What is a Certificate Revocation List (CRL) used for?

A Certificate Revocation List (CRL) serves as a crucial mechanism in public key infrastructure (PKI) for maintaining secure communications. It is primarily used to verify the validity of digital certificates that have been issued by a Certificate Authority (CA). The CRL contains a list of certificates that have been revoked before their expiration date, indicating that they should no longer be trusted for establishing secure connections.

When a system or service checks the validity of a certificate, it can refer to the CRL to determine whether the certificate in question is still valid or has been revoked. This process is essential to ensure that compromised certificates do not continue to provide access or authentication, thereby enhancing overall security.

Understanding the role of a CRL within the context of certificate management helps reinforce why the correct answer is focused on the verification of the validity of issued certificates, reflecting its role in ensuring ongoing trust in digital communications.