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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.

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 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.