The certificate may not have been distributed to specific directories because the issuing authority requires confirmation from the user that the certificate/smart card has been received, before publishing. Certificates that have not been published can be located using the CC and then distributed to the relevant directories. All certificates have a validity period. A certificate may, for various reasons, be revoked before the validity period expires. It is also possible to inhibit a certificate temporarily. The certificate is then put on hold. A certificate on hold may be reinstated. Certificates that are on hold or that have been revoked are published in certificate revocation lists (CRLs).