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Internet Engineering Task Force (IETF)                    O. GudmundssonRequest for Comments: 8078                                    CloudFlareUpdates:7344                                                 P. WoutersCategory: Standards Track                                        Red HatISSN: 2070-1721                                               March 2017Managing DS Records from the Parent via CDS/CDNSKEYAbstractRFC 7344 specifies how DNS trust can be maintained across key   rollovers in-band between parent and child.  This document elevatesRFC 7344 from Informational to Standards Track.  It also adds a   method for initial trust setup and removal of a 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   a 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.Gudmundsson & Wouters        Standards Track                    [Page 1]

RFC 8078                   Managing DS Records                March 2017Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc8078.Copyright Notice   Copyright (c) 2017 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Gudmundsson & Wouters        Standards Track                    [Page 2]

RFC 8078                   Managing DS Records                March 2017Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .31.1.  Introducing a DS Record . . . . . . . . . . . . . . . . .31.2.  Removing a DS Record  . . . . . . . . . . . . . . . . . .41.3.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .41.4.  Terminology . . . . . . . . . . . . . . . . . . . . . . .52.  The Three Uses of CDS . . . . . . . . . . . . . . . . . . . .52.1.  The Meaning of the CDS RRset  . . . . . . . . . . . . . .53.  Enabling DNSSEC via CDS/CDNSKEY . . . . . . . . . . . . . . .63.1.  Accept Policy via Authenticated Channel . . . . . . . . .63.2.  Accept with Extra Checks  . . . . . . . . . . . . . . . .63.3.  Accept after Delay  . . . . . . . . . . . . . . . . . . .73.4.  Accept with Challenge . . . . . . . . . . . . . . . . . .73.5.  Accept from Inception . . . . . . . . . . . . . . . . . .74.  DNSSEC Delete Algorithm . . . . . . . . . . . . . . . . . . .75.  Security Considerations . . . . . . . . . . . . . . . . . . .86.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .96.1.  PromotingRFC 7344 to Standards Track . . . . . . . . . .97.  References  . . . . . . . . . . . . . . . . . . . . . . . . .97.1.  Normative References  . . . . . . . . . . . . . . . . . .97.2.  Informative References  . . . . . . . . . . . . . . . . .10   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .10   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .101.  Introduction   CDS (Child DS) and CDNSKEY (Child DNSKEY) [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.   In addition, [RFC7344] lacks two different options for full automated   operation to be possible.  It does not define a method for the   initial trust establishment, leaving it open to each parent to come   up with an acceptance policy.  Additionally, [RFC7344] does 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 a 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.Gudmundsson & Wouters        Standards Track                    [Page 3]

RFC 8078                   Managing DS Records                March 2017   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 address 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 or 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, an algorithm rollover cannot be       performed.   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 are how information is   represented and who calculates the DS digest.  For clarity, this   document uses the term "CDS" to mean "either CDS or CDNSKEY".   When this 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.  ItGudmundsson & Wouters        Standards Track                    [Page 4]

RFC 8078                   Managing DS Records                March 2017   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 its parent to perform:   1.  Enable DNSSEC validation, i.e., place an initial DS Resource       Record Set (RRset) in the parent.   2.  Roll over the KSK.  This means updating the DS records in the       parent to reflect the new set of KSKs 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.   KSK rollover 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 Resets differ.Gudmundsson & Wouters        Standards Track                    [Page 5]

RFC 8078                   Managing DS Records                March 2017   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.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 pre-publish 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.Gudmundsson & Wouters        Standards Track                    [Page 6]

RFC 8078                   Managing DS Records                March 20173.3.  Accept after Delay   In this case, if the parent deems the request valid, it starts   monitoring the CDS RRset at the child nameservers over a 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 that 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.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.Gudmundsson & Wouters        Standards Track                    [Page 7]

RFC 8078                   Managing DS Records                March 2017   The contents of the CDS or CDNSKEY RRset MUST contain one RR and only   contain the exact fields as shown below.      CDS 0 0 0 0      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.   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 the 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 TTLs   -- the child can start the process of turning off DNSSEC.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, it has a reasonable assurance that the CDS/   CDNSKEY RRset 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 (Top-Level Domain (TLDs) in   particular), this document cannot give a definitive list of valid   acceptance criteria.  Parental zones should look at the listedGudmundsson & Wouters        Standards Track                    [Page 8]

RFC 8078                   Managing DS Records                March 2017   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   IANA has assigned entry number 0 in the "DNS Security Algorithm   Numbers" registry as follows:   +--------+--------------+----------+----------+---------+-----------+   | Number | Description  | Mnemonic | Zone     | Trans.  | Reference |   |        |              |          | Signing  | Sec.    |           |   +--------+--------------+----------+----------+---------+-----------+   | 0      | Delete DS    | DELETE   | N        | N       | [RFC4034] |   |        |              |          |          |         | [RFC4398] |   |        |              |          |          |         | [RFC8078] |   +--------+--------------+----------+----------+---------+-----------+6.1.  PromotingRFC 7344 to Standards Track   Experience has shown that CDS and CDNSKEY are useful in the   deployment of DNSSEC.  [RFC7344] was published as Informational; this   document elevatesRFC 7344 to Standards Track.7.  References7.1.  Normative 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>.   [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>.Gudmundsson & Wouters        Standards Track                    [Page 9]

RFC 8078                   Managing DS Records                March 20177.2.  Informative References   [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>.Acknowledgments   We thank a number of people that have provided feedback and useful   comments including Bob Harold, John Levine, Dan York, Shane Kerr,   Jacques Latour, and especially Matthijs Mekking.Authors' Addresses   Olafur Gudmundsson   CloudFlare   Email: olafur+ietf@cloudflare.com   Paul Wouters   Red Hat   Email: pwouters@redhat.comGudmundsson & Wouters        Standards Track                   [Page 10]