Also known as a “certificate authority,” a certification authority (CA) is an internal or third-party entity that creates, signs and revokes digital certificates that bind public keys to user identities. A repository or directory stores digital certificates and certificate revocation lists (CRLs) to allow users to obtain the public keys of other users and determine revocation status. Typically, the repository is a traditional X.500 directory or a database that supports Lightweight Directory Access Protocol (LDAP).