A Credential can be defined as any document, object, or data structure that vouches for the identity of a person through some method of trust and authentication. Simply put, a credential is the thing that a person presents—in person or remotely—to say “this is who I am.” The types of credentials issued in an ID system vary along multiple dimensions, including whether or not they are physical (i.e., they must be physically carried by a person in order to use them), and whether or not they are digital (i.e., they are machine readable and therefore can be used in a digital environment). In addition to credentials themselves, the authentication process may involve presenting the credential along with additional factors (i.e., “authenticators”) that bind the person to the credential, offering assurance that the person in possession of the credential is its rightful owner. Common types of credentials and authenticators are physical documents, card (such as a smart card), USB security token, biometrics, digital certificate or mobile phone.