JP2005117380A - Content distributing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a content distributing device which has an excellent characteristic such that a user can smoothly view and listen to contents in a terminal by solving the problem that a large amount of time is required to search a content key and making it possible to search an encrypted content key corresponding to a high speed in the content distributing device for distributing encrypted content keys obtained by encrypting encrypted contents and an encryption key for decrypting the encrypted contents by using a public key for each terminal. <P>SOLUTION: An encrypted content key corresponding to a terminal that has issued the first viewing request is acquired by searching an encrypted content key main database 105 having the information of all terminals registered therein. In the second and succeeding viewing requests, an encrypted content key is acquired by searching an encrypted content key subdatabase 107 which is created from the past history and in which only valid terminals connected to a distribution server are registered. Therefore, a search time is greatly reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a content distribution apparatus in which an encrypted content and an encryption key for decrypting the encrypted content are distributed and viewed from a server to a client terminal via a network.

As a conventional content distribution method, the one described in Patent Document 1 is known. FIG. 7 shows a content distribution method and apparatus disclosed in Patent Document 1. In the content distribution method disclosed in Patent Document 1, encrypted content is distributed from the server 11 of the operator 10 to the data storage device 31 arranged on the subscriber 30 side via the network 20, and the encryption from the subscriber side is performed. The content can be used by distributing the encryption key of the encryption key from the business operator 10 to the subscriber 30 when a request for using the encrypted content is received. Alternatively, the content to be distributed to each subscriber is encrypted using a different common key, and a different common key for each subscriber (after being encrypted with a different public key for each subscriber) is distributed.
Japanese Patent Application Laid-Open No. 2002-344924 “Embodiment of the Invention” (page 4-7, FIG. 2)

  However, with the conventional content distribution method disclosed in Japanese Patent Application Laid-Open No. 2002-344924, if the encryption key is distributed as it is when viewing the content, the content may be illegally leaked due to eavesdropping. In addition, when encrypting content to be distributed to each terminal using a common key that differs for each terminal, encryption keys corresponding to all existing terminals when terminals actually connected to the server are not managed are used. It is necessary to search the encryption key corresponding to the terminal that requested the viewing from the database in which the information of all terminals is managed every time a viewing request is received from each terminal. It takes time. In particular, when the difference between the total number of terminals and the number of terminals actually connected to the server is large, it takes a lot of time from the time when viewing is requested until the time when viewing is actually possible.

  The present invention solves the above-mentioned conventional problems, makes it possible to search for an encryption key corresponding to high speed, shorten the time until content can be viewed on the terminal, and realize smooth content viewing It is an object of the present invention to provide a content distribution apparatus that can perform the above.

  In order to solve the above-mentioned problems, the invention described in claim 1 of the present invention is composed of a distribution-side device that distributes content, a terminal that a user uses to view the content, and a network that connects them. The distribution side device stores the encrypted content and distributes it to each terminal, and the encrypted content is assigned to each terminal ID uniquely assigned to all existing terminals for the purpose of identifying individual terminals. An encrypted content key main database storing an encrypted content key main management table in which an encrypted content key in which a content key for decrypting the content key is encrypted with the public key of each terminal, and an encrypted content key sub-management A sub management table creating unit for creating a table, and an encryption for storing the encrypted content key sub management table Content key sub-database, and the sub-management table creation unit obtains the encrypted content key sub-management table from the history of encrypted content keys distributed from the encrypted content key main database to each terminal. A terminal that is created and managed in the encrypted content key sub-database and registered in the encrypted content key sub-database when the distribution apparatus receives a content viewing request from the terminal; It has the effect of retrieving the corresponding encrypted content key from the management table.

  The invention described in claim 2 comprises a content distribution server for distributing content, a terminal used by a user to view the content, and a network connecting them, and the content distribution server stores encrypted content And an encrypted content storage unit to be distributed to each terminal, and a content key for decrypting the encrypted content to each terminal ID uniquely assigned to all existing terminals for the purpose of identifying individual terminals. An encrypted content key main database storing an encrypted content key main management table associated with an encrypted content key encrypted with a public key, a sub management table creating unit for creating an encrypted content key sub management table, The encrypted content key sub-storage table storing the encrypted content key sub management table A database and a terminal address management database for managing the address of each terminal connected to the content distribution server, wherein the sub management table creation unit is configured to transmit the encrypted content key main database to each terminal. The encrypted content key sub-management table is created from the history of the distributed encrypted content key and is managed in the encrypted content key sub-database, and the content distribution server encrypts the encryption to each terminal according to the terminal address management table When distributing the content key, the terminal registered in the encrypted content key sub-database has an operation of searching the corresponding encrypted content key from the encrypted content key sub-management table.

  The invention according to claim 3 is composed of a distribution-side device that distributes content, a terminal that a user uses to view the content, and a network that connects them, and the distribution-side device stores encrypted content And an encrypted content storage unit to be distributed to each terminal, and a content key for decrypting the encrypted content to each terminal ID uniquely assigned to all existing terminals for the purpose of identifying individual terminals. An encrypted content key main database storing an encrypted content key main management table associated with an encrypted content key encrypted with a public key, a sub management table creating unit for creating an encrypted content key sub management table, An encrypted content key sub-database for storing the encrypted content key sub-management table. The encrypted content stored in the encrypted content storage unit and the encrypted content key main management table stored in the encrypted content key main database are stored in the new encrypted content and the encrypted content key main. When switching to the management table, the sub management table creation unit creates an encrypted content key corresponding to new content from the existing encrypted content key sub management table and the newly replaced encrypted content key main management table. A sub-management table is created, managed in the encrypted content key sub-database, and the terminal registered in the encrypted content key sub-database when the distribution apparatus receives a content viewing request from the terminal Content key sub-management It has the effect of searching for encrypted content key corresponding to from Buru.

  The content distribution method and the content distribution apparatus according to the present invention have the above-described configuration, and when a content viewing request is requested from an arbitrary terminal, the second and subsequent viewing requests from each terminal are stored in the server in the past. Encrypted content at high speed by searching and distributing the target encrypted content key from the encrypted content key sub-database in which only the terminal ID that requested viewing and the information corresponding to the encrypted content key are registered An excellent effect that the key can be distributed is obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings used below, the same reference numerals indicate the same components, and duplicate descriptions are omitted. In the following description, an example used for a video-on-demand system in an aircraft will be described. Any encryption method may be used in the present invention. In the following description, a common key encryption method such as 3DES is used for content encryption, and a public key such as elliptic curve encryption is used for content key encryption. Take the case of using an encryption method as an example.

(Embodiment 1)
FIG. 1 is a schematic diagram showing a key distribution procedure of a content distribution apparatus according to an embodiment of the present invention. In FIG. 1, 101 is a content distribution server that distributes encrypted content and an encrypted content key, 102B, 102E, 102N, and 102S are terminals for viewing the content, and 103 is a network that serves as a communication path between the content distribution server and the terminal. It is. The content distribution server 101 includes a content data storage unit 104 that stores encrypted content, and an encrypted content key main management table 105 that associates all existing terminal IDs with corresponding encrypted content keys. The encrypted content key main database 106 stores a sub management table creation unit that creates an encrypted content key sub management table from the content viewing history, and 107 the encrypted content key sub management table that stores the encrypted content key sub management table. It is a database.

  FIG. 2 is a conceptual diagram showing the role of each business operator related to the content distribution system in the embodiment of the present invention. In FIG. 2, 201 is a movie company / authoring company that produces and provides contents, 202 is a key management center that generates and manages encryption keys, 203 is a terminal manufacturer that manufactures terminals, and 204 is installation of terminals on aircraft. Or an airline that accumulates content on a server in an aircraft.

  FIG. 3 is a block diagram showing an internal configuration of terminal apparatus 102 (B, E,...) In the embodiment of the present invention. In FIG. 3, 301 is an encrypted content key obtained by encrypting a content key with a terminal public key, 302 is a terminal secret key memory for storing the terminal secret key, 303 is a terminal secret key used for decrypting the encrypted content key, 304 is an encrypted content key decrypting unit that decrypts the encrypted content key, 305 is a content key memory that stores the content key, 306 is an encrypted content obtained by encrypting the content using the content key, and 307 is an encrypted content. , 308 is an encrypted content decrypting unit, 309 is content, and 310 is a content display unit that uses the content.

  FIG. 4 is a schematic diagram of an encrypted content key main management table managed by the encrypted content key main database 105 according to the embodiment of the present invention. In FIG. 4, 401 is the first data managed in this database, and stores the terminal ID “DID-A” and the corresponding encrypted content key “CK-A”. Similar to 401, 402 to 406 are data indicating the ID value of each existing terminal and the corresponding encrypted content key. In the encrypted content key main management table, IDs of all existing terminals and corresponding encrypted content keys are registered.

  FIGS. 5A and 5B are schematic diagrams of an encrypted content key sub management table managed by the encrypted content key sub database 107 according to the embodiment of the present invention. In FIG. 5, reference numeral 501 denotes first data managed in this database, in which an ID value “DID-B” corresponding to the terminal ID of the terminal B and the corresponding encrypted content key “CK-B” are stored. Yes. Similarly to 501, 502 to 504 are data indicating the ID value of each terminal and the corresponding encrypted content key. In the encrypted content key sub management table, the ID value of the terminal that has received a viewing request in the past and the corresponding encrypted content key are registered.

  FIG. 6 is a flowchart for explaining the key distribution processing of the content distribution server 101 in the embodiment of the present invention.

  The operation of the content distribution apparatus configured as described above will be described below with reference to FIGS.

  First, the content viewing mechanism in the embodiment of the present invention will be described with reference to FIG. First, production of content used in the movie company / authoring company indicated by 201 in FIG. 2 and encryption with a content key are performed. The created encrypted content is sent to the airline, and at the same time, the content key used for content encryption is sent to the key management center 202. The key management center indicated by 202 generates a terminal encryption key (terminal secret key, terminal public key) for each terminal ID, and sends the terminal secret key to the terminal manufacturer 203. Also, the content key is received from the movie company / authoring company 201, encrypted using the terminal public key corresponding to each terminal ID, and sent to the airline 204. The terminal maker shown at 203 manufactures a terminal, receives a terminal secret key from the key management center 202, and incorporates it in accordance with the manufactured terminal ID. The manufactured terminal is sent to the airline. The airline shown at 204 receives a terminal from the terminal manufacturer 203 and installs it on the aircraft. Also, the encrypted content received from the movie company / authoring company 201 and the encrypted content key received from the key management center 202 are stored in the content distribution server in the aircraft. As described above, the encrypted content and the encrypted content key are stored in the content distribution server in the content distribution apparatus, and the terminal secret key is incorporated in each terminal.

  Next, the operation of the content distribution apparatus when a content viewing request is sent from the terminal 102E of FIG. 1 to the content distribution server 101 in accordance with the procedure of the flowchart shown in FIG. First, as shown at 601, the content distribution server 101 that has received the content viewing request confirms that the terminal ID of the transmission source is “DID-E” corresponding to the terminal E. Next, as shown at 602, the encrypted content key corresponding to “DID-E” is searched from the encrypted content key sub-database. If the encrypted content key sub-management table managed in the encrypted content key sub-database 107 is in the state shown in FIG. 5A, the ID “DID-E” of the terminal E is stored in the encrypted content key sub-database. Is not registered, it is determined in 603 that the corresponding encrypted content key could not be obtained. In this case, the search is performed from the encrypted content key main database 105 as indicated by 605. Since the encrypted content key main database 105 stores the encrypted content keys corresponding to the IDs of all the terminals as in the encrypted content key main management table shown in FIG. 3, it corresponds to “DID-E”. The encrypted content key “CK-E” can be acquired. Then, as shown at 606, the acquired information is added to the encrypted content key sub-database. Further, the encrypted content key distribution process is completed by returning the encrypted content key “CK-E” to the terminal E as indicated by 604. As a result, the encrypted content key sub management table is in the state shown in FIG.

  Here, the processing in the terminal that has received the encrypted content key will be described with reference to FIG. The encrypted content key 301 received by the terminal is decrypted by the encrypted content key decrypting unit 304 using the terminal secret key 303 read from the terminal secret key memory 302. The obtained content key is stored in the content key memory 305. Subsequently, the encrypted content 306 transmitted from the content distribution server is received and decrypted by the encrypted content decrypting unit 308 using the content key 307 read from the content key memory 305. The obtained content 309 is displayed on the content display unit 310 and can be viewed.

  Next, a case where a viewing request is received from the terminal N when the encrypted content key sub management table is in the state of FIG. In this case, since “DID-N” is registered in the encrypted content key sub-database as indicated by 502 in FIG. 5A (602, 603), the corresponding encrypted content key “CK-N” is stored. To get. Finally, the encrypted content key delivery process is completed by returning the encrypted content key “CK-N” to the terminal N as indicated by 604.

  As described above, according to the present embodiment, the content distribution server searches the encrypted content key main database in which information of all terminals is registered for the encrypted content key corresponding to the terminal that has issued the viewing request for the first time. Since the search result is added to the encrypted content key sub-database in which only the terminals that have been called in the past are registered, it is possible to reliably obtain the encrypted content key. For the second and subsequent viewing requests, since only valid terminals connected to the distribution server are created by searching from the registered encrypted content key sub-database, the search time is greatly increased. Can be reduced.

(Embodiment 2)
FIG. 8 is a conceptual diagram showing the internal configuration of the content distribution server in the embodiment of the present invention. In FIG. 8, reference numeral 801 denotes a terminal address database for storing a terminal address management table for managing address information of each terminal, and 802 creates an encrypted content key sub-management table from the terminal address management table and the distribution history of the encrypted content key. A sub management table creation unit 803 is an encrypted content key sub database that stores an encrypted content key sub management table. The same reference numerals as those in FIG. 1 denote the same components. Further, parts other than the content distribution server of the content distribution apparatus according to the present invention have the same configuration as that of the first embodiment.

  FIG. 9 is a schematic diagram of a terminal address management table managed by the terminal address database 801 in the embodiment of the present invention. In FIG. 9, reference numeral 901 denotes first data managed in this database, and the address “ADDR-001” of the first terminal is stored. Similarly to 901, reference numerals 902 to 904 denote data indicating the address of each terminal. In the terminal address management table, address information of each terminal connected to the content distribution server is registered.

  FIGS. 10A and 10B are schematic diagrams of an encrypted content key sub management table managed by the encrypted content key sub database 803 in the embodiment of the present invention. In FIG. 10, reference numeral 1001 denotes first data managed in this database. The first terminal address “ADDR-001”, its terminal ID “DID-B”, and the corresponding encrypted content key “CK-B”. Is remembered. Similar to 1001, 1002 to 1005 are data indicating the address of each terminal, the terminal ID value, and the corresponding encrypted content key. In this encrypted content key sub-management table, the address and terminal ID value of each terminal that has distributed the encrypted content key in the past, and the corresponding encrypted content key are registered.

  FIG. 11 is a flowchart for explaining key distribution processing of the content distribution server 101 in the embodiment of the present invention.

  The operation of the content distribution apparatus configured as described above will be described in accordance with the procedure shown in the flowchart of FIG. First, the content distribution server 101 inquires the terminal IDs of the connected terminals in accordance with the terminal address management table shown in FIG. 9 (1101, 1102). Next, as shown in 1103, the corresponding encrypted content key is searched from the encrypted content key sub-database. Here, consider a case where the terminal ID has acquired “DID-B” when there is no encrypted content key sub-database. Since the terminal ID “DID-B” is not registered in the encrypted content key sub-database in the initial state, the corresponding encrypted content key cannot be obtained (1104). In this case, the content key main database is searched as indicated by 1106. As shown in FIG. 3, since the encrypted content key corresponding to the IDs of all terminals is registered in the encrypted content key main database, the encrypted content key “CK-B” corresponding to “DID-B” is registered. Can be obtained. Then, as shown in 1107, the acquired information is added. Thereafter, the encrypted content key acquired as shown at 1105 is transmitted to the terminal. As a result of repeating the above processing from “ADDR-001” to “ADDR-n” shown in FIG. 8, the encrypted content key sub-table is in the state shown in FIG.

  Next, consider a case where the terminal ID acquired from “ADDR-001” is “DID-B” when the encrypted content key sub-database is in the state of FIG. 10A in 1102. In this case, since “DID-B” is registered in the encrypted content key sub-database as shown in FIG. 10A (1103, 1104), the corresponding encrypted content key is transmitted to the terminal. That is, when the result of acquiring the terminal IDs in order according to the address management table matches with FIG. 10A, the encrypted content keys stored in the encrypted content key sub-table are transmitted in order.

  A case will be described in which an existing terminal is replaced with another terminal due to a failure of the terminal or the like. For example, consider a case where the terminal ID acquired from “ADDR-002” is “DID-F” when the encrypted content key sub-database in 1102 is in the state of FIG. In this case, since it is different from the registration state of the encrypted content key sub-database shown in FIG. 10A, the corresponding encrypted content key is searched from the content key main database as indicated by 1106. Then, the encrypted content key “CK-F” corresponding to “DID-F” is acquired, and the acquired information is added as indicated by 1107. As a result, the encrypted content key sub-database is updated to the state shown in FIG.

  As described above, according to the present embodiment, the encrypted content key is distributed to all terminals connected to the distribution server when the content distribution device is started up. In the case of the state, the encrypted content key is searched and acquired from the database in which the information of all terminals is registered, and the search result is recorded in the database in the order of the registered address of the terminal. it can. In addition, since the encrypted content key is distributed for the second time or later and retrieved from the database in which the encrypted content key is registered in the order of the management address, the search time for the encrypted content key is compared with the first embodiment. In addition to being able to shorten the content, when each terminal requests viewing from the content distribution server, the content can be viewed immediately by only distributing the encrypted content from the content distribution server to the terminal. It has an excellent effect.

(Embodiment 3)
FIG. 12 is a schematic diagram of an encrypted content key main management table managed in the encrypted content key main database 105 according to the embodiment of the present invention.

  In FIG. 12, reference numeral 1201 denotes first data managed in this database, which stores the terminal ID “DID-A” and the corresponding encrypted content key “CK-A ′”. Similarly to 1201, 1202 to 1206 are data indicating the ID value of each existing terminal and the corresponding encrypted content key. In the encrypted content key main management table, IDs of all existing terminals and corresponding encrypted content keys are registered.

  FIG. 13 is a schematic diagram of an encrypted content key sub management table managed by the encrypted content key sub database 107 according to the embodiment of this invention.

  In FIG. 13, reference numeral 1301 denotes first data managed in this database, and an ID value “DID-B” corresponding to the terminal ID of the terminal B and the corresponding encrypted content key “CK-B ′” are stored. ing. Similar to 1301, 1302 to 1304 are data indicating the ID value of each terminal and the corresponding encrypted content key. In the encrypted content key sub management table, the ID value of the terminal that has received a viewing request in the past and the corresponding encrypted content key are registered.

  FIG. 14 is a flowchart for explaining the update processing of the encrypted content key sub-management table managed by the encrypted content key sub-database 107 in the embodiment of the present invention.

  The configuration of the content distribution apparatus in the embodiment of the present invention is the same as that shown in the first embodiment, and the encrypted content key sub-database is in the state shown in FIG.

  The operation of updating the content distribution server at the time of content exchange of the content distribution apparatus configured as described above will be described below according to the procedure shown in the flowchart of FIG. First, when the content in the content distribution server is replaced with another content, the encrypted content key main management table is also changed from the one shown in FIG. 4 to the one shown in FIG. Thereafter, as shown by 1401 and 1402 in FIG. 14, the terminal IDs registered in the encrypted content key sub-management table managed in the encrypted content key sub-database 107 shown in FIG. Subsequently, as shown in 1403, the corresponding encrypted content key is searched on the encrypted content key main management table shown in FIG. 12, and an encrypted content key for new content corresponding to the terminal ID is newly acquired. Then, as indicated by 1404, the contents of the encrypted content key sub-database are rewritten. The above process is repeated for all terminal IDs registered in the encrypted content key sub-database. Then, as shown in the encrypted content key sub-management table of FIG. 13, an encrypted content key sub-database in which all the encrypted content keys registered with respect to the original encrypted content key sub-database are updated is obtained. As a result, it is possible to obtain an encrypted content key sub-database in which the updated encrypted content key is registered even after the content and the encrypted content key are exchanged. When a viewing request is received from each terminal, the encrypted content key sub-database is encrypted. Since the corresponding encrypted content key is searched and acquired from the content key sub-database, the search time can be greatly reduced.

  As described above, according to the present embodiment, when the encrypted content and the encrypted content key stored in the content distribution server are exchanged, the encryption updated from the encrypted content key sub-database created so far By obtaining a new encrypted content key sub-database with registered encrypted content keys, and using the encrypted content key sub-database even after replacing the content, the search time for encrypted content keys can be greatly reduced Can do.

  In the above description, an example of a video on-demand system in an aircraft has been described. However, the embodiment of the present invention is not limited to this, and content distribution that distributes encrypted content and an encrypted content key via a network. Any system may be used.

  In the content distribution apparatus according to the present invention, when content viewing is requested from an arbitrary terminal, the terminal ID that has requested viewing from the server in the past for the second and subsequent viewing requests from each terminal. And the encrypted content key can be distributed at high speed by searching for and distributing the target encrypted content key from the encrypted content key sub-database in which only the information of the corresponding encrypted content key is registered. This is effective and is useful as a content distribution device or the like that distributes encrypted content and an encryption key for decrypting encrypted content from a server to a client terminal via a network.

Schematic diagram showing a key distribution procedure of the content distribution apparatus according to Embodiment 1 of the present invention. The conceptual diagram which shows the role of each provider regarding the content delivery system in Embodiment 1 of this invention The block diagram which shows the internal structure of the terminal in Embodiment 1 of this invention. Schematic diagram of an encrypted content key main management table in Embodiment 1 of the present invention Schematic diagram of an encrypted content key sub management table in Embodiment 1 of the present invention The flowchart explaining the key delivery process of the content delivery server in Embodiment 1 of this invention Schematic diagram showing a conventional content distribution method and apparatus The conceptual diagram which shows the internal structure of the content delivery server in Embodiment 2 of this invention. Schematic diagram of a terminal address management table in Embodiment 2 of the present invention Schematic diagram of an encrypted content key sub-management table in Embodiment 2 of the present invention The flowchart explaining the key delivery process of the content delivery server in Embodiment 2 of this invention Schematic diagram of an encrypted content key main management table in Embodiment 3 of the present invention Schematic diagram of an encrypted content key sub-management table in Embodiment 3 of the present invention The flowchart explaining the update process of the encryption content key sub management table in Embodiment 3 of this invention

Explanation of symbols

101 Content distribution server 102 Terminal (B, E, N, S)
DESCRIPTION OF SYMBOLS 103 Network 104 Content data storage part 105 Encrypted content key main database 106 Sub management table preparation part 107 Encrypted content key sub database

Claims (3)

The encrypted content and the encrypted content key obtained by encrypting the content key for decrypting the encrypted content with the public key of each terminal are distributed from the server to any terminal via the network. In the content distribution device that decrypts and uses the content using the content key on the terminal side,
A delivery side device for delivering content;
A terminal that a user uses to view content;
It consists of a network that connects them,
The distribution side device stores encrypted content and distributes the encrypted content to each terminal;
Corresponds to the content ID for decrypting the encrypted content with the public key of each terminal to the terminal ID uniquely given to all existing terminals for the purpose of identifying individual terminals An encrypted content key main database for storing the attached encrypted content key main management table;
A sub management table creation unit for creating an encrypted content key sub management table;
An encrypted content key sub-database that stores the encrypted content key sub-management table,
The sub management table creation unit creates the encrypted content key sub management table from the history of the encrypted content key distributed to each terminal from the encrypted content key main database, and in the encrypted content key sub database And when the distribution device receives a content viewing request from the terminal, the terminal registered in the encrypted content key sub-database searches the corresponding encrypted content key from the encrypted content key sub-management table. A content distribution apparatus characterized by the above. The encrypted content and the encrypted content key obtained by encrypting the content key for decrypting the encrypted content with the public key of each terminal are distributed from the server to any terminal via the network. In the content distribution device that decrypts and uses the content using the content key on the terminal side,
A content distribution server for distributing content;
A terminal that a user uses to view content;
It consists of a network that connects them,
The content distribution server stores encrypted content and distributes the encrypted content to each terminal;
Corresponding to an encrypted content key obtained by encrypting a content key for decrypting the encrypted content with a public key of each terminal to a terminal ID uniquely assigned to all existing terminals for the purpose of identifying individual terminals An encrypted content key main database for storing the attached encrypted content key main management table;
A sub management table creation unit for creating an encrypted content key sub management table;
An encrypted content key sub-database that stores the encrypted content key sub-management table;
A terminal address management database for managing the address of each terminal connected to the content distribution server,
The sub management table creation unit creates the encrypted content key sub management table from the history of encrypted content keys distributed to each terminal from the encrypted content key main database, and stores the encrypted content key sub database in the encrypted content key sub database. And when the content distribution server distributes the encrypted content key to each terminal according to the terminal address management table, the encrypted content key sub-management table for the terminals registered in the encrypted content key sub-database A content distribution apparatus for retrieving a corresponding encrypted content key from The encrypted content and the encrypted content key obtained by encrypting the content key for decrypting the encrypted content with the public key of each terminal are distributed from the server to any terminal via the network. In the content distribution device that decrypts and uses the content using the content key on the terminal side,
A delivery side device for delivering content;
A terminal that a user uses to view content;
It consists of a network that connects them,
The distribution-side device stores encrypted content and distributes the encrypted content to each terminal;
Corresponds to the content ID for decrypting the encrypted content with the public key of each terminal to the terminal ID uniquely given to all existing terminals for the purpose of identifying individual terminals An encrypted content key main database for storing the attached encrypted content key main management table;
A sub management table creation unit for creating an encrypted content key sub management table;
An encrypted content key sub-database that stores the encrypted content key sub-management table,
When replacing the encrypted content stored in the encrypted content storage unit and the encrypted content key main management table stored in the encrypted content key main database with new encrypted content and encrypted content key main management table The sub management table creation unit creates an encrypted content key sub management table corresponding to the new content from the existing encrypted content key sub management table and the newly replaced encrypted content key main management table. And the encrypted content key sub-database for terminals registered in the encrypted content key sub-database when the distribution apparatus receives a content viewing request from the terminal. Supported from the table Content delivery apparatus, characterized in that the search for encrypted content key that.

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