WO2007065995A1

WO2007065995A1 - System for securing by diffractively digitally encoding optical discs

Info

Publication number: WO2007065995A1
Application number: PCT/FR2006/002650
Authority: WO
Inventors: Idriss El Hafidi; Bernard Kress; Mandiaye Ndao; Patrick Meyrueis
Original assignee: Universite Louis Pasteur, U.L.P.
Priority date: 2005-12-06
Filing date: 2006-12-05
Publication date: 2007-06-14
Also published as: FR2894371B1; FR2894371A1

Abstract

The invention relates to a security system compatible with a standard reader provided with an updated firmware preventing from unauthorisedly accessing an optical disc data. Said system consists of at least one digital diffractive element which is carried by the optical disc and is readable by a four-cell detecting sensor of the standard reader reading head, wherein the set of the digital diffractive elements forms a diffractive code, and the optical reader firmware for carrying out a method for verifying the authenticity of said optical disc and for authorising the access to said data by comparing the diffractive code with a computer code.

Description

Security system by digital diffractive coding for optical discs.

The present invention relates to a security device by digital diffractive coding making it possible to prevent unauthorized access to the data stored on an optical recording medium, in particular of compact disc, audio, video or computer type.

The invention also relates to an optical audio, video or computer disc, more commonly called compact disc, CD, DVD, CDROM, DVDROM or other, having such a security system by digital diffractive coding.

Finally, the invention relates to a method for verifying the authenticity of an optical disc and authorizing access to its data.

The object of the invention is to provide a security system preventing illegal, unauthorized or unauthorized reading, writing or copying of audio, video or computer data from or onto a protected optical disc.

According to an essential aspect of the invention, this security system is compatible with current conventional devices for reading or using these optical discs. That is to say that the security system according to the invention, as well as the protected discs according to the invention operate with a suitable conventional reader, intended for unprotected optical discs, without modification or replacement of the physical elements constituting it. Only a simple firmware update, commonly called "firmware", managing the operation of the player is necessary.

To prevent the illegal use or copying of optical discs, there are currently several systems on the market. There are for example computer software, in particular video games, for which a code must be entered allowing the installation and the use of the software. Such a system based solely on computer code is unreliable and can easily be hacked. In addition, the original optical disc being conventional, nothing prevents to make a copy on a blank disc, which is very easily found in commerce, and to give with it the code which is generally supplied with the original record.

We also find software that is sold with a physical key constituting an unlock code. Such a system is much safer, but has a particularly high cost. In addition, it remains reserved for computer disks, the physical key having to be introduced into a port of the computer, for very specific software.

Also found in the prior art and for example in US Patent 6,226,109, optical discs which include a holographic mark to distinguish an original disc from a copy. Such a distinctive mark does not, however, prohibit access to data or unauthorized copying. In addition, this mark is not recognized by the optical disc drive. It is visible to the naked eye or becomes visible using a specific independent device.

Also known, in particular from applications WO 03/032300 and US 5,917,798, optical disks which, to prevent unauthorized reading of their content, include two media or data storage layers: a first conventional optical medium and a second analog holographic medium.

The data carried by these discs is divided into two parts. A first part of this data is recorded in the optical storage medium and can be read by a conventional optical read head.

The second part of the data is recorded in the holographic medium in the form of diffractive data. A specific read head corresponding to an appropriate holographic technology is then necessary to read them.

The complete information carried by the disc is a combination of these two types of data. Two read heads are therefore necessary to obtain the final data. A combined read head is proposed alternatively in US patent 5,917,798. However, this read head is very specific and absolutely does not correspond to the standard read head comprising a detector with four detection cells which is found in conventional readers.

Such a method of protecting optical discs therefore does not make it possible to achieve the essential objective of the invention, namely to provide a protection system compatible with current standard readers.

The holographic marks and diffractive data disclosed in the prior art for the purpose of authentication or protection of optical discs are each time analog diffractive components, namely components produced by the interference of two light beams from a coherent laser source, recorded in a photosensitive medium.

On the contrary, the invention uses digital diffractive elements, that is to say made from a digital computation by computer, then an engraving, for example according to the microlithography technique or that of direct writing by laser beam.

To solve the technical problem previously exposed, the invention provides a security system by digital diffractive coding making it possible to prevent unauthorized access to the data stored on an optical recording medium, in particular of optical, compact, audio, video type. or IT.

This system is compatible with an appropriate conventional optical reader without modification of the physical elements constituting this reader and by means of a simple update of the firmware “firmware” managing its operation.

According to the invention, this system is a combination between:

- at least one digital diffractive element carried by the optical recording medium, which can be read by the detector with four detection cells of the standard read head of the optical reader; and

the firmware of the optical reader which is intended to implement a method of verifying the authenticity of the optical recording medium and authorizing access to its data, by comparison of at least one digital diffractive element carried by the optical recording medium with a computer code.

The security system according to the invention being a combination between the digital diffractive microstructures of the optical disc and the “firmware” firmware of the reader, its hacking is much more difficult because it is necessary to act on these two aspects.

The system according to the invention is thus much more reliable than existing systems, all remaining at a reasonable cost. In addition, it is perfectly compatible with conventional reading devices.

The invention also provides an optical disc, in particular of the compact disc, audio, video or computer disc type, comprising three concentric zones, respectively from the center to the periphery: an inner ring constituting the starting zone of the optical disc and containing functional information intended in the firmware of the reader, a central zone intended for the data stored on the optical disc and an external crown, constituting the end zone of the optical disc.

According to the invention, it comprises at least one digital diffractive element, which can be read by the detector with four cells for detecting the standard read head of a suitable conventional optical disc player, all of the digital diffractive elements of the disc. optic forming a diffractive code.

In a preferred embodiment, the optical disc according to the invention may also include one or more of the following characteristics:

- At least one digital diffractive element is located on the outer ring of the optical disc.

- At least one digital diffractive element is a microstructure formed by a succession of hollows and bumps.

- This microstructure is produced by molding during manufacture by injection molding of the optical disc.

- At least one diffractive element has a substantially square or rectangular outline.

- The optical disc has at least one element digital diffractive in which the diffractive information is repeated several times in order to improve the intensity of the detected signal.

- The optical disc includes at least one binary digital diffractive element.

- The optical disc includes at least one digital diffractive element with at least four phase levels.

- The inner crown contains information or instructions allowing the optical disc reader to implement a method of verifying the authenticity of the optical disc and authorizing access to its data using the diffractive code.

The invention also teaches a method of verifying authenticity and authorizing access to the data contained on an optical disc according to the invention and in particular of compact disc, audio, video or computer type.

This process can be implemented by a conventional suitable optical disc reader without modification of the physical elements constituting this reader and by means of a simple update of the firmware “firmware” managing its operation.

It comprises the following stages:

- Positioning of the read head of the optical disc player facing the first digital diffractive element carried by the optical disc;

- reading of the digital diffractive element by the detector with four cells for detecting the read head and storing its value;

- possible repetition of the two previous steps for the next digital diffractive element until all the digital diffractive elements carried by the optical disc have been read, the set of stored values forming the code W

diffractive;

- verification of the diffractive code by comparison with a computer code stored in the optical disc drive;

- depending on the result of the previous step, refusal or authorization of access, total or partial, to the data contained on the optical disc.

According to a preferred variant of the invention, the method can also comprise at least one of the following steps:

- defocusing of the lens of the reading head of the optical disc player.

- decrease in the speed of rotation of the optical disc.

- Reading of the instructions and information concerning the implementation of the process located in the inner ring of the optical disc.

- Computer code entry.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, description made with reference to the appended drawings, in which:

. Figure 1 is a schematic front view of an optical disc illustrating different possible locations for the diffractive elements according to the invention;

. Figure 2 is a schematic front view of an example of an optical disc according to the invention;

. Figure 3 is an enlargement of the circled detail of Figure 2 and shows an example of a diffractive element according to the invention;

. Figure 4 is a schematic sectional view of an optical disc having a diffractive element according to the invention in front of which is a read head in the focused state;

. Figure 5 is a schematic sectional view of a optical disc having a diffractive element according to the invention in front of which is a read head in the defocused state;

. FIG. 6 is a schematic view illustrating the various possibilities of lighting the four-cell detector of a standard read head for a binary digital diffractive element;

. FIG. 7 is a schematic view illustrating the different possibilities of lighting the four-cell detector of a standard read head for a diffractive element with at least four phase levels;

. FIG. 8 is a schematic diagram illustrating the different stages of the method of verifying authenticity and authorization according to the invention.

The security device according to the present invention will now be described in detail with reference to Figures 1 to 8. The equivalent elements shown in the different figures will have the same reference numerals.

In Figure 1, an optical disc 1 has been shown schematically. Conventionally, this is in the form of a flat disc pierced with a circular opening 2 at its center. It has three concentric zones, respectively from the center to the periphery: an inner ring 3, a central area 4 and an outer ring 5.

The inner ring 3, commonly called "lead-in", constitutes the starting area of the optical disc 1 and contains functional information such as the size of the disc, a certain number of addresses and operating instructions intended for the firmware. " In addition to the normal information found in a conventional optical disc, the inner ring 3 of the disc optical device according to the invention contains a certain number of information and instructions allowing the optical disc player to implement the method of verifying authenticity and authorization according to the invention. These instructions will be explained below during the detailed description of the process according to the invention.

The central area 4 is reserved for the data stored on the optical disc. When the optical disc 1 is still blank, this zone contains a spiral track (not shown) along which the data must be written.

The outer ring 5, also called "lead-out", constitutes the end zone of the optical disc. It does not contain data, but only end information so that the reader understands that it has reached the end of the data.

According to the invention, this optical disc 1 must comprise at least one digital diffractive element 6, and preferably a plurality of these elements 6.

The digital diffractive elements 6 can be located anywhere on the optical disc 1 accessible to the read head 7 of a standard optical disc player.

Depending on the applications, these diffractive elements 6 can be located in any one of these three zones, or even be distributed in several of these zones. Different examples of possible locations for these diffractive elements 6 have been shown in FIG. 1.

The diffractive elements 6 must be located in locations not occupied by data. The inner crown 3, of small area and containing the functional data, offers a limited space for the diffractive elements 6 but can still be used when these are few.

Likewise, when the diffractive elements 6 are located in the central zone 4, they reduce the surface available for data storage. However, the central zone 4 can still be used when the data does not occupy its entire surface.

The outer ring 5 is therefore the preferential location area for the diffractive elements 6, because it contains little information and offers a large unoccupied area. A non-limiting example of such an installation has been shown in FIG. 2.

Each diffractive element 6 is a microstructure, molded in the optical disc 1 and preferably formed by a succession of hollows and bumps, which when illuminated by the laser beam 8 of a read head 7 projects by diffraction a signal optical capable of being picked up and recognized by the detector 9 of the read head 7.

An example of such a digital microstructure has been shown in the enlarged state in FIG. 3.

The example of microstructure 6 represented has a generally square contour that is substantially square. However, it can have any other suitable shape and for example a substantially rectangular contour advantageously allowing the diffractive information to be repeated several times in order to improve the intensity of the detected signal.

These microstructures are very small, their radial length ranging from a few tens to a few hundred microns, for example around fifty microns. A smaller size, more difficult to achieve, is however possible and even advantageous. Indeed, the microstructure is more difficult to copy. In addition, it requires less movement of the lens 10 of the read head 7, which makes the verification method according to the invention faster.

The tangential length of the digital diffractive microstructures 6 is slightly greater and varies from a hundred microns to a few millimeters depending on whether the diffractive information is repeated or not and as a function of the sensitivity of the detector 9 and of the time required for reading. of the digital diffractive element.

These digital diffractive microstructures are produced during the manufacture of the optical disc 1 by molding, before writing the data thereon or simultaneously with the latter when the data are directly molded during the step of injecting the optical disc.

To produce a digital diffractive element 6 according to the invention on an optical disc 1, a matrix is used, making it possible to produce the optical disc in series by molding, on the surface of which is engraved in three dimensions a digitally generated diffractive component. This diffractive component constitutes the inverted relief of the diffractive element 6 to be obtained.

The path of this diffractive component is previously calculated and optimized by computer. In general, one uses for this an iterative optimization method of the phase of the diffractive element to calculate.

For the design of the diffractive elements according to the invention, an iterative Fourier transformation algorithm is preferably used to find the phase of the image from the intensity distribution.

This algorithm, based on the algorithm of Gerchberg-Saxton, involves performing a number of back and forth movements between the plane of the diffractive element and the reconstruction plane, generated by specific propagators using Fourier transformations. Constraints are applied in each plane on the amplitude or on the phase. This operation is repeated in a loop until satisfactory optimization of the desired diffractive element is obtained.

Two main etching techniques can then be used to produce the matrix used to mold the diffractive element 6.

The first, called direct writing technique by laser beam, corresponds to the classic technique used to carry out on the matrix the inverted plot of the spiral track used for data recording. According to this technique, the trace of the diffractive component, developed as previously exposed by specific software, is recorded using a laser beam on a layer of photosensitive resin, commonly called “photoresist”. After development and chemical stripping, the inscribed line appears in hollow and in reliefs. The photosensitive resin is then covered by electrodeposition with a thin layer of nickel which reproduces the reliefs and hollows of the initial layer. This layer of nickel, after detachment and reinforcement, constitutes the matrix used to mold the optical discs of plastic material with their digital diffractive elements.

The second technique that can also be used is the microlithography technique which consists in etching a silicon layer by means of an electron beam. This layer is then used as a mask to transfer the engraved pattern onto a layer of photosensitive resin, illuminating the photosensitive resin through the etched silicon layer.

As before, the resin layer is, after chemical development and pickling, coated with a fine layer of nickel reproducing its relief, which, after reinforcement, is used to form the molding matrix.

By the microlithography technique, it is advantageous to produce smaller, more precise microstructures and have better resolution. This technique is however much more expensive.

The matrix obtained by any one of these methods makes it possible to injection mold the base layer 11 made of plastic of the optical discs 1. This base layer 11 has, on its surface, in relief and / or in hollow, the digital diffractive element (s) 6 according to the invention, the spiral track for recording the data, as well as possibly the data themselves.

To form the optical disc 1, this base layer 11 is covered with a layer of sensitizing material 12, commonly called a “dye”, subsequently making it possible to write the data thereon by etching by means of local lighting by a laser beam. The assembly is then coated with a thin reflective metallic layer, then with a transparent protective layer 13 of varnish or of plastic material, for example of polycarbonate.

When the diffractive element 6 is illuminated by the laser beam 8 of the read head 7, it projects by diffraction an optical signal programmed at conception, picked up by the detector 9 of the read head 7.

According to one of the essential objectives of the invention, the optical disc 1 according to the invention is compatible with a conventional reading device. The signal projected by the diffractive element 6 must therefore be able to be detected and recognized by a standard detector 9 fitted to these reading devices.

Such a standard detector 9 is conventionally composed of four detection cells 14 arranged so as to substantially form a square as illustrated in FIGS. 6 and 7.

The digital diffractive element 6 is produced so as, when it is lit by the laser beam 8, to project onto at least one of the detection cells 14 a spot of light 15 detectable by the latter.

Depending on the pattern of the diffractive element 6, one or more detection cells 14 are lit. The detector 9 comprising four cells 14, several lighting possibilities are offered by varying the number and the location of the light spots 15 generated by the diffractive element 6.

The lighting possibilities resulting from the detector depend on the number of phase levels (etching) when the digital diffractive element 6 is produced.

With two phase levels (binary diffractive element), the resulting lighting respects a symmetry relative to the center of the detector 9 with four cells 14, which limits the number of possibilities of resulting lighting. In this case, there are three possible lighting possibilities which have been shown diagrammatically in FIG. 6.

With four or more phase levels (etching), this limitation does not exist and the number of possibilities is much higher as can be seen in FIG. 7. To obtain four or more phase levels (etching), the realization of the element diffractive 6, however, requires a resolution much higher than that required to obtain only two. The difficulty and the cost of producing this digital diffractive element may therefore be increased.

A value, preferably a number, but which can also be a letter or any other suitable symbol, is assigned to each lighting possibility of the detector 9 and thereby to the type of digital diffractive element 6 programmed to generate such a configuration of lighting.

The set of values of all the digital diffractive elements 6 of an optical disc 1 according to the invention constitutes a code, preferably digital or alphanumeric, called the diffractive code. This diffractive code is the signature of the optical disc 1 and constitutes proof of its authenticity and its origin.

The number of possible values being structurally limited (three or fifteen depending on the number of phase levels), to multiply the possibilities of code, it suffices to increase the number of digital diffractive elements 6 present on the optical disc 1 according to the invention. The size of this code is however limited by the space available in the memory of the reader.

The method of verifying authenticity and authorization according to the invention will now be described with reference to FIG. 8.

This process begins with a first step of reading the diffractive code written on the optical disc 1 according to the invention.

When an optical disc 1 according to the invention is inserted into an optical disc player, the read head 7 begins by reading the operating instructions located in the inner ring 3, these instructions being analyzed by the firmware of the reader.

These instructions oblige the firmware to start by moving the read head towards the location where the diffractive elements 6 are located, preferably towards the outer crown 5. Advantageously, the exact address of each diffractive element 6 can be indicated in the inner crown 3.

After reading the instructions of the inner crown 3, the read head 7 is therefore positioned opposite the first diffractive element 6. To control this positioning, the firmware uses the address read previously or any optical reference being found in the area indicated.

The read head is then in the configuration illustrated in FIG. 4. The read head 7 is usually adjusted to read the data written on the disc in the form of micro-modulations of the surface, the size of which is of the order micron. The lens 10 is therefore positioned so as to focus the laser beam 8 on this data.

With such a read head 7 adjustment, the diffractive element 6, of larger dimensions than a conventional datum of the optical disc, is not entirely illuminated by the laser beam 8. The lens 10 must therefore be defocused to that the laser beam widens and fully illuminates the diffractive element 6. For this, the firmware “firmware” causes the lens 10 to approach the surface of the optical disc 1 as shown in FIG. 5.

It is thus advantageous to produce the smallest possible diffractive elements 6, even if the molding die is more difficult to produce and therefore more expensive. Indeed, the smaller these elements are and approach their size to that of the data, the less the lens will need to move during the defocusing operation. The process thus gains speed. In addition, the smaller the diffractive elements, the more difficult they are to reproduce.

When it is fully lit by the laser beam 8, the digital diffractive element 6 projects by diffraction light spots 15 onto the detector 9 of the read head 7. The value of this diffractive element is thus read, then recorded in the optical disc drive memory.

For the reading of the value of the diffractive element to be carried out under good conditions and without risk of error, it is preferable that the speed of rotation of the optical disc 1 is not too high during the reading phase in order to remain compatible with the standard data processing capacities of conventional readers. Even more preferably, the optical disc 1 can be stopped during this reading phase.

The method according to the invention can thus advantageously comprise at least one step of reducing the speed of rotation of the optical disc.

The read head 7 is then positioned in front of the second digital diffractive element 6, its value is detected and stored in memory as before. Of course, this positioning does not necessarily require displacement of the read head 7, but can be achieved simply by a rotational movement of the optical disc 1.

The procedure described above is repeated until the values of all the elements digital diffractive 6 of the optical disc 1 are detected and recorded.

The lens 10 of the read head 7 must be in the defocused state to allow the reading of each of the diffractive elements 6 of the optical disc 1. It can advantageously remain in this defocused state after the reading of the first diffractive element 6 and up to 'that all of the diffractive elements 6 have been read, without needing to replace themselves in the focused state between each element. The step of reading these elements is thus simplified and gains speed.

However, it can perfectly be envisaged that the lens 10 is refocused and then defocused again from time to time or even between each digital diffractive element 6. It is thus possible, for example, to verify the correct positioning of the read head on the optical disc 1 before reading the next diffractive element 6.

All of these detected and recorded values form a global code, called a diffractive code. During a second step of verifying the diffractive code, this code is compared by the “firmware” firmware to another code, called computer code, also in memory in the reader.

This computer code may have been previously entered by the user in the memory of the reader or may, for example, be part of the “firmware” firmware. This computer code is made available, by any suitable means imaginable, to any person who has legally purchased the optical disc or is authorized to use it. It can thus for example be downloaded in a secure manner or be given by a call center. If the diffractive code detected on the optical disk 1 is identical to the computer code stored in the reader, then the firmware

"Firmware" authorizes access to the data contained on the optical disk 1.

Depending on the case, this access can be total and thus allows the reading, writing and / or copying of the data. In other cases, it may be only partial and for example limited to reading the data written on the optical disc 1. Copying of the data can, according to another example, only be authorized to an optical disc having a appropriate diffractive code.

If the diffractive code and the computer code are not identical, access to the data is refused. The system can then for example request a new entry of the computer code in order to carry out a new comparison. The entire procedure for reading and verifying the diffractive code can also be repeated. From the first failure or after a certain number of attempts, the firmware can control the ejection of the optical disc 1.

The method of verifying authenticity and authorization according to the invention can be implemented by a completely conventional optical disc reader, without modification or replacement of its physical elements.

The movements of the read head 7 required by the method are carried out using conventional functions of the standard read heads. In fact, the horizontal displacements of the read head 7, symbolized by the double arrow 16 in FIGS. 4 and 5, can be achieved by means of the function called "tracking error" usually used for centering the read head by compared to the spiral track along which the data is written.

The vertical defocusing and refocusing movements of the lens 10, symbolized by the double arrow 17 in FIGS. 4 and 5, can be carried out by means of the function called "focusing error" usually used to correct the focusing of the laser beam on the data entered. .

The method of verifying authenticity and authorization according to the invention requires only a simple updating of the firmware of the optical disc player. This update, to be loaded into the EPROM of the reader, can be supplied with the optical disc 1 or can be obtained by an authorized user by any other appropriate means, for example by post, by a secure download or by through a call center.

The security device according to the invention is more reliable than the devices existing in the prior art, since it is a combination between a specific optical coding digitally engraved on an optical disc and a modified “firmware” firmware.

If an attempt is made to read an optical disc 1 comprising digital diffractive elements 6 according to the invention in a reader of which the “firmware” firmware is conventional, access to the data will be impossible.

In fact, the information contained in the inner ring leads the firmware to immediately move the read head to the location of the digital diffractive elements 6 in order to read these elements. If the firmware is not suitable, it does not understand these structures and is not capable of interpret them. The system then hangs and cannot read the data.

Obviously, the invention is not limited to the preferred embodiments described above and shown in the different figures, the person skilled in the art can make numerous modifications and imagine other variants without departing from the scope or of the scope of the invention.

It is for example conceivable to produce the diffractive elements 6, no longer by molding reliefs and hollows, but by changes in refractive index or polarization by means of a change of material and a technical production supplement of these types of digital diffractive components.

The invention is also not limited to optical discs, but can be applied to any optical recording medium or to optical reading.

It is also possible to envisage using the invention for non-optical information media, by adding an optical authentication and authorization authorization device according to the invention or by replacing an existing optical system with that of the invention. The readers of these media must then be adapted if necessary in order to be able to read the diffractive code of the recording medium.

As examples of additional application of the invention, mention may be made of: bank cards, social security cards, secure access cards, or any other medium requiring authentication or securing of its data.

Claims

1. Security system by digital diffractive coding making it possible to prevent unauthorized access to the data stored on an optical recording medium, in particular of the optical disc (1), compact, audio, video or computer type, characterized in that it is compatible with a suitable conventional optical reader without modification of the physical elements constituting this reader and by means of a simple update of the firmware “firmware” managing its operation, and in that it is a combination between:

- at least one digital diffractive element (6) carried by the optical recording medium (1), which can be read by the detector (9) with four detection cells (14) of the standard read head (7) of the reader optics; and

- the "firmware" firmware of the optical reader which is intended to implement a method for verifying the authenticity of the optical recording medium (1) and for authorizing access to its data, by comparison of at least one digital diffractive element (6) carried by the optical recording medium with a computer code.

2. Optical disc (1), in particular of compact disc, audio, video or computer type, comprising three concentric zones, respectively from the center to the periphery: an inner ring (3) constituting the starting zone of the optical disc (1) and containing functional information intended for the firmware of the reader, a central zone (4) intended for the data stored on the optical disc (1) and an external crown (5), constituting the end zone of the optical disc, characterized in that it comprises at least one digital diffractive element (6), which can be read by the detector (9) with four detection cells (14) of the standard read head (7) of a suitable conventional reader optical discs and in that the set of digital diffractive elements (6) of the optical disc (1) forms a diffractive code.

3. Optical disc (1) according to claim 2 characterized in that at least one digital diffractive element (6) is located on the outer ring (5) of the optical disc (1).

4. Optical disc (1) according to claim 2 or 3 characterized in that at least one digital diffractive element (6) is a microstructure formed of a succession of hollows and bumps.

5. Optical disc (1) according to the preceding claim characterized in that the microstructure is produced by molding during manufacture by injection molding of the optical disc (1).

6. Optical disc (1) according to any one of claims 2 to 5 characterized in that at least one diffractive element (6) has a substantially square or rectangular outline.

7. Optical disc (1) according to the preceding claim characterized in that it comprises at least one digital diffractive element (6) in which the diffractive information is repeated several times in order to improve the intensity of the detected signal.

8. Optical disc (1) according to any one of claims 2 to 7 characterized in that it comprises at least one digital diffractive element (6) binary.

9. Optical disc (1) according to one any one of claims 2 to 7 characterized in that it comprises at least one digital diffractive element (6) with at least four phase levels.

10. Optical disc (1) according to any one of claims 2 to 9 characterized in that its inner crown (3) contains information or instructions allowing the optical disc player to implement a method of verifying authenticity optical disk (1) and authorization to access its data using the diffractive code.

11. A method of verifying authenticity and authorizing access to the data contained on an optical disc (1) according to any one of claims 2 to 10 and in particular of compact disc, audio, video or computer type, characterized method in that it can be implemented by a conventional suitable optical disc reader without modification of the physical elements constituting this reader and by means of a simple update of the firmware “firmware” managing its operation, and in that '' it includes the following stages:

- positioning of the read head (7) of the optical disc player facing the first digital diffractive element (6) carried by the optical disc;

- Reading of the digital diffractive element (6) by the detector (9) with four detection cells (14) of the read head (7) and storage of its value;

- possible repetition of the two preceding steps for the next digital diffractive element (6) until all the digital diffractive elements (6) carried by the optical disc have been read, the set of stored values forming the diffractive code;

- verification of the diffractive code by comparison with computer code stored in the optical disc drive;

- depending on the result of the previous step, refusal or authorization of access, total or partial, to the data contained on the optical disc (1).

12. A method of verifying authenticity and authorizing access to the data contained on an optical disc (1) according to claim 11, characterized in that it also comprises at least one step of:

- defocusing of the lens (10) of the read head (7) of the optical disc player.

13. A method of verifying authenticity and authorizing access to the data contained on an optical disc (1) according to claim 11 or 12 characterized in that it further comprises at least one step of:

- decrease in the speed of rotation of the optical disc (1).

14. A method of verifying authenticity and authorizing access to the data contained on an optical disc (1) according to any one of claims 11 to 13 characterized in that it also comprises at least one step of:

- reading of the instructions and information concerning the implementation of the process located in the inner ring (3) of the optical disc

(1).

15. A method of verifying authenticity and authorizing access to the data contained on an optical disc (1) according to any one of claims 11 to 14 characterized in that in the event of authorization to access the data contained on the optical disc (1) the copying of this data is only authorized to an optical disc (1) having an appropriate diffractive code.

16. A method of verifying authenticity and authorizing access to the data contained on an optical disk (1) according to any one of claims 11 to 15 characterized in that it further comprises a step of entering the code computer science .