An optical disk and an optical disk reproduction apparatus

Abstract: An optical data disk on which data is recorded comprises an identifier in a prescribed region for indicating whether a barcode-like mark is present on said disk or not, said identifier and said barcode-like mark being in different locations on said disk. The disk comprises another marking marked by a laser beam on an information layer on said disk, and information based on the position of said additional marking is encrypted or is applied with a digital signature, and said encrypted information or digital signature, respectively, is included in said barcode-like mark. Further, a reproduction apparatus for use with such kind of disk is provided.

Description: The present invention relates to an optical disk according to the preamble portion of claim and an optical disk reproduction apparatus, for use with such disk. An optical disk and reproduction apparatus of this kind are known from EP-A-741 382, which is not prepublished. In the manufacturing process of optical disks, it has been commonly practiced to record a serial number, lot number, etc. on each optical disk in the form of a barcode. Since such information cannot be written to a pit information area of the optical disk, it has been practiced to write the barcoded information to a non-information area, or unused space, on the optical disk. When reproducing (playing back) such an optical disk, the pit information is read by an optical pickup; to read the barcoded information such as a serial number, etc. recorded in the non-information area, however, a separate reading device has been used. In the above prior art optical disk, since information carrying a serial number and the like is not recorded in a pit area but recorded in a non-information area, as described above, a separate reading device has had to be provided in addition to the usual optical pickup, the resulting problem being increased complexity of the playback apparatus construction. In view of the above problem with the prior art, it is an object of the present invention to provide an optical disk wherein data such as a disk ID number, etc. is converted into a barcode and recorded, thereby permitting the use of a single optical pickup to read both the bit data and barcode data, and an optical disk reproduction apparatus therefor. This object is attained by the features of claims 1 and 3 respectively. Preferred embodiments are subject matter of dependent claims. The invention is a disk wherein a marking is formed by a laser to a reflective film of said disk holding data written thereon, at least position information of said marking or information concerning said position information is encrypted or applied a digital signature, at least said encrypted information or digital signature-appended information is converted into a barcode, and said barcode is written on said disk on which data is recorded, with said barcode being written to a prescribed region of said disk. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram showing a disk manufacturing process and a secondary recording process; Figure 2(a) is a top plan view of a disk, (b) is a top plan view of the disk, (c) is a top plan view of the disk, (d) is a transverse sectional view of the disk, and (e) is a waveform diagram of a reproduced signal; Figure 3 is a flowchart illustrating a process of recording encrypted position information on a disk in the form of a barcode; Figure 4 is a diagram showing a disk fabrication process and a secondary recording process (part 1); Figure 5 is a diagram showing the disk fabrication process and the secondary recording process (part 2); Figure 6 is a diagram showing a two-layer disk fabrication process (part 1); Figure 7 is a diagram showing the two-layer disk fabrication process (part 2); Figure 8(a) is an enlarged view of a nonreflective portion of a laminated type, and (b) is an enlarged view of a nonreflective portion of a single-plate type; Figure 9(a) is a reproduced-waveform diagram for a nonreflective portion, (b) is a reproduced-waveform diagram for a nonreflective portion, (c) is a reproduced-waveform diagram for a nonreflective portion, and (d) is a plan view of a master disk produced by a master disk method; Figure 10(a) is a cross-sectional view of a nonreflective portion of the laminated type, and (b) is a cross-sectional view of a nonreflective portion of the single-plate type; Figure 11 is a schematic diagram, based on an observation through a transmission electron microscope, illustrating a cross section of the nonreflective portion; Figure 12(a) is a cross-sectional view of a disk, and (b) is a crosssectional view of the nonreflective portion of the disk; Figure 13(a) is a diagram showing a physical arrangement of addresses on a legitimate CD, and (b) is a physical arrangement of addresses on an illegally duplicated CD; Figure 14 is a diagram illustrating a piracy prevention algorithm; Figure 15 is a block diagram of a low-reflectivity position detector; Figure 16 is a diagram illustrating the principle of detecting address/clock positions of a low-reflectivity portion; Figure 17 is a diagram showing a comparison of low-reflectivity portion address tables for a legitimate disk and a duplicated disk; Figure 18A is a flowchart illustrating a procedure for encryption, etc. using an RSA function; Figure 18B is a flowchart illustrating a position information check process; Figure 19 is a flowchart illustrating a low-reflectivity position detecting program; Figure 20 is a diagram showing a detected waveform of a first-layer marking signal; Figure 21 is a diagram showing a detected waveform of a second-layer marking signal; Figure 22 is a diagram showing the arrangement of stripes on a disk and the contents of control data; Figure 23 is a flowchart illustrating how control mode is switched between CAV and CLV when playing back stripes; Figure 24 is a diagram showing a procedure for playing back a PCA area in a tracking ON condition; Figure.25 is a diagram for explaining barcode encryption; Figure 26 is a diagram showing a comparison of address coordinate positions on different master disks; We will first describe a general process flow from disk manufacturing to the completion of an optical disk by using the flowchart of Figure 1. 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 barcode, stripe, marking, or optical marking or, sometimes, as the physical ID unique to a 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 818a, a master disk is produced (step 818b), disks are pressed (steps 818e, 818g), reflective films are formed on the respective disks (steps 818f, 818h), the two disks are laminated together (step 818i), and a ROM disk such as a DVD or CD is completed (step 818m, 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 Figure 2, is formed (step 819a), and accurate position information of this mark is read by a measuring means (step 819b) 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 819c. The encrypted information is converted to a PE-RZ-modulated signal which is then recorded in step 819d 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 819c. 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 Figures 4 and 5 and Figures 8 to 12. A supplementary explanation will also be given dealing with a disk having two reflective layers with reference to Figures 6 and 7. In the following description, the marking formation process and the marking position reading process are collectively called the secondary recording process. First, the disk fabrication process will be described. In the disk fabrication process 806 shown in Figure 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. Next, the marking formation process will be described with reference to Figures 4 and 5. In Figure 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 Figure 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 Figure 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. At the rising edge of the thus obtained marking detection signal, a specific address (indicated by address n in Figure 5(d)) is read by the optical pickup from within the plurality of addresses shown in Figure 5(d). Figure 5(b) shows the physical location of the specific address in schematic form. On the other hand, Figure 5(e) shows the logical structure of the data. As shown in Figure 5(e), there are m frame synchronization signals under address n, and k reproduced clock pulses under each frame synchronization signal. Therefore, the position of the marking measured by the optical pickup can be represented by address, frame synchronization signal number, and reproduced clock count. As previously stated, a supplementary explanation will be given below of an alternative type of disk (a two-layer laminated disk) with reference to Figures 6 and 7. Figures 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, Figures 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. Parts (7), (8), and (9) of Figure 7 show the signal waveforms obtained from the first layer of the two-recording-layer disk. Likewise, parts (10), (11), and (12) of Figure 7 show the signal waveforms obtained from the second layer of the two-recording-layer disk. The contents of these signal waveforms are essentially the same as those of the waveforms described with reference to parts (a) to (c) of Figure 5. 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 Figures 8 to 12, etc., dealing with the laminated type in comparison with a single-plate type. Figures 8(a) and (b) are micrographs showing plan views of nonreflective optical marking portions, and Figure 10(a) is a simplified schematic cross-sectional view of a nonreflective portion of the two-layer laminated disk. (a) Using a 5 µ j/pulse YAG laser, a laser beam was applied to a 500angstrom aluminum layer lying 0.6 mm below the surface of a 1.2mm thick ROM disk consisting of two 0.6mm thick disks laminated together, and, as a result, a 12 µ m wide slit-like nonreflective portion 815 was formed, as shown in the X 750 micrograph of Figure 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 µ m wide, were observed along boundaries between the nonreflective portion 815 and reflective portions. As shown in Figure 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. Figure 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. And Figure 11 shows that the adhesive layer of the disk has been removed by using solvent. In the figure, if the aluminum film swollen portion is 1.3 µ m wide and 0.20 µ m thick, the amount of increased aluminum in that portion is 1.3 x (0.20 - 0.05) = 0.195 µ m 2 . The amount of aluminum originally deposited in a half portion (5 µ m) of the laser exposed region (10 µ m) was 5 x 0.05 = 0.250 µ m 2 . The difference is calculated as 0.250 - 0.195 = 0.055 µ m 2 . In terms of length, this is equivalent to 0.055/0.05 = 1.1 µ m. This means that an aluminum layer of 0.05 µ m thickness and 1.1 µ m 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. Next, the process of reading the position of the thus formed marking will be described. Figure 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. As shown in Figure 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, sinces 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 Figure 9(a), they can be clearly distinguished using a simple circuit. As shown in Figure 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 Figure 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 590a, for conversion into a digital signal. A clock regenerator 38a 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 38a, 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 Figure 16. As shown in the cross-sectional view of the optical disk in Figure 16(1), the low reflectivity portion 584 of mark number 1 is formed partially. A reflection selope signal such as shown in Figure 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 Figure 16(5), is output from the . low reflectivity light amount detector 586. As shown by a reproduced digital signal in Figure 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 Figure 16(6) is used along with address information. First, a reference clock 605 at address n in Figure 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 Figure 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 Figure 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 first converted into ciphertext or "signed" with a digital signature. Then, the marking position information thus encrypted or signed is converted into a barcode as an ID unique to the optical disk, and the barcode is recorded in overwriting fashion in a prescribed region of a pre-pit area on the optical disk. Barcode patterns 584c - 584e in Figure 2(a) indicate the barcode written to the prescribed region of the pre-pit area, that is, in the innermost portion of the pre-pit area. Parts (1) to (5) of Figure 3 show the process from the recording of the barcode to the demodulation of the barcode detection signal by a PE-RZ modulated signal demodulator. In part (1) of Figure 3, the reflective layer is trimmed by a pulsed laser, and a barcode-like trimming pattern, such as shown in part (2) of the figure, is formed. At the playback apparatus (player), an envelope waveform some portions of which are missing, as shown in part (3) of the figure, is obtained. The missing portions result in the generation of a low level signal that cannot occur with a signal generated from an ordinary pit. Therefore, this signal is sliced by a second slice level comparator to obtain a low-reflectivity portion detection signal as shown in part (4) of the figure. In part (5) of the figure, the playback signal of the barcode is demodulated from this low-reflectivity portion detection signal by the PE-RZ modulated signal demodulator 621 which will be described in detail in the second-half part (II). It will be appreciated that, instead of the PE-RZ modulated signal demodulator 621, a pulse-width modulated signal demodulator (PWM demodulator) may be used, in which case also, a similar effect can be obtained. When applying the above encryption or digital signature, a secret key of a public key encryption function is used. As an example of the encryption, Figures 18A and 18B show an encryption process using an RSA function. As shown in Figure 18 A, the process consists of the following major routines: step 735a 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 735w where a check is made to determine whether the disk is a legitimate optical disk or not. First, in step 735a, the marking position information on the optical disk is measured in step 735b. The position information is then compressed in step 735d, and the compressed position information H is obtained in step 735e. 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 695b, 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 695d, the ciphertext C is recorded on the optical disk. The optical disk is thus completed and is shipped (step 735k). In the reproduction apparatus, the optical disk is loaded in step 735m, and the ciphertext C is decrypted in step 698. More specifically, the ciphertext C is recovered in step 698e, and public keys, e and n, are set in step 698f; 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 698g. 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 735w shown in Figure 18 B. If an error is detected, it is decided that the data is not legitimate one, and the operation is stopped. In the next step 736a, the compressed position information H is expanded to recover the original position information. In step 736c, 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 736d, 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 736e, the process proceeds to step 736h 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 736g. RSA has the effect of reducing required capacity since only the ciphertext need be recorded. 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 Figure 14. 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. Namely in this case, the marking reading means 9106 checks whether the marking is actually located in the position on the optical disk indicated by the position information which is decrypted by the decrypting means 9105. 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 . In the present invention, as shown in Figure 22, the control data recorded in the control data area 936 of the optical disk contains a PCA stripe presence/absence identifier 937 recorded as a pit signal. Therefore, the optical head is first moved, in step 940n, to an outer area where the control data is recorded. And then the optical head moves inwardly jumping across a plurality of tracks until reaching the control data area 436. And then in step 940a, the control data is played back. It can thus be checked whether the stripes are recorded or not. If, in step 940b, the stripe presence/absence identifier is 0, the process proceeds to step 940f to initiate rotation phase control for normal playback with CLV. On the other hand, if, in step 940b, the presence/absence identifier 937 is 1, then the process proceeds to step 940h to check the presence or absence of a reverse-side record identifier 948 which indicates that the stripes are recorded on the side opposite from the side being played back, that is, on the reverse side. If the stripes are recorded on the reverse side, the process proceeds to step 940i to play back the recording surface on the reverse side of the optical disk. If the reverse side cannot be automatically played back, an indication is output for display, to urge the user to turn over the disk. If it is determined in step 940h that the stripes are recorded on the side being played back, the process proceeds to step 940c, where the head is moved to the stripe area 923 in the inner portion of the disk, and in step 940d, the control mode is switched to rotational speed control to play back the stripes 923 with CAV rotation. If the playback is completed in step 940e, then in step 940f the control mode is switched back to rotation phase control for CLV playback and the optical head is moved to the outer portion of the disk to play back pit signal data. Since the stripe presence/absence identifier 937 is recorded in the pit area holding the control data, etc., as described above, the second method has the effect of being able to play back the stripes more reliably and more quickly compared to the first playback method described with reference to Figure 23. When the PCA area is with tracking OFF, level of the noise signal which is generated by the pits drops. PCA signal level remains unchanged if tracking is set 0FF. Therefore, in the filtered waveform, the pit signal drops, making it easier to distinguish between the PCA signal and the pit signal. This has the effect of simplifying the circuitry and reducing the error rate. Furthermore, the provision of the stripe reverse-side record identifier 948 makes it possible to identify that the stripes are recorded on the reverse side of the disk; the effect is that the barcode stripes can be played back reliably in the case of a double-sided DVD optical disk. According to the present invention, since the stripes are recorded penetrating through the reflective films on both sides of a disk, the stripe pattern can also be read from the reverse side of the disk. The stripes can be played back from the reverse side of the disk by checking the stripe reverse-side identifier 948 and by playing back the code in the reverse direction when reading the stripes. The present invention uses a bit string "01000110" as the synchronization code. When played back from the reverse side, the synchronization code is played back as "01100010", from which it can be detected that the barcode is being played back from the reverse side. In this case, by demodulating the code in reverse direction, in the demodulator 942 in the playback apparatus of Figure 15, the barcode recorded in penetrating fashion can be correctly played back even if played back from the reverse side of a double-sided disk. The playback apparatus of Figure 15 will be described in more detail later. The playback operation will be described with reference to Figure 24. When a disk is inserted, the optical head is moved to the inner circumferential portion in step 947a. If no tracking is achieved in step 947n, the tracking mode is switched from phase control to push-pull mode in step 947p. In step 947b, rotational speed control (CAV control) is performed to play back address information. If an address cannot be played back in step 947c, the process proceeds to step 947i to move the optical head inward to play back the PCA stripes. If an address can be played back from an empty portion of the PCA area (a portion not overwritten), the process proceeds to step 947e where, based on the address, the optical head is moved in a radial direction to the address area where stripes are recorded. In step 947q, the presence or absence of PCA stripes is checked. If it is judged that there are no PCA stripes, the process proceeds to step 947r to try to read a PCA flag in the control data. Then, in step 947s, the presence or absence of the PCA flag is checked. If the presence of the PCA flag is detected, the process returns to step 947c; otherwise, the process jumps to step 947m. On the other hand, if it is judged in step 947q that there are PCA stripes, the process proceeds to step 947f to play back the PCA stripes. When the playback is completed in step 947g, then the mode is switched to rotation phase control and the optical head is moved to the outer area to play back a pit signal. In step 947t, the PCA flag in the control data is read; if there is no PCA flag, an error message is issued in step 947k, and the process returns to 947m to continue the process. Figure 15 is a block diagram of the playback apparatus already described above. Whereas above, the apparatus has been described as an apparatus for reading the position of a marking formed on the reflective film of an optical disk, but hereinafter, the apparatus of Figure 15 will now be described as a barcode reading apparatus, that is, a playback apparatus. An explanation will be given again referring to Figure 15, this time focusing on the demodulation operation. First, high-frequency components generated by pits are removed by a low-pass filter (LPF filter) 94 from a stripe signal output. In the case of a DVD, there is a possibility that a maximum 14T signal may be played back, where T = 0.13 µ m. In this case, it has been confirmed by experiment, a stripe signal and a high-frequency component generated by a pit can be separated by using a second-order or third-order Chevihov low-pass filter. That is, the use of a second- or higher-order LPF has the effect of being able to separate a pit signal and a barcode signal, thus ensuring stable playback of a barcode. In this way, by using the second- or higher-order LPF 943, the stripe playback signal can be output after substantially removing the pit playback signal; this ensures reliable demodulation of stripe signals. However, if the width of a stripe signal thus demodulated is smaller than the sampling interval width tm of a microcomputer, the stripe signal may not be measured accurately. To avoid this, a stripe signal obtained by reading a stripe is waveshaped using a flip-flop circuit so that the signal width becomes greater than the microcomputer sampling interval width tm. Referring back to Figure 15, a further description will be given. Digital data is demodulated by the PE-RZ demodulator 942 in the above manner. The data is then fed to an ECC decoder 928 for error correction. That is, deinterleaving is performed in a deinterleaver 928a, and Reed-Solomon code computation is performed in an RS decoder 928b for error correction. Next, an example of the above-described barcode encryption (including digital signature) will be described with reference to drawings, followed by a description of another application example of the barcode. First, the barcode encryption process and playback process will be described by way of example with reference to Figure 25. As shown in Figure 25, an ID number 4504 unique to each individual optical disk is generated by an ID generator 4502. At the same time, an ID signature section 4503 applies a digital signature to the ID number by using a specific secret key corresponding to a specific public key, and the thus applied digital signature 4505 and its associated ID number 4504 are sent together as a series of data to a press factory 4501. This digital signature is applied to the ID number encrypted in an encryption encoder 4508 using a secret key of a public key encryption function. The public key corresponding to this secret key is sent to the press factory 4501. At the press factory 4501, the ID number and its corresponding digital signature 4505 are recorded as a barcode in the PCA area of an optical disk 4506 by using a PCA writer 4507. The public key is prerecorded on the master disk, that is, in a pit portion of the disk. When the thus manufactured optical disk 4506 is loaded into a playback apparatus (player) 4509, the public key is read from the pit portion, and the ID number and the digital signature appended to it are read from the PCA area and decrypted with the public key. The result of the decryption is passed to a verification section 4511; if the digital signature data is found legitimate as the result of the verification, the playback operation of the optical disk is allowed to continue. If the digital signature data is found illegitimate as the result of the verification, the operation is stopped. Here, if the digital signature data is recorded in the PCA area together with the plaintext of the ID, the result of the decryption is checked against the plaintext of the ID to see if they match. If the digital signature data only is recorded in the PCA area, an error check is performed for verification. When the data is encrypted with public key cipher, as described above, only the software manufacturer that has the secret key can issue a new ID number. Accordingly, if pirated disks were made, the encrypted ID of the same number would be recorded in the PCA area of every disk; therefore, the use of such pirated disks would be greatly limited. The reason is that, in such cases, the illegal use of the software having the same number can be prevented by applying network protection. Needless to say, the above method described with reference to Figure 25 can also be used in the Internet. A low reflectivity portion address table, which is a position information list for the low reflectivity portion, will be explained. 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 µ m in the case of a DVD, to construct a low reflectivity portion address table 609 as shown in Figure 13(a). Here, Figure 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 Figure 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 Figure 18, and in the second reflective-layer forming step, a series of low reflectivity portions 584c to 584e, where the reflective layer is removed, is recorded in a barcode-like pattern on the innermost portion of the disk, as shown in Figure 2. Figure 18 is a flowchart illustrating a disk check procedure by the one-way function used for the encryption. As shown in Figure 13, the legitimate CD and the illegally duplicated CD have the low reflectivity portion address tables 609 and 609x, 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 Figure 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 A1, as shown in the address table 609. In the case of a DVD, one clock is equivalent to 0.3 µ m, 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 81st clock position in the sector of address A2, as shown in the address table 609x. 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 of address A1 must be formed with an accuracy of one clock unit, i.e., 0.13 µ m; otherwise, the pirated disk cannot be run. In the example of Figure 16, the legitimate disk and illegally duplicated disk have low reflectivity portion address tables 609 and 609x respectively, where values are different as shown in Figure 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 Figure 16(8), whereas in the case of the illegally duplicated disk these are m+24 and m+277, respectively, as shown in Figure 16(9). Therefore, the corresponding values in the low reflectivity portion address tables 609 and 609x are different, as shown in Figure 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 Figure 16(8). As shown in Figure 20(5) showing the waveform of a PLL reproduced clock signal out of reproduced optical signals, in the case of a DVD disk the period T of one reproduced clock pulse, when converted to a distance on the disk, that is, one pulse spacing on the disk, is 0.13 µ m. Accordingly, to make an illegal copy, the reflective film will have to be removed with a submicron resolution of 0.1 µ m. 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 Figure 9(c), and the distinct waveform 824 as shown in Figure 9(a) cannot be obtained unless the reflective film is removed. 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 semiconductor mask corrections, it is said that 1 µ m is the limit of the processing accuracy. This means that it is difficult to achieve a processing accuracy of 0.1 µ m at the mass production level. As a second method, X-ray exposure equipment for processing semiconductor 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. 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. 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 Figure 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 µ m in the case of the DVD standard, by using a conventional player, thereby to accurately measure the optical mark of the present invention. Figures 20 and 21 show the optical mark address reading method of Figure 16. Explanation of signals (1), (2), (3), (4), and (5) in Figures 20 and 21 will not be given here since the operating principle is the same as that shown in Figure 16. The correspondence between Figure 16, which illustrates the principle of the detection operation for detecting the position of a low reflectivity portion on a CD, and Figures 20 and 21, which are concerned with a DVD, is given below. Figure 16(5) corresponds to Figures 20(1) and 21(1). The reproduced clock signal in Figure 16(6) corresponds to that shown in Figures 20 (5) and 21(5). Address 603 in Figure 16(7) corresponds to that shown in Figures 20(2) and 21 (2). Frame synch 604 in Figure 16(7) corresponds to that shown in Figures 20 (4) and 21 (4). Starting clock number 605a in Figure 16(8) corresponds to reproduced channel clock number in Figure 20 (6). Instead of the end clock number 606 in Figure 16(7), in Figures 20(7) and 21(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 603a as shown in Figure 20(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 µ m, which increases the resolution for the detection of the position information and thus provides a greater anti-piracy effect. Shown in Figure 20 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. Figure 21 shows the condition of the signal from the second layer. To read the second layer, a first/second layer switching section 827 in Figure 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 Figure 20, 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 µ m on a conventional consumer DVD player. As described above, 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 µ m 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 µ m, while the required processing accuracy is two or three orders of magnitude lower, that is, several tens of microns. This means that a convectional 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 µ m. 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 µ m, 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. Figure 26 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 Figure 26, 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 Figure 26, 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. Figure 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 Figure 26, 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 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. Figure 19 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 Figure 20, 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 of 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 Figure 19. In Figure 19, the disk is reproduced in step 865a to recover the encrypted position information from the barcode recording portion or pit recording portion of the present invention. In step 865b, decryption or signature verification is performed, and in step 865c, 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 608a in the reproduction apparatus of Figure 15, TD is read out in step 865h and the process proceeds to step 865x. If TD is not stored in the reproduction apparatus, or if a measurement instruction is recorded on the disk, the process proceeds to step 865d 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 865f, the reference optical mark is detected. In step 865g, the circuit delay time TD is measured and stored. This operation is the same as the operation to be described later with reference to Figure 16(7). In step 865x, the optical mark located inside address Nm is measured. In steps 865i, 865j, 865k, and 865m, the optical mark position information is detected with a resolution of one clock unit, as in steps 865d, 865y, 865f, and 865y. Next, in step 865n, a pirated disk detection routine is entered. First, the circuit delay time TD is corrected. In step 865p, the tolerance 866, i.e., tA, and pass count 867 recorded on the disk, as shown in Figure 20, are read to check whether or not the position information measured in step 865g falls within the tolerance tA. If the result is OK in step 865r, then in step 865s it is checked whether the checked mark count has reached the pass count. If the result is OK, then in step 865u 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 865z. If the result is NO in step 865r, then it is checked in step 865f whether the error detection count is smaller than NA, and only when the result is OK, the process returns to step 865s. If it is not 0K, then in step 865v 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. As described in the above mode of embodiment, the piracy prevention method at the reflective layer level forms a physical mark in the pre-pit area of the reflective film on the disk, instead of the previously practiced physical marking at the master disk level. Pirated disk production can thus be prevented even if the disk is duplicated at the master disk level. In the above mode of embodiment, a new optical-disk recording means was used that performs secondary recording on a two-disk laminated optical disk by using a laser. In the first step, physical marks were randomly formed, and in the second step, the physical marks were measured with a measuring accuracy as high as 0.13 µ m. In the third step, their position information was encrypted and, using the secondary recording means, the encrypted information was recorded as a barcode on the optical disk with an accuracy of several tens of microns which was the usual processing accuracy. In this way, optical mark position information was obtained with an accuracy of, for example, 0.1 µ m, much higher than the processing accuracy of a conventional apparatus. Since such optical marks cannot be formed with the accuracy of 0.1 µ m by using commercially available equipment, production of pirated disks can be prevented. In an application mode, the barcode is used for a pirated-disk prevention method. In this case, as shown in Figure 2, the barcode (stripes) 584c - 584e is written over the prescribed region (stripe area) of the prepit area; therefore, the tracking is disturbed in that prescribed region. If a marking 584 by laser light is formed in the prescribed region where the barcode, 584c - 584e, is recorded, as shown in Figure 2, it becomes difficult to accurately measure the address/clock position of the marking. To avoid this problem, if the marking 941 is formed in a pit area 941a at a radius position different from the radius position of the stripe area 923a, the position of the marking 941 can be measured stably with an accuracy of one clock, as shown in Figure 20 (5). This has the effect of being able to identify pirated disks more stably.

Claims: An optical disk on which data is recorded and comprising a location (923) for receiving a barcode-like mark (9104) extending in a circumferential direction and having a plurality of bars (923a, 923b...) each extending in a radial direction, characterized in that said optical disk further comprises an identifier (937) for indicating whether a barcode-like mark is present or not on said location (923) of the disk, said identifier (937) being provided in a pit area holding control data (936) and in that a marking (9103) is provided on an information layer of said disk and in that position information of said marking (9103) is encrypted or applied with a digital signature and included in said barcode-like mark (9104). An optical disk according to claim 1, wherein one of said bars (923a), where present, has a lower reflectivity than an average reflectivity of an area between said one of said bars (923a) and another of said bars (923b). An optical disk reproduction apparatus for use with a disk according to claim 1 or 2 characterized by comprising: reproduction means (9106) for reproducing said barcode-like mark (9104) on said optical disk (9102), identifier detection means (9106) for detecting said identifier (937) on said optical disk, and control means (9107) for controlling a prescribed operation based on the contents of said identifier (937) detected by said identifier detection means (9106), wherein said reproduction means includes an optical head for performing reproduction, positional information read-out means (9101) for reproducing, from said barcode-like mark (9104), information regarding the position of said marking (9103), and marking measurement means (9106) for determining an actual position of said marking (9103), and reproducing means (9107) for reproducing data recorded on said optical disk (9102) based on a comparison of a) said information reproduced by said positional information read-out means (9101), and b) said actual position determined by said mark measurement means (9106). The optical disk reproduction apparatus according to claim 3, wherein said positional information read-out means (9101) decrypts the information obtained from said barcode-like mark (9104).

Inventors: GOTOH YOSHIHO, KOISHI KENJI, MORIYA MITSURO, OSHIMA MITSUAKI, TANAKA SHINICHI, GOTOH, YOSHIHO, KOISHI, KENJI, MORIYA, MITSURO, OSHIMA, MITSUAKI, TANAKA, SHINICHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1996
Main classification: G11B7
IPC codes: G11B20, G11B19, G06K19, G11B5, G11B7, G11B23, G11B27, G06K1, G11B13