US Patent 7822989 Controlling access to an area

Controlling access includes providing a barrier to access that includes a controller that selectively allows access, at least one administration entity generating credentials/proofs, wherein no valid proofs are determinable given only the credentials and values for expired proofs, the controller receiving the credentials/proofs, the controller determining if access is presently authorized, and, if access is presently authorized, the controller allowing access. The credentials/proofs may be in one part or may be in separate parts. There may be a first administration entity that generates the credentials and other administration entities that generate proofs. The first administration entity may also generate proofs or the first administration entity may not generate proofs. The credentials may correspond to a digital certificate that includes a final value that is a result of applying a one way function to a first one of the proofs.