Patent Publication Number: US-2002013940-A1

Title: Content rental system

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a content rental system for renting contents such as movies, post-broadcast television programs, and educational video programs.  
       [0003] 2. Description of the Prior Art  
       [0004]FIG. 1 shows an outlined structure of a conventional rental system for video software titles. Referring to FIG. 1, a video source production company  1  and a video software title production company  6  make a video software title distribution right practicing commission contract  15 . The video source production company  1  distributes a video software title production master tape as a master tape supply  17  to the video software title production company  6 . The video software title production company  6  produces a plurality of rental video software title copies using the distributed video software title master tape. The video software title production company  6  pays a royalty  16  for the master tape supply  17  to the video source production company  1 . The rental video software title copies are mainly magnetic tapes. The rental video software titles copies may be read-only optical discs such as laser discs and DVD-ROMs.  
       [0005] As an intermediate distributor disposed between the video software title production company  6  and a rental business operator  3 , there is a wholesaler  7 . The video software title production company  6  supplies rental stock  61  such as rental video software title copies as rental stock  71  to the rental business operator  3  through the wholesaler  7 . The wholesaler  7  pays a royalty  62  for the rental stock  71  to the video software title production company  6 . In addition, the rental business operator  3  pays the fee of the video software title copies to the wholesaler  7 . At that point, the rental business operator  3  reports the number of sold copies of the video software title to the wholesaler  7 . There may be a direct sales contract in which there is no wholesaler  7  as an intermediate distributor.  
       [0006] In addition, the video software title production company  6  and various copyright associations  5  make a royalty collection commission contract  51  for collecting copyright royalty of video software titles. The video software title production company  6  pays a copyright royalty  52  to the various copyright associations  5 .  
       [0007] About a licensing contract such as copyright, as shown in FIG. 2, there is a distribution right commission association (for example, Japan Video Soft Association, which is a special corporation)  8 . The distribution right commission association  8  and the video software title production company  6  makes a distribution right practicing commission contract  64 . In addition, the rental business operator  3  submits a rental licensing application  81  to the distribution right commission association  8 . When the distribution right commission association  8  grants the rental licensing application  81  to the rental business operator  3 , the distribution right commission association  8  provides a member store plate  83  to the rental business operator  3 . In addition, the distribution right commission association  8  and the rental business operator  3  makes a rental business licensing contract  84 . Likewise, the rental business operator  3  and the various copyright associations  5  make a rental business licensing contract  84 . Copyright royalty is paid as a system member fee  82 . The copyright royalty may be paid to the various copyright associations  5  through the distribution right commission association  8 .  
       [0008] The above-described conventional video software title rental system has the situations and problems as follows:  
       [0009] (1) When the rental business operator  3  purchases video software title copies, he or she should accurately predict the number of copies per video software title that will be rented at the same time and the turnover rate thereof in consideration of the demand. If the rental business operator  3  buys more copies than demanded copies because of an inaccurate prediction, he or she will have improper stock. In contrast, when more copies are demanded than predicted copies, the rental business operator  3  will lose a business chance because he or she does not have sufficient stock.  
       [0010] (2) Like the rental business operator  3 , the video software title production company  6  has the same problem. The video software title production company  6  should consider how many rental magnetic tapes he or she will produce from the master tape. For example, copies of a video software title whose turnover rate is low are circulated at low prices to the second hand market, the prices of sell copies of the video software title are lowered.  
       [0011] (3) Copies of conventional video software titles with magnetic tapes often contain previews of movies that will be produced by the video source production company and commercials of video software titles that will be newly sold. Although the commercials (namely, advertisements) contribute to reduce the prices of copies of video software titles, when the copies of the video software titles become old, the commercial effects will become low. In addition, the audiences will be confused by the commercials.  
       [0012] (4) As a problem that does not relate to the distribution system, the quality of a magnetic tape of a copy of a video software title deteriorates as the number of rental times increases. This adversely affects the customers of the rental services. The customers may not clearly view programs of rental video software title copies with noise due to a tracking error or the like.  
       [0013] (5) So far, there is a problem about illegal copies of video software titles. When video software titles are digitized, illegal copies thereof will become a critical problem that adversely affect the managements of the video source production company  1  and the video software title production company  6 .  
       SUMMARY OF THE INVENTION  
       [0014] The present invention is made in consideration of the above-described situations. An object of the present invention is to provide a content rental system that prevents a rental business operator from having improper stock and loosing a business chance, preventing the prices of sell copies of video software titles from lowering, allows the latest commercials to be inserted into rental copies of video software titles, and prevents illegal copies from being produced.  
       [0015] The present invention is a content rental system, comprising a content producer for producing a content, a rental business server, disposed in a store managed by a rental business operator, for recording a content produced by the content producer and downloading the content to a record medium corresponding to a command issued by a customer, and a reproducing device, disposed in the house of the customer, for reproducing the content from the record medium.  
       [0016] The rental business operator records an advertisement picture to the record medium along with the content.  
       [0017] When an icon contained in the advertisement picture is clicked, the reproducing device is connected to an advertisement server through the Internet.  
       [0018] The record medium comprises a content storing portion for storing the content encrypted, a memory for storing a decryption key for decrypting the content, and a capacitor for backing up the memory, wherein the capacitor is charged by the rental business server.  
       [0019] The record medium comprises a content storing portion for storing the content, a memory for storing a control algorithm for reading the content, and a capacitor for backing up the memory, wherein the capacitor is charged by the rental business server.  
       [0020] The record medium comprises a content storing portion for storing the content encrypted, a memory for storing a decryption key for decrypting the content, and a timer for causing data stored in the memory to be erased when a predetermined time period elapses after the record medium is connected to the rental business server.  
       [0021] The record medium comprises a content storing portion for storing the content, a memory for storing a control algorithm for reading the content, and a timer for causing data stored in the memory to be erased when a predetermined time period elapses after the record medium is connected to the rental business server.  
       [0022] The content rental system further comprises capacitor, charged by the rental business server, for supplying a power to the timer.  
       [0023] The present invention is a content rental system for downloading a content to a record medium of a customer and managing the security of the content corresponding to data stored in an IC card of the customer, comprising a content producer for producing the content, a management center for delivering the content produced by the content producer to a plurality of rental business operators, a rental business server, disposed in a store managed by each of the rental business operators, for recording the content delivered from the management center, downloading the recorded content to the record medium corresponding to a command issued by the customer, and managing the security of the content corresponding to the data stored in the IC card, and a reproducing device, disposed in the house of the customer, for restoring the content from the record medium and managing the security of the content corresponding to the data stored in the IC card.  
       [0024] When the IC card is set to the reproducing device, the reproducing device authenticates the IC card and the IC card authenticates the reproducing device.  
       [0025] The reproducing device is authenticated by a process in which the reproducing device transmits a reproducing device public key certificate to the IC card and the IC card authenticates the reproducing device public key certificate. The IC card is authenticated by a process in which the IC card transmits an IC card public key certificate to the reproducing device and the reproducing device authenticates the IC card public key certificate.  
       [0026] The reproducing device is authenticated in such a manner that the IC card encrypts a random number using a reproducing device public key and transmits the encrypted random number to the reproducing device, that the reproducing device decrypts the encrypted random number using a reproducing device secret key and transmits the decrypted random number to the IC card, and that the IC card authenticates the reproducing device using the decrypted random number.  
       [0027] The IC card is authenticated in such a manner that the reproducing device encrypts a random number using an IC card public key and transmits the encrypted random number to the IC card, that the IC card decrypts the encrypted random number using an IC card secret key and transmits the decrypted random number to the reproducing device, and that the reproducing device authenticates the IC card using the decrypted random number.  
       [0028] When the IC card is set to the rental business server, the rental business server authenticates the IC card in cooperation with the management center.  
       [0029] The IC card is authenticated by a process in which the IC card transmits an IC card public key certificate to the management center through the rental business server and the management center authenticates the IC card public key certificate.  
       [0030] The IC card is authenticated in such a manner that the management center encrypts a random number using an IC card public key and transmits the encrypted random number to the IC card through the rental business server, that the IC card decrypts the encrypted random number using an IC card secret key and transmits the decrypted random number to the management center through the rental business server, and that the management center authenticates the IC card using the decrypted random number.  
       [0031] When the IC card is set to the rental business server, the IC card transmits a reproducing device public key certificate to the management center through the rental business server and the management center authenticates the reproducing device corresponding to the reproducing device public key certificate.  
       [0032] When the record medium and the IC card are set to the rental business server and the customer selects a content, the rental business server transmits contract information to the IC card. The IC card encrypts the contract information and transmits the encrypted contract information to the management center through the rental business server. After the management center decrypts the encrypted contract information and authenticates the contract information, the management center encrypts an encryption key of the content selected by the customer and transmits the encrypted content to the IC card through the rental business server. After the IC card decrypts the encrypted content encryption key and authenticates the content, the IC card transmits a normal completion message to the rental business server. The rental business server receives the normal completion message and downloads the content to the record medium.  
       [0033] When the record medium and the IC card are set to the reproducing device, the reproducing device transmits a content encryption key transmission request to the IC card. The IC card receives the transmission request, encrypts a content encryption key, and transmits the encrypted content encryption key to the reproducing device. After the reproducing device decrypts the encrypted content encryption key and authenticates the decrypted content encryption key, the reproducing device reproduces the content using the decrypted content encryption key.  
       [0034] These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0035]FIG. 1 is a block diagram showing the structure of a conventional video tape rental system;  
     [0036]FIG. 2 is a block diagram showing the structure of the conventional video tape rental system;  
     [0037]FIG. 3 is a block diagram showing the structure of an embodiment of the present invention;  
     [0038]FIG. 4 is a block diagram showing a modification of the embodiment;  
     [0039]FIG. 5 is a block diagram showing an example of the structure of an RHDD (removable magnetic disk device) according to the embodiment shown in FIG. 3 or  4 ;  
     [0040]FIG. 6 is a flow chart for explaining the operation of the RHDD shown in FIG. 5;  
     [0041]FIG. 7 is a block diagram showing the state that the RHDD shown in FIG. 5 is connected to a reproducing device;  
     [0042]FIG. 8 is a block diagram for explaining a reproducing operation of the RHDD shown in FIG. 7;  
     [0043]FIG. 9 is a block diagram showing an example of another structure of the RHDD;  
     [0044]FIG. 10 is a block diagram for explaining the operation of the RHDD shown in FIG. 9;  
     [0045]FIG. 11 is a block diagram showing an example of another structure of the RHDD;  
     [0046]FIG. 12 is a block diagram showing an example of another structure of the RHDD;  
     [0047]FIG. 13 is a block diagram showing an example of another structure of the RHDD;  
     [0048]FIG. 14 is a block diagram for explaining the operation of the RHDD shown in FIG. 13;  
     [0049]FIG. 15 is a block diagram for explaining the operation of the RHDD shown in FIG. 13;  
     [0050]FIG. 16 is a block diagram showing an example of another structure of the RHDD;  
     [0051]FIG. 17 is a block diagram showing an example of a structure in which the reproducing device shown in FIG. 16 is substituted with a reproducing device having another structure;  
     [0052]FIG. 18 is a block diagram showing the structure of another embodiment of the present invention;  
     [0053]FIG. 19 is a block diagram showing the structure of a management center  160  according to the embodiment shown in FIG. 18;  
     [0054]FIG. 20 is a block diagram showing the structure of a server  162  according to the embodiment shown in FIG. 18;  
     [0055]FIG. 21 is a block diagram showing the structure of an IC card  167  according to the embodiment shown in FIG. 18;  
     [0056]FIG. 22 is a block diagram showing the structure of a reproducing device  170  according to the embodiment shown in FIG. 18;  
     [0057]FIG. 23 is a flow chart showing a mutual authenticating operation of the reproducing device  170  and the IC card  167  according to the embodiment shown in FIG. 18;  
     [0058]FIG. 24 is a flow chart showing a mutual authenticating operation of the management center  160  and the IC card  167  according to the embodiment shown in FIG. 18;  
     [0059]FIG. 25 is a flow chart showing a transferring process for a reproducing device public key certificate from the IC card  167  to the management center  160  according to the embodiment shown in FIG. 18;  
     [0060]FIG. 26 is a flow chart showing a content downloading process according to the embodiment shown in FIG. 18;  
     [0061]FIG. 27 is a flow chart showing a content reproducing process according to the embodiment shown in FIG. 18;  
     [0062]FIG. 28 is a block diagram showing the overall structure of another embodiment of the present invention;  
     [0063]FIG. 29 is a block diagram showing the structure of a store server  701  shown in FIG. 28;  
     [0064]FIG. 30 is a block diagram showing the structure of an RHDD  704  shown in FIG. 28; and  
     [0065]FIG. 31 is a block diagram showing the structure of a reproducing device  705  shown in FIG. 28. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
     [0066] &lt;First Embodiment&gt; 
     [0067]FIG. 3 is a block diagram showing the overall structure of a content rental system according to a first embodiment of the present invention. In FIG. 3, a video source production company  1  produces a video master. The video source production company  1  has a photographing camera, a digital picture converting—processing device, a computer, and so forth as hardware. The photographing camera photographs a picture corresponding to a scenario. The digital picture converting—processing device converts a photographed picture of a film into a digital picture. The computer manages and controls those devices.  
     [0068] A video software duplicator  2  has a duplicating device that duplicate the video master supplied from the video source production company  1  and produces child master record mediums thereof In addition, the video software duplicator  2  manages information such as the title name of the video master, the actor names of the video software title, and the performance duration thereof. Moreover, the video software duplicator  2  deals with management information and operational information such as the number of produced child master record mediums.  
     [0069] Various copyright associations  5  collect copyright royalty for video masters, music programs, arts, and so forth. In addition, the various copyright associations  5  deal with copyright infringements and allot collected money to copyright owners using server terminal units.  
     [0070] A rental business operator  3  has a server terminal unit which has interface units in order to duplicate the video software to a portable record medium, i.e., RHDD, using a child master record medium delivered from the video software duplicator  2 . When a customer wants to rent a content, the rental business operator  3  duplicates the content to RHDD using the server terminal unit and rents the RHDD to the customer. In addition, the rental business operator  3  has a service server terminal unit that calculates the rental period between the rental start date and the rental end date of the RHDD rented to the customer and the rental fee thereof and collects the rental fee from the customer. In addition, the rental business operator  3  has a network terminal unit that exchanges information with other cooperative rental business operators  3 , the various copyright associations  5 , and the video software duplicator  2 .  
     [0071] A customer  4  rents a rental RHDD from the rental business operator  3  for several hours or several days.  
     [0072] Next, the operation of the above-described system will be described.  
     [0073] The video source production company  1  produces video masters and supplies them to movie theaters, music concerts, and so forth. In addition, the video source production company  1  prepares rental video masters. The video source production company  1  and the video software duplicator  2  make a video software title distribution right practicing commission contract  11 . The video software duplicator  2  receives a digital master tape that can be directly recorded to a magnetic disk device from the video source production company  1  and pays the royalty  12  thereof to the video source production company  1 . To share rental information and return information data  14 , the video software duplicator  2  exchanges the title name of the video master, the number of produced child master record mediums, and return date with the video source production company  1 .  
     [0074] The video software duplicator  2  and the various copyright associations  5  make a royalty collection commission contract  51  as information notification duties for the title names of magnetic mediums of the video master and child masters, and the number of replicated copies. The video software duplicator  2  pays a copyright royalty  52  for child master record mediums to the various copyright associations  5 .  
     [0075] In addition, the video software duplicator  2  and the rental business operator  3  make a supply and maintenance contract  21  for child master record mediums and so forth. The video software duplicator  2  distributes a child master magnetic disc medium for video information recorded corresponding to the digital master tape and rental stock  22  to the rental business operator  3  using a physical distributing means such as a courier service. The rental business operator  3  pays a royalty  23  for the child master record medium to the video software duplicator  2  and notifies the video software duplicator  2  of the rental information and return information data  24 .  
     [0076] Alternatively, video information of a digital master tape may be delivered to a plurality of rental business operators  3  through a satellite broadcast or the Internet. In this case, the rental business operators  3  may directly produce child master magnetic disk devices.  
     [0077] The rental business operator  3  and the customer  4  make a rental contract  31  for a rental fee, a rental period, and so forth. The rental business operator  3  rents an RHDD  32  to the customer  4 . The customer  4  pays the rental fee to the rental business operator  3  in cash or by a credit card.  
     [0078] The video software duplicator  2  produces a child master magnetic disk device that contains a commercial picture that is inserted at the beginning or the end thereof for a sponsor who made an advertisement contract therewith in agreement with the video source production company  1 . Alternatively, the video software duplicator  2  produces a child master magnetic disk device for only a commercial picture. Like the video software title information, the commercial information may be delivered to a plurality of rental business operators  3  through a satellite broadcast or the Internet. Each rental business operators  3  may produce a child master magnetic disk device that contains the commercial information.  
     [0079] When a customer knows that the rental business operator  3  has prepared a rental title that the customer wants to rent, he or she can rent an RHDD for the video software title and commercial information. At that point, the rental business operator  3  duplicates the video software title to RHDD using the child master magnetic disk device and the child master magnetic disk device for the commercial information. The downloading process for the RHDD is performed by a dedicated server terminal unit disposed in the rental business operator  3 .  
     [0080] When the rental business operator  3  rents the RHDD to the customer  4 , the rental business operator  3  collects the rental fee from the customer  4  corresponding to the rental contract. When the rental business operator  3  rents the RHDD to the customer  4 , a label maker device integrated with the dedicated server terminal unit creates a rental and customer management label that indicates the title name recorded in the RHDD, the rental period, the customer name who rents the RHDD, and the customer management attribute data. The rental business operator  3  rents the RHDD with the label to the customer  4 . At that point, a POS (Point of Sales) terminal unit having a label reader is used to read the video software title name, the rental period, the customer name, and the customer management attribute data. Those data that is read by the POS terminal unit is shared by the various copyright associations  5 , the video source production company  1 , the video software duplicator  2 , and the rental business operator  3  so as to check the basis of the royalty charged thereamong.  
     [0081] When the customer  4  returns the RHDD to the rental business operator  3 , it reads the rental and customer management label and confirms the return of the RHDD. The server terminal units of the various copyright associations  5 , the video source production company  1 , the video software duplicator  2 , and the rental business operator  3  are connected through the Internet. The title name produced from the video master by the video software duplicator  2 , the number of child master magnetic disk mediums produced from the video digital master tape, the names of the rental business operators  3  to which the child master magnetic tape disk mediums were distributed, the title names of the video software titles produced from the child master magnetic disk mediums by the rental business operator  3 , the number of rented RHDDs, the rental periods thereof, the attributes of the rented customers  4 , and information about returns of the rented RHDDs from the customers  4  to the rental business operators  3  are shared by the various copyright associations  5 , the video source production company  1 , the video software duplicator  2 , and the rental business operators  3 . Predetermined fees for copyright royalty and transactions are charged and collected corresponding to the shared data based on the contracts made among the various copyright associations  5 , the video source production company  1 , the video software duplicator  2 , and the rental business operators  3 .  
     [0082] To accurately and effectively perform the above-described transactions, the server terminal units that deal with various management data information of the transactions and perform the downloading process should be integrally maintained and managed between the video software duplicator  2  and each rental business operator  3 . Thus, the video software duplicator  2  and each rental business operator  3  make a business commission contract for maintenance and management of the downloading server terminal unit of the rental business operator  3 , the label maker that creates rental labels in cooperation with the downloading server terminal unit, the driving device for child master magnetic disk mediums, and the rental RHDD record mediums. Fees for delivery, maintenance, and management of devices and record mediums corresponding to the commission contract are collected corresponding to information exchanged between each rental business operator  3  and the video software duplicator  2  through the Internet.  
     [0083] To prevent digital video information from being illegally copied and circulated, each child master record medium and each RHDD may have respective clock functions. In addition, an RHDD driving device may have a function for automatically erasing video information from the record medium when a predetermined time period elapses after the date of the contract made between the video software duplicator  2  and each rental business operator  3  or the contract between each rental business operator  3  and each customer  4  or when the number of times of the downloading operation exceeds a predetermined value.  
     [0084] Next, with reference to FIG. 4, a modification of the first embodiment will be described. In the modification, the video software duplicator  2  and an advertisement sponsor  9  make an advertisement contract. The video software duplicator  2  receives a commercial digital master tape from the advertisement sponsor  9  who has the copyright thereof. For the distribution of the commercial digital master tape, the advertisement sponsor  9  pays the advertisement fee to the video software duplicator  2 . The video software duplicator  2  produces a child master magnetic disk medium for the commercial information at the beginning or the end thereof. Alternatively, the video software duplicator  2  produces a child master magnetic disk medium for only commercial information. The video software duplicator  2  distributes the produced child master magnetic disk mediums to the rental business operators  3 . Alternatively, like a video software title, commercial information is delivered to the rental business operators  3  through a satellite broadcast or the Internet. Each rental business operator  3  produces the copy of the video software title and the commercial information on the RHDD using a delivered child master magnetic disk medium and rends the produced RHDD to a customer  4 .  
     [0085] The video software duplicator  2  collects rental information of RHDDs that contain the commercial information of the advertisement sponsor  9  from each rental business operator  3  through a communication network such as the Internet and charges the advertisement sponsor  9  for the advertisement fee of the commercial information. In addition, the video software duplicator  2  pays part of the commercial fee to each rental business operator  3  corresponding to the contact made therebetween. A commercial picture may contain icons jumped to information screens such as the home page of the advertisement sponsor  9 , a gift, and a lottery from which each customer  4  may have a benefit. When the customer  4  clicks an icon in the commercial picture, a relevant information screen appears through the Internet.  
     [0086] After the customer  4  sets the rented RHDD  17  to an RHDD reproducing device  18 , icons  1 ,  2 , and  3  appear on a television screen  19 . When the customer  4  clicks one of these icons  1 ,  2 , and  3  using an operation board such as a keyboard or a mouse, he or she can select desired information. When an icon is selected, the television is connected to a commercial server  10  through the Internet. As a result, a web page of the commercial server  10  appears on the television. The web page displays an advertisement, a gift, a lottery, or the like corresponding to the selected icon.  
     [0087] The video software duplicator  2  receives data such as the number of audiences of the commercial and customer attribute information corresponding to the selected icon from the commercial server  10  through the Internet. The video software duplicator  2  provides the attribute information of the customers  4  and the number of audiences of the commercial to the advertisement sponsor  9  and collects the commercial fee from the advertisement sponsor  9 . The video software duplicator  2  shares the collected fee with each rental business operator  3  corresponding to the contract made therebetween.  
     [0088] Since the advertisement sponsor  9  pays the advertisement fee corresponding to the advertisement results, the advertisement efficiency of the advertisement sponsor  9  becomes high. Thus, the advertisement achievement ratio becomes clearer than the method in which the advertisement fee is paid corresponding to the prediction although the relation between the advertisement results and the sales results is not considered.  
     [0089] According to the first embodiment, video software titles are rented. However, audio (music) information can be rented. Alternatively, information of dictionaries, art information, or a variety of multimedia such as computer programs as software can be rented.  
     [0090] &lt;Second Embodiment&gt; 
     [0091] Next, an RHDD  17 , a downloading server (managed by each rental business operator  3 ), and a reproducing device (of each customer) according to the first embodiment will be described.  
     [0092]FIG. 5 is a block diagram showing the structure of the RHDD  17 . In FIG. 5, a content storing portion  101  stores contents received from a downloading server  106  managed by each rental business operator  3 . The contents that are stored in the content storing portion  101  are read and written under the control of a controlling portion  102 . The RHDD  17  is composed of a magnetic disk, a non-volatile memory, or the like.  
     [0093] The controlling portion  102  receives a power from the server  106  and controls the reading and writing operations of the content storing portion  101  and a non-volatile memory  104 . The controlling portion  102  has a function for determining whether or not a device connected to the RHDD  17  is valid. An external interface  103  is an interface that connects the RHDD  17  to the server  106  or the reproducing device. The external interface  103  receives a power from the server  106  or the reproducing device and inputs and outputs contents and information necessary for reproducing the contents from or to an external device. When the external interface  103  is connected to the downloading server  106 , a capacitor  105  is charged with a power supplied from the server  106 . The non-volatile memory  104  is backed up by the capacitor  105 . The reading and writing operations of the non-volatile memory  104  are controlled by the controlling portion  102 . The non-volatile memory  104  stores a decryption key.  
     [0094] Next, with reference to a flow chart shown in FIG. 6, the operation of the RHDD  17  will be described.  
     [0095] The server  106  stores an encrypted content and a decryption key necessary for decrypting the encrypted content. The server  106  and the RHDD  17  are connected through the external interface  103  (at step S 1 ). At that point, the RHDD  17  determines whether or not the connected device is a valid server (at step S 2 ). There are many determining methods. As the simplest method, the RHDD  17  determines whether or not the outer shape of the external interface  103  is matched to the server  106 . As a complicated method, the controlling portion  102  of the RHDD  17  authenticates the server  106 . When the determined result of the external interface  103  or the controlling portion  102  represents that the connected server is not a valid server, the capacitor  105  is not charged. The RHDD  17  completes the process.  
     [0096] When the determined result of the external interface  103  or the controlling portion  102  represents that the server  106  is a valid server, the power of the server  106  is supplied to the capacitor  105  through the external interface  103  and the capacitor  105  is charged (at step S 3 ). In the case that only the outer shape of the external interface  103  is checked, when the RHDD  17  is connected to the server  106 , the power of the server  106  is supplied to the capacitor  105  through the external interface  103  and the capacitor  105  is charged. In other cases, the controlling portion  102  causes the external interface  103  to supply the power to the capacitor  105 . As a result, the capacitor  105  is charged.  
     [0097] Thereafter, the controlling portion  102  receives the encrypted content from the server  106  through the external interface  103  and stores the encrypted content to the content storing portion  101  (at step S 4 ). Likewise, the controlling portion  102  receives the decryption key necessary for reproducing the content from the server  106  through the external interface  103  and stores the decryption key to the non-volatile memory  104  (at step S 5 ).  
     [0098] The RHDD  17  to which the content has been written by the server  106  is connected to the reproducing device of the user. Thereafter, the reproducing device reproduces the content.  
     [0099]FIG. 7 is a block diagram showing the structure in the case that the RHDD  17  is connected to a reproducing device  109 . FIG. 8 is a flow chart showing the operation in the case.  
     [0100] First of all, the RHDD  17  is connected to the reproducing device  109  (at step S 11 ). Thereafter, the RHDD  17  determines whether or not the connected device is a valid reproducing device (at step S 12 ). The determining method for the reproducing device  109  can be the same as that for the server  106 . When the determined result at step S 12  represents that the connected device is a valid reproducing device, the controlling portion  102  reads the decryption key from the non-volatile memory  104  and supplies the decryption key to a decrypting portion  107  through the external interface  103  (at step S 13 ). Thereafter, the controlling portion  102  reads the encrypted content from the content storing portion  101  and supplies the encrypted content to the decrypting portion  107  through the external interface  103  (at step S 14 ). The decrypting portion  107  of the reproducing device  109  decrypts the encrypted content. Thereafter, a reproducing portion (displaying device)  108  reproduces the decrypted content (at step S 15 ).  
     [0101] When the connected device is not a valid reproducing device, the power is not supplied to the capacitor  105  of the RHDD  17  through the external interface  103 . Thus, the power charged in the capacitor  105  of the RHDD  17  decreases. When a predetermined time period elapses, the power charged in the capacitor  105  becomes lower than the backup voltage for the data stored in the non-volatile memory  104 . Thus, the decryption key stored in the non-volatile memory  104  is lost. Although the encrypted content is stored in the content storing portion  101 , since the decryption key necessary for decrypting the encrypted content is lost, even if the RHDD  17  is connected to the reproducing device  109 , it cannot reproduce the content. In such a manner, after a predetermined time period elapses, the content cannot be reproduced. The predetermined time period depends on both the capacitance of the capacitor and the amount of current that flow for backing up the non-volatile memory  104 . Thus, by properly selecting the capacitance of the capacitor  105 , the backup period can be controlled.  
     [0102] In the above-described operation, an encrypted content and a decryption key are supplied from the server  106  to the RHDD  17 . Alternatively, after an encrypted content is stored to the RHDD  17 , only a decryption key may be received from the server  106  and stored to the non-volatile memory  104 . In FIG. 7, for simplicity, the controlling portion  102  and the non-volatile memory  104  are described as different blocks. Alternatively, the controlling portion  102  may contain the non-volatile memory  104 . In this case, a bus that connects the controlling portion  102  and the non-volatile memory  104  is not exposed. Thus, data of the nonvolatile memory can be properly prevented from being copied.  
     [0103] The RHDD  17  may use control data for controlling the content reading operation of the controlling portion  102  instead of the above-described decryption key. Next, the operation in such a case will be described. In this case, since the structure is not changed, with reference to FIG. 5, the operation will be described.  
     [0104] The operation of the controlling portion  102  can be roughly divided into an operation for reading a content from the content storing portion  101  and the other operation. The control algorithm for the other operation is stored in the non-volatile memory  104 .  
     [0105] When the RHDD  17  is connected to the server  106 , the RHDD  17  determines whether or not the server  106  is a valid server. When the determined result represents that the connected server is a valid server, the capacitor  105  is charged through the external interface  103 . Thereafter, a reading control algorithm for reading a content from the content storing portion  101  is received from the server  106  and stored to the non-volatile memory  104 .  
     [0106] When the controlling portion  102  needs to read a content from the content storing portion  101 , the controlling portion  102  references the control algorithm of the non-volatile memory  104  and reads the content from the content storing portion  101 . However, unless the RHDD  17  is connected to the server, the power charged in the capacitor  105  decreases. When a predetermined time period elapses, the reading control algorithm stored in the non-volatile memory  104  is lost. Although the content storing portion  101  stores the content, since the reading control algorithm for reading the content is lost, even if the RHDD  17  is connected to the reproducing device, the content cannot be reproduced. Thus, when a predetermined time period elapses, the content cannot be reproduced.  
     [0107] When the above-described control algorithm is used to reproduce a content, it is not necessary to encrypt the content stored in the content storing portion  101 . In this case, an MPEG (Moving Picture Experts Group) decoder portion is disposed in the RHDD  17  so as to prevent the content data from flowing outside. Thus, content data that is not encrypted can be prevented from flowing outside. As information necessary for reproducing a content, a reading control parameter such as a disk format parameter may be used instead of the reading control algorithm.  
     [0108]FIG. 9 is a block diagram showing an example of a second structure of the RHDD. FIG. 10 is a flow chart showing the operation of the RHDD shown in FIG. 9. Referring to FIGS. 9 and 10, a server  106  stores rental time information of a content. The server  106  and an RHDD  17   a  are connected through an external interface  103  (at step S 21 ). At that point, the RHDD  17   a  determines whether or not the connected device is a valid server (at step S 22 ). Since the determining method is the same as the above-described method, the description thereof is omitted.  
     [0109] When the determined result at step S 22  represents that the connected device is a valid server, a controlling portion  102  receives the rental time information from the server  106  (at step S 23 ). The rental time information may be time data such as 2 days or 48 hours. Alternatively, the rental time information may be a timer count value such as 1728000. When the controlling portion  102  receives time data as the rental time information, the controlling portion  102  converts the time data into a timer value for a timer  109 . The controlling portion  102  sets the converted timer value to the timer  109  (at step S 24 ). The controlling portion  102  receives a content and a decryption key necessary for reproducing the content from the server  106  through the external interface  103 . The controlling portion  102  stores the received content to a content storing portion  101 . In addition, the controlling portion  102  stores the decryption key to a non-volatile memory  104  (at step S 25 ). Thereafter, the controlling portion  102  causes the timer  109  to count down (at step S 26 ).  
     [0110] When the timer  109  starts counting down, the controlling portion  102  determines whether or not the counter value of the timer  109  is 0 (at step S 27 ). When the counter value becomes 0, the timer  109  sends a command for causing the non-volatile memory  104  to erase the decryption key stored in the non-volatile memory  104  (at step S 28 ). As the erasing method, a circuit that writes 0s to a particular area of the non-volatile memory  104  may be disposed in the timer  109 . Alternatively, a mechanism that turns off a switch of a power line connected from a battery  110  to the non-volatile memory  104  may be disposed.  
     [0111] In the structure shown in FIG. 9, for simplicity, the controlling portion  102 , the non-volatile memory  104 , and the timer  109  are described as different blocks. Alternatively, the non-volatile memory  104  and the timer  109  may be disposed in the controlling portion  102 . In this case, the erase command that is sent from the timer  109  to the non-volatile memory  104  can be prevented from being falsified. As a result, the erasing operation can be securely performed.  
     [0112]FIG. 11 is a block diagram showing an example of a third structure of the RHDD. Referring to FIG. 11, the battery  110  of the RHDD  17   a  shown in FIG. 9 is substituted with a capacitor  105 . The capacitor  105  backs up the non-volatile memory  104  and the timer  109 . The structure of the RHDD  17   b  shown in FIG. 11 is the same as the structure of the RHDD  17   a  shown in FIG. 9 except that a power is supplied from the server to the capacitor  105  through the external interface  103  under the control of the controlling portion  102 .  
     [0113] In the example of the third structure, the capacitance of the capacitor  105  is selected so that the backup period becomes longer than the setup time of the timer  109 . Thus, even if a large value is mistakenly set to the timer  109 , it becomes impossible to reproduce a content in a shorter time than the structure in which the content is backed up by the battery  110 . Consequently, a situation in which the content is reproduced for a long time can be prevented.  
     [0114] In the above-described structures of the RHDDs, the content storing portion  101  is a non-volatile medium. Alternatively, the content storing portion  101  may be composed of a non-volatile memory. The content storing portion  101  may be backed up by a battery or a capacitor as a modification of each of the above-described structures. FIG. 12 is a block diagram showing an example of the structure of a fourth structure of the RHDD. Referring to FIG. 12, in an RHDD  17   c , a content storing portion  101  is composed of a non-volatile memory. A capacitor  105  also backs up the power of the content storing portion  101 . Thus, when the voltage of the capacitor  105  becomes low, not only a decryption key stored in a non-volatile memory  104 , but a content stored in the content storing portion  101  is erased. Thus, unless the capacitor  105  is properly charged, when a predetermined time period elapses, the content cannot be reproduced. In FIG. 12, for simplicity, the content storing portion  101  and the non-volatile memory  104  are described as different devices. Alternatively, the content storing portion  101  and the non-volatile memory  104  may be accomplished as one device.  
     [0115]FIG. 13 is a block diagram showing an example of a fifth structure of the RHDD. FIGS. 14 and 15 are flow charts showing the operation of the RHDD shown in FIG. 13.  
     [0116] A server and an RHDD  17   d  are connected through an external interface  103  (at step S 29 ). At that point, the RHDD  17   d  determines whether or not the connected device is a valid server (at step S 30 ). Since the determining method is the same as the above-described method, the description thereof is omitted.  
     [0117] When the determined result at step S 30  represents that the connected device is a valid server, a controlling portion  102  receives an encrypted content from the server through an external interface  103  and stores the content to a data storing portion  115  (at step S 31 ). Likewise, the controlling portion  102  receives a decryption key from the server through the external interface  103  and stores the received decryption key to the data storing portion  115  (at step S 32 ). Thereafter, the controlling portion  102  receives time information as validation time for the content from the server, sets the received validation time to a timer  119 , and causes the timer  119  to start counting (at step S 33 ). It should be noted that the sequence of steps S 31  to S 33  may be changed.  
     [0118] Once the controlling portion  102  receives the validation time information from the server, writes the validation time information to the timer  119 , and causes the timer  119  to start counting, since the timer  119  is backed up by a battery  110 , even if the RHDD  17   d  is disconnected from the server, the timer  119  continues to count. When the timer  119  is a count-down timer, if the count value becomes 0, the timer  119  stops counting.  
     [0119] When the timer  119  is a count-up timer, if the count value becomes a value corresponding to the validation time, the timer  119  stops counting and represents that the validation time elapsed.  
     [0120]FIG. 15 is a flow chart showing a first operation performed in the case that the RHDD  17   d  is connected to a reproducing device of a user. First of all, the RHDD  17   d  is connected to the reproducing device (at step S 34 ). At that point, the RHDD  17   d  receives a main power from the reproducing device. Thereafter, the controlling portion  102  of the RHDD  17   d  determines whether or not the timer value of the timer  119  exceeds the validation time (at step S 35 ). When the timer value exceeds the validation time, the controlling portion  102  erases the decryption key stored in the data storing portion  115 . When the timer value does not exceed the validation time, the reproducing device performs the content reproducing operation. Since the content reproducing operation is the same as the above-described operation (at steps S 11  to S 15 ), the description thereof is omitted.  
     [0121] In the structure shown in FIG. 13, as a backup power for the timer  119 , the battery  110  is used. Alternatively, a capacitor may be used. In this case, the capacitor is charged by the server or the reproducing device.  
     [0122] In such a manner, when the timer value exceeds the validation time, immediately after the main power is supplied to the RHDD  17   d  from the outside, the decryption key stored in the data storing portion is erased. Thus, after the validation time elapses, the decryption key cannot be illegally obtained.  
     [0123] In the above-described structures of the RHDDs, the controlling portion  102  controls the reading and writing operations for the content storing portion  101  or the data storing portion  115 . Alternatively, the reading and writing operations for the content storing portion  101  or the data storing portion  115  may be performed by a medium reading and writing portion of a valid server or a valid reproducing device. Thus, in such a modification, the RHDD does not have the medium reading and writing portion. FIG. 16 is a block diagram showing an example of a sixth structure of the RHDD as such a modification. Referring to FIG. 16, a content storing portion  101  is independent of a controlling portion  102 . The content storing portion  101  does not have a medium reading and writing portion. In contrast, a server has a medium reading and writing portion  111  that controls the reading and writing operations for the content storing portion  101 .  
     [0124] Referring to FIG. 16, a content and information necessary for reproducing the content are stored in a content information storing portion  113  of a server  121 . The server side controlling portion  112  reads the content from the server side content information storing portion  113 . The controlling portion  112  writes the content to the content storing portion  101  through the medium reading and writing portion  111 . On the other hand, the server side controlling portion  112  reads a decryption key from the server side content information storing portion  113  and sends the decryption key to the controlling portion  102  through an external interface  103  of the RHDD  17   e . The controlling portion  102  stores the decryption key to a non-volatile memory  104 . A capacitor  105  is charged in the above-described manner. Thus, the description of the charging method is omitted.  
     [0125]FIG. 17 is a block diagram showing an example of another structure of the reproducing device. A controlling portion  114  of a reproducing device  122  receives decryption key from a non-volatile memory  104  having a read restricting function through the controlling portion  102  and the external interface  103  and sends the decryption key to a decrypting portion  107 . When the non-volatile memory  104  stores control data for controlling the medium reading and writing portion  111 , the reproducing device side controlling portion  114  sends the data to the medium reading and writing portion  111 . Thereafter, the reproducing device  122  reads a content from a content storing portion  101  of the a medium having the content reproduction restricting mechanism. The decrypting portion  107  decrypts the content. Thereafter, the reproducing portion  108  reproduces the content. However, when the backup period of the capacitor  105  elapsed, even if an invalid medium contains a copied content, since the decryption key was erased, the reproducing device cannot reproduce the content.  
     [0126] According to the structures of the above-described RHDDs  17  to  17   e , when a predetermined period elapsed, since information necessary for reproducing a content is erased, the content cannot be reproduced. Thus, when the RHDDs  17  to  17   e  are used for a rental system, customers do not need to return content mediums to rental stores. When a timer is disposed, the time at which information necessary for reproducing a content can be accurately set.  
     [0127] In addition, when the connected server is a valid server, the capacitor is charged. Thus, the time at which information necessary for reproducing a content is erased can be prevented from being illegally prolonged by a false server. When a content has been stored to an RHDD, only information necessary for reproducing the content is received from the server. Thus, the operation time is remarkably reduced. In addition, when medium read-write control data is used as information necessary for reproducing the content, after a predetermined period elapses, the control data is lost. At that point, the content cannot be read. Thus, the risk that the content is illegally read is remarkably reduced. Alternatively, only the timer may be backed up by an internal battery (or capacitor). In this case, when the validation time elapsed, immediately after the main power is supplied from the outside, a decryption key stored in the data storing portion is erased. Thus, the capacity of the internal battery or the capacitor can be decreased. As a result, the cost of the RHDD can be reduced.  
     [0128] Alternatively, when a server or a reproducing device has a medium reading-writing portion, the structure of the medium having the content reproduction restricting mechanism can be simplified. Thus, the cost of the RHDD can be remarkably reduced. In addition, since control data for controlling the medium reading-writing portion of the reproducing device can be received from the medium having the content reproduction restricting mechanism, a content cannot be read from an invalid medium. Thus, the risk that a content is illegally reproduced can be remarkably reduced.  
     [0129] &lt;Third Embodiment&gt; 
     [0130] Next, a third embodiment of the present invention will be described. According to the third embodiment, an RHDD is composed of only a record medium for recording a content. In addition, according to the third embodiment, an IC card, a public key, and a secret key are used so as to strictly secure a content stored in the RHDD.  
     [0131]FIG. 18 is a block diagram showing the structure of the third embodiment. According to the third embodiment, a management center  160  is disposed. The management center  160  manages a plurality of rental business operators  3 . The management center  160  is connected to a downloading server  162  of each of the rental business operators  3  through a network  164 . The management center  160  corresponds to the video software duplicator  2  shown in FIG. 3. A content record medium  166  and an IC card  167  are connected to the server  162 . A reference numeral  170  is a reproducing device disposed in the house of each user. The content record medium  166  and the IC card  167  are connected to the reproducing device  170 . The content is reproduced from the content record medium  166 .  
     [0132] The management center  160  stores content encryption keys for individual contents, public key certificates of all IC cards, public key certificates of all reproducing devices, and pair information of all IC cards and all reproducing devices. The management center  160  receives an IC card public key certificate from an IC card  167  and a public key certificate of a reproducing device through a server  162  and determines whether or not the IC card  167  and the reproducing device are valid.  
     [0133] After the management center  160  mutually authenticates the IC card  167  through the server  162 , the management center  160  can deliver a content encryption key and rental period information to the IC card  167  through the server  162  corresponding to a predetermined process. The server  162  stores a content that has been encrypted using a content key stored in the management center  160 . The user can perform an operation for renting a content through the server  162 . The server  162  can download an encrypted content to a content record medium  166  corresponding to predetermined processes of the management center  160  and the IC card  167 .  
     [0134] The IC card  167  can download a content encryption key (of which a content has been encrypted) and rental period information through the server  162  and store the content key in the rental period. When the rental period elapsed, the IC card  167  can erase the content key. In addition, the IC card  167  can mutually authenticate a reproducing device  170  of the user. The IC card  167  can deliver the content key in the rental period corresponding to a predetermined process. The content record medium  166  can record a content stored in the server  162  corresponding to predetermined processes of the management center  160  and the IC card  167 . After a predetermined process is performed for the reproducing device  170  of the user, content data is read to the content record medium  166  under the control of the reproducing device  170 .  
     [0135] After the reproducing device  170  of the user authenticates the IC card  167 , corresponding to a predetermined process, the reproducing device  170  of the user stores the content key transmitted from the IC card  167  in the rental period. Until the rental period elapses or the power is turned off, the reproducing device  170  can store the content key. In addition, the reproducing device  170  can read the encrypted content from the content record medium  166  corresponding to a predetermined process, decrypt the encrypted content data using the content encryption key that is read from the IC card  167 , and reproduce the content in the rental period.  
     [0136] Next, the operations of the devices shown in FIG. 18 will be successively described.  
     [0137] The IC card  167  is pre-connected to the reproducing device  170 . The IC card  167  and the reproducing device  170  are mutually authenticated. When the IC card  167  is valid, it stores a reproducing device public key certificate. Thereafter, the user takes the IC card  167  and the content record medium  166  to a rental store and connects them to the server  162 . When the IC card  167  is connected to the server  162 , it reads an IC card public key certificate from the IC card  167  and transmits a request for mutually authenticating the IC card  167  to the management center  160  along with the IC card public key certificate.  
     [0138] After the management center  160  determines whether or not the IC card public key certificate is valid, the management center  160  mutually authenticates the IC card  167 . Thereafter, the server  162  reads a reproducing device public key certificate and transfers the reproducing device public key certificate to the management center  160 . The management center  160  determines whether or not the reproducing device public key certificate is valid. When the user inputs the title name of a content that he or she wants to rent and the rental period thereof to the server  162 , the server  162  transmits the title name of the content and the rental period to the IC card  167  and reads the reproduction information and the signature thereof from the IC card  167 . The server  162  transmits the reproduction information and the signature data thereof as data that requires a content encryption key to the management center  160 .  
     [0139] When the determined result represents that the data is valid corresponding to the reproduction information and the signature thereof received from the server  162 , the management center  160  encrypts the content encryption key corresponding to the content title name using the reproducing device public key and transmits the signature data to the IC card  167  through the server  162 . The IC card  167  determines whether or not the content encryption key and the signature data are valid. When the determined result represents that the content encryption key and the signature data are valid, the IC card  167  stores the content key in the rental period.  
     [0140] Thereafter, the server  162  transfers the encrypted content to the content record medium  166  corresponding to a predetermined process. After the user pays the rental fee for the content to the rental store, he or she receives the IC card  167  and the content record medium  166  from the rental store. Thereafter, the user connects the IC card  167  and the content record medium  166  to the reproducing device  170  of the user. The reproducing device  170  mutually authenticates the IC card  167 . When the authenticated result represents that they are valid, the reproducing device  170  can read the content encryption key, the rental information, and the signature data from the IC card  167 .  
     [0141] The reproducing device  170  determines whether or not the data is valid using the content key, the rental information, and the signature data. When the determined result of the reproducing device  170  represents that the data is valid, the reproducing device  170  stores the content key in the rental period or until the power is turned off. The reproducing device  170  reads the encrypted content from the content record medium  166 , decrypts the encrypted content using the content key, and reproduces the content in the rental period or until the power is turned off.  
     [0142]FIG. 19 shows an example of a detailed structure of the management center  160 . The management center  160  is composed of a controlling portion  201 , a decrypting portion  202 , an encrypting portion  203 , a compressing portion  204 , a random number generating portion  205 , an authenticating portion  206 , a communicating portion  207 , a management center secret key storing portion  208 , a management center public key storing portion  209 , a content key storing portion  210 , a public key database  211 , and a charge information database  212 . The management center secret key storing portion  208  stores a secret key that only the management center  160  has. The management center public key storing portion  209  stores a management center public key paired with the management center secret key. The content key storing portion  210  stores a common key encrypted for each content. The public key database  211  stores public key certificates of all IC cards and all reproducing devices and pair information of all the IC cards and all the reproducing devices. The charge information database  212  stores the title names of contents, the rental periods, and the rental fees of contents that users rented.  
     [0143] When the decrypting portion  202  receives encrypted data from the server  162  of the rental store through the communicating portion  207 , the decrypting portion  202  can decrypt the encrypted data using the management center secret key stored in the management center secret key storing portion  208  or the IC card public keys and the reproducing device public key stored in the public key database  211  under the control of the controlling portion  201 . When data is transmitted to the server  162  of the rental store through the communicating portion  207 , the encrypting portion  203  can encrypt the data using the management center secret key stored in the management center secret key storing portion  208  or the IC card public key and the reproducing device public key stored in the public key database  211  under the control of the controlling portion  201 . The compressing portion  204  can compress any data using the hash function under the control the controlling portion  201 . The random number generating portion  205  can generate a random number under the control of the controlling portion  201 . When a mutual authenticating operation is performed, the authenticating portion  206  can collate a transmitted random number with a received random number. In addition, the authenticating portion  206  can collate received data with signature data.  
     [0144]FIG. 20 is a block diagram showing a detailed structure of the server  162  shown in FIG. 18. The server  162  is composed of a controlling portion  301 , a communicating portion  302 , an IC card inputting-outputting portion  303 , a content record medium inputting-outputting portion  304 , an inputting portion  305 , a displaying portion  306 , and a content storing portion  307 . The communicating portion  302  can communicate with the management center  160  through the network  164  such as the Internet under the control of the controlling portion  301 . The IC card inputting outputting portion  303  can communicate with the IC card  167  under the control of the controlling portion  301 . The content record medium inputting-outputting portion  304  can output content data stored in the content storing portion  307  to the content record medium  166  under the control of the controlling portion  301 . The inputting portion  305  is a user interface through which the user can select a content that he or she will rent and the rental period thereof. The displaying portion  306  is a user interface that displays the title name of the content that the user will rent and the rental period thereof. The content storing portion  307  stores the encrypted content.  
     [0145]FIG. 21 shows a detailed structure of the IC card  167  shown in FIG. 18.  
     [0146] The IC card  167  is composed of a controlling portion  401 , an inputting-outputting portion  402 , a decrypting portion  403 , an encrypting portion  404 , a compressing portion  405 , a random number generating portion  406 , an authenticating portion  407 , an IC card secret key storing portion  408 , a management center public key storing portion  409 , an IC card public key certificate storing portion  410 , a reproducing device public key certificate storing portion  411 , a content encryption key storing portion  412 , a timer  413 , and a battery  414 .  
     [0147] The IC card secret key storing portion  408  stores a secret key. The management center public key storing portion  409  stores a management center public key. The IC card public key certificate storing portion  410  stores an IC card public key certificate issued by the management center  160 . The reproducing device public key certificate storing portion  411  stores a reproducing device public key certificate issued by the management center  160  and read from the reproducing device  170 . The content encryption key storing portion  412  is backed up by the battery  414 . The content encryption key storing portion  412  can store a content encryption key delivered from the management center  160  until the timer value of the timer  413  becomes a predetermined value. The timer  413  is backed up by the battery  414 . The timer value of the timer  413  varies from the initial value delivered from the management center  160  as time elapses. When the timer value of the timer  413  becomes a predetermined value, the timer  413  causes data of the content encryption key storing portion  412  to be cleared.  
     [0148] When the decrypting portion  403  receives encrypted data from the server  162  of the rental store through the inputting-outputting portion  402  or from the reproducing device  170  of the user through the inputting-outputting portion  402 , the decrypting portion  403  can decrypt the encrypted data using the IC card secret key or the management center public key under the control of the controlling portion  401 . When data is transmitted to the server  162  of the rental store or the reproducing device  170  of the user through the inputting-outputting portion  402 , the encrypting portion  404  can encrypt the data using the IC card secret key or the reproducing device public key under the control of the controlling portion  401 . The compressing portion  405  can compress any data using the hash function under the control of the controlling portion  401 . The random number generating portion  406  can generate a random number under the control of the controlling portion  401 . When a mutual authenticating operation is performed, the authenticating portion  407  can collate a transmitted random number with a received random number. In addition, the authenticating portion  407  can collate received data with signature data.  
     [0149]FIG. 22 is a block diagram showing a detailed structure of the reproducing device  170  shown in FIG. 18.  
     [0150] The reproducing device  170  is composed of a controlling portion  501 , an IC card inputting-outputting portion  502 , a decrypting portion  503 , an encrypting portion  504 , a compressing portion  505 , a random number generating portion  506 , an authenticating portion  507 , a content record medium inputting-outputting portion  509 , a reproducing device secret key storing portion  510 , a management center public key storing portion  511 , a reproducing device public key certificate storing portion  512 , a timer  513 , a content encryption key storing portion  514 , a content key decrypting portion  515 , and a content reproducing portion  516 .  
     [0151] The reproducing device secret key storing portion  510  stores a secret key of the reproducing device  170 . The management center public key storing portion  511  stores a management center public key paired with a management center secret key corresponding to a predetermined process. The reproducing device public key certificate storing portion  512  stores a reproducing device public key certificate issued by the management center  160 . A predetermined timer value that represents the rental period that the controlling portion  501  reads from the IC card  167  through the IC card inputting-outputting portion  502  is set to the timer  513 . The timer value of the timer  513  varies as time elapses. When the timer value of the timer  513  becomes the predetermined value of the end of the rental period, the timer  513  causes the data stored in the content encryption key storing portion  514  to be cleared. The content encryption key storing portion  514  stores a content encryption key that the controlling portion  501  reads from the IC card  167  through the IC card inputting-outputting portion  502 . When the decrypting portion  503  receives encrypted data and digital certificate data from the IC card  167  through the IC card inputting-outputting portion  502 , the decrypting portion  503  can decrypt the encrypted data using the reproducing device secret key or the management center public key under the control of the controlling portion  501 .  
     [0152] When data is transmitted to the IC card  167  through the IC card inputting-outputting portion  502 , the encrypting portion  504  can encrypt the data using the reproducing device secret key under the control of the controlling portion  501 . The compressing portion  505  can compress any data using the hash function under the control of the controlling portion  501 . The random number generating portion  506  can generate a random number under the control of the controlling portion  501 . When a mutual authenticating operation is performed, the authenticating portion  507  can collate a transmitted random number with a received random number. In addition, the authenticating portion  507  can collate received data with signature data.  
     [0153] Next, with reference to a flow chart shown in FIG. 23, the mutual authenticating operation of the reproducing device  170  and the IC card  167  will be described.  
     [0154] The mutual authenticating operation is performed (1) before the IC card  167  and the reproducing device  170  are shipped from the factory, (2) when the user uses the system for the first time, (3) when the model of the reproducing device  170  is changed, or (4) when a content is reproduced.  
     [0155] First of all, the IC card  167  is connected to the reproducing device  170  (at step S 101 ). The controlling portion  501  of the reproducing device  170  determines whether or not the IC card  167  has been connected to the reproducing device  170  through the IC card inputting-outputting portion  502 . The controlling portion  501  repeats the same process until the IC card  167  come to be connected to the reproducing device  170  (at step S 102 ). When the determined result at step S 102  represents that the IC card  167  come to be connected to the reproducing device  170 , the controlling portion  501  transmits a reproducing device public key certificate (Pkp 1 , S 1 ) stored in the reproducing device public key certificate storing portion  512  to the IC card  167  along with a mutual authenticating operation request (at step S 103 ). When the controlling portion  401  of the IC card  167  receives the reproducing device public key certificate (PKp 1  and S 1 ) and the mutual authenticating operation request through the inputting-outputting portion  402 , the decrypting portion  403  decrypts a signature S 1  of the reproducing device public key certificate using a management center public key PKcnt stored in the management center public key storing portion  409  to generate PKcnt (S 1 ). The compressing portion  405  compresses the management center public key PKp 1  using the hash function to generate H (PKp 1 ). The authenticating portion  407  collates PKcnt with H (PKp 1 ) (at step S 104 ).  
     [0156] When the determined result at step S 105  represents that PKcnt does not match H (PKp 1 ), the controlling portion  401  of the IC card  167  determines that the reproducing device public key certificate is an invalid certificate that has not been issued by the management center  160  and transmits an error message to the reproducing device  170  through the inputting-outputting portion  402  (at step S 106 ). When the controlling portion  501  receives the error message through the IC card inputting-outputting portion  502  (at step S 107 ), the controlling portion  501  stops the mutual authenticating operation (at step S 129 ).  
     [0157] When the determined result at step S 105  represents that PKcnt matches H (PKp 1 ), the controlling portion  401  of the IC card  167  determines that the reproducing device public key certificate is a valid certificate that has been issued by the management center  160  and transmits the IC card public key certificate (PKic, S 2 ) stored in the IC card public key certificate storing portion  410  to the reproducing device  170  through the inputting-outputting portion  402  (at step S 108 ). When the controlling portion  501  of the reproducing device  170  receives the IC card public key certificate (PKic, S 2 ) through the IC card inputting-outputting portion  502 , the decrypting portion  503  decrypts a signature S 2  using the management center public key PKcnt stored in the management center public key storing portion  511  to generate PKcnt (S 2 ). The compressing portion  505  compresses the IC card public key PKp 1  using the hash function to generate H (PKp 1 ). The authenticating portion  507  collates PKcnt (S 2 ) with H (PKp 1 ) (at step S 109 ). When the determined result at step S 110  represents that PKcnt (S 2 ) does not match H (PKp 1 ), the controlling portion  501  of the reproducing device  170  determines that the IC card public key certificate is an invalid certificate that has not been issued by the management center  160  and stops the mutual authenticating operation (at step S 129 ).  
     [0158] When the determined result at step S 110  represents that PKcnt (S 5 ) matches H (PKic), the controlling portion  501  of the reproducing device  170  determines that the public key certificate is a valid certificate that has been issued by the management center  160 . The random number generating portion  506  generates a random number Rp 1  (at step S 111 ). The controlling portion  501  of the reproducing device  170  causes the encrypting portion  504  to encrypt the random number Rp 1  using the IC card public key Pkic to generate PKic (Rp 1 ) (at step S 112 ), and transmit PKic (Rp 1 ) to the IC card  167  through the IC card inputting-outputting portion  502  (at step S 113 ). When the controlling portion  401  of the IC card  167  receives PKic (Rp 1 ) through the inputting-outputting portion  402 , the decrypting portion  403  decrypts PKic (Rp 1 ) using the IC card secret key SKic stored in the IC card secret key storing portion  408  to generate DRp 1  (at step S 114 ).  
     [0159] Next, the random number generating portion  406  generates a random number Ric (at step S 115 ). The encrypting portion  404  encrypts the random number Ric using the reproducing device public key PKp 1  to generate PKp 1  (Ric) (at step S 116 ) and transmits PKp 1  (Ric) and DRp 1  to the reproducing device  170  through the inputting-outputting portion  402  (at step S 117 ). When the controlling portion  501  of the reproducing device  170  receives PKp 1  (Ric) and DRp 1  from the IC card inputting-outputting portion  502  (at step S 118 ), the authenticating portion  507  collates the random number Rp 1  generated by the reproducing device  170  with DRp 1  decrypted by the IC card  167  (at step S 119 ). When the determined result at step S 119  represents that Rp 1  does not match DRp 1 , the controlling portion  501  of the reproducing device  170  determines that the IC card is an invalid IC card that has an IC card secret key that is not paired with the IC card public key and stops the mutual authenticating operation (at step S 129 ).  
     [0160] When the determined result at step S 119  represents that Rp 1  matches Drp 1 , the controlling portion  501  of the reproducing device  170  determines that the IC card is a valid IC card that has an IC card secret key paired with the IC card public key. The decrypting portion  503  decrypts PKp 1  (Ric) received at step S 118  using the reproducing device secret key SKp 1  stored in the reproducing device secret key storing portion  510  to generate DRic (at step S 120 ), and transmits DRic to the IC card  167  through the IC card inputting-outputting portion  502  (at step S 121 ). When the controlling portion  401  of the IC card  167  receives DRic from the inputting-outputting portion  402  (at step S 122 ), the authenticating portion  407  collates the random number Ric generated by the IC card  167  with DRic decrypted by the reproducing device (at step S 123 ). When the determined result at step S 123  represents that Ric does not match DRic, the controlling portion  401  of the IC card  167  transmits an error message to the reproducing device  170  through the inputting-outputting portion  402  (at step S 124 ). When the controlling portion  501  of the reproducing device  170  receives the error message from the IC card inputting-outputting portion  502  (at step S 125 ), the controlling portion  501  stops the mutual authenticating operation (at step S 129 ).  
     [0161] When the determined result at step S 123  represents that Ric matches DRic, the controlling portion  401  of the IC card  167  compares the content of the reproducing device public key certificate storing portion  411  with the reproducing device public key certificate (PKp 1 , S 1 ) received at step S 104  (at step S 126 A). When the content of the reproducing device public key certificate storing portion  411  does not match the reproducing device public key certificate (PKp 1 , S 1 ) received at step S 104 , the controlling portion  401  stores the public key certificate (PKp 1 , S 1 ) of the reproducing device  170  received at step S 104  to the reproducing device public key certificate storing portion  411  (at step S 126 B). When the content of the reproducing device public key certificate storing portion  411  matches the reproducing device public key certificate (PKp 1 , S 1 ) received at step S 104 , the flow advances to step S 127 .  
     [0162] Thereafter, the controlling portion  401  of the IC card  167  transmits a mutual authenticating operation normal completion message to the reproducing device  170  through the inputting-outputting portion  402  (at step S 127 ). When the controlling portion  501  of the reproducing device  170  receives the normal completion message through the IC card inputting-outputting portion  502 , the controlling portion  501  stops the mutual authenticating operation (at step S 128 ).  
     [0163] Next, with reference to a flow chart shown in FIG. 24, the mutual authenticating operation of the IC card  167  and the management center  160  shown in FIG. 18 will be described.  
     [0164] The user takes the IC card  167  and the content record medium  166  to a rental store. The IC card  167  and the content record medium  166  are connected to the server  162  of the rental store (at step S 201 ). When the controlling portion  301  of the server  162  determines that the IC card  167  come to be connected to the server  162  through the communicating portion  302  (at step S 202 ), the controlling portion  301  transmits a request for reading the IC card public key certificate to the IC card  167  through the communicating portion  302  so as to perform the mutual authenticating operation (at step S 203 ). When the controlling portion  401  of the IC card  167  receives the request for reading the IC card public key certificate from the inputting-outputting portion  402 , the controlling portion  401  transmits an IC card public key certificate (PKic, S 2 ) stored in the IC card public key certificate storing portion  410  to the server  162  through the inputting-outputting portion  402  (at step S 204 ).  
     [0165] When the controlling portion  301  of the server  162  receives the IC card public key certificate (PKic, S 2 ) from the IC card inputting-outputting portion  303 , the controlling portion  301  transmits the IC card public key certificate (PKic, S 2 ) and a mutual authenticating operation request to the management center  160  through the communicating portion  302  and the network  164  (at step S 205 ). When the controlling portion  201  of the management center  160  receives the mutual authenticating operation request and the IC card public key certificate (PKic, S 2 ) from the server  162  through the communicating portion  207  (at step S 206 ), the controlling portion  201  searches the public key database  211  for the same IC card public key as the IC card public key PKic in the IC card public key certificate (PKic, S 2 ) from the public key database  211  to determine whether or not the IC card public key PKic is valid (at step S 207 ).  
     [0166] When the determined result at step S 207  represents that the IC card public key PKic is invalid or expired, the controlling portion  201  of the management center  160  transmits an error message as a reply of the mutual authenticating operation request from the communicating portion  207  to the server  162  through the network  164  (at step S 208 ). When the controlling portion  301  of the server  162  receives the error message through the communicating portion  302 , the controlling portion  301  stops the mutual authenticating operation process (at step S 230 ).  
     [0167] When the determined result at step S 207  represents that the IC card public key PKic is valid, the decrypting portion  202  decrypts a signature S 2  in the IC card public key certificate (PKic, S 2 ) received at step S 206  using a management center public key PKcnt stored in the management center public key storing portion  209  to generate PKcnt (S 2 ) The compressing portion  204  compresses PKic using the hash function to generate H (PKic). Thereafter, the authenticating portion  206  collates PKcnt (S 2 ) with H (PKic) (at step S 2081 ).  
     [0168] When the determined result at step S 209  represents that PKcnt (S 2 ) does not match H (PKic), the controlling portion  201  of the management center  160  determines that the public key certificate (Pkic, S 2 ) is a certificate that has not issued by the management center  160  and transmits an error message to the server  162  through the communicating portion  207  and the communicating portion  207  (at step S 210 ). When the controlling portion  301  of the server  162  receives the error message through the communicating portion  302  (at step S 210 ), the controlling portion  301  stops the mutual authenticating operation (at step S 230 ).  
     [0169] When the determined result at step S 209  represents that PKcnt (S 2 ) matches H (PKic), the controlling portion  201  of the management center  160  determines that the IC card public key certificate (PKic, S 2 ) received at step S 206  is a public key certificate that has been issued by the management center  160 . The random number generating portion  205  generates a random number Rcnt (at step S 211 ). The encrypting portion  203  encrypts the random number Rcnt using an IC card public key PKic to generate PKic (Rcnt) (at step S 212 ). The controlling portion  201  transmits PKic (Rcnt) as reply data of the mutual authenticating operation request to the server  162  through the communicating portion  207  and the network  164  (at step S 213 ). When the controlling portion  301  of the server  162  receives the encrypted data PKic (Rcnt) through the communicating portion  302 , the controlling portion  301  transmits PKic (Rcnt) to the IC card  167  through the IC card inputting-outputting portion  303  (at step S 214 ).  
     [0170] When the controlling portion  401  of the IC card  167  receives PKic (Rcnt) from the inputting-outputting portion  402 , the decrypting portion  403  decrypts PKic (Rcnt) using an IC card secret key SKic stored in the IC card secret key storing portion  408  to generate DRcnt (at step S 215 ). Thereafter, the controlling portion  401  of the IC card  167  causes the random number generating portion  406  to generate a random number Ric (at step S 216 ). The encrypting portion  404  encrypts the random number Ric using a management center public key PKcnt stored in the management center public key storing portion  409  to generate PKcnt (Ric) (at step S 217 ) and transmits PKic (Ric) and DRcent as reply data to the mutual authenticating operation request to the server  162  through the inputting-outputting portion  402  (at step S 218 ).  
     [0171] When the controlling portion  301  of the server  162  receives PKcnt (Ric) and DRcnt from the IC card inputting-outputting portion  303 , the controlling portion  301  transmits PKcnt (Ric) and DRcnt as reply data of the mutual authenticating operation request to the management center  160  through the communicating portion  302  and the network  164  (at step S 219 ). When the controlling portion  201  of the management center  160  receives PKcnt (Ric) and DRcnt from the communicating portion  207  (at step S 220 ), the authenticating portion  206  collates the decrypted data DRcnt with the random number data Rcnt (at step S 221 ). When the determined result at step S 221  represents that DRcnt does not match Rcnt, the controlling portion  201  of the management center  160  determines that the IC card is an invalid IC card that does not have an IC card secret key paired with the IC card public key PKic and transmits an error message to the server  162  through the communicating portion  207  and the network  164  (at step S 222 ). When the controlling portion  301  receives the error message from the communicating portion  302 , the controlling portion  301  stops the mutual authenticating operation (at step S 230 ).  
     [0172] When the determined result at step S 221  represents that DRcnt matches Rcnt, the controlling portion  201  of the management center  160  determines that the IC card is a valid IC card that has an IC card secret key paired with the IC card public key PKic. The decrypting portion  202  decrypts PKcnt (Ric) using a management center secret key SKcnt stored in the management center secret key storing portion  208  to generate DRic and transmits DRic to the server  162  through the communicating portion  207  and the network  164  (at step S 223 ). When the controlling portion  301  of the server  162  receives DRic from the communicating portion  302 , the controlling portion  301  transmits DRic to the IC card  167  through the IC card inputting-outputting portion  303  (at step S 224 ). When the controlling portion  401  of the IC card  167  receives DRic from the server  162  through the inputting-outputting portion  402  (at step S 225 ), the authenticating portion  407  collates the random number Ric with DRic (at step S 226 ).  
     [0173] When the determined result at step S 226  represents that the random number Ric does not match DRic, the controlling portion  401  of the IC card  167  determines that the management center is an invalid management center that does not have the management center secret key SKcent and transmits an error message to the server  162  through the inputting-outputting portion  402  (at step S 227 ). When the controlling portion  301  of the server  162  receives the error message from the IC card inputting-outputting portion  303 , the controlling portion  301  stops the mutual authenticating operation. When the determined result at step S 226  represents that Ric matches the decrypted data DRic, the controlling portion  401  of the IC card  167  determines that the management center is a valid management center that has the secret key SKcnt and transmits a normal completion message to the server  162  through the inputting-outputting portion  402  (at step S 228 ). When the controlling portion  301  of the server  162  receives the normal completion message from the IC card inputting-outputting portion  303 , the controlling portion  301  normally completes the mutual authenticating operation (at step S 229 ).  
     [0174]FIG. 25 shows a process of transferring a reproducing device public key certificate from the IC card  167  to the management center  160  after they have been mutually authenticated.  
     [0175] First of all, the controlling portion  301  of the server  162  transmits a request for reading the reproducing device public key certificate to the IC card  167  through the IC card inputting-outputting portion  303  (at step S 301 ). When the controlling portion  401  of the IC card  167  receives the request for reading the reproducing device public key certificate from the server  162  through the inputting-outputting portion  402 , the controlling portion  401  transmits a reproducing device public key certificate (PKp 1 , S 1 ) stored in the reproducing device public key certificate storing portion  411  to the server  162  through the inputting outputting portion  402  (at step S 302 ). When the controlling portion  301  of the server  162  receives the reproducing device public key certificate (PKp 1 , S 1 ) from the IC card inputting-outputting portion  303 , the controlling portion  301  transmits the reproducing device public key certificate (PKp 1 , S 1 ) to the management center  160  through the communicating portion  302  and the network  164  (at step S 304 ). When the controlling portion  201  of the management center  160  receives the reproducing device public key certificate (PKp 1 , S 1 ) from the server  162  through the communicating portion  207  (at step S 305 ), the controlling portion  201  searches the public key database  211  for the same public key as the public key PKp 1  in the reproducing device public key certificate (PKp 1 , S 1 ) and determines whether or not the public key is valid (at step S 306 ).  
     [0176] When the determined result at step S 306  represents that the reproducing device public key certificate received at step S 305  is valid or expired, the controlling portion  201  of the management center  160  transmits an error message to the server  162  through the communicating portion  207  and the network (at step S 207 ). When the controlling portion  301  of the server  162  receives the error message from the communicating portion  302 , the controlling portion  301  stops the transferring process of the reproducing device public key certificate (at step S 312 ). When the determined result at step S 306  represents that the reproducing device public key certificate received at step S 305  is valid, the decrypting portion  202  decrypts a signature S 1  of the reproducing device public key certificate (PKp 1 , S 1 ) using a management center public key PKcnt stored in the management center public key storing portion  209  to generate PKcnt (S 1 ). The compressing portion  204  compresses PKp 1  of the reproducing device public key certificate (PKp 1 , S 1 ) using the hash function to generate H (PKp 1 ). The authenticating portion  206  collates PKcnt (S 1 ) with H (Pkp 1 ) (at step S 308 ).  
     [0177] When the determined result at step S 309  represents that PKcnt (S 1 ) does not match H (PKp 1 ), the controlling portion  201  of the management center  160  determines that the reproducing device is an invalid reproducing device that does not have a reproducing device secret key SKp 1  paired with the reproducing device public key PKp 1  and transmits an error message to the server  162  through the communicating portion  207  and the network  164  (at step S 3101 ). When the controlling portion  301  of the server  162  receives the error message from the communicating portion  302 , the controlling portion  301  stops the transferring process for the reproducing device public key certificate (at step S 312 ) When the determined result at step S 309  represents that PKcnt (S 1 ) matches H (PKp 1 ), the controlling portion  201  of the management center  160  determines that the reproducing device is a valid reproducing device that has the reproducing device secret key SKp 1  paired with the reproducing device public key PKp 1  and transmits a normal completion message to the server  162  through the decrypting portion  202  and the network  164  (at step S 3102 ). When the controlling portion  301  of the server  162  receives the normal completion message form the communicating portion  302 , the controlling portion  301  normally completes the transferring process for the reproducing device public key certificate (at step S 311 ).  
     [0178]FIG. 26 is a flow chart showing a downloading process of information necessary for reproducing a content. The downloading process is preceded by the transferring process for the reproducing device public key certificate.  
     [0179] First of all, the user selects a content that he or she wants to rent on the displaying portion  306  and inputs a title name C and a rental period T of the content using the inputting portion  305  (at step S 401 ). The controlling portion  301  of the server  162  transmits contract information CT that contains the title name C and the rental period T of the content and a contract data creation request to the IC card  167  through the IC card inputting-outputting portion  303  (at step S 402 ). When the controlling portion  401  of the IC card  167  receives the contact data creation request and the contract information CT from the inputting-outputting portion  402 , the compressing portion  405  compresses the contract information CT using the hash function to generate H (CT). The encrypting portion  404  encrypts H (CT) using an IC card secret key SKic stored in the IC card secret key storing portion  408  and generates a signature S 3  (at step S 403 ).  
     [0180] Thereafter, the controlling portion  401  of the IC card  167  transmits the contract information CT and the signature S 3  to the server  162  through the inputting-outputting portion  402  (at step S 404 ). When the controlling portion  301  of the server  162  receives the contract information CT and the signature S 3  from the IC card inputting-outputting portion  303 , the controlling portion  301  transmits the contract information CT, the signature S 3 , and a content key download request to the management center  160  through the communicating portion  302  and the network  164  (at step S 405 ). When the controlling portion  201  of the management center  160  receives the content encryption key download request, the contract information CT, and the signature S 3  from the communicating portion  207  (at step S 406 ), the decrypting portion  202  decrypts S 3  using the IC card public key PKic that has been determined as a valid public key by the above-described mutual authenticating operation to generate PKic (S 3 ). The compressing portion  204  compresses the contract information CT using the hash function to generate H (CT). The authenticating portion  206  collates PKic (S 3 ) with H (CT) (at step S 407 ).  
     [0181] When the determined result at step S 408  represents that PKic (S 3 ) does not match H (CT), the controlling portion  201  of the management center  160  determines that the IC card  167  is invalid or data thereof has been falsified and transmits an error message to the server  162  through the communicating portion  207  and the network  164  (at step S 409 ). When the controlling portion  301  of the server  162  receives the error message from the communicating portion  302 , the controlling portion  301  stops the downloading process for the content encryption key (at step S 426 ). When the determined result at step S 408  represents that PKic (S 3 ) matches H (CT), the controlling portion  201  of the management center  160  determines that the issuer of the contract information CT is the IC card  167  and that the data thereof has not been falsified and writes the contract information CT to the charge information database  212  (at step S 410 ).  
     [0182] Thereafter, the controlling portion  201  of the management center  160  reads a content encryption key CK for the title name of the content corresponding to the contract information CT stored in the content key storing portion  210 . The compressing portion  204  compresses CK using the hash function to generate H (CK). The encrypting portion  203  encrypts H (CK) using a management center secret key SKcnt stored in the management center secret key storing portion  208  to generate a signature S 4  (at step S 411 ). Thereafter, the encrypting portion  203  encrypts the content encryption key CK and the signature S 4  using a reproducing device public key PKp 1  to generate PKp 1  (CK, S 4 ) (at step S 412 ). Thereafter, the compressing portion  204  compresses PKp 1  (CK, S 4 ) and the contract information CT using the hash function to generate H (PKp 1  (CK, S 4 ), CT). The encrypting portion  203  encrypts H (PKp 1  (CK, S 4 ), CT) using the management center secret key SKcnt to generate a signature S 5  (at step S 413 ).  
     [0183] Next, the encrypting portion  203  encrypts the encrypted content encryption key PKp 1  (CK, S 4 ), the contract information CT, and the signature S 5  using an IC card public key PKic to generate PKic (PKp 1  (CK, S 4 ), CT, S 5 ) (at step S 414 ) and transmits PKic (PKp 1  (CK, S 4 ), CT, S 5 ) as content key data against the content key download request to the server  162  through the communicating portion  207  and the network  164  (at step S 415 ).  
     [0184] When the controlling portion  301  of the server  162  receives the content key data PKic (PKp 1  (CK, S 4 ), CT, S 5 ) from the communicating portion  302 , the controlling portion  301  transmits the content key data PKic (PKp 1  (CK, S 4 ), CT, S 5 ) and a content key storage request to the IC card  167  through the IC card inputting-outputting portion  303  (at step S 416 ). When the controlling portion  401  of the IC card  167  receives the content key storage request and the content key data PKic (PKp 1  (CK, S 4 ), CT, S 5 ) from the inputting-outputting portion  402 , the decrypting portion  403  decrypts PKic (PKp 1  (CK, S 4 ), CT, S 5 ) using an IC card secret key SKic stored in the IC card secret key storing portion  408  to generate PKp 1  (CK, S 4 ), CT, and S 5  (at step S 417 ). Thereafter, the decrypting portion  403  decrypts the signature S 5  using a management center public key PKcnt stored in the management center public key storing portion  409  and generates PKcnt (S 5 ). The compressing portion  405  compresses PKp 1  (CK, S 4 ) and CT using the hash function to generate H (PKp 1  (CK, S 4 ), CT). The authenticating portion  407  collates PKcnt (S 5 ) with H (PKp 1  (CK, S 4 ), CT) (at step S 418 ).  
     [0185] When the determined result at step S 419  represents that PKcnt (S 5 ) does not match H (PKp 1  (CK, S 4 ), CT)), the controlling portion  401  of the IC card  167  determines that the data is invalid or has been falsified and transmits an error message to the server  162  through the inputting-outputting portion  402  (at step S 420 ). When the controlling portion  301  of the server  162  receives the error message from the IC card inputting-outputting portion  303 , the controlling portion  301  stops the downloading process for the content encryption key (at step S 426 ). When the determined result at step S 419  represents that PKcnt (S 5 ) matches H (PKp 1  (CK, S 4 ), CT), the controlling portion  401  of the IC card  167  determines that the issuer of the data is the management center  160  and that the data has not been falsified, sets the contract period T of the contract information CT to the timer  413  (at step S 421 ), and stores the encrypted content key PKp 1  (CK, S 4 ) to the content encryption key storing portion  412  (at step S 422 ).  
     [0186] Thereafter, the controlling portion  401  of the IC card  167  transmits a normal completion message against the content key storage request to the server  162  through the inputting-outputting portion  402  (at step S 423 ). When the controlling portion  301  of the server  162  receives the normal completion message from the IC card inputting-outputting portion  303 , the controlling portion  301  writes content data stored in the content storing portion  307  to the content record medium  166  (at step S 424 ). After the content data has been written to the content record medium  166 , the user takes the IC card  167  and the content record medium  166  to home (at step S 425 ).  
     [0187]FIG. 27 is a flow chart showing a content reproducing process of the reproducing device  170  shown in FIG. 18. First of all, the user connects the content record medium  166  and the IC card  167  to the reproducing device  170 . The reproducing device  170  and the IC card  167  perform the mutual authenticating operation corresponding to the above-described process (at step S 501 ). The controlling portion  501  of the reproducing device  170  transmits a content encryption key transmission request to the IC card  167  through the IC card inputting-outputting portion  502  corresponding to a content reproduction command that is input from the operation inputting portion  508  (at step S 503 ). When the controlling portion  401  of the IC card  167  receives the content encryption key transmission request from the inputting-outputting portion  402  (at step S 504 ), the controlling portion  401  determines whether or not the content encryption key storing portion  412  stores data (at step S 505 ).  
     [0188] When the determined result at step S 505  represents that data has been erased from the content encryption key storing portion  412 , the controlling portion  401  of the IC card  167  transmits a message representing that the content encryption key has been erased to the reproducing device  170  through the inputting-outputting portion  402  (at step S 506 ). When the controlling portion  501  of the reproducing device  170  receives the message, the controlling portion  501  determines that the content reproducing operation cannot be performed and completes the content reproducing operation (at step S 520 ). When the determined result at step S 505  represents that data has been stored in the content encryption key storing portion  412 , the controlling portion  401  of the IC card  167  reads the encrypted content encryption key PKp 1  (CK, S 4 ) and reads a timer value t from the timer  413  (at step S 508 ). The compressing portion  405  compresses the encrypted content encryption key PKp 1  (CK, S 4 ) and the timer value t using the hash function to generate H (PKp 1  (CK, S 4 ), t). The encrypting portion  404  encrypts H (PKp 1  (CK, S 4 ), t) using an IC card secret key SKic stored in the IC card secret key storing portion  408  and generates a signature S 6  (at step S 509 ).  
     [0189] Thereafter, the controlling portion  401  of the IC card  167  transmits the encrypted content encryption key PKp 1  (CK, S 4 ), the timer value t, and the signature S 6  to the reproducing device  170  through the inputting-outputting portion  402  (at step S 510 ). When the controlling portion  501  of the reproducing device  170  receives the encrypted content encryption key PKp 1  (CK, S 4 ), the timer value t, and the signature S 6  from the IC card inputting-outputting portion  303 , the decrypting portion  503  decrypts the signature S 6  using an IC card public key PKic to generate PKic (S 6 ). The compressing portion  505  compresses the content encryption key PKp 1  (CK, S 4 ) and the timer value t using the hash function to generate H (PKp 1  (CK, S 4 ), t). The authenticating portion  507  collates PKic (S 6 ) with H (PKp 1  (CK, S 4 ), t) (at step S 511 ). When the determined result at step S 512  represents that PKic (S 6 ) does not match H (PKp 1  (CK, S 4 ), t), the controlling portion  501  of the reproducing device  170  determines that the data is invalid data or has been falsified and that the reproducing operation cannot be performed and completes the reproducing process (at step S 520 ).  
     [0190] When the determined result at step S 512  represents that PKic (S 6 ) matches H (PKp 1  (CK, S 4 ), t), the controlling portion  501  of the reproducing device  170  sets the timer value t to the timer  513  (at step S 513 ). Thereafter, the controlling portion  501  of the reproducing device  170  causes the decrypting portion  503  to decrypt the encrypted content encryption key PKp 1  (CK, S 4 ) using a reproducing device secret key SKp 1  stored in the reproducing device secret key storing portion  510  to generate the content encryption key CK and the signature S 4  (at step S 514 ). Thereafter, the decrypting portion  503  decrypts the signature S 4  using a management center public key PKcnt stored in the management center public key storing portion  511  to generate PKcnt (S 4 ). The compressing portion  505  compresses the content encryption key CK using the hash function to generate H (CK). The authenticating portion  507  collates PKcnt (S 4 ) with H (CK) (at step S 515 ). When the determined result at step S 516  represents that PKcnt (S 4 ) does not match H (CK), the controlling portion  501  of the reproducing device  170  determines that the data is invalid data or has been falsified and that the data cannot be reproduced and completes the reproducing process (at step S 520 ).  
     [0191] When the determined result at step S 516  represents that PKcnt (S 4 ) matches H (CK), the controlling portion  501  of the reproducing device  170  stores the content encryption key CK to the content encryption key storing portion  514  (at step S 517 ). Thereafter, the controlling portion  501  of the reproducing device  170  reads content data from the content record medium  166  through the content record medium inputting-outputting portion  509 . The content key decrypting portion  515  decrypts the content data using a content encryption key CK stored in the content encryption key storing portion  514  (at step S 518 ) and reproduces the content (at step S 519 ).  
     [0192] Next, the advantage of the structure shown in FIG. 18 will be described.  
     [0193] (1) Since a public key certificate of a reproducing device is stored to an IC card, the reproducing device can be securely restricted.  
     [0194] (2) Before a content is rented, a public key certificate of a reproducing device is stored to an IC card. Thus, the reproducing device can be securely and flexibly changed. As a result, the content can be securely reproduced by the changed reproducing device.  
     [0195] (3) Only a content encryption key, reproduction variation time information, and a public key certificate that have been issued by a management center are valid. Thus, the data is uniformly assured. Thus, contents can be securely circulated.  
     [0196] (4) Since an IC card stores reproduction validation time information and has a function for decreasing the reproduction variation period on real time, the reproduction variation period can be prevented from being falsified.  
     [0197] (5) An IC card and a reproducing device have a function for erasing a content encryption key necessary for reproducing a content. When the reproduction validation period expired, the erasing function works. Thus, the tampering resistance improves.  
     [0198] &lt;Fourth Embodiment&gt; 
     [0199] Next, with reference to FIG. 28 to FIG. 31, a fourth embodiment of the present invention will be described. According to the fourth embodiment, an RHDD contains a reading/writing circuit and a controlling circuit as well as a record medium.  
     [0200]FIG. 28 is a block diagram showing the structure of a content rental system according to the fourth embodiment of the present invention. In FIG. 28, reference numeral  701  is a store server disposed in a rental store. Reference numeral  702  is a center server that integrally manages a plurality of store servers  701 . The center server  702  is connected to the store servers  701  through the Internet  703 . The center server  702  is disposed in a management center that integrally manages the rental stores. The management center corresponds to the video software duplicator shown in FIG. 3. Reference numeral  704  is an RHDD that each user has. A user takes the RHDD to a rental store. At the rental store, the RHDD is connected to the store server  701 . A content is downloaded from the store server  701  to the RHDD. The user returns to the house with the RHDD. The user sets the RHDD  704  to a reproducing device  705 . The reproducing device  705  reproduces the content.  
     [0201]FIG. 29 is a block diagram showing the structure of the store server  701 . In FIG. 29, reference numeral  711  is a CPU (Central Processing Unit). Reference numeral  712  is a memory. Reference numeral  713  is a bridge circuit that mutually connects the CPU  711 , the memory  712 , and a PCI (Peripheral Component Interconnect) bus  714 . Reference numeral  716  is a master magnetic disk device that stores contents and disk commands supplied from the center server  702  (see FIG. 28) through the Internet  703 . Reference numeral  717  is an IDE (Integrated Drive Electronics) interface that connects the master magnetic disk device  716  to the PCI bus  714 . Reference numeral  718  is a bridge circuit that connects the PCI bus  714  and a terminal  719  that is connected to the RHDD  704 .  
     [0202]FIG. 30 is a block diagram showing the structure of the RHDD  704 . In FIG. 30, reference numeral  721  is a CPU. Reference numeral  722  is a serial interface. Reference numeral  723  is a terminal that is connected to the terminal  719  of the store server  701  or a terminal  734  (see FIG. 31) of the reproducing device  705 . Reference numeral  724  is a magnetic disk device that stores contents and disk commands that are read from the store server  701 . Reference numeral  725  is an IDE interface. Reference numeral  726  is an I/F (Interface) switching buffer. Reference numeral  727  is a real time clock that is backed up by a battery  728 . Reference numeral  729  is an IC card.  
     [0203]FIG. 31 is a block diagram showing the structure of the reproducing device  705 . In FIG. 31, reference numeral  31  is a CPU. Reference numeral  732  is a non-volatile memory. Reference numeral  733  is a serial interface. Reference numeral  734  is a terminal that is connected to the terminal  723  of the RHDD  704 . Reference numeral  735  is an IDE interface. Reference numeral  736  is a decrypting circuit that decrypts an encrypted content and disk command supplied from the RHDD  704  connected to the terminal  734  through the terminal  734 . Reference numeral  705  is an I/O circuit that connects the decrypting circuit  736  and an MPEG decoder  738 . The MPEG decoder  738  decompresses compressed data to original data corresponding to the MPEG standard. A graphic controlling circuit  739  displays a picture on a displaying device  740  corresponding to data that is output from the MPEG decoder  738 .  
     [0204] Next, the operation of the fourth embodiment will be described.  
     [0205] The center server  702  (see FIG. 28) delivers a content and a disk command to a store server  701  through the Internet  703 . In addition, the center server  702  delivers data that represents the permitted number of times of the downloading operation for the content to the store server  701 . The delivered content is pre-encrypted and pre-compressed corresponding to the MPEG standard by the center server  702 . The delivered content, disk command, and data representing the permitted number of times of the downloading operation are stored to the master magnetic disk device  716  through the PCI bus  714  and the IDE interface  717  of the store server  701  (see FIG. 29).  
     [0206] On the other hand, the user buys a set of an RHDD  704  and a reproducing device  705 . When the user buys them, attribute information (name, authorized number, charge information, address, telephone, and so forth) of the user (buyer) is stored to the IC card of the RHDD  704 . When the RHDD does not have the IC card, the attribute information is stored to the magnetic disk device  724 . In addition, the IC card stores the identification number of the reproducing device  705 . The memory  732  of the reproducing device  705  also stores the same identification number of the reproducing device  705 . The user takes the RHDD  704  to the rental store. The user sets the RHDD  704  to the store server  701  corresponding to an instruction of a store clerk.  
     [0207] When the RHDD  704  is set to the store server  701 , the CPU  721  of the RHDD  704  reads the user attribute information from the IC card  729  and outputs the user attribute information to the store server  701 . The attribute information is stored to the memory  712  through the bridge circuit  718 , the PCI bus  714 , and the bridge circuit  713 . The CPU  711  transmits the attribute information to the center server  702  through the Internet  703 . The center server  702  determines both (1) the availability that contents can be rented to the user and (2) the rental fee on the basis of the received attribute information, and transmits the results to the store server  701 .  
     [0208] Thereafter, when the results received from the center server  702  represent that contents can be rented to the user, the CPU  711  of the store server  701  causes a display screen (not shown) to display a list of contents stored in the master magnetic disk device  716 . When the user selects a content that he or she wants to download from the list, the selected content is read from the master magnetic disk device  716  and written to the magnetic disk device  724  of the RHDD  704 . Thereafter, the CPU  711  reads a decryption key from the memory  712  and outputs the decryption key to the RHDD  704 . In addition, the CPU  711  calculates the reproduction validation time and outputs the calculated result to the RHDD  704 . The decryption key is written to the IC card  729 . The data representing the reproduction validation time is written to the magnetic disk device  724 .  
     [0209] Thereafter, the CPU  711  increases the download times count area of the memory  712  by “1”. The value of the count area represents the number of times of the downloading operation for the content. Thereafter, the CPU  711  compares the value of the count area with the data representing the permitted number of times of the downloading operation stored in the master magnetic disk device  716 . When the value of the count area matches the permitted number of times of the downloading operation, the CPU  711  prohibits the downloading operation and transmits a message representing the prohibition of the downloading operation to the center server  702 .  
     [0210] When the content has been downloaded from the store server  701  to the RHDD  704 , the user returns home with the RHDD  704 . The user sets the RHDD  704  to the reproducing device  705  and presses the reproduction start button (not shown). When the user presses the reproduction start button, the CPU  721  of the RHDD  704  reads the identification number of the IC card  729  and outputs the identification number to the reproducing device  705 . The identification number is supplied to the CPU  731  through the serial interface  733 . The CPU  731  compares the supplied identification number with the identification number stored in the memory  732 . When those identification numbers match, the CPU  731  moves on to the content reproducing process. When they do not match, the CPU  731  issues an alarm and does not perform the content reproducing process.  
     [0211] After the CPU  721  of the RHDD  704  outputs the identification number, the CPU  721  reads data that represents the reproduction validation time from the magnetic disk device  724  and compares the reproduction validation time with the current time that is output from the real time clock  727 . When the current time exceeds the reproduction validation time, the CPU  721  issues an alarm and stops the process. When the current time does not exceed the reproduction validation time, the CPU  721  reads a decryption key from the IC card  729  and outputs the decryption key to the reproducing device  705 . The decryption key is supplied to the decrypting circuit  736  through the IDE interface  735 .  
     [0212] Thereafter, the content is successively read from the magnetic disk device  724  of the RHDD  704  and output to the reproducing device  705 . The decrypting circuit  736  of the reproducing device  705  decrypts the content using the decryption key and inputs the decrypted content to the MPEG decoder  738  through the I/O circuit  737 . The MPEG decoder  738  decompresses the content. The displaying device  740  displays the decompressed content through the graphic controlling circuit  739 .  
     [0213] According to the fourth embodiment, when a content stored in the RHDD is reproduced by a reproducing device having a different identification number, the different identification number may be stored to the magnetic disk device of the RHDD. When the user sets the RHDD to the store server, it detects the different identification number of the reproducing device and prohibits a content from being downloaded to the RHDD.  
     [0214] In addition, when the reproduction validation time expired, the CPU  721  of the RHDD  704  may erase the decryption key stored in the IC card  729 . Alternatively, the reproducing device  705  may have a real time clock. In this case, the RHDD  704  outputs data that represents the reproduction validation time. The reproducing device  705  determines whether or not the current time exceeds the reproduction validation time.  
     [0215] When a content is downloaded to the RHDD  704  of the user, data that represents the permitted number of times of the reproducing operation is stored to the magnetic disk device  724 . When the number of times of the reproducing operation exceeds the permitted number of times of the reproducing operation, the reproducing operation may be prohibited. The number of times of the reproducing operation can be determined in various manners. For example, a reproduction marker may be placed at a particular position in the range from the middle to the end of a content. Whenever the reproduction marker is detected, the reproducing operation is counted. The reproduction marker may be placed at any position of a content. For example, reproduction markers may be placed at the beginning and the end of a content. Only when both the reproduction markers are detected, the reproducing operation may be counted. Alternatively, the reproduction marker may be placed at the beginning of a content. Whenever the beginning of a content is detected, the reproducing operation may be counted.  
     [0216] According to the present invention (claim  1 ), the following effects can be obtained.  
     [0217] (1) The antinomy between improper stock and loss of business chance of video rental stores can be solved.  
     [0218] (2) Since part of rental fees collected from customers through the circulation system flows back to a video source production company, it can have higher sales than before.  
     [0219] (3) Rental video tapes at low prices can be prevented from flowing out to the sell video market.  
     [0220] According to the present invention (claim  2 ), new commercial information can be always placed in rental record mediums. Thus, customers can always view new commercials. In comparison with conventional commercials, high commercial effects can be expected. In addition, those commercials become new incomes. Thus, video software title companies and rental stores can be well managed. In addition, the customers can enjoy advantageous advertisements.  
     [0221] According to the present invention (claim  4  to claim  8 ), when a predetermined period elapsed, information necessary for reproducing a content is erased. Thus, the content cannot be reproduced. Thus, when the present invention is applied to a rental system, customers do not need to return content mediums to stores. When a timer is disposed, the period for which information necessary for reproducing a content is erased can be accurately set.  
     [0222] According to the present invention (claim  9  to claim  19 ), digital video information can be prevented from illegally copied and circulated. In addition, the video market can be prevented from getting confused.  
     [0223] Although the present invention has been shown and described with respect to the best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the present invention.