In each digital content utilize session, a memory card generates conversion key information for specifying a data conversion, while a player generates inverse conversion key information for specifying an inverse data conversion. The memory card then performs the data conversion specified by the conversion...http://www.google.com/patents/US6868404?utm_source=gb-gplus-sharePatent US6868404 - DIGITAL DATA RECORDING DEVICE, DIGITAL DATA MEMORY DEVICE, AND DIGITAL DATA UTILIZING DEVICE FOR CONVERTING MANAGEMENT INFORMATION WHICH CONTAINS RESTRICTIVE INFORMATION USING A DIFFERENT KEY IN EACH MANAGEMENT INFORMATION SEND/RECEIVE SESSION
