Internet Engineering Task Force (IETF)                        P. Hoffman
Request for Comments: 9364                                         ICANN
BCP: 237                                                   February 2023
Category: Best Current Practice
ISSN: 2070-1721


                   DNS Security Extensions (DNSSEC)

Abstract

  This document describes the DNS Security Extensions (commonly called
  "DNSSEC") that are specified in RFCs 4033, 4034, and 4035, as well as
  a handful of others.  One purpose is to introduce all of the RFCs in
  one place so that the reader can understand the many aspects of
  DNSSEC.  This document does not update any of those RFCs.  A second
  purpose is to state that using DNSSEC for origin authentication of
  DNS data is the best current practice.  A third purpose is to provide
  a single reference for other documents that want to refer to DNSSEC.

Status of This Memo

  This memo documents an Internet Best Current Practice.

  This document is a product of the Internet Engineering Task Force
  (IETF).  It represents the consensus of the IETF community.  It has
  received public review and has been approved for publication by the
  Internet Engineering Steering Group (IESG).  Further information on
  BCPs is available in 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
  https://www.rfc-editor.org/info/rfc9364.

Copyright Notice

  Copyright (c) 2023 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/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.  Code Components extracted from this document must
  include Revised BSD License text as described in Section 4.e of the
  Trust Legal Provisions and are provided without warranty as described
  in the Revised BSD License.

Table of Contents

  1.  Introduction
    1.1.  DNSSEC as a Best Current Practice
    1.2.  Implementing DNSSEC
  2.  DNSSEC Core Documents
    2.1.  Addition to the DNSSEC Core
  3.  Additional Cryptographic Algorithms and DNSSEC
  4.  Extensions to DNSSEC
  5.  Additional Documents of Interest
  6.  IANA Considerations
  7.  Security Considerations
  8.  References
    8.1.  Normative References
    8.2.  Informative References
  Acknowledgements
  Author's Address

1.  Introduction

  The core specification for what we know as DNSSEC (the combination of
  [RFC4033], [RFC4034], and [RFC4035]) describes a set of protocols
  that provide origin authentication of DNS data.  [RFC6840] updates
  and extends those core RFCs but does not fundamentally change the way
  that DNSSEC works.

  This document lists RFCs that should be considered by someone
  creating an implementation of, or someone deploying, DNSSEC as it is
  currently standardized.  Although an effort was made to be thorough,
  the reader should not assume this list is comprehensive.  It uses
  terminology from those documents without defining that terminology.
  It also points to the relevant IANA registry groups that relate to
  DNSSEC.  It does not, however, point to standards that rely on zones
  needing to be signed by DNSSEC, such as DNS-Based Authentication of
  Named Entities (DANE) [RFC6698].

1.1.  DNSSEC as a Best Current Practice

  Using the DNSSEC set of protocols is the best current practice for
  adding origin authentication of DNS data.  To date, no Standards
  Track RFCs offer any other method for such origin authentication of
  data in the DNS.

  More than 15 years after the DNSSEC specification was published, it
  is still not widely deployed.  Recent estimates are that fewer than
  10% of the domain names used for websites are signed, and only around
  a third of queries to recursive resolvers are validated.  However,
  this low level of deployment does not affect whether using DNSSEC is
  a best current practice; it just indicates that the value of
  deploying DNSSEC is often considered lower than the cost.
  Nonetheless, the significant deployment of DNSSEC beneath some top-
  level domains (TLDs) and the near-universal deployment of DNSSEC for
  the TLDs in the DNS root zone demonstrate that DNSSEC is applicable
  for implementation by both ordinary and highly sophisticated domain
  owners.

1.2.  Implementing DNSSEC

  Developers of validating resolvers and authoritative servers, as well
  as operators of validating resolvers and authoritative servers, need
  to know the parts of the DNSSEC protocol that would affect them.
  They should read the DNSSEC core documents and probably at least be
  familiar with the extensions.  Developers will probably need to be
  very familiar with the algorithm documents as well.

  As a side note, some of the DNSSEC-related RFCs have significant
  errata, so reading the RFCs should also include looking for the
  related errata.

2.  DNSSEC Core Documents

  What we refer to as "DNSSEC" is the third iteration of the DNSSEC
  specification; [RFC2065] was the first, and [RFC2535] was the second.
  Earlier iterations have not been deployed on a significant scale.
  Throughout this document, "DNSSEC" means the protocol initially
  defined in [RFC4033], [RFC4034], and [RFC4035].

  The three initial core documents generally cover different topics:

  *  [RFC4033] is an overview of DNSSEC, including how it might change
     the resolution of DNS queries.

  *  [RFC4034] specifies the DNS resource records used in DNSSEC.  It
     obsoletes many RFCs about earlier versions of DNSSEC.

  *  [RFC4035] covers the modifications to the DNS protocol incurred by
     DNSSEC.  These include signing zones, serving signed zones,
     resolving in light of DNSSEC, and authenticating DNSSEC-signed
     data.

  At the time this set of core documents was published, someone could
  create a DNSSEC implementation of signing software, of a DNSSEC-aware
  authoritative server, and/or of a DNSSEC-aware recursive resolver
  from the three core documents, plus a few older RFCs specifying the
  cryptography used.  Those two older documents are the following:

  *  [RFC2536] defines how to use the DSA signature algorithm (although
     it refers to other documents for the details).  DSA was thinly
     implemented and can safely be ignored by DNSSEC implementations.

  *  [RFC3110] defines how to use the RSA signature algorithm (although
     refers to other documents for the details).  RSA is still among
     the most popular signing algorithms for DNSSEC.

  It is important to note that later RFCs update the core documents.
  As just one example, [RFC9077] changes how TTL values are calculated
  in DNSSEC processing.

2.1.  Addition to the DNSSEC Core

  As with any major protocol, developers and operators discovered
  issues with the original core documents over the years.  [RFC6840] is
  an omnibus update to the original core documents and thus itself has
  become a core document.  In addition to covering new requirements
  from new DNSSEC RFCs, it describes many important security and
  interoperability issues that arose during the deployment of the
  initial specifications, particularly after the DNS root was signed in
  2010.  It also lists some errors in the examples of the core
  specifications.

  [RFC6840] brings a few additions into the core of DNSSEC.  It makes
  NSEC3 [RFC5155] as much a part of DNSSEC as NSEC is.  It also makes
  the SHA-256 and SHA-512 hash functions defined in [RFC4509] and
  [RFC5702] part of the core.

3.  Additional Cryptographic Algorithms and DNSSEC

  Current cryptographic algorithms typically weaken over time as
  computing power improves and new cryptoanalysis emerges.  Two new
  signing algorithms have been adopted by the DNSSEC community:
  Elliptic Curve Digital Signature Algorithm (ECDSA) [RFC6605] and
  Edwards-curve Digital Signature Algorithm (EdDSA) [RFC8080].  ECDSA
  and EdDSA have become very popular signing algorithms in recent
  years.  The GOST signing algorithm [GOST-SIGN] was also adopted but
  has seen very limited use, likely because it is a national algorithm
  specific to a very small number of countries.

  Implementation developers who want to know which algorithms to
  implement in DNSSEC software should refer to [RFC8624].  Note that
  this specification is only about what algorithms should and should
  not be included in implementations, i.e., it is not advice about
  which algorithms zone operators should or should not use for signing,
  nor which algorithms recursive resolver operators should or should
  not use for validation.

4.  Extensions to DNSSEC

  The DNSSEC community has extended the DNSSEC core and the
  cryptographic algorithms, both in terms of describing good
  operational practices and in new protocols.  Some of the RFCs that
  describe these extensions include the following:

  *  [RFC5011] describes a method to help resolvers update their DNSSEC
     trust anchors in an automated fashion.  This method was used in
     2018 to update the DNS root trust anchor.

  *  [RFC6781] is a compendium of operational practices that may not be
     obvious from reading just the core specifications.

  *  [RFC7344] describes using the CDS and CDNSKEY resource records to
     help automate the maintenance of DS records in the parents of
     signed zones.

  *  [RFC8078] extends [RFC7344] by showing how to do initial setup of
     trusted relationships between signed parent and child zones.

  *  [RFC8198] describes how a validating resolver can emit fewer
     queries in signed zones that use NSEC and NSEC3 for negative
     caching.

  *  [RFC9077] updates [RFC8198] with respect to the TTL fields in
     signed records.

5.  Additional Documents of Interest

  The documents listed above constitute the core of DNSSEC, the
  additional cryptographic algorithms, and the major extensions to
  DNSSEC.  This section lists some additional documents that someone
  interested in implementing or operating DNSSEC might find of value:

  *  [RFC4470] "describes how to construct DNSSEC NSEC resource records
     that cover a smaller range of names than called for by [RFC4034].
     By generating and signing these records on demand, authoritative
     name servers can effectively stop the disclosure of zone contents
     otherwise made possible by walking the chain of NSEC records in a
     signed zone".

  *  [RFC6975] "specifies a way for validating end-system resolvers to
     signal to a server which digital signature and hash algorithms
     they support".

  *  [RFC7129] "provides additional background commentary and some
     context for the NSEC and NSEC3 mechanisms used by DNSSEC to
     provide authenticated denial-of-existence responses".  This
     background is particularly important for understanding NSEC and
     NSEC3 usage.

  *  [RFC7583] "describes the issues surrounding the timing of events
     in the rolling of a key in a DNSSEC-secured zone".

  *  [RFC7646] "defines Negative Trust Anchors (NTAs), which can be
     used to mitigate DNSSEC validation failures by disabling DNSSEC
     validation at specified domains".

  *  [RFC7958] "describes the format and publication mechanisms IANA
     has used to distribute the DNSSEC trust anchors".

  *  [RFC8027] "describes problems that a Validating DNS resolver,
     stub-resolver, or application might run into within a non-
     compliant infrastructure".

  *  [RFC8145] "specifies two different ways for validating resolvers
     to signal to a server which keys are referenced in their chain of
     trust".

  *  [RFC8499] contains lists of terminology used when talking about
     DNS; Sections 10 and 11 cover DNSSEC.

  *  [RFC8509] "specifies a mechanism that will allow an end user and
     third parties to determine the trusted key state for the root key
     of the resolvers that handle that user's DNS queries".

  *  [RFC8901] "presents deployment models that accommodate this
     scenario [when each DNS provider independently signs zone data
     with their own keys] and describes these key-management
     requirements".

  *  [RFC9276] "provides guidance on setting NSEC3 parameters based on
     recent operational deployment experience".

  There will certainly be other RFCs related to DNSSEC that are
  published after this one.

6.  IANA Considerations

  IANA already has three registry groups that relate to DNSSEC:

  *  DNSSEC algorithm numbers (https://www.iana.org/assignments/dns-
     sec-alg-numbers)

  *  DNSSEC NSEC3 parameters (https://www.iana.org/assignments/dnssec-
     nsec3-parameters)

  *  DNSSEC DS RRtype digest algorithms
     (https://www.iana.org/assignments/ds-rr-types)

  The rules for the DNSSEC algorithm registry were set in the core RFCs
  and updated by [RFC6014], [RFC6725], and [RFC9157].

  This document does not update or create any registry groups or
  registries.

7.  Security Considerations

  All of the security considerations from all of the RFCs referenced in
  this document apply here.

8.  References

8.1.  Normative References

  [RFC3110]  Eastlake 3rd, D., "RSA/SHA-1 SIGs and RSA KEYs in the
             Domain Name System (DNS)", RFC 3110, DOI 10.17487/RFC3110,
             May 2001, <https://www.rfc-editor.org/info/rfc3110>.

  [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/info/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/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,
             <https://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,
             <https://www.rfc-editor.org/info/rfc4509>.

  [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,
             <https://www.rfc-editor.org/info/rfc5155>.

  [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,
             <https://www.rfc-editor.org/info/rfc5702>.

  [RFC6840]  Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and
             Implementation Notes for DNS Security (DNSSEC)", RFC 6840,
             DOI 10.17487/RFC6840, February 2013,
             <https://www.rfc-editor.org/info/rfc6840>.

8.2.  Informative References

  [GOST-SIGN]
             Belyavsky, D., Dolmatov, V., Ed., and B. Makarenko, Ed.,
             "Use of GOST 2012 Signature Algorithms in DNSKEY and RRSIG
             Resource Records for DNSSEC", Work in Progress, Internet-
             Draft, draft-ietf-dnsop-rfc5933-bis-13, 30 November 2022,
             <https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-
             rfc5933-bis-13>.

  [RFC2065]  Eastlake 3rd, D. and C. Kaufman, "Domain Name System
             Security Extensions", RFC 2065, DOI 10.17487/RFC2065,
             January 1997, <https://www.rfc-editor.org/info/rfc2065>.

  [RFC2535]  Eastlake 3rd, D., "Domain Name System Security
             Extensions", RFC 2535, DOI 10.17487/RFC2535, March 1999,
             <https://www.rfc-editor.org/info/rfc2535>.

  [RFC2536]  Eastlake 3rd, D., "DSA KEYs and SIGs in the Domain Name
             System (DNS)", RFC 2536, DOI 10.17487/RFC2536, March 1999,
             <https://www.rfc-editor.org/info/rfc2536>.

  [RFC4470]  Weiler, S. and J. Ihren, "Minimally Covering NSEC Records
             and DNSSEC On-line Signing", RFC 4470,
             DOI 10.17487/RFC4470, April 2006,
             <https://www.rfc-editor.org/info/rfc4470>.

  [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/info/rfc5011>.

  [RFC6014]  Hoffman, P., "Cryptographic Algorithm Identifier
             Allocation for DNSSEC", RFC 6014, DOI 10.17487/RFC6014,
             November 2010, <https://www.rfc-editor.org/info/rfc6014>.

  [RFC6605]  Hoffman, P. and W.C.A. Wijngaards, "Elliptic Curve Digital
             Signature Algorithm (DSA) for DNSSEC", RFC 6605,
             DOI 10.17487/RFC6605, April 2012,
             <https://www.rfc-editor.org/info/rfc6605>.

  [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
             of Named Entities (DANE) Transport Layer Security (TLS)
             Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
             2012, <https://www.rfc-editor.org/info/rfc6698>.

  [RFC6725]  Rose, S., "DNS Security (DNSSEC) DNSKEY Algorithm IANA
             Registry Updates", RFC 6725, DOI 10.17487/RFC6725, August
             2012, <https://www.rfc-editor.org/info/rfc6725>.

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

  [RFC6975]  Crocker, S. and S. Rose, "Signaling Cryptographic
             Algorithm Understanding in DNS Security Extensions
             (DNSSEC)", RFC 6975, DOI 10.17487/RFC6975, July 2013,
             <https://www.rfc-editor.org/info/rfc6975>.

  [RFC7129]  Gieben, R. and W. Mekking, "Authenticated Denial of
             Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129,
             February 2014, <https://www.rfc-editor.org/info/rfc7129>.

  [RFC7344]  Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
             DNSSEC Delegation Trust Maintenance", RFC 7344,
             DOI 10.17487/RFC7344, September 2014,
             <https://www.rfc-editor.org/info/rfc7344>.

  [RFC7583]  Morris, S., Ihren, J., Dickinson, J., and W. Mekking,
             "DNSSEC Key Rollover Timing Considerations", RFC 7583,
             DOI 10.17487/RFC7583, October 2015,
             <https://www.rfc-editor.org/info/rfc7583>.

  [RFC7646]  Ebersman, P., Kumari, W., Griffiths, C., Livingood, J.,
             and R. Weber, "Definition and Use of DNSSEC Negative Trust
             Anchors", RFC 7646, DOI 10.17487/RFC7646, September 2015,
             <https://www.rfc-editor.org/info/rfc7646>.

  [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/info/rfc7958>.

  [RFC8027]  Hardaker, W., Gudmundsson, O., and S. Krishnaswamy,
             "DNSSEC Roadblock Avoidance", BCP 207, RFC 8027,
             DOI 10.17487/RFC8027, November 2016,
             <https://www.rfc-editor.org/info/rfc8027>.

  [RFC8078]  Gudmundsson, O. and P. Wouters, "Managing DS Records from
             the Parent via CDS/CDNSKEY", RFC 8078,
             DOI 10.17487/RFC8078, March 2017,
             <https://www.rfc-editor.org/info/rfc8078>.

  [RFC8080]  Sury, O. and R. Edmonds, "Edwards-Curve Digital Security
             Algorithm (EdDSA) for DNSSEC", RFC 8080,
             DOI 10.17487/RFC8080, February 2017,
             <https://www.rfc-editor.org/info/rfc8080>.

  [RFC8145]  Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust
             Anchor Knowledge in DNS Security Extensions (DNSSEC)",
             RFC 8145, DOI 10.17487/RFC8145, April 2017,
             <https://www.rfc-editor.org/info/rfc8145>.

  [RFC8198]  Fujiwara, K., Kato, A., and W. Kumari, "Aggressive Use of
             DNSSEC-Validated Cache", RFC 8198, DOI 10.17487/RFC8198,
             July 2017, <https://www.rfc-editor.org/info/rfc8198>.

  [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
             Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
             January 2019, <https://www.rfc-editor.org/info/rfc8499>.

  [RFC8509]  Huston, G., Damas, J., and W. Kumari, "A Root Key Trust
             Anchor Sentinel for DNSSEC", RFC 8509,
             DOI 10.17487/RFC8509, December 2018,
             <https://www.rfc-editor.org/info/rfc8509>.

  [RFC8624]  Wouters, P. and O. Sury, "Algorithm Implementation
             Requirements and Usage Guidance for DNSSEC", RFC 8624,
             DOI 10.17487/RFC8624, June 2019,
             <https://www.rfc-editor.org/info/rfc8624>.

  [RFC8901]  Huque, S., Aras, P., Dickinson, J., Vcelak, J., and D.
             Blacka, "Multi-Signer DNSSEC Models", RFC 8901,
             DOI 10.17487/RFC8901, September 2020,
             <https://www.rfc-editor.org/info/rfc8901>.

  [RFC9077]  van Dijk, P., "NSEC and NSEC3: TTLs and Aggressive Use",
             RFC 9077, DOI 10.17487/RFC9077, July 2021,
             <https://www.rfc-editor.org/info/rfc9077>.

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

  [RFC9276]  Hardaker, W. and V. Dukhovni, "Guidance for NSEC3
             Parameter Settings", BCP 236, RFC 9276,
             DOI 10.17487/RFC9276, August 2022,
             <https://www.rfc-editor.org/info/rfc9276>.

Acknowledgements

  The DNS world owes a depth of gratitude to the authors and other
  contributors to the core DNSSEC documents and to the notable DNSSEC
  extensions.

  In addition, the following people made significant contributions to
  early draft versions of this document: Ben Schwartz and Duane
  Wessels.

Author's Address

  Paul Hoffman
  ICANN
  Email: [email protected]

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