Certificate Revocation: CRL vs OCSP — Which Is Better?

If a private key is compromised, the corresponding certificate needs to be revoked before it expires. Two mechanisms exist for communicating revocation to browsers: Certificate Revocation Lists (CRL) and Online Certificate Status Protocol (OCSP).

Certificate Revocation Lists (CRL)

A CRL is a signed list of serial numbers that a CA has revoked. CRLs are published periodically (daily or more frequently) at a URL embedded in the certificate's CRL Distribution Points extension.

Problem: For large CAs issuing millions of certificates, CRLs become enormous files. Downloading a multi-megabyte CRL file on every TLS connection is impractical. Browsers began ignoring CRLs for this reason.

Online Certificate Status Protocol (OCSP)

OCSP solves the size problem by allowing browsers to query a CA's responder for the status of a specific certificate. Instead of downloading the full list, the browser sends one serial number and gets one response. However, this creates a privacy problem — see our OCSP guide.

OCSP Stapling

OCSP stapling is the modern solution. The web server pre-fetches a signed OCSP response and delivers it during the TLS handshake — no external request from the browser, no privacy leak. See our OCSP stapling guide for implementation details.

The Uncomfortable Truth: Soft-Fail

In practice, most browsers use "soft-fail" for OCSP — if the OCSP server is unreachable, the browser proceeds anyway. This means revocation is not a strong real-time control for most connections. The security community continues to debate whether revocation is effective at all, leading to interest in shorter certificate lifetimes as a practical alternative.

Checking Revocation URLs

The SSL Certificate Decoder shows both the CRL Distribution Points URL and the OCSP responder URL from a certificate's extensions. This tells you where browsers would check for revocation status.