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This document retires the use of SHA-1 within DNSSEC.

Introduction The security of 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 DNSSEC originally made extensive use of SHA-1 as a cryptographic verification algorithm in RRSIG and Delegation Signer (DS) records, for example. Since then, multiple other signing algorithms with stronger cryptographic strength are now widely available for DS records (such as SHA-256 , SHA-384 ()) and for DNSKEY and RRSIG records (such as RSASHA256 (), RSASHA512 (), ECDSAP256SHA256 , ECDSAP384SHA384 , ED25519 , and ED448 ). Further, support for validating SHA-1 based signatures has been removed from some systems. As a result, SHA-1 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 algorithms in DNSSEC The RSASHA1 and RSASHA1-NSEC3-SHA1 algorithms MUST NOT be used when creating DNSKEY and RRSIG records. Validating resolvers 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. Validating resolvers MAY treat RRSIG records created from DNSKEY records using these algorithms as an unsupported algorithm.

Security Considerations This document reduces the risk that a zone cannot be validated due to lack of SHA-1 support in a validator, by guiding signers to choose a more interoperable signing algorithm.

Operational Considerations Zone owners currently making use of SHA-1 based algorithms should immediately switch to algorithms with stronger cryptographic strengths, such as those listed in the introduction.

IANA Considerations 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. 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. The Domain Name System Security Extensions (DNSSEC) add data origin authentication and data integrity to the Domain Name System. This document introduces these extensions and describes their capabilities and limitations. This document also discusses the services that the DNS security extensions do and do not provide. Last, this document describes the interrelationships between the documents that collectively describe DNSSEC. [STANDARDS-TRACK] 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 is part of a family of documents that describe the DNS Security Extensions (DNSSEC). The DNS Security Extensions are a collection of new resource records and protocol modifications that add data origin authentication and data integrity to the DNS. This document describes the DNSSEC protocol modifications. This document defines the concept of a signed zone, along with the requirements for serving and resolving by using DNSSEC. These techniques allow a security-aware resolver to authenticate both DNS resource records and authoritative DNS error indications. 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 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 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. 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.

Acknowledgments The authors appreciate the comments and suggestions from the following IETF participants in helping produce this document: Mark Andrews, Peter Dickson, Peter Thomassen, Paul Wouters 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