A person or organization that issues certificates. By such an act it asserts the validity of the certificate, and so the integrity and reliability of certificate authorities is crucial to the operation of public key infrastructure systems. They will therefore be expected to do appropriate checks before issuing certificates. Conceptually a certificate authority is a ‘trusted third party’. This might literally be true: in a small company that issues certificates for internal use, the certificate authority might be somebody who knows all the staff personally. At the other end of the scale specialist certificate authorities, especially those at the top of public key infrastructure hierarchies, build their trustworthiness by a track record of reliability based on care and extensive checking.