Patent Publication Number: US-2011072269-A1

Title: Network av contents playback system, server, program and recording medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national phase application of PCT International Patent Application No. PCT/JP2008/002081 filed Aug. 1, 2008, claiming the benefit of priority of Japanese Patent Application No. 2007-205913 filed Aug. 7, 2007, all of which are incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a system or the like that distributes contents by using a network and plays back the contents. 
     BACKGROUND ART 
     With the development of the Internet, technologies for downloading and playing back contents such as movies and music are becoming commonplace. More specifically, many services are provided that allow contents to be downloaded from servers that distributes contents such as movies and music to PCs, audio-video (AV) equipment, mobile phones, and portable devices through a network. 
     By applying the Digital Rights Management (DRM) technology for the purpose of the copyright protection to such services, contents rental systems that permit users to view and listen to contents limited only on a purchased terminal, have been implemented. 
       FIG. 12  illustrates a configuration of such a system according to a first example of the conventional art. A terminal  201  and a server  202  are interconnected through a network  222 . The terminal  201  is connected onto the network  222  typically by using a router  221  that relays IP communications. It is assumed that multiple terminals having a configuration similar to that of the terminal  201  are also connected onto the network  222 . 
     The terminal  201  comprises a network IF  204 , a contents acquiring section  213 , a storage section  214 , a decryption section  219 , a decoding section  209 , a HTML browser  205 , a control information acquiring section  206 , a control information storage section  216 , a license acquiring section  217  and a license storage section  218 . The decoding section  209  has a function of providing a decoded output  210 , which is corresponding to an output for an AV terminal of HDMI, for example. 
     The server  202  comprises a contents distributing section  225 , a storage device  226 , a HTML server  227 , a control information recording section  228 , an authorization recording section  230 , a license distributing section  229 , a router  223  and a LAN  224 . 
     The contents distributing section  225 , the HTML server  227 , the license distributing section  229  and other sections are a group of servers each of which has a CPU and operates independently and are interconnected by the LAN  224  installed in the server site to cooperate with each other to provide an integrated download server functionality as a whole. 
     The contents distributing section  225  is provided with the storage device  226  and allows the terminal  201  to download an AV contents file stored in the storage device  226  through the network  222 . The AV contents file referred to herein means real-time data containing video, audio and the like. For example, the AV contents file may be a MPEG2 file or a MP3 file. 
     An exemplary operation sequence according to the first example of the conventional art is shown in  FIG. 13 . Operation of the first example of the conventional art will be described with respect to  FIG. 13 . The terminal  201  and the server  202  are interconnected through the Internet and can communicate with each other. 
     In this configuration, a user operates the terminal  201  (contents purchase and download instruction  301 ) to access the server  202  by using the HTML browser  205  and can send a contents purchase and download instruction  302 . Upon receipt of the contents purchase and download instruction  302 , the server  202  generates a term t 1  to t 2  during which the user is permitted to rent the contents and stores the term t 1  to t 2  with an ID of the terminal  201  in the authorization recording section  230  of the server  202  at step  303 . The stored ID is used to record which terminal purchased the contents. 
     The server  202  then distributes download (DL) control information to the terminal  201  through the HTML server  227  as a response to the contents purchase and download instruction  302  at step  304 . Here, the DL control information is information used for acquiring contents and a license for the contents and includes the URL of the contents stored in the control information recording section  228  and the ID of the license stored in the authorization recording section  230 . 
     The terminal  201  having received the DL control information extracts the DL control information in the HTML by the control information acquiring section  206  and stores the DL control information in the control information storage section  216  at step  305 . The terminal  201  then downloads the contents according to the DL control information stored in the control information storage section  216  at step  306 . 
     For example, the download is performed as follows. That is, the contents acquiring section  213  issues a GET method of HTTP to the URL of the contents which the user hopes to purchase, based on the control information stored in the control information storage section  216 . The download is performed according to the GET method. The download is completed by acquiring and storing all of the contents in the storage section  214  of the terminal  201 . 
     Once the download is completed, in a license acquisition request  307 , the terminal  201  issues a license acquisition request to the server  202  by the license acquiring section  217  based on the DL control information stored in the control information storage section  216 . The license acquisition request  307  includes a license ID used for specifying a license to be acquired and a terminal ID of the terminal  201  used for specifying a terminal which requests the license. 
     The server  202  having received the license acquisition request  307  checks whether the specified license has been purchased in the name of the specified terminal ID or not by verifying the license acquisition request  307  by searching the authorization recording section  230 . When the specified license is purchased, the server  202  transmits a license acquisition response  308  by the license distributing section  229  as a response to the license acquisition request  307  and distributes the license. The license referred to herein is information for limiting the playback expiration period of the contents. For example, the license includes an encryption key for decrypting the encrypted contents and the available period of the encryption key. Because the server  202  generated the term t 1  to t 2  during which the user is permitted to rent the contents, the server  202  distributes the term t 1  to t 2  as a playback expiration period information. 
     The storage  201  having received the license stores the license in the license storage section  218  at step  309 . If the specified license is not purchased when the server  202  searches the authorization recording section  230 , the server  202  doesn&#39;t transmit the license acquisition response  308  and doesn&#39;t distribute the license. 
     By the sequence described above, download of the contents and acquisition of the relevant license are completed. 
     Then, the user operates the terminal  201  to instruct the terminal  201  to play back the downloaded contents at step  310 . The terminal  201  retrieves the license stored in the license storage section  218  at step  311 , compares the playback period information t 1  to t 2  in the license with the current time at step  312  and, if the current time is within the expiration time, starts decrypting of the encrypted contents using the encryption key in the license by the decryption section  219  at step  313 . As a result of the sequence described above, contents playback  314  of the contents can be performed. 
     If the user instructs to play back the contents at step  315  of the timing after the rental period t 1  to t 2  is expired, comparison at step  317  between the playback period information t 1  to t 2  in the license retrieved at step  316  and the current time will show the expiration of the rental period. Accordingly, a message will be displayed that notifies the user of the expiration at step  318 , without playing back the contents. 
     With the sequence described above, a contents rental system that permits viewing and listening to contents for a limited time only on a purchased terminal has been provided. 
     The terminal ID referred to herein is an ID for uniquely identifying a terminal for permitting users only limited use on a purchased terminal. The terminal ID is provided (e.g., built-in) in the storage section  214  before shipping, and spoofing of the terminal ID is prevented by issuing, for example a certificate of the ID. (The method of granting an authorization limited specified device in the above description, is referred to as the authorization granting method for device binding in the following, for distinguishing it from a method of granting an authorization to a limited specified user or media. 
     However, the first example of the conventional art has a first problem that a terminal without the storage section  214  can not perform downloading. For example, even if a network TV set has a HTML browser, can not download if the TV has no storage device. 
     To deal with the first problem, the TV can have a hard disk drive (abbreviated as HDD, hereinafter) built-in as a storage device. However, there is a second problem in this method. The second problem is that a cost for parts increases and a cost for repairs is needed for the HDD having short life because of having mechanical parts. 
     As another method to deal with the first problem, a general-purpose AV recorder is connected via a peripheral interface to the TV and is handled as equivalent to the HDD built-in the TV. The peripheral interface is USB, IEEE1394, Serial-ATA or the like. By this method, the second problem can be solved because a commercial existing recorder can be available by attaching externally. 
     By the way, if contents stored in a recorder can be played back by the recorder freely or the contents can be copied to a media or another recorder, the viewing and listening expiration date permitted for the TV by the server side, can not be secured properly. Then, when using this method, viewing and listening contents in the recorder is limited only for the relevant TV. (That is, the authorization for viewing and listening is granted for the given TV). 
     More specifically, playback by a TV other than the relevant TV is blocked in such manner that a license storage section and a decryption section are provided in the TV side and the contents are stored in the recorder with encrypted condition. 
     As a result, by this method, the contents downloaded can not be played back when an operation UI of the recorder side is made without operating an operation UI of the TV side. Furthermore, deleting the contents is difficult without cooperation with the TV side. In this way, there is a third problem that the operation is hard to use. 
     Another method to solve the third problem can be practical, that is, the contents purchased by the TV side can be played back at both the TV side and the recorder side by using DRM technology of the domain management type. The DRM technology of the domain management type is a technology that can grant an authorization enabled to play back same contents for plural devices. Examples of such DRM technology of the domain management type are disclosed at Japanese Patent Laid-Open No. 2005-196663 and Japanese Patent Laid-Open No. 2007-520011. 
     In the method of Japanese Patent Laid-Open No. 2005-196663, a domain attribute information is granted to the contents and only a terminal which is given with an attribute information same as the domain information of the contents, is permitted to play back the contents. When the domain attribute information is granted to both the TV and the recorder in this method, same contents can be played back by the operation UI of the TV and the operation UI of the recorder. 
     In the method of Japanese Patent Laid-Open No. 2007-520011, a home server has a master function which can grant an authorization enabled to play back for other devices and is installed in a home, and the home server grants the authorization enabled to play back for a playback device having slave function. When the master function is equipped with the TV and the slave function is equipped with the recorder in this method, same contents can be played back by the operation UI of the TV and the operation UI of the recorder. Then, the third problem may be solved by this method. 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, about each method of Japanese Patent Laid-Open No. 2005-196663 and Japanese Patent Laid-Open No. 2007-520011, there is a problem that each of the TV and the recorder has to have the DRM function. For equipping the DRM function, a standard for maintaining a constant security has to be satisfied. Furthermore, a terminal ID or a certificate for the DRM authentication has to be equipped. There is a fourth problem that the cost increases for providing these functions to all of the TV and the recorders. 
     In view of the problems from the first to the fourth of the conventional methods described above, it is an object of the present disclosure to provide a contents playback system or the like where the user can view and listen to the contents downloaded to the audio-visual terminal having no storage device, the storage terminal which is not an incorporate type (built-in type), can be used as the download destination device, the playing back of the contents can be performed by the operation UI of the audio-visual terminal and by the operation UI of the storage terminal, and the downloaded contents can be viewed and listened to without providing DRM function for all terminals. 
     Means for Solving the Problems 
     The 1 st  aspect of the present invention is a network AV contents playback system, comprising: 
     an audio-visual terminal; and 
     a storage terminal, 
     wherein said audio-visual terminal: 
     establishes a first connection protected by authentication and encryption, to one or more servers providing AV contents on a network, 
     acquires an authorization to use said AV contents by said first connection, concurrently acquires download control information including AV contents location information that indicates a location of said AV contents on said network and license information about said AV contents, and 
     transmits said acquired download control information to said storage terminal, and 
     said storage terminal: 
     acquires said download control information from said audio-visual terminal, downloads said AV contents from said server based on said AV contents location information via said network and stores said AV contents, 
     acquires a license of said AV contents from said server based on said license information and stores the license, and 
     uses said AV contents for a predetermined period based on said stored license. 
     The 2 nd  aspect of the present invention is the network AV contents playback system according to the 1 st  aspect of the present invention, wherein when said audio-visual terminal acquires an authorization to use, said audio-visual terminal acquires the authorization by specifying a purchase account and, as a result, acquires said download control information including at least the license information that permits decryption by said storage terminal, and 
     said license information includes a license ID that identifies the authorization to use in said server. 
     The 3 rd  aspect of the present invention is the network AV contents playback system according to the 2 nd  aspect of the present invention, wherein said storage terminal: 
     establishes a second connection protected by authentication and encryption, to said server, 
     by using said second connection, transmits a license acquisition request including the license ID of said AV contents and an ID of said storage terminal, to said server, 
     acquires the license of said AV contents from said server as a response to said license acquisition request and stores the license, and 
     decrypts said AV contents in said storage terminal by using an AV contents encryption key included in said license. 
     The 4 th  aspect of the present invention is the network AV contents playback system according to the 3 rd  aspect of the present invention, wherein said storage terminal: 
     establishes a third connection protected by authentication and encryption, and 
     transmits said decrypted AV contents via said third connection, and 
     said audio-visual terminal displays said AV contents received from said storage terminal via said third connection. 
     The 5 th  aspect of the present invention is the network AV contents playback system according to the 4 th  aspect of the present invention, wherein transmission of said download control information or said AV contents between said audio-visual terminal and said storage terminal is performed via a LAN or HDMI connection provided between said storage terminal and said audio-visual terminal. 
     The 6 th  aspect of the present invention is the network AV contents playback system according to the 3 rd  aspect of the present invention, wherein in a case where said storage terminal receives a request for playback of said AV contents from said audio-visual terminal, said storage terminal establishes a third connection protected by authentication and encryption, to said audio-visual terminal and transmits said decrypted AV contents via said third connection, and 
     said audio-visual terminal displays said AV contents received from said storage terminal via said third connection, and 
     in a case where said storage terminal receives a request for output of said AV contents from a user interface provided in said storage terminal itself, said storage terminal outputs said decrypted AV contents to an output destination specified by said user interface. 
     The 7 th  aspect of the present invention is the network AV contents playback system according to the 3rd aspect of the present invention, wherein said audio-visual terminal: 
     has a browser, 
     establishes said first connection protected by authentication and encryption, to said server on said network by an SSL connection of the browser, 
     acquires the authorization to use of said AV contents via said first connection, concurrently acquires the download control information including the AV contents location information that indicates the location of said AV contents on said network and the license information about said AV contents, and 
     transmits said acquired download control information to said storage terminal by a communication module activated via said browser. 
     The 8 th  aspect of the present invention is the network AV contents playback system according to the 3 rd  aspect of the present invention, wherein in a case where it is confirmed that said audio-visual terminal is LAN-connected to said storage terminal, said storage terminal acquires and uses said download control information, and in a case where said audio-visual terminal is not LAN-connected to said storage terminal, said storage terminal does not acquire said download control information. 
     The 9 th  aspect of the present invention is the network AV contents playback system according to the 3 rd  aspect of the present invention, wherein said storage terminal performs authentication for said audio-visual terminal and acquires and uses said download control information in a case where said audio-visual terminal is previously registered in a reliable connection target, but does not acquire said download control information in a case where said audio-visual terminal is not previously registered in a reliable connection target. 
     The 10 th  aspect of the present invention is the network AV contents playback system according to the 3 rd  aspect of the present invention, wherein said storage terminal acquires and uses said download control information in a case where it is confirmed that a certificate granted to said download control information is legitimate, but does not acquire said download control information in a case where it is not confirmed that the certificate is legitimate. 
     The 11 th  aspect of the present invention is the network AV contents playback system according to the 3 rd  aspect of the present invention, wherein said download control information is encrypted by inter-device authentication between said storage terminal and said audio-visual terminal. 
     The 12 th  aspect of the present invention is the network AV contents playback system according to the 1 st  aspect of the present invention, wherein said storage terminal is capable of outputting said AV contents to a medium based on said stored license. 
     The 13 th  aspect of the present invention is a server that communicates with an audio-visual terminal and a storage terminal via a network, 
     wherein said servers: 
     retains an account and a terminal ID associated with said account, 
     establishes a first connection protected by authentication and encryption, to said audio-visual terminal, 
     grants an authorization to use of an AV contents, to said account via said first connection, concurrently transmits download control information including AV contents location information that indicates the location of said AV contents on said network and license information including a license ID that identifies the authorization to use of said AV contents on said server, to said audio-visual terminal, and 
     establishes a second connection protected by authentication and encryption to said storage terminal, and 
     when the server receives a license acquisition request from said storage terminal via said second connection, the server compares a license ID of an AV contents included in said license acquisition request with the license ID of the AV contents whose authorization to use is granted to said account to check whether the license IDs agree with each other, further compares a terminal ID included in said license acquisition request with the terminal ID associated with said account to check whether the terminal IDs agree with each other, and distributes a license to said storage terminal in a case where both agree with each other. 
     The 14 th  aspect of the present invention is a network AV contents playback system, comprising: 
     an audio-visual terminal; 
     a storage terminal; and 
     one or more servers, 
     wherein 
     said servers retain an account and a terminal ID associated with said account, 
     said audio-visual terminal 
     establishes a first connection protected by authentication and encryption, to a server, 
     uses said first connection to acquire an authorization to use of AV contents granted to said account, 
     concurrently acquires download control information including AV contents location information that indicates the location of said AV contents on a network and license information including a license ID that identifies the authorization to use of said AV contents on said server, and 
     transmits said acquired download control information to said storage terminal, 
     said storage terminal 
     acquires said download control information from said audio-visual terminal, 
     establishes a second connection protected by authentication and encryption, to said server, and 
     uses said second connection to transmit a license acquisition request to said server, the license acquisition request including at least the license ID of said AV contents included in said license information and a terminal ID of said storage terminal, 
     said server: 
     compares the license ID of the AV contents included in said license acquisition request with the license ID of the AV contents whose authorization to use is granted to said account to check whether the license IDs agree with each other, further compares the terminal ID of said storage terminal included in said license acquisition request with the terminal ID associated with said account to check whether the terminal IDs agree with each other, and distributes a license to said storage terminal in a case where both agree with each other, and 
     said storage terminal: 
     acquires said license from said server, stores said license and decrypts said AV contents using an AV contents encryption key included in said license. 
     The 15 th  aspect of the present invention is a network AV contents playback system, comprising: 
     an instruction terminal; 
     a storage terminal; and 
     one or more servers, 
     wherein 
     said servers retain an account and a terminal ID associated with said account, 
     said instruction terminal establishes a first connection protected by authentication and encryption, to a server and uses said first connection to acquire an authorization to use of AV contents granted to said account, 
     said storage terminal regularly establishes a fourth connection protected by authentication and encryption, to said server to request distribution of download control information, 
     said server distributes download control information including AV contents location information that indicates the location of said AV contents on a network and license information including a license ID that identifies the authorization to use of said AV contents on said server, to the storage terminal corresponding to the terminal ID associated with said account via said fourth connection in response to the request for distribution of said download control information, 
     said storage terminal downloads said AV contents from said server based on said AV contents location information in said download control information, and stores said AV contents, 
     said storage terminal establishes a second connection protected by authentication and encryption, to said server and uses said second connection to transmit a license acquisition request to said server, the license acquisition request including at least the license ID of said AV contents included in said license information and a terminal ID of said storage terminal, 
     said server compares the license ID of the AV contents included in said license acquisition request with the license ID of the AV contents whose authorization to use is granted to said account to check whether the license IDs agree with each other, further compares the terminal ID of said storage terminal included in said license acquisition request with the terminal ID associated with said account to check whether the terminal IDs agree with each other, and distributes a license to said storage terminal in a case where both agree with each other, and 
     said storage terminal acquires said license from said server, stores said license and decrypts said AV contents using an AV contents encryption key included in said license. 
     The 16 th  aspect of the present invention is a network AV contents playback system, comprising: 
     an instruction terminal; 
     a storage terminal; and 
     one or more servers, 
     wherein 
     said servers retain an account and a terminal ID associated with said account, 
     said instruction terminal establishes a first connection protected by authentication and encryption, to a server and uses said first connection to acquire an authorization to use of an AV contents granted to said account, 
     said server, after said instruction terminal acquires the authorization to use of said AV contents, calls the storage terminal corresponding to the terminal ID associated with said account, to establish a fourth connection and distributes, to said storage terminal, download control information including AV contents location information that indicates the location of said AV contents on a network and license information including a license ID that identifies the authorization of said AV contents on said server, 
     said storage terminal downloads said AV contents from said server based on said AV contents location information in said download control information, and stores said AV contents, 
     said storage terminal establishes a second connection protected by authentication and encryption, to said server and uses said second connection to transmit a license acquisition request to said server, the license acquisition request including at least the license ID of said AV contents included in said license information and a terminal ID of said storage terminal, 
     said server compares the license ID of the AV contents included in said license acquisition request with the license ID of the AV contents whose authorization to use is granted to said account to check whether the license IDs agree with each other, further compares the terminal ID of said storage terminal included in said license acquisition request with the terminal ID associated with said account to check whether the terminal IDs agree with each other, and distributes a license to said storage terminal in a case where both agree with each other, and 
     said storage terminal acquires said license from said server, stores said license and decrypts said AV contents using an AV contents encryption key included in said license. 
     The 17 th  aspect of the present invention is the network AV contents playback system according to the 16 th  aspect of the present invention, wherein: 
     said server requests a download progress list from said storage terminal after said instruction terminal acquires the authorization to use of said AV contents, 
     said storage terminal transmits said download progress list to said server via said network, 
     said server acquires the download progress list from said storage terminal and transfers the download progress list to said instruction terminal, 
     said instruction terminal externally displays the download progress list, and 
     said server distributes said download control information to said storage terminal in response to receiving a download instruction from said instruction terminal. 
     The 18 th  aspect of the present invention is the network AV contents playback system according to the 15 th  aspect of the present invention, wherein: 
     said instruction terminal is a terminal that serves also as an audio-visual terminal having an audio-visual function or a terminal separate from an audio-visual terminal having an audio-visual function. 
     The 19 th  aspect of the present invention is the network AV contents playback system according to the 16 th  aspect of the present invention, wherein: 
     said instruction terminal is a terminal that serves also as an audio-visual terminal having an audio-visual function or a terminal separate from an audio-visual terminal having an audio-visual function. 
     The 20 th  aspect of the present invention is a program product that makes a computer operate as the audio-visual terminal and the storage terminal in the network AV contents playback system according to the 1 st  aspect of the present invention, 
     in which said audio-visual terminal establishes a first connection protected by authentication and encryption, to one or more servers providing AV contents on a network, uses said first connection to acquire an authorization to use of said AV contents, concurrently acquires download control information including AV contents location information that indicates the location of said AV contents on said network and license information about said AV contents and transmits said acquired download control information to said storage terminal, and 
     said storage terminal acquires said download control information from said audio-visual terminal, downloads said AV contents from said servers via said network based on said AV contents location information, stores said AV contents, acquires a license of said AV contents from said servers based on said license information, stores the license and uses said AV contents for a predetermined period based on said stored license. 
     The 21 st  aspect of the present invention is a program product that makes a computer operate as the instruction terminal, the storage terminal and the server in the network AV contents playback system according to the 15 th  aspect of the present invention, 
     in which said instruction terminal establishes a first connection protected by authentication and encryption, to said server and uses said first connection to acquire an authorization to use of an AV contents granted to said account, 
     said storage terminal regularly establishes a fourth connection protected by authentication and encryption, to said server to request distribution of said download control information, downloads said AV contents from said server based on said AV contents location information in said download control information, stores said AV contents, establishes a second connection protected by authentication and encryption, to said server, uses said second connection to transmit a license acquisition request to said server, the license acquisition request including at least the license ID of said AV contents included in said license information and a terminal ID of said storage terminal, acquires said license from said server, stores said license, and decrypts said AV contents using an AV contents encryption key included in said license, and 
     said server retains said account and the terminal ID associated with said account, distributes download control information including AV contents location information that indicates the location of said AV contents on the network and license information including a license ID that identifies the authorization of said AV contents on said server, to the storage terminal corresponding to the terminal ID associated with said account via said fourth connection in response to the request for distribution of said download control information, compares the license ID of the AV contents included in said license acquisition request with the license ID of the AV contents whose authorization to use is granted to said account to check whether the license IDs agree with each other, further compares the terminal ID of said storage terminal included in said license acquisition request with the terminal ID associated with said account to check whether the terminal IDs agree with each other, and distributes a license to said storage terminal in a case where both the license IDs and the terminal IDs agree with each other. 
     The 22 nd  aspect of the present invention is a program product that makes a computer operate as the instruction terminal, the server and the storage terminal in the network AV contents playback system according to the 16 th  aspect of the present invention, 
     in which said instruction terminal establishes a first connection protected by authentication and encryption, to said server and uses said first connection to acquire an authorization to use of an AV contents granted to said account, 
     said server retains said account and the terminal ID associated with said account, calls, after said instruction terminal acquires the authorization of said AV contents, the storage terminal corresponding to the terminal ID associated with said account to establish a fourth connection, distributes download control information including AV contents location information that indicates the location of said AV contents on a network and license information including a license ID that identifies the authorization of said AV contents on said server to said storage terminal, compares the license ID of the AV contents included in said license acquisition request with the license ID of the AV contents whose authorization to use is granted to said account to check whether the license IDs agree with each other, further compares the terminal ID of said storage terminal included in said license acquisition request with the terminal ID associated with said account to check whether the terminal IDs agree with each other, and distributes a license to said storage terminal in a case where both the license IDs and the terminal IDs agree with each other, and 
     said storage terminal downloads said AV contents from said server based on said AV contents location information in said download control information, stores said AV contents, establishes a second connection protected by authentication and encryption, to said server, uses said second connection to transmit a license acquisition request to said server, the license acquisition request including at least the license ID of said AV contents included in said license information and the terminal ID of said storage terminal, acquires said license from said server, stores said license and decrypts said AV contents using an AV contents encryption key included in said license. 
     The 23 rd  aspect of the present invention is a recording medium capable of being accessed by a computer, in which the program according to the 20 th  aspect of the present inventions is recorded. 
     The 24 th  aspect of the present invention is a recording medium accessible by a computer, in which the program according to the 21st aspect of the present invention is recorded. 
     The 25 th  aspect of the present invention is a recording medium accessible by a computer, in which the program according to the 22 nd  aspect of the present invention is recorded. 
     ADVANTAGES OF THE INVENTION 
     Advantages of the present invention include, but are not limited to, that the user can view and listen to the contents downloaded to the audio-visual terminal having no storage device, the storage terminal which is not incorporate type, can be used as the download destination device, the playing back of the contents can be performed by the operation UI of the audio-visual terminal and by the operation UI of the storage terminal, and the downloaded contents can be viewed and listened to without providing DRM function for all terminals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary configuration of a system according to a first embodiment of the present invention. 
         FIG. 2  illustrates an exemplary communication sequence between a terminal and a server according to a first embodiment of the present invention. 
         FIG. 3  illustrates an example of a table of authorization recording data according to a first embodiment of the present invention. 
         FIG. 4  illustrates an exemplary configuration of a system according to a second embodiment of the present invention. 
         FIG. 5  illustrates an exemplary communication sequence between a terminal and a server according to a second embodiment of the present invention. 
         FIG. 6  illustrates an exemplary configuration of a system according to a third embodiment of the present invention. 
         FIG. 7  illustrates an exemplary communication sequence between a terminal and a server according to a third embodiment of the present invention. 
         FIG. 8  illustrates an exemplary configuration of a system according to a fourth embodiment of the present invention. 
         FIG. 9  illustrates an exemplary communication sequence between a terminal and a server according to a fourth embodiment of the present invention. 
         FIG. 10  illustrates a part of a communication sequence between a terminal and a server according to a fourth embodiment of the present invention. 
         FIG. 11  illustrates an exemplary configuration of a system according to a fifth embodiment of the present invention. 
         FIG. 12  illustrates a configuration of a system in a example of the conventional art. 
         FIG. 13  illustrates a communication sequence between a terminal and a server in a example of the conventional art. 
     
    
    
     DESCRIPTION OF SYMBOLS 
     
         
           101  . . . Audio-visual terminal 
           102  . . . Server 
           103  . . . Storage terminal 
           104  . . . Network IF 
           105  . . . HTML browser 
           106  . . . Control information acquiring section 
           107  . . . Control information transferring section 
           108  . . . LAN transmission decryption section 
           109  . . . Decoding section 
           110  . . . Decoded output 
           111  . . . LAN 
           112  . . . Network IF 
           113  . . . Contents acquiring section 
           114  . . . Storage section 
           115  . . . Control information acquiring section 
           116  . . . Control information storage section 
           117  . . . License acquiring section 
           118  . . . License storage section 
           119  . . . Decryption section 
           120  . . . LAN transmission encryption section 
           121  . . . Router 
           122  . . . Network 
           123  . . . Router 
           124  . . . LAN 
           125  . . . Contents distributing section 
           126  . . . Storage device 
           127  . . . HTML server 
           128  . . . Control information recording section 
           129  . . . License distributing section 
           130  . . . Authorization recording section 
           201  . . . Audio-visual terminal 
           202  . . . Server 
           204  . . . Network IF 
           205  . . . HTML browser 
           206  . . . Control information acquiring section 
           209  . . . Decoding section 
           210  . . . Decoded output 
           211  . . . LAN 
           213  . . . Contents acquiring section 
           214  . . . Storage section 
           216  . . . Control information storage section 
           217  . . . License acquiring section 
           218  . . . License storage section 
           219  . . . Decryption section 
           221  . . . Router 
           222  . . . Network 
           223  . . . Router 
           224  . . . LAN 
           225  . . . Contents distributing section 
           226  . . . Storage device 
           227  . . . HTML server 
           228  . . . Control information recording section 
           229  . . . License distributing section 
           230  . . . Authorization recording section 
           301  . . . Contents purchase and download instruction 
           302  . . . Contents purchase and download instruction 
           303  . . . License expiration time generating step 
           304  . . . DL control information distribution 
           305  . . . DL control information storing step 
           306  . . . Download of contents 
           307  . . . License acquisition request 
           308  . . . License acquisition response 
           309  . . . License storing step 
           310  . . . Contents playback instruction 
           311  . . . License retrieving step 
           312  . . . License expiration time checking step 
           313  . . . Contents decryption starting step 
           314  . . . Contents playback 
           315  . . . Contents playback instruction 
           316  . . . License retrieving step 
           317  . . . License expiration time checking step 
           318  . . . License expiration display 
           401  . . . Registration sequence 
           402  . . . Download sequence 
           403  . . . Reproduction sequence 
           404  . . . Account login instruction 
           405  . . . Account login 
           406  . . . Terminal ID registration instruction 
           407  . . . Terminal ID registration 
           408  . . . Terminal ID storing 
           409  . . . Account login instruction 
           410  . . . Account login 
           411  . . . Contents purchase instruction 
           412  . . . Contents purchase 
           413  . . . Authorization grant 
           414  . . . Control information distribution 
           415  . . . Control information transfer 
           416  . . . Control information storing 
           417  . . . Contents download 
           418  . . . License acquisition request 
           419  . . . License acquisition response 
           420  . . . License storing 
           421  . . . Contents searching instruction 
           422  . . . Contents searching 
           423  . . . Contents playback instruction 
           424  . . . Contents playback request 
           425  . . . Transmit preparation 
           426  . . . Contents transmission 
           427  . . . Contents playback output 
           601  . . . Audio-visual terminal 
           603  . . . Storage terminal 
           607  . . . Control information transferring section 
           608  . . . HDMI decryption section 
           615  . . . Control information acquiring section 
           620  . . . HDMI encryption section 
           702  . . . Download sequence 
           703  . . . Reproduction sequence 
           715  . . . Control information transfer 
           721  . . . Contents searching instruction 
           722  . . . Contents searching 
           723  . . . Contents playback instruction 
           724  . . . Contents playback request 
           725  . . . Transmit preparation 
           726  . . . Contents transmission 
           727  . . . Contents playback output 
           801  . . . Audio-visual terminal 
           802  . . . Server 
           803  . . . Storage terminal 
           805  . . . HTML browser 
           815  . . . Control information acquiring section 
           828  . . . Control information distributing section 
           901  . . . Registration sequence 
           902  . . . Download sequence 
           907  . . . Terminal ID registration 
           908  . . . Terminal ID storing 
           914  . . . Control information transfer request 
           915  . . . Control information transfer 
           916  . . . Control information storing 
           1001  . . . Audio-visual terminal 
           1002  . . . Server 
           1003  . . . Storage terminal 
           1004  . . . Network IF 
           1008  . . . LAN transmission decryption section 
           1009  . . . Decoding section 
           1010  . . . Decoded output 
           1011  . . . LAN 
           1012  . . . Network IF 
           1013  . . . Contents acquiring section 
           1014  . . . Storage section 
           1015  . . . Control information acquiring section 
           1016  . . . Control information storage section 
           1017  . . . License acquiring section 
           1018  . . . License storage section 
           1019  . . . Decryption section 
           1020  . . . LAN transmission encryption section 
           1021  . . . Router 
           1022  . . . Network 
           1023  . . . Router 
           1024  . . . LAN 
           1025  . . . Contents distributing section 
           1026  . . . Storage device 
           1027  . . . HTML server 
           1028  . . . Control information distributing section 
           1029  . . . License distributing section 
           1030  . . . Authorization recording section 
           1031  . . . Control terminal 
           1032  . . . Network IF 
           1033  . . . HTML browser 
           1101  . . . Registration sequence 
           1102  . . . Download sequence 
           1103  . . . Reproduction sequence 
           1104  . . . Account login instruction 
           1105  . . . Account login 
           1106  . . . Terminal ID registration instruction 
           1107  . . . Terminal ID registration 
           1108  . . . Terminal ID storing 
           1109  . . . Account login instruction 
           1110  . . . Account login 
           1111  . . . Contents purchase instruction 
           1112  . . . Contents purchase 
           1113  . . . Authorization grant 
           1115  . . . Control information transfer 
           1116  . . . Control information storing 
           1117  . . . Contents download 
           1118  . . . License acquisition request 
           1119  . . . License acquisition response 
           1120  . . . License storing 
           1121  . . . Contents searching instruction 
           1122  . . . Contents searching 
           1123  . . . Contents playback instruction 
           1124  . . . Contents playback request 
           1125  . . . Transmit preparation 
           1126  . . . Contents transmission 
           1127  . . . Contents playback output 
           1203  . . . Storage terminal 
           1204  . . . CPRM encryption section 
           1205  . . . Medium 
           1301  . . . Address information retain sequence 
           1302  . . . Address notice 
           1303  . . . Step of searching address of the terminal ID 
           1304  . . . Connection request 
           1305  . . . TCP connection 
           1306  . . . Storage information request 
           1307  . . . Storage information distribute 
           1308  . . . Storage information distribute 
           1309  . . . Storage information display 
           1310  . . . Download instruction 
           1311  . . . Download instruction 
           1312  . . . TCP cutting 
           1313  . . . Address notice 
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     In the following, a first embodiment of the present invention will be described with reference to the drawings. 
       FIG. 1  shows an exemplary configuration of a system according to this embodiment. An audio-visual terminal  101  and a storage terminal  103  are connected to a LAN  111 . These terminals are connected to a server  102  via a router  121  and a network  122 . The audio-visual terminal  101  comprises a network IF  104 , a LAN transmission decryption section  108 , a decoding section  109 , a HTML browser  105 , a control information acquiring section  106  and a control information transferring section  107 . The decoding section  109  has a function of providing a decoded output  110 , which is corresponding to a function of outputting an image to, for example, a TV screen. 
     The storage terminal  103  comprises a network IF  112 , a contents acquiring section  113 , a storage section  114 , a decryption section  119 , a LAN transmission encryption section  120 , a control information acquiring section  115 , a control information storage section  116 , a license acquiring section  117  and a license storage section  118 . 
     The server  102  comprises a contents distributing section  125 , a storage device  126 , a HTML server  127 , a control information recording section  128 , an authorization recording section  130 , a license distributing section  129 , a router  123  and a LAN  124 . The contents distributing section  125 , the HTML server  127 , the license distributing section  129  and other sections are a group of servers each of which has a CPU and operates independently and are interconnected by the LAN  124  installed in the server site to cooperate with each other to provide an integrated download server functionality as a whole. Of course, alternatively, these functions can also be provided by one server. 
     The contents distributing section  125  is provided with the storage device  126  and allows the storage terminal  103  to download an AV contents file stored in the storage device  126  through the network  122 . 
     The AV contents file referred to herein means real-time data containing video, audio and the like. For example, the AV contents file may be a MPEG2 file or a MP3 file. The audio-visual terminal  101  may be, for example, a network digital TV set having a HTML browser. The storage terminal  103  may be, for example, a network digital recorder. Although not shown in  FIG. 1 , the audio-visual terminal  101  and the storage terminal  103  each have a user interface, such as a remote controller and a GUI screen, through which the functions of the terminals can be individually accessed by the user. 
       FIG. 2  shows a process and an exemplary communication sequence in which a user downloads and views and listens to contents by operating the terminals according to this embodiment. 
     In the following, the operations and the communication procedure will be described step-by-step with reference to  FIG. 2 . In  FIG. 2 , the audio-visual terminal  101 , the server  102  and the storage terminal  103  have the configurations shown in  FIG. 1  and therefore are denoted by the same reference numerals, and illustration of components that offer only well-known functions, such as the network, is omitted. The sequence shown in  FIG. 2  is generally divided into a registration sequence  401 , a download sequence  402  and a playback sequence  403 . Typically, these sequences are also temporally separated from each other. The registration sequence  401  is a service registration procedure that has to be performed only once, for example, when the storage terminal  103  is purchased and installed and the registration sequence is performed through the user interface of the storage terminal  103 . The download sequence  402  and the playback sequence  403  are performed any number of times by operations of the user on the user interface of the audio-visual terminal  101 . In the drawing, arrows indicate these operations. 
     In the registration sequence  401 , first, the user issues an account login instruction  404  to operate the storage terminal  103 , thereby accessing the server  102  using the HTML browser or other communication applications to perform an account login communication  405 . The account referred to herein is used for managing the history of purchase of contents or managing billing information about the purchased contents. The user previously acquires the account by making a contract with a contents distributor. The server  102  stores the account name and the account password for identifying each account and other entries including settlement method information required for billing. By issuing the account login instruction  404 , the user can enter the account name and the password to perform login. 
     Then, the user operates the storage terminal  103  to perform a terminal ID registration operation  406 . This operation can be performed, for example, by pushing a terminal ID registration button in a HTML page in the storage terminal  103 . The terminal ID referred to herein is an ID for uniquely identifying a terminal for granting an authorization to use per every terminal based on a device binding method. The terminal ID is built-in in the storage terminal  103  before shipping, and spoofing of the terminal ID is prevented by issuing a certificate of the ID, for example. 
     Once the terminal ID registration operation  406  occurs, the storage terminal  103  performs communication for a terminal ID registration  407  in response to an instruction received from a button in the HTML page via a plug-in and transmits the terminal ID of the storage terminal  103  to the server  102 . 
     The server  102  having received the terminal ID registration  407  registers the terminal ID of the storage terminal  103  in the account entries of the user in step  408 . Through the sequence described above, the terminal ID is registered in association with the account of the user. 
     In the above description, the storage terminal  103  identifies the terminal ID. Alternatively, however, the user can directly enter and register the terminal ID. Although the direct entry increases the effort of the user, it has an advantage that registration of the terminal ID can be performed on the audio-visual terminal  101 , a PC or the like, and thus the storage terminal  103  does not have to have the HTML browser. 
     The download sequence  402  is started when the user wants to purchase or rent contents. First, the user issues an account login instruction  409  on the audio-visual terminal  101  to access the server  102  using the HTML browser or other communication application, thereby performing an account login communication  410 . This operation is the same as in the registration sequence  401 . Then, the user browses the page provided by the server  102  using the HTML browser, selects desired contents and perform a contents purchase instruction operation  411 . This operation can be performed, for example, by pushing a button in a purchase form in the HTML page. The audio-visual terminal  101  having received the contents purchase instruction operation  411 , performs a contents purchase communication  412  by form post method or the like to specify the desired contents for the server  102 . 
     In step  413  the server  102  having received the contents purchase communication  412  performs a required billing information registration and the like and then grants an authorization to use the specified contents to the account logging. At the same time, the server  102  registers available period information, such as from t 1  to t 2 , and a use condition, such as the interface that can be used for output and the medium into which the contents can be copied, depending on the purchase condition. 
     According to this embodiment, at the same time, the server  102  grants an authorization to use based on the device binding to the terminal ID registered in association with the account to which the authorization to use is granted. More specifically, in step  413 , the server  102  stores a combination of the license ID for authorization identification, the terminal ID of the storage terminal  103  extracted from the entries for the account logging in, an encryption key for the contents and the use condition, in the authorization recording section  130 . 
       FIG. 3  shows an example of a data table stored in the authorization recording section  130 . In this drawing, it is assumed that the terminal ID of the storage terminal  103  is “0xABCDEF” and is registered in an entry whose license ID is “0001”. 
     Then, in step  414 , the server  102  responds to the contents purchase communication  412  by distributing DL control information to the audio-visual terminal  101  via the HTML server  127 . The DL control information referred to herein is information needed to acquire the contents and the license, and includes the contents URL stored in the control information recording section  128  and the ID of the license stored in the authorization recording section  130 . The DL control information particularly preferably includes the URL of the license server in addition to the ID of the license to acquire the license, and this is implemented for this embodiment. The URL of the contents referred to above is an example of AV contents location information indicating the location of the contents in the network according to the present invention. 
     The audio-visual terminal  101  having received the DL control information takes out the DL control information in the HTML by the control information acquiring section  106  and transmits the DL control information to the control information transferring section  107 . The control information acquiring section  106  is a plug-in program, a helper application or the like that is activated when the HTML browser  105  recognizes the MIME TYPE of the DL control information, for example. The plug-in program runs by the API of the HTML browser in the process of the HTML browser, and the helper application runs in the process other than that of the HTML browser. In this embodiment, either can be used. 
     The control information transferring section  107  is a communication module configured to communicate with the control information acquiring section  115  in the storage terminal  103  through the LAN  111 . The control information transferring section  107  immediately transfers the information received from the control information acquiring section  106  to the control information acquiring section  115  in a control information transfer communication  415 . 
     The storage terminal  103  having received the DL control information stores the DL control information in the control information storage section  116  in step  416 . This transfer can be achieved by an action compliant with the Universal Plug and Play (abbreviated as UPnP hereinafter) developed by the Universal Plug and Play Forum, for example. This arrangement is particularly preferred because the device discovery function of the UPnP allows the audio-visual terminal  101  and the storage terminal  103  to automatically recognize their residing in the same LAN, and the function identification function of the UPnP allows them to automatically confirm that both of them have the control information transferring function, and they can transfer the control information to each other. In the case where this arrangement is adopted, the control information transferring section  107  has an UPnP control point functionality, and the control information acquiring section  115  has an UPnP server functionality. 
     This embodiment is characterized in that the communication between the control information transferring section  107  and the control information acquiring section  115  does not involve any information that requires protection, such as a contents key included in the license, and therefore, information can be transferred in plain text without encryption. However, in order to prevent leakage of name of contents viewed and listened to by a person, from eavesdropping on the LAN  111 , encryption using inter-device authentication may be preferably used. 
     In this embodiment, the storage terminal  103  does not unconditionally accept the DL control information transferred from the audio-visual terminal  101  but checks the control information transfer communication  415  before accepting and stores the DL control information transferred from the audio-visual terminal  101 . This check prevents careless acceptance of the DL control information, when such DL control information that describes the URL of the destination of a DOS attack as the download target URL or describes the URL of advertising contents or the like, is transferred from a malicious third party. 
     Specifically, the DL control information may be accepted only if it checks the IP address of the source or the round-trip delay time between the source and the storage terminal  103  and confirms that the DL control information is not transferred via the Internet but transferred from a source directly connected to the LAN to which the storage terminal  103  is connected. Or the DL control information may be accepted only if the MAC address or other terminal ID of the source is previously registered in the storage terminal  103 . Or the DL control information may be accepted only if mutual authentication between the storage terminal  103  and the source is successful. All of these methods effectively block transfer of the DL control information from an outside third party to effectively prevent damage. 
     Alternatively, the server  102  may previously issue a certificate to the DL control information by using a secret key stored only by the server  102 , and the storage terminal  103  may accept the DL control information as legitimate information only if the storage terminal  103  verifies the signature using the public key. This method particularly effectively prevents damage regardless of the transfer path, compared with the other methods. 
     Then, in step  417 , the storage terminal  103  downloads the contents based on the DL control information stored in the control information storage section  116 . For example, the download is performed by an HTTP GET method for the URL of the contents, issued from the contents acquiring section  113 . The download is completed by acquiring the entire contents and storing the contents in the storage section  114  in the storage terminal  103 . 
     Once the download is completed, in step  418 , the storage terminal  103  issues a license acquisition request to the server  102  from the license acquiring section  117  based on the DL control information stored in the control information storage section  116 . The destination of the communication for requesting the license is the URL of the license server included in the DL control information. 
     In this embodiment, the audio-visual terminal  102  that acquires the DL control information from the server  102  and the storage terminal  103  that acquires the license, are separate terminals. Since the source of the requested information (URL of the contents and the URL of the source from which the license is acquired) is described as a full path URL including the domain name, the storage terminal  103  can request the license without missing or short information, using only the DL control information. Thus, the operation is simplified. 
     The license acquisition request  418  involves the license ID for specifying the desired license and the terminal ID of the storage terminal  103  that requests the license. 
     The server  102  having received the license acquisition request  418  checks whether the specified license has been purchased in the name of the specified terminal ID or not by verifying the license acquisition request  418  with searching the authorization recording section  130 . In this embodiment, since there is an entry that agrees with the specified terminal ID “0xABCDEF” and with the license ID “0001”, the server  102  determines that the license is granted and distributes the license in a license acquisition response  419 . The license referred to herein is information for limiting the method of playback of the contents. More specifically, the license includes an encryption key Kc 1  for decrypting the encrypted contents, the available period of the encryption key (t 1  to t 2 ) and the permitted destination (HDCP, DTCP). 
     The storage terminal  103  having received the license stores the license in the license storage section  118  in step  420 . By the sequence described above, the download of the contents and the acquisition of the relevant license are completed. 
     Then, the playback sequence  403  is started when the user wants to retrieve and play back the downloaded contents. More specifically, the playback sequence  403  is started by the user operating the audio-visual terminal  101  to issue an instruction to search the downloaded contents in step  421 . In this embodiment, the contents searching method is a contents searching method using the contents directory service (abbreviated as CDS, hereinafter) of the UPnP method compliant with the digital living network alliance (abbreviated as DLNA, hereinafter). 
     Although the detailed sequence is not shown, in response to the contents searching instruction, a contents searching communication  422  is bidirectionally performed a plurality of times between the audio-visual terminal  101  and the storage terminal  103 , and then, the desired contents can be displayed on the audio-visual terminal  101 . Using the UPnP method for contents searching is particularly advantageous in that modules for the device discovery function etc. can be made common, and the software size can be reduced, because the same method can be used for both the DL control information transferring and the contents searching, by adopting such system that the control information transferring section  107  has the UPnP control point functionality and the control information acquiring section  115  has the UPnP server functionality. 
     Then, in step  423 , the user operates the audio-visual terminal  101  to instruct to play back the downloaded contents. 
     The audio-visual terminal  101  having received the instruction issues a contents playback request  424  according to the DLNA method. The contents playback request  424  referred to herein has an inter-device authentication and transmission path encryption function compliant with the digital transmission contents protection (abbreviated as DTCP, hereinafter) standard as the contents protection method, the LAN transmission encryption section  120  has the functionality of a DTCP-IP server, and the LAN transmission decryption section  108  has the functionality of a DTCP-IP client. This transmission path protection method allows protection from eavesdropping and tampering and realizes proper observance of the specified expiration date even when the contents protected by DRM is transmitted between the audio-visual terminal  101  and the storage terminal  103 . 
     In step  425  the storage terminal  103  having received the contents playback request  424  prepares itself to determine whether to transmit the contents or not and to transmit the contents. More specifically, the storage terminal  103  retrieves the license from the license storage section  118 , compares the playback period information t 1  to t 2  in the license with the current time, and determines that transmission of the contents is permitted only if the current time is within the expiration date. Furthermore, the storage terminal  103  checks the permitted destination in the license and determines that transmission to the DTCP is permitted since the permitted destination includes the DTCP. The storage terminal  103  having determined that transmission is permitted, sets the encryption key Kc 1  in the decryption section  119  to start an operation of decrypting the downloaded encrypted contents into a plain text, encrypts the plain text again by using a DTCP encryption key by the LAN transmission encryption section  120 , and starts a contents transmission  426  to the LAN. 
     The audio-visual terminal  101  having received the contents transmission  426  decrypts the DTCP encryption by the LAN transmission decryption section  108 , starts decoding the compressed contents by the decoding section  109 , and provides the decoded output  110 . By the sequence described above, a contents playback  427  can be performed. 
     In the case where the user instructs to play back the contents after the rental period is expired, it turns out that the rental period is expired in step  425  where the playback period information t 1  to t 2  in the license is compared with the current time, and therefore, the contents transmission in step  426  is not performed. Thus, the expiration date can be observed. 
     By the sequence described above, such contents rental system can be realized that the contents downloaded to a terminal previously registered in the server  102  is permitted to be viewed and listened to only within the expiration date. 
     In this way, according to this embodiment, the first problem of the prior art can be solved because the user can view and listen to the contents downloaded to the audio-visual terminal  101  having no storage device. 
     Furthermore, the second problem of the prior art can also be solved because the audio-visual terminal  101  does not incorporate the storage terminal  103  but is connected to the storage terminal  103  via the network. 
     The terminal on which the user can view and listen to the contents is not limited to the audio-visual terminal  101 , and any terminal having the DTCP-IP client functionality can play back the contents by transmitting the contents playback request to the storage terminal  103 . That is, according to this embodiment, the server  102  only grants an authorization to use for the storage terminal  103  based on device binding method and performs neither registration nor checking of the ID of the terminal on which the contents is viewed and listened to. Furthermore, the storage terminal  103  only verifies whether the terminal is a legitimate DTCP-IP client or not and does not check whether the terminal is an audio-visual terminal  101  or not. Therefore, even when an arbitrary terminal having the DTCP-IP client functionality transmits the contents playback request to the storage terminal  103 , the storage terminal  103  performs the same operations as those in steps  424  and  425  described above and checks the entry having the license ID “0001” shown in  FIG. 3  only to confirm that the available period is not expired and that the output destination includes the DTCP so that the terminal can play back the contents. With this arrangement, even a client having no DRM client functionality can play back the contents on the audio-visual terminal having the DTCP-IP client functionality in the same LAN. For example, as a comparative example, such a method is assumed of distributing contents encrypted by a DRM key Kc, to an arbitrary audio-visual terminal without encryption in the transmission path. Although this method can also safely distribute the copyright-protected contents and permit the contents to be viewed and listened to only on the terminal that observes the use conditions. However, in this case, each audio-visual terminal has to have the DRM client functionality and acquire the key Kc. To the contrary, according to this embodiment, only the storage terminal  103  acquires the key Kc and performs decryption, and the contents are temporarily converted into a plain text and then are transmitted by another transmission path protecting instrument, so that the number of terminals having the DRM functionality can be reduced. Thus, the fourth problem of the prior art can be solved. 
     Furthermore, even when the user operates the local GUI of the storage terminal  103  itself to issue an instruction to play back the downloaded contents, the contents are decrypted into a plain text by the decryption section  119  and then decoded by a decoder (not shown) in the storage terminal  103 , to become capable of playback. Thus, the third problem of the prior art can be solved. 
     As described above, this embodiment can solve the first to fourth problems of the prior art at the same time. 
     Although the transmission path protecting means in this embodiment is the DTCP, any other protecting means, such as the HDCP, can also be used. 
     Furthermore, although the authorization to use is granted only to the storage terminal  103  in this embodiment, the authorization to use can also be granted to the audio-visual terminal  101  at the same time. 
     Second Embodiment 
     In the following, a second embodiment of the present invention will be described with reference to the drawings. 
     This embodiment differs from the first embodiment primarily in that a high definition multimedia interface (abbreviated as HDMI, hereinafter) connection is used for transmission of the download control information and transfer of the contents, instead of the LAN. In this embodiment, modules that operate in essentially the same way as in the first embodiment, are denoted by the same reference numerals as those in the first embodiment.  FIG. 4  shows an exemplary configuration of a system according to this embodiment. 
     An audio-visual terminal  601  and a storage terminal  603  are connected to the LAN  111 . These terminals  601  and  603  are connected to the server  102  via the router  121  and the network  122 . 
     The audio-visual terminal  601  comprises the network IF  104 , a HDMI decryption section  608 , the decoding section  109 , the HTML browser  105 , the control information acquiring section  106  and the control information transferring section  607 . The decoding section  109  has a function of providing the decoded output  110 , which is corresponding to the function of, for example, outputting an image to a TV screen. 
     The storage terminal  603  comprises the network IF  112 , the contents acquiring section  113 , the storage section  114 , the decryption section  119 , an HDMI encryption section  620 , a control information acquiring section  615 , the control information storage section  116 , the license acquiring section  117  and the license storage section  118 . 
     The server  102  is the same server as in the first embodiment. 
     The audio-visual terminal  601  may be a network digital TV set having a HTML browser, for example. The storage terminal  603  may be, for example, a network digital recorder. Although not shown in  FIG. 4 , the audio-visual terminal  601  and the storage terminal  603  each have a user interface, such as a remote controller and a GUI screen, through which the functions of the terminals can be individually accessed by the user. 
       FIG. 5  shows a process and a communication sequence in which a user downloads and views and listens to contents by operating the terminals according to this embodiment. In the following, the operations and the communication procedure will be described step-by-step with reference to  FIG. 5 . 
     In  FIG. 5 , the audio-visual terminal  601 , the server  102  and the storage terminal  603  have the configurations shown in  FIG. 4  and therefore are denoted by the same reference numerals, and illustration of components that offer only well-known functions, such as the network, is omitted. The sequence shown in  FIG. 5  is generally divided into the registration sequence  401 , a download sequence  702  and a playback sequence  703 . Typically, these sequences are also temporally separated from each other. The registration sequence  401  is the same as in the first embodiment, and therefore, description thereof will be omitted. 
     The download sequence  702  and the playback sequence  703  are performed any number of times by operations of the user on the user interface of the audio-visual terminal  601 . 
     The download sequence  702  is started when the user wants to purchase or rent contents. The process from the account login instruction  409  to the control information distribution  414  is the same as in the first embodiment, and therefore, description thereof will be omitted. 
     In step  715  the audio-visual terminal  601  having received the DL control information takes out the DL control information in the HTML by the control information acquiring section  106  and transmits the DL control information to the control information transferring section  607 . The control information transferring section  607  is a communication module capable of communicating with the control information acquiring section  615  in the storage terminal  603  through a CEC control line housed in the HDMI cable. The control information transferring section  607  immediately transfers the information received from the control information acquiring section  106  to the control information acquiring section  615  in the storage terminal  603 , in a control information transfer communication  715 . 
     The storage terminal  603  having received the DL control information stores the DL control information in the control information storage section  116  in step  416 . This embodiment is characterized in that the communication between the control information transferring section  607  and the control information acquiring section  615  does not involve any information that requires protection, such as a contents key included in the license, and therefore, information can be transferred in plain text without encryption. Furthermore, this embodiment differs from the first embodiment in that the storage terminal  603  does not accept the DL control information which is transferred from a terminal other than the terminal to which the storage terminal  603  is directly HDMI-connected and therefore has an advantage that the storage terminal  603  is less susceptible to an attack via the network. 
     Then, based on the DL control information stored in the control information storage section  116 , the storage terminal  603  performs the operations in steps  417  to  420  as in the first embodiment, to download the contents and acquire the relevant license. 
     Then, the playback sequence  703  is started when the user wants to search and play back the downloaded contents. More specifically, the playback sequence  703  is started by the user operating the audio-visual terminal  601  to issue an instruction to search the downloaded contents in step  721 . 
     In this embodiment, the contents searching method can be implemented using the UI of the storage terminal  603 , by setting the screen display of the audio-visual terminal  601  to display the HDMI input from the storage terminal  603  and then by transferring the operation on the audio-visual terminal  601  by the user to the storage terminal  603  via the CEC line. Such an UI linkage of this type has been put into practical use as a HDMI-based link system between a TV set and a recorder. In this way, the desired contents can be displayed on the audio-visual terminal  601 . 
     Then, in step  723 , the user operates the audio-visual terminal  601  to instruct to play back the downloaded contents. The audio-visual terminal  601  having received the instruction, issues a contents playback request  724  through the CEC line. The storage terminal  603  having received the contents playback request  724 , prepares itself to determine whether to transmit the contents or not and to transmit the contents in step  725 . More specifically, the storage terminal  603  retrieves the license from the license storage section  118 , compares the playback period information t 1  to t 2  in the license with the current time, and determines that transmission of the contents is permitted only if the current time is within the expiration date. 
     Furthermore, the storage terminal  603  checks the permitted destination in the license and determines that transmission to the HDMI is permitted since the permitted destination includes the HDCP, which indicates the inter-device authorization specification of the HDMI transmission line. The storage terminal  603  having determined that transmission is permitted sets the encryption key Kc 1  in the decryption section  119  to start an operation of decrypting the downloaded encrypted contents into a plain text, encrypts the plain text again by using HDCP encryption key by the HDMI encryption section  620 , and starts a contents transmission  726 . 
     The audio-visual terminal  601  having received the contents transmission  726  decrypts the HDCP encryption by the HDMI decryption section  608 , starts decoding the compressed contents by the decoding section  109 , and provides the decoded output  110 . This transmission path protection method allows protection from eavesdropping and tampering and realizes proper observance of the specified expiration date even when the contents protected by DRM is transmitted between the audio-visual terminal  601  and the storage terminal  603 . 
     By the sequence described above, a contents playback  727  can be performed, and such contents rental system can be realized that the contents downloaded to a terminal previously registered in the server  102  is permitted to be viewed and listened to only within the expiration date. 
     Third Embodiment 
     In the following, a third embodiment of the present invention will be described with reference to the drawings. 
     This embodiment differs from the first embodiment primarily in that transmission of the download control information does not occur between the audio-visual terminal and the server but directly between the server and the storage terminal. 
     In this embodiment, modules that operate in essentially the same way as in the first embodiment are denoted by the same reference numerals as those in the first embodiment.  FIG. 6  shows an exemplary configuration of a system according to this embodiment. 
     An audio-visual terminal according to the third embodiment is an example of an instruction terminal according to the present invention. 
     An audio-visual terminal  801  and a storage terminal  803  are connected to the LAN  111 . These terminals  801  and  803  are connected to a server  802  via the router  121  and the network  122 . 
     The audio-visual terminal  801  comprises the network IF  104 , a LAN transmission decryption section  108 , the decoding section  109  and a HTML browser  805 . 
     The storage terminal  803  comprises the network IF  112 , the contents acquiring section  113 , the storage section  114 , the decryption section  119 , the LAN transmission encryption section  120 , a control information acquiring section  815 , the control information storage section  116 , the license acquiring section  117  and the license storage section  118 . 
     The server  802  comprises the contents distributing section  125 , the storage device  126 , the HTML server  127 , a control information distributing section  828 , the authorization recording section  130 , the license distributing section  129 , the router  123  and the LAN  124 . The contents distributing section  125 , the HTML server  127 , the license distributing section  129 , the control information distributing section  828  and other sections are a group of servers each of which has a CPU and operates independently and are interconnected by the LAN  124  installed in the server site to cooperate with each other to provide an integrated download server functionality as a whole. 
     The audio-visual terminal  801  may be, for example, a network digital TV set having a HTML browser. The storage terminal  803  may be, for example, a network digital recorder. Although not shown in  FIG. 6 , the audio-visual terminal  801  and the storage terminal  803  each have a user interface, such as a remote controller and a GUI screen, through which the functions of the terminals can be individually accessed by the user. 
       FIG. 7  shows a process and an exemplary communication sequence in which a user downloads and views and listens to a contents by operating the terminals according to this embodiment. In the following, the operations and the communication procedure will be described step-by-step with reference to  FIG. 7 . In  FIG. 7 , the audio-visual terminal  801 , the server  802  and the storage terminal  803  have the configurations shown in  FIG. 6  and therefore are denoted by the same reference numerals, and illustration of components that offer only well-known functions, such as the network, is omitted. 
     The sequence shown in  FIG. 7  is generally divided into a registration sequence  901 , a download sequence  902  and the playback sequence  403 . Typically, these sequences are also temporally separated from each other. The registration sequence  901  is a service registration procedure that has to be performed only once, for example, when the storage terminal  803  is purchased and installed. The registration sequence  901  is performed through the user interface of the storage terminal  803 . The download sequence  902  and the playback sequence  403  are performed any number of times by operations of the user on the user interface of the audio-visual terminal  801 . 
     In the registration sequence  901 , first, the user issues the account login instruction  404  to operate the storage terminal  803 , thereby accessing the server  802  using the HTML browser or other communication applications to perform the account login communication  405 . 
     After the process from the account login instruction  404  to the terminal ID registration operation  406  is performed in the same way as in the first embodiment, the storage terminal  803  having received the terminal ID registration operation  406 , in a terminal ID registration  907 , transmits the terminal ID of the storage terminal  803  to the server  802  and then starts a polling operation to the server  802  of a DL control information distribution request. 
     In this polling operation, the storage terminal  803  regularly transmits a DL control information distribution request to the server  802  and checks the presence or absence of the DL control information concerning the terminal ID of the storage terminal  803 . 
     In step  908 , the server  802  having received the terminal ID registration  907  registers the terminal ID of the storage terminal  803  in the account entry of the user. By the sequence described above, the terminal ID is registered in association with the account of the user, and the polling from the storage terminal  803  is started. 
     The download sequence  902  is started when the user wants to purchase or rent a contents. Steps  409  to  413  are the same as in the first embodiment, and thus description thereof will be omitted. An authorization to use based on device binding shown in  FIG. 3  is granted to the terminal ID “0xABCDEF” of the storage terminal  803  and registered in the entry having the license ID “0001”. 
     Since the storage terminal  803  regularly transmits the DL control information distribution request as described above, the server  802  receives a control information transfer request  914  at times depending on the polling cycle. The control information transfer request  914  includes the ID “0xABCDEF” of the storage terminal  803 , which agrees with the ID in the entry having the license ID “0001”, and therefore, the server  802  confirms the agreement and then distributes the DL control information including the license ID “0001” to the storage terminal  803  via the control information distributing section  828  as a response to the control information transfer request  914  in step  915 . 
     The DL control information referred to herein is information necessary to acquire the contents and the license, and includes the URL of the contents stored in the control information distributing section  828  and the ID of the license stored in the authorization recording section  130 . 
     The control information acquiring section  815  of the storage terminal  803  having received the DL control information stores the DL control information in the control information storage section  116  in step  916 . Then, as in the first embodiment, the storage terminal  803  performs the operations in steps  417  to  420  based on the DL control information stored in the control information storage section  116 . 
     By the sequence described above, download of the contents and acquisition of the relevant license are completed. 
     This embodiment has an advantage that the audio-visual terminal  801  has only an ordinary browser and does not need a special plug-in and the storage terminal  803  performs polling and unauthorized registration by a third party can be easily prevented only by authentication of the server  802 . 
     The playback sequence  403  is the same as in the first embodiment, and description thereof will be omitted. 
     By the sequence described above, a contents rental system permits contents to be downloaded only to a terminal previously registered in the server  102  and the contents to be viewed and listened to on the terminal only within the expiration date. 
     Fourth Embodiment 
     In the following, a fourth embodiment of the present invention will be described with reference to the drawings. This embodiment differs from the third embodiment primarily in that a control terminal is provided as well as audio-visual terminal and a contents purchase instruction and so on are transmitted from the control terminal to a server. 
     A control terminal according to the embodiment is an example of an instruction terminal according to the present invention. 
       FIG. 8  shows an exemplary configuration of a system according to this embodiment. An audio-visual terminal  1001  and a storage terminal  1003  are connected to a LAN  1011 . These terminals  1001 , 1003  are connected to a server  1002  via a router  1021  and a network  1022 . The control terminal  1031  is connected to the server  1002  via a network  1022 . 
     The audio-visual terminal comprises a network IF  1004 , a LAN transmission decryption section  1008 , a decoding section  1009 . The decoding section  1009  has a function of providing a decoded output  1010 , which is corresponding to a function of, for example, outputting an image to a TV screen. 
     The storage terminal  1003  comprises a network IF  1012 , a contents acquiring section  1013 , a storage section  1014 , a decryption section  1019 , a LAN transmission encryption section  1020 , a control information acquiring section  1015 , a control information storage section  1016 , a license acquiring section  1017  and a license storage section  1018 . 
     The control terminal  1031  comprises a network IF  1032  and a HTML browser  1033 . 
     The server  1002  comprises a contents distributing section  1025 , a storage device  1026 , a HTML server  1027 , a control information distributing section  1028 , an authorization recording section  1030 , a license distributing section  1029 , a router  1023  and a LAN  1024 . The contents distributing section  1025 , the HTML server  1027 , the control information distributing section  1028 , the license distributing section  1029  and other sections are a group of servers each of which has a CPU and operates independently and are interconnected by the LAN  1024  installed in the server site to cooperate with each other to provide an integrated download server functionality as a whole. Of course, alternatively, these functions can also be provided by one server. 
     The contents distributing section  1025  is provided with the storage device  1026  and allows the storage terminal  1003  to download an AV contents file stored in the storage device  1026  through the network  1022 . 
     The AV contents file referred to herein means real-time data containing video, audio and the like. For example, the AV contents file may be a MPEG2 file or a MP3 file. The audio-visual terminal  1001  may be, for example, a network digital TV set. The storage terminal  1003  may be, for example, a network digital recorder. The control terminal  1031  may be, for example mobile telephone having a browser. Although not shown in  FIG. 8 , the audio-visual terminal  1001 , the storage terminal  1003  and the control terminal  1031  each have a user interface, such as a remote controller and a GUI screen, through which the functions of the terminals can be individually accessed by the user. 
       FIG. 9  shows a process and a communication sequence in which a user downloads and views and listens to contents by operating the terminals according to this embodiment. In the following, the operations and the communication procedure will be described step-by-step with reference to  FIG. 9 . 
     In  FIG. 9 , the audio-visual terminal  1001 , the server  1002 , the storage terminal  1003  and the control terminal  1031  have the configurations shown in  FIG. 8  and therefore are denoted by the same reference numerals, and illustration of components that offer only well-known functions, such as the network, is omitted. The sequence shown in  FIG. 9  is generally divided into a registration sequence  1101 , a download sequence  1102  and a playback sequence  1103 . Typically, these sequences are also temporally separated from each other. 
     The registration sequence  1101  is a service registration procedure that has to be performed only once when the storage terminal  1003  is purchased and installed, for example and the registration sequence is performed through the user interface of the storage terminal  1003 . The download sequence  1102  and the playback sequence  1103  are performed any number of times by operations of the user, on the user interface of the control terminal  1031  for the download sequence  1102  and on the user interface of the audio-visual terminal  1001  for the playback sequence  1103 . 
     In the registration sequence  1101 , first, the user issues an account login instruction  1104  to operate the storage terminal  1003 , thereby accessing the server  1002  using the HTML browser or other communication applications to perform an account login communication  1105 . The account referred to herein is used for managing the history of purchase of contents or managing billing information about the purchased contents. The user previously acquires the account by making a contract with a contents distributor. The account name and the account password for identifying each account and other entries including settlement method information required for billing are stored in the server  1002 . By issuing the account login instruction  1104 , the user can enter the account name and the password to perform login. 
     Then, the user operates the storage terminal  1003  to perform a terminal ID registration operation  1106 . This operation can be performed by pushing a terminal ID registration button in a HTML page in the storage terminal  1003 , for example. The terminal ID referred to herein is an ID for uniquely identifying a terminal for granting an authorization to use per every terminal based on a device binding method. The terminal ID is built-in in the storage terminal  1003  before shipping, and spoofing of the terminal ID is prevented by issuing a certificate of the ID, for example. 
     Once the terminal ID registration operation  1106  occurs, the storage terminal  1003  performs communication for a terminal ID registration  1107  in response to an instruction received from a button in the HTML page via a plug-in and transmits the terminal ID of the storage terminal  1003  to the server  102 . The server  1002  having received the terminal ID registration  1107  registers the terminal ID of the storage terminal  1003  in the account entries of the user in step  1108 . Through the sequence described above, the terminal ID is registered in association with the account of the user. 
     In the above description, the storage terminal  1003  identifies the terminal ID. Alternatively, however, the user can directly enter and register the terminal ID. Although the direct entry increases the effort of the user, it has an advantage that registration of the terminal ID can be performed on the control terminal  1031 , a PC or the like, and thus the storage terminal  1003  does not have to have the HTML browser. 
     Further in this embodiment address information which is used by the server  1002  for starting at any timing a communication to the storage terminal  1003 , is registered on the server  1002  (address information retain sequence  1301  of  FIG. 10  described after). 
     As the address information, an IP address of the storage terminal  1003 , by using a method which is known as dynamic DNS for example, can be registered on the server  1002 . Further it is particularly preferably to register and retain the address information according to a specified sequence (for example such sequence described in the U.S. Pat. No. 3,445,986) for communicating from the server  1002  to the storage terminal  1003  via the router  1021 . 
     That is concretely the storage terminal  1003  regularly sends an address notice UDP packet in which a terminal ID of the storage terminal is recorded, to the server  1002 . The server  1002  receiving the address notice UDP packet records a transmission source address of the address notice UDP packet, to the terminal ID registered in the account (address information retain sequence  1301  of  FIG. 10  described after). According to this method even when the IP address changes, the latest IP address can be recorded and therefore the server  1002  can start at any time the communication by transmitting for the recorded IP address a connection request UDP packet having same format as that of the response of the address notice UDP packet. 
     The download sequence  1102  is started when the user wants to purchase or rent contents. First, in the download sequence  1102 , the user issues an account login instruction  1109  on the control terminal  1031  to access the server  1002  using the HTML browser or other communication application, thereby performing an account login communication  1110 . This operation is the same as in the registration sequence  1101 . 
     Then, the user browses the page provided by the server  1002  using the HTML browser, selects desired contents and performs a contents purchase operation  1111 . This operation can be performed, for example, by pushing a button in a purchase form in the HTML page. The control terminal  1031  having received the contents purchase operation  1111 , performs a contents purchase communication  1112  by form post method or the like to specify the desired contents for the server  1002 . 
     In step  1113  the server  1002  having received the contents purchase communication  1112  performs a required billing information registration and the like and then grants an authorization to use the specified contents to the account logging. At the same time, the server  1002  registers available period information, such as from t 1  to t 2 , and a use condition, such as the interface that can be used for output and the medium into which the contents can be copied, depending on the purchase condition. 
     According to this embodiment, at the same time, the server  1002  grants an authorization to use based on the device binding to the terminal ID registered in association with the account to which the authorization to use is granted. More specifically, in step  1113 , the server  1002  stores a combination of the license ID for authorization identification, the terminal ID of the storage terminal  1003  extracted from the entries for the account logging in, an encryption key for the contents and the use condition, in the authorization recording section  1030 . 
       FIG. 3  shows an example of a data table stored in the authorization recording section  1030 . In this drawing, it is assumed that the terminal ID of the storage terminal  1003  is “0xABCDEF” and is registered in an entry whose license ID is “0001”. 
     Then, in step  1115 , the server  1002  distributes DL control information to the storage terminal  1003  via a control information distributing section  1028  as described below. A control information transfer communication  1115  is performed by above-mentioned specified communication method from a house outside server to a house inside device (see the U.S. Pat. No. 3,445,986). 
     The DL control information referred to herein is information necessary to acquire the contents and the license, and includes the contents URL stored in the control information distributing section  1028  and the ID of the license stored in the authorization recording section  1030 . The DL control information particularly preferably includes the URL of the license server in addition to the ID of the license to acquire the license, and this is implemented for this embodiment. 
     The storage terminal  1003  having received the DL control information by the control information acquiring section  1015 , stores the DL control information in the control information storage section  1016  at step  1116 . 
     In this embodiment, the storage terminal  1003  does not unconditionally accept the DL control information but checks the control information transfer communication  1115  before accepting and storing the DL control information. This check prevents damage by avoiding careless acceptance of the DL control information, when such DL control information that describes the URL of the destination of a DOS attack as the download target URL or describes the URL of advertising contents or the like, is transferred from a malicious third party. Specifically, the DL control information may be accepted only if a server authentication by the storage terminal  1003  is successful, or alternatively, the server  1002  may previously issue a certificate to the DL control information by using a secret key stored only by the server  1002 , and the storage terminal  1003  may accept the DL control information only if the storage terminal  1003  verifies the signature using the public key. This method has effective merits. 
     Then the above described specified communication method from the account login instruction  1109  to the control information transfer communication  1115  is described in detail according to  FIG. 10 . 
     The address information retain sequence  1301  is regularly performed after the registration sequence  1101  as described above, and in the sequence the storage terminal  1003  regularly, for example every several minutes, sends an address notice UDP packet  1302  in which a terminal ID is recorded, to the server  1002 . The server  1002  receiving the address notice UDP packet records a transmission source address of the address notice UDP packet, to the terminal ID registered in the account. 
     When the address information retain sequence  1301  is regularly performed, steps from the account login instruction  1109  to the granting of the authorization to use for the terminal ID  1113  are normally executed, the server  1002  extracts an IP address of the terminal ID registered in the account at step  1303 . Since the IP address is the latest IP address for the storage terminal  1003 , communication can be performed by using this, and the server  1002  transmits a connection request UDP packet  1304  having the same format as that of the response of the address notice UDP packet  1302 . 
     The storage terminal  1003  having received the connection request UDP packet  1304 , makes TCP connection  1305  to the server  1002 . Here the reason why the server  1002  does not make the connection directly to the storage terminal  1003  is that since generally the router  1021  intercepts the TCP connection request from internet side, communication from the internet side can be started by transmitting the connection request UDP packet  1304  as a response to the address notice UDP packet. Thereafter communication can be freely performed on the TCP connection. 
     Then the server  1002  transmits a storage information request  1306  to the storage terminal  1003 . 
     The storage terminal  1003  having received the storage information request, responds with a storage information  1307 . The storage information  1307  is described by HTML for example, and includes necessary information for controlling the downloading, such as information of contents list and empty capacity in the storage terminal  1003 , information of download sequence being executed, information of present possibility of acceptance of download request, and so on. 
     The server  1002  transmits the storage information to the control terminal  1031  at the storage information distribute  1308 , and the control terminal  1031  displays the storage information for the user by the HTML browser  1033  at the storage information display  1309 . 
     By such relay communication of HTML by the server  1002 , the user can confirm the information which is necessary to control downloading. Further the user can execute such operation as erasing unnecessary contents by using CGI to get empty capacity. 
     Then the user instructs the download instruction  1310  by using the control terminal  1031 , and the server  1002  having received the downloaded instruction at step  1311  transmits the control information transfer  1115  on the TCP connection to the storage terminal  1003 , and thereafter executes a TCP cutting process  1312  to complete the process series. 
     After the completion, the storage terminal  1003  further continues the regular address notice  1313 , to prepare for the next download instruction. 
     According to this method an API for obtaining HDD capacity or API for obtaining downloading status can be transmitted to be open, from the control terminal  1031  to the server  1002 . Therefore the control terminal  1031  can communicate with the storage terminal  1003  in real time via the server  1002  and control the storage terminal. 
     According to this method such functions that the control terminal  1031  confirms the empty capacity of HDD of the storage terminal  1003  to erase unnecessary contents and confirms the present downloading status, can be realized at the same time to show particularly convenient effects. 
     Then, in step  1117 , the storage terminal  1003  downloads the contents based on the DL control information stored in the control information storage section  1016 . For example, the download is performed by an HTTP GET method for the URL of the contents, issued from the contents acquiring section  1013 . The download is completed by acquiring the entire content and storing the contents in the storage section  1014  in the storage terminal  1003 . 
     Once the download is completed, in step  1118 , the storage terminal  1003  issues a license acquisition request to the server  1002  from the license acquiring section  1017  based on the DL control information stored in the control information storage section  1016 . The destination of the communication for requesting the license is the URL of the license server included in the DL control information. 
     The license acquisition request  1118  involves the license ID for specifying the desired license and the terminal ID of the storage terminal  1003  that requests the license. 
     The server  1002  having received the license acquisition request  1118  checks whether the specified license has been purchased in the name of the specified terminal ID or not by verifying the license acquisition request  1118  with searching the authorization recording section  1030 . In this embodiment, since there is an entry that agrees with the specified terminal ID “0xABCDEF” and with the license ID “0001”, the server  1002  determines that the license is granted and distributes the license in a license acquisition response  1119 . The license referred to herein is information for limiting the method of playback of the contents. More specifically, the license includes an encryption key Kc 1  for decrypting the encrypted contents, the available period of the encryption key (t 1  to t 2 ) and the permitted destination (HDCP, DTCP). 
     The storage terminal  1003  having received the license stores the license in the license storage section  1018  in step  0020 . By the sequence described above, the download of the contents and the acquisition of the relevant license are completed. 
     Then, the playback sequence  1103  is started when the user wants to retrieve and play back the downloaded contents. More specifically, the playback sequence  403  is started by the user operating the audio-visual terminal  1001  to issue an instruction to search the downloaded contents in step  0021 . In this embodiment, as the contents searching method such method is adopted using the contents searching service of the above described CDS of the UPnP method compliant with the DLNA. 
     Although the detailed sequence is not shown, in response to the contents searching instruction, a contents searching communication  1122  is bidirectionally performed a plurality of times between the audio-visual terminal  1001  and the storage terminal  1003 , and then, the desired contents can be displayed on the audio-visual terminal  1001 . 
     Then, in step  1123 , the user operates the audio-visual terminal  1001  to instruct to play back the downloaded contents. The audio-visual terminal  1001  having received the instruction issues a contents playback request  1124  according to the DLNA method. The contents playback request  1124  referred to herein has an inter-device authentication and transmission path encryption function compliant with the DTCP standard as the contents protection method, and the LAN transmission encryption section  1020  has the functionality of a DTCP-IP server, and the LAN transmission decryption section  1008  has the functionality of a DTCP-IP client. This transmission path protection method allows protection from eavesdropping and tampering and realizes proper observance of the specified expiration date even when the contents protected by DRM is transmitted between the audio-visual terminal  1001  and the storage terminal  1003 . 
     In step  1125  the storage terminal  1003  having received the contents playback request  1124  prepares itself to determine whether to transmit the contents or not and to transmit the contents. More specifically, the storage terminal  1003  retrieves the license from the license storage section  1018 , compares the playback period information t 1  to t 2  in the license with the current time, and determines that transmission of the contents is permitted only if the current time is within the expiration date. Furthermore, the storage terminal  1003  checks the permitted destination in the license and determines that transmission to the DTCP is permitted since the permitted destination includes the DTCP. The storage terminal  1003  having determined that transmission is permitted, sets the encryption key Kc 1  in the decryption section  1019  to start an operation of decrypting the downloaded encrypted contents into a plain text, encrypts the plain text again by using a DTCP encryption key by the LAN transmission encryption section  1020 , and starts a contents transmission  1126  to the LAN. 
     The audio-visual terminal  1001  having received the contents transmission  1126  decrypts the DTCP encryption by the LAN transmission decryption section  1008 , starts decoding the compressed contents by the decoding section  1009 , and provides the decoded output  1010 . By the sequence described above, a contents playback  1127  can be performed. 
     In the case where the user instructs to play back the contents after the rental period is expired, it turns out that the rental period is expired in step  1125  where the playback period information t 1  to t 2  in the license is compared with the current time, and therefore, the contents transmission in step  1126  is not performed. Thus, the expiration date can be observed. 
     By the sequence described above, such contents rental system can be realized that the contents downloaded to a terminal previously registered in the server  1002  is permitted to be viewed and listened to only within the expiration date. 
     In this way, according to this embodiment, the first problem of the prior art can be solved because the user can view and listen to the contents downloaded to the audio-visual terminal  1001  having no storage device. 
     Furthermore, the second problem of the prior art can also be solved because the audio-visual terminal  1001  does not incorporate the storage terminal  1003  but is connected to the storage terminal  1003  via the network. 
     The terminal on which the user can view and listen to is not limited to the audio-visual terminal  1001 , and any terminal having the DTCP-IP client functionality can play back the contents by transmitting the contents playback request to the storage terminal  1003 . With this arrangement, even a client having no DRM client functionality can play back the contents on the audio-visual terminal having the DTCP-IP client functionality in the same LAN so that the number of terminals having the DRM functionality can be reduced. Thus, the fourth problem of the prior art can be solved. 
     Furthermore, even when the user operates the local GUI of the storage terminal  1003  itself to issue an instruction to play back the downloaded contents, the contents are decrypted into a plain text by the decryption section  1019  and then decoded by a decoder not shown in the storage terminal  1003 , to become capable of playback. Thus, the third problem of the prior art can be solved. 
     As described above, this embodiment can solve the first to fourth problems of the prior art at the same time. 
     Further the control terminal  1031  does not need a special function other than HTML browser. Specifically the control terminal can be a conventional mobile telephone having a HTML browser, and therefore the user starts the download sequence at any place with no place limitation by running the browser. Then the downloaded contents can be viewed by the audio-visual terminal in a house after coming home. Therefore it is very convenient. Further by using the IR reception function and a bar-code reader function of the mobile telephone, the promotion of download contents at the places such as the outdoor advertisement or video rental store, can be performed to start the download sequence  1102  promptly as the result. Thus the system having high promotion effect can be realized. 
     Although the transmission path protecting means in this embodiment is the DTCP, any other protecting means, such as the HDCP, can also be used. 
     Now in the present embodiment the control information transfer communication  1115  is executed according to a communication from the server  1002  to the storage terminal  1003 , but instead of it the polling method can be used from the storage terminal  1003  to the server  1002  as described above. 
     Fifth Embodiment 
     In the following, a fifth embodiment of the present invention will be described with reference to the drawings. 
       FIG. 11  shows an exemplary configuration of a system according to this embodiment. Now the present embodiment is such system that medium output function is added to the storage terminal  103  of the first embodiment. The configuration of other terminal and server is same and then it is named as a storage terminal  1203  and only configuration of the storage terminal  1203  is described. 
     The storage terminal  1203  is connected to the server  102  via LAN  111 . The storage terminal  1203  comprises a network IF  112 , a contents acquiring section  113 , a storage section  114 , a decryption section  119 , a LAN transmission encryption section  120 , a control information acquiring section  115 , a control information storage section  116 , a license acquiring section  117 , a license storage section  118 , and further CPRM encryption section  1204 , DVD-R medium  1205 , and a drive which is necessary for DVD-writing though not shown. 
     In the embodiment sequences from the downloading of the contents to the storage terminal  1203  to the playback by the audio-visual terminal  101 , are equivalent to the first embodiment and  FIG. 2 , and then they are omitted. In the embodiment such operation differs from the operation of the first embodiment, that the user directly operates the local operation UI of the storage terminal  1203  to write the downloaded contents to the DVD-R. Here in the  FIG. 3  such operation in case that the terminal ID is “0x012345” and “DVD-CPRM” is included in media which are permitted under the use condition, is described. 
     When the user instructs that the downloaded contents are written on the DVD-R, the storage terminal  1203  confirms the use condition stored in the license storage section  118 . As the result the writing to the DVD is determined to be accepted, and then the storage terminal  1003  sets the encryption key Kc 2  in the decryption section  119  and starts an operation of decrypting the downloaded encrypted contents into a plain text. The storage terminal  1203  encrypts the plain text again by using a CPRM encryption key by the CPRM encryption section  1204 , to start the writing to the DVD-R medium. 
     According to such sequence the writing of the downloaded contents from the server  102  to the DVD-R medium can be permitted. For example in an assumed case where the audio-visual terminal  101  gets the DRM encryption key Kc 2 , the storage terminal  1203  can not get a necessary key, thereby not to decrypt it and writing it to DVD-R medium  1205 . However in the fifth embodiment the writing to the medium on the storage terminal  1203  and the function of viewing and listening on the audio-visual terminal  101  can be easily compatible. Such superior feature exists. 
     In the embodiment the output medium is DVD-R but any medium can be applied such as removable HDD, SD card and an external drive device connected via 1394 standard. 
     Now the audio-visual terminal  102  and the storage terminal of the present invention can be realized by using one STB. Or any one of both terminals can be realized by STB. 
     And in the above embodiment the server  102  has such configuration that the each server is connected via LAN but such configuration can be realized that each server operates independently but the servers are cooperated with each other by the interface such as WEB API via internet. According to this configuration similar effect can be realized even under such case that for example functions of one or some servers among the servers are offered as ASP server by different enterprise. 
     Alternatively, the functions of the servers of the present invention can be realized by one server. 
     The program according to the present invention is the program for enabling the computer to perform the functions of each part of the system etc. of the present invention as described above, and operated in cooperation with the computer. 
     Also, a recording medium according to the present invention records the program for enabling the computer to perform the functions of each part of the system etc. of the present invention as described above, and is readable by the computer, whereby the read program performs the functions in cooperation with the computer. 
     In one use form of the program according to the present invention, the program may be recorded in the recording medium such as ROM readable by the computer, and operated in cooperation with the computer. 
     Also, in another use form of the program according to the present invention, the program may be transmitted across the network such as the Internet, or through the transmission media such as light, electric wave or sound wave, read by the computer and operated in cooperation with the computer. 
     Also, the computer according to the present invention described above is not limited to the pure hardware such as CPU, but may comprise a firmware, OS, or peripheral devices. 
     As described above, the configuration of the present invention may be implemented by software or hardware. 
     INDUSTRIAL UTILITY 
     According to the present invention such contents rental service can be realized that the image or audio contents are downloaded via a network, and they are permitted to be played back only within the expiration date. 
     Then the present invention has such remarkable merits that the user can view and listen to the contents downloaded to the audio-visual terminal having no storage device, the storage terminal which is not incorporate type, can be used as the download destination device, the playing back of the contents can be performed by the operation UI of the audio-visual terminal and by the operation UI of the storage terminal, and the downloaded contents can be viewed and listened to without providing DRM function for all terminals. Therefore it is useful for a system where AV contents are distributed and played back by using a network.