In our continued efforts to improve the security of the web PKI, we are taking a multi-pronged approach to tackling some long-existing problems with revocation of TLS server certificates. In addition to our ongoing CRLite work, we added new requirements to version 2.8 of Mozilla’s Root Store Policy that will enable Firefox to depend on revocation reason codes being used consistently, so they can be relied on when verifying the validity of certificates during TLS connections. We also added a new requirement that CA operators provide their full CRL URLs in the CCADB. This will enable Firefox to pre-load more complete certificate revocation data, eliminating dependency on the infrastructure of CAs during the certificate verification part of establishing TLS connections. The combination of these two new sets of requirements will further enable Firefox to enforce revocation checking of TLS server certificates, which makes TLS connections even more secure.
Significant improvements have already been made in the web PKI, including the following changes to Mozilla’s Root Store Policy and the CA/Browser Forum Baseline Requirements (BRs), which reduced risks associated with exposure of the private keys of TLS certificates by reducing the amount of time that the exposure can exist.
Under those provisions, the maximum validity period and maximum re-use of domain validation for TLS certificates roughly corresponds to the typical period of time for owning a domain name; i.e. one year. This reduces the risk of potential exposure of the private key of each TLS certificate that is revoked, replaced, or no longer needed by the original certificate subscriber.
In version 2.8 of Mozilla’s Root Store Policy we added requirements stating that:
These new requirements will provide a complete accounting of all revoked TLS server certificates. This will enable Firefox to pre-load more complete certificate revocation data, eliminating the need for it to query CAs for revocation information when establishing TLS connections.
The new requirements about revocation reason codes account for the situations that can happen at any time during the certificate’s validity period, and address the following problems:
Section 6.1.1 of version 2.8 of Mozilla’s Root Store Policy states that when a TLS server certificate is revoked for one of the following reasons the corresponding entry in the CRL must include the revocation reason code:
RFC 5280 Reason Codes that are not listed above shall not be specified in the CRL for TLS server certificates, for reasons explained in the wiki page.
These new requirements are important steps towards improving the security of the web PKI, and are part of our effort to resolve long-existing problems with revocation of TLS server certificates. The requirements about revocation reason codes will enable Firefox to depend on revocation reason codes being used consistently, so they can be relied on when verifying the validity of certificates during TLS connections. The requirement that CA operators provide their full CRL URLs in the CCADB will enable Firefox to pre-load more complete certificate revocation data, eliminating dependency on the infrastructure of CAs during the certificate verification part of establishing TLS connections. The combination of these two new sets of requirements will further enable Firefox to enforce revocation checking of TLS server certificates, which makes TLS connections even more secure.