If a certificate is listed on the CA's certificate revocation list (CRL), which of the following is NOT a possible reason?

When a certificate is listed on the Certificate Authority's (CA) Certificate Revocation List (CRL), it means that the certificate is no longer considered valid for some reason. There are several situations that can lead to revocation, including when a certificate has been compromised, issued to a fraudulent entity, or is no longer needed by the certificate holder.

However, a certificate that has expired is not included in the CRL because expiration is a separate state from revocation. An expired certificate simply means that the validity period has lapsed, and this does not imply any security concern or the need for revocation. Instead, an expired certificate should be replaced with a new valid certificate, but it does not necessitate listing it on a CRL since it no longer has operational status due to the time limit being reached, rather than a policy violation or security issue. Thus, the expiration of a certificate is not a valid reason for it to appear on the CRL.