Patent Publication Number: US-2007101160-A1

Title: Information reproduction apparatus and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2005-317695, filed Oct. 31, 2005, the entire contents of which are incorporated herein by reference.  
     BACKGROUND  
      1. Field  
      The present invention relates to an information reproduction apparatus and method, and more particularly to an apparatus for reproducing encrypted content data stored in a large-capacity memory, such as a digital versatile disk (DVD) and hard disk, while decrypting the content data.  
      2. Description of the Related Art  
      When content data that requires copyright protection is stored in an information recording medium, it is stored, encrypted. Patent document 1 (Jpn. Pat. Appln. KOKAI Publication No. 2003-122637) discloses a technique of this type. To encrypt content data, key data (called, for example, a title key) is used. To further enhance the confidentiality of content data, a title key itself is encrypted into an encrypted title key and stored in a recording medium. To decrypt the encrypted title key, a medium ID, for example, which specifies a particular device key and disk itself, is used. In this case, if an illegitimate disk or illegitimate reproduction device is used, the encrypted title key cannot be decrypted. Concerning this, see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-122637.  
      In general, one title key is imparted to one title. In this case, if the title key is opened, the copyright of content data cannot be protected. In contrast, if a number of title keys are imparted to one title, and the title key used is switched from one to another during the reproduction of a data stream, the copyright protection of content data is much enhanced.  
      However, to process a large number of key data items, it is necessary to increase the memory capacity of a key data setting unit incorporated in a content decryption unit.  
      In general, it is desirable to form the content decryption unit of a semiconductor integrated circuit, so as to prevent the data processing units incorporated therein and currently processed data from being easily detected from the outside. If the memory capacity of the key data setting unit is increased, the size of the resultant hardware is increased, which makes it difficult to design the unit. This inevitably increases the required cost, degrades the yield of production, and makes it difficult to increase the memory capacity so as to increase the amount of key data stored in the memory.  
     BRIEF SUMMARY OF THE INVENTION  
      It is an object of embodiments according to the invention to provide an information reproduction apparatus that can prepare a large number of key data items and hence significantly contribute to the copyright protection of content data, even if the memory capacity of a key data setting unit incorporated in a content decryption unit is small, and to provide an information reproduction method employed in such an apparatus.  
      In accordance with an embodiment of the invention, there is provided an information reproduction apparatus for reproducing encrypted content data recorded in an accumulation medium, the encrypted content data being acquired by encrypting a plurality of partial content data items, to be successively read, using a plurality of key data items corresponding to the partial content data items, comprising:  
      a key data table which stores the plurality of key data items;  
      a read processing section configured to read, from the accumulation medium, the partial content data items to be successively read;  
      a decryption unit configured to decrypt the partial content data items read by the read processing section; and  
      a set-key selection section configured to read, from the key data table, a first key data item used to decrypt a first one of the partial content data items to be decrypted by the decryption unit, and a second key data item used to decrypt a second one of the partial content data items be processed next at least, the set-key selection section being also configured to set the read key data items in a key data setting unit.  
      Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be leaned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.  
       FIG. 1  is an exemplary block diagram showing the configuration of an embodiment of the invention;  
       FIGS. 2A and 2B  are views useful in explaining examples of arrangements of ILVU and examples of reproduced streams;  
       FIG. 3  is a flowchart useful in explaining an operation example of the apparatus of  FIG. 1 ;  
       FIG. 4  is a flowchart useful in explaining another operation example of the apparatus of  FIG. 1 ;  
       FIG. 5  is a block diagram showing the embodiment that operates as shown in  FIG. 4 ; and  
       FIG. 6  is a block diagram showing yet another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION  
      Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, in an embodiment of the invention, key data items are stored in a key data table unit prepared in addition to a decryption unit. Therefore, even if a large number of key data items are employed to encrypt a large number of partial content data items, it is sufficient if the key data items are stored in the table. This increases the degree of freedom in designing the apparatus.  
      An embodiment of the invention will be described with reference to the accompanying drawings.  FIG. 1  shows the configuration of an optical disk reproduction apparatus, to which the invention is applied. As shown, an optical disk (DVD)  11  is spun by a disk motor  10 . The information recorded on the optical disk  11  is read and converted into an electric signal by an optical head  12 , and then input to an amplifier  13 . The output of the amplifier  13  is input to a pickup-control/servo unit  17  and also to a demodulator  14  and address demodulator  16 .  
      The pickup-control/servo unit  17  generates a focusing error signal and tracking error signal, etc., based on the output of the amplifier  13 , thereby controlling the actuator of the optical head  12  to control focusing and tracking. The unit  17  also performs control for stabilizing the rotation of the disk motor  10 .  
      The demodulator  14  demodulates a read signal digitized by a digitizer, not shown. In this demodulation, a signal of, for example, 16 bytes is converted into a signal of, for example, 8 bytes, using a conversion table. The demodulated signal is input to an error correction unit  15 , where it is subjected to error correction.  
      The address demodulation unit  16  reads a physical address from the read signal. The read address is input to a system control unit  30  and managed by an address management section  301  incorporated in the control unit  30 .  
      The system control unit  30  can also control the moving position of the optical head  12  via the pickup-control/servo unit  17 , and the rotational speed of the disk motor  10 .  
      Management information, such as file system information, contained in the demodulated signal error-corrected by the error correction unit  15 , is input to a management information processing section  302  incorporated in the system control unit  30 . Key data as part of the management information is written to a key data table  31 . The key data table  31  may be formed of a semiconductor memory prepared as a secondary memory, or of a hard disk, not shown, incorporated in the apparatus. The key data recorded on the optical disk  11  is encrypted, and hence is decrypted before it is written to the key data table  31 .  
      The data (encrypted data or non-encrypted data) contained in the demodulated signal output from the error correction unit  15  is supplied to a protected-content decryption unit  18 . The protected-content decryption unit  18  includes a register capable of storing at least two key data items, i.e., a key data setting unit  32 . The protected-content decryption unit  18  decrypts the input encrypted content data, using the key data. If the input content data is non-encrypted one, it is processed under the control of the system control unit  30 , without using the protected-content decryption unit  18 .  
      The content data output from the protected-content decryption unit  18  is input to a stream processing unit  20  via a buffer  19 . The stream processing unit  20  subjects, to separation processing, a control packet including a video packet, audio packet, sub-video packet and navigation data, etc. The control packet, such as navigation data, is fetched by the system control unit  30  and managed by the management information processing unit  302 .  
      The video packet, audio packet and sub-video packet are input to an AV decoder  21 , where they are decoded. The sub-video packet contains, for example, subtitle data, and is combined with a video signal after being decoded.  
      The system control unit  30  will now be described in detail. The system control unit  30  controls the entire operation of the apparatus, and is connected to a remote control signal receiving unit  33 . The signals received by the remote control signal receiving unit  33  are recognized by an operation input processing section  306 . Assume here that the address management section  301  manages, as well as the physical address, the logical address included in the navigation data. Further, assume here that the management information processing section  302  manages, as well as file system management information, management information sent as navigation data, such as attribute information.  
      A data search table  303  also incorporated in the system control unit  30  comprises a read processing section  303   a  for reading, for example, the next ILVU (interleave unit or partial content data), and a set-key selection section  303   b.  The read processing section  303   a  recognizes the physical address of the ILVU, using the information stored in the address management section  301 , thereby controlling the read position of the optical head  12 . The set-key selection section  303   b  selects key data from the key data table  31  and sets it in the key data setting unit  32 . The key data set in the key data setting unit  32  is the key data corresponding to the read ILVU.  
      The system control unit  30  further comprises a stream determination section  304  for determining a reproduction stream for an interleaved block. The interleaved block will be described later in detail. When, for example, the optical disk  11  is loaded and the key unique to the disk is detected, the reproduction stream is determined, using this key and a device key  34  unique to the reproduction apparatus. Accordingly, different reproduction streams are determined between different reproduction apparatuses. The determined reproduction stream is the one allowed in the currently used reproduction apparatus.  
      After determining the reproduction stream, the order of reading of a plurality of ILVUs is specified. This enables the order of key data items corresponding to the ILVUs to be specified. A plurality of key data items are beforehand stored in the key data table  31 . A key data processing section  305  incorporated in the system control unit  30  determines the order of use of key data items, and then controls the set-key selection section  303   b.  On accordance with the order of use of the key data items, the set-key selection section  303   b  designates key data in the key data table  31 , and sets it in the key data setting unit  32 .  
       FIG. 2A  schematically shows part of an interleaved block provided on the track of an optical disk. The shown interleaved block is an example in which one stream is divided into six blocks. Assume that each one of the six blocks is set as an interleave unit block (ILVUB). In case of  FIG. 2A , interleave unit blocks ILVUB 1 , ILVUB 2 , ILVUB 3 , ILVUB 4 , ILVUB 5  and ILVUB 6  are acquired. Further, in each interleave unit block, interleave units A, B and C of the same data are prepared and interleaved.  
      Specifically, interleave units A 1 , A 2 , A 3 , A 4 , A 5  and A 6 , interleave units B 1 , B 2 , B 3 , B 4 , B 5  and B 6 , and interleave units C 1 , C 2 , C 3 , C 4 , C 5  and C 6 , which are identical in content, respectively, and have different encrypted key data items, are prepared. The interleave units A, B and C are alternately arranged in the interleave unit blocks. It is not always necessary to impart different key data items to the respective units. However, the greater the number of key data items, the greater the protection effect of content data. Since each of the interleave units is part of content data, it may also be called partial content data.  
      If the interleave units  1  to  6  are read in this order, the story of the content data is consistent. Accordingly, various reproduction streams as shown in  FIG. 2B  can be acquired. These streams provide the same story.  
      The reproduction stream employed in the reproduction apparatus is determined by the above-mentioned device key. Namely, different reproduction apparatuses employ different reproduction streams. Accordingly, if an illegally copied disk is detected, the reproduction apparatus used to illegally copy data on the disk is detected, which is a clue to the person who illegally copied the data.  
      Further, it is not necessary to form the interleave block on the entire track of the optical disk. If the interleave block is formed on the entire track, the disk may run out of capacity. To avoid this, the interleave block may be provided at part of content data, for example, at an important scene, or a plurality of interleave blocks may be provided intermittently.  
      Furthermore, in the above description, the reproduction streams provide the same content. However, it is a matter of course that they may provide different types of content acquired by photography carried out at different angles.  
      In this embodiment, assume that the interleave units are encrypted by different key data items. In this case, it is necessary to change key data whenever an interleave unit is fetched by the decryption unit  18 . Since it is difficult to simultaneously set a large number of key data items in the key data setting unit  32 , the reproduction apparatus of the embodiment employs a method for once accumulating the key data items in the key data table  31 . When necessary, a minimum necessary number of key data items are transferred from the table  31  to the key data setting unit  32 .  
       FIG. 3  shows an operation example of the apparatus. When the optical disk  11  is loaded into the apparatus main unit, the disk is rotated, and management information is read therefrom and accumulated in the management information processing unit  302  (step SA 1 ). Subsequently, the encrypted key data is read from the optical disk  11 , decoded and stored in the key data table (secondary memory)  31  (step SA 2 ).  
      If there is an instruction to replay the disk (step SA 3 ), a reproduction stream is determined from the device key and the key (or disk ID) unique to the disk. For instance, one of the streams shown in  FIG. 2B  is determined (step SA 4 ). When the stream is determined, the order of ILVUs is determined, and hence the order of selection and the order of use of a plurality of key data items for decrypting the ILVUs are determined (step SA 5 ).  
      Subsequently, the address assigned to the ILVU to be firstly read is set, and the key data corresponding to the ILVU is set in the key data setting unit  32  (step SA 6 ,  303   a  and  303   b  in  FIG. 1 ). Thus, the first ILUV is read and set in the protected-content decryption unit  18  (steps SA 7 , SA 8  and SA 9 ). While the decryption unit  18  is executing decryption, the address for reading the next ILVU is set in the next-ILVU read processing section  303   a  (step SA 10 ), and the key data corresponding to the next ILVU is read from the key data table  31  and set in the key data setting unit  32  (step SA 11 ).  
      After the decryption of the proceeding ILVU is finished (step SA 12 ), the ILVU is sent to the buffer  19  (step SA 13 ) for decoding, thereby starting the reading of the next ILVU (step SA 14 ). If it is determined that the stream processing of the ILVUs is finished (step SA 7 ), the next processing routine is started without decryption processing.  
      When the ILVUs are successively processed, the address assigned to each following ILVU is detected by the method described below.  
      Navigation packs including data search information (DSI) are provided as leading packs for the respective ILVUs. The DSI of a certain ILVU contains the logical address assigned to the next ILVU. Assume here that the ILVUB 2  is read, and the DSI of the leading navigation pack thereof is analyzed. In this case, ILVUA 1 , B 1  and C 1 , and ILVUA 3 , B 3  and C 3  are written as the addresses assigned to the ILVUs to be read next. Thus, the DSI of a single ILVU includes the addresses of the proceeding ILVU and next ILVU, which enables both backward replay and forward replay to be carried out. However, note that the reproduction stream is determined by the reproduction apparatus used. If the reproduction stream is not determined, the key data for decrypting the content data becomes useless.  
      In the above-described ILVU processing routine, the key data for decrypting the next ILVU is set while the proceeding ILVU is being decrypted. However, the invention is not limited to this.  
       FIG. 4  is a flowchart useful in explaining the operation of another embodiment. In  FIG. 4 , elements similar to those in  FIG. 3  are denoted by corresponding reference numbers. In  FIG. 3 , the address for reading the next ILVU from the accumulation medium is set at step SA 10 . Further, the key data corresponding to the next ILVU is set in the key data setting unit at step SA 11 . However, in the embodiment of  FIG. 4 , the address for reading the next ILVU from the accumulation medium is set when the decrypted ILVU has been transferred to the buffer  19  (step SB 2 ). Further, at the next step BS 3 , the key data corresponding to the next ILVU is set in the key data setting unit. At step BS 1 , it is determined whether the decrypted ILVU has been transferred to the buffer  19 .  
       FIG. 5  shows part of the hardware block configured to enable the operation shown in  FIG. 4 . In  FIG. 5 , elements similar to those in  FIG. 1  are denoted by corresponding reference numbers. In the case of  FIG. 5 , an ILVU-end detection unit  51  is interposed between the protected-content decryption unit  18  and buffer  19 . The ILVU-end detection unit  51  is formed of, for example, a counter for counting the read addresses in the register when the decrypted ILVU is transferred to the buffer. After all decrypted ILVUs are read and transferred to the buffer  19 , the ILVU-end detection unit  51  sets an end flag. The end flag is detected by an ILVU-end-flag detection section  308  incorporated in the system control unit  30 . Upon detecting the end flag, the ILVU-end-flag detection section  308  controls the next-ILVU read processing section  303   a  and set-key selection section  303   b  to thereby enable the operation as shown in  FIG. 4 .  
      The invention is not limited to the above-described embodiments. The trigger for controlling the next-ILVU read processing section  303   a  and set-key selection section  303   b  may be formed of the following means:  
       FIG. 6  shows yet another embodiment of the invention. In  FIG. 6 , elements similar to those in  FIG. 1  are denoted by corresponding reference numbers. In the case of  FIG. 6 , the amount of data stored in the buffer is monitored. In the DVD standards, to realize seamless replay, each ILVU is set so that the maximum and minimum data amounts fall within respective preset ranges. Accordingly, the time at which the next ILVU should be read can be detected by monitoring the data amount of each ILVU. To this end, a detection circuit  52  detects the data amount of the ILVU written to the buffer  19 . As a detection method, there is a method for counting the number of data items transferred to the buffer  19 , using a counter (data amount detection circuit  52 ). When an ILVU has substantially been transferred to the buffer  19 , i.e., the counter value exceeds a preset threshold value, an ILVU-data-amount determination section  307  incorporated in the system control unit  30  causes the next-ILVU read processing section  303   a  and set-key selection section  303   b  to start their operations. The other operations performed in this embodiment are similar to the above-described ones. The invention is not limited to the above-described embodiments, and it is not always necessary to impart different key data items to respective partial content data items.  
      The present invention is not limited to the above-described embodiments, but may be modified in various ways without departing from the scope. Various inventions can be realized by appropriately combining the structural elements disclosed in the embodiments. For instance, some of the disclosed structural elements may be deleted. Some structural elements of different embodiments may be combined appropriately.  
      While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.