What are OCSP and OCSP Stapling?

Short answer

OCSP (Online Certificate Status Protocol) is the protocol with which the OCSP responder of the CA that issued a certificate is asked whether the certificate has been revoked before its expiry (RFC 6960). Because the client asking the CA in every connection creates latency and privacy problems, in OCSP Stapling the server performs this query periodically and adds the current response signed by the CA to the TLS handshake; the client does not ask the CA separately. In TR7, when OCSP Stapling in the TLS Security Profile is turned on, the vService is configured to obtain the OCSP response for its certificate from the CA's OCSP service and add it to the handshake; if the response cannot be obtained, the certificate continues to be presented without a response.

Where It Is Used in TR7

Where	Field / label	What for
Certificates & PKI → TLS Security Profiles → Frontend-only Settings	OCSP Stapling (off by default)	Adding the OCSP response to the TLS handshake made with the client; the profile is selected in the SSL Security field of the HTTP or L7 TCP vService

For the OCSP response to be obtained, the certificate must carry an OCSP address in its AIA extension and TR7 must be able to reach this address; the requirements and the verification are on the Is OCSP Stapling supported? page.

How Does It Work?

1. The server asks the OCSP address in its certificate for the status of the certificate.
2. The CA's responder returns a signed response that contains the status (good, revoked, unknown) and the validity period.
3. The server stores this response and, in the handshake, sends it together with the certificate in reply to the status_request request coming from the client (RFC 6066).
4. The client verifies the CA signature of the response; the response is renewed by the server before its validity period expires.

Common Misconceptions

• "OCSP Stapling replaces a revoked certificate." It only presents the proof of the certificate's status; a revoked certificate must be replaced with a new one.
• "If the OCSP responder cannot be reached, connections are dropped." When the response cannot be obtained, the certificate is presented without a response; connections continue to be established.
• "OCSP Stapling also validates client certificates." The setting presents a response for the vService's own certificate; validating client certificates with OCSP in mTLS is not within the scope of this setting.

How it is done in the documentation

• TLS Security Profiles · OCSP Stapling
• TLS Security Profiles · Where the Settings Are Applied

Related questions

• Is OCSP Stapling supported?
• What is certificate revocation?
• What is AIA (Authority Information Access)?