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IETF RFC 7958
Last modified on Thursday, September 1st, 2016
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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/RFC 7958.
Abley, et al. Informational PAGE 1 
RFC 7958 Root Zone Trust Anchor Publication August 2016
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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RFC 7958 Root Zone Trust Anchor Publication August 2016
1. Introduction
The Domain Name System (DNS) is described in [RFC 1034] and [RFC 1035].
DNS Security Extensions (DNSSEC) are described in [RFC 4033],
[RFC 4034], [RFC 4035], [RFC 4509], [RFC 5155], and [RFC 5702].
A discussion of operational practices relating to DNSSEC can be found
in [RFC 6781].
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 [RFC 5011]. 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 [RFC 5011].
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RFC 7958 Root Zone Trust Anchor Publication August 2016
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. [RFC 4033] 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 [RFC 4033];
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 [RFC 2119].
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 [RFC 5280] that contain DS records and
the full public key of DNSKEY records
o Certificate Signing Requests (CSRs) in PKCS #10 format [RFC 2986]
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
[RFC 4034].
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RFC 7958 Root Zone Trust Anchor Publication August 2016
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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RFC 7958 Root Zone Trust Anchor Publication August 2016
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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RFC 7958 Root Zone Trust Anchor Publication August 2016
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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RFC 7958 Root Zone Trust Anchor Publication August 2016
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 [RFC 3339]. 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
[RFC 4034] resource record for the DNSSEC public key.
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RFC 7958 Root Zone Trust Anchor Publication August 2016
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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RFC 7958 Root Zone Trust Anchor Publication August 2016
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) [RFC 5652] 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 [RFC 4880] 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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RFC 7958 Root Zone Trust Anchor Publication August 2016
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
[RFC 1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC 1034, November 1987,
<http://www.rfc-editor.org/info/RFC 1034>.
[RFC 1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC 1035,
November 1987, <http://www.rfc-editor.org/info/RFC 1035>.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<http://www.rfc-editor.org/info/RFC 2119>.
[RFC 2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC 2986, November 2000,
<http://www.rfc-editor.org/info/RFC 2986>.
[RFC 3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC 3339, July 2002,
<http://www.rfc-editor.org/info/RFC 3339>.
[RFC 4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC 4033, March 2005,
<http://www.rfc-editor.org/info/RFC 4033>.
Abley, et al. Informational PAGE 11
RFC 7958 Root Zone Trust Anchor Publication August 2016
[RFC 4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC 4034, March 2005,
<http://www.rfc-editor.org/info/RFC 4034>.
[RFC 4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC 4035, March 2005,
<http://www.rfc-editor.org/info/RFC 4035>.
[RFC 4509] Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer
(DS) Resource Records (RRs)", RFC 4509,
DOI 10.17487/RFC 4509, May 2006,
<http://www.rfc-editor.org/info/RFC 4509>.
[RFC 5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC 5011,
September 2007, <http://www.rfc-editor.org/info/RFC 5011>.
[RFC 5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, DOI 10.17487/RFC 5155, March 2008,
<http://www.rfc-editor.org/info/RFC 5155>.
[RFC 5280] 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/RFC 5280, May 2008,
<http://www.rfc-editor.org/info/RFC 5280>.
[RFC 5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC 5652, September 2009,
<http://www.rfc-editor.org/info/RFC 5652>.
[RFC 5702] Jansen, J., "Use of SHA-2 Algorithms with RSA in DNSKEY
and RRSIG Resource Records for DNSSEC", RFC 5702,
DOI 10.17487/RFC 5702, October 2009,
<http://www.rfc-editor.org/info/RFC 5702>.
[RFC 6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
Operational Practices, Version 2", RFC 6781,
DOI 10.17487/RFC 6781, December 2012,
<http://www.rfc-editor.org/info/RFC 6781>.
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RFC 7958 Root Zone Trust Anchor Publication August 2016
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>.
[RFC 4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
Thayer, "OpenPGP Message Format", RFC 4880,
DOI 10.17487/RFC 4880, November 2007,
<http://www.rfc-editor.org/info/RFC 4880>.
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RFC 7958 Root Zone Trust Anchor Publication August 2016
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
Abley, et al. Informational PAGE 14
RFC TOTAL SIZE: 26072 bytes
PUBLICATION DATE: Thursday, September 1st, 2016
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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