JP2009520309A - How to write data with distinctive features - Google Patents

Abstract

  In the field of content distribution, a typical challenge is to protect digital rights information (DRM) appended to content and written on the record carrier in the form of a corresponding writing pattern from unauthorized use by malicious users. . According to one known scheme, the protection is implemented by associating DRM with certain physical distinguishing features of the corresponding writing pattern. From this distinguishing feature, fingerprint data can be extracted by some conventional method and used for DRM authentication. The present invention proposes a data writing method in which the formed writing pattern has a radial offset, which is formed during writing as a result of a substantially random process that cannot be controlled. Corresponding data writing devices, fingerprint data extraction methods and devices, and record carriers are also described.

Description

  The invention relates to a method for writing data to a record carrier and a corresponding method for extracting fingerprint data.

  The invention further relates to a device for writing data on a record carrier and a corresponding device for extracting fingerprint data.

  The invention further relates to a record carrier on which data from which fingerprint data can be extracted is recorded.

  With the advent of new online content distribution channels such as iTunes, MusicMatch, PressPlay, and Windows®-Media, Digital Rights Management (DRM) is starting to play an increasingly important role. Currently, three categories of DRM are used. These can be distinguished by the way they store and protect usage rights ("copy once", "watch until Wednesday", etc.).

  1. Network-centric: Rights are securely stored on a dedicated server in the network. A device that wants to access the content consults with the server to obtain rights (and update if necessary). The server may be somewhere on the Internet (eg, at the content owner) or in the home network. This DRM category requires that the device be (almost) always online when accessing content.

  2. (Personal) card-centric: Rights are securely stored on a removable card or token, eg, smart-card, SD card, MemoryStick, etc. Devices that wish to access the content contact the removable security card to obtain rights (and update if necessary). This DRM category requires that the device have a slot for a plug-in card.

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

  In the last few years, a fourth type has been developed. This essentially aims to combine the current optical media content distribution business model with DRM, giving the optical disc almost the same function as a flash memory card such as SD-card or MemoryStick.

  4). Medium-centric: Rights are stored securely on the recordable medium itself. A device that wants to access content has special circuitry to retrieve the rights on the media (and update if necessary). The result of this DRM category is that content can be consumed on any device (compatible with media-centric DRM) (rights turn around for content).

  The last category looks very attractive from the consumer's perspective, but is technically the most complex. This is because the layout of the optical media is standardized, giving the attacker direct access to all bits and bytes without requiring further authentication and knowledge of the system secret. Of course, for example, from disk-based copy protection systems (DVD, CD, etc.), encryption (encryption, key distribution scheme, broadcast encryption, etc.) and disc-mark / ROM side-channel (ROM side-channel) ( It is well known how to prevent such bits from being copied using tools from wobbles, BCAs with unique media IDs, etc.). However, none of these systems had to contend with the particularly malicious save-and-restore attacks inherent in DRM systems with consumable rights.

In contrast to static rights (copy never, copy free, EPN (encryption plus non-assertion state)), consumable rights are typically rights that are more limited each time content is consumed, For example, 4 playbacks or 3 recordings. The save-restore attack is performed as follows.
-Content with corresponding digital rights is purchased and legally downloaded to a storage medium.
-The attacker creates a temporary bit copy ("image") of the storage medium on some other storage medium such as a hard disk drive (HDD).
-The original storage medium is "consumed", i.e. used normally, which means decrementing in the right way.
-At any point in time, the attacker can restore the original rights by copying the image back from the alternate storage device (HDD). In this process, the original right is restored in the same way even if the attacker does not know what the re-copied (encrypted) bit means. That is, the medium is simply returned to its unused state. This is independent of the use of any ROM side channel such as “Disc Mark” (eg, a unique but fixed media identifier in BCA).

  A method for solving this hack is disclosed in International Patent Application Publication No. WO02 / 015184 A1. According to this method, a hidden channel (hidden channel (HC)) as a side channel is introduced. Side channel is a method of storing additional information on a recording medium by taking advantage of the fact that many read signals represent the same user data pattern (data available to the user). For example, additional messages may be encoded within the error correction parity. The error correction mechanism will remove these parities so that the user is not aware of the difference, but a dedicated circuit prior to the error correction mechanism will notice. Of course, in this example, the information capacity of the medium is increased at the expense of a reduced system error correction capability.

  According to International Patent Application Publication No. WO02 / 015184 A1, HC is a side channel on a storage medium that contains information that cannot be written by a user but can only be written by a compliant DRM application. , Hence lost in bit copy. A simple example is data stored in a certain part of the sector header and lead-in area. A more sophisticated example is the redundancy in the standard for storage media, in which the information makes a particular choice for such redundancy, for example, a merging bit pattern on a CD, such as the US Special trends in DVD DSV (digital sum value, channel bit running sum) as described in US Pat. No. 5,828,754, or intentional errors in sector data (which can be corrected by redundant ECC symbols) Stored by selecting. Yet another example is information stored in a slow variation of the channel bit clock as described, for example, in US Pat. No. 5,737,286.

When updating the rights, HC is used as follows.
1. When the digital right is updated (generated or overwritten), a data string is selected and recorded in the HC.
2. The new value of the digital right is cryptographically associated (among other things) with the data string written to the HC. An example would be to build a key that depends on the HC payload and give a digital signature to the digital right with this key, or alternatively encrypt the digital right with this key. The signature can be based on either symmetric key cryptography (so-called Message Authentication Code (MAC)) or public key cryptography (eg DSA or RSA based signature).

While reading the rights, the following checks are performed using the HC.
(I) When a digital right is read, a new random data string is retrieved from the HC.
(Ii) The key from step 2 above that relies on the HC data string is recreated to verify the cryptographic relationship between the digital right and the HC (check the signature on the digital right or decrypt the digital right) Used for.

  Step (ii) prevents save-restore attacks. That is, the image containing the original digital rights may be restored by the attacker, but the HC cannot be restored, so the check in step (ii) fails. Rights and content keys can be protected with a Key Locker, which is protected by a Key Locker Key that depends (partially) on the HC payload. Furthermore, the data in the HC need not be secret, but modifying these bits should be very difficult for an attacker.

  However, the known system from WO 02/015184 relies on a universal secret that exists in every consumer device, ie an algorithm that stores bits in a hidden channel. Thus suffering a disadvantage. Therefore, an attacker can build a non-compliant device that allows access to hidden information so that the hidden information can be manipulated, thus providing illegal access to the encrypted content by manipulating any digital rights Will. Therefore, it is desirable to take measures that make it very difficult, expensive or even impossible to build a device for such a reason that does not depend on the presence of a universal secret.

This disadvantage is overcome by the unpublished European application No. 04106504.6 (filed by the applicant on December 13, 2004). This describes a method for controlling the distribution and use of Digital Work (DW). Here, the DW is recorded on the record carrier together with additional right-of-use information (Usage Right Information (URI)) that specifies conditions for accessing the DW. The method prevents the user from exchanging the URI with another less restrictive URI without detecting the URI,
The URI is recorded on the record carrier,
The fingerprint data is extracted from the recorded URI, and the authentication data obtained from the fingerprint data is also recorded on the record carrier for later URI authentication,
I anticipate that.

  This method relies on extracting fingerprint data from a pattern recorded on a record carrier. In particular, a distinctive feature of the writing pattern known in the art as "fingerprint" is caused by the channel bit error of certain data recorded on the record carrier. It can be represented from the position of the zero crossing of the read signal with respect to the channel bit boundary of the predetermined data recorded or from the highest or lowest value at a predetermined position of the predetermined data recorded on the record carrier. In other words, a “fingerprint” of a writing pattern is a feature that can be distinguished from any other writing pattern even if the writing pattern represents the same data. Furthermore, the fingerprint is obtained in this case as a result of a non-control process inherent in the writing process, and therefore it is impossible or impossible to record a pattern with the desired fingerprint.

  It is a first object of the invention to provide a method for writing data to a record carrier, and a corresponding method for extracting fingerprint data, in which fingerprint data can be extracted in an alternative manner.

  It is a second object of the invention to provide a device for writing data to a record carrier, and a corresponding device for extracting fingerprint data, in which fingerprint data can be extracted in an alternative manner.

  A third object of the invention is to provide a record carrier with recorded data from which fingerprint data can be extracted in an alternative manner.

  According to the invention, the first object is achieved by a method for writing data according to claim 1 and by a corresponding method for extracting fingerprint data according to claim 7.

  Therefore, according to the present invention, the distinguishing feature of the writing pattern from which the fingerprint data is extracted is the radial offset from the recording track. According to the prior art, discriminative features are found in the unavoidable differences between writing patterns as a result of side effects of the writing process, whereas in the alternative method according to the invention, the discriminating features are Generated deliberately. This has the advantage of making fingerprint data extraction more robust and reliable. Because the writing process is easy enough to detect the discriminating features, i.e. it produces a writing pattern with a sufficiently high amplitude of the radial offset, in other words the discriminating features are high enough This is because it can be adapted to generate a writing pattern that can be detected with a signal-to-noise ratio. Furthermore, the distinguishing features are generated by a substantially random process that cannot be controlled, so it will generally not be possible to record a pattern with a given fingerprint. In this case, fingerprint data can be extracted from this irreproducible feature, for example by measuring radial displacement at a plurality of fixed sampling positions.

  Various advantageous embodiments of the method for writing data and the method for extracting fingerprint data according to the invention are described in the dependent claims.

  As is clear from the above description, the second object is achieved according to the invention by a device for writing data according to claim 13 and a corresponding device for extracting fingerprint data according to claim 14. Is done. Similarly, the third object is achieved by a record carrier according to claim 15.

  These and other aspects of the method and apparatus according to the present invention will be further detailed with reference to the drawings.

FIG. 1 shows a schematic diagram of a known method for writing data, a corresponding writing pattern and a known method for extracting fingerprint data. The data 10 is the input of the writing process 11, whereby a writing pattern 12 is formed on the record carrier. The write pattern 12 consists of a sequence of first areas 13 interleaved by the second area 14. The second region 14 is distinguishable from the first region 13 based on physical parameters such as reflectance, magnetization state or charge. 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, depending on which of the two conventions is employed. In general, the writing pattern 12 is related to the type of record carrier that affects the width or length of the region and the steepness of the transition from the first region to the second region or vice versa, for example. Must comply with certain standards given to Despite these standards that any writing pattern must be adhered to, as well as human fingerprints, it defines several characteristics that make it highly possible that the writing pattern will differ from any other writing pattern Is possible. These characteristics are, for example,
One or more parameters that do not have a standard, or one or more parameters that have a standard but are adhered to at a higher resolution level than that used in the standard,
Can be called. These characteristics can be used as a distinguishing feature of the writing pattern 12, ie a “fingerprint”, in the fingerprint extraction process 16 for extracting the fingerprint data 17 known from the prior art.

  FIG. 2 shows a schematic diagram of a method for writing data according to the present invention, a corresponding writing pattern and a method for extracting fingerprint data. The writing process 21 has a perturbation step 23 for imposing uncontrollable perturbation so that the writing pattern 22 formed on the record carrier has a radial offset 25 from the recording track 15. This is different from the known writing process 11. The dimensions shown are merely selected for the purpose of understanding. For example, the ratios related to the sizes of the first region 13 and the second region 14, the radial offset 25, and the rate of change thereof are actually drawn. Is not reflected. This radial offset 25 must be within the bounds of the maximum radial offset if such a specification is given. In this way, the overall tendency of the radial offset 25 can be used as the “fingerprint” of the writing pattern 22 in the complementary fingerprint extraction process 26. This fingerprint extraction process 26 is a known fingerprint extraction process 16 in that the fingerprint data 17 is obtained in the step of determining the fingerprint data from the radial offset 24 from the recording track 15 of the writing pattern 22. And different. The fingerprint data 17 may, for example, consist of a collection of samples with a radial offset 25 amplitude measured at a given sampling point. These predetermined sampling points may be determined based on the timing and / or synchronization information existing on the recording track 15 as in the case of a recordable optical disc. Timing and / or synchronization information is present on the recording track 15 in the form of track wobble frequency and / or encoded information.

  FIG. 3 shows an embodiment of a method for extracting fingerprint data according to the present invention. In this embodiment, the method for extracting the fingerprint data 17 shown in FIG. 2 is such that the authentication data 31 is generated based on the fingerprint data 17, in particular the authentication data 31 is also generated depending on the data 10. Enhanced by a subsequent authentication data acquisition step 30. For example, a one-way function such as a hash function or a cryptographic summary is suitable for use in this authentication data acquisition step 30.

  FIG. 4 illustrates one embodiment of a method for writing data according to the present invention. The writing pattern 22 generated by the writing process 21 is used in a subsequent fingerprint extraction process 26 for extracting the fingerprint data 17. The fingerprint data 17 is then stored as reference fingerprint data 41 for subsequent use in authentication of the data 10 in a storing step 40. In particular, the reference fingerprint data 41 may also be recorded on the record carrier.

  The reference fingerprint data 41 can then be used in an authentication method as schematically illustrated in FIG. The purpose of this is that the data 10 recorded on the record carrier in the form of a writing pattern 22 is altered, possibly contrary to the intentions of the parties involved, for example the owner of the data 10 or the authority controlling the content of the data 10. It is to confirm whether it is done.

  In this method, the fingerprint data 17 extracted from the writing pattern 22 in the fingerprint extraction process 26 is checked for consistency with the reference fingerprint data 41 in a consistency check step 50. This method is followed by the use of data 10 or permission for full access if these authentications are confirmed. This method relies on the fact that the data 10 recorded on the record carrier may be easily overwritten, but there are at least technical obstacles to be overcome when updating the reference fingerprint data 41. . Therefore, the data 10 can be easily falsified, but the reference fingerprint data 41 obtained from the original data 10 cannot be falsified. Therefore, by checking the consistency between the reference fingerprint data 41 and the fingerprint data 17 extracted from the writing pattern 22, it can be confirmed whether the data 10 is original.

  The above method can be enhanced by the use of helper data. Through the use of helper data, comparisons are made to portions of the fingerprint data 17 that are more reliably consistent at each point in the fingerprint extraction step 26.

  Obviously, if the method of extracting fingerprint data has the authentication data acquisition step 30 shown in FIG. 3, the consistency check step 50 must be directed to accompany the authentication data 31 and the reference authentication data.

  FIG. 6 illustrates a method for accessing a record carrier on which DRM data is protected using the present invention. In this embodiment, for example, a digital work (DW) such as a copyrighted movie, and a record carrier on which digital light management (DRM) information specifying the degree and conditions under which the DW can be used are accessed. Is done. The DRM information may have conditions such as viewing up to three times, viewing for one month, and copy once. In order to prevent the original DRM information from being replaced by other DRM information specifying conditions that are less restrictive than those specified in the original DRM information by a malicious user, Stores the reference fingerprint data 41 extracted by the present invention from the writing pattern 22 corresponding to the DRM information by writing the DRM information as data 10 by the method according to the present invention and for later authentication. It is protected by keeping.

  Therefore, the method begins with a DRM access step 60 for accessing the writing pattern 22 corresponding to the DRM information. Next, the DRM information is authenticated by the method described in FIG. If the authentication step 61 does not end successfully, the method ends. If not, the method continues with a DRM check step 62. In the DRM check step 62, it is confirmed whether the DRM information that is considered to be authenticated at this point permits access to the DW. If access to the DW is not permitted, the method ends. Otherwise, the method is followed by a DW access step 63. Since the DRM information may require a certain update, such as when the number of available accesses is specified and therefore such times must be decremented, the method is followed by a DRM update step 64. May be. In the DRM update step 64, the DRM information is updated and the DRM information originally written on the record carrier is the DRM information updated by the writing method according to the present invention so as to generate a new writing pattern 22 ′. It will be overwritten. New fingerprint data 17 ′ is then extracted from the new writing pattern 22 ′ in the fingerprint data extraction step 26, and the new fingerprint data 17 ′ is for authentication at a later time in this method of accessing the record carrier. In the storing step 40, the new reference fingerprint data 41 'is stored. The DRM update step 64, the fingerprint data extraction step 26 and the storage step 40 should be performed permanently together with the DW access step 63.

  The invention can also be used in an alternative way of protecting data recorded on a record carrier as shown in FIG. According to this method, the fingerprint data 17 is used in the key extraction step 70 for obtaining the encryption key 71. The encryption key 71 is then used in an encryption step 72 for encrypting the DW 73, thereby obtaining an encrypted DW 74. The data 10 may be random data intended only to be used to generate the writing pattern 22, but any auxiliary data, for example DRM information, could also be used as the data 10. . In the key extraction step 70, a one-way function is preferably used to obtain the encryption key 71 from the fingerprint data 17. However, since the fingerprint data extraction step 26 essentially has the property of a one-way function, the fingerprint data 17 is directly used as the encryption key 71 on condition that the size of the fingerprint data 17 is clearly taken into account. Can be used.

  FIG. 8 shows a schematic diagram of a tracking control loop in a known device for writing data to a record carrier. A tracking signal 86 reflecting the displacement of the writing means from the recording track 15 is compared with a set value 80. The resulting tracking error 81 is supplied to the controller 82. The controller 82 operates in response to several control parameters 83 and generates a control signal 84. The control signal 84 is supplied to the actuator 85. The actuator 85 physically positions the writing means. With respect to the optical disc system, the tracking signal 86 may be, for example, a push-pull signal.

  FIG. 9 shows how the control loop shown in FIG. 8 is modified in one embodiment of the device according to the invention. In order to generate a variable displacement of the writing means, a disturbance 90 is added to the control signal. This disturbance can be generated by using a noise generator 91, in particular a white noise generator. A bandpass filter 92 is generally not required because the actuator 85 already provides a special shaping of noise, but may be present. Obviously, the disturbance 90 will preferably have frequency components outside the bandwidth of the control loop.

  Further, when the recording track 15 has wobble, which is generally a recordable optical disc, the disturbance 90 may be designed to have a spectrum in which the radial offset 25 is distinguished from the wobble spectrum. preferable.

An alternative embodiment of the device according to the invention is shown in FIG. In this case, the displacement of the writing means is brought about by operating the control parameter 83 of the controller 82 by the control parameter changing unit 100. This applied operation may have any of the following combinations.
-Intentionally using a non-optimal value for the control parameter 83;
-Temporarily changing the value of the control parameter 83; and-adding a pseudo-randomly generated variable component to the value of the control parameter 83.

  In both the embodiments shown in FIGS. 9 and 10, what is achieved is that the writing means cannot remain consistently on the track but will have a radial displacement at some point. It is. However, the exact value of radial displacement at a given point is not controlled. As a result, the overall tendency of radial displacement can be seen as a result of uncontrolled and non-reproducible processing.

  The term “having” as used in this specification, including the claims, is taken as identifying the presence of the feature, integer, step or component referred to, but one or more other features It should also be noted that this does not exclude the presence or addition of integers, steps, components or collections thereof. It should also be noted that the singular terms in the claims do not exclude the presence of a plurality of such components. Furthermore, any reference signs do not limit the scope of the claims. The present invention can be realized by both hardware and software. Several "means" may also be represented by the same item of hardware. Furthermore, the present invention exists in any new feature or combination of features.

  The present invention can be summarized as follows. In the field of content distribution, a typical challenge is to protect digital rights information (DRM) appended to content and written on the record carrier in the form of a corresponding writing pattern from unauthorized use by malicious users. . According to one known scheme, the protection is implemented by associating DRM with certain physical distinguishing features of the corresponding writing pattern. From this discriminative feature, fingerprint data can be extracted by some agreed method and used for DRM authentication. The present invention proposes a data writing method in which the formed writing pattern has a radial offset, which is formed during writing as a result of a substantially random process that cannot be controlled. Corresponding data writing devices, fingerprint data extraction methods and devices, and record carriers are also described.

FIG. 1 shows a schematic diagram of a known method for writing data, a corresponding writing pattern and a known method for extracting fingerprint data. FIG. 2 shows a schematic diagram of a method for writing data according to the present invention, a corresponding writing pattern and a method for extracting fingerprint data. FIG. 3 shows an embodiment of a method for extracting a fingerprint according to the present invention. FIG. 4 illustrates one embodiment of a method for writing data according to the present invention. FIG. 5 shows a schematic diagram of an authentication method using the present invention. FIG. 6 illustrates a method for accessing a record carrier on which DRM data is protected using the present invention. FIG. 7 shows an alternative method of protecting data recorded on a record carrier using the present invention. FIG. 8 shows a schematic diagram of a tracking control loop in a known device. FIG. 9 shows an embodiment of the tracking control loop in the device according to the invention. FIG. 10 shows another embodiment of the tracking control loop in the device according to the invention.

Claims (16)

A method of writing data on a record carrier along a recording track so as to generate a writing pattern, wherein fingerprint data can be extracted from the writing pattern, the method comprising:
Using a writing means for writing the data; and- using a tracking means for writing the data while maintaining the writing means along the recording track.
A method,
A method in which an uncontrollable perturbation is imposed on the tracking means such that the writing pattern has a radial offset from the recording track.   2. A method according to claim 1, characterized in that a tracking means is used which comprises an actuator and a controller which operates in response to several control parameters and which supplies a control signal to the actuator.   The method of claim 2, wherein the uncontrollable perturbation is imposed by adding noise to the control signal.   The method of claim 3, wherein the noise is generated by a noise generator.   The method of claim 2, wherein the uncontrollable perturbation is imposed by intentionally setting a non-optimal value for the control parameter in the controller.   The method of claim 2, wherein the uncontrollable perturbation is imposed by temporarily changing a value of the control parameter in the controller. A method for extracting fingerprint data from data recorded on a record carrier along a recording track in the form of a writing pattern,
The method wherein the fingerprint data is determined based on a radial offset of the writing pattern from the record carrier, the radial offset being a distinguishing feature of the writing pattern.   8. The method of extracting fingerprint data according to claim 7, wherein authentication data is generated based on the fingerprint data.   The method of claim 8, wherein the authentication data is generated based on the fingerprint data depending on the data. Using fingerprint data from the data recorded on the record carrier, and storing the fingerprint data as reference fingerprint data for later authentication of the data,
The method according to claim 1.   The method of claim 10, wherein the reference fingerprint data is stored on the record carrier. Method for authenticating data written on a record carrier along a recording track in the form of a writing pattern, wherein fingerprint data can be extracted from said writing pattern, and the reference fingerprint data is used for authentication purposes Yes, and the method is
-Extracting the fingerprint data;
-Obtaining the reference fingerprint data; and-checking whether the fingerprint data is consistent with the reference fingerprint data;
A method,
8. The method of claim 7, wherein the writing pattern has a radial offset from the recording track, the radial offset being a distinguishing feature of the writing pattern and extracting the fingerprint data. Is used. An apparatus for writing data to a record carrier along a recording track so as to generate a writing pattern, wherein fingerprint data can be extracted from the writing pattern, the apparatus comprising:
A writing means for writing the data; and a tracking means for writing the data while maintaining the writing means along the recording track;
A device comprising:
An apparatus wherein there is means for imposing uncontrollable perturbations on the tracking means such that the writing pattern has a radial offset from the recording track. An apparatus for extracting fingerprint data from data recorded on a record carrier along a recording track in the form of a writing pattern,
The apparatus is constructed to determine the fingerprint data based on a radial offset from the recording track of the writing pattern, wherein the radial offset is a distinguishing feature of the writing pattern. Features device.   A record carrier in which data is recorded along a recording track in the form of a writing pattern, wherein fingerprint data can be extracted from the writing pattern, the writing pattern having a radial offset from the recording track And the radial offset is a distinguishing feature of the writing pattern.   16. The record carrier according to claim 15, wherein reference fingerprint data obtained as fingerprint data extracted from the data using the method according to claim 7 is stored.

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