Title:

Mark forming apparatus, method of forming laser mark on optical disk, reproducing apparatus, optical disk and method of producing optical disk

Document Type and Number:

United States Patent RE39653

Abstract:

An object of the present invention is to provide a marking forming apparatus, a method of forming a laser marking on an optical disk, a reproduction apparatus, an optical disk, and a method of manufacturing an optical disk, capable of providing a greatly improved copy prevention capability as compared to prior known construction. To achieve this object, in the optical disk of the invention, for example, a marking is formed by a laser on a reflective film of a disk holding data written thereon and at least position information of the marking or information concerning the position information is written on the disk in an encrypted form or with a digital signature appended thereto.

Inventors:

Oshima, Mitsuaki (Kyoto, JP)
Gotoh, Yoshiho (Osaka, JP)

Plaque It!

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a marking forming apparatus, a method of forming a laser marking to an optical disk, a reproduction apparatus, an optical disk, and a method of manufacturing an optical disk, which may be utilized, for example, to prevent duplication of optical disks.

2. Description of the Prior Art

With increasing use of ROM-type optical disks in recent years, pirated disks have also been spreading, infringing the rights of copyright owners.

This is because ROM disk manufacturing apparatus have been made readily available and also have become easy to operate.

A pirate can make a CD master disk just be extracting logic data from software contained on a CD, copying it onto a magnetic tape, and setting the tape on a mastering apparatus. Hundreds of thousands of pirated disks can be pressed from this single master disk. Since pirates do not, pay royalties, they make a profit by selling pirated disks at a low price. This necessarily means a financial loss to the copyright owner.

According to the current CD specification, only the function of reading logic data from a CD is provided, but no functions are provided to detect physical features of a disk. As a result, a pirated CD can be easily produced by bit-copying the logic data.

The prior art discloses a method of preventing piracy by adding a function to recognize disk physical features.

This method involves establishing a new specification that defines the inclusion of a physical mark on a master disk to prevent the pirating of disks made to this specification. As an example of the prior art, a piracy prevention method is known such as the one disclosed in Japanese Patent Unexamined Publication No. 5-325193. According to that method, in the cutting process the recording beam is deliberately swept in the tracking direction, when recording a designated region, to form a wobbling on the master disk. When the disk is played back on a reproducible apparatus equipped with a wobbling detection circuit, the disk is checked to see whether the wobbling is formed in the designated region. If it is detected that the wobbling of a designated wobbling frequency is formed in the designated region, the disk is judged to be a legitimate disk; otherwise, the disk is judged to be a pirated disk.

More specifically, based on predefined physical mark design data, a physical mark is formed on the masker disk by using a special mastering apparatus equipped with a wobbling function. This prevents pirates from making pirated disks since they do not have such special mastering apparatus nor physical mark design data. Such an anti-piracy mark needs to be formed on every disk made to this specification. However, since it is possible to extract this physical mark by examining a legitimate disk, the prior art method has had the problem that pirated disks may be made if such a special mastering apparatus falls into the hands of an illegal person. In this patent specification, piracy prevention methods of the type that forms a physical mark on the master disk will be referred to as master disk level methods.

Besides the above-described method, there has been proposed a more sophisticated master disk level method which involves forming a more complicated physical mark. On the other hand, a replica method is known that makes a replica having exactly the same physical features by melting the resin of a legitimate disk no matter how complicated the physical mark is made at the master disk level. This method requires much time and cost to produce one master disk, but since hundreds of thousands of disks can be produced from one pirated master disk, the cost per pirated disk is low. This has therefore given rise to the problem that as the replica method becomes widespread in the future, it may defeat the effectiveness of piracy prevention techniques at the master disk level.

As described above, the prior art piracy prevention techniques have several problems to be overcome.

These problems are summarized below.

Problems 1: The effectiveness of the master disk level piracy prevention techniques of the prior art is low since it is possible to replicate the physical mark.

Problem 2: In the prior art method that forms a physical mark based on physical mark design data, if a manufacturing apparatus of the same precision as the apparatus used by the legitimate disk manufacturer is obtained, illegal disks can be easily manufactured.

Problem 3: Since the security level provided by the prior art piracy prevention methods is fixed, its effectiveness decreases against constantly improving pirating techniques.

Problem 4: If a disk format without copy protection were allowed to exist along with a disk format with copy protection, pirated disks could be made with the disk format without copy protection. It has therefore been necessary to produce all disks with copy protection. The use of copy protection is therefore limited to closed specifications such as game disks.

Problem 5: According to the prior art methods, a limited number of licensing companies possess the special manufacturing apparatus and do not make the apparatus public. Therefore, software makers cannot make disks except at the licensing companies.

Problem 6: In the master-disk marking method, all disks pressed from the same master disk have the same disk ID. This means that all disks can be run by using the same password. As a result, password security cannot be maintained unless a floppy disk or a communication line is used in combination. Furthermore, the password has to be entered each time the disk is used since secondary recording is not possible.

SUMMARY OF THE INVENTION

In view of the above-outlined problems of the prior art, it is an object of the present invention to achieve a greatly improved copy prevention capability as compared to the prior art.

More specifically, the present invention provides the following means to overcome the above-outlined six problems of the prior art piracy prevention methods.

To overcome Problem 1, a piracy prevention method involving the use of a physical mark at a reflective film level, rather than the master disk level physical mark as used in the prior art, is provided wherein the physical mark is formed on a reflective film of a disk. This prevents the production of pirated disks if duplication is made at the master disk level.

To overcome Problem 2, a new ROM-recording means is used that performs secondary recording to a two-disk laminated ROM disk by using a laser. In a first step, physical marks are randomly formed, and in a second step, the physical marks are measured with a measuring accuracy as high as 0.13 μm. In a third step, their position information is encrypted and, using the secondary recording means, a barcode is recorded to the ROM disk with an accuracy of several tens of microns which is the usual processing accuracy. Optical mark position information can thus be obtained with an accuracy of, for example. 0.1 μm much higher than the processing accuracy of a conventional apparatus. Since optical marks cannot be formed with the accuracy of 0.1 μm by using commercially available equipment, production of pirated disks can be prevented.

To overcome Problem 3, both a first-generation cipher with a low degree of security and a second-generation cipher with a high degree of security, each enciphering the position information with a digital signature, are prerecorded on a medium and by using such a medium, piracy is prevented with the security corresponding to the applicable generation if the design of reproduction apparatus changes from one generation to the next.

To overcome Problem 4, an anti-piracy function identifier for indicating whether or not the software product is equipped with a copyright anti-piracy function is recorded on the master disk. To prevent the identifier from being altered, compressed information of software contents: and the anti-piracy function identifier are scrambled and encrypted together when recording the software contents on the master disk. Since the identifier cannot be altered, pirates cannot produce disks with a disk format without anti-piracy measures. This prevents the production of pirated disks.

To overcome Problem 5, as a secret key for digital signature encryption indispensable for the manufacture of disks, a subkey is generated from a master key, and the subkey is delivered to each software maker, thereby allowing the software maker to manufacture legitimate disks at its own factory.

To overcome Problem 6, position information of an antipiracy mark of the invention, which differs from one disk to another, is used as a disk identifier. The position information and the disk serial number, i.e., the disk ID, are combined and encrypted together with a digital signature, thus appending an unalterable disk ID to each disk. Since each completed disk has a different ID, the password is also different. The password does not work on other disks. This enhances password security.

Also, with the secondary recording of the invention, the password is secondary-recorded on the disk, permanently making the disk an operable disk.

Specific methods for overcoming the above six problems are disclosed below by way of embodiments.

The invention provides a marking forming apparatus comprising: marking forming means for applying at least one marking to at least one reflective film formed to a disk; marking position detecting means for detecting at least one position of said marking; and position information output means for outputting said detected position as position information of said marking.

The invention also provides a marking forming apparatus further comprising position information writing means for writing at least said output position information or information concerning said position information to said disk or to a different medium.

The invention also provides a method of forming a laser marking to an optical disk, comprising the steps of: forming at least one disk; forming a reflective film to said formed disk; laminating two disks together, said disks including at least one disk with said reflective film formed thereon; and forming at least one marking by a laser on said reflective layer of the laminated disks.

The invention also provides a reproduction apparatus comprising: position information reading means for reading position information of at least one marking or information concerning said position information, said marking being formed to at least one reflective film formed to a disk and being detected for a position thereof, at least the position thus detected being output as said position information of said marking; marking reading means for reading information concerning at least one actual position of said marking; comparing/judging means for performing comparison and judgement by using a result of reading by said position information reading means and a result of reading by said marking reading means; and reproducing means for reproducing recorded data on said optical disk in accordance with a result of the comparison and judgement performed by said comparing/judging means.

The invention also provides a method of manufacturing an optical disk, comprising the steps of: forming at least one disk; forming a reflective film to said formed disk; applying at least one marking to said reflective film; detecting at least one position of said marking; and outputting said detected position as position information of said marking, and encrypting said information for writing to said disk.

The invention also provides a method of manufacturing an optical disk, comprising the steps of: forming at least one disk; forming a reflective film to said formed disk; applying at least one marking to said reflective film; detecting at least one position of said marking; and outputting said detected position as position information of said marking, and applying a digital signature in relation to said position information for writing to said disk.

The invention also provides an optical disk wherein at least one marking is formed by a laser to at least one reflective film of the disk holding data written thereon and at least position information of said marking or information concerning said position information is written to said disk in an encrypted form or with a digital signature applied thereto.

The invention also provides an optical disk having a structure such that at least one reflective film is sandwiched directly or indirectly between two members formed from material resistant to laser light, wherein at least one marking is formed by a laser to said reflective film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a disk manufacturing process and a secondary recording process according to the present embodiment; FIG. 2 (a) is a top plan view of a disk according to the embodiment, (b) is a top plan view of the disk according to the embodiment, (c) is a top plan view of the disk according to the embodiment, (d) is a transverse sectional view of the disk according to the embodiment, and (e) is a waveform diagram of a reproduced signal according to the embodiment;

FIG. 3 is a flowchart illustrating a process of recording encrypted position information on a disk in the form of a barcode according to the present embodiment;

FIG. 4 is a diagram showing a disk fabrication process and a secondary recording process (part 1) according to the present embodiment;

FIG. 5 is a diagram showing the disk fabrication process and the secondary recording process (part 2) according to the present embodiment;

FIG. 6 is a diagram showing a two-layer disk fabrication process (part 1) according to the present embodiment;

FIG. 7 is a diagram showing the two-layer disk fabrication process (part 2) according to the present embodiment; FIG. 8 (a) is an enlarged view of a nonreflective portion of a laminated type according to the present embodiment, and (b) is an enlarged view of a nonreflective portion of a single-plate type according to the present embodiment;

FIG. 9 (a) is a reproduced-waveform diagram for a non-reflective portion according to the present embodiment, (b) is a reproduced-waveform diagram for a nonreflective portion according to the present embodiment, and (c) is a reproduced-waveform diagram for a nonreflective portion according to the present embodiment;

FIG. 10 (a) is a cross-sectional view of a nonreflective portion of the laminated type according to the present embodiment, and (b) is a cross-sectional view of a nonreflective portion of the single-plate type according to the present embodiment;

FIG. 11 is a schematic diagram, based on an observation through a transmission electron microscope, illustrating a cross section of the nonreflective portion according to the present embodiment;

FIG. 12 (a) is a cross-sectional view of a disk according to the present embodiment, and (b) is a crosssectional view of the nonreflective portion of the disk according to the present embodiment.

FIG. 13 (a) is a diagram showing a physical arrangement of addresses on a legitimate CD according to the embodiment, and (b) is a physical arrangement of addresses on an illegally duplicated CD according to the embodiment;

FIG. 14 is a block diagram for disk manufacturing according to the embodiment;

FIG. 15 is a block diagram of a low-reflectivity position detector according to the embodiment;

FIG. 16 is a diagram illustrating the principle of detecting address/clock positions of a low-reflectivity portion according to the embodiment;

FIG. 17 is a diagram showing a comparison of low-reflectivity portion address tables for a legitimate disk and a duplicated disk;

FIG. 18 is a flowchart illustrating a disk check procedure using a one-direction function according to the embodiment;

FIG. 19 is a diagram showing a comparison of address coordinate positions on different master disks according to the embodiment;

FIG. 20 is a flowchart illustrating a low-reflectivity position detecting program according to the embodiment;

FIG. 21 is a block diagram of a magnetic recording apparatus according to the embodiment;

FIG. 22 is a flowchart illustrating a procedure for encryption, etc. using an RSA function according to the embodiment; FIG. 23 is a flowchart illustrating a procedure for digital signature, etc. using an elliptic function according to the embodiment;

FIG. 24 is a flowchart illustrating a position information check process according to the embodiment;

FIG. 25 is a block diagram of an information processing apparatus according to the embodiment;

FIG. 26 is a top plan view of a second low-reflectivity portion according to the embodiment;

FIG. 27 is a diagram showing a detected waveform of a first-layer marking signal according to the present embodiment;

FIG. 28 is a diagram showing a detected waveform of a second-layer marking signal according to the present embodiment;

FIG. 29 is a block diagram of a disk manufacturing apparatus according to the present embodiment;

FIG. 30 is a code diagram for a nonreflective portion according to the present embodiment;

FIG. 31 is a diagram showing a detected waveform from the nonreflective portion according to the present embodiment;

FIG. 32 is a diagram for explaining the contents of barcode recorded information and the relative relationship thereof according to the present embodiment;

FIG. 33 is a perspective view showing the nonreflective portion formed in the two-layer disk according to the present embodiment;

FIG. 34 is a diagram for explaining data flow in disk distribution according to the present embodiment;

FIG. 35 is a diagram showing a process of disk distribution according to the present embodiment;

FIG. 36 is a block diagram for explaining a manufacturing process when applying complex encryption to position information, etc. by using a master key, subkey, etc. according to the present embodiment;

FIG. 37 is a block diagram for explaining the manufacturing process when applying complex encryption to position information, etc. by using the master key, subkey, etc. according to the present embodiment;

FIG. 38 is a flowchart in a reproduction apparatus according to the present embodiment;

FIG. 39 is a diagram showing a secret key cipher and a public key cipher used in combination on optical disks and their relationship with reproduction apparatus according to the present embodiment;

FIG. 40 is a block diagram showing an outline of a process of recording position information, etc., encrypted with a master key, subkey, etc., on an optical disk and a process of reproducing such information according to the present embodiment;

FIG. 41 is a block diagram of an optical disk reproduction apparatus according to the present embodiment; and

FIG. 42 is a flowchart illustrating the function of a scramble identifier and the switching between drive ID and disk ID in a program installation process according to the present embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The constitution and operation of a marking forming apparatus, a method of forming a laser marking to an optical disk, a reproduction apparatus, an optical disk, and a method of manufacturing an optical disk will be described below in accordance with an embodiment of the present invention.

In the description of the present embodiment given herein, the first half part (1) deals with such operations as manufacturing a disk, forming a marking by using a laser, reading position information of the marking, performing encryption and other processing on the position information, etc. for writing on an optical disk, and reproducing the optical disk on a player. The encryption and reproduction operations are briefly described in the first part (1).

Next, in the second half part (2), the encryption and other processing of the marking position information, etc. and the decryption and reproduction of the position information, etc. on the optical disk, briefly described in the first part (1), will be described in further detail. The second part (2) also deals with various techniques for preventing piracy.

In this patent specification, laser trimming is also referred to as laser marking, while a nonreflective optical marking portion is simply referred to as the marking or optical marking or, sometimes, as the physical ID unique to the disk (1) FIG. 1 is a flowchart illustrating a general process flow from disk manufacturing to the completion of an optical disk.

First, the software company performs software authoring in software production process 820 . The completed software is delivered from the software company to the disk manufacturing factory. In disk manufacturing process 816 at the disk manufacturing factory, the completed software is input in step 818 a, a master disk is produced (step 818 b), disks are pressed (steps 818 e, 818 g), reflective films are formed on the respective disks (steps 818 f, 818 h), the two disks are laminated together (step 818 i), and a ROM disk such as a DVD or CD is completed (step 818 m, etc.).

The thus completed disk 800 is delivered to the software maker or to a factory under control of the software maker, where, in secondary recording process 817 , an anti-piracy marking 584 , such the one shown in FIG. 2, is formed (step 819 a), and accurate position information of this mark is read by a measuring means (step 819 b) to obtain the position information which serves as the physical feature information of the disk. This physical feature information of the disk is encrypted in step 819 c. The encrypted information is converted to a PWM-modulated signal which is then recorded in step 819 d as a barcode signal on the disk by using a laser. The disk physical feature information may be combined together with software feature information for encryption in step 819 c.

The above processes will be described in further detail. That is, a disk fabrication process, a marking formation process, a marking position reading process, and an encrypted information writing process for an optical disk according to the present invention will be described in detail with reference to FIGS. 4 and 5 and FIGS. 8 to 12 . A supplementary explanation will also be given dealing with a disk having two reflective layers with reference to FIGS. 6 and 7. In the following description, the marking formation process and the marking position reading process are collectively called the secondary recording process.

(A) First, the disk fabrication process will be described. In the disk fabrication process 806 shown in FIG. 4, first a transparent substrate 801 is pressed in step (1). In step (2), a metal such as aluminum or gold is sputtered to form a reflective layer 802 . An adhesive layer 804 formed from an ultraviolet curing resin is applied by spin coating to a substrate 803 formed in a different processing step, and the substrate 803 is bonded to the transparent substrate 801 having the reflective layer 802 , and they are rotated at high speed to make the bonding spacing uniform. By exposure to external ultraviolet radiation, the resin hardens, thus firmly bonding the two substrates together. In step (4), a printed layer 805 where a CD or DVD title is printed, is printed by screen printing or offset printing. Thus, in step (4), the ordinary laminated-type optical ROM disk is completed.

(B) Next, the marking formation process will be described with reference to FIGS. 4 and 5. In FIG. 4, a laser beam from a pulsed laser 813 such as a YAG laser is focused through a converging lens 814 onto the reflective layer 802 , to form a nonreflective portion 815 as shown in step (6) in FIG. 5 . That is, a distinct waveform, such as the waveform (A) shown in step (7), is reproduced from the nonreflective portion 815 formed in step (6) in FIG. 5 . By slicing this waveform, a marking detection signal such as shown by waveform (B) is obtained, from which hierarchial marking position information comprising an address, such as shown in signal (d), and an address, a frame synchronizing signal number, and a reproduced clock count, such as shown in signal (e), can be measured.

As previously stated, a supplementary explanation will be given below of an alternative type of disk (a two-layer laminated disk) with reference to FIGS. 6 and 7.

FIGS. 4 and 5 showed a disk generally known as a single-layer laminated disk which has a reflective layer only on one substrate 801 . On the other hand, FIGS. 6 and 7 show a disk generally known as a two-layer laminated disk which has reflective layers on both substrates 801 and 803 . For laser trimming, the processing steps (5) and (6) are fundamentally the same for both types of disks, except with significant differences which are briefly described below. First, while the single-layer disk uses a reflective layer formed from an aluminum film having reflectivity as high as 70% or over, in the two-layer disk the reflective layer 801 formed on the reading-side substrate 801 is a semitransparent gold (Au) film having a reflectivity of 30%, while the reflective layer 802 formed on the print-side substrate 803 is the same as that used in the single-layer disk. Second, as compared with the single-layer disk, the two-layer disk is required to have high optical accuracy; for example, the adhesive layer 804 must be optically transparent and be uniform in thickness, and the optical transparency must not be lost due to laser trimming. FIGS. 7 ( 7 ), 7 ( 8 ), and 7 ( 9 ) show the waveform from the first layer of the two-recording-layer disk. The waveform from the second layer is similar to that from the first layer, though the signal level is lower than from the first layer. However, since the first and second layers are bonded together, relative positional accuracy between them is random and can be controlled only with an accuracy of a few hundred microns. As will be described later, since the laser beam passes through the two reflective films, to make an illegal disk the position informations on the first and second layers for the first mark, for example, have to be made to match the same value on the legitimate disk. But making them match would require a near-submicron accuracy in laminating, and consequently, making illegal disks of the two-layer type is practically impossible.

The technique for forming the nonreflective optical marking portion will be described in further detail in sections (a) to (d) below with reference to FIGS. 8 to 12 , etc., dealing with the laminated type in comparison with a single-plate type. FIGS. 8 (a) and (b) are micrographs showing plan views of nonreflective optical marking portions, and FIG. 10 is a simplified schematic cross-sectional view of a nonreflective portion of the two-layer laminated disk. (a) Using a 5 μj/pulse YAG laser, a laser beam was applied to a 500-angstrom aluminum layer lying 0.6 mm below the surface of a 1.2-mm thick ROM disk consisting of two 0.6-mm thick disks laminated together, and, as a result, a 12 μm wide slit-like nonreflective portion 815 was formed, as shown in the X 750 micrograph of FIG. 8 (a). In this X 750 micrograph, no aluminum residues were observed on the nonreflective portion 815 . Thick swollen aluminum layers, 2000 angstroms thick and 2 μm wide, were observed along boundaries between the nonreflective portion 815 and reflective portions. As shown in FIG. 10 (a), it was confirmed that no significant damage had occurred inside. In this case, the application of the pulsed laser presumably melted the aluminum reflective layer, causing a phenomenon of molten aluminum buildup along the boundaries on both sides due to the surface tension. We call this a hot melt surface tension (HMST) recording method. This is a characteristic phenomenon observed only on a laminated disk 800 . FIG. 11 is a schematic diagram, based on an observation through a transmission electron microscope (TEM), illustrating a cross section of the nonreflective portion formed by the above laser trimming process. In the figure, if the aluminum film swollen portion is 1.3 μm wide and 0.20 μm thick, the amount of increased aluminum in that portion is 1.3×(0.20−0.05)=0.195 μm ². The amount of aluminum originally deposited in a half portion (5 μm) of the laser exposed region (10 μm) was 5×0.05=0.250 μm ². The difference is calculated as 0.250−0.195=0.055 μm ². In terms of length, this is equivalent to 0.055/0.05=1.1 μm. This means that an aluminum layer of 0.05 μm thickness and 1.1 μm length remained, and therefore, it can be safely said that almost all aluminum was drawn to the film swollen portion. Thus, the result of the analysis of the figure also verifies the explanation about the above-described characteristic phenomenon.

(b) We will next deal with the case of a single-plate optical disk (an optical disk comprising a single disk). An experiment was conducted by applying laser pulses of the same power to a 0.05 μm thick aluminum reflective film formed on a single-sided molded disk, of which result is shown in FIG. 8 (b). As shown in the figure, aluminum residues were observed, and since these aluminum residues cause reproduction noise, it can be seen that the single-plate type is not suitable for secondary recording of optical disk information of which a high density and a low error rate are demanded. Furthermore, unlike the laminated disk, in the case of the single-plate disk, the protective layer 862 is inevitably damaged, as shown in FIG. 10 (b), when the nonreflective portion is subjected to laser trimming. The degree of damage depends on the laser power, but the damage cannot be avoided even if the laser power is controlled accurately. Moreover, according to our experiment, the printed layer 805 formed by screen printing to a thickness of a few hundred microns on the protective layer 862 was damaged when its thermal absorptance was high. In the case of the single-plate disk, to address the problem of protective layer damage, either the protective layer has to be applied once again or the laser cut operation should be performed before depositing the protective layer. In any case, the single-plate type may present a problem in that the laser cut process has to be incorporated in the pressing process. This limits the application of the single-plate disk despite its usefulness.

(c) A comparison between single-plate disk and laminated disk has been described above, using a two-layer laminated disk as an example. As is apparent from the above description, the same effect as obtained with the two-layer laminated disk can be obtained with the single-layer laminated disk. Using FIGS. 12 (a), 12 (b), etc., a further description will be given dealing with the single-layer type. As shown in FIG. 12 (a), the reflective layer 802 has the transparent substrate 801 of polycarbonate on one side, and the hardened adhesive layer 804 and a substrate on the other side, the reflective layer 802 thus being hermetically sealed therebetween. In this condition, pulsed laser light is focused thereon for heating; in the case of our experiment, heat of 5 μJ/pulse is applied to a circular spot of 10 to 20 μm diameter on the reflective layer 802 for a short period of 70 ns. As a result, the temperature instantly rises to 600° C., the melting point, melting state is caused. By heat transfer, a small portion of the transparent substrate 801 near the spot is melted, and also a portion of the adhesive layer 804 is melted. The molted aluminum in this state is caused by surface tension to build up along boundaries 821 a and 821 b, with tension being applied to both sides, thus forming buildups 822 a and 822 b of hardened aluminum, as shown in FIG. 12 (b). The nonreflective portion 584 free from aluminum residues is thus formed. This shows that a clearly defined nonreflective portion 584 can be obtained by laser-trimming the laminated disk as shown in FIG. 10 (a). Exposure of the reflective layer to the outside environment due to a damaged protective layer, which was the case with the single-plate type, was not observed even when the laser power was increased more than 10 times the optimum value. After the laser trimming, the nonreflective layer 584 has the structure shown in FIG. 12 (b) where it is sandwiched between the two transparent substrates 801 and sealed on both sides with the adhesive layer 804 against the outside environment, thus producing the effect of protecting the structure from environmental effects.

(d) Another benefit of laminating two disks together will be described next. When secondary recording is made in the form of a barcode, an illegal manufacturer can expose the aluminum layer by removing the protective layer in the case of a single-plate disk, as shown in FIG. 10 (b). This gives rise to a possibility that nonecrypted data may be tampered with by redepositing an aluminum layer over the barcode portion on a legitimate disk and then laser-trimming a different barcode. For example, if the ID number is recorded in plaintext or separately from main ciphertext, in the case of a single-plate disk it is possible to alter the ID number, enabling illegal use of the software by using a different password. However, if the secondary recording is made on the laminated disk as shown in FIG. 10 (a), it is difficult to separate the laminated disk into two sides. In addition, when removing one side from the other, the aluminum reflective film is partially destroyed. When the anti-piracy marking is destroyed, the disk will be judged as being a pirated disk and will not run. Accordingly, when making illegal alterations to the laminated disk, the yield is low and thus illegal alterations are suppressed for economic reasons. Particularly, in the case of the two-layer laminated disk, since the polycarbonate material has temperature/humidity expansion coefficients, it is nearly impossible to laminate the two disks, once separated, by aligning the anti-piracy markings on the first and second layers with an accuracy of a few microns, and to mass produce disks. Thus, the two-layer type provides a greater effectiveness in piracy prevention. It was thus found that a clearly defined slit of a nonreflective portion 584 can be obtained by laser-trimming the laminated disk 800 .

The technique for forming the nonreflective optical marking portion has been described in (a) to (d) above.

FIG. 15 is a block diagram showing a low reflectivity light amount detector 586 for detecting the nonreflective optical marking portion, along with its adjacent circuitry, in an optical disk manufacturing process. FIG. 16 is a diagram illustrating the principle of detecting address/clock positions of the low reflectivity portion. For convenience of explanation, the following description deals with the operating principle when a read operation is performed on a nonreflective portion formed on an optical disk constructed from a single disk. It will be recognized that the same operating principle also applies to an optical disk constructed from two disks laminated together.

As shown in FIG. 15, the disk 800 is loaded into a marking reading apparatus equipped with a low reflectivity position detector 600 to read the marking, and in this case, since a signal waveform 823 due to the presence and absence of pits and a signal waveform 824 due to the presence of the nonreflective portion 584 are significantly different in signal level, as shown in the waveform diagram of FIG. 9 (a), they can be clearly distinguished using a simple circuit.

The start position and end position of the nonreflective portion 564 having the above waveform can be easily detected by the low reflectivity light amount detector 586 shown in the block diagram of FIG. 15 . Using the reproduced clock signal as the reference signal, position information is obtained in a low reflectivity position information output section 596 .

As shown in FIG. 15, a comparator 587 in the low reflectivity light amount detector 586 detects the low reflectivity light portion by detecting an analog light reproduced signal having a lower signal level than a light amount reference value 588 . During the detection period, a low reflectivity portion detection signal of the waveform shown in FIG. 16 ( 5 ) is output. The addresses and clock positions of the start position and end position of this signal are measured.

The reproduced light signal is waveshaped by a waveform shaping circuit 590 having an AGC 590 a, for conversion into a digital signal. A clock regenerator 38 a regenerates a clock signal from the waveshaped signal. An EFM demodulator 592 in a demodulating section 591 demodulates the signal, and an ECC corrects errors and outputs a digital signal. The EFM-demodulated signal is also fed to a physical address output section 593 where an address of MSF, from Q bits of a subcode in the case of a CD, is output from an address output section 594 and a synchronizing signal, such as a frame synchronizing signal, is output from a synchronizing signal output section 595 . From the clock regenerator 38 a, a demodulated clock is output.

In a low reflectivity portion address/clock signal position signal output section 596 , a low reflectivity portion start/end position detector 599 accurately measures the start posistion and end position of the low reflectivity portion 584 by using an (n−1) address output section 597 and an address signal as well as a clock counter 598 and a synchronizing clock signal or the demodulated clock. This method will be described in detail by using the waveform diagrams shown in FIG. 16 . As shown in the cross-sectional view of the optical disk in FIG. 16 ( 1 ), the low reflectivity portion 584 of mark number 1 is formed partially. A reflection selope signal such as shown in FIG. 16 ( 3 ), is output, the signal level from the reflective portion being lower than the light amount reference value 588 . This is detected by the light level comparator 587 , and a low reflectivity light detection signal, such as shown in FIG. 16 ( 5 ), is output from the low reflectivity light amount detector 586 . As shown by a reproduced digital signal in FIG. 16 ( 4 ), no digital signal is output from the mark region since it does not have a reflective layer.

Next, to obtain the start and end positions of the low reflectivity light detection signal, the demodulated clock or synchronizing clock shown in FIG. 16 ( 6 ) is used along with address information. First, a reference clock 605 at address n in FIG. 16 ( 7 ) is measured. When the address immediately preceding the address n is detected by the (n−1) address output section 597 , it is found that the next sync 604 is a sync at address n. The number of clocks from the synch 604 to the reference clock 605 , which is the start position of the low reflectivity light detection signal, is counted by the clock counter 598 . This clock count is defined as a reference delay time TD which is measured by a reference delay time TD measuring section 608 for storage therein.

The circuit delay time varies with reproduction apparatus used for reading, which means that the reference delay time TD varies depending on the reproduction apparatus used. Therefore, using the TD, a time delay corrector 607 applies time correction, and the resulting effect is that the start clock count for the low reflectivity portion can be measured accurately if reproduction apparatus of different designs are used for reading. Next, by finding the clock count and the start and end addresses for the optical mark No. 1 in the next track, clock m+14 at address n+12 is obtained, as shown in FIG. 16 ( 8 ). Since TD=m+2, the clock count is corrected to 12, but for convenience of explanation, n+14 is used. We will describe another method, which eliminates the effects of varying delay times without having to obtain the reference delay time TD in the reproduction apparatus used for reading. This method can check whether the disk is a legitimate disk or not by checking whether the positional relationship of mark 1 at address n in FIG. 16 ( 8 ) relative to another mark 2 matches or not. That is, TD is ignored as a variable, and the difference between the position, A1=a1+TD, of mark 1 measured and the position, A2=a2+TD, of mark 2 measured is obtained, which is given as A1−A2=a1−a2. At the same time, it is checked whether this difference matches the difference, a1-a2, between the position a1 of the decrypted mark 1 and the position information a2 of the mark 2 , thereby judging whether the disk is a legitimate disk or not. The effect of this method is that the positions can be checked after compensating for variations of the reference delay time TD by using a simpler constitution.

(D) Next, the encrypted information writing process will be described. The position information read in the process (C) is encrypted (digital signature), as will be described in detail in the next section ( 2 ), and is written on the optical disk using a barcode or other method. FIG. 3 shows how this is done. In FIG. 3 ( 1 ), the reflective layer is trimmed by a pulsed laser, and a barcode-like trimming pattern, such as shown in FIG. 3 ( 2 ), if formed. At a reproduction apparatus (player), an envelope waveform some portions of which are missing as shown in FIG. 3 ( 3 ) is obtained. The missing portions generate a low level signal which is different from a signal generated from an ordinary pit, and this signal is sliced by a second slice level comparator to obtain a low reflectivity portion detection signal as shown in FIG. 3 ( 4 ). From this low reflectivity portion detection signal, a PWM demodulator 621 in FIG. 3 ( 5 ) demodulates the signal containing encrypted information.

The processing steps in the optical disk manufacturing process have been described above. Next, the constitution and operation of a reproduction apparatus (player) for reproducing the thus completed optical disk on a player will be described with reference to FIG. 41 .

In the figure, the construction of an optical disk 9102 will be described first. A marking 9103 is formed on a reflective layer (not shown) deposited on the optical disk 9102 . In the manufacturing process of the optical disk, the position of the marking 9103 was detected by position detecting means, and the detected position was encrypted as marking position information and written on the optical disk in the form of a barcode 9104 .

Position information reading means 9101 reads the barcode 9104 , and decrypting means 9105 contained therein decrypts the contents of the barcode for output. Marking reading means 9106 reads the actual position of the marking 9103 and outputs the result. Comparing/judging means 9107 compares the decrypted result from the decrypting means 9105 contained in the position information reading means 9101 with the result of reading by the marking reading means 9106 , and judges whether the two agree within a predetermined allowable range. If they agree, a reproduction signal 9108 for reproducing the optical disk is output; if they do not agree, a reproduction stop signal 9109 is output. Control means (not shown) controls the reproduction operation of the optical disk in accordance with these signals; when the reproduction stop signal is output, an indication to the effect that the optical disk is an illegal duplicated disk is displayed on a display (not shown) and the reproduction operation is stopped. In the above operation, it will be recognized that it is also possible for the marking reading means 9106 to use the decrypted result from the decrypting means 9105 when reading the actual position of the marking 9103 .

Thus the reproduction apparatus of the above construction can detect an illegally duplicated optical disk and stop the reproduction operation of the disk, and can prevent illegal duplicates practically.

The foregoing description has dealt with the process from optical disk manufacturing to the reproduction operation of the player, and we will now proceed to a description of appertaining matters relating to the details of the above process.

(A) A low reflectivity portion address table, which is a position information list for the low reflectivity portion, will be explained.

(a) Laser markings are formed at random in the anti-piracy mark formation process at the factory. No laser markings formed in this manner can be identical in physical feature. In the next process step, the low reflectivity portion 584 formed on each disk is measured with a resolution of 0.13 μm in the case of a DVD, to construct a low reflectivity portion address table 609 as shown in FIG. 13 (a). Here, FIG. 13 (a) is a diagram showing a low reflectivity portion address table, etc. for a legitimate CD manufactured in accordance with the present embodiment, and FIG. 13 (b) is concerned with an illegally duplicated CD. The low reflectivity portion address table 609 is encrypted using a one-direction function such as the one shown in FIG. 18, and in the second reflective-layer forming step, a series of low reflectivity portions 584 c to 584 e, where the reflective layer is removed, is recorded in a barcode-like pattern on the innermost portion of the disk, as shown in FIG. 2 . Alternatively, it may be recorded on a magnetic recording portion 67 of a CD-ROM, as shown in FIG. 14 . FIG. 18 is a flowchart illustrating a disk check procedure by the one-way function used for the encryption, and FIG. 14 is a block diagram of a disk making apparatus and a special recording/reproduction apparatus. As shown in FIG. 13, the legitimate CD and the illegally duplicated CD have the low reflectivity portion address tables 609 and 609 x, respectively, which are substantially different from each other. One factor resulting in this difference is that laser markings identical in physical feature cannot be made, as earlier noted. Another factor is that the sector address preassigned to the disk is different if the master disk is different.

Referring now to FIG. 13, we will describe how the marking position information differs between the legitimate disk and pirated disk. The figure shows an example in which the above two factors are combined. In the example shown, two markings are formed on one disk. In the case of the legitimate CD, the first marking of mark number 1 is located at the 262nd clock position from the start point of the sector of logical address A 1 , as shown in the address table 609 . In the case of a DVD, one clock is equivalent to 0.13 μm, and the measurement is made with this accuracy. On the other hand, in the case of the pirated CD, the first marking is located at the 81 st clock position in the sector of address A2, as shown in the address table 609 x. By detecting this difference of the first marking position between the legitimate disk and pirated disk, the pirated disk can be distinguished. Likewise, the position of the second marking is also different. To make the position information match that of the legitimate disk, the reflective film at the 262nd position in the sector or address A1 must be formed with an accuracy of one clock unit, i.e., 0.13 μm; otherwise, the pirated disk cannot be run.

Accordingly, as shown in FIG. 14, in the reproduction apparatus, the encrypted table is decrypted to reconstruct the legitimate table which is then checked by a check program 535 to differentiate between the legitimate disk and illegally duplicated disk, and to stop the reproduction operation in the case of a duplicated disk. In the example of FIG. 16, the legitimate disk and illegally duplicated disk have low reflectivity portion address tables 609 and 609 x respectively, where values are different as shown in FIG. 17 . In the case of the legitimate disk, in the track following the mark 1 the start and end positions are m+14 and m+267, respectively, as shown in FIG. 16 ( 8 ), whereas in the case of the illegally duplicated disk these are m+24 and m+277, respectively, as shown in FIG. 16 ( 9 ). Therefore, the corresponding values in the low reflectivity portion address tables 609 and 609 x are different, as shown in FIG. 17, thus making it possible to distinguish the duplicated disk. If an illegal manufacturer desires to make a copy of the disk having the low reflectivity portion address table 609 , they will have to perform a precise laser trimming operation with the resolution of the reproduced clock signal as shown in FIG. 16 ( 8 ). In the case of a DVD disk, the period T of the reproduced clock pulse, when converted to a distance on the disk, is 0.13 μm as shown in FIG. 27 ( 5 ). Accordingly, to make an illegal copy, the reflective film will have to be removed with a submicron resolution of 0.1 μm. It is true that when an optical head designed for an optical disk is used, a recording can be made on a recording film such as a CD-R with a submicron resolution. But in this case, the reproduced waveform will be as shown in FIG. 9 (c), and the distinct waveform 824 as shown in FIG. 9 (a) cannot be obtained unless the reflective film is removed.

(b) A first method of achieving mass production of pirated disks by removing the reflective film may be by laser trimming using a high output laser such as a YAG laser. At the present state of technology, even the most highly accurate machining laser trimming can only achieve a processing accuracy of a few microns. In the laser trimming for software mask corrections, it is said that 1 μm is the limit of the processing accuracy. This means that it is difficult to achieve a processing accuracy of 0.1 μm at the mass production level.

(c) As a second method, X-ray exposure equipment for processing software masks for VLSIs and ion beam processing equipment are known at the present time as equipment that can achieve a processing accuracy of the order of submicrons, but such equipment is very expensive and furthermore, it takes much time to process one piece of disk, and if each disk were processed using such equipment, the cost per disk would be very high. At the present time, therefore, the cost would become higher than the retail price of most legitimate disks, so that making pirated disks would not pay and meaningless.

(d) As described above, with the first method that involves laser trimming, it is difficult to process with a submicron accuracy, and therefore, it is difficult to mass produce pirated disks. On the other hand, with the second method using the submicron processing technology such as X-ray exposure, the cost per disk is so high that making pirated disks is meaningless from an economic point of view. Accordingly, making illegal copies can be prevented until some day in the future when low-cost submicron processing technology for mass production becomes practical. Since practical implementation of such technology will be many years into the future, production of pirated disks can be prevented. In the case of a two-layer disk with a low reflectivity portion formed on each layer as shown in FIG. 33, an illegally duplicated disk cannot be manufactured unless the pits on top and bottom are aligned with good accuracy when laminating, and this enhances the effectiveness in preventing piracy.

(B) Next, we will describe how the arrangement angle of the low reflectivity portion on the disk can be specified.

In the present invention, sufficient effectiveness in piracy prevention is provided by the reflective layer level mechanism, that is, by the low reflective marking alone. In this case, the prevention is effective even if the master disk is a duplicate. However, the effectiveness can be enhanced by combining it with the piracy prevention technique at the master disk level. If the arrangement angle of the low reflectivity portion on the disk is specified as shown in Table 532 a and Table 609 in FIG. 13 (a), an illegal manufacturer would have to accurately duplicate even the arrangement angle of each pit on the master disk. This would increase the cost of pirated disks and hence enhance the capability to deter piracy.

(C) The points of the present invention will be summarized below. In the present invention, a legitimate manufacturer can make a legitimate disk by processing the disk using a general-purpose laser trimming apparatus having a processing accuracy of several tens of microns. Though a measuring accuracy of 0.13 μm is required, this can be achieved by conventional circuitry contained in a consumer DVD player. By encrypting the measured result with a secret encryption key, a legitimate disk can be manufactured. That is, the legitimate manufacturer need only have a secret key and a measuring apparatus with a measuring accuracy of 0.13 μm, while the required processing accuracy is two or three orders of magnitude lower, that is, several tens of microns. This means that a conventional laser processing apparatus can be used. On the other hand, an illegal manufacturer, who does not have a secret key, will have to directly copy the encrypted information recorded on the legitimate disk. This means that a physical mark corresponding to the encrypted position information, that is, the position information on the legitimate disk, must be formed with a processing accuracy of 0.13 μm. That is, the low reflective mark has to be formed using a processing apparatus having a processing accuracy two orders of magnitude higher than that of the processing apparatus used by the legitimate manufacturer. Volume production with an accuracy higher by two orders of magnitude, i.e., with an accuracy of 0.1 μm, is difficult both technically and economically, even in the foreseeable future. This means that production of pirated disks can be prevented during the life of the DVD standard. One point of the invention is to exploit the fact that the measuring accuracy is generally a few orders of magnitude higher than the processing accuracy.

In the case of CLV, the above method exploits the fact that the address coordinate arrangement differs from one master disk to another, as previously noted. FIG. 19 shows the result of the measurement of address locations on actual CDs. Generally, there are two types of master disk, one recorded by rotating a motor at a constant rotational speed, i.e., with a constant angular velocity (CAV), and the other recorded by rotating a disk with a constant linear velocity (CLV). In the case of a CAV disk, since a logical address is located on a predetermined angular position on the disk, the logical address and its physical angular position on the disk are exactly the same no matter how many master disks are made. On the other hand, in the case of a CLV disk, since only the linear velocity is controlled, the angular position of the logical address on the master disk is random. As can be seen from the result of the measurement of logical address locations on actual CDs in FIG. 19, the tracking pitch, start point, and linear velocity vary slightly from disk to disk even if exactly the same data is recorded using the same mastering apparatus, and these errors accumulate, resulting in different physical locations. In FIG. 19, the locations of each logical address on a first master disk are indicated by white circles, and the locations on second and third master disks are indicated by black circles and triangles, respectively. As can be seen, the physical locations of the logical addresses vary each time the master disk is made. FIG. 17 shows the low reflectivity portion address tables for a legitimate disk and an illegally duplicated disk for comparison.

The method of piracy prevention at the master disk level has been described above. This is, when master disks of CLV recording, such as a CD or DVD, are made from the same logic data by using a mastering apparatus, as shown in FIG. 19, the physical location of each pit on the disk varies between master disks, that is, between the legitimate disk and pirated disk. This method distinguishes a pirated disk from a legitimate disk by taking advantage of this characteristic. The piracy prevention technology at the master disk level can prevent pirated disks at the logic level made by simply copying data only from the legitimate disk. However, recent years have seen the emergence of pirate manufacturers equipped with more advanced technologies, who can make a master disk replica identical in physical feature to a legitimate disk by melting the polycarbonate substrate of the legitimate disk. In this case, the piracy prevention method at the master disk level is defeated. To prevent this new threat of pirated disk production, the present invention has devised the piracy prevention method at the reflective layer level wherein a marking is formed on a reflective film.

According to the method of the present invention, the marking is formed on each disk pressed from a master disk, even if disks are pressed from the master disk, by removing a portion of the reflective film in the reflective film formation process. As a result, the position and shape of the resulting low reflective marking is different from one disk to another. In a usual process, it is next to impossible to partially remove the reflective film with an accuracy of submicrons. This serves to enhance the effectiveness in preventing duplication since duplicating the disk of the invention does not justify the cost.

FIG. 20 shows a flowchart for detecting a duplicated CD by using the low reflectivity portion address table. The delay time needed to detect the optical mark varies only slightly due to the optical head and circuit designs of the reproduction apparatus used. This of the delay time TD circuit can be predicted at the design stage or at the time of mass production. The optical mark position information is>obtained by measuring the number of clocks, that is, the time, from the frame synchronizing signal. Due to the effect of the circuit delay time, an error may be caused to detected data of the optical mark position information. As a result, a legitimate disk may be erroneously judged as being a pirated disk, inconveniencing a legitimate user. A measure to reduce the effect of the circuit delay time TD will be described below. Further, a scratch made on a disk after purchase may cause an interruption in the reproduced clock signal, causing an error of a few clocks in the measurement of the optical mark position information. To address this problem, a tolerance 866 and a pass count 867 , shown in FIG. 27, are recorded on a disk, and while allowing a certain degree of tolerance on the measured value according to the actual situation at the time or reproduction, the reproduction operation is permitted when the pass count 867 is reached; the margin allowed for an error due to a surface scratch on the disk can be controlled by the copyright owner prior to the shipment of the disk. This will be described with reference to FIG. 20 .

In FIG. 20, the disk is reproduced in step 865 a to recover the encrypted position information from the barcode recording portion or pit recording portion of the present invention. In step 865 b, decryption or signature verification is performed, and in step 865 c, a list of optical mark position information is recovered. Next, if the delay time TD of a reproduction circuit is stored in the circuit delay time storing section 608 a in the reproduction apparatus of FIG. 15, TD is read out in step 865 h and the process proceeds to step 865 x. If TD is not stored in the reproduction apparatus, or if a measurement instruction is recorded on the disk, the process proceeds to step 865 d to enter a reference delay time measurement routine. When address Ns-1 is detected, the start position of the next address Ns is found. The frame synchronizing signal and the reproduced clock are counted, and in step 865 f, the reference optical mark is detected. In step 865 g, the circuit delay time TD is measured and stored. This operation is the same as the operation to be described later with reference to FIG. 16 ( 7 ). In step 865 x, the optical mark located inside address Nm is measured. In steps 865 i, 865 j, 865 k, and 865 m, the optical mark position information is detected with a resolution of one clock unit, as in steps 865 d, 865 y, 865 f, and 865 y. Next, in step 865 n, a pirated disk detection routine is entered. First, the circuit delay time TD is corrected. In step 865 p, the tolerance 866 , i.e., tA, and pass count 867 recorded on the disk, as shown in FIG. 27, are read to check whether or not the position information measured in step 865 g falls within the tolerance tA. If the result is OK in step 865 r, then in step 865 s it is checked whether the checked mark count has reached the pass count. If the result is OK, then in step 865 u the disk is judged as being a legitimate disk and reproduction is permitted. If the pass count is not reached yet, the process returns to step 865 z. If the result is NO in step 865 r, then it is checked in step 865 f whether the error detection count is smaller than NA, and only when the result is OK, the process returns to step 865 s. If it is not OK, then in step 865 y the disk is judged as being an illegal disk and the operation is stopped.

As described, since the circuit delay time TD of the reproduction apparatus is stored in the IC ROM, optical mark position information can be obtained with increased accuracy. Furthermore, by setting the tolerance 866 and pass count for the software on each disk, the criteria for pirated disk detection can be changed according to the actual condition to allow for a scratch made on the disk after purchase. This has the effect of reducing the probability of a legitimate disk being erroneously judged as an illegal disk.

(D) A further description will be given of the operation of reading the nonreflective optical marking portion of the two-disk laminated optical disk, focusing on points that were not touched on in the foregoing description of the operating principle.

That is, as shown in FIG. 16, the start position address number, frame number, and clock number can be measured accurately with a resolution of 1 T unit, that is, with a resolution of 0.13 μm in the case of the DVD standard, by using a conventional player, thereby to accurately measure the optical mark of the present invention. FIGS. 27 and 28 show the optical mark address reading method of FIG. 16 as applied to the DVD standard. Explanation of signals ( 1 ), ( 2 ), ( 3 ), ( 4 ), and ( 5 ) in FIGS. 27 and 28 will not be given here since the operating principle is the same as that shown in FIG. 16 .

The correspondence between FIG. 16, which illustrates the principle of the detection operation for detecting the position of a low reflectivity portion on a CD, and FIGS. 27 and 28, which are concerned with a DVD, is given below.

FIG. 16 ( 5 ) corresponds to FIGS. 27 ( 1 ) and 28 ( 1 ). The reproduced clock signal in FIG. 16 ( 6 ) corresponds to that shown in FIGS. 27 ( 5 ) and 28 ( 5 ). Address 603 in FIG. 16 ( 7 ) corresponds to that shown in FIGS. 27 ( 2 ) and 28 ( 2 ).

Frame synch 604 in FIG. 16 ( 7 ) corresponds to that shown in FIGS. 27 ( 4 ) and 28 ( 4 ). Starting clock number 605 a in FIG. 16 ( 8 ) corresponds to reproduced channel clock number in FIG. 27 ( 6 ). Instead of the end clock number 606 in FIG. 16 ( 7 ), in FIGS. 27 ( 7 ) and 28 ( 7 ) data is compressed using a 6-bit marking length.

As illustrated, the detection operation is fundamentally the same between CD and DVD. A first difference is that a 1-bit mark layer identifier 603 a as shown in FIG. 27 ( 7 ) is included for identifying whether the low reflectivity portion is of the one-layer type or two-layer type. The two-layer DVD structure provides a greater anti-piracy effect, as previously described. A second difference is that since the line recording density is nearly two times as high. 1 T of the reproduced clock is as short as 0.13 μm, which increases the resolution for the detection of the position information and thus provides a greater anti-piracy effect.

Shown in FIG. 27 is the signal from the first layer in a two-layer optical disk having two reflective layers. The signal ( 1 ) shows the condition when the start position of an optical mark on the first layer is detected. FIG. 28 shows the condition of the signal from the second layer.

To read the second layer, a first/second layer switching section 827 in FIG. 15 sends a switching signal to a focus control section 828 which then controls a focus driving section 829 to switch the focus from the first layer to the second layer. From FIG. 27, it is found that the mark is in address (n), and by counting the frame synchronizing signal ( 4 ) using a counter, it is found that the mark is in frame 4 . From signal ( 5 ), the PLL reproduced clock number is found, and the optical marking position data as shown by the signal ( 6 ) is obtained. Using this position data, the optical mark can be measured with a resolution of 0.13 μm on a conventional consumer DVD player.

(E) Additional matters relating to the two-disk laminated optical disk will be further described below.

FIG. 28 shows address position information pertaining to the optical marking formed on the second layer. Since laser light penetrates the first and second layers through the same hole, as shown in the process step (b)(sic) in FIG. 7, the nonreflective portion 815 formed on the first reflective layer 802 and the nonreflective portion 826 formed on the second reflective layer 825 are identical in shape. This is depicted in the perspective view of FIG. 33 . In the present invention, after the transparent substrate 801 and the second substrate 803 are laminated together, laser light is applied penetrating through to the second layer to form an identical mark thereon. In this case, since coordinate arrangements of pits are different between the first and second layers, and since the positional relationship between the first and second layers is random when laminating them together, the pit positions where the mark is formed are different between the first and second layers, and entirely different position information is obtained from each layer. These two kinds of position information are encrypted to produce an anti-piracy disk. If it is attempted to duplicate this disk illegally, the optical marks on the two layers would have to be aligned with a resolution of about 0.13 μm. As previously described, at the present state of technology it is not possible to duplicate the disk by aligning the optical marks with the pits with an accuracy of 0.13 μm, that is, with an accuracy of the order of 0.1 μm, but there is a possibility that mass production technology may be commercially implemented in the future that enables large quantities of single-layer disks to be trimmed with a processing accuracy of 0.1 μm at low cost. Even in that case, since the top and bottom disks are trimmed simultaneously in the case of the two-layer laminated disk 800 , the two disks must be laminated together with the pit locations and optical marks aligned with an accuracy of a few microns. However, it is next to impossible to laminate the disks with this accuracy because of the temperature coefficient, etc. of the polycarbonate substrate. When optical marks were formed by applying laser light penetrating through the two-layer disk 800 , the resulting anti-piracy mark is extremely difficult to duplicate. This provides a greater anti-piracy effect The optical disk with an anti-piracy mechanism is thus completed. For piracy prevention applications, in cases where the disk process and laser cut process are inseparable as in the case of the single-plate type, the encryption process, which is an integral part of the laser cut process, and processing involving a secret encryption key have to be performed at the disk manufacturing factory. This means that in the case of the single-plate type the secret encryption key maintained in the software company have to be delivered to the disk manufacturing factory. This greatly reduces the security of encryption. On the other hand, according to the method involving laser processing of laminated disks, which constitutes one aspect of the invention, the laser trimming process can be completely separated from the disk manufacturing process. Therefore, laser trimming and encryption operations can be performed at a factory of the software maker. Since the secret encryption key that the software maker keeps need not be delivered to the disk manufacturing factory, the secret key for encryption can be kept in the safe custody of the software maker. This greatly increases the security of encryption.

(2) (A) Encryption (digital signature) of marking position information, etc. and decryption and reproduction of optical disk position information, etc., which have been briefly described in (1), will now be described in more detail. (B) Various mechanism for piracy prevention will also be described below.

(A) Encryption (digital signature) and its reproduction will be described.

(a) Simple encryption (digital signature)

(Implementation by RSA function)

First, an example of encryption in which encryption is performed using a function of a message recovery type signature method, such as an RSA function, will be described with reference to the flowcharts shown in FIGS. 22 and 24.

As shown in FIG. 22, the process consists of the following major routines: step 735 a where marking position information is measured at the optical disk maker, step 695 where the position information is encrypted (or a digital signature is appended), step 698 where the position information is decrypted (or the signature is verified or authenticated) in the reproduction apparatus, and step 735 w where a check is made to determine whether the disk is a legitimate optical disk or not.

First, in step 735 a, the marking position information on the optical disk is measured in step 735 b. The position information is then compressed in step 735 d, and the compressed position information H is obtained in step 735 e.

In step 695 , the ciphertext of the compressed position information H is constructed. First, in step 695 , a secret key, d, of 512 or 1024 bits, and secret keys, p and q, of 256 or 512 bits, are set, and in step 695 b, encryption is performed using an RSA function. When the position information H is denoted by M, M is raised to d-th power and mod n is calculated to yield ciphertext C. In step 695 d, the ciphertext C is recorded on the optical disk. The optical disk is thus completed and is shipped (step 735 k).

In the reproduction apparatus, the optical disk is loaded in step 735 m, and the ciphertext C is decrypted in step 698 . More specifically, the ciphertext C is recovered in step 698 e, and public keys, e and n, are set in step 698 f; then in step b, to decrypt the ciphertext C, the ciphertext C is raised to e-th power and the mod n of the result is calculated to obtain plaintext M. The plaintext M is the compressed position information H. An error check may be performed in step 698 g. If no errors, it is decided that no alterations have been made to the position information, and the process proceeds to the disk check routine 735 w shown in FIG. 24 . If an error is detected, it is decided that the data is not legitimate one, and the operation is stopped.

In the next step 736 a, the compressed position information H is expanded to recover the original position information . In step 736 c, measurements are made to check whether the marking is actually located in the position on the optical disk indicated by the position information. :In step 736 d, it is checked whether the difference between the decrypted position information and the actually measured position information falls within a tolerance. If the check is OK in step 736 e, the process proceeds to step 736 h to output software or data or execute programs stored on the optical disk. If the check result is outside the tolerance, that is, if the two pieces of position information do not agree, a display is produced to the effect that the optical disk is an illegally duplicated one, and the operation is stopped in step 736 g. RSA has the effect of reducing required capacity since only the ciphertext need be recorded.

(Implementation by elliptic function)

Next, another type of signature system, that is, an imprint type signature system using an elliptic function for encryption, will be described with reference to the flowcharts shown in FIGS. 23 and 24.

As shown in FIG. 23, etc., the process consists of the following major routines: step 735 a where marking position information is measured at the optical disk maker, step 735 f where authentication ciphertext (i.e., signature) for the position information is computed, step 735 n where position information authentication (signature verification) is performed in the reproduction apparatus, and step 735 w where a check is made to determine whether the disk is a legitimate optical disk or not.

The process from step 735 a to step 735 e is the same as that for the RSA function.

In step 735 f, authentication ciphertext for the compressed position information H is constructed. First, in step 735 g, secret keys X (128 bits or over) and K are set, and in step 735 h, a public system parameter G, a point on an ellipse, is determined, and with f(x) as a one-direction function. R=f (K×G) is obtained first, and then R′=f(R) is obtained; then from equation S=(K×R′−H)X ⁻¹mod Q, R and S as authentication ciphertext are generated. In step 735 j, the authentication ciphertext R and S and the plaintext H of the compressed position information are recorded on the optical disk, and in step 735 k, the completed disk is shipped.

In the reproduction apparatus, the optical disk is loaded in step 735 m, and an authentication operation is performed in step 735 n to authenticate the position information.

First, in step 735 p, the authentication ciphertext R and S and the compressed position information H are recovered from the loaded optical disk. In step 735 r, public keys Y, G, and Q are set, and in step 735 s, an authentication operation is performed whereby f(A×Y+B×G) is obtained from A=SR ⁻¹mod Q and B=HR ⁻¹mod Q. In step 735 t, it is checked if the above value matches R. If they match, it is decided that no alterations have been made to the position information, and the process proceeds to the optical disk check routine 735 w in FIG. 24 . If they do not match, it is decided that the data is not legitimate one, and the operation is stopped.

The subsequent process from step 736 a to step 736 g is the same as that for the RSA function. That is, if the optical disk is judged as being an illegally duplicated one, a display to that effect is produced, and in step 736 g, the operation is stopped. Compared to the RSA function, the elliptic function has the advantage that the computation time is short, which serves to reduce the time before reproduction starts. This system therefore is suitable for application to consumer reproduction apparatus.

(b) Complex encryption (digital signature) using master key, subkey, etc.

Not only the marking position information but information concerning the features of contents of the software stored on the optical disk and an anti-piracy identifier are subjected to encryption (digital signature). Furthermore, two kinds of encryption keys, master key and subkey, are used. A specific example is described below in which a secret key encryption function is used in combination with a public key encryption function.

Before proceeding to a detailed description of the specific example, a basic functional description of this system will be given first with reference to FIG. 40 to facilitate understanding of the basics thereof.

In the example treated in the following basic description, encryption is performed using a public key encryption function, and encryption using a secret key encryption function is not treated here. Therefore, the master secret key for public key encryption and the sub secret key for public key encryption are simply referred to as the master secret key and sub secret key, respectively. Likewise, the master public key for public key encryption and the sub public key for public key encryption are simply referred to as the master public key and sub public key, respectively.

As shown in FIG. 40, a key management center 9001 securely manages the master secret key to maintain its secrecy, and is linked to a software maker 9002 , to be described later, via a communication line 9003 . When a request for encryption is made from the software maker 9002 , the key management center 9001 receives data, to be encrypted, via a network 9003 and encrypts the data using the master secret key.

For simplicity of explanation, it is assumed here that the software maker 9002 also includes a disk manufacturing factory. Therefore, the software maker 9002 here is a department that performs the manufacturing process at the disk manufacturing factory illustrated in FIG. 1, in addition to the production of software. That is, when manufacturing optical disks of movie software, encryption for prevention of illegal duplications is also performed. To accomplish the encryption, the software maker 9002 obtains an exclusive sub secret key from the key management center 9001 . The above has described the arrangement at the optical disk maker side.

On the other hand, there is a player 9004 at the user side where the optical disk is used. The player 9004 is an apparatus for reproducing an optical disk, and contains a ROM in which is prestored a master public key corresponding to the master secret key maintained at the key management center. A function to stop the reproduction of an illegally duplicated optical disk is also incorporated.

Having described the general arrangement, we will now describe the operation.

(b-1) First, the processing steps for encryption performed at the software maker 9002 will be described.

The encryption step first performed (the first encryption step) involves encryption at the stage of disk mold manufacturing, and the encrypted information is reflected in the shape of the disk mold. The encryption step performed finally (the second encryption step) concerns encryption performed at a stage after the formation of a marking by laser trimming.

(1-1) In the first encryption step, encryption is performed using a sub public key corresponding to the sub secret key to be used in the second encryption step, and using a software feature information and anti-piracy identifier. The information is transferred to the key management center 9001 via the communication line 9003 . The software feature information refers to the information describing the contents of the movie software written on the optical disk, and it is unique to each movie software and is different from one software to another. The anti-piracy identifier is provided to make it possible to detect whether the manufactured optical disk is processed with piracy prevention. The identifier of an optical disk processed with piracy prevention using second ciphertext is “1”; otherwise, the identifier is “0”. In this example, the identifier is “1”, needless to say.

(1-2) The key management center 9001 encrypts the information transferred from the software maker 9002 , by using the master secret key maintained at the center, and sends the encrypted information back to the software maker 9002 . The thus created ciphertext is referred to as the first ciphertext.

(1-3) The software maker 9002 records the first ciphertext on the disk mold (or master) along with the movie software, etc.

(1-4) The software maker 9002 molds disks by using the thus completed mold.

(1-5) Next, the software maker 9002 fabricates optical disks from the molded disks, and performs the laser trimming, as previously described, to form a marking on each optical disk.

(1-6) Further, the software maker 9002 detects the position of the marking and encrypts the obtained position information by using the sub secret key maintained at the maker. The thus encrypted information is referred to as the second ciphertext. Since it is created by encrypting the position information, the second ciphertext is different from one optical disk to another even if they are pressed from the same mold. This is the difference from the first ciphertext.

(1-7) Finally, the software maker 9002 records the second ciphertext as a barcode on the optical disk. The optical disk is thus completed.

(b-2) Next, we will describe the operation when the user who purchased the thus completed optical disk plays it back on the player 9004 .

(2-1) First, the player 9004 reads the first ciphertext recorded on the optical disk, and using the master public key stored in the ROM, decrypts the first ciphertext which contains in encrypted form the sub public key corresponding to the sub secret key, the software feature information, and the anti-piracy identifier.

(2-2) In the meantime, the player 9004 extracted the software feature information from the contents of the movie software recorded on the optical disk. The extracted software feature information is compared with the software feature information obtained by decryption in (2-1); if they do not agree, the optical disk is judged as being an illegally duplicated one, and the subsequent reproduction operation is stopped. If they agree, the process proceeds to the next step.

(2-3) It is checked whether the anti-piracy identifier obtained by decryption in (2-1) is “1” or “0”. If it is “0”, the reproduction operation is immediately started, skipping the process hereinafter described. If it is “1”, the process further continues.

In this manner, if the optical disk happens to be a disk not processed with the piracy prevention using the second ciphertext, the disk can be reproduced on the player 9004 as long as its identifier is set to “0” in a legitimate way. If a pirate attempts to make an illegal copy by altering the identifier to “0”, his effort will be thwarted because the identifier is encrypted using the master secret key after being combined with the software feature information, etc., as earlier described.

(2-4) First, the second ciphertext recorded on the optical disk is read out. Then, the second ciphertext, which is the encrypted version of the position information, is decrypted using the sub public key obtained by decryption in (2-1).

(2-5) Using the decrypted position information, it is checked whether the marking is actually formed in the position on the optical disk indicated by the position information. Then, the actually measured marking position information is compared with the position information decrypted in (2-4). If they do not agree, the optical disk is judged as being an illegally duplicated one, and the reproduction operation is stopped. If they agree, the optical disk is judged as being a legitimate one, and the reproduction operation is started.

An outline of the system has

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