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Home / Glossary / OCSP
Glossary · Protocol

OCSP

Online Certificate Status Protocol

In plain language

A quick check a browser can make to find out whether a website's security certificate is still valid.

The metaphor

Like phoning the bank to check a cheque has not been cancelled.

Going deeper

How it works

  • The browser asks the company that issued the certificate.
  • It gets back an answer: good, revoked or unknown.
  • It lets a stolen or mistaken certificate be cancelled.
  • Some systems attach the answer to the site's connection to speed things up.

What can go wrong (example scenario)

A company's old website certificate was copied by someone who left. The issuer cancelled it, and browsers learned that through this check.

In practice
  • A browser checks a banking site's certificate.
  • A web server includes a recent answer with its response.
  • A certificate for a retired site is cancelled.

A question owners ask

Do I need to set it up?

No. Your web host handles it, and it works in the background.

Related terms
AHAuthentication HeaderARPAddress Resolution ProtocolBGPBorder Gateway ProtocolCCMPCounter Mode/CBC-MAC ProtocolCHAPChallenge Handshake Authentication ProtocolCRCCyclical Redundancy CheckEAPExtensible Authentication ProtocolESPEncapsulated Security Payload

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