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This document deprecates the use of the RSASHA1 and RSASHA1-NSEC3-SHA1 algorithms for the creation of DNS Public Key (DNSKEY) and Resource Record Signature (RRSIG) records. It updates RFC4034 and RFC5155 as it deprecates the use of these algorithms.

Introduction The security of the protection provided by the SHA-1 algorithm has been slowly diminishing over time as various forms of attacks have weakened its cryptographic underpinning. DNSSEC originally made extensive use of SHA-1, for example as a cryptographic hash algorithm in RRSIG and Delegation Signer (DS) records. Since then, multiple other algorithms with stronger cryptographic strength have become widely available for DS records and for Resource Record Signature (DNSKEY) and DNS Public Key (RRSIG) records . Operators are encouraged to consider switching to one of the recommended algorithms listed in the and tables, respectively. Further, support for validating SHA-1 based signatures has been removed from some systems. As a result, SHA-1 as part of a signature algorithm is no longer fully interoperable in the context of DNSSEC. As adequate alternatives exist, the use of SHA-1 is no longer advisable. This document thus further deprecates the use of RSASHA1 and RSASHA1-NSEC3-SHA1 for DNS Security Algorithms.

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.

Deprecating SHA-1 from DNSSEC Signatures and Delegation RRs The RSASHA1 and RSASHA1-NSEC3-SHA1 algorithms MUST NOT be used when creating DS records. Validating resolvers MUST treat RSASHA1 and RSASHA1-NSEC3-SHA1 DS records as insecure. If no other DS records of accepted cryptographic algorithms are available, the DNS records below the delegation point MUST be treated as insecure. The RSASHA1 and RSASHA1-NSEC3-SHA1 algorithms MUST NOT be used when creating DNSKEY and RRSIG records. Validating resolver implementations ( section 10) MUST continue to support validation using these algorithms as they are diminishing in use but still actively in use for some domains as of this publication. Because of RSASHA1 and RSASHA1-NSEC3-SHA1's non-zero use, deployed validating resolvers MAY be configured to continue to validate RRSIG records that use these algorithms. Validating resolvers deployed in more security strict environments MAY treat these RRSIG records as an unsupported algorithm.

Security Considerations This document deprecates the use of RSASHA1 and RSASHA1-NSEC3-SHA1 for DNSSEC Delegation and DNSSEC signing since these algorithms are no longer considered to be secure.

Operational Considerations Zone owners currently making use of SHA-1 based algorithms should immediately roll to algorithms with stronger cryptographic algorithms, such as the recommended algorithms in the and tables. Operators should take care when deploying software packages and operating systems that may have already removed support for the SHA-1 algorithm. In these situations software may need to be manually built and deployed by an operator to continue supporting the required levels indicated by the "Use for DNSSEC Validation" and "Implement for DNSSEC Validation" columns, which this document is not changing.

IANA Considerations [Note to IANA, to be removed by the RFC Editor: the registry fields listed above will be created by draft-ietf-dnsop-rfc8624-bis.] IANA is requested to set the "Use for DNSSEC Delegation" field of the "Digest Algorithms" registry for SHA-1 (1) to MUST NOT. IANA is requested to set the "Use for DNSSEC Signing" column of the DNS Security Algorithm Numbers registry to MUST NOT for the RSASHA1 (5) and RSASHA1-NSEC3-SHA1 (7) algorithms. All other columns should remain as currently specified.

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. This document describes how to produce RSA/SHA1 SIG resource records (RRs) in Section 3 and, so as to completely replace RFC 2537, describes how to produce RSA KEY RRs in Section 2. [STANDARDS-TRACK] The purpose of this document is to make the SHA-1 (Secure Hash Algorithm 1) hash algorithm conveniently available to the Internet community. This memo provides information for the Internet community. 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] 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 Domain Name System (DNS) is defined in literally dozens of different RFCs. The terminology used by implementers and developers of DNS protocols, and by operators of DNS systems, has changed in the decades since the DNS was first defined. This document gives current definitions for many of the terms used in the DNS in a single document. This document updates RFC 2308 by clarifying the definitions of "forwarder" and "QNAME". It obsoletes RFC 8499 by adding multiple terms and clarifications. Comprehensive lists of changed and new definitions can be found in Appendices A and B. 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. USC/ISI Google 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 replaces and obsoletes RFC8624 and moves 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 of requirements 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. This document also incorporates the revised IANA DNSSEC considerations from RFC9157. The document does not change the status (MUST, MAY, RECOMMENDED, etc.) of the algorithms listed in RFC8624; that is the work of future documents.

Acknowledgments The authors appreciate the comments and suggestions from the following IETF participants in helping produce this document: Mark Andrews, Steve Crocker, Peter Dickson, Thomas Graf, Paul Hoffman, Russ Housley, Shumon Huque, Barry Leiba, S Moonesamy, Yoav Nir, Florian Obser, Peter Thomassen, Stefan Ubbink, Paul Wouters, Tim Wicinski, and the many members of the DNSOP working group that discussed this draft.

Current algorithm usage levels The DNSSEC scanning project by Viktor Dukhovni and Wes Hardaker highlights the current deployment of various algorithms on the https://stats.dnssec-tools.org/ website. <RFC Editor: please delete this section upon publication>

Github Version of this document While this document is under development, it can be viewed, tracked, fill here: https://github.com/hardaker/draft-hardaker-dnsop-must-not-sha1 <RFC Editor: please delete this section upon publication>