Online Certificate Status Protocol

An Internet protocol [R2560] used by a client to obtain from a server the validity status and other information about a digital certificate. (Mentioned in [X509] but not specified there.)

Tutorial: In some applications, such as those involving high-value commercial transactions, it may be necessary either (a) to obtain certificate revocation status that is timelier than is possible with CRLs or (b) to obtain other kinds of status information. OCSP may be used to determine the current revocation status of a digital certificate, in lieu of or as a supplement to checking against a periodic CRL. An OCSP client issues a status request to an OCSP server and suspends acceptance of the certificate in question until the server provides a response.