DNSSEC Trust Anchor Publication for the Root Zone
draft-ietf-dnsop-rfc7958bis-06

Network Working Group                                           J. Abley
Internet-Draft                                                Cloudflare
Obsoletes: 7958 (if approved)                                J. Schlyter
Intended status: Informational                                  Kirei AB
Expires: 8 March 2025                                          G. Bailey
                                                             Independent
                                                              P. Hoffman
                                                                   ICANN
                                                        4 September 2024

           DNSSEC Trust Anchor Publication for the Root Zone
                     draft-ietf-dnsop-rfc7958bis-06

Abstract

   The root zone of the global Domain Name System (DNS) is
   cryptographically signed using DNS Security Extensions (DNSSEC).

   In order to obtain secure answers from the root zone of the DNS using
   DNSSEC, a client must configure a suitable trust anchor.  This
   document describes the format and publication mechanisms IANA uses to
   distribute the DNSSEC trust anchors.

   This document obsoletes RFC 7958.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-dnsop-rfc7958bis/.

   Source for this draft and an issue tracker can be found at
   https://github.com/paulehoffman/draft-bash-rfc7958bis.

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 https://datatracker.ietf.org/drafts/current/.

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   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 8 March 2025.

Copyright Notice

   Copyright (c) 2024 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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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  IANA DNSSEC Root Zone Trust Anchor Format and Semantics . . .   4
     2.1.  XML Syntax  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  XML Semantics . . . . . . . . . . . . . . . . . . . . . .   5
     2.3.  XML Example . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Root Zone Trust Anchor Retrieval  . . . . . . . . . . . . . .   8
     3.1.  Retrieving Trust Anchors with HTTPS and HTTP  . . . . . .   8
     3.2.  Accepting DNSSEC Trust Anchors  . . . . . . . . . . . . .   9
     3.3.  Changes in the Trust Model for Distribution . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
     4.1.  Security Considerations for Relying Parties . . . . . . .  10
       4.1.1.  validUntil  . . . . . . . . . . . . . . . . . . . . .  10
       4.1.2.  Comparison of Digest and a publickeyinfo  . . . . . .  10
       4.1.3.  Different Outputs from Processing the Trust Anchor
               File  . . . . . . . . . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Changes from RFC 7958  . . . . . . . . . . . . . . .  13
   Appendix B.  Historical Note  . . . . . . . . . . . . . . . . . .  13
   Appendix C.  Acknowledgemwents  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

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1.  Introduction

   The global Domain Name System (DNS) is described in [RFC1034] and
   [RFC1035].  DNS Security Extensions (DNSSEC) are described in
   [RFC9364].

   In the DNSSEC protocol, Resource Record Sets (RRSets) are signed
   cryptographically.  This means that a response to a query contains
   signatures that allow the integrity and authenticity of the RRSet to
   be verified.  DNSSEC signatures are validated by following a chain of
   signatures to a "trust anchor".  The reason for trusting a trust
   anchor is outside the DNSSEC protocol, but having one or more trust
   anchors is required for the DNSSEC protocol to work.

   The publication of trust anchors for the root zone of the DNS is an
   IANA function performed by ICANN, through its affiliate Public
   Technical Identifiers (PTI).  A detailed description of corresponding
   key management practices can be found in [DPS].

   This document describes the formats and distribution methods of
   DNSSEC trust anchors that is used by IANA for the root zone of the
   DNS.  Other organizations might have different formats and mechanisms
   for distributing DNSSEC trust anchors for the root zone; however,
   most operators and software vendors have chosen to rely on the IANA
   trust anchors.

   The formats and distribution methods described in this document are a
   complement to, not a substitute for, the automated DNSSEC trust
   anchor update protocol described in [RFC5011].  That protocol allows
   for secure in-band succession of trust anchors when trust has already
   been established.  This document describes one way to establish an
   initial trust anchor that can be used by [RFC5011].

   This document obsoletes [RFC7958].

1.1.  Definitions

   The term "trust anchor" is used in many different contexts in the
   security community.  Many of the common definitions conflict because
   they are specific to a specific system, such as just for DNSSEC or
   just for S/MIME messages.

   In cryptographic systems with hierarchical structure, a trust anchor
   is an authoritative entity for which trust is assumed and not
   derived.  The format of the entity differs in different systems, but
   the basic idea, the decision to trust this entity is made outside of
   the system that relies on it, is common to all the common uses of the
   term "trust anchor".

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   The root zone trust anchor formats published by IANA are defined in
   Section 2.  [RFC4033] defines a trust anchor as "A configured DNSKEY
   RR or DS RR hash of a DNSKEY RR".  Note that the formats defined here
   do not match the definition of "trust anchor" from [RFC4033];
   however, a system that wants to convert the trusted material from
   IANA into a Delegation Signer (DS) RR can do so.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "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.  IANA DNSSEC Root Zone Trust Anchor Format and Semantics

   IANA publishes trust anchors for the root zone as an XML document
   that contains the hashes of the DNSKEY records and optionally the
   keys from the DNSKEY records.

   This format and the semantics associated are described in the rest of
   this section.

   Note that the XML document can have XML comments.  For example, IANA
   might use these comments to add pointers to important information on
   the IANA web site.  XML comments are only used as human-readable
   commentary, not extensions to the grammar.

   The XML document contains a set of hashes for the DNSKEY records that
   can be used to validate the root zone.  The hashes are consistent
   with the defined presentation format of a DS resource.

   The XML document also can contain the keys and flags from the DNSKEY
   records.  The keys and flags are consistent with the defined
   presentation format of a DNSKEY resource.

   Note that the hashes are mandatory in the syntax, but the keys are
   optional.

2.1.  XML Syntax

   A RELAX NG Compact Schema [RELAX-NG] for the documents used to
   publish trust anchors is:

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   datatypes xsd = "http://www.w3.org/2001/XMLSchema-datatypes"

   start = element TrustAnchor {
     attribute id { xsd:string },
     attribute source { xsd:string },
     element Zone { xsd:string },
     keydigest+
   }

   keydigest = element KeyDigest {
     attribute id { xsd:string },
     attribute validFrom { xsd:dateTime },
     attribute validUntil { xsd:dateTime }?,

     element KeyTag {
         xsd:nonNegativeInteger { maxInclusive = "65535" } },
     element Algorithm {
         xsd:nonNegativeInteger { maxInclusive = "255" } },
     element DigestType {
         xsd:nonNegativeInteger { maxInclusive = "255" } },
     element Digest { xsd:hexBinary },
     publickeyinfo?
   }

   publickeyinfo =
     element PublicKey { xsd:base64Binary },
     element Flags {
        xsd:nonNegativeInteger { maxInclusive = "65535" } }

2.2.  XML Semantics

   The TrustAnchor element is the container for all of the trust anchors
   in the file.

   The id attribute in the TrustAnchor element is an opaque string that
   identifies the set of trust anchors.  Its value has no particular
   semantics.  Note that the id element in the TrustAnchor element is
   different than the id element in the KeyDigest element, described
   below.

   The source attribute in the TrustAnchor element gives information
   about where to obtain the TrustAnchor container.  It is likely to be
   a URL and is advisory only.

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   The Zone element in the TrustAnchor element states to which DNS zone
   this container applies.  The element is in presentation format as
   specified in [RFC1035], including the trailing dot.  The root zone is
   indicated by a single period (.) character without any quotation
   marks.

   The TrustAnchor element contains one or more KeyDigest elements.
   Each KeyDigest element represents the digest of a past, current, or
   potential future DNSKEY record of the zone defined in the Zone
   element.  The values for the elements in the KeyDigest element are
   defined in [RFC4034].  The IANA registries for these values are
   described in [RFC9157].

   The id attribute in the KeyDigest element is an opaque string that
   identifies the hash.  Note that the id element in the KeyDigest
   element is different than the id element in the TrustAnchor element
   described above.

   The validFrom and validUntil attributes in the KeyDigest element
   specify the range of times that the KeyDigest element can be used as
   a trust anchor.

   The KeyTag element in the KeyDigest element contains the key tag for
   the DNSKEY record represented in this KeyDigest.

   The Algorithm element in the KeyDigest element contains the DNSSEC
   signing algorithm identifier for the DNSKEY record represented in
   this KeyDigest.

   The DigestType element in the KeyDigest element contains the DNSSEC
   digest algorithm identifier for the DNSKEY record represented in this
   KeyDigest.

   The Digest element in the KeyDigest element contains the hexadecimal
   representation of the hash for the DNSKEY record represented in this
   KeyDigest.

   The publickeyinfo named pattern in the KeyDigest element contains two
   mandatory elements: the base64 representation of the public key for
   the DNSKEY record represented in this KeyDigest, and the flags of the
   DNSKEY record represented in this KeyDigest.  The publickeyinfo named
   pattern is optional and is new in this version of the specification.
   It can be useful when IANA has a trust anchor that has not yet been
   published in the DNS root, and for calculating a comparison to the
   Digest element.

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2.3.  XML Example

   The following is an example of what the trust anchor file might look
   like.  The full public key is only given for the trust anchor that
   does not have a validFrom ttime in the past.

   <?xml version="1.0" encoding="UTF-8"?>
   <TrustAnchor id="E9724F53-1851-4F86-85E5-F1392102940B"
     source="http://data.iana.org/root-anchors/root-anchors.xml">
     <Zone>.</Zone>
     <KeyDigest id="Kjqmt7v"
         validFrom="2010-07-15T00:00:00+00:00"
         validUntil="2019-01-11T00:00:00+00:00">  <!-- This key
         is no longer valid, since validUntil is in the past -->
       <KeyTag>19036</KeyTag>
       <Algorithm>8</Algorithm>
       <DigestType>2</DigestType>
       <Digest>
   49AAC11D7B6F6446702E54A1607371607A1A41855200FD2CE1CDDE32F24E8FB5
       </Digest>
     </KeyDigest>
     <KeyDigest id="Klajeyz" validFrom="2017-02-02T00:00:00+00:00">
       <KeyTag>20326</KeyTag>
       <Algorithm>8</Algorithm>
       <DigestType>2</DigestType>
       <Digest>
   E06D44B80B8F1D39A95C0B0D7C65D08458E880409BBC683457104237C7F8EC8D
       </Digest>
       <PublicKey>
         AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3+/4Rg
         WOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kvArMtNROxVQ
         uCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF0jLHwVN8efS3rCj
         /EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+eoZG+SrDK6nWeL3c6H5Ap
         xz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfdRUfhHdY6+cn8HFRm+2hM8AnXG
         Xws9555KrUB5qihylGa8subX2Nn6UwNR1AkUTV74bU=
       </PublicKey>
       <Flags>257</Flags>
     </KeyDigest>
     <!-- The following is called "KSK-2024" as a shorthand name -->
     <KeyDigest id="Kmyv6jo" validFrom="2024-07-18T00:00:00+00:00">
       <KeyTag>38696</KeyTag>
       <Algorithm>8</Algorithm>
       <DigestType>2</DigestType>
       <Digest>
   683D2D0ACB8C9B712A1948B27F741219298D0A450D612C483AF444A4C0FB2B16
       </Digest>
     </KeyDigest>
   </TrustAnchor>

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   The DS RRset derived from this example would be:

   . IN DS 20326 8 2
      E06D44B80B8F1D39A95C0B0D7C65D08458E880409BBC683457104237C7F8EC8D
   . IN DS 38696 8 2
      683D2D0ACB8C9B712A1948B27F741219298D0A450D612C483AF444A4C0FB2B16

   Note that this DS record set only has two records.  The potential
   third record, the one that would have included the key tag 19036, is
   already invalid based on the validUntil attribute's value and is thus
   not part of the trust anchor set.

   The DNSKEY RRset derived from this example would be:

   . IN DNSKEY 257 3 8
     AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3
     +/4RgWOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kv
     ArMtNROxVQuCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF
     0jLHwVN8efS3rCj/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+e
     oZG+SrDK6nWeL3c6H5Apxz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfd
     RUfhHdY6+cn8HFRm+2hM8AnXGXws9555KrUB5qihylGa8subX2Nn6UwN
     R1AkUTV74bU=

   Note that this DNSKEY record set only has one record.  One potential
   second record, the one that would have been based on the key tag
   19036, is already invalid based on the validUntil attribute's value
   and is thus not part of the trust anchor set.  The other potential
   second record, the one that would have been based on the key tag
   38696, does not contain the optional publickeyinfo named pattern and
   therefore the DNSKEY record for it cannot be calculated.

3.  Root Zone Trust Anchor Retrieval

3.1.  Retrieving Trust Anchors with HTTPS and HTTP

   Trust anchors are available for retrieval using HTTPS and HTTP.

   In this section, all URLs are given using the "https:" scheme.  If
   HTTPS cannot be used, replace the "https:" scheme with "http:".

   The URL for retrieving the set of hashes in the XML file described in
   Section 2 is <https://data.iana.org/root-anchors/root-anchors.xml>.

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3.2.  Accepting DNSSEC Trust Anchors

   A validator operator can choose whether or not to accept the trust
   anchors described in this document using whatever policy they want.
   In order to help validator operators verify the content and origin of
   trust anchors they receive, IANA uses digital signatures that chain
   to an ICANN-controlled Certificate Authority (CA) over the trust
   anchor data.

   It is important to note that the ICANN CA is not a DNSSEC trust
   anchor.  Instead, it is an optional mechanism for verifying the
   content and origin of the XML and certificate trust anchors.

   The content and origin of the XML file can be verified using a
   digital signature on the file.  IANA provides a detached
   Cryptographic Message Syntax (CMS) [RFC5652] signature that chains to
   the ICANN CA with the XML file.
   This can be useful for validator operators who have received a copy
   of the ICANN CA's public key in a trusted out-of-band fashion.  The
   URL for a detached CMS signature for the XML file is
   <https://data.iana.org/root-anchors/root-anchors.p7s>.

   Another method IANA uses to help validator operators verify the
   content and origin of trust anchors they receive is to use the
   Transport Layer Security (TLS) protocol for distributing the trust
   anchors.  Currently, the CA used for data.iana.org is well known,
   that is, one that is a WebTrust-accredited CA.  If a system
   retrieving the trust anchors trusts the CA that IANA uses for the
   "data.iana.org" web server, HTTPS SHOULD be used instead of HTTP in
   order to have assurance of data origin.

3.3.  Changes in the Trust Model for Distribution

   IANA used to distribute the trust anchors as a self-signed PGP
   message and as a self-issued certificate signing request; this was
   described in [RFC7958].  This document removes those methods because
   they relied on a trust model that mixed out-of-band trust of
   authentication keys with out-of-band trust of the DNSSEC root keys.
   Note, however, that cryptographic assurance for the contents of the
   trust anchor now comes from the web PKI or the ICANN CA as described
   in Section 3.2.  This cryptographic assurance is bolstered by
   informal comparisons made by users of the trust anchors, such as
   software vendors comparing the trust anchor files they are using.

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4.  Security Considerations

   This document describes how DNSSEC trust anchors for the root zone of
   the DNS are published.  Many DNSSEC clients will only configure IANA-
   issued trust anchors for the DNS root to perform validation.  As a
   consequence, reliable publication of trust anchors is important.

   This document aims to specify carefully the means by which such trust
   anchors are published, with the goal of making it easier for those
   trust anchors to be integrated into user environments.  Some of the
   methods described (such as accessing over the web with or without
   verifying the signature on the file) have different security
   properties; users of the trust anchor file need to consider these
   when choosing whether to load the set of trust anchors.

4.1.  Security Considerations for Relying Parties

   The body of this document does not specify any particular behavior
   for relying parties.  In specific, it does not say how a relying
   party should treat the trust anchor file as a whole.  However, some
   of the contents of the trust anchor file require particular attention
   for relying parties.

4.1.1.  validUntil

   Note that the validUntil attribute of the KeyDigest element is
   optional.  If the relying party is using a trust anchor that has a
   KeyDigest element that does not have a validUntil attribute, it can
   change to a trust anchor with a KeyDigest element that does have a
   validUntil attribute, as long as that trust anchor's validUntil
   attribute is in the future and the KeyTag, Algorithm, DigestType, and
   Digest elements of the KeyDigest are the same as the previous trust
   anchor.

   Relying parties SHOULD NOT use a KeyDigest outside of the time range
   given in the validFrom and validUntil attributes.

4.1.2.  Comparison of Digest and a publickeyinfo

   A KeyDigest element can contain both a Digest and a publickeyinfo
   named pattern.  If the Digest element would not be a proper DS record
   for a DNSKEY record represented by the publickeyinfo named pattern,
   relying parties MUST NOT use that KeyDigest as a trust anchor.  A
   relying party that wants to make such a comparison needs to marshall
   the elements of the DNSKEY record that became the DS record using the
   algorithm specified in Section 5.1.4 of [RFC4034].

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   Relying parties need to implement trust anchor matching carefully.  A
   single trust anchor represented by a KeyDigest element can
   potentially change its Digest and KeyTag values between two versions
   of the trust anchor file, for example when the key is revoked or the
   flag value changes for some other reason.  Relying parties which fail
   to take this property into account are at risk of using an incorrect
   set of trust anchors.

4.1.3.  Different Outputs from Processing the Trust Anchor File

   Relying parties that require the optional publickeyinfo named pattern
   to create trust anchors will store fewer trust anhcors than those
   that only require a Digest element.  Thus, two systems processing the
   same trust anchor file can end up with a different set of trust
   anchors.

5.  IANA Considerations

   Each time IANA produces a new trust anchor, it MUST publish that
   trust anchor using the format described in this document.

   IANA MAY delay the publication of a new trust anchor for operational
   reasons, such as having a newly-created key in multiple facilities.

   When a trust anchor that was previously published is no longer
   suitable for use, IANA MUST update the trust anchor document
   accordingly by setting a validUntil date for that trust anchor.  The
   validUntil attribute that is added MAY be a date in the past or in
   the future, depending on IANA's operational choices.

   More information about IANA's policies and procedures for how the
   cryptographic keys for the DNS root zone are managed (also known as
   "DNSSEC Practice Statements" or "DPSs") can be found at
   https://www.iana.org/dnssec/procedures (https://www.iana.org/dnssec/
   procedures).

   [RFC7958] defined id-mod-dns-resource-record, value 70, which was
   added to the the "SMI Security for PKIX Module Identifier" registry.
   This document no longer uses that identifier.

6.  References

6.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/rfc/rfc1034>.

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   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/rfc/rfc1035>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [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,
              <https://www.rfc-editor.org/rfc/rfc4033>.

   [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,
              <https://www.rfc-editor.org/rfc/rfc4034>.

   [RFC5011]  StJohns, M., "Automated Updates of DNS Security (DNSSEC)
              Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
              September 2007, <https://www.rfc-editor.org/rfc/rfc5011>.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <https://www.rfc-editor.org/rfc/rfc5652>.

   [RFC7958]  Abley, J., Schlyter, J., Bailey, G., and P. Hoffman,
              "DNSSEC Trust Anchor Publication for the Root Zone",
              RFC 7958, DOI 10.17487/RFC7958, August 2016,
              <https://www.rfc-editor.org/rfc/rfc7958>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC9157]  Hoffman, P., "Revised IANA Considerations for DNSSEC",
              RFC 9157, DOI 10.17487/RFC9157, December 2021,
              <https://www.rfc-editor.org/rfc/rfc9157>.

   [RFC9364]  Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237,
              RFC 9364, DOI 10.17487/RFC9364, February 2023,
              <https://www.rfc-editor.org/rfc/rfc9364>.

6.2.  Informative References

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   [DPS]      Root Zone KSK Operator Policy Management Authority,
              "DNSSEC Practice Statement for the Root Zone KSK
              Operator", n.d., <https://www.iana.org/dnssec/procedures>.

   [RELAX-NG] Clark, J., "RELAX NG Compact Syntax", 2002,
              <https://www.oasis-open.org/committees/relax-ng/compact-
              20021121.html>.

Appendix A.  Changes from RFC 7958

   This version of the document includes the following changes:

   *  There is a significant technical change from erratum 5932
      <https://www.rfc-editor.org/errata/eid5932>.  This is in the
      seventh paragraph of Section 2.2.

   *  Added the optional publickeyinfo named pattern with two mandatory
      elements, PublicKey and Flags.

   *  Removed the certificates and certificate signing mechanisms.

   *  Removed the detached OpenPGP signature mechanism.

   *  The reference to the DNSSEC Practice Statement [DPS] was updated.

   *  Say explicitly that the XML documents might have XML comments in
      them.

   *  Clarified the use of the detached CMS signature.

   *  Updated the IANA Considerations section to indicate requirements
      on IANA.

   *  Simplified the description of using the validFrom and validUntil
      attributes.

   *  Added new security considerations.

   *  There was a bit of editorial cleanup.

Appendix B.  Historical Note

   The first KSK for use in the root zone of the DNS was generated at a
   key ceremony at the ICANN Key Management Facility (KMF) in Culpeper,
   Virginia, USA on 2010-06-16.  This key entered production during a
   second key ceremony held at an ICANN KMF in El Segundo, California,
   USA on 2010-07-12.  The resulting trust anchor was first published on
   2010-07-15.

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   The second KSK for use in the root zone of the DNS was generated at
   key ceremony #27 at the ICANN KMF in Culpeper, Virginia, USA on
   2016-10-27.  This key entered production during key ceremony #28 held
   at the ICANN KMF in El Segundo, California, USA on 2017-02-02.  The
   resulting trust anchor was first published on 2018-11-11.

   More information about the key ceremonies, including full records of
   previous ceremonies and plans for future ceremonies, can be found at
   <https://www.iana.org/dnssec/ceremonies>.

Appendix C.  Acknowledgemwents

   Many pioneers paved the way for the deployment of DNSSEC in the root
   zone of the DNS, and the authors hereby acknowledge their substantial
   collective contribution.

   RFC 7958 incorporated suggestions made by Alfred Hoenes and Russ
   Housley, whose contributions are appreciated.

Authors' Addresses

   Joe Abley
   Cloudflare
   Amsterdam
   Netherlands
   Email: jabley@cloudflare.com

   Jakob Schlyter
   Kirei AB
   Email: jakob@kirei.se

   Guillaume Bailey
   Independent
   Email: guillaumebailey@outlook.com

   Paul Hoffman
   ICANN
   Email: paul.hoffman@icann.org

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