JP2008123021A - Digital information sharing system, digital information sharing server, terminal equipment, and digital information sharing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital information sharing system, a digital information sharing server, terminal equipment and a digital information sharing method for preventing the leakage of digital information to any user other than a specific user with whom digital information is shared by managing the use circumstances of digital information. <P>SOLUTION: A client terminal 3 transmits the condition data of the automatic erasure of digital information to be shared with the other client terminal 3 and digital information to a server 2, and an information control part 7 of the server 2 associates the conditions of the automatic erasure of the digital information with the digital information for management, and stores the digital information in an information storage part 6. When judging that the digital information is matched with the conditions of the automatic erasure, the information control part 7 erases the digital information. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a system for sharing digital information via a network.

  In general, in information sharing via networks, especially the Internet, leakage of personal information, eavesdropping such as unauthorized access to digital information, tampering such as deletion of digital information due to Internet viruses, unauthorized distribution, etc. are serious problems. .

  On the other hand, access control by proxy server (Proxy Server), public key cryptosystem such as RSA (Rivest Shamir Adleman), elliptic curve cryptography, DES (Data Encryption Standard), AES (Advanced Encryption Standard) common key Scheme, SSL (Secure Socket Layer) that combines public key cryptography and common key cryptography, etc., a standard for performing encrypted communications over the Internet, and IPsec (Security Architecture) that encrypts and transmits IP (Internet Protocol) packets security system using advanced encryption technology such as for Internet Protocol) A certain level of safety is ensured by the stem.

Also, when managing personal information, the personal information data is divided and stored in two in the database of the two certificate authorities, and when there is a request for acquisition of the personal information data, the divided personal information data is combined. A technique for restoring and providing is disclosed (for example, see Patent Document 1).
JP 2003-46500 A

  However, for example, in an information sharing environment using a PC (Personal Computer) placed in a general home as a server, supporting an advanced security system as described in Patent Document 1 is costly and maintenance-friendly. It cannot be easily realized by a point.

  In addition, information sharing within a limited range is highly likely to be personal information, and it is desired to avoid leakage of information, and it is necessary to ensure high safety easily.

  In addition, when sharing information under the control of an external server, management such as deletion of information is necessary and forgotten, such as when the useful value of digital information decreases after a certain period of time. When this happens, the risk of information leakage increases.

  In view of such circumstances, the present invention manages the usage status of digital information in order to prevent leakage of digital information, and can prevent information from leaking to other than a specific user who shares the digital information. An object is to provide a digital information sharing system, a digital information sharing server, a terminal device, and a digital information sharing method.

In view of such a situation, the digital information sharing system according to the first aspect of the present invention manages digital information shared between the terminal devices by the server and a plurality of terminal devices transmitting and receiving digital information via a network. A digital information sharing system that
The terminal device transmits the digital information and condition data for automatic deletion of the digital information to the server, and the server receives the digital information and condition data for automatic deletion of the digital information, and If it is determined that the deletion condition is met, the digital information is deleted.

A digital information sharing server according to a second invention is a digital information sharing server that transmits and receives digital information to and from a plurality of terminal devices via a network, and manages digital information shared between the terminal devices.
A communication control unit that receives the digital information and condition data for automatic deletion of the digital information from the terminal device; an information control unit that associates and manages the digital information and conditions for automatic deletion of the digital information; and the digital An information storage unit for storing information, and when the information control unit determines that the conditions for the automatic deletion are met, the digital information is deleted from the information storage unit.

  According to a third aspect of the present invention, there is provided a digital information sharing server including a user management unit that manages the terminal device and a user who uses the terminal device for each group, and the automatic deletion condition permits access to the digital information. All the given terminal devices download the digital information, and the information control unit refers to the user management unit to determine whether or not the automatic deletion condition is met. And

  According to a fourth aspect of the present invention, there is provided a digital information sharing server in which a terminal device whose automatic deletion condition is not registered to permit the user management unit to access the digital information is to access the digital information. It is characterized by that.

  According to a fifth aspect of the present invention, there is provided a digital information sharing server comprising an encryption unit for encrypting the digital information, wherein the terminal device is encrypted and transmitted, and access to the digital information is permitted. An encryption key capable of decrypting the encrypted digital information is transmitted only to the terminal device.

  In the digital information sharing server according to the sixth invention, when the information control unit automatically deletes the digital information, the digital information sharing server notifies the terminal device that has shared the digital information of the deletion. It is characterized by.

A terminal device according to a seventh invention is a terminal device that transmits and receives digital information to and from a server via a network, and manages digital information shared between the terminal devices by the server,
A main control unit that generates condition data for automatic deletion of the digital information, and a communication control unit that transmits the digital information and the condition data for automatic deletion.

According to an eighth aspect of the present invention, there is provided a terminal device comprising an encryption unit for decrypting encrypted data,
The communication control unit receives the encrypted digital information and encryption key, and the encryption unit decrypts the digital information with the encryption key.

  The terminal device according to the ninth invention is characterized in that the automatic deletion condition data includes designation of a user who shares the digital information.

According to a tenth aspect of the present invention, there is provided a digital information sharing method that allows a server and a plurality of terminal devices to transmit and receive digital information via a network, thereby allowing the server to manage digital information shared between the terminal devices. A digital information sharing method,
Causing the terminal device to execute a step of transmitting condition data for automatic deletion of the digital information to the server, and a step of transmitting the digital information;
Determining whether or not the digital data automatic deletion condition data and the digital information are received by the server, the automatic deletion condition and the digital information are associated with each other, and whether or not the automatic deletion condition is satisfied. A step, and a step of deleting the digital information when it is determined that the condition of the automatic deletion is met.

According to an eleventh aspect of the present invention, there is provided a digital information sharing method comprising: encrypting the digital information to the server; transmitting the encrypted digital information to the terminal apparatus; and the access permitted terminal apparatus Sending the encryption key only to
The terminal device is configured to execute a step of receiving the encrypted digital information and the encryption key, and a step of decrypting the encrypted digital information with the encryption key.

  As described above, in the system for sharing digital information via the network according to the present invention, setting conditions for automatic deletion of the digital information in the server storing the digital information to be shared If this condition is met, the digital information is automatically deleted, so that confidential information can be easily managed.

  The conditions for automatic deletion can be set by the user who provided the information. For example, if the digital information is automatically deleted after a certain period of time, information maintenance can be performed thereafter. Since there is no need to perform the automatic deletion and the automatic deletion is performed, there is no fear of subsequent information leakage, and a free memory area can be secured. Alternatively, conditions can be set as appropriate according to the importance of the provided information, which increases the convenience for the user.

  In addition, in order to prevent leakage of digital information, the usage status of digital information is managed, it is determined that it has been used, and for digital information that has been used, the digital information itself is automatically deleted, Information can be prevented from leaking to non-specific users who share digital information, and it is not necessary to perform maintenance of information after digital information is deleted. Furthermore, a free memory area can be secured.

  In addition, when digital information shared by other than the specific user is accessed, it is possible to prevent information leakage by forcibly erasing the digital information. At this time, it may be possible to notify a specific user that it has been forcibly erased by e-mail or the like. This allows the user who provided the information to provide digital information again, which is convenient for the user. Increase.

  Further, when the digital information is downloaded, it is automatically encrypted, and when the download is performed by a specific user who is permitted to use the digital information, the digital information is decrypted. By separately providing an encryption key for the user, the digital information can be decrypted only by a user who is permitted to browse, and safety can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[First Embodiment]
First, as an embodiment of a digital information sharing system according to the present invention, a system for sharing information between a server and a client via a network will be described as an example.
FIG. 1 is a block diagram showing an outline of a digital information sharing system in the first embodiment.

  As shown in FIG. 1, in a digital information sharing system 1, a server 2 and a plurality of client terminals 3 are connected via a network 4. The network 4 may be wired or wireless.

  The server 2 includes a user management unit 5 that manages a specific user registered in advance, an information storage unit 6 that holds digital information shared within the specific user, and a relationship between the specific user information and the digital information. An information control unit 7 that performs control such as management and a communication control unit 8 are included.

  The client terminal 3a is a terminal used by a user, a communication control unit 9 that controls communication with the server 2, a main control unit 10 that controls each unit, a key input unit 11 that performs operations of the client terminal 3a, and the like. A video input unit 12 having a camera function and the like, and a display unit 13 for displaying digital information and the like are included.

  The client terminal 3b, the client terminal 3c, ..., the client terminal 3i are used by the user Ub, the user Uc, ..., the user Ui, respectively, and have the same configuration as the client terminal 3a.

  Information regarding the client terminal 3a to the client terminal 3i is assumed to be associated with the user Ui to the user Ui in the user management unit 5 of the server 2 and managed as a specific user group registered in advance.

  Communication between the server 2 and the client terminal 3 is performed via the respective communication control units 8 and 9, and any communication means such as wired communication or wireless communication may be used.

  Here, as an example of use of the present invention, a case will be described in which the user Ua provides information on an image captured by the video input unit 12 to other users included in a specific user group.

  FIG. 2 is a flowchart illustrating a procedure until the image captured by the user Ua is stored in the server 2.

  For example, the user Ua inputs an image captured by a video camera or the like from the video input unit 12 via a USB or the like. Then, the user Ua selects provision of digital information from the menu of the client terminal 3a. When a command for providing digital information is selected, the main control unit 10 displays a list of digital information input so far on the display unit 13.

  First, as shown in FIG. 2, in S11, the user Ua performs input for selecting information to be provided from the key input unit 11 of the client terminal 3a. When this input is performed, the main control unit 10 displays on the display unit 13 a screen that allows the user Ua to select whether or not to set an automatic deletion condition for the selected provision information.

  In S12, the main control unit 10 determines whether or not the user Ua has made an input for setting the automatic deletion condition from the key input unit 11. When the main control unit 10 determines that an input for setting the automatic deletion condition has been performed, the process proceeds to “Yes” and proceeds to the process of S13. When the main control unit 10 determines that the input for setting the automatic deletion condition has not been performed, the process proceeds to “No”, and in S14, the main control unit 10 performs “automatic deletion setting” via the communication control unit 9. The message is transmitted to the server 2 as “none”. As a case where the automatic deletion setting is not performed, it can be assumed that the provided information is information that does not cause a problem even if leaked to the outside. Here, when the server 2 receives a message indicating no automatic deletion setting, for example, the information control unit 7 of the server 2 forcibly sets an expiration date for storage of the provided information, and is a member of a specific user group. If the registered client terminal 3 is notified that it can be viewed only within a predetermined period, and if the provision information is deleted after the set expiration date has passed, the information storage unit 6 of the server Can be used efficiently.

  If it is determined in S12 that the automatic deletion condition setting has been input, the main control unit 10 of the client terminal 3a generates a deletion condition setting message in S13. Here, the following example can be considered as the setting of the automatic deletion condition. For example, the provision information has an expiration date, and the provision information is automatically deleted when the expiration date has passed, or all other users included in a specific user group have downloaded the provision information There are settings that are automatically deleted by, and settings that force deletion when data is accessed by an unauthorized user not included in a specific user group.

  In S14, when performing the automatic deletion setting, the main control unit 10 of the client terminal 3a sends a message including condition data about the automatic deletion setting via the communication control units 8 and 9 of the server 2 and the client terminal 3a. The condition data is temporarily stored in the information control unit 7 and controlled.

  Next, in S15, the main control unit 10 of the client terminal 3a sends the provided information selected in S11 to the information control unit 7 of the server 2 via the server 2 and the communication control units 8 and 9 of the client terminal 3a. The information control unit 7 stores the received provision information and the automatic deletion condition data received in S14 so as to be associated with each other, and stores them in the information storage unit 6.

Next, in S16, the information control unit 7 of the server 2 recognizes the user group including the user Ua from the user information of the transmission source included in the condition data with reference to the user management unit 5, and performs user management in advance. Notifying members of a specific user group registered in the section 5 that the shared information has been stored. For example, the user management unit 5 also registers the user's e-mail address, and the information control unit 7 acquires the address of a specific user group from the user management unit 5 and stores the shared information by e-mail. May be notified.
Up to this point, a member of a specific user group including the user Ua recognizes that the provision information from the user Ua is stored in the server 2.

  Next, a description will be given of the provision information stored in the server with the automatic deletion condition from the client terminal 3a until it is deleted after satisfying the automatic deletion condition.

  FIG. 3 is a flowchart showing a procedure until the provision information is deleted by the server 2 after satisfying the automatic deletion condition.

  Here, conditions for automatic deletion from the client terminal 3a include, for example, that the provision information has been downloaded by all users other than the user Ua belonging to the specific user group, and that the provision information is accessed from other than the specific user group. The description will be made assuming that this is set.

  First, S <b> 21 indicates a waiting state for communication access to the communication control unit 8 in the information control unit 7 of the server 2. For example, the user Ub performs an operation via the key input unit 11 of the client terminal 3b, and the main control unit 10 of the client terminal 3b transmits a provision information acquisition request message from the communication control unit 9 to the server 2. And The information control unit 7 of the server 2 detects the access from the client terminal 3b, and the flow proceeds to S22. In step S22, the information control unit 7 first refers to the user management unit 5 to determine whether the client terminal 3b is a client terminal belonging to the same group as the client terminal 3a registered in the user management unit 5. Make a decision. When it is determined that the client terminal 3b is a user terminal belonging to a specific group, the information control unit 7 proceeds to S23 and permits the client terminal 3b to download. When downloading by the client terminal 3b is completed, the flag for the client terminal 3b of the provided information in the information storage unit 6 is updated as downloaded.

  Next, in S24, the information control unit 7 verifies whether or not all the other client terminals 3 belonging to the specific user group other than the client terminal 3a have downloaded the provided information with reference to the flag of the information storage unit 6. . Since the flag has already been downloaded only for the client terminal 3b, the flow of S24 proceeds to “No”, and the information control unit 7 enters the next access waiting state in S21.

  Here, the client terminal 3a belongs to the specific group as the client terminal 3i, and all the client terminals 3 other than the client terminal 3a from the client terminal 3b to the client terminal 3i complete the download via S23, and the information storage It is assumed that all the flags indicating whether or not the part 6 has been downloaded are already downloaded.

  The information control unit 7 recognizes that the client terminal 3 belonging to the specific user group other than the client terminal 3a has downloaded the provided information in the determination of S24, proceeds to “Yes”, and stores the information in S25. The provision information from the client terminal 3a stored in the unit 6 is deleted.

  Next, in S26, the client U3 is notified to all client terminals 3 of the specific user group that the information provided by the user Ua has been successfully transmitted to the users belonging to the specific user group and then deleted. Thereby, all users belonging to the specific user group can know that there is no possibility of subsequent leakage of information about the provided information.

  With the above configuration, in order to prevent leakage of digital information, the usage status of digital information is managed to determine that it has been used, and for digital information that has been used, digital information By automatically deleting itself, it is possible to prevent information from leaking to non-specific users who share digital information, eliminating the need for maintenance of information after digital information deletion, and free memory space Can also be secured.

  Also, the conditions for automatic deletion can be set by the user who provided the information, and the conditions can be set as appropriate according to the importance of the provided information, increasing the convenience for the user.

  Here, in the determination in S22, if it is determined that the user who accesses the server 2 is a user other than the specific user group, that is, if unauthorized access is made, the process proceeds to “No”, and S25 is performed. The information control unit 7 deletes the provided information from the information storage unit 6 and performs automatic deletion. At this time, all the users may be notified by e-mail or the like that the provided information has been forcibly deleted due to unauthorized access. This makes it possible to take measures such as re-providing information shared by the specific user group from the user Ua thereafter.

  With the above configuration, when digital information shared by other than the specific user is accessed, it is possible to prevent information leakage by forcibly erasing the digital information. .

[Second Embodiment]
Next, an embodiment in which the provided information is encrypted when the provided information is downloaded from the server will be described.
FIG. 4 is a block diagram showing an outline of the digital information sharing system 21 in the second embodiment.

  The server 22 includes a user management unit 5, an information storage unit 6, an information control unit 7, and a communication control unit 8, similar to the server 2 of the first embodiment. It is a point to have.

  The client 23a is a terminal used by the user Ua, and includes the communication control unit 9, the main control unit 10, the key input unit 11, the video input unit 12, and the display unit 13, like the client terminal 3 of the first embodiment. The difference from the client terminal 3 is that it includes an encryption unit 25 that decrypts encrypted information.

  The client terminal 23b, the client terminal 23c,..., And the client terminal 23i are used by the user Ub, the user Uc,..., And the user Ui, respectively, and have the same configuration as the client terminal 23a.

  Information regarding the client terminal 23a to the client terminal 23i is assumed to be managed as a specific user group registered in advance in the user management unit 5 of the server 22 in association with the user Ui to the user Ui.

  Communication between the server 22 and the client terminal 23 is performed via the respective communication control units 8 and 9, and any communication means such as wired communication and wireless communication may be used.

  Here, as an example of use of the present invention, a case will be described in which the user Ua provides information on an image captured by the video input unit 12 to other users included in a specific user group. Since the procedure until the image captured by the user Ua is stored in the server 22 is the same as that in the first embodiment, the description thereof is omitted.

  FIG. 5 is a flowchart showing a procedure until the provision information is deleted by the server 22 after the automatic deletion condition is satisfied for the provided information.

  Here, the condition for automatic deletion by the client terminal 23a is that provision information has been downloaded by all client terminals 23 belonging to a specific user group other than the client terminal 23a.

  First, as shown in FIG. 5, S 31 indicates a waiting state for communication access to the communication control unit 8 in the information control unit 7 of the server 22. For example, the user Ub performs an operation via the key input unit 11 of the client terminal 23b, and the main control unit 10 of the client terminal 23b transmits a provision information acquisition request message from the communication control unit 9 to the server 22. And The information control unit 7 of the server 22 detects an access from the client terminal 3b, and the flow proceeds to S32.

  In S32, the information control unit 7 of the server 22 controls the encryption unit 24 to perform encryption processing on the provided information when downloading from the client terminal 23b. The encryption key used for the encryption process of the provided information is general and is not particularly limited. However, in consideration of the time required for the encryption / decryption processing, it is desirable that the encryption processing is a common key cryptosystem.

  The encrypted provision information is downloaded to the terminal used by the user Ub and the client terminal 23b, but the user Ub cannot see the information because there is no encryption key for decrypting the provision information at this time.

In next S33, the information control unit 7 of the server 22 refers to the user management unit 5 and determines whether or not the client terminal 23b is registered as the client terminal 23 of the specific user group to which the client terminal 23a belongs. Do. When it is determined that the client terminal 23b is registered as a specific user group in the user management unit 5 and is determined to be applicable, the process proceeds to S34, and the information control unit 7 obtains the encryption key used for encrypting the provided information from the encryption unit 24 Obtain and send to the client terminal 23b. Alternatively, for example, an arbitrary character string called a random seed may be generated and transmitted as a generated value for generating the common key.
The encryption key is encrypted to prevent eavesdropping by a third party. For example, it may be encrypted with the public key of the client terminal 23b by a public key cryptosystem. When the transmission of the encryption key to the client terminal 23b is completed, the information control unit 7 updates the flag for the client terminal 3b of the provided information in the information storage unit 6 as downloaded.

  When receiving the encryption key from the server 22, the communication control unit 9 of the client terminal 23 b outputs the received encryption key to the encryption unit 25. In the encryption unit 25, for example, when the encryption key is encrypted by the public key encryption method described above, the encryption key in the encrypted state is decrypted with the private key of the client terminal 23b, and is obtained by decryption. The encrypted provided information is decrypted with the encryption key, the provided information is displayed on the display unit 13, and the user Ub can view the provided information.

  Here, when the provided information is downloaded at the client terminal 23 other than the specific user group at S32, that is, at S33, the information control unit 7 of the server 22 refers to the user management unit 5 and is illegal. If it is determined that access has been made, the process proceeds to “No”, returns to S31, and enters the next access waiting state. At this time, the unauthorized user who downloaded the provision information cannot obtain the encryption key and cannot decrypt the provision information encrypted, and therefore cannot view the provision information.

  Following the process of transmitting the encryption key in S34 to the client terminal 23b, in S35, the information control unit 7 determines whether or not all the other client terminals 23 in the specific user group have downloaded the provided information. Verify by referring to the flags. Since only the flag for the client terminal 23b is “downloaded” at the present time, the process proceeds to “No” and waits for the next access in S31.

  In the determination of S35, assuming that the specific group to which the client terminal 23a belongs is the client terminal 23a to the client terminal 23i, all the client terminals 23 belonging to the specific user group other than the client terminal 23a from the client terminal 23b to the client terminal 23i are S34. Suppose that the download of the provided information is completed via. In S35, the information control unit 7 refers to the flag of the information storage unit 6 and recognizes that the flags for all the client terminals 23 belonging to the specific user group other than the client terminal 23a are “downloaded”. In step S36, the information control unit 7 deletes the provision information registered by the client terminal 23a stored in the information storage unit 6.

  Next, in S37, the information control unit 7 transmits to the client terminals 23 belonging to the specific user group a notification that the provided information has been deleted after being normally transmitted to all users. This notification may be sent by e-mail after the user management section 5 registers the user's e-mail address, but the method is not particularly limited. Thereby, the user belonging to the specific user group recognizes that there is no possibility of leakage of the provision information thereafter.

  With the above configuration, when provided information is downloaded, it is automatically encrypted, and the downloaded information is a specific user who is permitted to use the provided information Since the encryption key for decrypting the digital information is separately provided to the user, the provided information cannot be decrypted by a user other than the user who is permitted to browse, and the security can be improved.

  In the first and second embodiments, sharing of the provided information has been described as a user belonging to the same group as the user who provided the digital information. When transmitting the setting data for the automatic information deletion condition, the user who shares the digital information may also be transmitted as the condition data. In this case, the information control unit of the server that has received the data about the user sharing digital information from the client terminal refers to the user management unit, extracts the client terminal information registered by the user, and extracts the digital information. A table may be temporarily generated in the user management unit as an access permission group for managing whether or not the extracted client terminal has been accessed. Alternatively, a plurality of groups may be designated as users who share digital information.

  The digital information sharing system, digital information sharing server, terminal device, and digital information sharing method of the present invention are not limited to the above-described illustrated examples, and various modifications can be made without departing from the scope of the present invention. Of course, it can be added.

It is the block diagram which showed the outline of the digital information sharing system in 1st Embodiment. It is the flowchart figure which showed the procedure until it stores information in the server in 1st Embodiment. It is the flowchart figure which showed the procedure until the provision information which satisfied the automatic deletion conditions by the server in 1st Embodiment is deleted. It is the block diagram which showed the outline of the digital information sharing system in 2nd Embodiment. It is the flowchart figure which showed the procedure until the provision information which satisfy | filled the automatic deletion conditions by the server in 2nd Embodiment is deleted.

Explanation of symbols

1, 21 Digital information sharing system 2, 22 Server 3, 23 Client terminal 4 Network 5 User management unit 6 Information storage unit 7 Information control unit 8, 9 Communication control unit 10 Main control unit 11 Key input unit 12 Video input unit 13 Display Part 24, 25 encryption part

Claims (11)

A digital information sharing system in which a server and a plurality of terminal devices transmit and receive digital information via a network, and the server manages digital information shared between the terminal devices,
The terminal device transmits the digital information and condition data for automatic deletion of the digital information to the server,
The server receives the digital information and condition data for automatic deletion of the digital information, and deletes the digital information when it is determined that the conditions for the automatic deletion are met. Shared system. A digital information sharing server that transmits and receives digital information to and from a plurality of terminal devices via a network and manages digital information shared between the terminal devices,
A communication control unit that receives the digital information and condition data for automatic deletion of the digital information from the terminal device;
An information control unit that associates and manages the digital information and conditions for automatic deletion of the digital information;
An information storage unit for storing the digital information,
The digital information sharing server, wherein the information control unit deletes the digital information from the information storage unit when it is determined that the automatic deletion condition is met. A user management unit that manages the terminal device and a user using the terminal device for each group;
The condition for the automatic deletion is that all the terminal devices to which access permission has been given to the digital information are downloaded, and the information control unit refers to the user management unit for the automatic deletion. The digital information sharing server according to claim 2, wherein it is determined whether or not a condition is met.   The condition for the automatic deletion is that a terminal device that has not been registered to permit access to the digital information in the user management unit is to access the digital information. The digital information sharing server described. An encryption unit for encrypting the digital information;
The terminal device is transmitted by encrypting the digital information and transmitting an encryption key capable of decrypting the encrypted digital information only to the terminal device permitted to access the digital information. The digital information sharing server according to claim 2, wherein:   6. The information control unit according to claim 2, wherein when the digital information is automatically deleted, the information control unit notifies the terminal device that has shared the digital information that the digital information has been deleted. The digital information sharing server according to any one of the above. A terminal device that transmits and receives digital information to and from a server via a network, and manages digital information shared between the terminal devices by the server,
A main control unit for generating condition data for automatic deletion of the digital information;
A terminal device comprising: a communication control unit that transmits the digital information and the automatic deletion condition data. An encryption unit for decrypting the encrypted data;
8. The terminal device according to claim 7, wherein the communication control unit receives the encrypted digital information and an encryption key, and the encryption unit decrypts the digital information with the encryption key.   9. The terminal device according to claim 7, wherein the automatic deletion condition data includes designation of a user who shares the digital information. A digital information sharing method for managing digital information shared between the terminal devices by causing the server and a plurality of terminal devices to transmit and receive digital information via a network,
Transmitting to the terminal device condition data for automatic deletion of the digital information to the server;
Transmitting the digital information; and
Receiving the condition data for automatic deletion of the digital information and the digital information to the server;
Associating the digital information with the automatic deletion condition;
Determining whether the conditions for automatic deletion are met,
And a step of deleting the digital information when it is determined that the condition for automatic deletion is met. Encrypting the digital information on the server;
Transmitting the encrypted digital information to the terminal device;
Transmitting the encryption key only to the terminal device to which access is permitted, and
Receiving the encrypted digital information and the encryption key in the terminal device;
The digital information sharing method according to claim 10, further comprising: decrypting the encrypted digital information with the encryption key.

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