The Common Access Card, also commonly referred to as the CAC or CAC card, is a smart card about the size of a credit card. It is the standard identification for Active Duty United States Defense personnel, to include the Selected Reserve and National Guard, United States Department of Defense (DoD) civilian employees, United States Coast Guard (USCG) civilian employees and eligible DoD and USCG contractor personnel.
It is also the principal card used to enable physical access to buildings and controlled spaces, and it provides access to defense computer networks and systems. It also serves as an identification card under the Geneva Conventions (esp. the Third Geneva Convention).
In combination with a personal identification number, a CAC satisfies the requirement for two-factor authentication: something the user knows combined with something the user has. The CAC also satisfies the requirements for digital signature and data encryption technologies: authentication, integrity and non-repudiation.
The CAC is a controlled item. As of 2008, DoD has issued over 17 million smart cards. This number includes reissues to accommodate changes in name, rank, or status and to replace lost or stolen cards. As of the same date, approximately 3.5 million unterminated or active CACs are in circulation.
DoD has deployed an issuance infrastructure at over 1,000 sites in more than 25 countries around the world and is rolling out more than one million card readers and associated middleware.