X509CRL

X509CRL, or X.509 Certificate Revocation List, is a standard format for a list of digital certificates that have been revoked by the issuing Certificate Authority (CA) before their scheduled expiration date. The primary purpose of a CRL is to provide a mechanism for distributing information about certificates that should no longer be trusted, due to reasons such as private key compromise, certificate mis-issuance, or changes in the certificate's status.

A CRL is a signed data structure that contains a list of revoked certificates, each identified by its serial number. It also includes the revocation date and, optionally, the reason for revocation. The CRL is issued and signed by the CA, ensuring its authenticity and integrity.

CRLs are typically distributed via HTTP or LDAP, and clients can periodically check the CRL to ensure that the certificates they are using have not been revoked. This process is known as CRL checking or CRL validation.

While CRLs are widely used, they have some limitations, such as the potential for large CRLs, which can be inefficient to distribute and process, and the lack of real-time revocation information. To address these issues, alternative revocation mechanisms like Online Certificate Status Protocol (OCSP) have been developed. However, CRLs remain an essential component of the X.509 public key infrastructure (PKI) and are widely supported by various systems and applications.