Remove SHA-1 from active use within DNSSEC

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Table of Contents

1. Introduction

The security of the SHA-1 algorithm [RFC3174] has been slowly diminishing over time as various forms of attacks have weakened its cryptographic underpinning. DNSSEC [RFC4033] [RFC4034] [RFC4035] originally made extensive use of SHA-1 as a cryptographic verification algorithm in RRSIG and Delegation Signer (DS) records, for example.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 [RFC4509], SHA-384 ([RFC6605])) and for DNSKEY and RRSIG records (such as RSASHA256 ([RFC5702]), RSASHA512 ([RFC5702]), ECDSAP256SHA256 [RFC6605], ECDSAP384SHA384 [RFC6605], ED25519 [RFC8080], and ED448 [RFC8080]), the use of SHA-1 is no longer needed.¶

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

2. Deprecating SHA-1 algorithms in DNSSEC

The SHA-1 [RFC3685] algorithm MUST NOT be used when creating DS records. Validating resolvers MUST treat 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 [RFC4034], DSA-NSEC3-SHA1 [RFC5155], and RSASHA1-NSEC3-SHA1 [RFC5155] algorithms MUST NOT be used when creating DNSKEY and RRSIG records. Validating resolvers MUST treat RRSIG records created from DNSKEY records using these algorithms as insecure. If no other RRSIG records of accepted cryptographic algorithms are available, the validating resolver MUST consider the associated resource records as Bogus.¶

3. Security Considerations

This document increases the security of the DNSSEC ecosystem by deprecating algorithms that make use of older algorithms with SHA-1 derived uses.¶

4. Operational Considerations

Zone owners currently making use of SHA-1 based algorithms should immediate switch to algorithms with stronger cryptographic strengths, such as those listed in the introduction. DNS registries [RFC8499] should prohibit their clients to upload and publish SHA-1 based DS records.¶

5. IANA Considerations

IANA is requested to set the "DNSSEC Validation" of the "Digest Algorithms" registry [DS-IANA] for SHA-1 (1) to MUST NOT.¶

IANA is requested to set the "Recommended for DNSSEC Validation" column of the DNS Security Algorithm Numbers registry [DNSKEY-IANA] to MUST NOT:¶

• RSASHA1 (5)¶

• RSASHA1-NSEC3-SHA1 (7)¶

Appendix A. Acknowledgments

TBD¶

Appendix B. 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]¶

Appendix C. 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¶

Authors' Addresses