Today we’re excited to announce a new certificate verification library for Mozilla Products – mozilla::pkix! While most users will not notice a difference, the new library is more robust and maintainable. The new code is more robust because certificate path building attempts all potential trust chains for a certificate before giving up (acknowledging the fact that the certificate space is a cyclic directed graph and not a forest). The new implementation is also more maintainable, with only 4,167 lines of C++ code compared to the previous 81,865 lines of code which had been auto-translated from Java to C. The new library benefits from C++ functionality such as memory cleanup tools (e.g., RAII).

To provide some more background, Gecko has historically used the certificate verification processing in NSS to ensure that the certificates presented during a TLS/SSL handshake is valid. NSS currently has two code paths for doing certificate verification: “classic” used by Gecko for Domain Validated (DV) certificate verification, and libPKIX used by Gecko for Extended Validation (EV) certificate verification. The NSS team has wanted to replace the “classic” verification with libPKIX for some time because libPKIX handles cross-signed certificates better and properly handles certificate policies required for Enhanced Validation (EV) certificates. However, libPKIX has proven to be very difficult to work with.

We also took the opportunity to enforce some requirements in Mozilla’s CA Certificate Policy and in the CA/Browser Forum’s Baseline Requirements (BRs). The changes are listed here. While we have performed extensive compatibility testing, it is possible that your website certificate will no longer validate with Firefox 31. This should not be a problem if you use a certificate issued by one of the CAs in Mozilla’s CA Program, because they should already be issuing certificates according to Mozilla’s CA Certificate Policy and the BRs. If you notice an issue due to any of these changes, please let us know.

We are looking for feedback with respect to compatibility and security. For compatibility, we ask all site operators and security testers to install Firefox 31 and use it to browse to your favorite sites. In addition, we ask for willing C++ programmers out there to review our code. This new mozilla::pkix library is located at security/pkix and security/certverifier. A more detailed description is here. If you find an issue, please help us make it better by filing a Bugzilla bug report.

We look forward to your feedback on this new certificate verification library.

Mozilla Security Engineering Team