Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1999-01-04
2001-05-01
Baker, Stephen M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C369S047360, C369S053130, C714S811000
Reexamination Certificate
active
06226770
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of providing an optical data carrier with identity information, said data carrier when manufactured being provided with digital information, which is written and stored according to at least one previously defined encoding method for error correction and which may be read and decoded at a later stage by means of an optical reader with correction of errors in accordance with said encoding method.
DESCRIPTION OF THE PRIOR ART
Compact discs (CD) are a common type of optical data carriers according to the above. Compact discs are provided in various forms, such as CD-Audio (containing for instance music), CD-ROM (secondary computer read-only memory), CD-I (interactive CD), and Photo-CD (containing digital photographs). In the context of this document the term compact disc will be used in a broader sense relating to any kind of optical compact discs—also such types not explicitly specified in this document. In particular, it should be understood that the discussion in this document is applicable also to the high density compact disc standard called DVD (Digital Video Disc), which was recently introduced by Toshiba, Japan.
Compact disc applications are today taken for granted in our daily lives. We listen to music on compact discs at home as well as in our cars. When working with computers we often use information stored on CD-ROM. An increasing number of commercial software products are nowadays available on CD-ROM, such as utility programs (e.g. word processors and spread-sheat programs) or entertainment programs (e.g. computer games). Some of us choose to store our vacation pictures on Photo-CD rather than keeping our pictures as paper-printed photographs or slide photographs.
As a consequence of the use of compact discs having become increasingly popular, it has become desirable to provide compact discs with identity marking. It may for instance be convenient to provide a compact disc with information regarding, e.g., manufacturer, author, article number, etc. Another example is preventing the production of illegal copies, considering that is has become increasingly attractive to less scrupulous individuals to copy and plagiarize commercially available compact discs products, CD-Audio and CD-ROM in particular. In certain parts of the world a complete industry has been developed to mass-produce illegal copies of copyright-protected compact disc products and to sell these illegal copies to prospective buyers. Since the legitimate author or owner of the property will get no compensation for his work and his costs, there is a risk of a cultural as well as a technical impoverishment, should the illegal copying and plagiarizing be permitted to continue its explosive growth.
EP-A-0 637 023 discloses a method of protecting an optical data carrier, such as an optical disc, from illegal copying by providing it with a plurality of irregular storage pits, which are automatically corrected during normal copying and which, as a consequence, will not be copied onto the disc copy. The irregular pits have a physical shape deviating from a perfect or normal shape. Furthermore, the irregular pits are arranged in an irregular sequence, which generates a tracking error signal indicative of the presence of the irregular pits. In addition, the irregular pits may be detected by the deviations in symmetry for the analog HF-signal waveform. By scanning the disc for such irregular pits, it is possible to determine whether the disc is a legal and original disc (containing said irregular pits), or an illegal copy (lacking said irregular pits).
U.S. Pat. No. 5,513,260 relates to a similar method and apparatus for protecting various recording media. An authenticating signature is recorded on the media by radially position modulating the writing head or varying the specific data blocks.
A drawback of a copy-protection principle according to EP-A-0 637 023 is that additional hardware or equipment is required for creating the physical irregularities in the storage layer of the disc. Furthermore, since these irregularities are of a physical nature (i.e., the physical shape or arrangement of the irregular pits is different from that of a normal pit), an infringer or plagiarist may be capable of locating those positions on the disc, in which the copy-protecting information (the irregular pits) are located, whereupon the irregularities thus located may be transferred to, or recreated on, the disc copy.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved identity marking for an optical data carrier in such a way, that only authorized users are able to read identity information stored on the data carrier, while said identity information will be hidden from and unavailable to all other users. One embodiment of the invention aims at rendering it possible to determine the authenticity of an optical data carrier, such as a compact disc, in order to be able to decide, whether a certain disc has been produced by the rightful manufacturer, or by an unauthorized person or manufacturer.
Such an improved identity marking principle, which does not suffer from the disadvantages described above, may be obtained by providing the data carrier with intentionally arranged errors on a logical level (bit or symbol errors, e.g. errors among the digital ones and zeroes stored on the disc), rather than a physical level.
Thus, the object is achieved by a method with features according to the characterizing part of the appended independent patent claims. Preferred alternatives to the method according to the invention are specified in the dependent claims.
REFERENCES:
patent: 5371750 (1994-12-01), Inoue et al.
patent: 5513260 (1996-04-01), Ryan
patent: 5608717 (1997-03-01), Ito et al.
patent: 5828754 (1998-10-01), Hogan
patent: 5996111 (1999-11-01), Yoshida et al.
patent: 0545472A1 (1993-06-01), None
patent: 0637023A1 (1995-02-01), None
patent: 0703576A1 (1996-03-01), None
Baker Stephen M.
Gray Cary Ware & Freidenrich LLP
Ifunga Test Equipment B.V.
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