A method of and device for granting access to content on a storage medium, including obtaining cryptographic data from a property, such as a wobble, of the storage medium, reading helper data from the storage medium, and granting the access based on an application of a delta-contracting function to the...http://www.google.com.hk/patents/US8065533?utm_source=gb-gplus-share專利 US8065533 - Reliable storage medium access control method and device
