dnsop                                                     O. Gudmundsson
Internet-Draft                                                CloudFlare
Intended status: Informational                                P. Wouters
Expires: September 21, 2016                                      Red Hat
                                                          March 20, 2016

            Managing DS records from parent via CDS/CDNSKEY


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

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

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

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 21, 2016.

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Copyright Notice

   Copyright (c) 2016 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
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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.  Removing a DS Record  . . . . . . . . . . . . . . . . . .   3
     1.2.  Introducing a DS record . . . . . . . . . . . . . . . . .   3
     1.3.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.4.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  The Three Uses of CDS . . . . . . . . . . . . . . . . . . . .   4
     2.1.  The meaning of the CDS RRset  . . . . . . . . . . . . . .   5
   3.  Enabling DNSSEC via CDS/CDNSKEY . . . . . . . . . . . . . . .   5
     3.1.  Accept policy via authenticated channel . . . . . . . . .   5
     3.2.  Accept with extra checks  . . . . . . . . . . . . . . . .   5
     3.3.  Accept after delay  . . . . . . . . . . . . . . . . . . .   6
     3.4.  Accept with challenge . . . . . . . . . . . . . . . . . .   6
   4.  DNSSEC Delete Algorithm . . . . . . . . . . . . . . . . . . .   6
   5.  Security considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

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

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   [RFC7344] did not include a method for the Initial Trust
   establishment and left it to each parent to come up with an
   acceptance policy.

1.1.  Removing a DS Record

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

   1  alternative to doing a proper DNSSEC algorithm rollover due to
      operational limitations such as software limitations.

   2  moving from a DNSSEC operator to a non-DNSSEC capable operator.

   3  moving to an operator that cannot/does-not-want to do a proper
      DNSSEC rollover.

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

   5  the domain holder no longer wants DNSSEC enabled.

   The lack of a "remove my DNSSEC" option is cited as a reason why some
   operators cannot deploy DNSSEC, as this is seen as an operational

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

1.2.  Introducing a DS record

   The converse issue is how a child domain instructs the parent that it
   wants to have a DS record added.  This problem can be solved using a
   few simplifying assumptions.  This document makes the assumption that
   there are reasonable policies that can be applied and will allow
   automation of trust introduction.

   Not being able to enable trust via an easily automated mechanism is
   hindering DNSSEC at scale for DNS hosters that do not have automated
   access to the "registry" of the child zone's parent.

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1.3.  Notation

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

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

   When the document uses the word "parent" it implies an entity that is
   authorized to insert DS records into the parent zone on behalf of the
   child domain.  Which entity this exactly is does not matter.  It
   could be the Registrar or Reseller that the child domain was
   purchased from.  It could be the Registry that the domain is
   registered in when allowed.  It could be some other entity when the
   RRR framework is not used.

1.4.  Terminology

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

2.  The Three Uses of CDS

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

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

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

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

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

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2.1.  The meaning of the CDS RRset

   The semantic meaning of publishing a CDS RRset is interpreted to

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

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

3.  Enabling DNSSEC via CDS/CDNSKEY

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

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

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

3.1.  Accept policy via authenticated channel

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

3.2.  Accept with extra checks

   In this case the parent checks that the source of the notification is
   allowed to request the DS insertion.  The checks could include
   whether this is a trusted entity, whether the nameservers correspond
   to the requestor, whether there have been any changes in registration

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   in the last few days, etc.  The parent can also send a notification
   requesting a confirmation.

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

3.3.  Accept after delay

   In this case, if the parent deems the request valid, it starts
   monitoring the CDS RRset at the child nameservers over period of time
   to make sure nothing changes.  After some time or after a number of
   checks, preferably from different vantage points in the network, the
   parent accepts the CDS RRset as a valid signal to update its DS RRset
   for this child.

3.4.  Accept with challenge

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

4.  DNSSEC Delete Algorithm

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

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

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

   In the context of CDS and CDNSKEY records, DNSSEC algorithm 0 is
   defined to mean that the entire DS RRset MUST be removed.  The
   contents of the CDS or CDNSKEY RRset MUST contain one RR and only
   contain the fixed fields as shown below.

   1  CDS 0 0 0

   2  CDNSKEY 0 3 0

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   The keying material payload is represented by a single 0.  This
   record is signed in the same way as regular CDS/CDNSKEY RRsets are

   Strictly speaking the CDS record could be "CDS X 0 X" as only the
   DNSKEY algorithm is what signals the DELETE operation, but for
   clarity the "0 0 0" notation is mandated - this is not a definition
   of DS Digest algorithm 0.  The same argument applies to "CDNSKEY 0 3
   0", the value 3 in second field is mandated by RFC4034 section 2.1.2.

   Once the parent has verified the CDS/CDNSKEY RRset and it has passed
   other acceptance tests, the parent MUST remove the DS RRset.  After
   waiting a sufficient amount of time - depending the the parental
   TTL's - the child can start the process of turning off DNSSEC.

5.  Security considerations

   This document's main goal is to avoid validation failures when a
   domain moves from one DNS operator to another.  Turning off DNSSEC
   reduces the security of the domain and thus should only be done as a
   last resort.

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

   Users SHOULD keep in mind that re-establishing trust in delegation
   can be hard and takes a long time.  Before deciding to complete the
   rollover via an unsigned state, all options SHOULD be considered.

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

6.  IANA considerations

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

   Algorithm 0 adds a reference to this document.

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7.  References

7.1.  Normative References

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,

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

7.2.  Informative References

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

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

Appendix A.  Acknowledgements

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

Authors' Addresses

   Olafur Gudmundsson

   Email: olafur+ietf@cloudflare.com

   Paul Wouters
   Red Hat

   Email: pwouters@redhat.com

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