Authentication is a "Security measure designed to establish the validity of a transmission, message, originator, or a means of verifying an individual\'s authorization to receive specific categories of information." Passwords and smart cards are used by government employees to authenticate their messages. Biometric methods of authentication, such as thumbprints and retinal scans are becoming more popular. Unfortunately, many of these authentication methods can be tricked or circumvented. Combinations of authentication methods provide the best promise of security.