SC-061v4: new CRL entries must carry a revocation reason code

SC-061v4 requires CAs to record why they revoked a TLS certificate. Since 2023-07-15, when a CA revokes a TLS certificate, the new CRL entry must carry the reason code that fits the situation, such as keyCompromise or superseded, using the rules Mozilla had already put into its root store policy.

What changed

SC-061v4 modified §4.9.1.1 (reasons for revoking a subscriber certificate) and §7.2.2 (CRL extensions) of the Baseline Requirements. Each revocation reason in §4.9.1.1 now maps to a CRL reason: keyCompromise (#1) when the private key leaked or can be computed, superseded (#4) when the certificate was misissued or replaced, cessationOfOperation (#5) when the domain is no longer used, affiliationChanged (#3) when subscriber details changed, and privilegeWithdrawn (#9) when the CA withdraws the certificate, for example for misuse. A revocation without a stated reason is "unspecified", which is expressed by leaving the reasonCode extension out. The ballot was proposed by Mozilla and endorsed by Google Trust Services and Microsoft.

Effective dates

The BR change took effect on 2023-07-15.

Who is affected

SC-061v4 mainly affects CAs and anyone analysing revocations. Revocation reasons give relying parties and researchers a clearer picture, for example to tell key compromise apart from routine replacement.

What to do

When you ask a CA to revoke a certificate, state the reason honestly: report a leaked key as key compromise, so the CA can also block the key under SC-073. With ACME you can pass the reason code in the revocation request.