Which protocol is known for providing a more efficient way to check a certificate's status without a complete list?

The Online Certificate Status Protocol (OCSP) is designed to provide a more efficient method for checking the status of a digital certificate. Unlike the Certificate Revocation List (CRL), which requires users to download a complete list of revoked certificates, OCSP allows a user to query a specific certificate's status directly from the certificate authority (CA).

When a user needs to verify whether a particular certificate is still valid or has been revoked, they send a request to the OCSP responder—typically managed by the issuing CA. This responder checks the status of the requested certificate in real-time and returns a response indicating if it is valid, revoked, or unknown.

Using OCSP is particularly beneficial in scenarios where quick decision-making is essential, as it reduces the overhead associated with downloading a full revocation list, especially in environments where there are potentially large volumes of certificates. This efficiency makes OCSP a more suitable choice for systems that require timely and efficient certificate status checking.

Registration Authority (RA) and Certificate Signing Request (CSR) are not directly involved in the status checking of certificates. The RA plays a role in the initial processes of issuing certificates, including verifying identities before a certificate is issued, while a CSR is a request for a certificate that contains information such