Patent Application
20060104449
This invention relates to a record carrier storing copy-protected information. Examples of such record carriers are mainly Audio CDs, CD-ROMs, CD-Rs, CD-RWs, DVDs etc., but the invention is equally applicable to other record carriers as well, as e.g. magnetic tapes, diskettes, and hard disks.
Record carriers such as CDs or DVDs are nowadays a mass product used e.g. for distributing audio and video content for entertainment purposes and to supply software and computer games. Moreover, certain kinds of these media such as the CD-R and the CD-RW+ are once or several times recordable e.g. by using a CD burner. They are therefore also usable for short-term backup as well as for long-term archiving purposes. Moreover, the increasing storage capacities of these devices extend their applicability even further.
On the other hand, the existence of these easy to handle and durable recordable media in connection with the digital representation of the media contents opened an easy way of taking one-to-one copies of copyrighted CDs, which nowadays presents a major commercial problem for the content industries.
Accordingly, several methods for copy protection of such record carriers have been proposed in the state of the art. Typically, there is a trade-off between the effort spend for copy protection, measured e.g. in the amount of computing power and memory required or public infrastructure to be installed, and the level of protection reached. Therefore, while there exist methods like e.g. asymmetric keying allowing a protection level currently being regarded as safe, most methods being actually used with CDs do not completely prevent copying but just make it more difficult.
For copy protection, many methods propose to store the content to be protected in an encrypted form on the record carrier. Then, in order to utilize the content, e.g. to play a song from an audio CD, a corresponding decryption information is needed. This decryption information may be stored on the record carrier together with the content or on a separate medium. Storing the decryption information on the record carrier together with the content has e.g. the drawback that a one-to-one copy is indistinguishable from the original and, thus, constitutes an easy way to break the copy protection. Storing the decryption information on a separate medium can prevent such easy copying by choosing a more difficult to copy medium as e.g. a smart card. On the other hand, using a separate medium has at least the drawback that the record carrier can only be used in conjunction with the separate medium and, thus, requires from the user a careful joint usage and storage of both the record carrier and the separate medium.
U.S. Pat. No. 6,044,046 A therefore proposes to use as a separate medium a chip being physically integrated within the record carrier. This renders the record carrier with built-in chip as easy to handle as a record carrier itself. Furthermore, U.S. Pat. No. 6,044,046 A discloses the communication interfaces of the chip and of a corresponding device for reading and/or writing the record carrier with built-in chip. In particular, a solution is described for allowing the reading and/or writing device simultaneous access to the record carrier and the built-in chip. For the full description of these and related issues the contents of U.S. Pat. No. 6,044,046 A is herewith incorporated into this application by reference.
While being an elegant solution, also the copy-protection scheme of U.S. Pat. No. 6,044,046 A has its drawbacks. Consider e.g. the following situation of content distribution over the Internet, first examples of which have already been introduced. A user might buy and download content as e.g. a video via the Internet in order to store it on a record carrier. While, of course, the internet is an insecure channel, there are methods known as e.g. the already mentioned asymmetric keying for conducting secure communications over insecure links, turning such insecure channels into so-called secure authenticated channels. For a more explicit description of the issues relating to secure communications over insecure links the contents of U.S. Pat. No. 5,949,877 A is herewith incorporated into this application by reference.
Thus, assuming that also the hardware and applications being installed at the user's premises and participating in the process of downloading the content have a high enough level of copy protection the content can be securely written e.g. to a record carrier with built-in chip at the user's premises. But in order to do so the decrypting information for the bought content has to be written to the chip at the user's premises, i.e., this part of the chip's memory has to be programmable. Accordingly, recordable record carriers with in such a way programmable built-in chips have to be commercially available.
As a consequence, if the decryption information of a specific content once is tapped, e.g. by tapping the channel between the device writing to the chip and the chip, which might e.g. be realized by optical coupling elements, then the decryption information might be stored e.g. on a hard disk. Subsequently, the decryption information then might be published on the Internet and/or counterfeit chips might be programmed with it. Doing a one-to-one copy of the contents of the record carrier on record carriers with such counterfeit built-in chips breaks the security mechanism.
Therefore, it is an object of this invention to provide a record carrier and a corresponding device for reading from it and/or writing to it that provides a higher level of protection than the known record carriers with built-in chips without significantly increasing the complexity of producing and operating such record carriers and devices.
These objects are accomplished by
Whereas a device for reading from and/or writing to an inventive record carrier may well be designed to take over the tasks of obtaining complete decryption information and/or decrypting and/or encrypting an asset these tasks may also be transferred to another device being coupled to the reading and/or writing device. E.g., a processor of a PC containing such a reading and/or writing device as a peripheral device may take over one or both of these tasks. On the other hand, in a home entertainment system as e.g. an audio CD or video DVD player the integration of these tasks in the reading and/or writing device is preferable.
Together, the record carrier and the device for reading from and/or writing to it form a system for supporting copy protection according to the invention. Moreover, the invention provides a method for reading copy-protected information from and/or writing copy-protected information to an inventive record carrier.
Thus, the higher level of protection stems from distributing the decryption information on at least two areas of a record carrier instead of concentrating it e.g. on the built-in chip alone. Distributing the decryption information on the first and second areas thus complicates an illegal copying of the record carrier.
In this construction the first area typically serves for storing the payload information, e.g. the songs and/or videos and/or the computer games a user wants to purchase. The second area might also be a pure storage area, but in a preferred embodiment comprises a chip as in the record carrier with built-in chip disclosed in U.S. Pat. No. 6,044,046 A. The stores on the first and second areas might be of the same physical nature, e.g. both being a pattern of pits and lands to be read via a laser, but preferably they utilize different physical implementations, e.g. pits and lands for the first area and some simple circuitry coupled with an induction coil for the second area. This gives the advantage of different physical channels, e.g. an optical and a radio frequency one, that can be accessed in parallel. In the same manner, in some embodiments it will be advantageous to physically clearly separate the first and second areas, e.g. implementing the first area as the conventional spiral pattern of a CD and positioning the second area between the center hole and the inner data track of the CD. This avoids mutual interference of the communication channels between the two areas of the record carrier and a reading and/or writing device.
Embodying an inventive record carrier and its reading and/or writing device in a manner that the record carrier's first and second areas can be read and/or written in parallel offers the advantage that the reading and/or writing device can handle the data on the two areas independently of each other, i.e. the two data streams can be processed without disturbing each other. This offers e.g. the possibility to continuously check, e.g. at regular or irregular intervals in time, the authenticity and/or integrity of the record carrier, thus further complicating the use of an illegal record carrier. E.g., if the reading and/or writing device reads the second part of decryption information, e.g. via a radio frequency channel, only once when the record carrier is inserted in the device a hacker may betray the device by supplying the decryption information using specialized hacked equipment. This kind of attack gets much more involved if the reading and/or writing device requests the second part of decryption information several times at e.g. irregular time intervals.
Using an inventive record carrier, the content distribution and copy-protection scheme can be structured in a way that at least part of the second part of decryption information on the second area of the record carrier need not be written at the user's premises while purchasing and downloading new content e.g. from the Internet. Accordingly, the user's equipment can be designed by industry in a way that it not able to make a complete one-one-copy of an inventive record carrier. Thus, the above-mentioned attack of tapping the decryption information and doing a one-to-one copy would not be possible with legal devices for writing record carriers, as e.g. a CD burner.
Choosing a non-re-writable or more difficult to re-write memory type for the parts of the second area that need not be re-written can further increase this level of protection. E.g., if the second area comprises a chip one may choose a ROM, a PROM, or a flash ROM. Then, one-to-one copying of the second area of the record carrier requires specialized equipment or may be even completely impossible.
The remaining claims and sub-claims disclose further advantageous embodiments of the invention.
Having the second part of decryption information comprising an identifier, and, in particular, an identifier being unique among all such identifiers, yields an especially high level of protection as even record carriers carrying the same payload can then be made different from each other. Thus, the invention also relates to the corresponding selection of an identifier, the construction of the second part of decryption information from the identifier, and the production of the record carrier with said second part of decryption information. Such construction may e.g. simply consist in equating the identifier with the second part of decryption information but may also first encrypt the identifier and/or enhance it with further data before using it as the second part of decryption information.
In preferred embodiments, symmetric methods using two or even three cryptographic keys are used for en- and decryption. As these methods are computationally more efficient than asymmetric ones processing time is saved and memory requirements are lower.
If an inventive record carrier is constructed by using a built-in chip, implementing active procedures on this chip further increases the level of protection. Examples for such procedures are a counter mechanism as well as an access checking procedure. For the latter, well-known password or PIN checking methods are known in the state of the art. To this end, the contents of EP 0 919 904 A2 are included in this application by reference. Thus, different parts of the record carrier may be protected by different passwords, allowing e.g. the use of the record carrier by different people and/or for different purposes and/or kinds of data being stored, e.g. entertainment data, business data, and account data.
The second area of an inventive record area, in particular, if it is realized as a built-in chip, further offers the advantageous possibility of storing account information on the usage of the record carrier or the data and/or programs stored on it, e.g. the scores obtained in playing a stored computer game. Moreover, other personalizing information on the way a user wants to handle the record carrier can be stored in the second area. These user-specific settings, possibly in connection with the above-mentioned password mechanism, can serve in selecting the data, which are accessible on the record carrier, and/or on the way such data are presented. E.g., a particular setting may determine which songs are played from an audio CD and in which sequence they are played. Thus, functionalities as e.g. Favorite Track Selection FTS and Parental Lock, currently being programmed into the player, will become available in the record carrier itself and, consequently, carry over to every appropriate player. Other examples for user-specific settings can be found in the personalization of web pages found on the Internet as e.g. in “My Yahoo!”, which analogously carry over to corresponding applications concerning data being stored on an inventive record carrier.
If the second part of decryption information comprises an identifier, and, in particular, a unique identifier, this identifier can be advantageously used for indexing illegal record carriers on a revocation list, sometimes also called a black list. Thus, if an illegal copy of an inventive record carrier appears on the market, the copy including a copy of the identifier, this identifier can be placed on a revocation list. One can then distribute such revocation lists to the reading and/or writing devices e.g. via legal record carriers or via the Internet while downloading legal content. Subsequently, these devices can refuse to play these illegal record carriers and/or can even block their services completely or for a certain time. For further details concerning the well-known procedure of employing such revocation lists of counterfeit media the contents of U.S. Pat. No. 6,028,936 are included in this application by reference.
Of course, as is obvious to one skilled in the art, one may combine the above-described measures for obtaining an even improved copy protection. E.g., one may combine symmetric encryption methods with a counter mechanism and a password checking, and enhance the record carrier's functionality by storing user-specific settings on the chip.
These and further aspects and advantages of the invention will be further illustrated by the embodiments and, in particular, by the description of the attached figures.
In the embodiment of
In this implementation, the hidden-channel key HCK can be scrambled and/or encrypted in a secret way on the first area 3 within the payload data EAK(data). I.e. the HCK can be encrypted and/or additionally scattered within the EAK(data), this scattering e.g. being performed by flipping some bits of the EAK(data). Then, a reading device not knowing this scrambling and/or encryption scheme, in the following just referred to as scrambling scheme for short, typically will ignore these few changed bits as reading errors. Thus, as long as the scrambling scheme is kept secret a user will not be able to obtain the hidden-channel key HCK explicitly. In this sense, the hidden-channel key HCK is read via a hidden channel between the first area 3 of the record carrier 1 and the reading device.
The second area 4 stores as a second part of decryption information a unique identifier, called the unique chip-in-disc identifier UCID, e.g. a serial number being unique among all inventive record carriers, and stores furthermore the asset key AK in a form encrypted by a symmetric encryption method using a second cryptographic key, called the chip-in-disc key CIDK. The such encrypted asset key is referred to as ECIDK(AK). This symmetric encryption method may the same or may be a different one than the one used for the encryption of the payload data above. In that, the chip-in-disc key CIDK is chosen in a way that it is deducible from the joint usage of the first and second parts of decryption information, i.e. from the joint usage of the hidden-channel key HCK and the unique chip-in-disc identifier UCID.
The reading and decrypting of the data on record carrier 1 proceed as follows: The reading device reads e.g. via an optical channel the hidden-channel key HCK from the first area 3 into its internal block 10. Of course, if the hidden-channel key HCK is scrambled within the encrypted payload data EAK(data), typically, part of these data will have to be read as well. Subsequently or simultaneously it further reads the unique chip-in-disc identifier UCID into the block 12 and the encrypted asset key ECDK(AK) into the block 13. Typically these two latter read processes from the second area 4 use a different channel than the reading from the first area 3, e.g. if the second area 4 comprises a chip a radio frequency channel can be used.
Internally the reading device transfers the hidden-channel key HCK from block 10 into block 12, where both parts of decryption information, i.e. the hidden-channel key HCK as well as the unique chip-in-disc identifier UCID are used to compute the chip-in-disc key CIDK. E.g., as a concrete example, the chip-in-disc key CIDK might be computed via a one-way collision-resistant hash function H( . . . ) from the concatenation of the bit sequences of the unique chip-in-disc identifier UCID and the hidden-channel key HCK: CIDK=H(UCID 11 HCK). Using such a hash function offers the additional advantage of the chip-in-disc key CIDK requiring only a small storage area on the second area 4 of record carrier 1. But, of course, instead of a hash function H( . . . ), for deriving the chip-in-disc key CIDK, other methods may be used as well. Further examples are the usage of a symmetric encryption method employing the UCID as cryptographic key and the HCK as data to be encrypted or vice versa, i.e. computing: CIDK=EUCID(HCK) or CIDK=EHCK(UCID).
The chip-in-disc key CIDK is then internally transferred into the block 13, where it is used for decrypting the encrypted asset key ECIDK(AK). Afterwards, the thus obtained asset key AK is internally transferred into the block 11. These processes typically will take place, together e.g. with reading some index and/or table of contents information on the record carrier 1, immediately after having inserted the record carrier 1 into the reading device.
Then, if encrypted payload data EAK(data) is to be decrypted, e.g. if a song from an audio CD is to be played, the reading device will read said encrypted payload data EAK(data) into its internal block 10, e.g. via an optical channel, and, typically, will continuously transfer it further into internal block 11. In block 11, the asset key AK is used for decrypting the encrypted payload data EAK(data). The decrypted payload data can then be further processed in the reading device, e.g. a digitally stored song will be converted to analog and played via the loudspeakers, which is not shown in the figure.
In detail, the writing of new content on the record carrier 1 then takes place as follows: External block 15 transfers via a secure authenticated channel the new encrypted payload data EAK(data), the hidden-channel key HCK, and the asset key AK to the writer-internal block 16. Block 16 writes the new encrypted payload data EAK(data) and the hidden-channel key HCK, e.g. via an optical channel, on the first area 3 of the record carrier 1. As already mentioned, advantageously, on the first area 3, the hidden-channel key HCK is scrambled within the encrypted payload data EAK(data). This scrambling might already be performed in the external block 15 or it might be performed in the writer-internal block 16. Furthermore, block 16 transfers the asset key AK to writer-internal block 17.
To conclude the writing process the asset key AK has to be encrypted and written to the second area 4. For that, at first the hidden-channel key HCK has to be transferred to the writer-internal block 10. This can be performed as in the reading process, i.e., after the hidden-channel key HCK has been written to the first area 3, block 10 can read it from the first area 3. Alternatively, if in block 16 the hidden-channel key HCK is known explicitly, block 16 can directly transfer it to block 10, which is indicated in
Besides the encrypted payload data EAK(data) and the asset key AK, the external block 15 might further provide additional information. An example for that are access rights. Access rights e.g. determine how often a song on an audio disc may be played. They can be written to the first area 3 and/or the second area 4 of the record carrier 1, and they can be administrated by the reading and/or writing device and/or by a built-in chip of the record carrier 1.
One skilled in the art will notice that distribution of decryption information disclosed in
Such non-unique chip-in-disc identifiers may e.g. result from overlaps between different manufacturers, i.e. whereas each manufacturer may produce its record carriers with unique chip-in-disc identifiers UCID, e.g. by using a serial number, manufacturers may want to save the effort to negotiate disjoint ranges of chip-in-disc identifiers between them. The thus resulting very rare occasions of identical chip-in-disc identifiers will not much compromise the level of protection of inventive record carriers.
Concerning the hidden-channel keys HCK, especially if they are to be scrambled within the encrypted payload data EAK(data), an advantageous choice is to generate one hidden-channel key HCK per title of record carrier. I.e., record carriers with the same title, i.e. those carrying the same payload share its hidden-channel keys HCK while record carriers with different titles also use different hidden-channel keys HCK.
Considering some possible attacks on the inventive copy-protection mechanism, one can make the following observations, where in all cases it is assumed that the unique chip-in-disc identifier UCID cannot be re-programmed by a user.
In trying to copy a first disc to a second one, a user may do a one-to-one copy of the first area 3, thereby copying the encrypted payload data EAK(data) and the hidden-channel key HCK. After once having tapped the transmission of the encrypted asset key ECIDK1(AK) of the first record carrier, this might e.g. be published on the Internet and a user disposing of the right equipment might write it on the second area 4 of the second record carrier. But the first and second record carriers will differ in their unique chip-in-disc identifiers UCID1 and UCID2 and thus in their chip-in-disc keys CIDK1 and CIDK2. Accordingly, the copied encrypted asset key ECIDK1(AK) of the first record carrier cannot be decrypted with the chip-in-disc key CIDK2 of the second record carrier rendering the copy unreadable. Thus, even if a user is able to do a one-to-one copy of all re-programmable parts of an inventive record carrier, the non-reprogrammable unique chip-in-disc identifiers UCID1 and UCID2 prohibit this kind of attack.
Copying a disc to itself is of interest just in the case of diminishing access rights, e.g. in the case that a video DVD may only be played once or N times. Then, when starting to play such a disc the encrypted asset key ECIDK(AK) may be tapped and later be re-written to the second area 4 of this record carrier. When buying new content e.g. by downloading from the Internet, alternatively, instead of tapping the encrypted asset key ECIDK(AK) when starting to play such a disc, a user may tap this key while it is written to the second area 4 of the record carrier. Thus, this kind of attack cannot be prohibited by the inventive copy-protection method. But, of course, a user will need the right equipment for such re-programming, e.g. he will need to hack a legal player.
In large parts
In
Reading of the record carrier 1 of
The comparison block 18 also reads the internal counter Ci from the chip 4′ and then compares the external counter Ce with the internal counter Ci. It transfers the result of this comparison to the payload decryption block 11′, which will now only then decrypt the payload data EAK(data) if the external counter Ce coincided with the internal counter Ci.
To complete the counter mechanism, after the external counter Ce and the internal counter Ci have been read, the chip 4′ increments the internal counter Ci by 1, the reading and/or writing device in block 17′ increments the external counter Ce by 1, encrypts the concatenation of the asset key AK with the just incremented external counter Ce using the chip-in-disc key CIDK, i.e. computes ECIDK(AK∥Ce), and writes the result ECIDK(AK∥Ce) back to the chip 4′. This cares for both the external counter Ce and the internal counter Ci on the chip 4′ being incremented by 1 and, thus, coinciding again, and the record carrier 1 being ready for the next legal access.
One skilled in the art will notice that the counter mechanism is based on the facts that the internal counter Ci cannot be influenced from outside the chip 4′ while the value of the external counter Ce is not known to a user because the hidden-channel key HCK is secret. Then, the incrementing of the two counters in safe environments together with the requirement of them keeping identical values creates a further increased level of protection as can be seen by re-visiting the attack of copying a disc to itself already discussed in connection with
As already mentioned, the counter mechanism successfully blocks the copying of a disc to itself. This follows from the observation that restoring ECIDK(AK∥Ce) to its initial value after having played the disc, i.e. restoring it to its value when starting to play the record carrier, also restores the external counter Ce to its initial value while the internal counter Ci already has been incremented one or more times. Thus, the two counters will no more coincide and the reading and/or writing device will deny access to the record carrier.
As mentioned in the summary of the invention, these protection mechanisms can further be complemented by a revocation list of illegal record carriers, i.e. a revocation list can be used e.g. in addition to the above counter mechanism or also instead of it. On detection of an illegal record carrier the reading and/or writing device can execute, besides denying access to this record carrier, a counterfeit response routine ranging from a simple warning message to locking the device. For details, again reference is made to U.S. Pat. No. 6,028,936.
The previous embodiments shown in
Instead of the hidden-channel key HCK itself the first area 3 of the record carrier 1 now stores it in encrypted form EDNK(HCK), this encryption using a symmetric method employing as a cryptographic key a fourth cryptographic key denoted as the device-node key DNK. This device-node key DNK is stored within a new block 19 within the reading and/or writing device for the record carrier 1, and as such is a property of a legal such device. Accordingly, block 10′ of the reading and/or writing device, which corresponds to block 10 in
In the same way, if storing an encrypted version EDNK(HCK) of the hidden-channel key HCK, the writing of new content on a record carrier 1, as compared to
To provide the hidden-channel key HCK to block 10′ for the writing process, as in
As is obvious to one skilled in the art the above embodiments can be modified in a variety of ways while still implementing the invention. E.g., the functionalities of the distinct blocks mentioned in the figures can be distributed in other ways or can be concentrated in a single or a few chips only. Therefore, above embodiments are not to be taken as limiting the extent of protection of this application.
| Number | Date | Country | Kind |
|---|---|---|---|
| 02015057.9 | Jul 2002 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB03/02504 | 6/26/2003 | WO | 10/31/2005 |
