OCSP Protocol Reference
Reference for Online Certificate Status Protocol (OCSP) for real-time certificate revocation checking.
Protocol Operation
OCSP (RFC 6960) allows clients to query a responder for certificate revocation status in real time. The request contains the certificate serial number and issuer hash. The response indicates good, revoked, or unknown. Revoked responses include revocation time and reason. Responses are signed by the CA or a delegated responder. The protocol reduces latency compared to downloading large CRLs. OCSP over HTTP is the most common transport.
- request
- Serial + issuer hash
- response
- good/revoked/unknown
- revoked
- Time + reason
query statussigned by CAkeyCompromise etc.Privacy and Performance
OCSP leaks which sites a user visits to the CA responder. OCSP stapling (Certificate Status Request TLS extension) embeds the OCSP response in the TLS handshake, improving privacy and performance. Must-staple extension requires clients to reject certificates without a stapled response. OCSP responders must be highly available; failures cause soft-fail (accept) or hard-fail (reject). CRLite aggregates revocation in Firefox for efficient local checking. OCSP nonce prevents replay but complicates caching.
- privacy
- Leaks site visits
- stapling
- TLS extension
- must-staple
- Require stapled
to CA responderembedded responsehard fail if missing