Automating DNSSEC delegation trust maintenance
draft-kumari-ogud-dnsop-cds-02

dnsop                                                          W. Kumari
Internet-Draft                                                    Google
Intended status: Informational                            O. Gudmundsson
Expires: December 19, 2013                                 Shinkuro Inc.
                                                              G. Barwood

                                                           June 17, 2013

             Automating DNSSEC delegation trust maintenance
                     draft-kumari-ogud-dnsop-cds-02

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.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements notation . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  DNS delegations . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Relationship between Parent and Child DNS operator  . . .   4
       2.2.1.  Roles . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Solution Space  . . . . . . . . . . . . . . . . . . . . .   6
     2.4.  DNSSEC key change process . . . . . . . . . . . . . . . .   6
   3.  CDS (Child DS) record definition  . . . . . . . . . . . . . .   7
     3.1.  CDS Resource Record Format  . . . . . . . . . . . . . . .   7
       3.1.1.  Going unsigned  . . . . . . . . . . . . . . . . . . .   7
   4.  Automating DS maintainance with CDS records . . . . . . . . .   8
     4.1.  CDS Publication . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  CDS Consumption . . . . . . . . . . . . . . . . . . . . .   8
     4.3.  Usage . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     4.4.  Parent calculates DS  . . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Changes / Author Notes.  . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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
   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.

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   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 and draft-wkumari-dnsop-ezkeyroll

   This document outlines a technique in which the parent (frequently
   registrar / registry) periodically (or upon request) polls its signed
   children and automatically publish new DS records.  To a large
   extent, the procedures this document follows are 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 to automated tools, that
   the tools can perform all the actions needed w/o human intervention,
   and monitor when it is save to move to next step.

1.1.  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].

1.2.  Terminology

   In this section we define terms used in the document.  There are also
   definitions we use in section Section 2.2.1.

   RRR:  This is our shorthand for the common registration model used in
         many delegation mainly zones, this stands for Registry/
         Registrar/Registrant.  Registry = the domain the registration
         takes place in, and also refers to the operator of said
         registry.  Registrar on the other hand deals with "customers",
         "sells'' registrations and provides support.  Registrant is the
         party "buying'' the registration.  In some cases there is the
         4th R in this -- Reseller which is under contract with a
         Registrar allowing it to sell registrations and record them via
         the Registrar's systems.

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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
   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 sometime 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.

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.

   A domain name holder (child) may operate its own DNS servers or out
   source 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.  For example in many of the TLD
   cases there is the RRR model (Registry, Registrar and Registrant).
   The Registry operates DNS for 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.

   Another common case is the enterprise case where an organization may
   delegate parts of its namespace to be operated by a group that is not
   the same as operates the enterprises 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 is supposed to cover
   all organization 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.  Roles

   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"

   o  Parental Agent: "The entity that the child has relationship with,
      to change its delegation information."

   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 services'
      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 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 APIs and there are no humans are involved.

   In the RRR world, the different parties are frequently from different
   organizations.  In the single enterprise world there are also
   organizational/geographical/clutural seperations that affect how
   information flows from a child delegation 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.

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

2.3.  Solution Space

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

   In many RRR cases the Registrar and Registry communicate via
   EPP[RFC5730] and use the EPP DNSSEC extension [RFC5910].  In 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.

   A further complication is when the DNS Operation is separate from the
   Registrant.  There are two common cases of this, registrar handles
   the DNS operation and a third party takes care of the DNS operation.
   In the case of a third party DNS operator, the Registrant either
   needs to relay changes in DNS delegation or give the operator access
   to its registration account.  If the Registrar is the DNS operator,
   life is much easier, as it can inject any delegation changes directly
   into the Registry data bases.  The techniques described below are not
   needed in the case when Registrar is the DNS operator.  To reflect
   that the Registrant is not always the DNS Operator we will use the
   word "Child Operator" to describe the party that makes changes in the
   child zone.

   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.

2.4.  DNSSEC key change process

   After a DNS operator first signs its zone, there is a need to
   interact with the parent via the registration interface to "upload/
   paste-in the zone's DS information".  The action of logging in
   through the registration interface authenticates that the user is
   authorized to change delegation information published in the parent
   zone.  In the case where "Child Operator" does not have access to the
   registration account, the Registrant needs to perform the action.

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   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 this is a manual
   process with cut and paste; operational mistakes will happen.

3.  CDS (Child DS) record definition

   The DS record can only be present at the parent RFC4034 [RFC4034]
   some other 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.  The SEP bit is an optional bit to
   indicate that the key is allowed to sign 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.

   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 thus it is a "replace" operation, 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.  IANA has allocated RR code 59 for the
   CDS record.

   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.

3.1.1.  Going unsigned

   In theory the child can use the CDS to reflect to the parent that it
   wants DS records removed.  This can be accomplished by publishing CDS
   record with the following contents:

   @ IN CDS 0 0 0

   This is a suggestion and its security implications have not been
   fully examined but if like process like [RFC5011] should be used
   before this is accepted.  It is important that the Child remain
   signed until the DS record has been removed from the parent and the
   DS has timed out from all caches.

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   Note: maybe it is better to register a special DS digest algorithm
   number for this ?

   If the child zone does go unsigned, the Parental Agent should not
   treat that as intent to go unsigned since that could be an attack.
   An attacker could spoof unsigned responses to queries from the
   Parental Agent in an attempt to force a break in the DNSSEC chain.

4.  Automating DS maintainance with CDS records

4.1.  CDS Publication

   CDS records are intended to be "consumed" by delegation trust
   maintainers, to enable this constraints are placed on how the CDS
   record as follows:

   o  Location: "the CDS record 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 RR-set's."

   o  Continuity: "MUST not break the current delegation if applied"

   If any these conditions fail the CDS record MUST be ignored,
   similarly the absence of CDS record signals "No change" in the
   current DS set.  The use of CDS is optional.

4.2.  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 thus it is
   not be able to use a standard validator.

   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.  If one exits it applies the checks from section X
         and if the CDS and DS ``differ'' it applies the changes.

   Pushing  The Parental Agent in its user interface has a button {Fetch
         DS} when pushed preforms the CDS processing.

   In the "Polling" case the Parental Agent may apply additional rules
   that defer the acceptance of CDS information, these rules include CDS
   remain in place for some time.  For example RFC 5011 [RFC5011] uses

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   hold down timers that require new keying information to be published
   for a month before acceptance as new trust anchor.  It is up to each
   "Parent" and "Parental Agent" to publish minimal rules they apply for
   child to follow in these cases.  The rules SHOULD also include the
   list of understood digest algorithms.

   If at least one DS and one CDS records exist, the Parental Agent
   validates and then copies the contents of the CDS RRset and replaces
   the entire existing DS set with the new one.

   When using CDS to publish its key rollover information it is the
   child's responsibility to monitor the parent for changes to the DS
   RRset before performing the next action in the key rollover sequence.
   What this implies is that the child MUST NOT follow a strict time-
   line but rather strict sequence of steps with time checks.

4.3.  Usage

   The Parental Agent SHOULD ensure that old versions of the CDS RRset
   do not overwrite newer versions, which could occur if the parent
   performs the checks too frequently.  In that case when there is a
   delay updating the secondary name servers for the child zone.  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.

   If the CDS RRset does not exist, the parent MUST take no action.
   Specifically it MUST NOT delete the existing DS RRset.

   If the child zone loses the secret key(s) for the zone, and needs to
   reset the parent DS RRset, this can only be accomplished by an out-
   of-band mechanism not defined here.

   To mitigate situations where a key signing key has been compromised,
   the Parental Agent MAY take extra security measures, for example
   informing ( by email or other methods ) the child zone administrator
   of the change, or by delaying the acceptance of the new DS RRset for
   some period of time.  However the precise out-of-band measures that a
   parent zone SHOULD take are outside the scope of this document.

4.4.  Parent calculates DS

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   There are cases where the Parent wants to calculate the DS record for
   them self 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 the Parent operates in "calculate DS" mode it can operate in one
   of two modes "full" i.e. it only publishes DS records it calculates
   from DNSKEY records, and "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.  In the RRR case this
   calculation can take place either at the Registry or the Registrar
   (as Parental Agent).  If the Registry performs the calculation
   Parental Agent needs to submit DNSKEY records and possibly (C)DS
   records as well.

5.  IANA Considerations

   IANA has assigned RR Type code 59 for CDS.  This was done for an
   earlier version of this document (draft-barwood-dnsop-ds-publish).

6.  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 DNSKEY's 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.

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   A compromise of the 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.

   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.

7.  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.

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

8.  References

8.1.  Normative References

   [IANA.AS_Numbers]
              IANA, "Autonomous System (AS) Numbers", ,
              <http://www.iana.org/assignments/as-numbers>.

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

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8.2.  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.

   [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.

   [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.

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

Appendix A.  Changes / Author Notes.

   [RFC Editor: Please remove this section before publication ]

   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,

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   o  added more people to acks.

   o  added description of enterprise situations

   o  Unified on usign 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.

   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

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Internet-Draft         automating delegation maint             June 2013

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

   Email: ogud@ogud.com

   George Barwood
   33 Sandpiper Close
   Gloucester  GL2 4LZ
   United Kingdom

   Email: george.barwood@blueyonder.co.uk

Kumari, et al.          Expires December 19, 2013              [Page 14]