A method and apparatus is described for preparing and assessing machine readable payment documents such as bank or postal checks to avoid fraud. The checks are prepared by enciphering the serial number and the amount for which the check is made out with secret code data to provide a crypto number which...http://www.google.com.tw/patents/US3990558?utm_source=gb-gplus-share專利 US3990558 - Method and apparatus for preparing and assessing payment documents
