Reliable storage medium access control method and device

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 cryptographic data and the helper data. The delta-contracting function allows the choice of an appropriate value of the helper data, such that any value of the cryptographic data which sufficiently resembles the original primary input value leads to the same output value. Substantially different values of the cryptographic data lead to different values of the output.