Managing DS Records from the Parent via CDS/CDNSKEY
draft-ietf-dnsop-maintain-ds-06

dnsop                                                     O. Gudmundsson
Internet-Draft                                                CloudFlare
Intended status: Standards Track                              P. Wouters
Expires: July 14, 2017                                           Red Hat
                                                        January 10, 2017

            Managing DS records from parent via CDS/CDNSKEY
                    draft-ietf-dnsop-maintain-ds-06

Abstract

   RFC7344 specifies how DNS trust can be maintained across key
   rollovers in-band between parent and child.  This document elevates
   RFC7344 from informational to standards track and adds a standard
   track method for initial trust setup and removal of secure entry
   point.

   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 the organizations
   involved.  The inability to disable DNSSEC via in-band signaling is
   seen as a problem or liability that prevents some DNSSEC adoption at
   large scale.  This document adds a method for in-band signaling of
   these DNSSEC status changes.

   This document describes reasonable policies to ease deployment of the
   initial acceptance of new secure entry points (DS records)

   It is preferable that operators collaborate on the transfer or move
   of a domain.  The best method is to perform a Key Signing Key ("KSK")
   plus Zone Signing Key ("ZSK") rollover.  If that is not possible, the
   method using an unsigned intermediate state described in this
   document can be used to move the domain between two parties.  This
   leaves the domain temporarily unsigned and vulnerable to DNS
   spoofing, but that is preferred over the alternative of validation
   failures due to a mismatched DS and DNSKEY record.

Status of This Memo

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

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

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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on July 14, 2017.

Copyright Notice

   Copyright (c) 2017 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
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   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Introducing a DS record . . . . . . . . . . . . . . . . .   3
     1.2.  Removing 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 . . . . . . . . .   6
     3.2.  Accept with extra checks  . . . . . . . . . . . . . . . .   6
     3.3.  Accept after delay  . . . . . . . . . . . . . . . . . . .   6
     3.4.  Accept with challenge . . . . . . . . . . . . . . . . . .   6
     3.5.  Accept from inception . . . . . . . . . . . . . . . . . .   7
   4.  DNSSEC Delete Algorithm . . . . . . . . . . . . . . . . . . .   7
   5.  Security considerations . . . . . . . . . . . . . . . . . . .   8
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Promoting RFC7344 to standards track  . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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1.  Introduction

   CDS/CDNSKEY [RFC7344] records are used to signal changes in secure
   entry points.  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.  This document elevates [RFC7344] from
   informational to standards track RFC.

   In addition, [RFC7344] is lacking two different options for full
   automated operation to be possible.  It did not define a method for
   the Initial Trust establishment, leaving it open to each parent to
   come up with an acceptance policy.  Additionally, [RFC7344] did not
   provide a "delete" signal for the child to inform the parent that the
   DNSSEC security for its domain must be removed.

1.1.  Introducing a DS record

   Automated insertion of DS records has been limited for many zones by
   the requirement that all changes pass through a "registry" of the
   child zone's parent.  This has significantly hindered deployment of
   DNSSEC at large scale for DNS hosters, as the child zone owner is
   often not aware or able to update DNS records such as the DS record.

   This document describes a few possible methods for the parent to
   accept a request by the child to add a DS record to its zone.  These
   methods have different security properties that addresses different
   deployment scenarios, all resulting in an automated method of trust
   introduction.

1.2.  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, 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
      performed.

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   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
   risk.

   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.

1.3.  Notation

   Signaling can happen via CDS or CDNSKEY records.  The only
   differences between the two records is how information is
   represented, and who calculates the DS digest.  For clarity, this
   document uses the term "CDS" throughout the document to mean "either
   CDS or CDNSKEY".

   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.  Or it could be some other entity.

1.4.  Terminology

   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.  The Three Uses of CDS

   In general there are three operations that a domain wants to instruct
   their parent to perform:

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

   2  Roll over the Key Signing Key ("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.

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

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   Rolling the KSK is covered in [RFC7344].  It is considered the safest
   use case of a CDS/CDNSKEY record as it makes no change to the trust
   relationship between parent and child.  Introduction and removal of
   DS records are defined in this document.  As these CDS/CDNSKEY use
   cases create or end the trust relationship between the parent and
   child, these use cases should be carefully implemented and monitored.

2.1.  The meaning of the CDS RRset

   The semantic meaning of publishing a CDS RRset is interpreted to
   mean:

   "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 the
   DS RRset if the CDS and DS Reset's 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.  As
   long as the child is insecure, DNS answers can be forged.  The goal
   is to promote the child from insecure to secure as soon as reasonably
   possible by the parent.  This means that the period from the child's
   publication of CDS/CDNSKEY RRset to the parent publishing the
   synchronized DS RRset should be as short as possible.

   One important use 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.

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3.1.  Accept policy via authenticated channel

   In this case the parent is notified via authenticated channel UI/API
   that a CDS/CDNSKEY RRset exists.  In the case of a CDS RRset the
   parent retrieves the CDS RRset and inserts the corresponding DS RRset
   as requested.  In the case of CDNSKEY the parent retrieves the
   CDNSKEY RRset and calculates the DS record(s).  Parents may limit the
   DS record type based on local policy.  Parents SHOULD NOT refuse CDS/
   CDNSKEY updates that do not (yet) have a matching DNSKEY in the child
   zone.  This will allow the child to prepublish a spare (and
   potentially offline) DNSKEY.

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 requester, whether there have been any changes in registration
   in the last few days, etc.  The parent can also send a notification
   requesting a confirmation, for example by sending email to the
   registrant 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.  Any extra checks should have proper rate
   limiting in place to prevent abuse.

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 requester 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).  This method imposes a new task on the
   parent to monitor the child zone to see if the challenge has been
   added to the zone.  The parent should verify the challenge is
   published by all the child's nameservers and should test for this
   challenge from various diverse network locations to increase the
   security of this method as much as possible.

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3.5.  Accept from inception

   If a parent is adding a new child domain that is not currently
   delegated at all, it could use the child CDS/CDNSKEY RRset to
   immediately publish a DS RRset along with the new NS RRset.  This
   would ensure that the new child domain is never active in an insecure
   state.

4.  DNSSEC Delete Algorithm

   This document defines the previously reserved DNS Security Algorithm
   Number of value 0 in the context of CDS and CDNSKEY records to mean
   that the entire DS RRset at the parent must be removed.  The value 0
   remains reserved for the DS and DNSKEY records.

   No DNSSEC validator can treat 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 present.  In
   general the value 0 should never be used in the context of DNSKEY and
   DS records.

   The CERT record [RFC4398] defines the value 0 similarly to mean the
   algorithm in the CERT record is not defined in DNSSEC.

   The contents of the CDS or CDNSKEY RRset MUST contain one RR and only
   contain the exactly the fields as shown below.

   1  CDS 0 0 0 0

   2  CDNSKEY 0 3 0 0

   The keying material payload is represented by a single 0.  This
   record is signed in the same way as regular CDS/CDNSKEY RRsets are
   signed.  This is a change in format from strict interpretation of
   [RFC7344] and may cause problems with some deployed software.

   Strictly speaking the CDS record could be "CDS X 0 X 0" as only the
   DNSKEY algorithm is what signals the DELETE operation, but for
   clarity the "0 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 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 on the parental TTL's
   - the child can start the process of turning off DNSSEC.

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5.  Security considerations

   Turning off DNSSEC reduces the security of the domain and thus should
   only be done as a last resort in preventing DNSSEC validation errors
   due to mismatched DS and DNSKEY records.

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

   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 topologically diverse view.  It SHOULD also
   ensure that 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 amount of wait time - thus allowing a
   child administrator to cancel the request.

   This document describes a few possible acceptance criteria for the
   Initial Trust establishment.  Due to a large variety of legal
   frameworks surrounding parent domains (TLDs in particular) this
   document cannot give a definitive list of valid acceptance criteria.
   Parental zones should look at the listed methods and pick the most
   secure method possible within their legal and technical scenario,
   possibly further securing the acceptance criteria, as long as the
   deployed method still enables a fully automated method for non-direct
   parties such as third party DNS hosters.

6.  IANA considerations

   This document updates entry number 0 of the "DNS Security Algorithm
   Numbers" IANA Registry as follows:

   +------+---------+-------+-------+-------+--------------------------+
   | Numb | Descrip | Mnemo | Zone  | Trans | Reference                |
   | er   | tion    | nic   | Signi | .     |                          |
   |      |         |       | ng    | Sec.  |                          |
   +------+---------+-------+-------+-------+--------------------------+
   | 0    | Delete  | DELET | N     | N     | [RFC4034][RFC4398]RFC-   |
   |      | DS      | E     |       |       | THIS-DOCUMENT]           |
   +------+---------+-------+-------+-------+--------------------------+

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6.1.  Promoting RFC7344 to standards track

   Experience has shown that CDS/CDNSKEY are useful in the deployment of
   DNSSEC.  [RFC7344] was published as Informational, this document
   elevates RFC7344 to standards track.

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,
              <http://www.rfc-editor.org/info/rfc4034>.

   [RFC7344]  Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
              DNSSEC Delegation Trust Maintenance", RFC 7344,
              DOI 10.17487/RFC7344, September 2014,
              <http://www.rfc-editor.org/info/rfc7344>.

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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4398]  Josefsson, S., "Storing Certificates in the Domain Name
              System (DNS)", RFC 4398, DOI 10.17487/RFC4398, March 2006,
              <http://www.rfc-editor.org/info/rfc4398>.

Appendix A.  Acknowledgments

   This document is generated using the mmark tool that Miek Gieben has
   developed.  We thank number of people that have provided feedback and
   useful comments including Bob Harold, John Levine, Matthijs
   Mekking(!), Dan York, Shane Kerr, Jacques Latour.

Authors' Addresses

   Olafur Gudmundsson
   CloudFlare

   Email: olafur+ietf@cloudflare.com

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   Paul Wouters
   Red Hat

   Email: pwouters@redhat.com

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