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paul.hoffman@icann.org

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. This document obsoletes RFC 9364. This document is being tracked at (https://github.com/paulehoffman/rfc9364bis).

Introduction The core specification for what we know as DNSSEC (the combination of , , and ) describes a set of protocols that provide origin authentication of DNS data. 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) .

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 go to recursive resolvers that validate. 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.

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.

DNSSEC Core Documents What we refer to as "DNSSEC" is the third iteration of the DNSSEC specification; was the first, and was the second. Earlier iterations have not been deployed on a significant scale. Throughout this document, "DNSSEC" means the protocol initially defined in , , and . The three initial core documents generally cover different topics: is an overview of DNSSEC, including how it might change the resolution of DNS queries. specifies the DNS resource records used in DNSSEC. It obsoletes many RFCs about earlier versions of DNSSEC. 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: 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. 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, changes how TTL values are calculated in DNSSEC processing.

Addition to the DNSSEC Core As with any major protocol, developers and operators discovered issues with the original core documents over the years. 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. brings a few additions into the core of DNSSEC. It makes NSEC3 as much a part of DNSSEC as NSEC is. It also makes the SHA-256 and SHA-512 hash functions defined in and part of the core.

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) and Edwards-curve Digital Signature Algorithm (EdDSA) . ECDSA and EdDSA have become very popular signing algorithms in recent years. The GOST signing algorithm 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 . 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.

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: 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. is a compendium of operational practices that may not be obvious from reading just the core specifications. describes using the CDS and CDNSKEY resource records to help automate the maintenance of DS records in the parents of signed zones. extends by showing how to do initial setup of trusted relationships between signed parent and child zones. describes how a validating resolver can emit fewer queries in signed zones that use NSEC and NSEC3 for negative caching. updates with respect to the TTL fields in signed records.

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: "describes how to construct DNSSEC NSEC resource records that cover a smaller range of names than called for by . 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". "specifies a way for validating end-system resolvers to signal to a server which digital signature and hash algorithms they support". "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. "describes the issues surrounding the timing of events in the rolling of a key in a DNSSEC-secured zone". "defines Negative Trust Anchors (NTAs), which can be used to mitigate DNSSEC validation failures by disabling DNSSEC validation at specified domains". "describes problems that a Validating DNS resolver, stub-resolver, or application might run into within a non- compliant infrastructure". "specifies two different ways for validating resolvers to signal to a server which keys are referenced in their chain of trust". contains lists of terminology used when talking about DNS; Sections 10 and 11 cover DNSSEC. "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". "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". "provides guidance on setting NSEC3 parameters based on recent operational deployment experience". "allows managed DNS operators to securely announce DNSSEC key parameters for zones under their management, including for zones that are not currently securely delegated". "describes the format and publication mechanisms IANA has used to distribute the DNSSEC trust anchors". There will certainly be other RFCs related to DNSSEC that are published after this one.

IANA Considerations IANA already has three registry groups that relate to DNSSEC: DNSSEC algorithm numbers DNSSEC NSEC3 parameters DNSSEC DS RRtype digest algorithms The rules for the DNSSEC algorithm registry were set in the core RFCs and updated by , , and . This document does not update or create any registry groups or registries.

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

&RFC3110; &RFC4033; &RFC4034; &RFC4035; &RFC4509; &RFC5155; &RFC5702; &RFC6840; &RFC2065; &RFC2535; &RFC2536; &RFC4470; &RFC5011; &RFC6014; &RFC6605; &RFC6698; &RFC6725; &RFC6781; &RFC6975; &RFC7129; &RFC7344; &RFC7583; &RFC7646; &RFC8027; &RFC8078; &RFC8080; &RFC8145; &RFC8198; &RFC8509; &RFC8624; &RFC8901; &RFC9077; &RFC9157; &RFC9276; &RFC9499; &RFC9558; &RFC9615; &RFC9718; &I-D.ietf-dnsop-compact-denial-of-existence; &I-D.ietf-dnsop-rfc8624-bis; &I-D.ietf-dnsop-must-not-sha1; &I-D.ietf-dnsop-must-not-ecc-gost;

Changes Since RFC 9364 This document obsoletes RFC 9364, which is BCP 237. The changes from that document are: was added to this document RFC 7958 became RFC 8499 became was added to this document The following drafts are currently in the RFC Editor's queue and will added here when they become RFCs. , "Compact Denial of Existence in DNSSEC" , "DNSSEC Cryptographic Algorithm Recommendation Update Process" , "Deprecating the use of SHA-1 in DNSSEC signature algorithms" , "Deprecate usage of ECC-GOST within DNSSEC"

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.