Abstract:
A device to be used with digital data copying apparatus for preventing fraudulent copies of a digital data is disclosed. The digital data includes an encrypted data main body and encrypted copy management information for controlling permission with regard to copying the data main body. A determining section determines if permission be granted for copying the digital data or not depending on if the copy management information satisfies predetermined requirements or not. A prohibition processing section prohibits any operation of effectively copying the digital data when the determining section determines that permission should not be granted for copying the digital data.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a device and a method for preventing fraudulent copies of data and also to a recording medium. More specifically, this invention relates to a device and a method for preventing fraudulent copies of data on digitized documents, sounds, images and/or programs and also to a recording medium to be suitably used with such a device. 
     In recent years, the development and commercialization of digital recording/reproducing apparatus has made it possible to transfer data from a such apparatus to another for the purpose of copying without degrading the quality of data particularly in terms of the images and/or the sounds to be reproduced by the data. 
     However, the ability of copying data without degrading the quality thereof can inevitably entail illegal sales of copies of audio-visual works or pirating, infringing the copyright of the authors of the works. Illegal copies have to be firmly prevented from taking place because it is technologically easy to copy digitized works and distribute copies to indefinite people by means of large capacity digital recording/reproducing apparatus such as D-VCRs and DVD-RAMs. Now, many authors of digitized images and other digitized works share a sense of crisis under these circumstances. 
     While various techniques may be conceivable for pirating, any pirate has to follow a process of receiving the data for the object of pirating from a data reproducing device such as a DVD-ROM drive or a DVD-ROM and then copying the data by means of a digital recording device such as a DVD-RAM. 
     There is known a management system called SCMS (serial copy-management system) to be used with digital recording/reproducing apparatus such as DATs and MDs having a capacity smaller than DVDs for preventing fraudulent copies from being made. 
     Data to copied from a CD to an MD (or a DAT) or from an MD (or a DAT) to another MD (or another DAT) by means of an SCMS carries a piece of copy information added to the data head. The copy information is a 2-bit data. If the copy information on the master disc is “00”, any data copied from the master disc will carry the copy information of “00” to indicate that it is free for copying. 
     If, the copy information on the master disc is “10”, any data may copied directly from the master disc (to produce a first generation copy) but no data can be copied form the first generation copy (to produce a second generation copy). In other words, when data are copied from the master disc, the copy information carried by the copied data, or the data of the first generation copy, is counted up to become “11” and no data can be copied if it carries the copy information of “11” so that any second generation copy will be prevented from being produced. 
     The above described system refers to a method for preventing fraudulent copies by means of a digital recording/reproducing apparatus designed to prevent copies that infringe the copyright of the author of the original from being fraudulently made. However, if each apparatus is provided with anti-fraud measures, a pirate can illegally copy the data being transmitted from an apparatus to another somewhere on the transmission path to make such anti-fraud measures powerless. 
     As known and popular anti-fraud measures for data transmission, confidential data are often encrypted. Encryption systems are generally categorized as open key systems and secret key systems, although the latter are popularly used when data are to be transmitted and processed at high speed. 
     For encrypting data by means of a secret key, the two parties at the opposite end of the transmission line talk with each other to determine the secret key to be used for the coming communication in a cryptic system. 
     Thus, if the secret key is identified by a third party and fraudulently used for pirating, then the two parties will have to select a new secret key to continue the communication to maintain, if not lost, the confidentiality of the data. Thus, there is a need for effective cryptic systems that can be used for data transmission among digital recording/reproducing apparatus. 
     There is also a need for devices that can effectively prevent fraudulent copies of data. The above cited SCMS allows to produce first generation copies so that pirates can freely produce such copies for sale. Additionally, frauds can forge the copy information of “00” to freely make illegal copies. 
     Therefore, there is a strong need for a copy management method that is more reliable, more elaborate and more realistic than the SCMS and can be applied to large capacity digital recording/reproducing apparatus that potentially involve serious copyright problems. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the above identified circumstances, it is therefore a first object of the present invention to provide a device and a method for effectively and reliably preventing any illegal access to the copy-management information contained in the data to be handled and also to a recording medium to be suitably used with such a device. 
     A second object of the invention is to provide a device and a method for effectively preventing any fraudulently copied data from being reproduced. 
     A third object of the invention is to provide a device and a method for preventing fraudulent copies by means of an elaborate copy management system. 
     According to a first aspect of the invention, the above objects and other objects are achieved by providing a device to be used with digital data copying apparatus for preventing fraudulent copies of a digital data; 
     the digital data including an encrypted data main body and encrypted copy management information for controlling permission with regard to copying the data main body; 
     the device comprising: 
     a determining section for determining if permission be granted for copying the digital data or not based on if the copy management information satisfies predetermined requirements or not; and 
     a prohibition processing section for prohibiting any operation of effectively copying the digital data when the determining section determines that permission should not be granted for copying the digital data. 
     According to a second aspect of the invention, there is provided a device to be used with digital data copying apparatus for preventing fraudulent copies of a digital data; 
     the digital data containing an encrypted data main body, encrypted copy management information for controlling permission with regard to copying the data main body and key information for decrypting the data main body; 
     the device comprising: 
     a determining section for determining if permission be granted for copying the digital data or not based on if the copy management information satisfies predetermined requirements or not; and 
     a key altering section for altering the key information contained in the digital data when the determining section determines that permission should not be granted for copying the digital data. 
     According to a third aspect of the invention, there is provided a method to be used with digital data copying apparatus for preventing fraudulent copies of a digital data; 
     the digital data containing an encrypted data main body, encrypted copy management information for controlling permission with regard to copying the data main body and key information for decrypting the data main body; 
     the method comprising steps of: 
     determining if permission be granted for copying the digital data or not based on if the copy management information satisfies predetermined requirements or not; and 
     altering the key information contained in the digital data when the determining section determines that permission should not be granted for copying the digital data. 
     According to a fourth aspect of the invention, there is provided a method to be used with digital data copying apparatus for preventing fraudulent copies of a digital data comprising steps of: 
     adding to the digital data copy management information containing generation management information to indicate the generation of the digital data as descendent of the original data and numerical management information to indicate the number of copies made from the digital data; 
     prohibiting any operation of copying the digital data when the generation management information indicates a predetermined generation and the numerical management information indicates a predetermined number of copies. 
     According to a fifth aspect of the invention, there is provided a recording medium for storing data having a computer-readable data structure; 
     the data structure comprising: 
     an encrypted data main body; 
     encrypted copy management information for controlling permission with regard to copying the data main body; 
     first key information for decrypting the data main body; and 
     second key information for decrypting the copy management information. 
     According to a sixth aspect of the invention, there is provided a recording medium for storing data having a computer-readable data structure; 
     the data structure comprising: 
     an encrypted data main body; 
     first key information obtained by encrypting a data encryption key to be used for decrypting the data main body; 
     a plurality of second key information obtained by encrypting the data encryption key by means of a plurality of encryption keys; and 
     a plurality of third key information obtained by encrypting copy management information for controlling permission with regard to copying the data main body by means of the plurality of encryption keys. 
     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 learned 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 DRAWING 
     The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a schematic block diagram of a digital recording/reproducing apparatus to which a first embodiment of device for preventing fraudulent copies of a digital data according to the invention and which are connected with each other. 
     FIG. 2 is a schematic illustration showing how to configure a data structure to be used with the embodiment of FIG.  1 . 
     FIG. 3 is a schematic illustration of a data structure applicable to the embodiment of device for preventing fraudulent copies in FIG.  1 . 
     FIG. 4 is a schematic block diagram of a digital recording/reproducing apparatus to which the embodiment of device for preventing fraudulent copies in FIG. 1 is applied. 
     FIG. 5 is a schematic block diagram of the CF altering section of the embodiment of FIG. 1, illustrating its operation. 
     FIG. 6 is a schematic block diagram of the data reproduction/copying processing section, illustrating its operation. 
     FIG. 7 is a schematic illustration of the configuration of copy management flag CF. 
     FIG. 8 is a schematic illustration showing how the state of the copy generation management bits changes. 
     FIG. 9 is a schematic illustration showing how to configure a data structure to be used with a second embodiment of the invention. 
     FIG. 10 is a schematic illustration of another data structure applicable to the second embodiment of device for preventing fraudulent copies. 
     FIG. 11 is a schematic block diagram of the data reproduction/copying processing section of the second embodiment of device for preventing fraudulent copies, illustrating its operation. 
     FIGS. 12A and 12B are schematic illustrations of two different data structures applicable to a third embodiment of device for preventing fraudulent copies. 
     FIG. 13 is a schematic illustration of a system designed for a pair of digital recording/reproducing apparatus to share a temporary encryption key by utilizing the respective master key bundles in a fourth embodiment of the invention. 
     FIG. 14 is a schematic flow chart of the operation of the embodiment of FIG.  13 . 
     FIG. 15 is a schematic block diagram of a key sharing circuit to be used in a fifth embodiment of the invention. 
     FIG. 16 is a schematic illustration of a system designed for a pair of digital recording/reproducing apparatus to share a temporary encryption key by means of a key sharing circuit without using the master key bundle. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now, the present invention will be described by referring to the accompanying drawing that illustrate preferred embodiments of the invention. 
     In the description of cryptic systems that follows, an encrypting operation is expressed by Ey(x), where x represents the data to be encrypted and y represents the encryption key to be used for the encrypting operation. On the other hand, a decrypting operation is expressed by Dy(z), where z represents the data to be decrypted and y represents the decryption key to be used for the decrypting operation. Thus, 
     Ey(Dy(x))=x and 
     Dy(Ey(x))=x. 
     In the illustrations of the embodiments, a broken dotted line indicates key information to be used for encryption or decryption and a solid line indicates information to be encrypted or decrypted. 
     1st Embodiment of the Invention 
     FIG. 1 is a schematic block diagram of a digital recording/reproducing apparatus to which a first embodiment of device for preventing fraudulent copies of a digital data according to the invention and which are connected with each other. 
     Referring to FIG. 1, multimedia information in the form of sounds/images/characters is distributed by way of a cable television network and, for example, transmitted to an STB (set top box)  101 . 
     In the illustrated system, the STB  101  is connected to a digital VCR (D-VCR)  103  by way of an IEEE 1394 cable  102  and further connected to a display  106  and a DVD-RAM  107  by way of the digital VCR  103  and respective IEEE 1394 cables  104 ,  105 . Since a plurality of digital recording/reproducing apparatus are connected with each other in the illustrated system, data can be transmitted among any of the apparatus for copying. 
     In the illustrated system, the STB  101 , the digital VCR  103  or the DVD-RAM  107  are used as transmitter for transmitting data, whereas the digital VCR  103  or the DVD-RAM  107 , whichever appropriate, is used as receiver for receiving data. Now, a method of preventing fraudulent copies from being produced between the transmitter and the receiver according to the invention will be described. 
     More specifically, the STB  101  is used to decipher (deshuffle) scrambled multimedia data and store/transmit billing data. The multimedia data input to the STB  101  is transmitted to the devices  103 ,  106 ,  107  by way of the respective IEEE 1394 cables  102 ,  104  and  105 . IEEE  1394  refers to a high speed serial digital interface defined by the IEEE and adapted to high speed data transmission either in the asynchronous mode or in the isochronous mode. Thus, IEEE 1394 is popularly used for connecting personal computers, digital TVs, digital VCRs, DVD-RAMs and other digital AV equipment. 
     Now, a data structure that can be used for this embodiment of method of preventing fraudulent copies of data according to the invention will be described. 
     FIG. 2 is a schematic illustration showing how to configure a data structure to be used with the embodiment. 
     The contents of the data stored in the DVD are encrypted by means of a title key or a disc key. Assume that the contents are encrypted in this embodiment by means of data encryption key Dk, which is referred to as disc key. FIG. 2 shows how the data is encrypted by the data encryption key Dk in the encryption circuit  204  to become EDk (data). The suppliers of the digital recording/reproducing apparatus would not be informed of the data encryption key Dk in advance. 
     In the digital recording/reproducing apparatus, said data encryption key Dk is encrypted and added as part of the data structure in order to reproduce the data that may be image data. As a matter of fact, encrypted data encryption keys Dk of two different types will be prepared. One is used to encrypt the data encryption key Dk by using itself as encryption key in the encryption circuit  203  to produce EDk (Dk). The other is encrypted by means of each master key of the master key bundle Mkn in the encryption circuit  202  to produce encrypted data EMk 1  (Dk), EMk 2  (Dk), . . . , EMkn (Dk), the number of which is equal to the number of keys of the key bundle. 
     The master key bundle Mkn is controlled typically by a key management firm and the suppliers of the digital recording/reproducing apparatus are provided by the key management firm with a master key bundle Mks that is part of the master key bundle Mkn. The master key bundle Mks comprises a plurality of master keys, which are different from supplier to supplier so that the keys may be controlled effectively. Since each of the suppliers possess at least part of the master keys Mk 1 , Mk 2 , . . . , Mkn, he or she can take out data encryption key Dk safely and reliably if the data structure contains encrypted data EMk 1  (Dk), EMk 2  (Dk), . . . , EMkn (Dk) and EDK (Dk). The technique to be used for taking out the data encryption key Dk will be described in detail hereinafter. 
     Additionally, according to the invention, the data structure is made to contain encrypted copy management flag CF to securely control the operation of copying data. Referring to FIG. 2, the copy management flag CF is encrypted by the master key bundle Mkn in the encryption circuit  201  to produce a string of encrypted data EMKl (CF), EMk 2  (CF), . . . , EMkn (CF). 
     FIG. 3 is a schematic illustration of a data structure applicable to the embodiment of device for preventing fraudulent copies. 
     It will be seen from FIG. 3 that the encrypted data described above by referring to FIG. 2 are combined to form a data structure. Pairs  211  of a copy management flag CF and a data encryption key Dk are arranged in line to form a master key encrypting section  212  and a disc key encrypting section  213  that is EDk (Dk) is added to the tail of the master key encrypting section  212 . Then, the data main body  214  that is EDk (data) is arranged at the rear end of the disc key encrypting section  212  to produce a complete data structure  215 . 
     As described earlier, the data main body  214  contains data obtained by encrypting data on digitized documents, sounds, images and/or programs and the data structure  215  formed by adding data encryption key Dk and copy management flag CF to the data main body  214  is processed or unprocessed before it is temporarily stored in the DVD-RAM  107  or the D-VCR and then transmitted to the STB  101  typically by way of a communication network. Thus, the data structure  215  is used for transmission and recorded on a recording medium. Then, copies of the data structure  215  carried by a recording medium are distributed and sold to users. 
     According to the invention, the CF, or the copy management flag CF that has been encrypted and protected against illegal external access and is contained in the data structure, is utilized for copy management (generation management, management of the number of copies) with regard to the data to prevent any effective reproduction of fraudulently copied data. 
     Now, the operation of reproducing and copying data in a digital recording/reproducing apparatus adapted to use a data structure  215  having a configuration as described above will be discussed. 
     FIG. 4 is a schematic block diagram of a digital recording/reproducing apparatus to which the above embodiment of device for preventing fraudulent copies is applied. 
     Referring to FIG. 4, a DVD-RAM is used for transmitter  301  and D-VCR is used for receiver  302 , which transmitter  301  and receiver  302  are connected with each other by way of an IEEE 1394 cable  303 . While the transmitter  301  and the receiver  302  are exclusively used for data transmission and data reception respectively in the following description for the purpose of simplification, it may be appreciated that each of them may operates both as transmitter and receiver. It may also be appreciated from FIG. 1 that the transmitter  301  and the receiver  302  may be realized in many different ways by appropriately combining various componental devices. 
     The transmitter  301  comprises an IEEE 1394 chip  311  and a read/write circuit  313  for reading data stored in the form of a data structure  215  from DVD-RAM  312  and write data. The IEEE 1394 chip  311  has an IEEE 1394 I/F section  314  for performing IEEE 1394 interface operations to communicate with the receiver  302 , a key sharing circuit  315 , an encryption circuit  316  and a CF altering section  317 . 
     On the other hand, the receiver  302  comprises IEEE 1394 chips  321 ,  322 , a display processing section  323  for processing the reproduced data, regulating the image quality and other factors and displaying the data on display  304 , a write processing section  325  for storing the data structure  215  output from data reproduction/copying processing section  334  of the IEEE 1394 chip  321  in DV cassette  324  and a read processing section  326  for reading the data structure  215  from the DV cassette  324  and inputting it into the data reproduction/copying processing section  334 . The IEEE 1394 chip  321  comprises an IEEE 1394 I/F section  331  for performing IEEE 1394 interface operations to communicate with the transmitter  301 , a key sharing circuit  332 , a decryption circuit  333  and a data reproduction/copying processing section  334 . 
     Of the above components, the key sharing circuits  315 ,  332 , the encryption circuit  316  and the decryption circuit  333  are used to encrypt the data structure  215  when transmitting it by way of the IEEE 1394 cable  303 . 
     The key sharing circuits  315 ,  332  are adapted to securely share the temporary key Stk by the information transmitted through the IEEE 1394 cable  303 . The encryption circuit  316  encrypts the DVD-RAM data (the data structure  215 ) output from the CF altering section  317  by means of the temporary key Stk from the key sharing circuit  315 . The decryption circuit  333  decrypts the encrypted data structure  215  received from the IEEE 1394 I/F section  331  by means of the temporary key Stk form the key sharing circuit  332  and delivers it to the data reproduction/copying processing section  334 . The method of sharing the temporary key Stk will also be discussed in detail by referring to the fourth and fifth embodiments of the invention. 
     The CF altering section  317  of the transmitter  301  delivers the data structure  215  read out on the read/write circuit  313  to the encryption circuit  316  and alters the copy management flag CF. Then, the CF altering section  317  updates the same data structure  215  stored in the DVD-RAM  312 , using the new data structure  215  obtained by altering the CF. 
     The data reproduction/copying processing section  334  of the receiver  302  deciphers the data structure  215  received from the decryption circuit  333  or the read processing section  326  by means of the key bundle Mks it has and takes out the data encryption key Dk and the copy management flag CF. Then, the data reproduction/copying processing section  334  outputs the decrypted data to the display processing section  323  and, after altering the copy management flag CF, prepares a new data structure  215 , using its own master key bundle Mks, which is then output to the write processing section  325  as data to be preserved (copy data). 
     Now, the operation of the embodiment of device for preventing fraudulent copies of data according to the invention and having the above described configuration will be described. 
     When a data is to be transferred, the transmitter  301  and the receiver  302  firstly share the temporary key Stk by means of the key sharing circuits  315 ,  332 . 
     Then, the data structure  215  stored in the DVD-RAM  312  is read out and input to the encryption circuit  316  by way of the CF altering section  317 , where it is encrypted by means of the temporary key Stk. Then, the encrypted data structure  215  is transmitted to the receiver  302  over the IEEE 1394 cable  303  by the IEEE 1394 I/F section  314 . 
     Meanwhile, the copy management flag CF is altered by the CF altering section  317 . 
     FIG. 5 is a schematic block diagram of the CF altering section of the above embodiment, illustrating its operation. 
     Referring to FIG. 5, the data structure  215  read from the DVD-RAM  312  is sent to the encryption circuit  316  and also input to data read control circuit  401 . 
     The data read control circuit  401  is adapted to divide the received data structure  215  into: 
     EMk 1  (Dk), EMk 2  (Dk), . . . , Emkn (Dk) . . .  215   a,    
     EMk 1  (CF), EMk 2  (CF), . . . , EMkn (CF) . . .  215   b,    
     EDk (Dk); disc key encrypting section . . .  213  and 
     EDk (data); data main body . . .  214 . All the components except EDk (data) have a fixed length and hence it is easy to separate the header from the rest of each component as shown in FIG.  3 . 
     The data encryption keys  215   a  encrypted by using keys of the master key bundle Mkn or Mks as encryption keys are part of the master key encrypting section  212  of FIG.  3  and hence stored in an area where the users of the IEEE 1394 chips cannot arbitrarily take it out. The data encryption keys  215   a  encrypted by the master key bundle is then decrypted by sequentially using the keys of the master key bundle Mks provided to the suppliers of the apparatus as decryption keys. 
     Note that EMk 1  (Dk), EMk 2  (Dk), . . . , EMkn (Dk)  215   a  are temporarily taken into memory  402  and then sequentially decrypted typically from EMk 1  (Dk) on in the decryption circuit  403  as the keys of the master key bundle Mks in the IEEE 1394 chips are sequentially taken out by control signal  1  and used as decryption keys. 
     Then, Dk′ obtained by the decryption is used as decryption key to decrypt EDk (Dk) in the decryption circuit  404  and obtain Dk″. Then, Dk′ and Dk″ are compared by determining circuit  405 . If Dk′=Dk″, it indicates that the master key used for encrypting the data encryption key is identical with the master key used for decrypting the encrypted data encryption key. If, however Dk′≠Dk″, it indicates that the master key used for encrypting the data encryption key is different from the master key used for decrypting the encrypted data encryption key. If Dk′≠Dk″ holds true for all the master keys, it signifies that the crypt, EMk 1  (Dk) for example, cannot be decrypted by the master key bundle Mks possessed by the chip. 
     If such is the case, then control signal  2  calls EMk 2  (Dk) located next to EMk 1  (Dk) in the memory  402  and the above processing operation is repeated by using the master key bundle Mks in the IEEE 1394 chip. In this way, the processing operation will be repeated until EMki that makes Dk′=Dk″ is found. 
     When Dk′=Dk″ is achieved, it indicates that the data encryption key Dk is taken out from EMki (Dk) by means of the current master key. Then, EMki (CF) is taken out of EMk 1  (CF), EMk 2  (CF), . . . , EMkn (CF) stored in the memory  406  by control signal  3 . It is easy to identify EMki (CF) because the copy management flags CF encrypted by the master key bundle are arranged in the order starting from 1 and terminating by n (or s) just as the data encryption keys  215   a  encrypted by the master key bundle. 
     Then, CF is obtained by decrypting EMki (CF) by means of the master key identified by the decryption circuit  407 . Then, the copy management flag CF is altered by the CF altering circuit  408  and input to the encryption circuit  410  of data altering circuit  409 . 
     The data altering circuit  409  is adapted to receive EDk (data), or the data main body  214  of the data structure  215 , from the data read control circuit and also Dk, or the altered CF, which is then encrypted by the master key bundle Mks and the data encryption key Dk in encryption circuit  410  and added to the data main body  214  as header. 
     The data structure  215  (having a structure same as that of FIG. 3 except that Mkn is replaced by Mks) containing copy management flags CF encrypted by the master key bundle Mks specific to the apparatus supplier and altered is then output to the read/write circuit  313  and the corresponding part of the DVD-RAM  312  is updated by this new data structure  215 . 
     Note that a copy management flag CF comprises generation management information and numerical management information to indicate the number of copies. Generation management refers to an activity of controlling the operation of copying the master disc, then copying the produced copy and so on. On the other hand, numerical management for the number of copies refers to an activity of controlling the number of copies made by a data structure. As for a data structure  215  delivered to the encryption circuit  316 , passing through the CF altering section  317 , the encryption circuit  316  will be responsible for generation management. As for a data structure  215  returned to the DVD-RAM  312  and updated by the CF altering section  317 , on the other hand, the CF altering section  408  counts up the number of copies but would not do anything about generation management. When the count gets to the largest possible number, the receiver  302  can no longer properly copy the data. 
     Thus, the transmitter  301  is charged with the task of generation management, while the receiver  302  is also responsible for controlling the received data structure  215  for copying. Now, the processing operation of the receiver will be discussed below. 
     Firstly, the encrypted data structure is received by the IEEE 1394 I/F section  331  of the receiver  302  and decrypted by the decryption circuit  333 , using the temporary key Stk provided by the key sharing circuit  332  before input to the data reproduction/copying processing section  334 . 
     FIG. 6 is a schematic block diagram of the data reproduction/copying processing section, illustrating its operation. Note that the components same as those of FIG. 5 are denoted respectively by the same reference symbols. 
     The data structure  215  to be input to the data reproduction/copying processing section  334  is firstly input to the data read control circuit  401 , which divides it into components as in the case of the CF altering section  317  in FIG.  5 . Note that the processing steps down to the step where the data encryption key DK is taken out by the determining circuit  405  and the copy management flags CF is taken out by the decryption circuit  407  are identical with the respective corresponding steps as described above by referring to the CF altering section  317  in FIG.  5 . 
     Thereafter, the status of the taken out copy management flag CF is determined by the CF determining circuit  411 . The function of the copy management flag CF for generation management and numerical management for copies will be discussed in detail hereinafter. The CF determining circuit determines if the copy management flag CF indicates that a copy can be made for the next generation or not and, if a copy can be made for the next generation, it determines if the largest possible number has been reached for copying or not to decide if it is permitted to copy the data structure or not. Then, the copy management flag CF and the result of the decision on the permissibility for copying (control signal  4 ) of the CF determining circuit  411  are given to key altering circuit  412 . 
     Upon receiving a control signal  5  indicating that a recording command and/or a reproduction command are entered by the user, the key altering circuit  412  outputs the copy management flag CF and the data encryption key Dk given to it in advance without or after altering it. 
     For reproducing data and simply displaying it on the display  304 , EDk (data) which is the data main body  214  of the data structure  215  is decrypted by the decryption circuit  413  before it is taken out and output to the display processing section  323 . At this time, the data encryption key Dk taken out by the determining circuit  405  is always given from the key altering circuit  412  to the decryption circuit  413  as decryption key. Therefore, as long as a normal data encryption key Dk is taken out, the operation of data reproduction is performed properly regardless of the status of the copy management flag CF. 
     For copying data on the DV cassette  314 , on the other hand, the processing operation to be performed varies depending on the outcome of the decision of the CF determining circuit  411 . 
     Firstly, assume that the copy management flag CF is in a status that permits copying. Then, a copy management flag CF is input from the key altering circuit  412  to CF altering circuit  414 , while the data encryption key Dk is input to the encryption circuit  416  of copy circuit  415  as data to be encrypted and also as encryption key. 
     The CF altering circuit  414  operates for a generation shift. More specifically, the generation management information of the copy management flag CF is modified to identify the data structure as that of the next generation. The modified copy management flag CF is then input to the copy circuit  415 . 
     Thus, EDk (data) is input from the data read control circuit  401  to the copy circuit  415  as data main body of the data structure along with Dk and the modified CF. In the encryption circuit  416 , Dk and CF are encrypted by the master key bundle Mks and the data encryption key Dk and added to the data main body  214  as header. 
     Then, the data structure  215  encrypted by the master key bundle Mks specific to the apparatus supplier and provided with the altered copy management flag CF (said data structure  215  being same as the one shown in FIG. 3 except that Mkn is changed to Mks) is output to the write processing section  325  and stored in the DV cassette  324  as copy data. Since the master key bundle Mkn is altered to Mks by the copying operation, the stored data structure  215  is no longer interchangeable among apparatus suppliers and hence cannot be reproduced nor copied by means of an apparatus having no master key bundle Mks. 
     For reproducing the stored data structure  215 , the data structure  215  that is encrypted by means of the master key bundle Mks is input from the read processing section  326  to the data read control circuit  401  and processed in a manner as described above. 
     Now, assume that the copy management flag CF is in a status that does not permit copying. Then, the copy management flag CF is not altered at all in the CF altering circuit  414  because the data structure  215  can no longer be copied. On the other hand, the key altering circuit  412  outputs a data encryption key different from the one output in a status that permits copying to the encryption circuit  416 . 
     More specifically, in a status that does not permit copying, the key altering circuit  412  inputs a fake data encryption key Dk* that is different from the proper data encryption key Dk taken out in the determining circuit  405  to the encryption circuit  215  as data encryption key that is to be encrypted as data and also to be used as encryption key. Dk may be altered to produce a fake data encryption key Dk* by inverting the bits of Dk, by shifting the bits or by determining the exclusive logical OR of it and a specific value. 
     The operation of the copy circuit  415  and that of the encryption circuit  416  performed when a data is given to them are identical with the above described operations. However, as for the data structure  215  generated by this circuit  415  and stored, the encryption key of EDk (data) remains to be Dk as shown in FIG. 3, whereas all the data encryption keys Dk* used by the master key encrypting section  212  and the disc key encrypting section  213  that operate as header and stored will be fake keys. Therefore, when trying to decrypt the data structure  215 , the fake data encryption key Dk* are taken out and hence random data reproduction will occur. 
     The above description applied to an effort for copying the data structure  215  from the transmitter  301  to the receiver  302  and reproducing the data. Thus, the number of copies made from the original data is controlled by the transmitter  301  and the generation management for controlling the operation of copying a copied data will be carried out by the receiver  302 . 
     Now, the copy management flag CF and the operation of controlling copy generations and the number of copies will be specifically described by referring to FIGS. 7 and 8. 
     FIG. 7 is a schematic illustration of the configuration of copy management flag CF. Note that, in this embodiment, a byte comprises eight bits and the upper three bits are used for controlling copy generations (generation management information) and the lower five bits are used for controlling the number of copies (numerical management information relating to the number of copies). 
     FIG. 8 is a schematic illustration showing how the state of the copy generation management bits changes. The upper three bits are used as shown below for controlling copy generations. 
     000 . . . copy permitted 
     001 . . . 1st generation copy permitted (2nd generation copy prohibited) 
     → The 1st generation copy will be indicated by 111. 
     011 . . . 2nd generation copy permitted (3rd generation copy prohibited) 
     → The 1st generation copy will be indicated by 001 and the 2nd generation copy will be indicated by 111. 
     111 . . . copy prohibited 
     Thus, as shown in FIG. 8, if the upper three bits for controlling copy generations are all “0s”, those of any copy will remain to be all “0s”. However, if they are “001” to indicate that the first generation copy is permitted but the second generation copy is prohibited, the bits for controlling copy generations are turned to “111” to prohibit the second generation copy once the original is copied. If, on the other hand, the upper three bits for controlling copy generations are “011” to indicate that the second generation copy is permitted but the third generation copy is prohibited, the bits for controlling copy generations of the first generation copy are turned to “001” to permit the second generation copy and those of the second generation copy are turned to “111” to prohibit the third generation copy. Thus, copy generations are controlled in this way. 
     As for the number of copies, when the number of copies gets to a predetermined limit number, no further copies will be permitted regardless of the values of the three bits for controlling copy generations. While the permitted largest number of copies will be 32 in this embodiment because the lower five bits are used for limiting the number of copies, a larger number may be assigned as the largest number of copies by increasing the number of bits that can be used for controlling the number of copies. 
     For instance, this feature of controlling the number of copies may be advantageously used to limit the number of users of a master disc that stores software. The copy made by a user may be prevented from being copied further if the copy generation management flag of the master disc is set to “001” to allow only the first generation copy. 
     Then, the bits to be used for controlling the number of copies represents the number of users who are authorized to copy the software stored in the master disc. In this embodiment, the number authorized users will be between 0 and 32. 
     Assume here that ten users are authorized to copy the software stored in the master disc. Then, the bits for the largest number of permitted copies will be “01010”. When a user has made a copy, CF of the master disc and that of the user will be altered to become as shown below. 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 CF of the master disc: 
                 00101001 
               
               
                   
                 CF of the user: 
                 11100000 
               
               
                   
                   
               
             
          
         
       
     
     Thus, the software obtained by the user by copying the original can no longer be recorded on any other recording medium. 
     When all the ten authorized users have made respective copies of the software, CF of the mater disc will be altered to become as shown below. 
     CF of the master disc: 00100000 
     Thus, while the first generation copy is still permitted to take place, no further copy is possible because zero copy is permitted to make. 
     Alternatively, the copy generation management bits of the master disc may be turned to “111” when the last authorized user made a copy. 
     As described above, with the embodiment of device for preventing fraudulent copies, a copy management flag CF to be used for controlling copies is encrypted and contained in the data structure  215  so that any attempt to alter the copy management flag CF and fraudulently copy the data structure on the way of transmission can be prevented for succeeding and any illegal access to the data structure can be eliminated effectively and reliably to securely protect the copyright. 
     Additionally, the data reproduction/copying processing section  334  comprises a CF determining circuit  411  and a key altering circuit  412  so that, if there is an attempt for copying a data structure that is not permitted to be copied, the data encryption key is automatically altered to make it impossible to effectively reproduce the fraudulently copied data. In other words, if it is determined that copying a digital data is prohibited, the key information contained in the digital data is altered so that any copy of the digital data cannot effectively be reproduced. This arrangement provides the effect of prohibiting any attempt for fraudulently copying a digital data. 
     The CF altering section  317  is used to count up the number of copies made from the data structure by counting the number of times of data transmission. Thus, the data copying operation can be controlled in an elaborate manner. 
     The data reproduction/copying processing section  334  comprises a CF determining circuit  411  and a CF altering circuit  414  to update the data structure to be copied so that the data copying operation can be further controlled in an elaborate manner. 
     Additionally, the data structure to be transmitted is encrypted by means of the key sharing circuits  315 ,  332  and the encryption circuit  316  so that the data structure cannot be utilized by the receiving party if the latter is not provided with an decryption circuit  333 . Furthermore, data are encrypted by means of a temporary encryption key before they are transmitted between the apparatus located at the opposite ends of the line so that they are protected against being fraudulently copied on to some other recording medium from the cable connecting the apparatus. 
     Still furthermore, the copy management flag CF to be used for indicating if making a copy is permitted or not has a function of controlling copy generations and that of controlling the number of copies, copies can be controlled in an elaborate fashion. 
     While the CF altering section  317  and the data reproduction/copying processing section  334  are contained respectively in the IEEE 1394 chips  311  and  321  in the above embodiment, the present invention is not limited thereto and the CF altering section  317  and the data reproduction/copying processing section  334  may be realized in the form of independent chips. 
     2nd Embodiment of the Invention 
     A different data structure will be used in this embodiment to prevent fraudulent copies of data. 
     FIG. 9 is a schematic illustration showing how to configure a data structure to be used with the second embodiment. Note that the elements in FIG. 9 that are identical with their counterparts of FIG. 2 will be denoted respectively by the same reference symbols and will not be described here any further. 
     The data encrypting procedures of the second embodiment is identical with that of the first embodiment except that data encryption key Dk is used as encryption key for encrypting the copy management flag CF. Note that, while a plurality of encrypted data are used for CF in the embodiment of FIG. 2 because the master key bundle is utilized there, only a single encrypted data is used in this embodiment because data encryption key Dk is employed in this embodiment. 
     FIG. 10 is a schematic illustration of sill another data structure that can be used with the second embodiment of device for preventing fraudulent copies. 
     In FIG. 10, the encrypted data shown in FIG. 9 are combined to form a data structure. The data structure  226  comprises a copy management flag section  221  encrypted by the data encryption key Dk, a master key encrypting section  223  containing data encryption keys  222  that are encrypted by the master key and arranged sequentially and a disc key encrypting section  224 , which is EDk (Dk), to form a header for the data structure  226  and the data main body  225 , which is EDk (data), takes the lead in the header. 
     Then, the data structure  226  having the above configuration is used as data to be recorded and reproduced by digital recording/reproducing apparatus provided with a device for preventing fraudulent copies in order to effectively control copies of the data and prevent fraudulent copies from being made. 
     The second embodiment is also applicable to digital recording/reproducing apparatus as described above by referring to the first embodiment. Thus, although part of the components of the data structure  226  divided by the data read control circuit is modified and Dk is used as key for encrypting and decrypting CF, the data structure  226  can be used with any apparatus shown in FIGS. 1,  4 ,  5  and  6 . 
     FIG. 11 schematically shows the configuration of the data reproduction/copying processing section  334   b  adapted to the data structure  226 . Note that the configuration resembles to that of FIG.  6 . 
     FIG. 11 is a schematic block diagram of the data reproduction/copying processing section of the second embodiment. In FIG. 11, the components that are same as those of FIG. 6 are denoted respectively by the same reference symbols. Note that the entire system comprising the second embodiment of device for preventing fraudulent copies is identical with that of FIG.  4 . 
     Referring to FIG. 11, this embodiment differs from the first embodiment (FIG. 6) in that, in this embodiment, the data structure  226  is entered to the data read control circuit  401  and divided so that EDk (CF) is entered to the memory  406  and the master key encrypting section  223  is input to the copy circuit  415   b  along with the data main body  225 , that the decryption key to be used in the decryption circuit  407  is the data encryption key Dk obtained by the deter-mining circuit  405  and that the copy circuit  415   b  produces not the data structure  215  but the data structure  226  out of the inputs from the related sections. Note that the master key encrypting section  223  input from the data read control circuit  401  is utilized as part of the header of the data structure  226  in the copy circuit  415   b . If Dk is altered to Dk* under the condition where no copy is permitted to be made, the data encryption key Dk would not be taken out from the master key encrypting section  223  of the data structure because it is different from Dk* of the new disc encrypting section  224  that becomes EDK* (Dk*). 
     As a result, the data structure  226  output from the copy circuit  416  is same as the data structure  226  input to the data reproduction/copying processing section  334   b  except that CF is altered and DK* is produced in a fraudulent copy. In particular, since the master key encrypting section  223  is not replaced by the master key bundle Mks that is specific to the supplier of the apparatus, the copied data remain interchangeable among the apparatus suppliers. 
     Note that the CF altering section of the transmitter used in this embodiment is obtained by altering the CF altering section  317  of FIG. 5 in a manner as described above by referring to FIGS. 6 through 11 (not shown). In other words, the data encryption key Dk is input to the decryption circuit  407  as decryption key and the master key encrypting section  223  is entered to the data altering section  409  and utilized in the header of the data structure  226  at the time of updating. Thus, the data structure  226  remains interchangeable among the apparatus suppliers when the number of copies is controlled. 
     As described above, since a data structure  226  is used with this embodiment of device for preventing fraudulent copies having a configuration similar to that of the first embodiment, it provides the advantages as listed above by referring to the first embodiment and, additionally, it maintains the data encryption key encrypted by the first master key Mkn for copying data so that the copied data and the original data can remain interchangeable among the apparatus suppliers. 
     3rd Embodiment of the Invention 
     While only data structures  215  as illustrated in FIG.  3  and data structures  226  as illustrated in FIG. 10 are applicable to the respective systems of the first and second embodiments, the third embodiment is adapted to be used with any of such data structures. 
     FIGS. 12A and 12B are schematic illustrations of two different data structures applicable to the third embodiment of device for preventing fraudulent copies. 
     The data structure  215   b  of FIG. 12A is obtained by adding an identifier bit  231   a  to the top of the data structure  215 . 
     On the other hand, the data structure  226   b  of FIG. 12B is obtained by adding an identifier bit  231   b  to the top of the data structure  226 . 
     The data read control circuit  401  of the data reproduction/copying processing section  334  or  334   b , whichever appropriate, and the CF altering section  317  (including that of the second embodiment) of the third embodiment reads the identifier bit  231   a  or  231   b , whichever appropriate, and outputs a control signal to the related sections showing the processing operation to be performed on the data structure. 
     As described above, both the data structure  215   b  and the data structure  226   b  can be used as digital data for the third embodiment of device for preventing fraudulent copies configured like the first and second embodiments so that the third embodiment provides the advantages of the first and second embodiments and, additionally, is adapted to data structures having different formats. 
     4th Embodiment of the Invention 
     The configurations of data structures and modes of controlling data copies by means of the copy management flag CF contained in the structure are described above by referring to the preceding embodiments. However, a data structure can be fraudulently copied on the data transmission path however rigorously data copies are controlled by any of the above described modes to nullify the effects of the above embodiments. This is the reason for arranging the key sharing circuits  315 ,  332  in the above embodiments so that the apparatus at the opposite ends of the line share temporary key Stk and the data encrypted by the temporary key Stk is transmitted through the transmission path (an IEEE 1394 cable  303 ). 
     The method of sharing temporary key Stk will be described by referring to the fifth embodiment. Thus, it should be realized that the key sharing system as described hereinafter can be used for the key sharing circuits  315 ,  332  of the first through third embodiments. 
     FIG. 13 is a schematic illustration of a system designed for a pair of digital recording/reproducing apparatus to share a temporary key by utilizing the respective master key bundles of the apparatus. The apparatus are connected with each other by a network or a cable and share a temporary key for encrypting/decrypting confidential information to be transmitted through the network or the cable. In the following description, the transmitter and the receiver are connected with each other by an IEEE 1394 cable and share a temporary key. 
     Referring to FIG. 13, the transmitter  501  and the receiver  503  are connected with each other by way of an IEEE 1394 cable  502 . The master key bundle  504   a  (Mks) is recorded in the transmitter and the master key bundle  504   b  (Mks) is recorded in the receiver  503 . While the two master key bundles may be different from each other, they have to share a certain number of keys. It is assumed in the following description that the two master key bundles (Mks) are identical. 
     The transmitter  501  comprises a temporary key generating circuit  505  and encryption circuits  507   a ,  507   b , which operate for sharing a key. 
     The temporary key generating circuit  505  is adapted to generate a temporary key to be used for temporarily encrypting the data being transmitted through the network or the cable. The temporary key generation circuit  505  preferably has a random number generator adapted to generate random numbers having a specific length. 
     The temporary key  506  (Sk) is generated by the temporary key generating circuit  505 . 
     The encryption circuit  507   a  is adapted to encrypt the temporary key  506  by means of one of the keys of the master key bundle  504   a  and the encryption circuit  507   b  is adapted to encrypt the temporary key Sk by means of the temporary key Sk. However, the encryption circuits  507   a  and  507   b  may be made identical relative to each other if they are adapted to operate identically for encrypting the temporary key. In FIG. 13, EMki (Sk)  508  denotes the output of the encryption circuit  507   a , whereas ESk (Sk)  509  denotes the output of the encryption circuit  507   b.    
     On the other hand, the receiver  503  comprises decryption circuits  510   a ,  510   b  and a temporary key judging circuit  513 , which operate for sharing a key. 
     The decryption circuit  510   a  decrypts the output of the encryption circuit  507   a  by means of the master key bundle Mki. The decryption circuit  510   b  decrypts the output of the encryption circuit  507   a  by means of the output of the decryption circuit  510   a.    
     In FIG. 13, Ska  511  denotes the output of the decryption circuit  510   a , whereas Skb  512  denotes the output of the decryption circuit  510   b.    
     The temporary key judging circuit  513  is a circuit that compares the output of the decryption circuit  510   a  and that of the decryption circuit  510   b  and decides the right key. Control signal  514  is used to alter the master key bundle depending on the judgment of the circuit  513  and Sk  515  in FIG. 13 denotes the temporary key obtained as a result of the judgment. 
     Now, the operation of the key sharing device of this embodiment having the above configuration will be described below. 
     If there is only one master key (which will be referred to as Mk 0 ), the transmitter  501  simply encrypts the Mk 0  by means of Sk and the encrypted key, which is EMk (Sk), is sent to the receiver  503 , which decrypts the SMk (Sk) by means of the Mk 0  to take out Sk. However, if the confidentiality of the master key is lost, it has to be replaced by a new one and the old device may become no longer interchangeable with the new device. 
     In view of this problem, with this embodiment, the information for directly identifying the master key Mki selected and used out of a plurality of master keys of the master key bundle Mks is not transmitted from the transmitter  501  to the receiver  503 . Instead, information adapted to identify the master key Mki (which refers to EMki (Sk)  508  and ESk (Sk)  509  in this embodiment) is transmitted from the transmitter  501  to the receiver  503  and the receiver  503  identifies the master key Mki used for encrypting the Sk out of the plurality of master keys and actually acquires the Sk. 
     FIG. 14 is a schematic flow chart of the operation of the embodiment of FIG.  13 . 
     Referring to FIG. 14, firstly the temporary key generating circuit  505  of the transmitter  501  generates a temporary key  506  to be shared by the receiver  503  (S 11 ). 
     The processing operation of Step S 12  in FIG. 14 will be described in detail below. 
     The generated Sk is then encrypted by one (Mki) of a total of n master keys (corresponding to the common key of a common key encryption system) of the master key bundle  504   a , that is randomly or sequentially selected. In other words, the temporary key Sk is encrypted by Mki selected out of Mks (S=1, . . . , n; n being an integer equal to or greater than 2) by means of the encryption circuit  507   a  to obtain EMki (Sk). 
     The master key Mks has been registered in advance but the user cannot see it. If it is recognized that the confidentiality of some of the master keys has been lost, they will be eliminated from the master key bundle of the transmitter. The may or may not be eliminated from the master key bundle of the receiver. However, in the case of IEEE 1394, there is no saying which apparatus operates as transmitter or receiver (because digital recording/reproducing apparatus such as D-VCRs and DVD-RAMs can operate both as transmitter and receiver), it is desirable that the master keys having lost their confidentiality are eliminated from the master key bundle of the receiver either. Note that the entire operation is controlled by the controller (not shown) of each apparatus. The controller may be realized by a built-in CPU contained in the apparatus and provided with a program. 
     Then, Sk is encrypted by the encryption circuit  507   b , using Sk itself, to obtain ESk (Sk). Then, the EMki (Sk) and the ESk (Sk) are transmitted to the data main body by way of the IEEE 1394 cable  502 . 
     The receiver  503  firstly selects a master key (which will be Mkp). The selected Mkp is used as encryption key by the decryption circuit  510   a  to obtain DMkp (EMki (Sk))=Ska. 
     Then, ESk (Sk) is decrypted by the decryption circuit  510   b , using the output Ska of the decryption circuit  510   a  as decryption key to obtain 
     DSka (ESk (Sk))=Skb. 
     Thereafter, the temporary key judging circuit  513  checks if Ska and Skb agree with each other. If the master key Mki used for encrypting Sk in the transmitter  501  is Mkp, then 
     Ska=DMkp (EMki (Sk))=Sk and therefore 
     Skb=DSka (ESk (Sk))=DSk (ESk (Sk))=Sk, hence 
     Ska=Skb=Sk. 
     Thus, if the temporary key judging circuit  513  determines that Ska and Skb agree with each other, 
     Mki=Mkp and Ska=Skb=Sk. 
     Then, the temporary key judging circuit  513  outputs 
     Ska=Skb=Sk. 
     If, on the other hand, the temporary key judging circuit  513  determines that Ska and Skb do not agree with each other, then 
     Mki≠Mkp 
     so that the transmitter  501  can find out that the Mkp is not used but some other master key is used to encrypt Sk. Then, the temporary key judging circuit  513  does not output anything or the output of the temporary key judging circuit  513  will not be sent to the downstream. 
     Thereafter, Mkp is shifted until Ska comes to agree with Skb, repeating the above described decrypting operation. For example, if Ska and Skb do not agree with each other when Mkp and Mk 1  are used for the above operation, then the operation will be repeated by using Mk 2 . 
     Thus, with the above described operation, the receiver  503  can identify the master key used by the transmitter  501  for the encryption and the transmitter  501  and the data main body can securely share the temporary key Sk. 
     As described above, this embodiment of device for preventing fraudulent copies is adapted to make the transmitter  501  and the receiver  503  share a temporary key Sk by using a master key to provide an additional effect relative to the first through third embodiments so that it can reliably and effectively baffle any attempt of fraudulently drawing out the data from the cable connecting the related apparatus and recording it for pirating. 
     5th Embodiment of the Invention 
     With this embodiment, a technique of sharing a temporary key other than the one using master keys will be described by referring to FIGS. 15 and 16. 
     This technique is realized by utilizing the technology described in “Nikkei Electronics, No. 676, pp. 13-14, 1996. 11. 18”. 
     FIG. 15 is a schematic block diagram of a key sharing circuit to be used in the fifth embodiment of the invention. 
     FIG. 16 is a schematic illustration of a system designed for a pair of digital recording/reproducing apparatus to share a temporary encryption key by means of a key sharing circuit without using a master key bundle. 
     Assume that nodes are allocated to the apparatus mutually connected by IEEE 1394 and node #1 and node #2 shown in FIG. 16 share a temporary key. Referring firstly to FIG. 15, key sharing circuits  630   a ,  630   b  to be used for the key sharing procedure of this embodiment will be described. 
     The key sharing circuit  630   a  comprises a challenge key generating circuit  631   a , a verification key generating circuit  633   a , a comparator circuit  635   a  and a temporary key generating circuit  637   a.    
     Similarly, the key sharing circuit  630   b  comprises a challenge key generating circuit  631   b , a verification key generating circuit  633   b , a comparator circuit  635   b  and a temporary key generating circuit  637   b.    
     The challenge key generating circuits  631   a ,  631   b  are adapted to generate challenge keys that vary by each generation by means of a random number generating algorithm. 
     The verification key generating circuit  633   a ,  633   b  generate verification keys from a challenge key typically by means of a one-directional function. 
     The comparator circuits  635   a ,  635   b  compares if any given two verification keys agree with each other or not. 
     The temporary key generating circuits  637   a ,  637   b  generates temporary keys from a pair of verification keys, utilizing a one-directional function. 
     The verification key generating circuit  633   a  and the verification key generating circuit  633   b  are adapted to generate identical verification keys for a same challenge key by using a same algorithm. 
     The temporary key generating circuit  637   a  and the temporary key generating circuit  637   b  are adapted to generate identical temporary keys from two identical verification keys by using a same algorithm. 
     Now, the procedure of sharing a key will be described by referring to FIGS. 15 and 16. 
     Firstly in phase  1  of the key sharing means, the challenge key generating circuit  631   a  generates challenge key CK 1  at the node #2 and transmits it to the node #1. 
     Then, the verification key generating circuit  633   a  at the node #2 and the verification key generating circuit  633   b  at the node #1 generate respective verification keys (key 1 ) K 1 , K 1  from the challenge key CK 1  and the verification key K 1  generated at the node #1 is transferred to the node #2. 
     Then, the comparator circuit  635   a  at the node #2 compares the two verification keys K 1 , K 1  generated at the node #2 and at the node #1 respectively. If they agree with each other, the operation proceeds to phase  2 . If they do not, the operation will be abnormally terminated. 
     Then, in phase  2 , the challenge key generating circuit  631   b  at the node #1 generate a challenge key CK 2  and transmits it to the node #2. 
     Thereafter, the verification key generating circuit  633   b  at the node #1 and the verification key generating circuit  633   a  at the node #2 generate respective verification keys (key 1 ) K 2 , K 2  from the challenge key CK 2  and the verification key K 2  generated at the node #2 is transferred to the node #1. 
     Then, the comparator circuit  635   b  at the node #1 compares the two verification keys K 2 , K 2  generated at the node #1 and at the node #2 respectively. If they agree with each other, the operation proceeds to phase  3 . If they do not, the operation will be abnormally terminated. 
     In phase  3 , the temporary key generating circuit  637   a  at the node #2 and the temporary key generating circuit  637   b  at the node #1 respectively generate temporary keys (BUS keys) or temporary keys (Skt) from the verification keys K 1 , K 1  and the verification keys K 2 , K 2 . 
     Thus, the node #1 a nd the node #2 securely share the temporary key Skt. 
     As described above, this embodiment of device for preventing fraudulent copies is adapted to make the transmitter and the receiver share a temporary key Sk without using a master key to provide an additional effect relative to the first through third embodiments so that it can reliably and effectively baffle any attempt of fraudulently drawing out the data from the cable connecting the related apparatus and recording it for pirating. 
     It should be noted that present invention is not limited to the above described embodiments, which may be modified in various ways without departing from the scope of the invention. 
     The techniques described above by referring to the embodiments may be realized in the form of programs that can be executed by a computer and stored in a memory such as a magnetic disc (floppy disc, hard disc, etc.), an optical disc (CD-ROM, DVD, etc.) or a semiconductor memory so that they may be transmitted and distributed by way of telecommunication media. The computer selected to realize the invention will then read the program stored in the memory and be controlled by the program to carry out any of the above described operations. For the purpose of the invention, the computer refers to any information processing apparatus such as digital recording/reproducing apparatus. 
     Thus, as described above in detail, the present invention provides a device and method for preventing any fraudulent copies of data by prohibiting access to the copy management section of the data. 
     Additionally, the present invention provides a device and method for preventing any fraudulent copies of data by prohibiting any effective reproduction of fraudulently copied data. 
     A device and method for preventing any fraudulent copies of data according to the invention are elaborately designed and operate highly effectively. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.