polling . . . . . . . . . . . . . . . . . . . . .   8
     6.2.  Usign the new CDS . . . . . . . . . . . . . . . . . . . .   8
       6.2.1.  Parent calculates DS  . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  RRR background . . . . . . . . . . . . . . . . . . .  12
   Appendix B.  Changes / Author Notes.  . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   When a DNS operator first signs their zone, they need to communicate
   their DS record(s) (or DNSKEY(s)) to their parent through some out-
   of-band method to complete the chain of trust.

   Each time the child changes/rolls the key that is represented in the
   parent, the new and/or deleted key information has to be communicated
   to the parent and published there.  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 roll, there may be two interactions with the parent.  Any
   manual process is susceptible to mistakes and/or errors.  In

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   addition, due to the annoyance factor of the process, operators may
   avoid performing key rollovers 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 is a compilation of two earlier drafts: draft-barwood-
   dnsop-ds-publish[I-D.ds-publish] and draft-wkumari-dnsop-ezkeyroll

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

   This technique is in some ways similar to RFC 5011 style rollovers,
   but for sub-domains DS records, instead of trust anchors

   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.  Humans can look at the CDS and DS
   records and easily see if there is a difference.

1.1.  Terminology

   There terminology we use is defined in this section

   Highlighted roles

   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  Parent DNS operator: "The entity that maintains and publishes the
      zone information for the parent DNS"

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   o  Parental Agent: "The entity that the child has 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."

   RRR is our shorthand for Registry/Registrar/Registrant model of
   parent child relationship see Appendix A for more.

1.2.  Requirements notation

   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 [RFC2119].

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
   child.

   In DNS, the parent publishes information about the delegations to the
   child; for the name-servers it publishes an NS RRset that lists a
   hint for name-servers that are authoritative for the child.  The
   child also publishes a 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 set.  The
   DS RRset provides information about the key(s) that the child has
   told the parent it will use to sign its DNSKEY RRset.  In DNSSEC
   trust relationship between zones is provided by the following chain:

   parent DNSKEY --> DS --> child DNSKEY.

   A prior proposal [I-D.auto-cpsync] suggested that the child send an
   "update" to the parent via a mechanism similar to Dynamic 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, the proposal died.

   As the DS record can only be present at the parent RFC4034 [RFC4034],
   some other record/method is needed to automate the expression of what
   the parental zone DS records contents ought to be.  One possibility
   is to use flags in the DNSKEY record.  If the SEP bit is set, this
   indicates that the DNSKEY is intended for use as a secure entry

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   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 what DS
   digest algorithms are used and DS records can only be published for
   keys that are in the DNSKEY RRset.

2.2.  Relationship between Parent and Child DNS operator

   In the real world, there are many different relationships between the
   parent and child DNS operators.  The type of relationship affects how
   the child operator communicates with the parent.  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 EPP[RFC5730] used by many TLDs is an
      example of this.  Another example is the web service's
      programmatic interfaces that Registrars make available to their
      Reseller's.

   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 out-of-band
      between two parties, such as email, telephone etc.. This is common
      when the Child's 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 API's and there are no humans are involved.

   A domain name holder (Child) may operate its own DNS servers or
   outsource the operation.  While we use the word parent as a singular,
   parent can consist of 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.

   Another common case is the enterprise case in which an organization
   may delegate parts of its name-space to be operated by a group that
   is not the same as that which operates the enterprise's DNS servers.
   In this case the flow of information is frequently handled in either
   an ad hoc manner or via some corporate mechanism; this can range from
   email to fully-automated operation.  The word enterprise above covers
   all organizations where the domains are not sold on the open market
   and there is some relationship between the entities.

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2.2.1.  Solution Space

   This document is aimed at the cases in which there is an
   organizational separation of the child and parent.

   A further complication is when the Child DNS Operation 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.

   If the Parental Agent is the DNS operator, life is much easier, as
   the Parental Agent can inject any delegation changes directly into
   the Parents Provisioning system.  The techniques described below are
   not needed in the case when 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 Operator access to
   its delegation/registration account.

   Some parents want the child to express the changes in trust anchors
   via DS records, while others want to receive DNSKEY records and
   calculate the DS records themselves.  There is no consensus on which
   method is better; both have good reasons to exist.  The proposal
   below can operate with both models, but the child needs to be aware
   of the parental policies.

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 the delegation account
   interface, to "upload/paste-in the zone's DS information".  The
   action of logging in through the delegation account user interface
   authenticates that the user is authorized to change delegation
   information published in the parent zone.  In the case where "Child
   DNS Operator" does not have access to the registration account, the
   Child needs to perform the action.

   At a later date, the Child Operator may want to publish a new DS
   record in the parent, either because they are rolling keys, or
   because they want to publish a stand-by 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 in not performed at all.

3.  CDS (Child DS) record definition

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   This document specifies a new DNS RRtype CDS that indicates what the
   Child wants to be in the parents DS RRset.

   The CDS record can be published in the child zone and gives the child
   more control of what is published for it in the parental zone.  The
   CDS RRset expresses what the DS RRset SHOULD look like after the
   change; it is a "replace" operation, and it is up to the consumer of
   the records to translate that into the appropriate add/delete
   operations in the registration systems.

3.1.  CDS Resource Record Format

   The wire and presentation format of the CDS ("Child DS") record is
   identical to the DS record [RFC4034].  IANA has allocated RR code 59
   for the CDS record via expert review [I-D.ds-publish].

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

4.  Automating DS maintainance with CDS records

   CDS records are intended to be "consumed" by delegation trust
   maintainers.  The use of CDS is optional.

4.1.  CDS processing rules

   Absence of CDS in child signals "No change" to the current DS set.
   Following acceptance rules are placed on the CDS record as follows:

   o  Location: "the CDS record MUST be at the child zone apex".  Q: is
      "_cds.example. a better location for .example?

   o  Signer: "MUST be signed with a key that is represented in both the
      current DNSKEY and DS RRset's."

   o  Continuity: "SHOULD not break the current delegation if applied to
      DS RRset"

   If any these conditions fail the CDS record MUST be ignored.

5.  Child's CDS Publication

   Child DNS Operator SHOULD only publish a CDS RRset when it wants to
   make a change to the DS RRset in the Parent.  The CDS RRset SHOULD be
   compliant with the rules in Section 4.1.  When the Parent DS is "in-
   sync" with the CDS, the Child DNS Operator SHOULD/MUST delete the CDS
   RRset.

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6.  Parent side CDS Consumption

   The CDS RRset MAY 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 signing rules from Section 4.1 so it may not
   be able to use a standard validator.  Parent SHOULD treat the
   Continuity rule as "MUST".

6.1.  Detecting a changed CDS

   How the Parental Agent gets the CDS record may differ, below are two
   examples as 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 record.

   Pushing  The delegation user interface has a button {Fetch DS} when
         pushed preforms the CDS processing.  If the Parent zone does
         not contain DS for this delegation then the "push" MUST be
         ignored.

   In either case the Parental Agent MAY apply additional rules that
   defer the acceptance of a CDS change, these rules may include a
   condition that the CDS 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 Polling

   This is the only defined use of CDS in this document.  There are
   limits to the scalabilty of polling techniques, thus some other
   mechanism is likely to be specified later that addresses CDS usage in
   the situation where polling does not scale to.  Having said that
   Polling will work in many important cases like enterprises,
   universities, small TLD's etc.

   If the CDS RRset does not exist, the Parental Agent MUST take no
   action.  Specifically it MUST NOT delete or alter the existing DS
   RRset.

6.2.  Usign the new CDS

   Regardless of how the Parent DNS operator detected changes to a CDS
   RR, the Parent DNS operator MUST use a DNSSEC validator to obtain a
   validated CDS RRset from the Child zone.  It would be a good idea if
   the Parent DNS operator checked all NS RRs listed at the delegation.

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   However, due to the use of technologies such as load balancing and
   anycast, this should not be taken as proof that the new CDS is
   present on all nodes serving the Child zone.

   The Parent DNS operator MUST ensure that old versions of the CDS
   RRset do not overwrite newer versions.  This MAY be accomplished by
   checking that the signature inception in the RRSIG for CDS is newer
   and/or the serial number on the child's SOA is greater.  This may
   require the Parent DNS operator to maintain some state information.

   The Parent DNS operator MAY take extra security measures.  For
   example, to mitigate the possibility that a Child's key signing key
   has been compromised, the Parent DNS operator may, for example,
   inform ( by email or other methods ) the Child DNS operator of the
   change.  However the precise out-of-band measures that a parent zone
   SHOULD take are outside the scope of this document.

   Once the Parent DNS operator has obtained a valid CDS it MAY double
   check the publication rules from section 4.1.  In particular the
   Parent DNS operator MUST double check the Continuity rule and do its
   best not to invalidate the Child zone.  Once checked and if the CDS
   and DS ``differ'' it may apply the changes to the parent zone.

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 can still publish a CDS
   records instructing the parent which DNSKEY's to represent in the DS
   RRset.  This requires publication of future keys in the DNSKEY RRset
   for the parent to be able to calculate the DS record.  The DNS Parent
   needs to publish guidelines for the children as to what digest
   algorithms are acceptable in the CDS record.

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

   full  i.e. it only publishes DS records it calculates from DNSKEY
      records,

   augment  i.e. it will make sure there are DS records for the digest
      algorithm(s) it requires(s).

   Implications on Parental Agent are that the CDS and DS are not
   exactly the same after update thus it needs to take that into
   consideration when checking CDS records.  Same goes for the Child
   Operator, it needs to be able to detect that the new DS RRset is
   "equivalent" to the current CDS RRset, thus it can remove the CDS
   RRset.

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7.  IANA Considerations

   IANA has assigned RR Type code 59 for CDS.  This was done for an
   earlier version of this document[I-D.ds-publish] This document is to
   become the reference for CDS RRtype.

8.  Security Considerations

   [ This needs more work, suggestions welcome.]

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

   If 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 records.  The modified CDS records will be picked up
   by this technique and so may allow the attacker to extend the
   effective time of his attack.  If there 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 parent is changed.  If this type of
   change takes place, the child need 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/
   modify the DS records at will.

   While it may be tempting, this 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 is used, strict rules for inclusion of
   keys like hold down times, challenge data inclusion etc., ought to be
   used, along with some kind of challenge mechanism.

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

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   If there is a failure in applying changes in 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 not perform action because
   it gets different answers on different checks or CDS validation
   fails.  In the worst case Parental Agent performs an action reversing
   a prior action but after the child signing system decides to take the
   next step in rollover, 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] and [I-D.key-time]

9.  Acknowledgements

   This is by no means the invention of the authors.  This idea has been
   floating around for a long time.  This simply documents it for
   discussion.

   We would like to thank: Joe Abley, Roy Arends, Jim Galvin, Cricket
   Liu, Stephan Lagerholm, Matt Larson, Olaf Kolkman, Suzanne Woolf,
   Paul Wouters, Wes Hardaker, Doug Barton, Brian Dickinson, Marco Sanz,
   Tony Finch, Antoin Verschuren, Edward Lewis Matthijs Meeking, John
   Dickinson.

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

10.  References

10.1.  Normative References

   [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.

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   [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.

10.2.  Informative References

   [I-D.auto-cpsync]
              Mekking, W., "Automated (DNSSEC) Child Parent
              Synchronization using DNS UPDATE", draft-mekking-dnsop-
              auto-cpsync-01 (work in progress), December 2010.

   [I-D.ds-publish]
              Barwood, G., "DNS Transport", draft-barwood-dnsop-ds-
              publish-02 (work in progress), June 2011.

   [I-D.key-time]
              Mekking, W., "DNSSEC Key Timing Considerations", draft-
              ietf-dnsop-dnssec-key-timing-03 (work in progress), July
              2012.

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

   [RFC5734]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Transport over TCP", STD 69, RFC 5734, 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.

Appendix A.  RRR background

   In the RRR world, the different parties are frequently from different
   organizations.  In the single enterprise world there are also
   organizational/geographical/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 been punted in the past.
   There have been some 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 and Registrant).  The Registry operates DNS for

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   the TLD, the Registrars accept registrations and place information
   into the Registries 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 == Parent.

   In many RRR cases the Registrar and Registry communicate via
   EPP[RFC5730] and use the EPP DNSSEC extension [RFC5910].  In a number
   of 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.  Changes / Author Notes.

   [RFC Editor: Please remove this section before publication ]

   From 02 to 03

   o  Applied comments by Matthijs Mekking

   o  Incorporated suggestions from Edward Lewis about structure

   o  Reworked structure to be easier for implementors to follow

   o  Applied many suggestions from a wonderful thorough review by John
      Dickinson

   o  Removed the going Unsigned option

   From 01 to 02

   o  Major restructuring to facilitate easier discussion

   o  Lots of comments from DNSOP mailing list incorporated, including
      making draft DNSKEY/DS neutral, explain different relationships
      that exists,

   o  added more people to acks.

   o  added description of enterprise situations

   o  Unified on using Parental Agent over Parental Representative

   o  Removed redundant text when possible

   o  Added text to explain what can go wrong if not all child DNS
      servers are in sync.

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   o  Reference prior work by Matthijs Mekking

   o  Added text when parent calculates DS from DNSKEY

   From - to -1.

   o  Removed from section .1: "If a child zone has gone unsigned, i.e.
      no DNSKEY and no RRSIG in the zone, the parental representative
      MAY treat that as intent to go unsigned.  (NEEDS DISCUSSION)."
      Added new text at end. -- suggestion by Scott Rose 20/Feb/13.

   o  Added some background on the different DNS Delegation operating
      situations and how they affect interaction of parties.  This moved
      some blocks of text from later sections into here.

   o  Number of textual improvements from Stephan Lagerholm

   o  Added motivation why CDS is needed in CDS definition section

   o  Unified terminology in the document.

   o  Much more background

Authors' Addresses

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

   Email: warren@kumari.net

   Olafur Gudmundsson
   Shinkuro Inc.
   4922 Fairmont Av, Suite 250
   Bethesda, MD  20814
   USA

   Email: ogud@ogud.com

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   George Barwood
   33 Sandpiper Close
   Gloucester  GL2 4LZ
   United Kingdom

   Email: george.barwood@blueyonder.co.uk

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