The Online Certificate Status Protocol (OCSP) stapling, formally known as the TLS Certificate Status Request extension, is a standard for checking the revocation status of X.509 digital certificates. It allows the presenter of a certificate to bear the resource cost involved in providing Online Certificate Status Protocol (OCSP) responses by appending ("stapling") a time-stamped OCSP response signed by the CA to the initial TLS handshake, eliminating the need for clients to contact the CA, with the aim of improving both security and performance. Motivation The original OCSP implementation has a number of issues. Firstly, it can introduce a significant cost for the certificate authorities (CA) because it requires them to provide responses to every client of a given certificate in real time. For example, when a certificate is issued to a high traffic website, the servers of CAs are likely to be hit by enormous volumes of OCSP requests querying the validity of the certificate. Also, OCSP checking potentially impairs users' privacy and slows down browsing, since it requires the client to contact a third party (the CA) to confirm the validity of each certificate that it encounters. Moreover, if the client fails to connect to the CA for an OCSP response, then it is forced to decide between: (a) continuing the connection anyway; defeating the purpose of OCSP or (b) terminating the connection based on the assumption that there is an attack; but which could result in excessive false warnings and blocks. OCSP stapling is aimed at addressing these issues with the original OCSP implementation. Solution OCSP stapling resolves both problems in a fashion reminiscent of the Kerberos ticket. In a stapling scenario, the certificate holder itself queries the OCSP server at regular intervals, obtaining a signed time-stamped OCSP response. When the site's visitors attempt to connect to the site, this response is included ("stapled") with the TLS/SSL handshake via the Certificate Status Request extension response (note: the TLS client must explicitly include a Certificate Status Request extension in its ClientHello TLS/SSL handshake message). While it may appear that allowing the site operator to control verification responses would allow a fraudulent site to issue false verification for a revoked certificate, the stapled responses can't be forged as they need to be directly signed by the certificate authority, not the server. If the client does not receive a stapled response, it will just contact the OCSP server by itself. However,