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 DNSSEC [RFC4033] [RFC4034] [RFC4035] originally made extensive use of SHA-1 as a cryptographic verification algorithm in RRSIG and Delegation Signer (DS) records, for example.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]). Further, support for validating SHA-1 based signatures has been removed from some systems. As a result, SHA-1 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 further deprecates the use of RSASHA1 and RSASHA1-NSEC3-SHA1 for DNS Security Algorithms.¶

2. Deprecating SHA-1 algorithms in DNSSEC

The RSASHA1 [RFC4034] and RSASHA1-NSEC3-SHA1 [RFC5155] algorithms MUST NOT be used when creating DNSKEY and RRSIG records.¶

Validating resolvers 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. Validating resolvers MAY treat RRSIG records created from DNSKEY records using these algorithms as an unsupported algorithm.¶

3. Security Considerations

This document reduces the risk that a zone cannot be validated due to lack of SHA-1 support in a validator, by guiding signers to choose a more interoperable signing algorithm.¶

4. Operational Considerations

Zone owners currently making use of SHA-1 based algorithms should immediately switch to algorithms with stronger cryptographic strengths, such as those listed in the introduction.¶

5. IANA Considerations

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

IANA is requested to set the "Use for DNSSEC Signing" column of the DNS Security Algorithm Numbers registry [DNSKEY-IANA] to MUST NOT for the RSASHA1 (5) and RSASHA1-NSEC3-SHA1 (7) algorithms.¶

All other columns should remain as currently specified.¶

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