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RFC 7958

Informational
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DNSSEC Trust Anchor Publication for the Root Zone

 


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Independent Submission                                          J. Abley
Request for Comments: 7958                                     Dyn, Inc.
Category: Informational                                      J. Schlyter
ISSN: 2070-1721                                                 Kirei AB
                                                               G. Bailey
                                                             Independent
                                                              P. Hoffman
                                                                   ICANN
                                                             August 2016


           DNSSEC Trust Anchor Publication for the Root Zone

Abstract

   The root zone of the Domain Name System (DNS) has been
   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 has
   used to distribute the DNSSEC trust anchors.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7958.

[Page 2] 
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
   (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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  IANA DNSSEC Root Zone Trust Anchor Formats and Semantics  . .   4
     2.1.  Hashes in XML . . . . . . . . . . . . . . . . . . . . . .   4
       2.1.1.  XML Syntax  . . . . . . . . . . . . . . . . . . . . .   5
       2.1.2.  XML Semantics . . . . . . . . . . . . . . . . . . . .   5
       2.1.3.  Converting from XML to DS Records . . . . . . . . . .   7
       2.1.4.  XML Example . . . . . . . . . . . . . . . . . . . . .   8
     2.2.  Certificates  . . . . . . . . . . . . . . . . . . . . . .   8
     2.3.  Certificate Signing Requests  . . . . . . . . . . . . . .   9
   3.  Root Zone Trust Anchor Retrieval  . . . . . . . . . . . . . .   9
     3.1.  Retrieving Trust Anchors with HTTPS and HTTP  . . . . . .   9
   4.  Accepting DNSSEC Trust Anchors  . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Historical Note  . . . . . . . . . . . . . . . . . .  14
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

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1.  Introduction

   The Domain Name System (DNS) is described in [RFC1034] and [RFC1035].
   DNS Security Extensions (DNSSEC) are described in [RFC4033],
   [RFC4034], [RFC4035], [RFC4509], [RFC5155], and [RFC5702].

   A discussion of operational practices relating to DNSSEC can be found
   in [RFC6781].

   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.  A detailed description of
   corresponding key management practices can be found in [DPS], which
   can be retrieved from the IANA Repository at
   <https://www.iana.org/dnssec/>.

   This document describes the formats and distribution methods of
   DNSSEC trust anchors that have been used by IANA for the root zone of
   the DNS since 2010.  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.

   It is important to note that at the time of this writing, IANA
   intends to change the formats and distribution methods in the future.
   If such a change happens, IANA will publish the changes on its web
   site at <https://www.iana.org/dnssec/files>.

   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].

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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, that trust is assumed and not derived, is common to
   all the common uses of the term "trust anchor".

   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", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  IANA DNSSEC Root Zone Trust Anchor Formats and Semantics

   IANA publishes trust anchors for the root zone in three formats:

   o  an XML document that contains the hashes of the DNSKEY records

   o  certificates in PKIX format [RFC5280] that contain DS records and
      the full public key of DNSKEY records

   o  Certificate Signing Requests (CSRs) in PKCS #10 format [RFC2986]
      that contain DS records and the full public key of DNSKEY records

   These formats and the semantics associated with each are described in
   the rest of this section.

2.1.  Hashes in XML

   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 DS resource records from
   [RFC4034].

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2.1.1.  XML Syntax

   A RELAX NG Compact Schema [RELAX-NG] for the documents used to
   publish trust anchors is given in Figure 1.

   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 }
   }

                                 Figure 1

2.1.2.  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 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 DNSKEY record in
   the zone defined in the Zone element.

   The id attribute in the KeyDigest element is an opaque string that
   identifies the hash.  Its value is used in the file names and URI of
   the other trust anchor formats.  This is described in Section 3.1.
   For example, if the value of the id attribute in the KeyDigest
   element is "Kjqmt7v", the URI for the CSR that is associated with
   this hash will be <https://data.iana.org/root-anchors/Kjqmt7v.csr>.
   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.  Note that the KeyDigest element is optional; if it
   is not given, the trust anchor can be used until a KeyDigest element
   covering the same DNSKEY record, but having a validUntil attribute,
   is trusted by the relying party.  Relying parties SHOULD NOT use a
   KeyDigest outside of the time range given in the validFrom and
   validUntil attributes.

   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 signing
   algorithm identifier for the DNSKEY record represented in this
   KeyDigest.

   The DigestType element in the KeyDigest element contains the 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.

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2.1.3.  Converting from XML to DS Records

   The display format for the DS record that is the equivalent of a
   KeyDigest element can be constructed by marshaling the KeyTag,
   Algorithm, DigestType, and Digest elements.  For example, assume that
   the TrustAnchor element contains:

   <?xml version="1.0" encoding="UTF-8"?>
   <TrustAnchor
      id="AD42165F-3B1A-4778-8F42-D34A1D41FD93"
      source="http://data.iana.org/root-anchors/root-anchors.xml">
   <Zone>.</Zone>
   <KeyDigest id="Kjqmt7v" validFrom="2010-07-15T00:00:00+00:00">
   <KeyTag>19036</KeyTag>
   <Algorithm>8</Algorithm>
   <DigestType>2</DigestType>
   <Digest>
   49AAC11D7B6F6446702E54A1607371607A1A41855200FD2CE1CDDE32F24E8FB5
   </Digest>
   </KeyDigest>
   </TrustAnchor>

   The DS record would be:

   . IN DS 19036 8 2
      49AAC11D7B6F6446702E54A1607371607A1A41855200FD2CE1CDDE32F24E8FB5

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2.1.4.  XML Example

   Figure 2 describes two fictitious trust anchors for the root zone.

   <?xml version="1.0" encoding="UTF-8"?>

   <TrustAnchor
       id="AD42165F-B099-4778-8F42-D34A1D41FD93"
       source="http://data.iana.org/root-anchors/root-anchors.xml">
       <Zone>.</Zone>
       <KeyDigest id="42"
                  validFrom="2010-07-01T00:00:00-00:00"
                  validUntil="2010-08-01T00:00:00-00:00">
           <KeyTag>34291</KeyTag>
           <Algorithm>5</Algorithm>
           <DigestType>1</DigestType>
           <Digest>c8cb3d7fe518835490af8029c23efbce6b6ef3e2</Digest>
       </KeyDigest>
       <KeyDigest id="53"
                  validFrom="2010-08-01T00:00:00-00:00">
           <KeyTag>12345</KeyTag>
           <Algorithm>5</Algorithm>
           <DigestType>1</DigestType>
           <Digest>a3cf809dbdbc835716ba22bdc370d2efa50f21c7</Digest>
       </KeyDigest>
   </TrustAnchor>

                                 Figure 2

2.2.  Certificates

   Each public key that can be used as a trust anchor is represented as
   a certificate in PKIX format.  Each certificate is signed by the
   ICANN certificate authority.  The SubjectPublicKeyInfo in the
   certificate represents the public key of the Key Signing Key (KSK).
   The Subject field has the following attributes:

   O:   the string "ICANN".

   OU:  the string "IANA".

   CN:  the string "Root Zone KSK" followed by the time and date of key
      generation in the format specified in [RFC3339].  For example, a
      CN might be "Root Zone KSK 2010-06-16T21:19:24+00:00".

   resourceRecord:  a string in the presentation format of the DS
      [RFC4034] resource record for the DNSSEC public key.

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   The "resourceRecord" attribute in the Subject is defined as follows:

   ResourceRecord
     { iso(1) identified-organization(3) dod(6) internet(1) security(5)
       mechanisms(5) pkix(7) id-mod(0) id-mod-dns-resource-record(70) }

   DEFINITIONS IMPLICIT TAGS ::=

   BEGIN

   -- EXPORTS ALL --

   IMPORTS

   caseIgnoreMatch FROM SelectedAttributeTypes
       { joint-iso-itu-t ds(5) module(1) selectedAttributeTypes(5) 4 }

   ;

   iana OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
       dod(6) internet(1) private(4) enterprise(1) 1000 }

   iana-dns OBJECT IDENTIFIER ::= { iana 53 }

   resourceRecord ATTRIBUTE ::= {
       WITH SYNTAX IA5String
       EQUALITY MATCHING RULE caseIgnoreMatch
       ID iana-dns
   }

   END

2.3.  Certificate Signing Requests

   Each public key that can be used as a trust anchor is represented as
   a CSR in PKCS #10 format.  The SubjectPublicKeyInfo and Subject field
   are the same as for certificates (see Section 2.2 above).

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:".

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   The URL for retrieving the set of hashes described in Section 2.1 is
   <https://data.iana.org/root-anchors/root-anchors.xml>.

   The URL for retrieving the PKIX certificate described in Section 2.2
   is <https://data.iana.org/root-anchors/KEYDIGEST-ID.crt>, with the
   string "KEYDIGEST-ID" replacing the "id" attribute from the KeyDigest
   element from the XML file, as described in Section 2.1.2.

   The URL for retrieving the CSR described in Section 2.3 is
   <https://data.iana.org/root-anchors/KEYDIGEST-ID.csr>, with the
   string "KEYDIGEST-ID" replacing the "id" attribute from the KeyDigest
   element from the XML file, as described in Section 2.1.2.

4.  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.  It is
   also important to note that the ICANN CA cannot be used to verify the
   origin of the trust anchor in the CSR format.

   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.  The URL for a detached CMS signature
   for the XML file is
   <https://data.iana.org/root-anchors/root-anchors.p7s>.

   (IANA also provided a detached OpenPGP [RFC4880] signature as a
   second parallel verification mechanism for the first trust anchor
   publication but has indicated that it will not use this parallel
   mechanism in the future.)

   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.

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5.  IANA Considerations

   This document defines id-mod-dns-resource-record, value 70 (see
   Section 2.2), in the "SMI Security for PKIX Module Identifier"
   registry.

6.  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.

7.  References

7.1.  Normative References

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

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

   [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>.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              DOI 10.17487/RFC2986, November 2000,
              <http://www.rfc-editor.org/info/rfc2986>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <http://www.rfc-editor.org/info/rfc3339>.

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

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   [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>.

   [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,
              <http://www.rfc-editor.org/info/rfc4035>.

   [RFC4509]  Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer
              (DS) Resource Records (RRs)", RFC 4509,
              DOI 10.17487/RFC4509, May 2006,
              <http://www.rfc-editor.org/info/rfc4509>.

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

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
              <http://www.rfc-editor.org/info/rfc5155>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

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

   [RFC5702]  Jansen, J., "Use of SHA-2 Algorithms with RSA in DNSKEY
              and RRSIG Resource Records for DNSSEC", RFC 5702,
              DOI 10.17487/RFC5702, October 2009,
              <http://www.rfc-editor.org/info/rfc5702>.

   [RFC6781]  Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
              Operational Practices, Version 2", RFC 6781,
              DOI 10.17487/RFC6781, December 2012,
              <http://www.rfc-editor.org/info/rfc6781>.

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7.2.  Informative References

   [DPS]      Ljunggren, F., Okubo, T., Lamb, R., and J. Schlyter,
              "DNSSEC Practice Statement for the Root Zone KSK
              Operator", October 2015,
              <https://www.iana.org/dnssec/icann-dps.txt>.

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

   [RFC4880]  Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
              Thayer, "OpenPGP Message Format", RFC 4880,
              DOI 10.17487/RFC4880, November 2007,
              <http://www.rfc-editor.org/info/rfc4880>.

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Appendix A.  Historical Note

   The first KSK for use in the root zone of the DNS was generated at a
   key ceremony at an 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.

Acknowledgements

   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.

   This document incorporates suggestions made by Alfred Hoenes and Russ
   Housley, whose contributions are appreciated.

Authors' Addresses

   Joe Abley
   Dyn, Inc.
   300-184 York Street
   London, ON  N6A 1B5
   Canada

   Phone: +1 519 670 9327
   Email: jabley@dyn.com


   Jakob Schlyter
   Kirei AB

   Email: jakob@kirei.se


   Guillaume Bailey
   Independent

   Email: GuillaumeBailey@outlook.com


   Paul Hoffman
   ICANN

   Email: paul.hoffman@icann.org