rfc9905v1.txt   rfc9905.txt 
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The security of the protection provided by the SHA-1 algorithm The security of the protection provided by the SHA-1 algorithm
[RFC3174] has been slowly diminishing over time as various forms of [RFC3174] has been slowly diminishing over time as various forms of
attacks have weakened its cryptographic underpinning. DNSSEC attacks have weakened its cryptographic underpinning. DNSSEC
[RFC9364] (originally defined in [RFC3110]) made extensive use of [RFC9364] (originally defined in [RFC3110]) made extensive use of
SHA-1, for example, as a cryptographic hash algorithm in Resource SHA-1, for example, as a cryptographic hash algorithm in Resource
Record Signature (RRSIG) and Delegation Signer (DS) records. Since Record Signature (RRSIG) and Delegation Signer (DS) records. Since
then, multiple other algorithms with stronger cryptographic strength then, multiple other algorithms with stronger cryptographic strength
have become widely available for DS records and for RRSIG and DNS have become widely available for DS records and for RRSIG and DNS
Public Key (DNSKEY) records [RFC4034]. Operators are encouraged to Public Key (DNSKEY) records [RFC4034]. Operators are encouraged to
consider switching to one of the recommended algorithms listed in the consider switching to one of the recommended algorithms listed in the
[DNSKEY-IANA] and [DS-IANA] tables, respectively. Further, support "DNS Security Algorithm Numbers" [DNSKEY-IANA] and "DNS Security
for validating SHA-1-based signatures has been removed from some Algorithm Numbers" [DS-IANA] registries, respectively. Further,
systems. As a result, SHA-1 as part of a signature algorithm is no support for validating SHA-1-based signatures has been removed from
longer fully interoperable in the context of DNSSEC. As adequate 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. alternatives exist, the use of SHA-1 is no longer advisable.
This document thus deprecates the use of RSASHA1 and This document thus deprecates the use of RSASHA1 and
RSASHA1-NSEC3-SHA1 for DNS Security Algorithms. RSASHA1-NSEC3-SHA1 for DNS Security Algorithms.
1.1. Requirements Notation 1.1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
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support validation using these algorithms as they are diminishing in support validation using these algorithms as they are diminishing in
use but still actively in use for some domains as of this use but still actively in use for some domains as of this
publication. Operators of validating resolvers MUST treat DNSSEC publication. Operators of validating resolvers MUST treat DNSSEC
signing algorithms RSASHA1 and RSASHA1-NSEC3-SHA1 as unsupported, signing algorithms RSASHA1 and RSASHA1-NSEC3-SHA1 as unsupported,
rendering responses insecure if they cannot be validated by other rendering responses insecure if they cannot be validated by other
supported signing algorithms. supported signing algorithms.
3. Security Considerations 3. Security Considerations
This document deprecates the use of RSASHA1 and RSASHA1-NSEC3-SHA1 This document deprecates the use of RSASHA1 and RSASHA1-NSEC3-SHA1
for DNSSEC Delegation and DNSSEC signing since these algorithms are for DNSSEC delegation and DNSSEC signing since these algorithms are
no longer considered to be secure. no longer considered to be secure.
4. Operational Considerations 4. Operational Considerations
Zone owners currently making use of SHA-1-based algorithms should Zone owners currently making use of SHA-1-based algorithms should
immediately roll to algorithms with stronger cryptographic immediately switch to algorithms with stronger cryptographic
algorithms, such as the recommended algorithms in the [DNSKEY-IANA] algorithms, such as the recommended algorithms in the IANA registries
and [DS-IANA] tables. [DNSKEY-IANA] [DS-IANA].
Operators should take care when deploying software packages and Operators should take care when deploying software packages and
operating systems that may have already removed support for the SHA-1 operating systems that may have already removed support for the SHA-1
algorithm. In these situations, software may need to be manually algorithm. In these situations, software may need to be manually
built and deployed by an operator to continue supporting the required built and deployed by an operator to continue supporting the required
levels indicated by the "Use for DNSSEC Validation" and "Implement levels indicated by the "Use for DNSSEC Validation" and "Implement
for DNSSEC Validation" columns, which this document is not changing. for DNSSEC Validation" columns, which this document is not changing.
5. IANA Considerations 5. IANA Considerations
IANA has set the "Use for DNSSEC Delegation" column of the "Digest IANA has updated the SHA-1 (1) entry in the "Digest Algorithms"
Algorithms" registry [DS-IANA] [RFC9904] to MUST NOT for SHA-1 (1) registry [DS-IANA] [RFC9904] as follows and has added this document
and has added this document as a reference for the entry. as a reference for the entry:
IANA has set the "Use for DNSSEC Signing" column of the "DNS Security Value: 1
Algorithm Numbers" registry [DNSKEY-IANA] [RFC9904] to MUST NOT for Description: SHA-1
the RSASHA1 (5) and RSASHA1-NSEC3-SHA1 (7) algorithms and has added Use for DNSSEC Delegation: MUST NOT
this document as a reference for these entries. Use for DNSSEC Validation: RECOMMENDED
Implement for DNSSEC Delegation: MUST NOT
Implement for DNSSEC Validation: MUST
All other columns should remain as currently specified. 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:
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
6. Normative References 6. Normative References
[DNSKEY-IANA] [DNSKEY-IANA]
IANA, "Domain Name System Security (DNSSEC) Algorithm IANA, "DNS Security Algorithm Numbers",
Numbers",
<https://www.iana.org/assignments/dns-sec-alg-numbers>. <https://www.iana.org/assignments/dns-sec-alg-numbers>.
[DS-IANA] IANA, "DNSSEC Delegation Signer (DS) Resource Record (RR) [DS-IANA] IANA, "Digest Algorithms",
Type Digest Algorithms",
<http://www.iana.org/assignments/ds-rr-types>. <http://www.iana.org/assignments/ds-rr-types>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3110] Eastlake 3rd, D., "RSA/SHA-1 SIGs and RSA KEYs in the [RFC3110] Eastlake 3rd, D., "RSA/SHA-1 SIGs and RSA KEYs in the
Domain Name System (DNS)", RFC 3110, DOI 10.17487/RFC3110, Domain Name System (DNS)", RFC 3110, DOI 10.17487/RFC3110,
May 2001, <https://www.rfc-editor.org/info/rfc3110>. May 2001, <https://www.rfc-editor.org/info/rfc3110>.
skipping to change at line 189 skipping to change at line 213
[RFC9364] Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237, [RFC9364] Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237,
RFC 9364, DOI 10.17487/RFC9364, February 2023, RFC 9364, DOI 10.17487/RFC9364, February 2023,
<https://www.rfc-editor.org/info/rfc9364>. <https://www.rfc-editor.org/info/rfc9364>.
[RFC9499] Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219, [RFC9499] Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
RFC 9499, DOI 10.17487/RFC9499, March 2024, RFC 9499, DOI 10.17487/RFC9499, March 2024,
<https://www.rfc-editor.org/info/rfc9499>. <https://www.rfc-editor.org/info/rfc9499>.
[RFC9904] Hardaker, W. and W. Kumari, "DNSSEC Cryptographic [RFC9904] Hardaker, W. and W. Kumari, "DNSSEC Cryptographic
Algorithm Recommendation Update Process", RFC 9904, Algorithm Recommendation Update Process", RFC 9904,
DOI 10.17487/RFC9904, October 2025, DOI 10.17487/RFC9904, November 2025,
<https://www.rfc-editor.org/info/rfc9904>. <https://www.rfc-editor.org/info/rfc9904>.
Acknowledgments Acknowledgments
The authors appreciate the comments and suggestions from the The authors appreciate the comments and suggestions from the
following IETF participants in helping produce this document: Mark following IETF participants in helping produce this document: Mark
Andrews, Steve Crocker, Peter Dickson, Thomas Graf, Paul Hoffman, Andrews, Steve Crocker, Peter Dickson, Thomas Graf, Paul Hoffman,
Russ Housley, Shumon Huque, Barry Leiba, S. Moonesamy, Yoav Nir, Russ Housley, Shumon Huque, Barry Leiba, S. Moonesamy, Yoav Nir,
Florian Obser, Peter Thomassen, Stefan Ubbink, Paul Wouters, Tim Florian Obser, Peter Thomassen, Stefan Ubbink, Paul Wouters, Tim
Wicinski, and the many members of the DNSOP Working Group that Wicinski, and the many members of the DNSOP Working Group that
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