| RFC 9905 | Deprecating SHA-1 in DNSSEC Signature Al | November 2025 |
| Hardaker & Kumari | Standards Track | [Page] |
This document deprecates the use of the RSASHA1 and RSASHA1-NSEC3-SHA1algorithms for the creation of DNS Public Key (DNSKEY) and ResourceRecord Signature (RRSIG) records.¶
It updates RFCs 4034 and 5155 as it deprecates the use of these algorithms.¶
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 athttps://www.rfc-editor.org/info/rfc9905.¶
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 (https://trustee.ietf.org/license-info) 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.¶
The security of the protection provided by the SHA-1 algorithm[RFC3174] has been slowly diminishingover time as various forms of attacks have weakened its cryptographicunderpinning. DNSSEC[RFC9364] (originally defined in[RFC3110]) made extensive useof SHA-1, for example, as acryptographic hash algorithm in Resource Record Signature (RRSIG) and Delegation Signer (DS)records. Since then, multiple other algorithms withstronger cryptographic strength have become widely available for DS records and for RRSIG and DNS Public Key (DNSKEY) records[RFC4034].Operators are encouraged to consider switching to one of the recommended algorithms listed in the "DNS Security Algorithm Numbers"[DNSKEY-IANA] and "DNS Security Algorithm Numbers"[DS-IANA] registries, respectively.Further, support for validating SHA-1-based signatures has beenremoved from some systems. As a result, SHA-1 as part of a signature algorithm is no longer fully interoperablein the context of DNSSEC. As adequate alternatives exist, the use of SHA-1 isno longer advisable.¶
This document thus deprecates the use of RSASHA1 andRSASHA1-NSEC3-SHA1 for DNS Security Algorithms.¶
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[RFC2119][RFC8174] when, and only when, they appear in all capitals, as shown here.¶
The RSASHA1[RFC4034] and RSASHA1-NSEC3-SHA1[RFC5155] algorithmsMUST NOTbe used when creating DS records. Operators of validating resolversMUST treat RSASHA1and RSASHA1-NSEC3-SHA1 DS records as insecure. If no other DS records ofaccepted cryptographic algorithms are available, the DNS records below thedelegation pointMUST be treated as insecure.¶
The RSASHA1[RFC4034] and RSASHA1-NSEC3-SHA1[RFC5155] algorithmsMUST NOT beused when creating DNSKEY and RRSIG records. Validating resolver implementations([RFC9499],Section 10)MUST continue to support validation using thesealgorithms as they are diminishing in use but still actively in use for somedomains as of this publication. Operators of validating resolversMUST treat DNSSEC signing algorithms RSASHA1 and RSASHA1-NSEC3-SHA1 as unsupported, rendering responses insecure if they cannot be validated by other supported signing algorithms.¶
This document deprecates the use of RSASHA1 and RSASHA1-NSEC3-SHA1 forDNSSEC delegation and DNSSEC signing since these algorithms are nolonger considered to be secure.¶
Zone owners currently making use of SHA-1-based algorithms shouldimmediately switch to algorithms with stronger cryptographic algorithms,such as the recommended algorithms in the IANA registries[DNSKEY-IANA][DS-IANA].¶
Operators should take care when deploying software packages andoperating systems that may have already removed support for the SHA-1algorithm. In these situations, software may need to be manually builtand deployed by an operator to continue supporting the required levelsindicated by the "Use for DNSSEC Validation" and "Implement for DNSSECValidation" columns, which this document is not changing.¶
IANA has updated the SHA-1 (1) entry in the "Digest Algorithms" registry[DS-IANA][RFC9904] as follows and has added this document as a reference for the entry:¶
IANA has updated the RSASHA1 (5) and RSASHA1-NSEC3-SHA1 (7) algorithm entries in the "DNS Security Algorithm Numbers" registry[DNSKEY-IANA][RFC9904] as follows and has added this document as a reference for the entries:¶
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 specification.¶