KR20080078726A - Method for writing data having a distinctive feature - Google Patents

Abstract

In the field of content distribution a typical problem is the protection of Digital Rights information (DRM), which is appended to the content and written on a record carrier in the form of a corresponding written pattern, from tampering by malicious users. According to some known schemes, the protection is implemented by linking the DRM to some physical distinctive feature of the corresponding written pattern. From this distinctive feature fingerprint data can be extracted with some conventional method, and used for the authentication of the DRM. The invention proposes a method of writing data wherein the formed written pattern has a radial offset, which is formed during writing as result of a non- controllable substantially random process. A corresponding apparatus for writing data, a method and an apparatus for extracting fingerprint data and a record carrier are also described.

Description

{METHOD FOR WRITING DATA HAVING A DISTINCTIVE FEATURE}

The present invention relates to a method of recording data on a record carrier and a method of extracting fingerprint data corresponding thereto.

The present invention also relates to an apparatus for recording data on a recording medium and an apparatus for extracting fingerprint data corresponding thereto.

The present invention also relates to a recording medium in which data is recorded and fingerprint data can be extracted from the data.

With the advent of new online content distribution, channels such as iTunes, MusicMatch, PressPlay and Windows-Media Digital Rights Management (DRM) are starting to play an increasingly important role. Currently, three categories of DRM are used. These categories can be distinguished by the manner in which they store and protect usage rights (“one-time replication time”, “view until Wednesday”, etc.).

1. Network-centric: Rights are securely stored on a dedicated server in the network. Devices that want to access the content consult the server to get the rights (update if necessary). The server resides somewhere on the Internet (eg, content owner) or on a home network. This DRM category requires devices to always be online when accessing content.

2. (Private) card-centric: rights are securely stored on removable cards or tokens, eg smart cards, SD cards, memory sticks, etc. Devices that want to access the content contact the removable security card to obtain rights (update if necessary). This DRM category requires devices to have a slot for a plug-in card.

3. Device-centric: Rights are securely stored inside a fixed playback or storage device (eg, a PC with content present). The device that wants to access the content manages the rights itself. The result of this DRM category is that the content is always locked to one device. MusicMatch and the original Windows DRM service are examples of such a system.

In the last few years, a fourth change has been made, aiming at combining the original DRM and the current optical media content distribution business model, with features such as flash memory cards such as SD cards or MemorySticks. Most are provided on optical discs.

4. Media-centric: Rights are securely stored on the recordable media itself. Devices that want to access content have special circuitry to retrieve (update if necessary) rights on the media. The result of this DRM category is that content can be consumed on some device (media-centric DRM compatibility) (rights move with content).

The last category seems to be very pleading from the customer's point of view, but since the layout of the optical media has been standardized to give attackers direct access to all bits and bytes without the need for knowledge and authentication such as step confidentiality, this is the most technically complex will be. Of course, for example, from disk-based copy protection systems (DVD, CD, etc.), tools from cryptography (passwords, key distribution schemes, broadcast cryptography, etc.) and disk-marks / ROM side channels (wobble, unique It is well known how to prevent such bits from being duplicated, using a BCA with a media ID, ...). However, these systems do not have to compete with various save-and-restore attacks that are unique to DRM with consumable rights.

Contrary to static rights (no cloning, free copying, encryption plus non-assertion state), consumable rights are generally more restrictive rights whenever content is consumed, for example 4x playback, or 3x recording. . The save and restore attack is as follows:

Content with a corresponding digital copyright is acquired on the storage medium and legally downloaded;

The attacker makes a temporary bit copy of the storage medium (“image”) on some other storage medium, such as a hard disk drive (HDD);

The original storage medium is usually " consumed, "

At any time, an attacker can regain original rights by copying an image from a replaceable storage medium (HDD). In this process, the original right can be restored, even if the attacker doesn't know what the (encrypted) bits that were copied mean: this medium has simply returned to its original state. This is irrelevant to the use of all ROM side channels, such as " disc mark " (e.g. unique but fixed media identifier in BCA).

A method for solving this hack is described in WO02 / 015184 A1. According to this method, the hidden channel HC as a side channel is introduced. Side channels are a method of storing additional information on a record carrier by taking advantage of the fact that multiple read signals represent the same user data pattern (data available to the user). For example, additional messages may be coded in error correction parities. As the error correction mechanism removes these parity, the user sees no difference, but the dedicated circuit before the error correction mechanism sees the difference. Of course, in this example, the information capacity of the medium has increased due to the decrease of the error correction capacity of the system.

According to WO02 / 015184 A1, HC is a side channel on a storage medium that contains information observing constraints that cannot be written by the user but by some compliant DRM applications, and thus is lost in bit duplication. Simple examples are data stored in sector headers and specific portions of the lead-in area. More complex examples are the redundancy of the standard for storage media, where the information is made by making a special choice for such redundancy, e.g. specific merging bit patterns on a CD, or DVD as described, for example, in US 5,828,754. Select a particular trend in the digital sum value (DSV) on the running sum of channel-bits (DSV), or intentional errors in sector data (which can be corrected by redundant ECC-symbols) Are stored. Another example is information stored in slow variations of the channel bit clock as described, for example, in US 5,737,286.

During the renewal of rights, HC is used as follows:

1. When the digital copyright is updated (created or overwritten), a new random data string is selected and written to the HC;

2. The new value of the digital copyright is bound cryptographically (among other things) to the data string recorded in the HC. One example would be to construct a key that depends on the HC payload, which would be digitally signing the digital copyright, or to encrypt the digital copyright with this key instead. This signature may be based on symmetric key cryptography (so-called message authentication code, or MAC) or public key cryptography (eg, DSA- or RSA-based signatures).

During the reading of the rights, the HC performs the following checks:

(i) when the digital copyright is read, the data string is retrieved from the HC;

(ii) The key from step 2 or above depending on the HC data string is recreated and used to verify the cryptographic relationship between the digital copyright and the HC (check the signature on the digital copyright, or decrypt the digital copyright).

Step (ii) saves and restores the attack: The image containing the original digital copyright is restored by the attacker, but HC is impossible, so the check in step (ii) fails. The copyright and content keys may be protected in a key locker protected by a Key Locker Key (partly) dependent on the payload of the HC. In addition, the data in the HC need not be confidential, but it should be very difficult for an attacker to change these bits.

However, the system known from WO 02/015184 has a drawback because this known system relies on an algorithm that stores the whole secret, ie the bits, in the hidden channel, present in all consumer devices. Thus, an attacker can create a non-compliant device that can access the concealed information so that the attacker can manipulate the concealed information, thereby tampering illegal access to encrypted content by manipulating all digital copyrights. Can be provided to an attacker. Therefore, it is desirable to provide a countermeasure that is very difficult, expensive, and impossible to construct such a device only because it does not depend on the existence of the whole secret.

This drawback will be overcome according to a closed EP application 04106504.6 (submitted on 13 December 2004 by the same applicant) that discloses a method of controlling distribution and using Digital Work (DW), where According to the added URI (Usage Right Information) that specifies the conditions under which the DW can be accessed, the DW is recorded on the recording medium. The above method predicts the following:

The URI is recorded on the record carrier,

Fingerprint data is extracted from the recorded URI,

Authentication data derived from fingerprint data is also recorded on the recording medium for the next authentication of the URI,

Prevents the user from replacing a URI with another URI that is less restrictive, without detecting it.

This method relies on extracting fingerprint data from a pattern recorded on a recording medium. In particular, the distinctive feature of the recorded pattern, known in the art as a "fingerprint", can be represented by a channel bit error of predetermined data recorded on the recording medium, or previously recorded on the recording medium. Representation from the highest or lowest value, respectively, from the position of zero-crossings of the read signal relative to the channel bit boundary of the determined data or at a predetermined position of the predetermined data recorded on the record carrier, respectively. Can be. That is, the "fingerprint" of the recorded pattern is a feature that can distinguish the recorded pattern from any other recorded pattern, even when indicating the same data. In addition, since the fingerprint is acquired as a result of some uncontrolled process and is unique to the recording process in that case, it is impossible or impossible to record the pattern with the desired fingerprint.

It is a first object of the present invention to provide a data recording method on a recording medium capable of extracting fingerprint data in a selective manner and a fingerprint data extraction method corresponding thereto.

It is a second object of the present invention to provide a data recording apparatus on a recording medium capable of extracting fingerprint data in a selective manner, and a fingerprint data extracting apparatus corresponding thereto.

It is a third object of the present invention to provide a recording medium having recorded data, from which fingerprint data can be extracted in a selective manner.

According to the present invention, the first object is achieved by the data recording method according to claim 1 and the fingerprint data extraction method according to claim 7 corresponding thereto.

Thus, according to the present invention, the distinctive feature of the recorded pattern from which the fingerprint data is extracted is the radial offset from the recording track. According to the prior art, this distinctive feature is found in the inevitable difference between recorded patterns, which occurs as a side effect of the recording processor, and instead in this method according to the invention, the distinctive feature is deliberately created. This has the advantage that the extraction of fingerprint data is more robust and reliable because it is easy to detect a radial offset with a sufficiently high amplitude, or in other words, with a signal-to-noise ratio where the distinctive feature is sufficiently high. This recording process can be adapted to create a recorded pattern that can be. Nevertheless, since this distinctive feature is created in an uncontrollable and substantially random process, it is generally not possible to record the pattern with a predetermined fingerprint. This fingerprint data can be extracted from this non-reproducible feature, for example by measuring radial displacement at a plurality of fixed sampling positions.

Various preferred embodiments of the data recording method and the fingerprint data extraction method according to the invention are claimed in the dependent claims.

As is clear from the above description, the second object is achieved by the data recording apparatus according to claim 13 and the fingerprint data extracting apparatus according to claim 14 according to the present invention. Similarly, a third object is achieved by the recording medium of claim 15.

1 is a schematic diagram of a known data recording method, a recorded pattern corresponding thereto, and a known fingerprint data extraction method.

2 is a schematic diagram of a data recording method, a recorded pattern corresponding thereto, and a fingerprint data extraction method according to the present invention.

3 illustrates an embodiment of a fingerprint data extraction method according to the present invention.

4 shows an embodiment of a data recording method according to the present invention.

5 shows a schematic diagram of an authentication method using the present invention.

6 shows a method of accessing a recording medium for protecting DRM data using the present invention.

7 shows an optional method of protecting data recorded on a recording medium utilizing the present invention.

8 shows a schematic diagram of a tracking control loop in a known apparatus.

9 shows an embodiment of a tracking control loop in an apparatus according to the invention.

10 shows another embodiment of a tracking control loop in an apparatus according to the invention.

1 shows a schematic diagram of a known data recording method, a recorded pattern corresponding thereto, and a known fingerprint data extraction method. The data 10 is an input of the recording process 11, and a pattern 12 recorded by this recording process is formed on the recording medium. The recorded pattern 12 is interleaved by a second region 14 which is distinguishable from the first region 13 based on physical parameters such as, for example, reflectivity, state of magnetization or electrical charge, It consists of a sequence of the first regions 13. The first area 13 and the second area 14 exist along the recording track 15 and correspond to logical values 1 and 0 or vice versa, respectively, as employed among the two conventions.

Generally, the recorded pattern 12 is associated with a related type of record carrier, for example, affected by the width or length of the region, the steepness of the transition from the first region to the second region, or vice versa. Some standard specifications given should be taken into account. Despite these standard specifications for attaching any recorded pattern, like a human fingerprint, some characteristics can be defined as the recorded pattern can be very different from any other recorded pattern. These properties may be mentioned, for example, as follows:

One or more parameters without standard specifications, or

One or more parameters that are observed at a higher resolution level than those used in the standard specification, although there is a standard specification. These characteristics can be used as "fingerprints" or distinctive features of the recorded pattern 12 in the fingerprint extraction process 16 to extract the fingerprint data 17, as known from the prior art.

2 shows a schematic diagram of a data recording method, a recorded pattern corresponding thereto, and a fingerprint data extraction method according to the present invention. The recording process 21 is a perturbation step 23 for imposing an uncontrollable perturbation such that the recorded pattern 22 formed on the recording medium has a radial offset 25 from the recording track 15. It differs from the well-known recording process 11 in that it contains. The dimensions shown in the figures have been chosen merely for the sake of understanding and reflect the characteristics involved between the size of the first region 13 and the second region 14 and the overall rate of variation of the radial offset 25 and its rate of change. It doesn't actually reflect. This radial offset 25 is still within the bounds of the maximum radial offset, given such specifications. In this way, the overall tendency of the radial offset 25 is derived in the step of determining the fingerprint data from the radial offset 24 from the recording track 15 of the pattern 22 in which the fingerprint data 17 was recorded. It can be used as a "fingerprint" of the pattern 22 recorded in the complementary fingerprint extraction process 26, which is different from the known fingerprint extraction process 16 in this respect. This fingerprint data 17 consists of a collection of samples of the amplitude of the radial offset 25, for example measured at a predetermined sampling point. These predetermined sampling points may be determined according to timing and / or synchronization information present in the recording track 15, as in the case of a recordable optical disc, where the timing and / or synchronization information is a track encoded here. And / or in the recording track 15 in the form of a wobble frequency of information.

3 illustrates an embodiment of a fingerprint data extraction method according to the present invention. In this embodiment, the extraction method of the fingerprint data 17 shown in Fig. 2 is characterized in that the authentication data 31 is generated in accordance with the fingerprint data 17; In particular, it is improved by the next authentication data flow step 30 in which the authentication data 31 is generated even depending on the data 10. A one-way function such as, for example, a hash function or cipher summary is suitable for use in this authentication data derivation step 30.

4 shows an embodiment of a data recording method according to the present invention. The recorded pattern 22 generated by the recording process 21 is used in the fingerprint extraction process 26 for extracting the fingerprint data 17. These fingerprint data 17 are stored in the storage step 40 as reference fingerprint data 41 for later use in authenticating the data 10. In particular, the reference fingerprint data 41 may also be recorded on the recording medium.

The reference fingerprint data 41 can in fact be used in the authentication method, as shown schematically in FIG. 5, the purpose of which is probably the involved party, for example the owner or data of the data 10. Against the intention of the authority to control the content of (10), it is to verify whether the data 10 recorded on the recording medium in the form of the recorded pattern 22 has been manipulated.

In this method, the fingerprint data 17 extracted from the recorded pattern 22 in the fingerprint extraction process 26 is compared with the reference fingerprint data 41 in the consistency check step 50. Checked for consistency. This method continues to use the data 10 or full access to the data 100 when it is confirmed that the data has been authenticated. Although easily overwritten, it relies on the fact that there are at least technical barriers to overcome when updating the reference fingerprint data 41. Thus, although the data 10 can be easily manipulated, the original data ( The reference fingerprint data 41 derived from 10 cannot be manipulated. Therefore, by checking the correspondence between the reference fingerprint data 41 extracted from the recorded pattern 22 and the fingerprint data 17, It can be verified whether the data 10 is original or not.

This method can be improved by using helper data, which is used to compare parts of these fingerprint data 17 that more reliably match each case of the fingerprint extraction step 26. Is done.

Obviously, when the method of extracting fingerprint data includes an authentication data derivation step 30 as shown in Fig. 3, the consistency check step 50 is performed by comparing the authentication data 31 with the reference authentication data. You must think of it as accompanying.

6 shows a method of accessing a recording medium protecting DRM data using the present invention. In this embodiment, a recording medium on which digital rights management (DRM) information, such as a film protected by copyright, and DRM (Digital Rights Management) information specifying the range and conditions under which DW (Digital Work) can be used are recorded To access it. The DRM information may be provided with, for example, max. 3 views, 1 month views, 1 replication, and the like. In order to prevent a malicious user from replacing the original DRM information with other DRM information that specifies conditions that are less restrictive than those specified in the original DRM information, the original DRM information may be added to the DRM information for subsequent authentication. It is protected by having the stored reference fingerprint data 41 extracted according to the invention from the corresponding recorded pattern 22 and by recording the DRM information as the data 10 in the method according to the invention.

Thus, the method starts a DRM access step 60 for accessing the recorded pattern 22 corresponding to the DRM information. Next, the DRM information is authenticated in the authentication step 61, by the method described in FIG. If the authentication step 61 is unsuccessful, this method ends, otherwise the DRM check step 62 continues, at which step it verifies that the DRM information that is deemed to be authenticated at this point allows access to the DW. do. If access to the DW is not allowed, the method ends, otherwise the method continues with the DW access step 63. Since the DRM information requires some updates, such as in the case where a number of available accesses are specified and therefore the number should be reduced, the method continues with the DRM update step 64, where the DRM The information is updated, and the DRM information updated by the recording method according to the present invention is overwritten with the DRM information originally recorded on the recording medium, thereby creating a new recorded pattern 22 '. Next, the new fingerprint data 17 'is extracted from the newly recorded pattern 22' in the fingerprint data extraction step 26, and the new fingerprint data 17 'accesses the recording medium. Is stored in the storage step 40 as new reference fingerprint data 41 'for authentication during the following cases. The DRM update step 64, the fingerprint data extraction step 27, and the storage step 40 must occur together with the DW access step 63.

The present invention can also be used in a method for protecting data recorded on a recording medium as shown in FIG. According to this method, the fingerprint data 17 is encrypted by obtaining the encryption key 71, which is used in the key extraction step 70 and used in the encryption step 72 for encrypting the DW 73. Obtain the DW 74. This data 10 may be random data uniquely used to generate the recorded pattern 22, but any auxiliary data, for example DRM information, may be used as the data 10. In the key extraction step 70, the encryption key 71 is obtained from the fingerprint data 17, preferably using a one-way function. However, since the fingerprint data extraction step 26 is essentially a one-way function, the fingerprint data 17 will be used directly as the encryption key 71, evidently taking into account the size of the fingerprint data 17. Can be.

8 shows a schematic diagram of a tracking control loop in a known apparatus for recording data on a record carrier. The tracking signal 86 reflecting the displacement of the recording means from the recording track 15 is compared with the set point 8, and the resulting tracking error 81 operates in accordance with some control parameters 83, It is supplied to a controller 82 that generates a control signal 84. This control signal 84 is supplied to the actuator 85 which physically positions the recording means. As for the optical disc system, this tracking signal 86 may be a push-pull signal, for example.

9 illustrates how the control loop shown in FIG. 8 is changed in an embodiment of the apparatus according to the present invention. In order to generate a variable displacement of the recording means, a disturbance 90 is added to the control signal. This disturbance can occur using a noise generator 91, in particular a white noise generator. This band pass filter 92 is generally not necessary because the actuator 85 has already affected the formation of the spectrum of noise, but there is a band pass filter 92. Clearly, it would be desirable for the disturbance 90 to have a frequency component that is outside the bandwidth of the control loop.

In addition, when the recording track 15 has a wobble, since it is generally the case of a recordable optical disc, it is preferable that the disturbance 90 be designed so that the radial offset 25 has a spectrum distinct from the spectrum of this wobble. Do.

Another embodiment of the device according to the invention is shown in FIG. 10. In this case, the displacement of the recording means occurs by manipulating the control parameter 83 of the controller 82 with the control parameter variation unit 100. This operation includes the following combinations:

Carefully use non-optimal values for control parameter 83,

-Temporarily change the value of the control parameter 83,

Add a pseudo-randomly occurring variable component to the value of the control parameter 83.

In both embodiments shown in FIGS. 9 and 10, what is achieved is that the recording means cannot always remain on the track, but has radial displacement at some point. However, the exact value of the radial displacement at this given point is not controlled. As a result, the tendency of the overall radial displacement can be understood as the result of an uncontrolled non-reproducible process. Although the present invention has been described with respect to an optical recording medium, it is apparent that other applications are possible for example in a rotatable non-optical recording medium. Therefore, the scope of the present invention is not limited to the above-described embodiment.

The above-described embodiments illustrate rather than limit the invention, and those skilled in the art can design many other embodiments without departing from the scope of the invention as defined by the appended claims. It should be noted that you will be able to. The term "comprising, comprising" in this specification does not exclude the presence of other elements and steps than those listed in the claims or throughout the specification.

The present invention can be summarized as follows. In the field of content distribution, a representative problem is to protect the Digital Rights Information (DRM) that is added to the content in the form of corresponding recorded patterns and recorded on the recording medium from interference by malicious users. According to some known schemes, protection is achieved by connecting the DRM to some physical distinctive feature of the corresponding recorded pattern. From this distinctive feature, fingerprint data can be extracted in some agreed manner and used for authentication of the DRM. The present invention proposes a data recording method having a radial offset formed upon recording as a result of a substantially random process in which the formed recorded pattern is out of control. Correspondingly, a data recording apparatus, a method and apparatus for extracting fingerprint data, and a recording medium are also described.

Claims (16)

In order to create the recorded pattern 22 from which the fingerprint data 17 can be extracted, a method of recording the data 10 on the recording medium along the recording track 15, Recording data using recording means; Recording data while supporting the recording means along the recording track using tracking means; Imposing an uncontrollable perturbation on the tracking means, such that the recorded pattern has a radial offset from the recording track. The method of claim 1, Using a tracking means comprising an actuator 85 and a controller 82, said controller operating according to several control parameters 83 to provide a control signal 84 to said actuator. . The method of claim 2, The uncontrollable perturbation is imposed by adding noise (90) to the control signal (84). The method of claim 3, wherein The noise (90) is generated by a noise generator (91). The method of claim 2, And said uncontrollable perturbation is imposed by intentionally setting a non-optimal value for a control parameter (83) in said controller (82). The method of claim 2, And said uncontrollable perturbation is imposed by temporarily changing the value of a control parameter (83) in said controller (82). A method of extracting fingerprint data from data 10 recorded on a recording medium along a recording track 15 in the form of a recorded pattern 22, Fingerprint data 17 is determined for the radial offset 25 of the recorded pattern 22 from the recording track 15, the radial offset being a distinctive feature of the recorded pattern. How to extract print data. The method of claim 7, wherein Fingerprint data extraction method further comprises generating authentication data (31) for the fingerprint data (17). The method of claim 8, Fingerprint data extraction method, characterized in that for generating authentication data (31) for the fingerprint data (17) in dependence on data (10). The method of claim 1, Extracting fingerprint data 17 from the data 10 recorded on the recording medium by applying the method of claim 7; And storing said fingerprint data (17) as reference fingerprint data (41) for subsequent authentication of said data (10). The method of claim 10, And the reference fingerprint data (41) is stored on the recording medium. A method of authenticating data 10 recorded on a recording medium along a recording track 15 in the form of a recorded pattern 22, wherein fingerprint data 17 can be extracted from the recorded pattern, and authentication is performed. Reference fingerprint data 41 is available for this purpose, and the authentication method includes: Extracting the fingerprint data 17; Acquiring the reference fingerprint data 41; Checking whether the fingerprint data matches the reference fingerprint data, The recorded pattern 22 has a radial offset 25 from the recording track 15, the radial offset being a distinctive feature of the recorded pattern, and the method of claim 7 when extracting the fingerprint data. Authentication method characterized in that using. An apparatus for recording data 10 on a recording medium along a recording track in order to create a recorded pattern 22 from which fingerprint data 17 can be extracted. Recording means for recording data, Tracking means for recording data while supporting the recording means along the recording track, Means for imposing an uncontrollable perturbation on the tracking means, such that the recorded pattern has a radial offset (25) from the recorded track. An apparatus for extracting fingerprint data 17 from data 10 recorded on a recording medium along a recording track 15 in the form of a recorded pattern 22, And to determine the fingerprint data 17 for the radial offset 25 from the recording track 15 of the recorded pattern 22, wherein the radial offset is a distinctive feature of the recorded pattern. Extraction device. A recording medium in which data 10 is recorded along a recording track 15 in the form of a recorded pattern 22 from which fingerprint data 17 can be extracted. The recorded pattern (22) having a radial offset (25) from the recording track (15), the radial offset being a distinctive feature of the recorded pattern. The method of claim 15, And reference fingerprint data (41) obtained as fingerprint data (17) extracted from the data (10) by the method of claim 7.

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