U.S. PATENT DOCUMENTS
5,526,338 A 5,841,861 A 5,917,798 A
6/1996 Hasmanetal. 11/1998 Kondoetal. .. 6/1999 Horimaietal.
FOREIGN PATENT DOCUMENTS
0 751 517 A2 6/1996
Primary Examiner—Nasser Moazzami
Assistant Examiner—Fikremariam Yalew
(7'4) Attorney, Agent, or Firm—Norris McLaughlin & Marcus
There is disclosed a method and apparatus for coding data, for the purpose of preventing unauthorised readout of information. In the method, user information is converted into digital data (UD), and the digital data is recorded in a first data set (CD) and a second data set (HD), where the first data set (CD) is recorded in a first optical storage medium of a data carrier, and the second data set (HD), is recorded in a second, holographic storage medium of the data carrier. According to the method, the digital data (UD) is divided between the first and second data sets (CD,HD) in a manner so that a part of the user information is contained only in the first data set (CD), and another part of the user information is contained only in the second data set (HD), and the relative proportion of the user information in the data sets is selected so that the information contained in any one of the data sets is insufficient by itself to restore the complete user information (UD) contained in both data sets.
29 Claims, 9 Drawing Sheets