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OPS dnsop 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 RFCs 4034 and 5155 as it deprecates the use of these algorithms.

Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents () in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

Table of Contents

• .  Introduction
  • .  Requirements Notation
• .  Deprecating SHA-1 from DNSSEC Signatures and Delegation RRs
• .  Security Considerations
• .  Operational Considerations
• .  IANA Considerations
• .  Normative References
• Acknowledgments
• Authors' Addresses

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 defined in ) made extensive use of SHA-1, for example, as a cryptographic hash algorithm in Resource Record Signature (RRSIG) and Delegation Signer (DS) records. Since then, multiple other algorithms with stronger cryptographic strength have become widely available for DS records and for RRSIG and DNS Public Key (DNSKEY) records . Operators are encouraged to consider switching to one of the recommended algorithms listed in the "DNS Security Algorithm Numbers" and "DNS Security Algorithm Numbers" registries, 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 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. Operators of 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 () 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. Operators of validating resolvers MUST treat DNSSEC signing algorithms RSASHA1 and RSASHA1-NSEC3-SHA1 as unsupported, rendering responses insecure if they cannot be validated by other supported signing algorithms.

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 switch to algorithms with stronger cryptographic algorithms, such as the recommended algorithms in the IANA registries . 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 IANA has updated the SHA-1 (1) entry in the "Digest Algorithms" registry as follows and has added this document as a reference for the entry:

Value:

1

Description:

SHA-1

Use for DNSSEC Delegation:

MUST NOT

Use for DNSSEC Validation:

RECOMMENDED

Implement for DNSSEC Delegation:

MUST NOT

Implement for DNSSEC Validation:

MUST

IANA has updated the RSASHA1 (5) and RSASHA1-NSEC3-SHA1 (7) algorithm entries in the "DNS Security Algorithm Numbers" registry as follows and has added this document as a reference for the entries:

Number:

5

Description:

RSA/SHA-1

Mnemonic:

RSASHA1

Zone Signing:

Y

Trans. Sec.:

Y

Use for DNSSEC Signing:

MUST NOT

Use for DNSSEC Validation:

RECOMMENDED

Implement for DNSSEC Signing:

NOT RECOMMENDED

Implement for DNSSEC Validation:

MUST

Number:

7

Description:

RSASHA1-NSEC3-SHA1

Mnemonic:

RSASHA1-NSEC3-SHA1

Zone Signing:

Y

Trans. Sec.:

Y

Use for DNSSEC Signing:

MUST NOT

Use for DNSSEC Validation:

RECOMMENDED

Implement for DNSSEC Signing:

NOT RECOMMENDED

Implement for DNSSEC Validation:

MUST

Normative References 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. 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. 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. USC/ISI Google

Acknowledgments The authors appreciate the comments and suggestions from the following IETF participants in helping produce this document: , , , , , , , , , , , , , , , and the many members of the DNSOP Working Group that discussed this specification.

Authors' Addresses USC/ISI

ietf@hardakers.net

Google

warren@kumari.net