What functionality does the OCSP protocol provide?

The Online Certificate Status Protocol (OCSP) is specifically designed to address the need for real-time certificate status checking. Its primary functionality is to allow clients to inquire about the status of a digital certificate, which includes determining whether it has been revoked.

When a client receives a digital certificate, it often needs to ensure that the certificate is still valid and has not been revoked by the issuing Certificate Authority (CA). OCSP provides a way to obtain this information in a timely manner, allowing for quick verification without the need for downloading large Certificate Revocation Lists (CRLs). Instead, the client sends a request to an OCSP responder, which then returns a response indicating whether the certificate is good, revoked, or unknown.

In contrast, the other options do not accurately reflect the purpose or functionality of OCSP. Encryption relates to securing data, VPN connectivity pertains to creating secure connections over a public network, and hashing is a technique for data integrity verification. These functionalities are distinct from the certificate status checking that OCSP provides.