Patent Publication Number: US-2007106906-A1

Title: Digital data storage/reproduction method and device

Description:
TECHNICAL FIELD  
      The present invention relates to a method of, and device for, storing digital data such as audio data or the like, and also to a method of, and device for, reproducing the digital data.  
      This application claims the priority of the Japanese Patent Application No. 2003-107278 filed on Apr. 11, 2003, the entirety of which is incorporated by reference herein.  
     BACKGROUND ART  
      As the digital processing and network technology have moved forward, there have been proposed techniques for distributing digital audio data to the users via broadcasting and network. An audio device for use with such techniques is known from the disclosure in the Japanese Patent Application Laid Open No. 2003-30018. In the audio server disclosed in this Patent document, distributed audio data is stored once in a hard disk drive (HDD) built therein, and retrieved when necessary. Also, another audio server is proposed in the Japanese Patent Application Laid Open No. 2001-243705. The device disclosed in this Patent document is adapted to encrypt digital audio data for storage, and decrypt the encrypted digital audio data and output the data only when it is authenticated.  
      Note here that since the audio server can only operate according to software installed therein, it is not possible to copy digital audio data stored in the builtin HDD to a CD-R (CD Recordable) or the like. However, by physically taking out the builtin HDD from the audio server and connecting it to a personal computer, it is possible to copy digital audio data stored in the HDD to another HDD, CD-R or the like. In this case, the right of the copyright holder cannot be protected.  
      On this account, it is proposed to encrypt distributed digital audio data before storage into the built-in HDD in the audio server. Thereby, it is possible to reproduce a music or the like for normal listening by decrypting the encrypted digital audio data in an authenticated audio server.  
      However, even if the builtin HDD taken out of the audio server is connected to a personal computer, it will not be possible to decrypt the encrypted digital audio data. As a result, the copyright on the digital audio data can be protected.  
      However, since the CPU (central processing unit) used in most of the home-use audio servers is low in processing power, it cannot continuously decrypt digital audio data for reproduction. Of course, a high-power CPU or a decrypt-only IC (integrated circuit), if any, used in the home-use server can continuously decrypt encrypted digital audio data for reproduction. In this case, however, such an audio server will be expensive.  
     DISCLOSURE OF THE INVENTION  
      Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the related art by providing an improved and novel digital data storing method and device, data reproducing method and device, and a recording medium for recording digital data.  
      The above object can be attained by providing a digital data storing method including, according to the present invention, the steps of:  
      encrypting part of digital data; and  
      storing the encrypted digital data and non-encrypted remainder of the digital data.  
      The above digital data storing method according to the present invention further includes the step of dividing the digital data into blocks each of a predetermined data size, part of each of the digital data blocks being encrypted to encrypted digital data.  
      Also the above object can be attained by providing a data storing device including according to the present invention:  
      an encrypting means for encrypting part of digital data; and  
      a storing means for storing the digital data encrypted by the encrypting means and non-encrypted remainder of the digital data.  
      The above data storing means according to the present invention further includes a dividing means for dividing the digital data into blocks each of a predetermined size, the encrypting means encrypting part of each the digital data blocks supplied from the dividing means to provide encrypted digital data.  
      Also the above object can be attained by providing a digital-data recording medium having recorded therein encrypted digital data resulted from encryption of part of digital data, and non-encrypted remainder of the digital data.  
      In the above recording medium, there is recorded the encrypted digital data resulted from encryption of part of each of digital data blocks each of a predetermined data size.  
      Also the above object can be attained by providing a data reproducing method including, according to the present invention, the steps of:  
      acquiring digital data including encrypted digital data and non-encrypted digital data;  
      extracting the encrypted digital data from the digital data and decrypting the encrypted digital data; and  
      outputting, as read data, the decrypted digital data and the non-encrypted digital data extracted from the digital data.  
      Also the above object can be attained by providing a data reproducing device including according to the present invention:  
      an input means for inputting digital data including encrypted digital data and non-encrypted digital data;  
      a decrypting means for extracting the encrypted digital data from the digital data acquired by the input means and decrypting the extracted encrypted digital data; and  
      a reproducing means for extracting the digital data decrypted by the decrypting means and non-encrypted digital data extracted from the digital data and outputting the digital data together as read data.  
      In the above data reproducing device, the digital data includes the encrypted digital data and non-encrypted digital data in each of digital data blocks each of a predetermined data size, and the decrypting means extracts the encrypted digital data from each block of the predetermined data size and decrypts the encrypted digital data.  
      Also, the input means acquires information indicative of the encrypted digital data along with the digital data, and the decrypting means extracts the encrypted digital data on the basis of the acquired positional information and decrypts the encrypted digital data.  
      The above data reproducing device according to the present invention further includes a second decrypting means for decrypting encrypted information indicative of the position of the encrypted digital data, the input means acquires the encrypted positional information along with the digital data, and the decrypting means extracts the encrypted digital data on the basis of the information indicative of the position of the encrypted digital data decrypted by the second decrypting means and decrypts the encrypted digital data.  
      These objects and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the best mode for carrying out the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of an audio server according to the present invention.  
       FIG. 2A  schematically illustrates digital audio data to be encrypted,  FIG. 2B  schematically illustrates the digital audio data supplied from an encryption circuit, and  FIG. 2C  schematically illustrates disk audio data whose encrypted part has become a noise sound.  
       FIG. 3  is a block diagram of a CD player according to the present invention.  
       FIG. 4  schematically illustrates digital audio data encrypted for each arbitrary period τi at each arbitrary time interval Ti (i=1 to n).  
       FIG. 5  shows a table showing the arbitrary time intervals Ti (i=1 to n) and τi used to encrypt digital audio data for each arbitrary period τi at each arbitrary time interval Ti (i=1 to n). 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      The present invention will be described in detail below concerning the embodiments thereof with reference to the accompanying drawings.  
      First, an audio server according to the present invention will be illustrated and described. The audio server, generally indicated with a reference numeral  30 , has connected thereto a source  10  of various audio signals and an audio output device  20  as shown in  FIG. 1 .  
      The source  10  used with the audio server  30  according to the present invention is a signal source such as a network, CD, digital broadcast tuner or the like to provide an audio signal in the form of digital data, that is, in the form of digital audio data. The output device  20  includes a D-A (digital-to-analog) converter, speaker, etc. (not shown). When supplied with digital audio data from the source  10  or audio server  30 , the output device  20  outputs the digital audio data as sound.  
      Further, according to an instruction given by the user, the audio server  30  stores the digital audio data supplied from the source  10  or reproduces the stored digital audio data and outputs the data to the output device  20 . On this account, the audio server  30  includes a microcomputer.  
      That is, the audio server  30  includes a CPU (central processing unit)  31  that executes various programs, ROM (read-only memory)  32 , work-area RAM (random-access memory)  33  and a user interface  34 . These server elements are connected to each other via a system bus  39 . In this embodiment, the ROM  32  has written therein various programs to be executed by the CPU  31 . The user interface  34  is provided with various operation keys (controls) that are to be used by the user, and a display that displays the state or the like of the audio server  30 .  
      Further, the source  10  is connected to the system bus  39  via an input interface  35 , and the system bus  39  is connected to the output device  20  via an output interface  36 . Also, a hard disk drive (HDD)  38 , for example, is provided as a large-capacity storage means in the audio server  30 , and it is connected to the system bus  39  via an HDC (hard disk controller)  37 . It should be noted that the HDD  38  may be an HDD used in a general personal computer or the like.  
      Also, the system bus  39  has connected thereto an encryption circuit  41 , decryption circuit  42 , and an authentication circuit  43 . In this embodiment, however, the encryption circuit  41 , decryption circuit  42  and authentication circuit  43  are implemented by software. That is to say, the CPU  31  executes programs in the ROM  32  to implement the encryption, decryption and authentication, respectively. Therefore, since encryption of data in the encryption circuit  41  for storage of the data and decryption of the encrypted data in the decryption circuit  42  for extraction of the data are implemented in parallel with the data storage and data extraction, they will be a load to the CPU  31 . It should be noted that the encryption circuit  41  makes data encryption by a method in which encrypted text data like a random noise is generated with little correlation with initial digital data, for example, DES (data encryption standard) method.  
      Further, the authentication circuit  43  is provided to permit outputting of digital audio data to the output device  20  only when the latter has been identified, by checking, to be a preset legal one.  
      In this system, when the audio server  30  is to store digital audio data supplied from the source  10 , the digital audio data is supplied via the input interface  35  to the encryption circuit  41  where it will be encrypted as shown in  FIGS. 2A  to  2 C.  
       FIG. 2A  shows digital audio data for supply to the encryption circuit  41 , and  FIG. 2B  shows the digital audio data outputted from the encryption circuit  41 . As shown, only hatched part of the digital audio data from the encryption circuit  41  has been encrypted in this case. That is, the encryption circuit  41  encrypts only the part (hatched) for a predetermined period T at each predetermined time interval T. In this embodiment, the values T and τ are prepared as part of the encryption circuit  41  in the programs in the ROM  32 . For example, T=23 msec and τ=1 msec.  
      The partially encrypted digital audio data is written to the HDD  38  via the HDC  37 .  
      On the other hand, for using digital audio data stored in the audio server  30 , first the authentication circuit  43  authenticates the output device  20 . When the output device  20  has been identified, as the result of the authentication of the output device  20 , to be a legal output device, desired digital audio data is read from the HDD  38  via the HDC  37  and supplied to the decryption circuit  42  where encrypted part of the digital audio data for the period τ at each time interval T is decrypted to extract initial digital audio data, and the extracted digital audio data is supplied via the output interface  36  to the output device  20  that will reproduce the data as sound.  
      Note that if the output device  20  is identified, as the result of authentication of the output device  20 , not to be any legal output device, no digital audio data will be read from the HDD  38 . Hence, it is not permitted to output any digital audio data to the output device  20 .  
      Thus, the aforementioned audio server  30  can store digital audio data and retrieve the data when necessary. In this embodiment, by physically taking out the HDD  38  from the audio server  30  and connecting it to a personal computer, it is possible to copy the digital audio data stored in the HDD  38  to another HDD, CD-R or the like and reproduce the data.  
      However, since the digital audio data copied to the other HDD or CD-R (CD recordable) has a part thereof encrypted for the period τ at each time interval T as shown in  FIG. 2B  and the encrypted digital audio data is reproduced as sound without being decrypted in the personal computer, the encrypted part will be outputted as noise sound N as shown in  FIG. 2C .  
      That is to say, even if the digital audio data in the HDD  38  is copied to another HDD or CD-R, the reproduced sound thus contains noise sound at the regular intervals, which will cause any try of reproducing any music to result in substantial failure. Therefore, it is possible to protect the right of the copyright holder on the music.  
      In addition, since the CPU  31  executes the programs for encryption in the encryption circuit  41  and decryption in the decryption circuit  42  for the period τ at each time interval T, that is, for only τ/T of the whole period, presetting a smaller ratio τ/T and value τ will lead to a reduced load to the CPU  31  that executes the encryption and decryption. Thus, the CPU  31  may not be any high-power one. Namely, even a CPU  31  having a small processing power can execute the encryption and decryption. Thus, any IC (integrated circuit) dedicated for encryption and decryption has not to be provided in the audio server  30 . Therefore, the audio server  30  can be produced at a lower cost.  
       FIG. 3  shows an application of the present invention to a CD (compact disk) and CD player. First, for producing a CD (recording data to a CD), analog audio signals L and R are supplied to an analog-to-digital (A-D) converter  51  where they will be converted into digital audio data, and the digital audio data is supplied to an encryption circuit  52 . Also, a signal indicative of the period τ at each time interval T is supplied from a signal generation circuit  54  to the encryption circuit  52 . Thus, in the encryption circuit  52 , the supplied digital audio data is encrypted for a period τ at each time interval T as shown being hatched in  FIG. 2B .  
      The encrypted part of the digital audio data is supplied to a recording circuit  53  where it will be encoded for error correction, EFM (eight to fourteen modulation), etc., and the EFM signal is recorded to a master disk for a CD. It should be noted that at this time, data indicative of the values T and τ is supplied from the signal generation circuit  54 , encrypted into encrypted text data by the encryption circuit  52 , and then supplied to the recording circuit  53  where the encrypted text data indicative of the values T and τ will be recorded as sub codes to the CD master disk. Thus, a CD  60  having recorded therein digital audio data partially encrypted as shown in  FIG. 2B  is formed based on the master disk.  
      The CD  60  is played in a CD player  70 . More particularly, an optical pickup  71  reads an EFM signal from the CD  60 , and the read EFM signal is supplied to a reproduction circuit  721  of a DSP (digital signal processor)  72 . The DSP  72  executes programs that perform the functions of the reproduction circuit  721  and a decryption circuit  722  provided at the next stage. Also, the DISP  72  has connected thereto a microcomputer  80  that controls the system operation of the CD player  70 .  
      The reproduction circuit  721  operates in a complementary manner with the recording circuit  53 , namely, it makes demodulation and error correction of the EFM signal. The reproduction circuit  721  extracts the encrypted part of the digital audio data and encrypted sub codes, and supplies the digital audio data to the decryption circuit  722 . Also, the sub codes extracted by the reproduction circuit  721  are supplied to the microcomputer  80 . When the CD  60  has been pre-authenticated, the data on the initial values T and τ are decrypted, extracted and supplied to the decryption circuit  722 .  
      Then, using the values T and τ, the decryption circuit  722  decrypts the encrypted part of the digital audio data into the initial digital audio data. The digital audio data thus decrypted is supplied to a D-A (digital-to-analog) converter  73  where it will be subjected to D-A conversion into the initial analog audio signal L and R.  
      Thus, the aforementioned CD  60  can normally be played in the CD player  70  which has been authenticated. However, if the CD  60  is played in any CD player not authenticated, the encrypted part of the digital audio data read from the CD  60  will be reproduced as sound without being decrypted, and so the encrypted part will be outputted as noise sound. Therefore, if the CD  60  is played in any CD player not authenticated, the CD playing will result in substantial failure and thus it is possible to protect the right of the holder of the copyright on the data.  
      Since the DSP  72  implements the decryption in the decryption circuit  722  for only τ/T of the whole period, presetting smaller ratio τ/T and value τ will reduce the load to the DSP  72  in performing the decryption. Thus, the DSP  72  may not be any high-power one. Even a DSP  72  having a small processing power can execute the encryption and decryption. Thus, any IC (integrated circuit) dedicated for encryption and decryption may not be provided in the CD player  70 . Therefore, the CD player  70  can be produced at a lower cost.  
      Further, a legal user of the CD  60  can back up the CD  60  because the CD  60  can be played by copying it to a CD-R or the like.  
      Note that the audio server  30  or CD player  70  may be authenticated by any arbitrary method, or permission for decryption of an encrypted part may be obtained by any arbitrary method. Although it has been described in the foregoing that digital audio data has a part thereof encrypted for each period τ at each time interval T, the digital audio data may be partially encrypted (as shown being hatched) for each arbitrary period τi at each arbitrary time interval Ti (i=1 to n) as shown in  FIG. 4 . Especially, digital audio data that is a music can effectively be encrypted by phrasing a time interval Ti into several tens bar lines and assigning a period τi to a deep or low sound point.  
      In the above case, the values Ti and τi can be prepared in the form of a table as shown in  FIG. 5  for example, and stored in the ROM  32  in the audio server  30  shown in  FIG. 1 . Alternatively, the table can be recorded along the sub track for the CD player  70  shown in  FIG. 3 .  
      Also, although it has been described in the foregoing that the values T and τ (or Ti and τi) are stored in the ROM  32  in the audio server  30  shown in  FIG. 1 , the values T and τ may be supplied from the source  10  as in the CD  60  shown in  FIG. 3 . In this case, the values T and τ may be encrypted, and the encrypted values T and τ be decrypted for use to decrypt an encrypted part of digital audio data when the audio server  30  is authenticated.  
      Also, although the present invention has been described above concerning the digital audio data, the audio server  30  is also compatible with digital data such as digital video signals and moving pictures so long-as the data continuously vary as the time elapses. Also, a nonvolatile memory may be used in place of the HDD  38 .  
      In the foregoing, the present invention has been described in detail concerning certain preferred embodiments thereof as examples with reference to the accompanying drawings. However, it should be understood by those ordinarily skilled in the art that the present invention is not limited to the embodiments but can be modified in various manners, constructed alternatively or embodied in various other forms without departing from the scope and spirit thereof as set forth and defined in the appended claims.  
     INDUSTRIAL APPLICABILITY  
      As having been described in the foregoing, since according to the present invention, digital data is partially encrypted and the encrypted part of the digital data is read as a noise even when an HDD having the digital data stored therein is used in another personal computer, the digital data cannot normally be reproduced in practice and thus it is possible to protect the right of the copyright holder on the digital data.  
      By presetting a smaller part of the digital data for encryption, a CPU not high in processing power can be used to reproduce the digital data, any IC dedicated for data decryption is not required, and thus the device can be produced with a reduced cost.