A method and apparatus for determining the distance between transitions from a first logical state to a second logical state stored on a medium (i.e., a document). This determination is used to precisely characterize the information pattern in order to authenticate the information and the medium on which...http://www.google.de/patents/US20080028460?utm_source=gb-gplus-sharePatent US20080028460 - METHOD AND APPARATUS FOR SECURING AND AUTHENTICATING ENCODED DATA AND DOCUMENTS CONTAINING SUCH DATA
