Certificate Revocation List Status

What is CRL Status?

Certificate Revocation List (CRL) Status indicates whether an SSL/TLS certificate has been checked against the Certificate Authority’s revocation list and shows the current revocation status of the certificate. CRLs are digitally signed lists published by Certificate Authorities that contain the serial numbers of certificates that have been revoked before their natural expiration date.

CRL Checking Process

The CRL validation process involves several steps to ensure certificate validity:

• CRL Download: Client retrieves the latest CRL from the CA’s distribution point
• Signature Verification: Confirms the CRL is signed by the issuing CA
• Serial Number Check: Searches for the certificate’s serial number in the list
• Freshness Validation: Ensures the CRL is within its validity period
• Result Caching: Stores results to improve performance

Limitations and Modern Alternatives

While CRLs provide important security functionality, they have limitations including size constraints, update delays, and bandwidth requirements for large lists. Modern implementations often prefer OCSP (Online Certificate Status Protocol) for real-time revocation checking. However, CRLs remain important for offline validation scenarios and as a backup mechanism when OCSP is unavailable. The CRL status should show whether the certificate appears in any revocation lists and may include timing information about when the status was last verified. Understanding CRL status helps administrators ensure their certificates maintain their intended security posture throughout their lifecycle.