OCSP (Online Certificate Status Protocol)

OCSP (RFC 6960) is a protocol for real-time verification of the revocation status of a digital certificate, by querying an OCSP responder operated by the certification authority. It is a lighter and more responsive alternative to CRL. OCSP Stapling allows the server to attach the OCSP response directly in the TLS handshake, avoiding an additional round-trip. OCSP responses are also embedded in signed documents for long-term validation (LTV).