The invention relates to the copy protection for recorded media.
The invention relates to a system for copy protection of recorded information, includes an information carrier having a medium mark representing a first bitpattern, a recorder for recording the information on the information carrier and a player for reproducing the recorder information from the information carrier.
The invention further relates to a recorder for recording information on an information carrier with a medium mark representing a bitpattern.
The invention further relates to an information carrier with recorded information and a medium mark representing a bitpattern.
The invention further relates to a player for reproducing information from an information carrier and the system including for detecting a medium mark representing a bitpattern.
Copy protection has a long history in audio publishing. The presently installed base of equipment, including PC's with audio cards, provide little protection against unauthorized copying. In any copy-protection scheme, the most difficult issue is that a pirate can always attempt to playback an original disc, he can treat the content as if it were an analog home recording and record this. Consumer recorders should be able to copy recordings of consumer's own creative productions without any limitation, but prohibit the recording of copy-right material. Thus, the copy protection mechanism must be able to distinguish between consumers' own creations and content that originates from professional music publishers. The equipment must make this distinction based on the content only, as any reference to the physical source of content (e.g. disc or microphone) is unrealiable. For digital storage media such as DCC, “copy bits” have been defined, which bits indicate a copyright status, e.g. “no copy allowed”, “free copy” or “one generation of copy allowed”. Other copy bits may indicate that the medium storing the information must be a “professional” medium manufactured by pressing and not a “recordable” disc.
A system for copy protection of recorded information comprising a recorder, information carrier and player, is known from EP-0545472 corresponding to U.S. Pat. No. 5,724,327 to Timmermans et al. (listed as document D1 below). The copy protection is based on a so-called medium mark, i.e. a physical mark representing a bitpattern indicating the status of the medium, e.g. a code indicating a “professional” disk manufactured by pressing. A medium mark should not be copyable or changeable by standard recording equipment, and therefore it is to be stored on the information carrier in a manner different from the recorded information, such as audio or video. The medium mark is detected by the player and if it is not present or indicates a different status (e.g. “recordable disc” on an illegal copy), reproduction is blocked. The known information carrier has a prearranged guiding track, a so-called pregroove. In the track determined by the pregroove, information can be written in a predefined manner represented by optically readable patterns which are formed by variation of a first physical parameter, such as the height of the scanned surface. The pregroove has variations in a second physical parameter, such as an excursion in a transverse direction, also denoted as wobble. The wobble is FM modulated and this modulation represents a bitpattern which is used for recovering the information, e.g. a descramble code for recovering information stored as scrambled information. The bitpattern constitutes a medium mark, because the track wobble cannot be copied to a recordable disc on standard recording equipment. The known player includes a reader for reading the optical patterns and recovering apparatus for recovering the bitpattern from the medium mark. The player and information carrier form a system for controlled information reproduction. For this purpose, the player has apparatus for controlling the reproducing of the information depending on the medium mark. If the information is copied on a writable information carrier, the information of this copy will not be reproduced by a player, because during the writing process only the optical patterns are written in the predefined manner and the copy itself does not contain any medium mark.
Those skilled in the art are referred to the following documents:
The above references are hereby incorporated herein in whole by reference.
The inventors recognize a problem in the known system. The problem is that copying the information after reproduction cannot be sufficiently controlled. If the information includes the copy bits, such bits can be manipulated easily, e.g. on a PC or in a small electronic circuit. The information with the manipulated bits can be copied freely. If the information is recorded in a scrambled way and de-scrambled during reproduction using the medium mark bitpattern, the information can be recorded in its plain (descrambled) status and is not protected against copying at all.
It is an object of the invention to provide a system in which copying is better controlled and the copy protection cannot be circumvented by simple manipulation of the copy bits.
For this purpose, in the system according to the invention, the recorded information includes a watermark representing a second bitpattern. The second bitpattern has a predefined relationship to the first bitpattern, and the recorder includes an encoder for embedding the watermark in the information and a generator for generating the second bitpattern according to the predefined relationship between the first and the second bitpattern. The player also includes a verifier for verifying the relationship between the second bitpattern and the first bitpattern. The watermark is indicative of the copyright status of the recorded information. This has the advantage, that a signal representing the information after reproduction still contains the watermark and a recorder can be aware of the copyright status of the signal offered for copying, whereas the copyright status of the signal indicated by the watermark cannot be changed or manipulated without disturbing the signal. The prior art system using the medium mark as a descramble key or a fixed code is vulnerable to an ‘illegal’ recordable disc have a fixed, false medium mark. For example, any information read from a scrambled copy protected disc can be recorded on an illegal copy after (re-)scrambling using the fixed, false key. The relation between the watermark bitpattern and the medium mark bitpattern requires that the medium mark bit correlates with the recorded information. Hence in the system according to the invention a fixed, false medium mark cannot be used to make illegal copies. As there is a predefined relation defined between the first (medium) bitpattern and the second (watermark) mark bitpattern, a strong copy protection is realized, because an illegal copy must contain the specific medium mark correlated to the watermark according to the predefined relation and therefore the malicious party is forced to obtain the relation for manipulation. Choosing a suitable relation can create a barrier against such manipulation. The detection of the watermark in the player is relatively simple and the information read from the information carrier does not require any processing, such as descrambling. Verification in the player of the watermark bitpattern against the medium mark is a strong protection against copying, as neither of the marks can be easily manipulated. A further advantage is, that the verification function in the player can be relatively slow, as the verification of the predefined relationship needs to be performed only once when starting the reproduction of the recorded information.
It is to be noted, that WO 97/13248-A1, which is filed before but published after the priority date of this invention (PHN 15391, document D2 listed above) describes a watermarking system for a video signal. The watermarked video signal is recorded on a disk containing a medium mark. However the medium mark only indicates the type of medium and has no correlation with the signal or the watermark.
In a preferred embodiment of the system, the relationship includes a cryptographic one-way function. The one-way function prevents, when the required result (e.g. the watermark bitpattern) is known, that the source (e.g. the medium mark bitpattern) can be found by calculating ‘backwards’. This has the advantage, that the malicious party is forced to obtain the medium mark bitpattern directly from the original medium. The original medium may not be available to him or the player may be equipped not to make the medium mark bitpattern externally available. This creates a significant barrier for the malicious party trying to make an illegal copy with a “chinese” copy of the medium mark.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter and with reference to the accompanying drawings, in which
We propose a copy control method for bitstream- or DSD-signals (Direct Stream Digital) stored on storage media such as DVD audio (Digital Versatile Disc). The method relies on a watermarking method, such as the one proposed by A. A. M. Bruekers et al, in document D3 listed above. Recently, it has been realized that watermarks or embedded signalling can be used to make copy protection methods more robust against attacks. Embedded signaling or watermarking is a method of burying information in the audio content. In this text we use the word professional for any product that is officially registered with a trusted party which represents the interests of the recording industry and hardware manufacturers. We denote any other product as a consumer product. Consumer products are assumed to obey copyright rules, enforced either by a patent licensing agreement or by law, or both.
For Copy Protection a total solution is needed. Watermarking is not restricted to digital formats, but can also be embedded and detected in analog signals. Often, spread-spectrum technology is proposed for embedding watermarks into audio. A technical difficulty of spread-spectrum methods is that retrieval or detection of such embedded data requires substantial signal processing. Although this is not a problem for professional equipment used in legal cases to prove the origin of the audio material, the computational effort appears far beyond what is feasible and economically reasonable within consumer electronic products to support copy protection. A particular problem is that the audio quality requirements set by the music industry would require such large spreading gains that synchronization and data detection would take excessively long integration times. Parameters considered in spread spectrum watermarking presumably do not satisfy current audio quality requirements. Future standards aim at further enhancing the audio quality and simultaneously require secure protection of music IPR. It is our strong belief that it is unlikely that satisfactory methods will indeed be found in near future to combine these two requirements at reasonable cost. Particularly, the absence of protective measures in the installed base of audio equipment causes a problem. It appears virtually impossible to avoid that signals can be copied by going back to analog. Moreover, consumer expectations are that some kind of home taping, e.g. to listen in the car, should be possible. On top of that, some countries levy a fee on blank tape for analog copying for private use, and certain technical means to restrict analog copying are not legally acceptable. There appears an opportunity to set new standards for storage and representation of digital audio (e.g. DVD), but technology to solve the copy protection issue completely (i.e., including analog copying) is unlikely to become available soon. For audio, a bitstream-only solution may be of use. Given this situation, it can be useful to protect new audio storage media against unauthorized copying of discs, even if analog copying remains possible. In order to copy, conversion into other domains (e.g. analog) are needed and some loss of quality occurs. The scheme proposed here using digital watermarking does not solve the existing problem of piracy and excessive home taping whereby the audio signal is converted to analog as part of the copy process. If the industry adopts a copy protection scheme based on watermarking, it will presumably come to a layered approach. The most robust watermark should withstand D/A and A/D conversion, but this will require long integration times for the detection. This implies that the record or playback inhibit decision will be delayed. A watermark in the bitstream can be detected within milliseconds and trigger copy protective measures immediately. Such fast detection appears essential if bitstream signals are transferred over open busses (such as P 1394). In summary, the method described in this document has the following properties:
In the invention we propose a scheme that protects against direct (bitwise) copying of high quality digital DSD streams. The method does not technically protect against conversion of DSD to PCM or analogue. However, some protection is provided against such attacks in the sense that if a bitstream/DSD signal, it is converted back into DSD may be watermarked with the serial number of the consumer DSD encoder. The method relies on a watermarking method, such as the one proposed by A. A. M. Bruekers et al. Our method can coexist with many other forms of copy protection, including serial copy management bits and the embedded signaling of spread spectrum watermarking. The additional hardware in consumer equipment appears very small. Another tool used in the system embodiment is a medium mark, i.e. a method to distinguish a professionally mastered disc from a recordable. Implementations of such tool can be a wobble key (as known from document D1 above), modulation of channel code errors (e.g. EFM) or intentional modulation the jitter of pits and lands of a disc, or embedding an on-disc chip, or just data written in the lead-in area which is not accessible by consumer recorders. These two tools (watermark and medium mark) are used to support the following features (both or just one):
Conditional playback will make sure that such a pirate disc can not playback on consumer players. That is, pirates cannot commercially distribute illegal copies. In conditional playback, a consumer DVD audio player will only play audio discs if certain copyright conditions are met. The player identifies the audio content either as a consumer recording or as professionally published audio content, by detecting or checking for a watermark in the audio stream. In the latter case (professional content protected by copyright), the player checks whether the physical disc is original and professionally mastered, rather than a copy on a consumer recorder or consumer disc press. This requires both a marking method for the content (watermarking) and a method for marking the physical storage medium that can only be produced by a professional recorder or pressing machine.
In a first embodiment of the system professionally mastered audio discs carry an identifier unique to the publisher, which can not be copied. This identifier can for instance be a set of bits written in an area that is not accessible for recorders, it can be a wobble key or a special pattern in the running DC component of the EFMplus channelcode used in DVD. The DVD audio player checks for this mark. If this mark is unavailable or if it contains a special code reserved for home disc recorders, it will only playback the DSD stream if a special watermark is found that identifies the DSD encoder. If this watermark is not found, as would be the case if a professionally released audio stream is copied illegally to a recordable disc, the audio is not played back at all. To avoid any degradation of the quality of professional DSD releases this scenario does not require that the audio content of professionally released audio titles is watermarked, but this scenario requires that the watermark embedding method is used in consumer equipment. Besides a frequently repeated copy control bit, a unique serial number is embedded into the audio stream by all DSD encoders/recorders in the consumer market. The circuitry to embed this number appears simple. The consumer can not copy professional DSD audio directly to a DVD audio disc, as it will not playback (because of the watermark be absent). If he converts the signal to analog, PCM or another format, and then re-creates DSD, the particular DSD recorder can be traced. Moreover, the scheme can be defined in such a way that home recordings have smaller dynamic range. A further strengthening is achieved if each player not only checks whether a watermark is present on consumer discs, but also check whether a valid serial number is embedded. Known cryptographic methods can be used for integrity checks, e.g. concatenating a digital signature to the serial number. This avoids that a pirate can tamper with serial numbers.
A second embodiment is similar to the first, but the bit stream of professionally released audio does also contain a watermark. This watermark is used to verify the medium mark in a cryptographic way. The medium mark now differs from title to title. The relation between the bitpattern represented by the watermark and the bitpattern represented by the medium mark is not easy to manipulate. Preferably, the crytographic relation is chosen as follows. Let y=F(x) and x=G(u) be two cryptographic one-way functions, i.e. their inverse is computationally infeasible to compute with finite arithmetic resources. This scenario uses a seed u to create x and y, according to x=G(u) and y=F(x)=F(G(u)). In this concept G and F may be the same function, but this is not necessary. On a professionally mastered disc, the embedded watermark contains y and the medium mark carries x. Professional recorders always perform the G function before writing a medium mark. That is, they embed a medium mark x which is internally generated from the user input u. All (consumer) players perform F to verify the medium mark if a watermark is found that indicates that the content is copy protected. Consumer recorders are assumed not to be able to write a medium mark at all. Using the system the copy-right owner can decide himself whether or not to release the seed u, which allows copying. In professional music publishing, it can be necessary to create a tape master of the music title. The audio is then pre-encoded with embedded the watermark y. During the production process, the professional recorder (disc master generator machine) directly accepts the watermarked DSD 30 and inserts this after the DSD encoder/watermarker 23 of
In this scenario, a pirate must have access to a professional recorder to create media marks on a pirate disc. A pirate can copy the audio and recover y, but he cannot calculate x. This system adds security to the copy protection scheme, particularly if we can ensure that x cannot easily be read from the disc, i.e., remains within the first chip in the basic engine (that must use x to verify watermark y). Moreover, even if a pirate can read x, he must find u to enter it into the recorder and to have x written as a medium mark. No recorder will directly accept to x and write it to disc. In this scenario, a pirate must physically modify both his (officially registered mastering) recorder (to bypass the G function) and his player (to extract x).
In a further embodiment copy protection can be provided for consumer recordings. It can be envisioned that consumers want to publish or disseminate their own recorded audio creations at a small scale. We now describe how consumer recorders can implement some of the elements of the above scheme. This gives consumers the possibility to create discs that can only be copied directly (bit-by-bit) if the recipient also knows seed u. Part of the medium mark must be recordable by the recipient. A possible embodiment is to split x into two parts, with x=x1||x2, such that y=F(x1||x2). Then x1 acts as a medium mark, similar to the scenario described above, and x2 is written as a separate file on the disc. Professional recorders can write x1 as well as x2. Consumer recorders can write x2 but on recordable discs, x1 has a default value x1=x_c prepressed on the disc. The consumer recorder embeds watermark y=F(x_c||x2) where x2 is generated from a seed u, i.e., by taking a portion of the bits of G(u). The owner can copy his own creations because he knows u. In players, neither x1 nor x2 leaves the basic engine, so it remains hidden for the user.
For the above embodiment, a suitable relation between the watermark bitpattern and the medium mark bitpattern is a one-way function. An implementation of the one-way function can be y=x2 mod N with N a public modulus. Here N is the product of two secret large primes (N=pq). In fact N can be part of the data that is embedded in the watermark, i.e., concatenated to y. Another possibility is the discrete-log one-way function conjectured by Diffie and Hellman [1976] (=document D6 listed above): F(x)=αx in GF(p) with α a primitive element of GF(p). Here p is a large prime such that p−1 has a large prime factor. The above two implementations bear the disadvantage that the size of the arguments, i.e., the number of bits needed to be secure, is quite large. A practical system based on fewer bits can be to apply an appropriate secret-key encryption algorithm, e.g. the DES, with y=F(x)=x{circle around (x)}DES(x). This is illustrated in the circuit of
In its pure form, a conditional recording scenario does not perform checks during playback. In a different embodiment the consumer DSD recorder accepts an analog signal, possibly conditional to some analog copy information check. The on-board DSD encoder embeds a watermark into the stream. This mark consists of two parts: copy protection data and a serial id. number of the recorder. The consumer DSD recorder accepts a digital DSD stream only if it can recognize valid copy control data. This copy control data should state that this material may legally be copied onto a disc. Such a recorder is similar to the recorder shown in
The consumer DSD recorder does not accept a DSD stream that contains Copy Control Marks that prohibit recording. In an embodiment of a strong form, the absence of Copy Control Information is interpreted as “no copy allowed”. In a weaker form, signals without copy control information are automatically resampled and watermarked. This weakens the copy protection, but leads to some quality degradation.
In a further embodiment a copy once feature is included. A professional DSD stream contains embedded copy-right data that grants permission to copy once. This can be implemented by embedding a further watermark yco (in addition to mark described earlier). Moreover the professional disc contains a special permission mark xco where yco=H(xco) with H( ) a cryptographic one-way function. The mark yco remains with the audio (possibly embedded) during playback, but it is removed by the consumer recorder.
It is noted that, hybrid solutions using conditional recording and conditional playback can co-exist. Of particular interest is a scenario in which (despite technical difficulties described in the introduction) a watermark check in the analog domain should be performed by recorders. If a pirate manages to modify his recorder to bypass this conditional recording check, and put professional DSD on a disc anyhow, the copy protection schemes described here can prevent playback on players in the market.
Although the invention has been explained mostly by embodiments using DSD audio, several embodiments of the watermarking of audio and/or video can be used. Watermarking is also possible for PCM audio. An example is hiding data in the LSB's, possibly including a spectral shaping of their effect. An implementation for such embedding scheme has been presented by Oomen et al. in 1994 (see document D4 listed above). For our application, we preferably would only embed data in a limited number of preselected samples, with one bit per selected sample. Such embedding scheme can be implemented within the same device that converts professional (24 bit) audio into lower resolution (e.g. 16 bits) The method previously mentioned for DSD watermarking (in document D3 listed above) may also be used for embedding data in PCM. Another option is to use the loss-less encoding for embedded signaling. One method for lossless encoding was proposed by Bruekers et al (described in document D5 listed above) A possible method of embedding data is by choosing the properties or parameters of the predictive filter (
In the embodiments a disc has been described as information carrier, but any other carrier can be used in the invention, such a tape or broadcast, as long as the medium mark is supplied in a way which cannot be easily copied. Further the invention lies in each and every novel feature or combination of features.
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97200165 | Jan 1997 | EP | regional |
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