it unique to the card and stored on a centralized database. If checked, it will quickly become clear that the ID is false; either the number on the ID is not registered for the holder, or no ID has the number at all. Online verification also has the advantage that it allows easy revocation of lost or stolen documents. Using verifiable credentials is another effective method to detect ID forgery. The ID can include a verifiable credential, with a proof (such as a cryptographic signature by the legitimate issuer), that represents the information on the ID. The proof on the verifiable credential allows authentication of the ID. If the verifiable credential of a fake ID is checked, it will be evident that the ID is fake, because either the information on the ID and the verifiable credential do not match, the verifiable credential was not signed by the legitimate issuer, or the verifiable credential was issued by the legitimate issuer, but the information on it was modified without the legitimate issuer signing the modified verifiable credential. Many modern credentials now contain some kind of barcode. For example, many U.S. driving licences include a 2-dimensional code in PDF417 format, which contains the same information as on the front of the license. Barcodes allow rapid checking of credentials for low-security applications, and may potentially contain extra information which can be used to verify other information on the card. Systemic attacks The combination of multiple high-security features, biometrics, and well-trained document inspectors with technical assistance can be very effective at preventing forged documents from being easily produced. Instead of acquiring the expensive specialized equipment needed to make fake documents, it may be more economical to produce a "genuine fake"⁠ ⁠—⁠ ⁠a legitimate document, but one which contains false information. One way of doing this is to present the document issuing authority with false credentials, which they will then endorse by issuing a new document. In this way, false identities and credentials can be "bootstrapped" over a period of time. Another simpler way of generating false credentials is to suborn one of the officials involved in the document-issuing process through bribery or intimidation. This may also be combined with the bootstrapping process mentioned above to mount complex attacks. Corruption in the document-issuing process is hard to counter, since as the value of a credential increases, the economic incentives for corruption also increase. This is