]> USC/ISI

ietf@hardakers.net

Google

warren@kumari.net

The DNSSEC protocol makes use of various cryptographic algorithms to provide authentication of DNS data and proof of non-existence. To ensure interoperability between DNS resolvers and DNS authoritative servers, it is necessary to specify both a set of algorithm implementation requirements and usage guidelines to ensure that there is at least one algorithm that all implementations support. This document updates RFC8624 by moving the canonical source of algorithm implementation requirements and usage guidance for DNSSEC from RFC8624 to an IANA registry. This is done both to allow the list to be more easily updated, and to allow the list to be more easily referenced. Future extensions to this registry can be made under new, incremental update RFCs. The document does not change the status (MUST, MAY, RECOMMENDED, etc) of any of the algorithms listed in RFC8624; that is the work of future documents.

Introduction DNS Security Extensions (DNSSEC) is used to provide authentication of DNS data. The DNSSEC signing algorithms are defined by various RFCs, including , , , , , , . To ensure interoperability, a set of "mandatory-to-implement" DNSKEY algorithms are defined in . To make the current status of the algorithms more easily accessible and understandable, and to make future changes to these recommendations easier to publish, this document moves the canonical status of the algorithms from to the IANA DNSSEC algorithm registries. Additionally, as advice to operators, it adds recommendations for deploying and the usage of these algorithms. This is similar to the process used for the registry, where the canonical list of ciphersuites is in the IANA registry, and the RFCs reference the IANA registry.

Document Audience The columns added to the IANA "DNS Security Algorithm Numbers" and "DNSSEC Delegation Signer (DS) Resource Record (RR) Type Digest Algorithms" registries target DNSSEC operators and implementers. Implementations need to meet both high security expectations as well as provide interoperability between various vendors and with different versions. The field of cryptography evolves continuously. New, stronger algorithms appear, and existing algorithms may be found to be less secure than originally thought. Therefore, algorithm implementation requirements and usage guidance need to be updated from time to time in order to reflect the new reality, and to allow for a smooth transition to more secure algorithms, as well as deprecation of algorithms deemed to no longer be secure. Implementations need to be conservative in the selection of algorithms they implement in order to minimize both code complexity and the attack surface. The perspective of implementers may differ from that of an operator who wishes to deploy and configure DNSSEC with only the safest algorithm. As such this document also adds new recommendations about which algorithms should be deployed regardless of implementation status. In general it is expected that deployment of aging algorithms should generally be reduced before implementations stop supporting them.

Updating Algorithm Requirement Levels By the time a DNSSEC cryptographic algorithm is made mandatory-to-implement, it should already be available in most implementations. This document defines an IANA registration modification to allow future documents to specify the implementation recommendations for each algorithm, as the recommendation status of each DNSSEC cryptographic algorithm is expected to change over time. For example, there is no guarantee that newly introduced algorithms will become mandatory-to-implement in the future. Likewise, published algorithms are continuously subjected to cryptographic attack and may become too weak, or even be completely broken, and will require deprecation in the future. It is expected that the deprecation of an algorithm will be performed gradually. This provides time for implementations to update their implemented algorithms while remaining interoperable. Unless there are strong security reasons, an algorithm is expected to be downgraded from MUST to NOT RECOMMENDED or MAY, instead of directly from MUST to MUST NOT. Similarly, an algorithm that has not been mentioned as mandatory-to-implement is expected to be first introduced as RECOMMENDED instead of a MUST. Since the effect of using an unknown DNSKEY algorithm is that the zone is treated as insecure, it is recommended that algorithms which have been downgraded to NOT RECOMMENDED or lower not be used by authoritative nameservers and DNSSEC signers to create new DNSKEY's. This will allow for deprecated algorithms to become used less and less over time. Once an algorithm has reached a sufficiently low level of deployment, it can be marked as MUST NOT, so that recursive resolvers can remove support for validating it. Validating recursive resolvers are encouraged to retain support for all algorithms not marked as MUST NOT.

Requirements notation 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 when, and only when, they appear in all capitals, as shown here. considers the term SHOULD equivalent to RECOMMENDED, and SHOULD NOT equivalent to NOT RECOMMENDED. The authors of this document have chosen to use the terms RECOMMENDED and NOT RECOMMENDED, as this more clearly expresses the recommendations to implementers.

Adding usage and implementation recommendations to the IANA DNSSEC registries Per this document, the following columns are being added to the following DNSSEC algorithm registries registered with IANA: Registry Column added Domain Security Algorithm Numbers Use for DNSSSEC Signing Domain Security Algorithm Numbers Use for DNSSSEC Validation Domain Security Algorithm Numbers Implement for DNSSSEC Signing Domain Security Algorithm Numbers Implement for DNSSSEC Validation Digest Algorithm Use for DNSSSEC Delegation Digest Algorithm Use for DNSSSEC Validation Digest Algorithm Implement for DNSSSEC Delegation Digest Algorithm Implement for DNSSSEC Validation Adding a new entry to the "DNS System Algorithm Numbers" registry with a recommended value of "MAY" in the "Use for DNSSSEC Signing", "Use for DNSSSEC Validation", "Implement for DNSSSEC Signing", or "Implement for DNSSSEC Validation" columns is via the "Specification Required" policy as defined in in order to promote continued evolution of DNSSEC algorithms and DNSSEC agility. New entries add through the "Specification Required" process will have the value of "MAY" for all columns. (Ed note (RFC Editor - please delete this before publication): As a reminder: the "Specification Required" policy includes a requirement for a designated expert to review the request.) Adding a new entry to, or changing existing values in, the "DNS System Algorithm Numbers" registry for the "Use for DNSSSEC Signing", "Use for DNSSSEC Validation", "Implement for DNSSSEC Signing", or "Implement for DNSSSEC Validation" columns to any other value than "MAY" requires a Standards Action. Adding a new entry to the "Digest Algorithms" registry with a recommended value of "MAY" in the "Use for DNSSSEC Delegation", "Use for DNSSSEC Validation", "Implement for DNSSSEC Delegation", or "Implement for DNSSSEC Validation" columns is via the "Specification Required" policy as defined in . Adding a new entry to, or changing existing values in, the "DNS System Algorithm Numbers" registry for the "Use for DNSSSEC Delegation", "Use for DNSSSEC Validation", "Implement for DNSSSEC Delegation", or "Implement for DNSSSEC Validation" columns to any other value than "MAY" requires a Standards Action. If an item is not marked as "RECOMMENDED", it does not necessarily mean that it is flawed; rather, it indicates that the item either has not been through the IETF consensus process, has limited applicability, or is intended only for specific use cases. The following sections state the initial values to be populated into these rows, with Implementation values transcribed from . Use for columns was also set to the same values from , as there is no existing documented values and general interpretation of the registries to date indicate they should be the same, although may differ in the future.

DNS System Algorithm Numbers Column Values Initial recommendation columns of use and implementation recommendations for the "Domain Name System Security (DNSSEC) Algorithm Numbers" are shown in Table 2. When there are multiple RECOMMENDED algorithms in the "use" column, operators should choose the best algorithm according to local policy. N Mnemonics Use for DNSSEC Signing Use for DNSSEC Validation Implement for DNSSEC Signing Implement for DNSSEC Validation 1 RSAMD5 MUST NOT MUST NOT MUST NOT MUST NOT 3 DSA MUST NOT MUST NOT MUST NOT MUST NOT 5 RSASHA1 NOT RECOMMENDED RECOMMENDED NOT RECOMMENDED MUST 6 DSA-NSEC3-SHA1 MUST NOT MUST NOT MUST NOT MUST NOT 7 RSASHA1-NSEC3- SHA1 NOT RECOMMENDED RECOMMENDED NOT RECOMMENDED MUST 8 RSASHA256 RECOMMENDED RECOMMENDED MUST MUST 10 RSASHA512 NOT RECOMMENDED RECOMMENDED NOT RECOMMENDED MUST 12 ECC-GOST MUST NOT MAY MUST NOT MAY 13 ECDSAP256SHA256 RECOMMENDED RECOMMENDED MUST MUST 14 ECDSAP384SHA384 MAY RECOMMENDED MAY RECOMMENDED 15 ED25519 RECOMMENDED RECOMMENDED RECOMMENDED RECOMMENDED 16 ED448 MAY RECOMMENDED MAY RECOMMENDED

DNSSEC Delegation Signer (DS) Resource Record (RR) Type Digest Algorithms Column Values Initial recommendation columns of use and implementation recommendations for the "DNSSEC Delegation Signer (DS) Resource Record (RR) Type Digest Algorithms" registry are shown in Table 3. When there are multiple RECOMMENDED algorithms in the "use" column, operators should choose the best algorithm according to local policy. Number Mnemonics Use for DNSSEC Delegation Use for DNSSEC Validation Implement for DNSSEC Delegation Implement for DNSSEC Validation 0 NULL (CDS only) MUST NOT [*] MUST NOT [*] MUST NOT [*] MUST NOT [*] 1 SHA-1 MUST NOT RECOMMENDED MUST NOT MUST 2 SHA-256 RECOMMENDED RECOMMENDED MUST MUST 3 GOST R 34.11-94 MUST NOT MAY MUST NOT MAY 4 SHA-384 MAY RECOMMENDED MAY RECOMMENDED 5 GOST R 34.11-2012 MAY MAY MAY MAY 6 SM3 MAY MAY MAY MAY

Security Considerations This document makes no modifications to the security of the existing protocol or recommendations described in . Thus, the security considerations remain the same, which we quote below. The security of cryptographic systems depends on both the strength of the cryptographic algorithms chosen and the strength of the keys used with those algorithms. The security also depends on the engineering of the protocol used by the system to ensure that there are no non- cryptographic ways to bypass the security of the overall system. This document concerns itself with the selection of cryptographic algorithms for the use of DNSSEC, specifically with the selection of "mandatory-to-implement" algorithms. The algorithms identified in this document as "MUST" or "RECOMMENDED" to implement are not known to be broken at the current time, and cryptographic research so far leads us to believe that they are likely to remain adequately secure unless significant and unexpected discovery is made. However, this isn't necessarily forever, and it is expected that future documents will be issued from time to time to reflect the current best practices in this area. Retiring an algorithm too soon would result in a zone signed with the retired algorithm being downgraded to the equivalent of an unsigned zone. Therefore, algorithm deprecation must be done very slowly and only after careful consideration and measurement of its use.

Operational Considerations DNSKEY algorithm rollover in a live zone is a complex process. See and for guidelines on how to perform algorithm rollovers. DS algorithm rollover in a live zone is also a complex process. Upgrading algorithm at the same time as rolling the new KSK key will lead to DNSSEC validation failures, and users MUST upgrade the DS algorithm first before rolling the Key Signing Key.

IANA Considerations The IANA is requested to update the and registries according to the following sections.

Update to the "DNS Security Algorithm Numbers" registry This document requests IANA update the "DNS Security Algorithm Numbers" registry () registry with the following additional columns: "Use for DNSSEC Signing" "Use for DNSSEC Validation" "Implement for DNSSEC Signing" "Implement for DNSSEC Validation" These values must be populated using values from Table 2 of this document. Additionally, the registration policy for the registry should match the text describing the requirements in this document.

Update to the "Digest Algorithms" registry This document requests IANA update the "Digest Algorithms" registry () registry with the following additional columns: "Use for DNSSEC Delegation" "Use for DNSSEC Validation" "Implement for DNSSEC Delegation" "Implement for DNSSEC Validation" These values must be populated using values from Table 3 of this document. Update the registration policy for the registry to match the text describing update requirements above. Mark values 128 - 252 as "Reserved" Mark values 253 and 254 as "Reserved for Private Use" Delete the (now superfluous) column "Status" from the registry Additionally, the registration policy for the registry should match the text describing the requirements in this document.

Acknowledgments This document is based on, and extends, RFC 8624, which was authored by Paul Wouters, and Ondrej Sury. The content of this document was heavily discussed by participants of the DNSOP working group. The authors appreciate the thoughtfulness of the many opinions expressed by working group participants that all helped shaped this document. We thank Paul Hoffman and Paul Wouters for their contributed text, and also Shumon Huque, S Moonesamy, Peter Thomassen, Paul Wouters, Stefan Ubbink, and Loganaden Velvindron for their reviews and comments.

In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. The DNSSEC protocol makes use of various cryptographic algorithms in order to provide authentication of DNS data and proof of nonexistence. To ensure interoperability between DNS resolvers and DNS authoritative servers, it is necessary to specify a set of algorithm implementation requirements and usage guidelines to ensure that there is at least one algorithm that all implementations support. This document defines the current algorithm implementation requirements and usage guidance for DNSSEC. This document obsoletes RFC 6944. This document is part of a family of documents that describe the DNS Security Extensions (DNSSEC). The DNS Security Extensions are a collection of resource records and protocol modifications that provide source authentication for the DNS. This document defines the public key (DNSKEY), delegation signer (DS), resource record digital signature (RRSIG), and authenticated denial of existence (NSEC) resource records. The purpose and format of each resource record is described in detail, and an example of each resource record is given. This document obsoletes RFC 2535 and incorporates changes from all updates to RFC 2535. [STANDARDS-TRACK] This document specifies how to use the SHA-256 digest type in DNS Delegation Signer (DS) Resource Records (RRs). DS records, when stored in a parent zone, point to DNSKEYs in a child zone. [STANDARDS-TRACK] The Domain Name System Security (DNSSEC) Extensions introduced the NSEC resource record (RR) for authenticated denial of existence. This document introduces an alternative resource record, NSEC3, which similarly provides authenticated denial of existence. However, it also provides measures against zone enumeration and permits gradual expansion of delegation-centric zones. [STANDARDS-TRACK] This document describes how to produce RSA/SHA-256 and RSA/SHA-512 DNSKEY and RRSIG resource records for use in the Domain Name System Security Extensions (RFC 4033, RFC 4034, and RFC 4035). [STANDARDS TRACK] This document describes how to produce digital signatures and hash functions using the GOST R 34.10-2001 and GOST R 34.11-94 algorithms for DNSKEY, RRSIG, and DS resource records, for use in the Domain Name System Security Extensions (DNSSEC). This document describes how to specify Elliptic Curve Digital Signature Algorithm (DSA) keys and signatures in DNS Security (DNSSEC). It lists curves of different sizes and uses the SHA-2 family of hashes for signatures. [STANDARDS-TRACK] This document describes a set of practices for operating the DNS with security extensions (DNSSEC). The target audience is zone administrators deploying DNSSEC. The document discusses operational aspects of using keys and signatures in the DNS. It discusses issues of key generation, key storage, signature generation, key rollover, and related policies. This document obsoletes RFC 4641, as it covers more operational ground and gives more up-to-date requirements with respect to key sizes and the DNSSEC operations. This document describes the issues surrounding the timing of events in the rolling of a key in a DNSSEC-secured zone. It presents timelines for the key rollover and explicitly identifies the relationships between the various parameters affecting the process. This document describes how to specify Edwards-curve Digital Security Algorithm (EdDSA) keys and signatures in DNS Security (DNSSEC). It uses EdDSA with the choice of two curves: Ed25519 and Ed448. 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.

ChangeLog

Changes from ietf-05 to ietf-06

Changes from ietf-03 to ietf-05

Changes from ietf-02 to ietf-03 Fixed the reference in the Abstract (no links in Abstracts) Added Updates: to the header.

Changes from ietf-01 to ietf-02 Changed the MUST values in the tables for the Use columns to RECOMMENDED based on discussions no the dnsop mailing list. Other minor wording and formatting changes

Changes from ietf-00 to ietf-01 Only NIT fixing

Changes from hardaker-04 to ietf-00 Just a draft name and number change.

Changes from -03 to -04 Changed the columns being added from 2 per table to 4, based on discussion within the dnsop working group mailing list. This was a fairly major set of changes.

Changes since RFC8624 The primary purpose of this revision is to introduce the new columns to existing registries. It makes no changes to the previously defined values. Merged in RFC9157 updates. Set authors as Wes Hardaker, Warren Kumari.