JP2005094481A - Content providing system, server device, and client terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent the illegal reproduction of pre-encrypted contents by an unspecified third party even if the contents are distributed to a client terminal. <P>SOLUTION: In the content providing system when the client terminal 2 executes the decoding of the contents distributed from a server device 1, if the distribution of the license is requested to the server device 1 and the license is received from the server device 1, the contents are decoded by using a decoding key included in the license and the license is discarded. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a content providing system, a server device, and a client terminal that prevent unauthorized reproduction of content by an unspecified third party.

For example, when a contract is established between an administrator of a server device and a client regarding the reproduction of content, the conventional content providing system distributes the content encrypted by the server device to the client terminal and distributes the content. The decryption key used at the time of decryption, the use conditions of the content (for example, the use period, the number of times of use) and the like are distributed to the client terminal.
The client terminal stores the content distributed from the server device, and stores its decryption key and usage conditions.
When the client terminal decrypts the content and satisfies the use conditions, the client terminal decrypts the content using the decryption key and reproduces the content (see, for example, Patent Document 1).

JP 2001-358706 A (paragraph numbers [0062] to [0063], FIG. 1)

  Since the conventional content providing system is configured as described above, the decryption key and use conditions used when decrypting the content are stored in the client terminal. For this reason, contrary to the intention of the administrator of the server device, a threat arises that an unspecified third party including the client changes the use conditions stored in the client terminal. When content usage conditions are illegally changed, for example, there is a problem that content is illegally reproduced beyond the usage period or the number of times that the content can be used.

  The present invention has been made to solve the above-described problems, and can reliably prevent unauthorized reproduction of content by an unspecified third party even when pre-encrypted content is distributed to client terminals. It is an object of the present invention to obtain a content providing system, a server device, and a client terminal that can be used.

  The content providing system according to the present invention requests the server device to distribute a decryption key when the client terminal decrypts the content distributed from the server device, and uses the decryption key when receiving the decryption key from the server device. The content is decrypted and the decryption key is discarded.

  According to the present invention, when the client terminal decrypts the content distributed from the server device, the client terminal requests the server device to distribute the decryption key, and receives the decryption key from the server device. Since the decryption key is decrypted and the decryption key is discarded, the decryption key must be distributed from the server device every time the client terminal performs the decryption processing of the content. Even if it is distributed to the client terminal, it is possible to reliably prevent unauthorized reproduction of content by an unspecified third party.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a content providing system according to Embodiment 1 of the present invention. In the figure, a server device 1 and a client terminal 2 are connected via a network 3 such as the Internet.
The key generation unit 11 of the server device 1 generates an encryption key used when encrypting content to be distributed, and generates a decryption key used when decrypting the encrypted content. The encryption unit 12 encrypts the content to be distributed using the encryption key generated by the key generation unit 11, and stores the encrypted content and the content ID for identifying the content in the content DB 13 as a package. . Hereinafter, the content stored in the content DB 13 is referred to as packaged content. The key generation unit 11 and the encryption unit 12 constitute an encryption unit.

The key DB 14 stores the decryption key generated by the key generation unit 11 and the content ID as a pair, and the usage condition DB 15 stores the usage conditions (for example, the usage period, the number of times of use, etc.) of the content encrypted by the encryption unit 12. ) And the content ID as a pair. The usage history DB 16 includes a license by the client terminal 2 (license: a decryption key stored in the key DB 14, a usage condition stored in the usage condition DB 15, and client information (the MAC address of the client terminal 2, CPU number, login user). Name, H / W identifier (SCSI, NIC, FDD, motherboard, etc.))). The key DB 14, the usage condition DB 15, the usage history DB 16, and the following license DB 20 constitute management means.
When the network I / F 18 receives a content distribution request from the client terminal 2, the content distribution unit 17 distributes the packaged content stored in the content DB 13 to the client terminal 2 via the network I / F 18. Is configured. The network I / F 18 includes a connection function for the network 3 and a communication function for transmitting and receiving data to and from the client terminal 2. The communication function may be a wired communication device or a wireless communication device.

  When the network I / F 18 receives a license distribution request from the client terminal 2, the license issuing unit 19 refers to the usage history stored in the usage history DB 16, and the client terminal 2 satisfies the usage conditions. As long as the license is issued, the license is distributed to the client terminal 2 via the network I / F 18. The license issuing unit 19 constitutes a key distribution unit, but a license distributed to the client terminal 2 is added with a license ID for identifying the license, and the license is stored in the license DB 20. The

In the server device 1, the content DB 13, the key DB 14, the usage condition DB 15, the usage history DB 16, and the license DB 20 may be configured on the internal memory or on the hard disk.
The key generation unit 11, the encryption unit 12, the content distribution unit 17, and the license issuance unit 19 may be configured by dedicated hardware such as an IC integrated circuit. It may be prepared and a CPU (not shown) of the server device 1 may execute the program.

The distribution request unit 31 of the client terminal 2 constitutes distribution request means for requesting distribution of contents and licenses via the network I / F 32. The network I / F 32 has a connection function for the network 3 and a communication function for transmitting and receiving data to and from the server device 1, and the communication function may be a wired communication device or a wireless communication device.
When the network I / F 32 receives the packaged content distributed from the server device 1, the content DB 33 constitutes content storage means for storing the packaged content.
When the network I / F 32 receives the license distributed from the server device 1, the content decrypting unit 34 decrypts the packaged content stored in the content DB 33 using the decryption key included in the license. Is configured.
When the decrypting process of the packaged content by the content decrypting unit 34 is completed, the license discarding unit 35 stores the license ID added to the license in the license ID DB 36 in a pair with the content ID, and then discards the license. It constitutes a disposal means.

In the client terminal 2, the content DB 33 and the license ID DB 36 may be configured on the internal memory or on the hard disk.
Further, the distribution request unit 31, the content decryption unit 34, and the license discard unit 35 may be configured by dedicated hardware such as an IC integrated circuit, for example, but a program describing these processing contents is prepared, and the client terminal Two CPUs (not shown) may execute the program.
FIG. 2 is a flowchart showing the processing contents of the server device 1, and FIGS. 3 and 4 are flowcharts showing the processing contents of the client terminal 2.

Next, the operation will be described.
The server device 1 encrypts the content permitted to be distributed in advance and stores the encrypted content in the content DB 13 in order to cope with the case where a content distribution request is received from the client terminal 2.
That is, the key generation unit 11 of the server device 1 generates an encryption key used when the encryption unit 12 encrypts the content and a decryption key used when the client terminal 2 decrypts the encrypted content. . As shown in FIG. 5, the key generation unit 11 stores the decryption key and the content ID in a pair in the key DB 14.
When the key generation unit 11 generates the encryption key, the encryption unit 12 of the server device 1 encrypts the content to be distributed using the encryption key, and stores the encrypted content and content ID in the content DB 13 as a package. save.
At this time, as shown in FIG. 6, the administrator of the server apparatus 1 sets the usage conditions (for example, usage period, usable frequency, etc.) of the content stored in the content DB 13 in combination with the content ID in the usage condition DB 15. save.

Next, when the client wishes to reproduce content that is not yet stored in the content DB 33 of the client terminal 2, a content distribution request is input by operating a keyboard or a mouse (not shown).
When a content distribution request is input (step ST21), the distribution request unit 31 of the client terminal 2 transmits a content distribution request to the server device 1 via the network I / F 32 (step ST22).
When the network I / F 18 receives a content distribution request from the client terminal 2 (step ST1), the content distribution unit 17 of the server device 1 extracts the packaged content from the content DB 13, and the package is transmitted via the network I / F 18. The distributed content is distributed to the client terminal 2 (step ST2).
Upon receiving the packaged content distributed from the server device 1, the network I / F 32 of the client terminal 2 stores the packaged content in the content DB 33 (step ST23).

When the packaged content is stored in the content DB 33, the distribution request unit 31 of the client terminal 2 extracts the content ID from the packaged content and searches the license ID DB 36 for a license ID corresponding to the content ID.
However, in this case, since the content has never been tried in the past and the license ID corresponding to the content ID is not registered in the license ID DB 36, the license ID corresponding to the content ID is not searched.
If the distribution request unit 31 of the client terminal 2 does not find a license ID corresponding to the content ID in this way, the distribution request unit 31 transmits a license distribution request attached with the content ID to the server device 1 via the network I / F 32. (Step ST24).

When the network I / F 18 receives a license distribution request from the client terminal 2 (step ST3), the license issuing unit 19 of the server apparatus 1 determines whether the ID attached to the distribution request is a content ID or a license ID. It is determined whether or not there is (step ST4).
In this example, since the content ID is attached to the distribution request, the processing contents when the content ID is attached will be described below. However, when the content reproduction is not started (second time, third time) ...), the license ID is attached to the distribution request.

When the content ID is attached to the license distribution request, the license issuing unit 19 determines whether the client terminal 2 satisfies the usage conditions (step ST5), and only when the usage conditions are satisfied. Then, a new license is issued that includes the decryption key stored in the key DB 14, the use conditions stored in the use condition DB 15, and the client information of the client terminal 2 (step ST6).
For example, if the usage condition DB 15 includes a usage period as a content usage condition, if the distribution request time from the client terminal 2 is within the usage period, it is determined that the usage condition is satisfied. Issue a new license.
Here, for convenience of explanation, the client information of the client terminal 2 is, for example, notified from the client to the administrator when the contract between the administrator and the client is negotiated, and is registered in the server device 1 by the administrator. And
However, the notification of the client information is not limited to when the contract is negotiated. For example, the client device 2 may notify the server device 1 when requesting issuance of a license.

When the client terminal 2 satisfies the use conditions and issues a license, the license issuing unit 19 distributes the license to the client terminal 2 via the network I / F 18 (step ST7). At this time, the license issuing unit 19 charges the client along with the license issuance (step ST8). For example, content usage fees are deducted from the client's bank account described in a contract agreed between the administrator and the client.
A license ID for identifying the license is added to the license distributed to the client terminal 2, and the license is stored in the license DB 20.

When the network I / F 32 receives the license distributed from the server device 1 (step ST25), the content decrypting unit 34 of the client terminal 2 is stored in the content DB 33 using the decryption key included in the license. The packaged content is decrypted (step ST26).
However, if the client information included in the license does not match your client information, there is a possibility that the license has been sent by an unauthorized person. Not implemented.

  When the content decryption unit 34 of the client terminal 2 completes the decryption of the content, the content decryption unit 34 reproduces the content (step ST27). However, if the usage conditions included in the license include items related to function restrictions (for example, printing is not possible, playback functions (for example, fast forward, rewind, pause, etc.) are not possible) The content is reproduced within the range of the function restriction. That is, even if a request for performing an item related to function restriction is received from a client during content reproduction, the request is rejected.

When the decrypting process of the packaged content by the content decrypting unit 34 is completed, the license discarding unit 35 of the client terminal 2 pairs the license ID added to the license with the content ID in preparation for the next content playback request. And stored in the license ID DB 36 (step ST28).
Further, in order to eliminate threats such as changing usage conditions by storing the license in the memory of the client terminal 2, when the decryption process is completed, the license is discarded (step ST29).

Next, when the client wishes to reproduce the content already stored in the content DB 33 of the client terminal 2 (when the content has been reproduced in the past), the operation is performed by operating a keyboard or mouse (not shown). Specify the desired content.
When the content to be reproduced is designated (step ST31), the distribution request unit 31 of the client terminal 2 reads the designated content from the content DB 33, extracts the content ID from the content, and obtains a license corresponding to the content ID. The ID is searched from the license ID DB 36 (step ST32).
When a license ID corresponding to the content ID is found, the distribution request unit 31 transmits a license distribution request attached with the license ID to the server device 1 via the network I / F 32 (step ST33).

When the network I / F 18 receives a license distribution request from the client terminal 2 (step ST3), the license issuing unit 19 of the server apparatus 1 determines whether the ID attached to the distribution request is a content ID or a license ID. It is determined whether or not there is (step ST4).
In this example, since the license ID is attached to the distribution request, processing contents when the license ID is attached will be described below.

When the license ID is attached to the license distribution request, the license issuing unit 19 searches the license stored in the license DB 20 for the license to which the license ID is added (step ST9).
When the license issuing unit 19 finds a license to which the license ID is added, the license issuing unit 19 determines whether the client terminal 2 satisfies the usage conditions included in the license (step ST10).
For example, when a usage period is included as a usage condition for content, if the timing of a distribution request from the client terminal 2 is within the usage period, it is determined that the usage condition is satisfied.
Further, when the usage count of content includes the usage count, the usage history of the client terminal 2 stored in the usage history DB 16 is referred to, and the past usage count of the client terminal 2 is determined as the usage count. If not, it is determined that the use condition is satisfied (see FIG. 7). For example, when the number of times of use is “30” and the number of times of use history of the client terminal 2 is “29” or less, it is determined that the use condition is satisfied.

When the license issuing unit 19 determines that the client terminal 2 satisfies the use conditions, the license issuing unit 19 distributes the searched license to the client terminal 2 via the network I / F 18 (step ST11).
Further, the license issuing unit 19 increments the usage history count of the client terminal 2 stored in the usage history DB 16 by “1” (step ST12). However, the initial value of the usage history count of the client terminal 2 is “0”.
If the client terminal 2 cannot satisfy the usage conditions, the license issuing unit 19 deletes the license including the usage conditions and deletes information related to the license in the usage history DB. Thereby, an increase in search data can be suppressed and an efficient search can be performed. Alternatively, the license usage conditions stored in the license DB 20 may be periodically checked, and licenses that can no longer satisfy the usage conditions may be deleted.
Incidentally, if the license issuing unit 19 cannot find the license to which the license ID is added, it is highly likely that the license is issued from an unauthorized person, and therefore, the license issuing unit 19 does not perform the license distribution process.

When the network I / F 32 receives the license distributed from the server device 1 (step ST34), the content decrypting unit 34 of the client terminal 2 is stored in the content DB 33 using the decryption key included in the license. The packaged content is decrypted (step ST35).
However, if the client information included in the license does not match your client information, there is a possibility that the license has been sent by an unauthorized person. Not implemented.

When the content decryption unit 34 of the client terminal 2 completes the decryption of the content, the content decryption unit 34 reproduces the content (step ST36). However, if the usage conditions included in the license include an item regarding function restriction, the content is reproduced within the scope of the function restriction. That is, even if a request for performing an item related to function restriction is received from a client during content reproduction, the request is rejected.
For example, when there is a printable number of times as a function restriction, the printable number of times and the print history number are recorded in the usage history DB 16 for each license ID (see FIG. 8), and the print history number reaches the printable number of times. The content print request is permitted only until. The initial value of the print history count is set to “0”, and the license issuing unit 19 increments the print history count stored in the usage history DB 16 by “1” every time a content print request is received from the client.
The license discarding unit 35 of the client terminal 2 discards the license when the decryption processing of the packaged content by the content decrypting unit 34 is completed (step ST37).

As is apparent from the above, according to the first embodiment, when the client terminal 2 decrypts the content distributed from the server device 1, the server device 1 is requested to distribute the license, and the license is transmitted from the server device 1. Since the content is decrypted using the decryption key included in the license and the license is discarded, each time the client terminal 2 performs the content decryption process, the server device 1 The license can be distributed from the client, and even if the pre-encrypted content is distributed to the client terminal 2, it is possible to reliably prevent unauthorized reproduction of the content by an unspecified third party. Play. In other words, contrary to the intention of the administrator of the server device 1, there is an effect that it is possible to eliminate threats such as an unspecified third party including the client rewriting the contents of the license.
Further, according to the first embodiment, since the license is distributed to the client terminal 2 only when the client terminal 2 satisfies the content usage conditions, the client terminal 2 that does not satisfy the usage conditions. It is possible to reliably prevent the use of content in

  In the first embodiment, when the distribution request unit 31 of the client terminal 2 requests the distribution of the license, the content request or the license ID is attached to the distribution request. However, as the license distribution request, A license distribution request accompanied by a new issue or an issued license distribution request may be transmitted to the server apparatus 1.

Embodiment 2. FIG.
In the first embodiment, the content usage conditions include the usage period and the number of times that the content can be used. However, the present invention is not limited to this, and for example, the following items are included as the content usage conditions: You may do it.

Items to include as content usage conditions ・ Printability ・ Number of printable times ・ Printable devices (Only xxx printers can be output)
・ Printed page number ・ Number of printed pages ・ Editability ・ Changeability ・ Additional information ・ Partial information availability (Cut function)
・ Zoom magnification ・ Image reduction / enlargement function ・ Possibility of individual playback functions (for example, stop, rewind, fast forward, etc. for video and music) ・ Number of playback functions (for example, stop for video and music, Rewind, fast forward, etc.)
Available user type information (for example, administrator authority, general user, guest, etc.)
-Available user information (for example, a user whose account name is abc)
-Available terminal information (for example, MAC address is xxx, CPU number is yyy, host name is zzz, IP address is ppp, etc.)
・ Saveable device information (can be saved only in model number xxx)
・ Displayable device information (displayable only for model number xxx)
・ License validity period

Therefore, the license issuing unit 19 of the server device 1 is equipped with a control function in which the client terminal 2 satisfies the functional condition when the content usage condition includes a functional condition such as the Cut function. However, it may be determined that the client terminal 2 satisfies the usage conditions.
Thereby, in order to use the content, for example, when it is necessary to implement the Cut function, the license can be distributed only to the client terminal 2 having such a control function. become able to.
Incidentally, the content decrypting unit 34 side of the client terminal 2 also assumes that the usage conditions are satisfied from the server device 1, and when the license distribution is received, the control function that satisfies the functional conditions such as the Cut function is applied by itself. It is determined whether the content is installed, and the content is decrypted and reproduced only when the control function is installed.
In other words, the client terminal 2 (an application running on the client terminal 2) controls its own processing according to the function condition control function described in the use condition. For example, in the case of a license in which the Cut function cannot be used, the client terminal 2 presents the user with the Cut function disabled.

Embodiment 3 FIG.
In the first embodiment, the initial value of the usage history count of the client terminal 2 is set to “0”, and the license issuing unit 19 is stored in the usage history DB 16 every time a license distribution request is received from the client terminal 2. In this example, the usage history count of the client terminal 2 is incremented by “1”, but the remaining usage count (= usable count) of the client terminal 2 is set as the usage history of the client terminal 2 as shown in FIG. Then, every time a license distribution request is received from the client terminal 2, the license issuing unit 19 may decrement the remaining usage count of the client terminal 2 stored in the usage history DB 16 by “1”.

Embodiment 4 FIG.
FIG. 10 is a block diagram showing a content providing system according to Embodiment 4 of the present invention. In the figure, the same reference numerals as those in FIG.
The license changing unit 21 constitutes a changing unit that changes the use conditions of the contents constituting the license stored in the license DB 20.

In the first embodiment, the license issuing unit 19 issues a license composed of the decryption key stored in the key DB 14, the use conditions stored in the use condition DB 15, and the client information of the client terminal 2, Although the license stored in the license DB 20 has been shown, the license changing unit 21 may change the use conditions of the contents constituting the license stored in the license DB 20.
As a result, after the license issuing unit 19 issues a license, it is possible to change the usage conditions of the content as necessary without performing processing such as reissuing the license.

For example, when it is necessary to extend the usage period of some clients, the license changing unit 21 can cope with it by changing the usage conditions of some clients. When such a license changing unit 21 does not exist, a request for extension of the usage period is transmitted from the client terminal 2 to the server device 1, the license issued previously by the server device 1 is deleted, and a new license is issued It is necessary to perform complicated processing such as.
According to the fourth embodiment, after the license is issued, there is an effect that the usage conditions can be easily changed as necessary.

Embodiment 5 FIG.
In the first embodiment, the license issuing unit 19 of the server device 1 distributes the license to the client terminal 2 via the network I / F 18 only when the client terminal 2 satisfies the usage conditions. However, when the license issuance unit 19 distributes the license to the client terminal 2, the license version (= use condition version) stored in the license DB and the version of the license that the client terminal 2 can handle (= The usage conditions may be changed according to the comparison result. However, the version of the license that can be supported by the client terminal 2 is notified to the server device 1 when, for example, a license distribution request is made.

For example, if the version of the license that the client terminal 2 can handle is newer than the version of the license stored in the license DB, when the client terminal 2 is distributed a license stored in the license DB, use of the license Content can be played according to conditions.
However, if the version of the license that can be handled by the client terminal 2 is older than the version of the license stored in the license DB, the license is used when the license stored in the license DB is distributed to the client terminal 2. Content may not be played according to conditions.
Therefore, in such a case, the contents of the license stored in the license DB are changed to the extent that the client terminal 2 can cope, and the license is distributed to the client terminal 2. For example, the use conditions are changed so that the client terminal 2 can use a printer or a display device that can be used.

As another example, when the license version that the client terminal 2 can handle is older than the license version stored in the license DB, the license version stored in the license DB In the version of the license that the client terminal 2 can handle, the license number to be distributed to the client terminal 2 is set so that the number of usable times is one when the license number is compatible with the client terminal 2. Change usage conditions.
Further, when the version of the license that can be supported by the client terminal 2 is newer than the version of the license stored in the license DB, the license version stored in the license DB can be “printable / non-printable”. If the version of the license that the client terminal 2 can handle is “cannot be set to print”, the usage conditions of the license distributed to the client terminal 2 are changed so that printing is not possible .
According to the fifth embodiment, for example, the processing content of the client terminal 2 can be changed according to the function of the client terminal 2 and the like.

Embodiment 6 FIG.
In the first embodiment, the license issuing unit 19 distributes the license to the client terminal 2 if the client terminal 2 satisfies the use conditions. However, the client terminal 2 is listed in the non-distributable user list. If so, the license issuing unit 19 may refuse to distribute the license.
Specifically, when a non-distributable user list in which client information of users who are not permitted to be distributed is listed and the license issuing unit 19 distributes the license to the client terminal 2, the client information of the client terminal 2 is stored. If it is listed in the non-distributable user list, distribution of the license to the client terminal 2 is rejected.
As a result, even if the license issuance unit 19 issues a license once, if it is subsequently determined that the license issuance destination is an unauthorized person or a device, then the license distribution to the client terminal 2 is refused. As a result, the content can be prevented from being reproduced.

It is a block diagram which shows the content provision system by Embodiment 1 of this invention. It is a flowchart which shows the processing content of a server apparatus. It is a flowchart which shows the processing content of a client terminal. It is a flowchart which shows the processing content of a client terminal. It is explanatory drawing which shows the correspondence of content ID and a decryption key. It is explanatory drawing which shows the utilization conditions of a content. It is explanatory drawing which shows the usage log | history count etc. FIG. It is explanatory drawing which shows the printing history frequency etc. FIG. It is explanatory drawing which shows the frequency | count of remaining utilization. It is a block diagram which shows the content provision system by Embodiment 4 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Server apparatus, 2 Client terminal, 3 Network, 11 Key generation part (encryption means), 12 Encryption part (encryption means), 13 Content DB, 14 Key DB (management means), 15 Usage condition DB (management means) ), 16 usage history DB (management means), 17 content distribution section (content distribution means), 18 network I / F, 19 license issuing section (key distribution means), 20 license DB (management means), 21 license change section ( Change means), 31 distribution request section (distribution request means), 32 network I / F, 33 content DB (content storage means), 34 content decryption section (decryption means), 35 license discard section (key discard means), 36 licenses IDDB.

Claims (13)

  While encrypting the content and distributing the encrypted content, the server device that manages the decryption key used when decrypting the content, and the decryption key distribution when decrypting the content distributed from the server device And a client terminal that decrypts the content using the decryption key when the decryption key is received from the server device and discards the decryption key.   2. The content providing system according to claim 1, wherein the server device distributes the decryption key to the client terminal only when the client terminal satisfies the content use condition.   An encryption unit for encrypting content, a content distribution unit for distributing the content encrypted by the encryption unit to a client terminal, and a decryption key used when decrypting the content encrypted by the encryption unit Management means for managing the usage conditions of the content, and upon receiving a decryption key distribution request from the client terminal, the management means manages only when the client terminal satisfies the usage conditions A server device comprising: key distribution means for distributing the decryption key being distributed to the client terminal.   The key distribution means distributes the decryption key to the client terminal if the period of use of the content is included in the use condition of the content and the distribution request time from the client terminal is within the use period. The server device according to claim 3.   When the content usage conditions include the number of times that the content can be used, the key distribution means assigns the decryption key to the client if the past usage count of the client terminal has not yet reached the usage count. 4. The server device according to claim 3, wherein the server device is distributed to a terminal.   The key distribution means distributes the decryption key to the client terminal if the client terminal has a control function that satisfies the functional condition when the content usage condition includes the functional condition. The server device according to claim 3, wherein   4. The server apparatus according to claim 3, further comprising changing means for changing a use condition of contents managed by the management means.   The key distribution means compares the version of the usage conditions managed by the management means with the version of the usage conditions that can be handled by the client terminal, and changes the usage conditions according to the comparison result. Item 4. The server device according to Item 3.   The key distribution means rejects the distribution of the decryption key managed by the management means when the client terminal is listed in the non-distributable user list in which users who are not permitted to be distributed are listed. 3. The server device according to 3.   Content storage means for storing the content distributed from the server apparatus, distribution request means for requesting the server apparatus to distribute a decryption key used for decrypting the content stored in the content storage means, and decryption from the server apparatus A client terminal comprising: a decryption unit that decrypts the content using the decryption key when the key is distributed; and a key discard unit that discards the decryption key when the decryption processing of the content by the decryption unit is completed.   11. The client terminal according to claim 10, wherein when the use condition is distributed from the server device, the decrypting means reproduces the content within a function restriction range included in the use condition.   12. The client terminal according to claim 11, wherein when discarding the decryption key, the key discarding unit discards the usage conditions distributed from the server device.   When the client information is distributed from the server device, the decrypting means decrypts the content using the decryption key distributed from the server device only when the client information is its own client information. The client terminal according to claim 10.

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