Image Number 4 for United States Patent #6031815.
A system for controlled reproduction of information according to the invention comprises an information carrier and a reading device. The information carrier contains information in blocks written in a track. The information carrier has reference patterns which divide the track into sectors for writing the information blocks, and auxiliary information written in the reference patterns. The auxiliary information is related to the information, for example, a decoding key, access code or digital signature. The reading device comprises a demodulation means for recovering both the information and the auxiliary information. The device may include means for processing the information and/or auxiliary information in dependence on the auxiliary information. Since the auxiliary information cannot be transferred to an illegal copy, this copy is unusable.