Network Working Group J. Abley
Internet-Draft Cloudflare
Obsoletes: 7958 (if approved) J. Schlyter
Intended status: Informational Kirei AB
Expires: 14 September 2023 G. Bailey
Independent
P. Hoffman
ICANN
13 March 2023
DNSSEC Trust Anchor Publication for the Root Zone
draft-bash-rfc7958bis-00
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 Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 14 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Changes from RFC 7958 . . . . . . . . . . . . . . . . . . 4
2. IANA DNSSEC Root Zone Trust Anchor Formats and Semantics . . 4
2.1. Hashes in XML . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1. XML Syntax . . . . . . . . . . . . . . . . . . . . . 4
2.1.2. XML Semantics . . . . . . . . . . . . . . . . . . . . 5
2.1.3. Converting from XML to DS Records . . . . . . . . . . 6
2.1.4. XML Example . . . . . . . . . . . . . . . . . . . . . 7
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 . . . . . . . . . . . . . . . . . 12
Appendix A. Historical Note . . . . . . . . . . . . . . . . . . 12
Appendix B. Acknowledgemwents . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
The 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.
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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 .
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.
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 RFC 5011.
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", "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.
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1.2. Changes from RFC 7958
This version of the document includes the following changes:
* There is a signficant technical change from erratum 5932
. This is in the
seventh paragraph of Section 2.1.2.
* The reference to the DNSSEC Practice Statement [DPS] was updated.
2. IANA DNSSEC Root Zone Trust Anchor Formats and Semantics
IANA publishes trust anchors for the root zone in three formats:
* an XML document that contains the hashes of the DNSKEY records
* certificates in PKIX format [RFC5280] that contain DS records and
the full public key of DNSKEY records
* 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 .
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.
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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 }
}
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.
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.
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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. 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 . 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 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 DNSKEY 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.
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.
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:
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.
19036
8
2
49AAC11D7B6F6446702E54A1607371607A1A41855200FD2CE1CDDE32F24E8FB5
The DS record would be:
. IN DS 19036 8 2
49AAC11D7B6F6446702E54A1607371607A1A41855200FD2CE1CDDE32F24E8FB5
2.1.4. XML Example
Figure 2 describes two fictitious trust anchors for the root zone.
.
34291
5
1
c8cb3d7fe518835490af8029c23efbce6b6ef3e2
12345
5
1
a3cf809dbdbc835716ba22bdc370d2efa50f21c7
Figure 2
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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
resource record for the DNSSEC public key.
The "resourceRecord" attribute in the Subject is defined as follows:
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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:".
The URL for retrieving the set of hashes described in Section 2.1 is
.
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The URL for retrieving the PKIX certificate described in
Section 2.1.1 is , 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 2.2 is
, 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 .
[ Need to check with IANA on the paragraph below ]
(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,
.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, .
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
.
[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,
.
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[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
September 2007, .
[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,
.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, .
[RFC9364] Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237,
RFC 9364, DOI 10.17487/RFC9364, February 2023,
.
7.2. Informative References
[DPS] Root Zone KSK Operator Policy Management Authority,
"DNSSEC Practice Statement for the Root Zone KSK
Operator", 2020, .
[RELAX-NG] Clark, J., "RELAX NG Compact Syntax", 2002,
.
[RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
Thayer, "OpenPGP Message Format", RFC 4880,
DOI 10.17487/RFC4880, November 2007,
.
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.
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The second KSK for use in the root zone of the DNS was [ MORE GOES
HERE ].
Appendix B. 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.
This document incorporates 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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