Dell Configuration Guide for the S4048–ON System 9.14.2.4

Online Certificate Status Protocol (OSCP)

Use the Online Certificate Status Protocol (OSCP) to obtain the revocation status of a X.509v3 certificate.

A device or a Certificate Authority (CAs) can check the status of a X.509v3 certificate by sending an OCSP request to an OCSP server or responder. An OCSP responder, a server typically run by the certificate issuer, returns a signed response signifying that the certificate specified in the request is 'good', 'revoked', or 'unknown'. The OCSP response indicates whether the presented certificate is valid.

OCSP provides a way for Certificate Authorities to revoke signed certificates before the expiration date. In a CA certificate, OCSP Responder information is specified in the authorityInfoAccess extension.

A CA can verify the revocation status of a certificate with multiple OCSP responders. When multiple OCSP responders exist, you can configure the order or preference the CA takes while contacting various OCSP responders for verification.

Upon receiving a presented certificate, the system sends an OCSP request to an OCSP responder through HTTP. The system then verifies the OCSP response using either a trusted public key or the OCSP responder’s own self-signed certificate. This self-signed certificate installs on the device's trusted location even before an OCSP request is made. The system accepts or rejects the presented certificate based on the OCSP response.

In a scenario where all OCSP responders are unreachable, the switch accepts the certificate. This action is the default behavior. You can also configure an alternate system behavior when all OCSP responders are unreachable. However, the switch may become vulnerable to denial-of-service attack if you configure the system to deny the certificate when OCSP responders are not reachable. For more information, see Configuring Revocation Behavior.

The system creates logs for the following events:

• Failures to reach OCSP responders
• Invalid OCSP responses—for example, cannot verify the signed response with an installed CA certificate.
• Rejection of a certificate due to OCSP