A method for authenticating a printed document is described. A document producer
sends information to be included in a document to an authentication authority.
The authentication authority cryptographically generates an authentication code
from this information, and sends the authentication code back to the document producer.
The document producer then prints the document, including both the information
and the authentication code, and a bar code representing the authentication code.
A document checker scans in the bar code, and cryptographically checks the authentication
code against the information in the document.
