In a Public Key Infrastructure (PKI), what is the role of a directory server?

In a Public Key Infrastructure (PKI), the role of a directory server is to make user certificates available to others. This is a critical function because a directory server maintains a repository of public-key certificates and their associated attributes, which enables users and applications to easily retrieve and verify the public keys of individuals or entities.

When a user wants to establish a secure connection or verify a digital signature, they need access to the public key of the other party. The directory server serves as a centralized location where these certificates can be stored and accessed, facilitating trust and enabling secure communications.

The other options refer to different roles in the PKI hierarchy: issuing certificates is handled by Certificate Authorities (CAs), the authorization of CA servers does not fall under the directory server's responsibilities, and the root authority role is specifically designated to the root CA, which establishes the top level of trust in the PKI system.