Network Working Group J. Abley
Internet-Draft Cloudflare
Obsoletes: 7958 (if approved) J. Schlyter
Intended status: Informational Kirei AB
Expires: 2 March 2025 G. Bailey
Independent
P. Hoffman
ICANN
29 August 2024
DNSSEC Trust Anchor Publication for the Root Zone
draft-ietf-dnsop-rfc7958bis-05
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 2 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
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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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 . . . . . . . . . . . . . 8
3.3. Changes in the Trust Model for Distribution . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
4.1. Security Considerations for Relying Parties . . . . . . . 9
4.1.1. validUntil . . . . . . . . . . . . . . . . . . . . . 9
4.1.2. Comparison of Digest and a publickeyinfo . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Normative References . . . . . . . . . . . . . . . . . . 11
6.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Changes from RFC 7958 . . . . . . . . . . . . . . . 12
Appendix B. Historical Note . . . . . . . . . . . . . . . . . . 13
Appendix C. Acknowledgemwents . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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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.
.
19036
8
2
49AAC11D7B6F6446702E54A1607371607A1A41855200FD2CE1CDDE32F24E8FB5
20326
8
2
E06D44B80B8F1D39A95C0B0D7C65D08458E880409BBC683457104237C7F8EC8D
AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3+/4Rg
WOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kvArMtNROxVQ
uCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF0jLHwVN8efS3rCj
/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+eoZG+SrDK6nWeL3c6H5Ap
xz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfdRUfhHdY6+cn8HFRm+2hM8AnXG
Xws9555KrUB5qihylGa8subX2Nn6UwNR1AkUTV74bU=
257
38696
8
2
683D2D0ACB8C9B712A1948B27F741219298D0A450D612C483AF444A4C0FB2B16
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The DS record derived from this example would be:
. IN DS 20326 8 2
E06D44B80B8F1D39A95C0B0D7C65D08458E880409BBC683457104237C7F8EC8D
Note that this DS record set only has one record because the record
that would have included the key tag 19036 is already invalid based
on the validUntil attribute's value.
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 .
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
.
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
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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.
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
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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].
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.
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.
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6. References
6.1. 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,
.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC4034, March 2005,
.
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
September 2007, .
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
.
[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,
.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, .
[RFC9157] Hoffman, P., "Revised IANA Considerations for DNSSEC",
RFC 9157, DOI 10.17487/RFC9157, December 2021,
.
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[RFC9364] Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237,
RFC 9364, DOI 10.17487/RFC9364, February 2023,
.
6.2. Informative References
[DPS] Root Zone KSK Operator Policy Management Authority,
"DNSSEC Practice Statement for the Root Zone KSK
Operator", n.d., .
[RELAX-NG] Clark, J., "RELAX NG Compact Syntax", 2002,
.
Appendix A. Changes from RFC 7958
This version of the document includes the following changes:
* There is a significant technical change from erratum 5932
. 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.
* There was a bit of editorial cleanup.
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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.
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
.
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
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Paul Hoffman
ICANN
Email: paul.hoffman@icann.org
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