]> USC/ISI

ietf@hardakers.net

Google

warren@kumari.net

[EDITOR NOTE: This document does not change the status (MUST, MAY, RECOMMENDED, etc) of any of the algorithms listed in ; that is the work of future documents. Instead, this document moves the canonical list of algorithms from to an IANA registry. This is done for two reasons: 1) to allow the list to be updated more easily, and, much more importantly, 2) to allow the list to be more easily referenced.] 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 by moving the canonical source of algorithm implementation requirements and usage guidance for DNSSEC from to an IANA registry. Future extensions to this registry can be made under new, incremental update RFCs.

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, this document moves the canonical status of the algorithms from to the IANA DNSSEC algorithm registries. [ Editor: 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. ] This document simply moves the canonical list of algorithms from to the IANA registry, and defines the registry policies for updating the registry. It does not change the status of any of the algorithms listed in ; this is left to future documents.

Document Audience The recommendations columns added to the "DNS Security Algorithm Numbers" and "Digest Algorithms" IANA tables target DNSSEC implementers, as implementations need to meet both high security expectations as well as high interoperability between various vendors and with different versions. Interoperability requires a smooth transition to more secure algorithms. This perspective may differ from that of a user who wishes to deploy and configure DNSSEC with only the safest algorithm.

Updating Algorithm Implementation Requirements and Usage Guidance The field of cryptography evolves continuously. New, stronger algorithms appear, and existing algorithms may be found to be less secure then originally thought. Therefore, algorithm implementation requirements and usage guidance need to be updated from time to time in order to reflect the new reality. Cryptographic algorithm choices implemented in and required by software must be conservative to minimize the risk of algorithm compromise.

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 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 "Recommended" Columns to existing IANA tables Per this document, the following "Recommended" columns have been added to the following DNSSEC algorithm tables registered with IANA: Table Column added Domain Security Algorithm Numbers Recommended for DNSSSEC Signing Domain Security Algorithm Numbers Recommended for DNSSSEC Validation Digest Algorithms Recommended

Adding a new entry to the "DNS System Algorithm Numbers" registry with a recommended value of MAY in both the "Recommended for DNSSSEC Signing" and "Recommended for DNSSSEC Validation" columns requires RFC publication. Adding a new entry to, or changing existing values in the "DNS System Algorithm Numbers" registry with a value in the "Recommended for DNSSSEC Signing" or "Recommended for DNSSSEC Validation" columns other than MAY requires a Standards Action. Adding a new entry to the "Digest Algorithms" registry with a recommended value of MAY in the "Recommended" column requires RFC publication. Adding a new entry to the "Digest Algorithms" registry with a value in the "Recommended" column other 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 values transcribed from .

DNS System Algorithm Numbers Column Values Initial recommendation columns of implementation recommendations for the "Domain Name System Security (DNSSEC) Algorithm Numbers" are show in Table 2.     Recommended for Recommended for Number Mnemonics DNSSEC Signing DNSSEC Validation 1 RSAMD5 MUST NOT MUST NOT 3 DSA MUST NOT MUST NOT 5 RSASHA1 NOT RECOMMENDED MUST 6 DSA-NSEC3-SHA1 MUST NOT MUST NOT 7 RSASHA1-NSEC3-SHA1 NOT RECOMMENDED MUST 8 RSASHA256 MUST MUST 10 RSASHA512 NOT RECOMMENDED MUST 12 ECC-GOST MUST NOT MAY 13 ECDSAP256SHA256 MUST MUST 14 ECDSAP384SHA384 MAY RECOMMENDED 15 ED25519 RECOMMENDED RECOMMENDED 16 ED448 MAY RECOMMENDED

DNSSEC Delegation Signer (DS) Resource Record (RR) Type Digest Algorithms Column Values Initial recommendation columns of implementation recommendations for the "DNSSEC Delegation Signer (DS) Resource Record (RR) Type Digest Algorithms" registry are shown in Table 3. Number Mnemonics DNSSEC Delegation DNSSEC Validation 0 NULL (CDS only) MUST NOT [*] MUST NOT [*] 1 SHA-1 MUST NOT MUST 2 SHA-256 MUST MUST 3 GOST R 34.11-94 MUST NOT MAY 4 SHA-384 MAY RECOMMENDED

Security Considerations 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 secure into the foreseeable future. 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 as follows: Add "Recommended for DNSSSEC Signing" and "Recommended for DNSSSEC Validation" columns to the "DNS Security Algorithm Numbers" registry () and populate these columens with the values from Table 1. Add a "Recommended" column to the "Digest Algorithms" registry () and populate this column with the values from Table 2. Update the registration policy for the registry to match the text describing update requirements above. {Ed: We're not sure if this is the right policy, and this requires a good discussion with the WG. The purpose of much of this document is so that we can introduce TheNextBestAlgorithm by documenting TheNextBestAlgorithm in a new RFC and having it updating the IANA registry, instead of having to update RFC8624-bis-bis-bis-bis. We also, obviously, don't want someone to do something silly and mark an algorithm as "Recommended" without a good reason. This implies Standards Track. On the other hand we want to allow the ISE to add new algorithms (like the latest GOST algorithm), and, rightly or wrongly, the ISE doesn't publishes Std Track RFCs. Standards Action or IESG Approval seems like a reasonable compromise, but I'm not sure if it's the right one. We hope to present this to the WG at IEFT119 and get feedback.}

Acknowledgments This document is based on, and extends, RFC 8624, which was authored by Paul Wouters, and Ondrej Sury.

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. 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 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 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] 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). [STANDARDS-TRACK] 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.

ChangeLog

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.