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DNSSEC Bootstrapping

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Document Type This is an older version of an Internet-Draft whose latest revision is Replaced
Author Peter Thomassen
Last updated 2021-06-29
Replaced by draft-ietf-dnsop-dnssec-bootstrapping
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DNSOP Working Group                                         P. Thomassen
Internet-Draft                         deSEC, Secure Systems Engineering
Intended status: Standards Track                            30 June 2021
Expires: 1 January 2022

                          DNSSEC Bootstrapping


   This document describes an authenticated in-band method for automatic
   signaling of a DNS zone's delegation signer information from the
   zone's DNS operator.  The zone's registrar or registry may
   subsequently use this signal for automatic DS record provisioning in
   the parent zone.

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 1 January 2022.

Copyright Notice

   Copyright (c) 2021 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 (
   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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Notation . . . . . . . . . . . . . . . . . .   4
   2.  Description . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Preconditions . . . . . . . . . . . . . . . . . . . . . .   4
       2.1.1.  Example . . . . . . . . . . . . . . . . . . . . . . .   4
       2.1.2.  Zone Cut Clarification  . . . . . . . . . . . . . . .   5
     2.2.  Bootstrapping Method  . . . . . . . . . . . . . . . . . .   5
       2.2.1.  Steps Taken by the Child DNS Operator . . . . . . . .   5
       2.2.2.  Steps Taken by the Parental Agent . . . . . . . . . .   6
   3.  Implementation Status . . . . . . . . . . . . . . . . . . . .   7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Appendix A.  Change History (to be removed before final
           publication)  . . . . . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   *TODO remove*: this section is inspired by [RFC7344], Section 1.

   The first time a DNS Operator signs a zone, they need to communicate
   the keying material to the Parent.  Depending on the desires of the
   Parent, the Child might send their DNSKEY record, a DS record, or

   So far, out-of-band methods are typically used to complete the chain
   of trust.  In-band methods exist, in particular based on the CDS and
   CDNSKEY record types as specified in [RFC7344] and [RFC8078].
   However, such communication is only authenticated when performing a
   rollover of the Child's keys represented in the parent.  An
   authenticated in-band channel for enabling DNSSEC so far has been

   How the keying material is conveyed to the Parent during initial
   DNSSEC bootstrapping depends on the relationship the Child has with
   the Parent.  In many cases this is a manual process -- and not an
   easy one.  The communication has to occur between the DNS Operator
   and, depending on the circumstances, the Registry or the Registrar,
   possibly via the Registrant (for details, see [RFC7344], Appendix A).
   Any manual process is susceptible to mistakes and/or errors.  In
   addition, due to the annoyance factor of the process, Operators may
   avoid the process of getting a DS record set published 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 inital DS records for a hitherto insecure delegation.

   Readers are expected to be familiar with DNSSEC, including [RFC4033],
   [RFC4034], [RFC4035], [RFC6781], [RFC7344], and [RFC8078].

   This document describes a method for automated provisioning of the
   delegation trust information and proposes a polled/periodic trigger
   for simplicity.  Some users may prefer a different trigger.  These
   alternate additional triggers are not discussed in this document.

1.1.  Terminology

   The terminology we use is defined in this section.  The highlighted
   roles are as follows:

   Child  The entity on record that has the delegation of the domain
      from the Parent.

   Parent  The domain in which the Child is registered.

   Child DNS Operator  The entity that maintains and publishes the zone
      information for the Child DNS.

   Parental Agent  The entity that the Child has a relationship with to
      change its delegation information.

   Bootstrapping Domain  Given an authoritative nameserver hostname from
      the Child's NS record set, that hostname prefixed the label

   Signaling Name  A Bootstrapping Domain prefixed with a label encoding
      the Child's name.

   CDS/CDNSKEY  This notation refers to CDS and/or CDNSKEY, i.e., one or

   Base32hex Encoding  "Base 32 Encoding with Extended Hex Alphabet" as
      per [RFC4648].

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1.2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Description

   When setting up initial trust, the child generally 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

   This goal is achieved by transferring trust from the Child DNS

2.1.  Preconditions

   In order to use this technique, the following conditions have to be

   1.  The Child DNS Operator SHOULD publish CDS/CDNSKEY records at the
       Child's apex, as described in [RFC7344].

   2.  Each Bootstrapping Domain MUST be part of a securely delegated
       zone, i.e. has a valid DNSSEC chain of trust from the root.

   3.  The Child DNS Operator MUST be able to maintain and publish DNS
       information in these zone (i.e. under the Bootstrapping Domains).

   For operational or other reasons, a Bootstrapping Domain MAY coincide
   with a zone cut.

2.1.1.  Example

   When performing DNSSEC bootstrapping for the Child zone ""
   using NS records "" and "", the Child
   DNS Operator

   1.  should publish CDS/CDNSKEY records at "";

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   2.  needs to ensure that a valid DNSSEC chain of trust exists for the
       zone(s) that are authoritative for the Bootstrapping Domains
       "" and "";

   3.  must be able to maintain and publish DNS information in these

2.1.2.  Zone Cut Clarification

   A Bootstrapping Domain such as "" may be a zone
   of its own, in which case it needs to be secure and under the control
   of the Child DNS Operator.  If the Bootstrapping Domain does not
   coincide with a zone cut, these conditions are instead imposed on the
   containing zone (such as "").

   The "Bootstrapping Domain" terminology is necessary to describe the
   bootstrapping mechanism without regard to whether there is a zone cut
   at these names or not.

2.2.  Bootstrapping Method

2.2.1.  Steps Taken by the Child DNS Operator

   To perform DNSSEC bootstrapping for the Child zone, the Child DNS
   Operator MUST (re-)publish the Child's CDS/CDNSKEY records at the
   corresponding Signaling Name under each Bootstrapping Domain (see
   example below).  These records belong to the autoritative zone of the
   Bootstrapping Domain, and as such they MUST be signed with that
   zone's keys, and MUST NOT be signed with the Child zone's keys.

   The Signaling Name contains a label identifying the Child's name.
   This label MUST be equal to the SHA-256 hash digest of the Child's
   name in "Base 32 Encoding with Extended Hex Alphabet", as specified
   in [RFC4648].  Trailing padding characters ("=") MUST be dropped.

   Previous uses of CDS/CDNSKEY records are specified at the apex only
   ([RFC7344], Section 4.1).  This protocol extends the use of these
   record types on non-apex owner names for the purpose of DNSSEC
   bootstrapping.  To avoid the possibility of semantic collision, there
   MUST NOT be a zone cut at a Signaling Name.

   *TODO Remove Note 1:* The purpose of the hash function is to avoid
   the possibility of exceeding the maximum length of a DNS name.  This
   could occur if the Child name was used as is.

   *TODO Remove Note 2:* The encoding choice is like in NSEC3, except
   that SHA-256 is used instead of SHA-1.  This is to prevent other
   tenants in shared hosting environments from creating collisions.

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   To bootstrap the Child zone "" using NS records
   "" and "", the Bootstrapping Domains
   are "" and "".  The Child
   DNS Operator thus (re-)publishes the Child's CDS/CDNSKEY records
   under the names

   where "kdsqdtnelusqanhnhg8o0d72ekf6gbtbjsmj1aojq895b1me353g" is the
   unpadded Base32hex Encoding of "".  The records are
   accompanied by RRSIG records created using the key(s) of the zone
   which is authoritative for the respective Bootstrapping Domain.

   *TODO remove:* Should hash input include trailing dot?  (Command was:
   "echo -n | openssl dgst -binary -sha256 | base32hex | tr
   -d =")

2.2.2.  Steps Taken by the Parental Agent

   When the Parental Agent receives a new NS record set (or additionally
   at any other time considered appropriate), the Parental Agent,
   knowing both the Child zone name and its NS hostnames,

   1.  MUST query the CDS/CDNSKEY records located at each of the
       Signaling Names (using standard DNS resolution);

   2.  MUST perform DNSSEC validation of all responses retrieved in Step

   3.  SHOULD query the CDS/CDNSKEY records located at the Child zone
       apex, directly from each of the authoritative nameservers as
       given in the Child NS record set;

   4.  MUST checks that all CDS/CDNSKEY record sets retrieved in Steps 1
       and 3 have equal record contents;

   5.  SHOULD derive a DS record set from the retrieved CDS/CDNSKEY
       record sets and publish it in the Parent zone, as to secure the
       Child's delegation.

   If an error condition occurs during Steps 1--4, in particular:

   *  DNS resolution failure during retrieval of CDS/CDNSKEY records
      from any Signaling Name (Step 1), or failure of DNSSEC validation
      (Step 2),

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   *  Failure to retrieve CDS/CDNSKEY records located at the Child apex
      from all of the Child's authoritative nameservers (Step 3),

   *  Inconsistent responses (Step 4),

   the Parental Agent MUST NOT proceed to Step 5.  Example

   To bootstrap the Child zone "" using NS records
   "" and "", the Parental Agent

   1.  queries CDS/CDNSKEY records, using standard DNS resolution, for
       the names

   2.  performs DNSSEC validation of the responses retrieved in Step 1;

   3.  queries CDS/CDNSKEY records for "" directly from
       "" and "";

   4.  checks that CDS record sets retrieved in Step 1 agree across
       responses and also with the CDS record sets retrieved in Step 3;
       ditto for CDNSKEY;

   5.  publishes a DS record set according to the information retrieved
       in the previous steps.  Opt-out

   As a special case of Step 4 failure, the Child MAY opt out from
   DNSSEC bootstrapping by publishing a CDS/CDNSKEY record with
   algorithm 0 and other fields as specified in [RFC8078], Section 4, at
   its apex.  (This opt-out mechanism is without regard to whether the
   Child DNS Operator signs the zones and publishes records at the
   Signaling Names.)

3.  Implementation Status

   *Note to the RFC Editor*: please remove this entire section before

   *  PowerDNS supports manual creation of CDS/CDNSKEY records on non-
      apex names.

   *  TODO Proof of concept

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4.  Security Considerations

   Thoughts (to be expanded):

   *  We use at least one established chain of trust (via the secure
      delegations of the zones containing the NS hostnames).  As a

      -  communication is authenticated;

      -  process is immediate (no need for observing CDS/CDNSKEY records
         via TCP for several days);

      -  an active on-wire attacker cannot tamper with the delegation.

   *  When validating against CDS/CDNSKEY records at the Child's apex,
      the security level of the method is strictly higher than the
      "accept CDS/CDNSKEY after a while"-approch that is already in use
      at several ccTLD registries ("Accept after Delay", [RFC8078],
      Section 3.3).  This is because the method described here adds
      stronger guarantees, but removes nothing.  Perhaps this means that
      co-publication of CDS/CDNSKEY at the Child apex should be
      mandatory.  (This in turn may interact somehow with the Child's
      opt-out option.)

   *  Actors in the chain(s) of trust of the zone(s) used for
      bootstrapping (the DNS Operator themselves, plus entities further
      up in the chain) can undermine the protocol.  However,

      -  that's also possible in the case of CDS/CDNSKEY (see previous

      -  if the Child DNS Operator doesn't control the zones in which
         its NS hostnames live (including their nameservers' A records)
         because the path from the root is untrusted, you probably don't
         want to trust that operator as a whole;

      -  when bootstrapping is done upon receipt of a new NS record set,
         the window of opportunity is very small (and easily monitored
         by the Child DNS operator);

      -  mitigation exists by diversifying e.g. the nameserver
         hostname's TLDs, which is advisable anyways.

5.  IANA Considerations

   *TODO:* reserve "_boot"?

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   This document has no IANA actions.

6.  Acknowledgements

   Thanks to TODO for reviewing draft proposals and offering comments
   and suggestions.

   Thanks also to Steve Crocker, Hugo Salgado, and Ulrich Wisser for
   early-stage brainstorming.

7.  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,

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,

   [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,

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,

   [RFC6781]  Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
              Operational Practices, Version 2", RFC 6781,
              DOI 10.17487/RFC6781, December 2012,

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

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   [RFC8078]  Gudmundsson, O. and P. Wouters, "Managing DS Records from
              the Parent via CDS/CDNSKEY", RFC 8078,
              DOI 10.17487/RFC8078, March 2017,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

Appendix A.  Change History (to be removed before final publication)

   *  draft-thomassen-dnsop-dnssec-bootstrapping-00

   |  Initial public draft.

Author's Address

   Peter Thomassen
   deSEC, Secure Systems Engineering


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