What term describes when a certificate establishes a trust relationship between two different certification authorities?

Cross certification refers to the process where two different certification authorities (CAs) establish a trust relationship, allowing them to recognize each other's certificates. This is significant in environments where multiple organizations need to establish a mutual trust in each other's certificates without having a single, centralized authority.

By implementing cross certification, organizations can facilitate secure communications and interoperability between systems that otherwise might not share the same certificate hierarchy. It enables trust to be extended across different CA domains, thereby enhancing cooperation and secure exchanges of information in a distributed environment.

In contrast, the other terms describe different concepts in public key infrastructure. Trusted providers usually refer to entities that users trust to issue certificates, but does not specifically address relationships between different CAs. A single CA implies a centralized system where trust is maintained within one authority, which does not involve inter-CA relationships. Hierarchical CA refers to a model where certificates are issued in a structured manner from a root CA to subordinate CAs, focusing on a single chain of trust rather than establishing inter-CA relations.