Changes

mozilla::pkix was originally implemented as part of mozilla-central (i.e. gecko) but has since been moved into NSS. However, it is not part of NSS' stable C API. As a library, mozilla::pkix uses the notion of a "trust domain" provided by the application to build a trusted chain from an end-entity certificate to a root. The trust domain is responsible for saying what trust level a certificate has, finding potential issuers of a certificate, and [[CA/Revocation_Checking_in_Firefox|checking the revocation for a certificate]]. A certificate can be a trust anchor, it can inherit its trust, or it can be [[CA/Maintenance_and_Enforcement#Actively_Distrusting_a_Certificate|actively distrusted]]. Given an end-entity certificate and a trust domain, the library will perform issuer-independent checks on that certificate (e.g. expiration, appropriate key usages), get a list of potential issuers, and perform a [https://en.wikipedia.org/wiki/Depth-first_search depth-first traversal]. If it encounters a distrusted certificate, it abandons searching that path. If it finds a trust anchor, it queries the trust domain again to see if that path is acceptable (this is where gecko implements checks that are specific to the platform and not the abstract problem of building a trusted certificate chain). If so, the end-entity certificate has successfully been verified.