JP4956969B2 - Document distribution apparatus, program, and document distribution system - Google Patents

Description

  The present invention relates to a technique for encrypting a document composed of text, an image, and the like and decrypting it.

A technique for encrypting a document and presenting the content of the document only to a limited client user has been proposed. For example, Patent Document 1 proposes that a reliability level and a confidential level are set for a document, and encryption is performed with a strength corresponding to each level. Patent Document 2 proposes a technique for securely updating a digital certificate used for encrypting a document.
JP-A-5-244150 JP 2005-130444 A

  In the technique described in Patent Document 1, since the encryption strength is determined according to the set reliability level and confidentiality level, for example, it is no longer necessary to keep the document secret after a certain period of time. Even in this case, the encrypted state with the initially determined strength remains maintained. When it is no longer necessary to keep the confidentiality of the document, it can be said that it is preferable to release the contents after decrypting the encrypted state, but the technology described in Patent Document 1 can meet the demand. Can not. In the technique described in Patent Document 2, the entire document is encrypted with a digital certificate. In many cases, the contents of a document need to contain confidential information and unnecessary information, but the technique described in Patent Document 2 encrypts even documents that originally do not need to be confidential. become. For example, it is convenient if it is possible to encrypt a part of a document and leave the part unencrypted in plain text, but the technique described in Patent Document 2 cannot meet such a request. .

  The present invention has been made in view of the above-described background, and the object thereof is to enable encryption of a part of a document and contents of the encrypted part when the confidentiality expiration date has passed. It is to provide a mechanism that can publish.

In order to solve the above-described problem, the present invention is a document storage unit that stores document data representing a document, a separation unit that separates a document represented by the document data into a plurality of partial areas, and the separation unit. From a client device, a secret retention term setting means for setting a secret retention term for each partial area, a key storage means for storing a common key, and a public key corresponding to a secret key assigned to each client device, In response to the request for the document data, the encryption means for encrypting the partial area of the requested partial area of the document data for which the secret retention period has not passed with the common key, and the encryption means Of the partial area, the document data that has been encrypted with respect to the partial area for which the secret retention period has not passed, and the public data corresponding to the requesting client device. And the common key encrypted with the key, and transmitting means for transmitting to said requesting client device, the secret holding time limit setting means, the importance of the criteria and the partial areas included in the document In the time limit storage means for storing the secret retention period to be set for the partial area in association with the secret retention period, the secret retention period stored in association with the determination criterion satisfied by the partial area separated by the separation means is providing document delivery apparatus characterized that you set for the partial region.

  According to the present invention, a document is separated into predetermined areas, and an area of each area that has not yet expired for keeping the encrypted state is encrypted and provided to the client device. Accordingly, it is possible to encrypt a part of the document and to make the contents of the encrypted part public when the encrypted part has a confidentiality expiration date.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.
(1) First Embodiment (1-1) Configuration FIG. 1 is a diagram showing a configuration of a document distribution system according to a first embodiment of the present invention. The document distribution system 1 includes a server device 10, client devices 20 a, 20 b and 20 c, and a network 30. The network 30 is, for example, an intranet or the Internet, but is not particularly limited with respect to the scale of the network and whether the communication line is wired or wireless. In FIG. 1, only three client devices 20a, 20b, and 20c are shown. However, actually, a larger number of client devices may be provided. Hereinafter, when it is not necessary to distinguish each of the plurality of client devices, they are collectively referred to as “client device 20”.

  The server device 10 stores document data representing a plurality of documents, a common key for encrypting the document data, and a public key corresponding to a secret key assigned to each of the client devices 20a, 20b, and 20c. is doing. On the other hand, each of the client devices 20a, 20b, and 20c stores a secret key assigned to itself. Each of the server device 10 and the client device 20 has an operator who operates each device. In order to avoid confusion between them, hereinafter, the operator of the server device 10 is referred to as an “administrative user”, and the client device 20. The operator is referred to as a “client user”.

Next, configurations of the server device 10 and the client device 20 will be described.
FIG. 2 is a block diagram illustrating a hardware configuration of the server device 10. The server device 10 includes a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, a storage unit 14 such as an HD (Hard Disk) for storing various data, Because the server device 10 communicates with the client device 20 via the network 30, the operation unit 15 such as a keyboard or a mouse that receives input from the management user, the display unit 16 such as a liquid crystal display device that displays various types of information, and the like. Communication unit 17 and a time measuring unit 18 for measuring the current date and time. The storage unit 14 stores a plurality of document data representing a plurality of documents in association with document identification information assigned to each document, and describes a procedure for the CPU 11 to execute an operation described later. Stored programs. In the present embodiment, documents are managed separately for each area according to a predetermined condition. For each of these areas, a time limit (hereinafter referred to as a secret retention time) for keeping the encrypted state is set, and information such as the secret retention time is described in a management table described in detail later. . This management table is also stored in the storage unit 14.

  FIG. 3 is a diagram illustrating an example of the management table stored in the storage unit 14. Here, as conceptually shown in FIG. 4, an example in which the content of the document D is separated into three areas A, B, and C is shown. For example, the area A is an area in which the title of the document is described, the area B is an area in which the text is described, and the area C is an area in which an image (image) is described. As shown in FIG. 3, document identification information “Did001” is assigned to document D, and area identification information “Area1”, “Area2”, and “Area3” are assigned to areas A, B, and C, respectively. It shall be. If the areas A, B, and C are the title, text, and image of the document, respectively, the areas B, C, and A are set in order from the highest importance. It is necessary to set a longer secret retention period for a region with higher importance because it is necessary to restrict disclosure to client users by restricting disclosure permission. Accordingly, the secret retention period of the area A of the area identification information “Area1” is set to “2005/11/1”, the secret retention period of the area B of “Area2” is set to “2005/11/30”, and the area of “Area3” Let C's secret retention period be “2005/11/15”. Also, different common keys are used as encryption keys used for encryption processing of the respective areas. 3 and 4, the area A of the area identification information “Area1” is encrypted using the common key “Key1”, the area B of “Area2” is encrypted using the common key “Key2”, and the area of “Area3” An example in which C is encrypted using a common key “Key3” is shown.

  As shown in FIG. 5, the client apparatus 20 requests a document by specifying document identification information. When the CPU 11 of the server device 10 receives the document identification information transmitted from the client device 20, should each of the areas included in the document to which the document identification information is assigned be encrypted with reference to the management table? Judge whether or not. Specifically, the CPU 11 determines that it is not necessary to encrypt the area if the date and time measured by the timing unit 18 has passed the confidentiality expiration date described in the management table, and the confidentiality is maintained. If the time limit has not passed, it is determined that encryption is necessary. Then, the CPU 11 encrypts the area determined to be encrypted, and transmits a document including the encrypted area and other unencrypted areas to the client device 20 as an encrypted document. In the example of FIGS. 3 to 5, an example in which the area is separated into three areas is shown, but the area can be divided into a smaller area or a larger area.

(1-2) Operation First, processing in which the server device 10 stores document data and creates a management table will be described. When the administrative user creates a document using the document creation software, the administrative user stores the document in the storage unit 14 of the server device 10 in a state where the document is separated in units of areas. Specifically, in a state where the management user displays the document on the display unit 16, for example, the region where the title is described, the region where the body text is displayed, and the region where the image exists are respectively separated from the mouse of the operation unit 15. Specify by dragging with. The CPU 11 assigns document identification information to the created document according to the program stored in the storage unit 14 and describes it in the management table, and separates the above-described areas and stores them in the storage unit 14. That is, the CPU 11 assigns area identification information to each area and describes it in the management table, and further stores the area identification information in association with position information indicating the position of each area on the document in the storage unit 14.

  Next, the management user sets a secret retention period for each area. Specifically, the management user inputs a secret retention period of 2005/11/1 for the area where the document title is described, and 2005/11/30 for the area where the text is displayed. The confidentiality expiration date is input, and the confidentiality expiration date of 2005/11/15 is input to the area where the image exists. In response to this operation, the CPU 11 writes the input secret retention period in the management table. Further, the CPU 11 determines a common key for encrypting each area, and writes the common key ID in the management table. The management table is created by the above processing.

Next, FIG. 6 is a flowchart illustrating a procedure executed when the CPU 11 of the server apparatus 10 transmits document data to the client apparatus according to the program stored in the storage unit 14.
In FIG. 6, the CPU 11 stores the document data in the storage unit 14 in the procedure as described above (S101). When the CPU 11 receives a document request from the client device 20a (S102; YES), the CPU 11 activates software necessary for encrypting the requested document (S103). The document request from the client device 20a includes document identification information, and the CPU 11 reads document data from the storage unit 14 based on the document identification information and loads it into the RAM 13 (S104).

  Next, the CPU 11 determines whether or not the processing of the subsequent steps S106 to S108 has been performed for each area of the document represented by the document data (S105). When the processing of steps S106 to S108 is not performed for each area of the document (S105; NO), the CPU 11 focuses on a certain area of the document represented by the document data, and the area identification information of the area (here, “Area1”). ”) Is read from the management table. Then, the CPU 11 determines whether or not the current date and time measured by the time measuring unit 18 has passed the secret retention time limit (step S106). If it is determined that the secret retention period has passed (S106; NO), the CPU 11 returns to the process of step S105 without performing the encryption process on the same area, and keeps the confidentiality for another area of the same document. Determine whether the deadline has passed.

  On the other hand, if the secret retention period of the area has not elapsed (S106; YES), the CPU 11 performs encryption by referring to the common key ID “Key1” assigned to the area identification information “Area1” of the area in the management table. A common key used for encryption is specified, and the contents of the area are encrypted using the common key (S107). Next, the CPU 11 encrypts the common key itself used for encryption using a public key corresponding to the secret key of the client device 20a (S108). That is, as conceptually shown in FIG. 7, when an encrypted document is provided to the client device 20a of the client user A, the common key Key1 used for encrypting the area A is used as the secret key of the client device. When encrypting with the corresponding public key “A1” and providing the encrypted document to the client device 20b of the client user B, the common key Key1 used to encrypt the area A is used as the secret key of the client device 20b. Encrypt with the corresponding public key “B1”. Similarly to the areas B and C of “Area 1”, the common keys Key2 and Key3 are encrypted with the corresponding public keys.

  If the CPU 11 determines that all the areas of the document represented by the document data have been processed in steps S106 to S108 (S105; YES), the CPU 11 performs the encryption including the area encrypted as described above. The document data and the encrypted common key are transmitted to the client device 20 (S109).

  Next, FIG. 8 is a flowchart showing a process in which the client device 20 decrypts the document. First, the client device 20 transmits a document request to the server device 10 according to the operation of the client user (S201). This document request includes document identification information. In response to this document request, the client device 20 receives the encrypted document data and the encrypted common key from the server device 10 (S202). Next, the client device 20 activates software necessary for decrypting them (S203), and reads them (S204).

  Next, the client device 20 determines whether or not the processing of the subsequent steps S206 to S208 has been performed on each area of the encrypted document (S205). When the processing of steps S206 to S208 is not performed for each area of the encrypted document (S205; NO), the CPU 11 pays attention to a certain area of the document represented by the encrypted document data, and the encryption process is performed on the area. It is determined whether it has been applied (S206). If the client device 20 recognizes that the encryption process has not been applied to the same area (S206; NO), the process for the same area is terminated and the process proceeds to the process for the next area.

  On the other hand, if the client device 20 determines that the encryption processing has been performed on the same area (S206; YES), it determines whether the encrypted common key can be decrypted (S207). As described above, the encrypted common key can be decrypted with the secret key possessed by the client device 20. Therefore, if the client device 20 does not have a secret key corresponding to the public key obtained by encrypting the common key, it is determined that the common key cannot be decrypted (S207; NO). In this case, the client device 20 ends the process without performing the decryption process on the same area, and moves to the process for the next area.

  If the client device 20 has a secret key that can decrypt the encrypted common key, it is determined that the common key can be decrypted (S207; YES), and the common key encrypted with the secret key is determined. Decrypt. Further, the client device 20 decrypts the encrypted area using the decrypted common key (S208). Then, the processing of the client device 20 shifts to processing for the next area.

  When the client device 20 executes the above-described processing for all areas of the encrypted document (S205; YES), these areas are combined to create a document (that is, plaintext) before being encrypted (S209), The plaintext is displayed (S210). In this way, when the client device 20 stores the secret key corresponding to the public key used for encryption of the common key, the content decrypted by the client device 20 and the secret retention period are set. The client user can know the contents of the area that has not been encrypted because it has passed. On the other hand, if the client device 20 does not store the secret key corresponding to the public key used for encrypting the common key, the contents of the area that has not been encrypted because the secret retention period has passed. Client users can know.

  Here, a specific example will be described along the contents of the management table in FIG. 3 with reference to the conceptual diagram in FIG. For example, on 2005/11/10, the server apparatus 10 receives the document identification information “Did001” shown in FIG. 3 from the client apparatuses 20a (client user A), 20b (client user B), and 20c (client user C). Assume that a document request for is received. At this time, since the current date and time is 2005/11/10, the server apparatus 10 performs the encryption process for the area A of the area identification information “Area 1” because the secret retention period 2005/11/1 has passed. Do not give. In addition, since the secret retention period 11/30 has not elapsed for the area B of the area identification information “Area2”, the server apparatus 10 encrypts the area B using the common key with the common key ID “Key2”, and further uses the common key. Is encrypted with the public key of the client device 20. At this time, the server device 10 encrypts the client device 20a with a public key corresponding to the secret key A2 of the client device 20a, and uses the secret key B2 of the client device 20b for the client device 20b. Encryption is performed with a corresponding public key, and encryption is performed on the client device 20c with a public key that cannot be acquired by the client device 20c.

  Similarly, since the secret retention period 2005/11/15 has not elapsed for the area C of the area identification information “Area3”, the server apparatus 10 encrypts the area C using the common key with the common key ID “Key3” The common key is encrypted with the public key of the client device 20. At this time, the server device 10 encrypts the client device 20a with a public key corresponding to the secret key A3 of the client device 20a, and the client device 20b uses the secret key B3 of the client device 20b. Encryption is performed with a corresponding public key, and encryption is performed on the client device 20c with a public key that cannot be acquired by the client device 20c. The server device 10 transmits the encrypted document data and the encrypted common key set obtained as described above to the client devices 20a, 20b, and 20c, respectively.

  Upon receiving the encrypted document data and the encrypted common key, the client devices 20a, 20b, and 20c decrypt them. For example, the client device 20a receives the encrypted document data and the encrypted common keys (common key IDs “Key2” and “Key3”). As shown in FIG. 9, since the client device 20a possesses the secret keys “A2” and “A3” necessary for decrypting the encrypted common key, the area identification information “Area2” and The areas B and C of “Area 3” are decoded. Then, the client device 20a displays the contents of the area A of the area identification information “Area 1” that has not been encrypted and the contents of the areas B and C of the area identification information “Area 2” and “Area 3”.

  Similarly, the client apparatus 20b also receives the encrypted document data and the encrypted common keys (common key IDs “Key2” and “Key3”). Since the client apparatus 20b possesses the secret keys “B2” and “B3” necessary for decrypting the encrypted common key, the area B of the area identification information “Area2” and “Area3” is used by using them. Decrypt C. Then, the client device 20b displays the contents of the area A of the area identification information “Area 1” that has not been encrypted and the contents of the areas B and C of the area identification information “Area 2” and “Area 3”.

  On the other hand, the client device 20c receives the encrypted document data and the encrypted common key (common key IDs “Key2” and “Key3”), but stores a secret key necessary for decrypting the common key. Not. Therefore, the client device 20c can display the contents of the area A of the area identification information “Area 1” that has not been encrypted, but the areas B and C of the area identification information “Area 2” and “Area 3”. The contents cannot be decrypted and displayed.

  According to the first embodiment described above, by encrypting a partial area of a document, the area can be kept secret from a client device that cannot decrypt the area. In addition, since a confidentiality retention period is set for each area of the document and the area after the expiration is not encrypted, the contents of the area can be disclosed to a third party.

(2) Second Embodiment Next, a second embodiment of the present invention will be described.
In the first embodiment, an administrative user arbitrarily designates an area in a document, determines the importance thereof, and sets a secret retention period for each area. In the second embodiment described below, the server apparatus 10 itself analyzes the layout of the document, separates the areas according to the layout obtained as a result, further determines the importance of each area, and sets the secret retention period. The storage unit 14 stores a program describing a procedure for the CPU 11 to perform these operations. The configuration other than the content of the program of the second embodiment is the same as the content shown in FIG.

  When the document data is input, the server device 10 (CPU 11) first extracts text (characters) and images (images) included in the document represented by the document data in accordance with a program stored in the storage unit 14. A layout analysis is performed, and a confidentiality expiration date is determined for each area (text area or image area) obtained as a result. Specifically, the position information indicating the position in the document and the secret retention period (or information for specifying the secret retention period) are stored in the storage unit 14 in association with each other, and the CPU 11 is obtained by layout analysis. The position of each area is specified, and the secret retention period stored in association with the position is written in the management table. When storing positional information in a document in association with a confidentiality expiration date, for example, for a title located in the beginning area of the document, the confidentiality period is set to a relatively short one week, and a sentence (description) For the sentence (sentence), the confidentiality period is made a little longer to 4 weeks, and for the sentence (conclusion) in the last area of the document, the confidentiality period is made the longest to 2 months. Then, the CPU 11 refers to the attribute information of the document file and the date in the document, and writes the date and time that has passed the secret holding period of each area from the creation date as the secret holding deadline in the management table. According to the second embodiment, it is possible to save the administrative user from manually setting each area and setting the secret retention period.

(3) Modifications The embodiment described above can be modified as follows.
In the second embodiment described above, the server apparatus 10 sets the secret retention period based on the position in the document in the process of creating the management table. However, in addition to this, the server apparatus 10 sets the secret retention period based on the keyword. There is a way to set. For example, keywords related to personal information such as personal names and addresses, keywords that express important meanings such as “confidential” and “confidential”, and important in commercial transactions such as “release date” and “price” A possible keyword and a secret retention period (or information for specifying the secret retention period) exemplified in the second embodiment are associated with each other and stored in the storage unit 14. Then, the CPU 11 extracts a keyword included in the document represented by the document data, and is specified from the secret retention period (period) stored in association with the extracted keyword, the attribute information of the document file, and the date in the document. The secret retention period of each area is specified based on the creation date and written in the management table.

There are also the following methods.
When there are a plurality of image areas having different resolutions in a document, the higher the resolution, the more important information is set, and the secret retention period is set longer. Specifically, the storage unit 14 stores the resolution level and the secret retention period (or information for specifying the secret retention period) in advance in association with each other. The CPU 11 extracts an image area included in the document represented by the document data, and from the confidentiality retention period (period) stored in association with the resolution of the extracted image area, the attribute information of the document file, and the date in the document. Based on the specified creation date, the secret retention period of each area is specified, and this is written in the management table. For example, if the same image contains a low-resolution thumbnail and a high-resolution original image in the document, the thumbnails will be released early and the original image will be released. Information can be disclosed.

  In the first and second embodiments, each area is simply encrypted. However, after the area is encrypted, the entire document is subjected to encryption processing without setting a confidentiality expiration date. You may do it. In the conceptual diagram of FIG. 10, for example, the server apparatus 10 is moved from the client apparatuses 20 a (client user A), 20 b (client user B), 20 c (client user C), and 20 d (client user D) on 2005/11/10. Assume that a document request for the document having the document identification information “Did001” shown in FIG. 3 is received. It is assumed that client user A in FIG. 10 is the president of an organization, client user B is a general manager, client user C is a general employee, and client user D is an external user of the organization.

  At this time, since the current date and time is 2005/11/10, the server apparatus 10 performs the encryption process for the area A of the area identification information “Area 1” because the secret retention period 2005/11/1 has passed. Do not give. In addition, since the secret retention period 11/30 has not elapsed for the area B of the area identification information “Area2”, the server apparatus 10 encrypts the area B using the common key with the common key ID “Key2”, and further uses the common key. Is encrypted with the public key of the client device 20. At this time, the server device 10 encrypts the client device 20a with a public key corresponding to the secret key A2 of the client device 20a, and uses the secret key B2 of the client device 20b for the client device 20b. Encryption is performed with a corresponding public key, encryption is performed on the client device 20c with a public key that cannot be acquired by the client device 20c, and encryption is performed on the client device 20d with a public key that cannot be acquired by the client device 20d. . Similarly, since the secret retention period 2005/11/15 has not elapsed for the area C of the area identification information “Area3”, the server apparatus 10 encrypts the area C using the common key with the common key ID “Key3” The common key is encrypted with the public key of the client device 20. At this time, the server device 10 encrypts the client device 20a with a public key corresponding to the secret key A3 of the client device 20a, and the client device 20b uses the secret key B3 of the client device 20b. Encrypt with the corresponding public key, encrypt with the public key corresponding to the private key C3 of the client device 20c for the client device 20c, and open to the client device 20d that cannot be obtained by the client device 20d Encrypt with key. Then, the server device 10 uses another encryption key (common key) shared with the client devices 20a, 20b, and 20c by the encrypted document data and the encrypted common key set obtained as described above. And then transmitted to the client devices 20a, 20b, 20c, and 20d.

When the client devices 20a, 20b, and 20c receive the encrypted document data and the encrypted common key, the client devices 20a, 20b, and 20c first decrypt them all with the common key shared with the server device 10. After decrypting the whole, the client devices 20a and 20b decrypt the encrypted common key using their own private key, and decrypt the encrypted document using the common key. However, the client device 20c can display the contents of the area A of the area identification information “Area 1” that has not been encrypted and the contents of the area C of the “Area 3” that can be decrypted, but cannot display the contents of the “Area 2” that cannot be decrypted. The contents of area B cannot be displayed. In addition, since the client device 20d cannot decrypt the entire document, the client device 20d cannot refer to the unencrypted area A as well as the areas B and C where the confidentiality expiration date has not passed.
In this way, if the job title in the organization is a key job, you can know the contents of important information in the document from an early stage, and even other employees know information about the document as time passes. Will be able to. In addition, since the entire document is kept encrypted regardless of the passage of time, it is possible to keep the information private to external users. Therefore, it is possible to expect an improvement in security.

The program executed by the CPU 11 can be recorded on a recording medium such as a magnetic recording medium, an optical recording medium, or a ROM that can be read by a computer and provided to the server device 10. It is also possible to download to the server device 10 via a network such as the Internet.
Further, the client device may output the decryption result, for example, by storing it in a recording medium or transmitting it to another display device without displaying the decryption result of the encrypted document.

It is the figure which showed notionally the network structure which concerns on embodiment of this invention. It is the block diagram which showed the hardware constitutions of the server apparatus which concerns on the same embodiment. It is a figure showing an example of a management table concerning the embodiment. It is a figure explaining the process of the process which the document delivery system concerning the embodiment performs. It is a figure explaining the process of the process which the document delivery system concerning the embodiment performs. It is a flowchart which shows the execution procedure of CPU of the server apparatus which concerns on the embodiment. It is a figure explaining the process of the process which the document delivery system concerning the embodiment performs. It is a flowchart which shows the execution procedure of CPU of the client apparatus which concerns on the embodiment. It is a figure explaining the process of the process which the document delivery system concerning the embodiment performs. It is a figure explaining the process of the process which a document delivery system performs in a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Document delivery system, 10 ... Server apparatus, 20, 20a, 20b, 20c, 20d ... Client apparatus, 30 ... Network, 11 ... CPU, 12 ... ROM, 13 ... RAM, 14 ... Memory | storage part, 15 ... Operation part, 16 ... display unit, 17 ... communication unit.

Claims (5)

Document storage means for storing document data representing a document;
Separating means for separating the document represented by the document data into a plurality of partial areas;
A secrecy period setting unit for setting a secrecy period for each partial area separated by the separation unit;
Key storage means for storing a common key and a public key corresponding to a secret key assigned to each client device;
In response to a request for document data from a client device, an encryption unit that encrypts a partial area of the requested partial area of the document data for which the secret retention period has not passed, with the common key;
Encrypted with the public key corresponding to the requesting client device and the document data that has been encrypted with respect to the partial area of the partial area for which the confidentiality expiration date has not passed. A transmission means for transmitting the shared key to the requesting client device ,
The secret retention time setting means includes:
In the term storage means for storing the criterion for determining the importance of the partial area included in the document and the confidentiality deadline to be set for the partial area, the determination that the partial area separated by the separating means satisfies a confidentiality deadline stored in association with the reference, document delivery and wherein the you set for partial areas. Document storage means for storing document data representing a document;
Separating means for separating the document represented by the document data into a plurality of partial areas;
A secrecy period setting unit for setting a secrecy period for each partial area separated by the separation unit;
Key storage means for storing a common key and a public key corresponding to a secret key assigned to each client device;
In response to a request for document data from a client device, an encryption unit that encrypts a partial area of the requested partial area of the document data for which the secret retention period has not passed, with the common key;
Encrypted with the public key corresponding to the requesting client device and the document data that has been encrypted with respect to the partial area of the partial area for which the confidentiality expiration date has not passed. Transmitting means for transmitting the shared key thus made to the requesting client device;
And a position limit storage means for storing in association with each position and confidentiality deadline region in the document represented by the document data,
The secret retention period setting means identifies the position of each partial area separated by the separating means, and associates the secret retention period stored in the position expiration storage means in association with the identified position with the partial area. features and be Rubun document distribution device that you set as a confidentiality period of. Document storage means for storing document data representing a document;
Separating means for separating the document represented by the document data into a plurality of partial areas;
A secrecy period setting unit for setting a secrecy period for each partial area separated by the separation unit;
Key storage means for storing a common key and a public key corresponding to a secret key assigned to each client device;
In response to a request for document data from a client device, an encryption unit that encrypts a partial area of the requested partial area of the document data for which the secret retention period has not passed, with the common key;
Encrypted with the public key corresponding to the requesting client device and the document data that has been encrypted with respect to the partial area of the partial area for which the confidentiality expiration date has not passed. Transmitting means for transmitting the shared key thus made to the requesting client device;
And a keyword deadline storage means for storing in association with predetermined keywords and confidentiality deadline,
The secret retention term setting unit extracts a predetermined keyword stored in the keyword term storage unit from the document data, and stores the secret retention stored in the keyword term storage unit in association with the extracted keyword. deadline, the separating means by the feature and be Rubun document distribution device to be set as confidentiality period of partial regions including the keyword among the separated partial areas. Computer
Document storage means for storing document data representing a document;
Separating means for separating the document represented by the document data into a plurality of partial areas;
A secrecy period setting unit for setting a secrecy period for each partial area separated by the separation unit;
Key storage means for storing a common key and a public key corresponding to a secret key assigned to each client device;
In response to a request for document data from a client device, an encryption unit that encrypts a partial area of the requested partial area of the document data for which the secret retention period has not passed, with the common key;
Encrypted with the public key corresponding to the requesting client device and the document data that has been encrypted with respect to the partial area of the partial area for which the confidentiality expiration date has not passed. A program for causing the common key to function as a transmission means for transmitting to the requesting client device ,
The secret retention time setting means is
In the term storage means for storing the criterion for determining the importance of the partial area included in the document and the confidentiality deadline to be set for the partial area, the determination that the partial area separated by the separating means satisfies A program for setting a secret retention period stored in association with a reference for the partial area . A document delivery device, and a plurality of client devices connected to the document delivery device via communication means,
The document distribution device includes:
Document storage means for storing document data representing a document;
Separating means for separating the document represented by the document data into a plurality of partial areas;
A secrecy period setting unit for setting a secrecy period for each partial area separated by the separation unit;
Key storage means for storing a common key and a public key corresponding to a secret key assigned to each client device;
In response to a request for document data from the client device, an encryption unit that encrypts a partial area of the requested partial area of the document data for which the confidentiality expiration date has not passed with the common key;
Encrypted with the public key corresponding to the requesting client device and the document data that has been encrypted with respect to the partial area of the partial area for which the confidentiality expiration date has not passed. A transmission means for transmitting the shared key to the requesting client device,
The confidentiality retention time setting means of the document distribution device is:
In the term storage means for storing the criterion for determining the importance of the partial area included in the document and the confidentiality deadline to be set for the partial area, the determination that the partial area separated by the separating means satisfies Set the confidentiality period stored in association with the reference for the partial area,
The client device is
A document designating means for designating document identification information;
A document request transmitting means for transmitting a document request including the document identification information specified by the document specifying means to the document distribution apparatus via the communication means;
Display control means for displaying on the display means a document represented by the encrypted document data transmitted by the document distribution apparatus in response to the document request transmitted by the document request transmission means and received via the communication means;
Using the secret key assigned to the own device, the common key transmitted by the document delivery device in response to the document request and received via the communication means is decrypted, and the partial key is used by using the decrypted common key. And decoding means for decoding the area,
The document distribution system, wherein the transmission unit of the document distribution apparatus transmits encrypted document data corresponding to document data identified by document identification information included in the document request.

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