JP2004185263A - Dispersed cooperative content delivery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the load on a content delivery server even in an environment where contents vary irregularly; to check to see if the contents stored in the cache of a client device have been modified illicitly; and to allow other client devices to access only the cache storage device of the client device. <P>SOLUTION: A dispersed cooperative content delivery system includes contents 12; a content delivery server 11 which delivers characteristic information specifying the contents 12; a client device 20 with a cache storage device 21 for storing the contents 12 acquired; and a cache index server 17 with a cache index database 19 for storing the characteristic information corresponding to the contents 12 and data about the client device 20. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a distributed cooperative content distribution system.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, when an information terminal such as a personal computer equipped with a browser function accesses (visits) a web server connected to the Internet, a web site opened in the web server is stored. Various contents such as images and sounds can be used. In recent years, with the expansion of use of the Internet, access to a content distribution server as a web server storing the content has been increasing. However, when access to the content distribution server increases, a load for the content distribution server to distribute the content increases, so that access to the content distribution server becomes difficult, and it takes time to acquire the content. Or the acquisition of the content becomes impossible.
[0003]
Therefore, in order to reduce the load on the content distribution server, a technique using a cache server that temporarily stores the content of the content has been provided.
Further, in order to reduce the load on the cache server, a technique for further distributing the cache server has been provided (for example, see Patent Documents 1 to 3).
[0004]
[Patent Document 1] Japanese Patent Publication No. 2001-511551
[0005]
[Patent Document 2] JP-A-10-222412
[0006]
[Patent Document 3] JP-A-10-222449
[0007]
[Problems to be solved by the invention]
However, in the conventional system, when the access from the information terminal increases, the load on the cache server increases, and it takes time to acquire the content from the cache server, or the content cannot be acquired. Would. Although it is possible to reduce the load on each cache server by increasing the number of cache servers, the cost and management burden increase.
[0008]
Therefore, an information terminal as a client device is provided with a cache function for temporarily storing content, and a cache index indicating a cache as a cache storage device for temporarily storing content is distributed instead of distributing the content. And a distributed cooperative content distribution system using a cache index server that performs the above. In this case, when a content distribution request is transmitted from a certain information terminal, the cache index server returns a cache index of the content. Then, the information terminal directly accesses the information terminal in which the content is stored according to the cache index to acquire the content. In addition, the technology in which the information terminals directly access and acquire the contents stored in the respective devices is generally called PtoP (Peer to Peer or P2P: Peer to Peer).
[0009]
However, in the distributed cooperative content distribution system, when the content of the content is changed irregularly, the access to the content distribution server increases, so that the load on the content distribution server increases. In addition, there is a possibility that the contents stored in the cache of the information terminal may be illegally changed. Furthermore, since the information terminals directly access each other, there is a possibility that private information stored in the information terminal may be acquired by another information terminal.
[0010]
The present invention solves the problems of the conventional distributed cooperative content distribution system, and can reduce the load on the content distribution server even in an environment where contents change irregularly. Provides a distributed cooperative content distribution system that can check whether the content stored in the client has been tampered with, and allows other client devices to access only the cache device of the client device. The purpose is to do.
[0011]
[Means for Solving the Problems]
Therefore, in the distributed cooperative content distribution system of the present invention, a content distribution server that distributes a content and a value specifying the content, a client device including a cache storage device that stores the acquired content, A cache index server having a cache index database for storing unique information corresponding to each and data relating to the client device.
[0012]
In another distributed cooperative content distribution system according to the present invention, further, one client device acquires specific information corresponding to predetermined content from the content distribution server, and stores the content corresponding to the specific information. An inquiry about whether or not there is a client device is transmitted to the cache index server, and if there is the other client device, the content is obtained from the other client device, and unique information corresponding to the content is calculated. The unique information is compared with the unique information acquired from the content distribution server to determine whether the content is true or false. If the content is true, the content is output and stored in the cache storage device.
[0013]
In still another distributed cooperative content distribution system according to the present invention, a third party guarantees the content, unique information specifying the content, a content signature value obtained by a public key (key) encryption method, and a public key. A content distribution server that distributes a public key certificate, a client device including a cache storage device that stores the acquired content and a public key certificate store that stores the acquired public key certificate, and A cache index server having a cache index database for storing unique information and data relating to the client device, and a public key certificate verification server for verifying the validity of the public key certificate.
[0014]
In still another distributed cooperative content distribution system according to the present invention, when one client device does not store a public key certificate of a predetermined content distribution server, the client device transmits the public key certificate to the content distribution server. And transmits a request for validity verification of the public key certificate to the public key certificate server, and the public key certificate server transmits a verification result of the public key certificate to the one client device. If the public key certificate is valid, the one client device stores the public key certificate, acquires a public key from the public key certificate, and obtains a predetermined content from the content distribution server. Obtaining a signature value, obtaining unique information of the predetermined content from the content signature value based on the public key, and storing a content corresponding to the unique information An inquiry as to whether or not there is another client device is sent to the cache index server.If there is the other client device, the content is obtained from the other client device, and unique information corresponding to the content is obtained. Calculating and comparing the unique information with the unique information obtained from the content distribution server to determine the authenticity of the content, and when the content is true, outputs the content and stores it in the cache storage device. .
[0015]
According to still another distributed cooperative content distribution system of the present invention, a content, unique information for specifying the content, a content signature value obtained by a public key encryption method, and a public key certificate in which a public key is guaranteed by a third party. Content distribution server for distributing a certificate, a client device including a cache storage device for storing the obtained content and a public key certificate store for storing the obtained public key certificate, and unique information corresponding to each of the content. And a cache index server having a cache index database for storing data relating to the client device, and a public key certificate store for storing the obtained public key certificate, and obtaining, storing and validating the public key certificate. A public key certificate verification server for performing verification.
[0016]
In still another distributed cooperative content distribution system of the present invention, one client device transmits the public key distribution request to a public key certificate management verification server, and the public key certificate server A key is obtained and verified, a valid public key is transmitted to the one client device, and the one client device obtains a content signature value of predetermined content from the content distribution server, and obtains a content signature value based on the public key. Determining the unique information of the predetermined content from the content signature value, transmitting an inquiry to the cache index server as to whether or not there is another client device that stores the content corresponding to the unique information, If there is a device, the content is obtained from the other client device, and the content corresponding to the content is acquired. Calculating the information, comparing the unique information with the unique information obtained from the content distribution server to determine the authenticity of the content, and when the content is true, outputs the content and sends it to the cache storage device. Store.
[0017]
In still another distributed cooperative content distribution system according to the present invention, the client device stores the content in the cache storage device after it is determined that the acquired content is true.
[0018]
In still another distributed cooperative content distribution system of the present invention, the client device stores the content in the cache storage device according to the name, type, and the like of the content.
[0019]
In still another distributed cooperative content distribution system according to the present invention, the cache index server may further include, when there are a plurality of other client devices that store predetermined content requested by one client device, the other client device. A list obtained by rearranging the device list according to a predetermined algorithm is transmitted to the one client device, and the one client device attempts to acquire contents in the order of the rearranged list.
[0020]
In still another distributed cooperative content distribution system according to the present invention, the cache index server deletes predetermined information from a cache index database according to a request from the client device.
[0021]
In still another distributed cooperative content distribution system according to the present invention, the client device may further include a request when a storage amount of the content stored in the cache storage device exceeds a condition determined by an administrator of the client device. Send to the cache index server.
[0022]
In still another distributed cooperative content distribution system according to the present invention, the client device deletes the content from the cache storage device according to a request from the cache index server.
[0023]
In still another distributed cooperative content distribution system according to the present invention, the cache index server periodically checks the use frequency of the cache index database and transmits a request to delete the content whose use frequency is low.
[0024]
In still another distributed cooperative content distribution system according to the present invention, the cache index server transmits a request to delete content that is used less frequently when the amount of cached data exceeds a predetermined condition.
[0025]
In still another distributed cooperative content distribution system according to the present invention, the cache index server transmits a request to delete a content whose unique information is older among registered contents having the same name and type.
[0026]
In still another distributed cooperative content distribution system according to the present invention, the cache index server further includes a case where another client device that stores the predetermined content requested by one client device is not included in the cache index database. Query other cache index servers.
[0027]
In still another distributed cooperative content distribution system according to the present invention, the unique information is a hash value.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0029]
FIG. 1 is a diagram showing a configuration of a distributed cooperative content distribution system according to the first embodiment of the present invention.
[0030]
As shown in the figure, the distributed cooperative content distribution system 10 in the present embodiment has a content distribution server 11a and a content distribution server 11b as web servers. It should be noted that the content distribution server may be singular or plural, and the number is arbitrary. However, in the present embodiment, for the sake of explanation, all the content distribution servers 11a and 11b Represents a content distribution server. When the content distribution server 11a and the content distribution server 11b are described in an integrated manner, the content distribution server 11 will be described. Here, the content distribution server 11 is a computer including arithmetic means such as a CPU and an MPU, storage means such as a magnetic disk and a semiconductor memory, a communication interface, and the like. The content distribution server 11 may exist independently, may be a part of another device such as a large computer, or may be a distributed type in which a plurality of servers are organically coupled. It may be a server.
[0031]
The content distribution server 11a and the content distribution server 11b store data such as the content 12a and the content 12b, and the hash value 13a and the hash value 13b for specifying the content 12a and the content 12b, respectively, in the storage unit. And distributes the data in response to a request from. Here, the content 12a and the content 12b are, for example, web pages, character data, audio data such as music, image data such as videos and photographs, software, and the like, but may be of any type. The content 12a and the content 12b may be singular or plural, and the number is arbitrary. The hash value 13a and the hash value 13b correspond to the content 12a and the content 12b, respectively. When the contents 12a and 12b and the hash values 13a and 13b are described in an integrated manner, they are described as the contents 12 and the hash value 13.
[0032]
Incidentally, the hash value 13 is a pseudo-random number generated by a hash function based on input data, and is fixed-length data uniquely determined for the original data. In this case, if the original data is modified even by one bit, the generated hash value 13 becomes different. Then, even if the original data is a content having a large data amount, the hash value 13 is a fixed length data having a small data amount. A digital signature for preventing data tampering is usually realized by a combination of a public key encryption technique and a hash function. Commonly used hash functions include MD2, MD5, SHA1, and the like.
[0033]
In addition, reference numeral 14 denotes the Internet as an external network, but any type of network may be used, such as a LAN (Local Area Network) or a WAN (Wide Area Network). The content distribution server 11 is connected to the Internet 14 and can distribute the data such as the content 12 and the hash value 13 via the Internet 14.
[0034]
Reference numeral 16 denotes an intranet as an internal network, to which a cache index server 17, a client device 20a, a client device 20b, and the like are connected. The intranet 16 is connected to the Internet 14 via a router 15. Here, the router 15 does not output communication data between devices connected to the intranet 16 to the Internet 14, and transmits communication data between a device connected to the intranet 16 and a device connected to the Internet 14. , And plays a role of selecting and relaying an appropriate route. The router 15 is generally called a router device.
[0035]
Here, the client device may be singular or plural, and the number is arbitrary. However, in the present embodiment, for convenience of explanation, the client devices 20a and 20b are connected to all the client devices. To represent. When the client device 20a and the client device 20b are described in an integrated manner, the client device 20 will be described as the client device 20. The client device 20 is a computer including a computing unit such as a CPU and an MPU, a storage unit such as a magnetic disk and a semiconductor memory, a display unit such as a CRT and a liquid crystal display, and a communication interface. It is an information terminal, but may be of any type. The client device 20a and the client device 20b function as a cache for storing the downloaded content 12, and include a cache storage device 21a and a cache storage device 21b, respectively. Here, the cache storage device 21a and the cache storage device 21b may be a part of the storage device of the client device 20a and the client device 20b, or all or one of the external storage devices such as a so-called external hard disk device. Department. When the cache storage device 21a and the cache storage device 21b are described in an integrated manner, the cache storage device 21 will be described as the cache storage device 21. In the present embodiment, the content 12 downloaded by the client device 20 accessing the content distribution server 11 is temporarily stored in the cache storage device 21.
[0036]
Further, the cache index server 17 is a computer including an arithmetic unit such as a CPU and an MPU, a storage unit such as a magnetic disk and a semiconductor memory, a communication interface, and the like. May be a part of an apparatus such as a large computer, or a distributed server in which a plurality of servers are organically combined. The cache index server 17 is for centrally managing cache index data such as the name of the client device 20 functioning as a cache of the content 12 acquired from the content distribution server 11, and includes a cache index database 19. Here, the cache index database 19 may be a part of the storage means of the cache index server 17, or may be all or a part of an external storage means such as a so-called external hard disk device. In the present embodiment, the cache index server 17 returns a cache index of the content 12 in response to a distribution request of the content 12.
[0037]
Next, the contents of the cache index database 19 will be described.
[0038]
FIG. 2 is a diagram showing the contents of the cache index database according to the first embodiment of the present invention.
[0039]
As shown in the figure, the cache index database 19 stores, as cache index data, a content name (for example, a URL (Uniform Resource Locator) name), a hash algorithm as a hash function, a hash value 13, and the content 12 in a cache storage device. Information such as the client device name (eg, the IP address or host name of the client device 20) stored in the storage device 21, the registration date and time as the date and time when the content 12 was stored in the cache storage device 21, and the total number of times the content 12 is used are stored. Have been. The name of the client device that stores the content 12 in the cache storage device 21 may include the names of a plurality of client devices 20.
[0040]
Next, the operation of the distributed cooperative content distribution system 10 having the above configuration will be described.
[0041]
First, an operation until the client device 20a and the client device 20b acquire the content 12 will be described.
[0042]
FIG. 3 is a first flowchart showing an operation until the client device of the distributed cooperative content distribution system according to the first embodiment of the present invention acquires the content, and FIG. 4 is a flowchart showing the operation of the first embodiment of the present invention. 9 is a second flowchart illustrating an operation until a client device of the distributed cooperative content distribution system acquires content.
[0043]
In this case, the cache index data of the client device 20a that acquires the content 12 from now on, the client device 20b that already holds the cache, and the client device 20 connected to the intranet 16 including the client device 20a and the client device 20b. 2 shows the flow of processing between the cache index server 17 that centrally manages the content and the content distribution server 11 that stores the content 12 and the hash value 13.
[0044]
First, the client device 20a transmits a distribution request of the hash value 13 corresponding to the content 12 to be acquired to the content distribution server 11.
[0045]
Next, the content distribution server 11 transmits the hash value 13 and the hash algorithm to the client device 20a. If the hash value 13 is obtained in advance by a hash algorithm as a hash function, since the hash value 13 has a small data amount and a short transmission time, the time required for the content distribution server 11 to respond to one client device 20a And the processing can be completed in a very short time. That is, the burden on the content distribution server 11 in this processing is light.
[0046]
Subsequently, the client device 20a confirms whether or not the content 12 having the same name and type as the content 12 and having the same hash value 13 is stored in its own cache storage device 21a. When the content 12 is stored in the cache storage device 21a, the content 12 is displayed (or operated) on a display unit by a browser function.
[0047]
If the content is not stored in the cache storage device 21a, the client device 20a stores in the cache index server 17 a content having the same name as the content 12 and the same hash value 13 in another client device 20. An existence check request for checking whether or not the information is registered is transmitted to the cache index server 17.
[0048]
When the cache index server 17 receives the existence confirmation request, the cache index server 17 searches its own cache index database 19 to determine whether or not a content having the same name as the content 12 and the same hash value 13 is registered. If it is registered, the cache index server 17 returns the name of the client device storing the corresponding content 12 in the cache storage device 21 to the client device 20a. If it has not been registered, it notifies the client device 20a that it has not been registered. If there are a plurality of client devices storing the corresponding content 12 in the cache storage device 21, all client device names may be returned. The method of replying in this case will be described later. As described above, since the cache index server 17 only returns the name of the client device storing the corresponding content 12 in the cache storage device 21, the time for responding to the client device 20a is shortened, and the time is extremely short. Can be completed. That is, the load on the cache index server 17 in this process becomes light.
[0049]
Next, when the client device 20a receives the name of the client device that stores the corresponding content 12 in the cache storage device 21 from the cache index server 17, whether or not the client device 20b as the client device is running is determined. Judge. In this case, for example, it is possible to determine whether or not the client device 20b is running by using an Internet protocol called ICMP (Internet Control Message Protocol: RFC792 / RFC1812).
[0050]
Then, when the client device 20b is activated, the client device 20a transmits a distribution request for the content 12 stored in the cache storage device 21b to the client device 20b. Subsequently, the client device 20b distributes the content 12 stored in the cache storage device 21b to the client device 20a.
[0051]
Subsequently, the client device 20a obtains a hash value 13 of the content 12 received from the client device 20b, and compares the hash value 13 with the hash value 13 obtained from the content distribution server 11 to determine the authenticity of the content 12. If the two hash values 13 match, the content received from the client device 20b is true, that is, the content 12, and the content 12 is output. Display (or operate).
[0052]
Further, when the same name as the content 12 and the same hash value 13 are not registered in another client device 20, when the client device 20b is not activated, and when both the hash values 13 Do not match, the client device 20a transmits a distribution request for the content 12 to the content distribution server 11. Subsequently, the content distribution server 11 transmits the content 12 to the client device 20a. Since it is not necessary to perform the next process after the display processing of the content 12 is completely completed, the display processing of the content 12 and the subsequent processing may be performed in parallel.
[0053]
Next, upon displaying the content 12 received from the client device 20b or the content distribution server 11, the client device 20a determines whether to store the content 12 in its own cache storage device 21a according to a preset condition. . Details of this processing content will be described later.
[0054]
Then, when the above condition is satisfied, the client device 20a transmits the hash value 13 and the hash algorithm to the cache index server 17, and applies for registration of the content 12. Subsequently, the cache index server 17 that has received the registration application performs additional registration in the cache index database 19. Note that, even if a content having the same name as the content 12 is already registered, if the respective hash values are different, the cache index server 17 determines that the content 12 has been updated and has already been registered. Data related to content can also be deleted.
[0055]
Subsequently, the client device 20a stores the content 12 in the cache storage device 21a, and ends a series of processing.
[0056]
Next, the flowchart will be described.
Step S1 The client device 20a transmits a distribution request for the hash value 13 to be obtained to the content distribution server 11.
Step S2: The content distribution server 11 transmits the hash value 13 and the hash algorithm to the client device 20a.
Step S3: The client device 20a determines whether or not the corresponding content 12 having the same hash value 13 exists in its own cache storage device 21a. If it is in the cache storage device 21a, the process proceeds to step S4.
Step S4: The client device 20a displays (or operates) the content 12 on a browser or the like.
Step S5: The client device 20a transmits an existence confirmation request to the cache index server 17 as to whether or not the corresponding content 12 having the same hash value 13 is registered in another client device 20.
Step S6: The cache index server 17 determines whether or not the corresponding content 12 is registered in the cache index database 19. If registered, the process proceeds to step S7, and if not registered, the process proceeds to step S8.
Step S7: The cache index server 17 transmits to the client device 20a the name of the client device that stores the corresponding content 12 in the cache.
Step S8: The cache index server 17 transmits “no registration” to the client device 20a.
Step S9: The client device 20a determines whether or not the client device 20b holding the corresponding content 12 is running. If the client device 20b holding the corresponding content 12 is running, the process proceeds to step S10. If the client device 20b holding the corresponding content 12 is not running, the process proceeds to step S14.
Step S10: The client device 20a transmits a distribution request for the content 12 stored in the cache storage device 21b. .
Step S11: The client device 20b transmits the content 12 held in the cache storage device 21b to the client device 20a.
Step S12: The client device 20a checks the received hash value 13.
Step S13: The client device 20a determines whether or not the hash values 13 match. If they match, the process proceeds to step S16. If they do not match, the process proceeds to step S14.
Step S14: The client device 20a requests the content distribution server 11 to transmit the content 12.
Step S15: The content distribution server 11 transmits the content 12 to the client device 20a.
Step S16: The client device 20a displays (or operates) the received content 12.
Step S17: The client device 20a determines whether or not the condition for storing the content 12 in the cache storage device 21a is satisfied. When the condition is satisfied, the process proceeds to step S18, and when the condition is not satisfied, the process ends.
Step S18: The client device 20a makes an application for registration of the content 12 to the cache index server 17.
Step S19: The cache index server 17 additionally registers in the cache index database 19.
Step S20: The client device 20a stores the content 12 in the cache storage device 21a, and ends the processing.
[0057]
Next, a case where there are a plurality of client devices 20 storing the same content 12 in the cache storage device 21 will be described.
[0058]
In this case, when there is a plurality of other client devices 20 storing the predetermined content 12 requested by a certain client device 20, the cache index server 17 sorts the list of the other client devices 20 according to a predetermined algorithm. The list is transmitted to the client device 20, and the client device 20 tries to acquire the contents 12 in the order of the sorted list. That is, in step S6, when a plurality of client devices 20 storing the content 12 corresponding to the cache index database 19 in the cache storage device 21 are registered, the cache index server 17 transmits the client device 20a to the client device 20a. The list of names is randomly rearranged or regularly shifted each time so that access is not always concentrated on a specific client device 20.
[0059]
Then, the client device 20a attempts to acquire the content 12 from the client device 20 listed first in the list of client device names received from the cache index server 17, and if there is no response within a predetermined time, the next Attempt to acquire the content 12 from the client device 20.
[0060]
Next, conditions for determining whether to store the content 12 in its own cache storage device 21a will be described.
[0061]
In this case, since the content 12 is reused in other client devices 20, the content 12 must not include personal information.
[0062]
Therefore, for example, conditions are set such that the personal information (prohibited word) is not included in the content name, and the keyboard is not used in the operation until the content 12 is obtained. The prohibited word is registered in advance.
[0063]
In addition, as the simplest method, there is a method in which only a content name having no argument is targeted. For example, in the case of HTTP, it can be determined whether or not the content name has an argument. That is, if the content name is http: // www. aaa. bbb. ccc. In the case of html, there is no argument, and the content name is http: // www. aaa. bbb. ccc. If html & userid = 1234..., there is an argument.
[0064]
Further, it may be set so as not to be saved depending on the type or data format of the content 12.
[0065]
Next, an operation of deleting the content 12 stored in the cache storage device 21 in order to suppress an infinite increase in the content 12 stored in the cache storage device 21 will be described.
[0066]
In this case, in order to delete the content 12 stored in the cache storage device 21, a method of deleting the content according to an instruction from the client device 20 (for example, when a certain amount of content is accumulated (accumulated)) and a cache index server There are two methods of deleting with the instruction of 17 (when the old content 12 exists, when the content 12 is updated, etc.).
[0067]
In the present embodiment, the two methods described above can be performed simultaneously.
[0068]
Next, an operation of deleting the content 12 stored in the cache storage device 21 according to an instruction from the client device 20 will be described.
[0069]
FIG. 5 is a flowchart showing an operation of deleting content stored in the cache storage device according to an instruction of the client device according to the first embodiment of the present invention.
[0070]
In this case, the cache index server 17 deletes predetermined information from the cache index database 19 according to a request from the client device 20. Note that this processing is started when new content 12 is acquired. Specifically, this is after the processing of step S19 in FIG. 4 has been completed.
[0071]
First, it is determined whether or not the total amount of the contents 12 stored in the cache storage device 21 of the client device 20 itself is equal to or more than a predetermined threshold value. The threshold can be freely set by the administrator of the client device 20.
[0072]
If it is smaller than the threshold value, the process ends. If the value is equal to or larger than the threshold value, the client device 20 transmits an index deletion request to the cache index server 17. Subsequently, when the cache index server 17 receives the index deletion request, the cache index server 17 deletes the cache index data of the corresponding content 12 from the cache index server 17 (only the client device name when other client devices 20 are also registered). Then, an index deletion result as a result of the deletion is transmitted to the client device 20.
[0073]
Next, upon receiving the index deletion result from the cache index server 17, the client device 20 deletes the content 12 stored in its own cache storage device 21 and ends the processing.
[0074]
Next, the flowchart will be described.
Step S21: The client device 20 determines whether or not the total amount of the contents 12 in the cache storage device 21 is equal to or larger than a threshold. If it is equal to or greater than the threshold, the process proceeds to step S22, and if it is smaller than the threshold, the process ends.
Step S22: The client device 20 transmits an index deletion request to the cache index server 17.
Step S23: The cache index server 17 deletes the information of the corresponding content from the cache index database 19.
Step S24: The cache index server 17 transmits the index deletion result to the client device 20.
Step S25: The client device 20 deletes the content 12 from the cache storage device 21, and ends the processing.
[0075]
Next, an operation of deleting the content 12 stored in the cache storage device 21 according to an instruction from the cache index server 17 will be described.
[0076]
FIG. 6 is a flowchart showing the operation of deleting the content stored in the cache storage device according to the instruction of the cache index server in the first embodiment of the present invention.
[0077]
In this case, the cache index server 17 periodically checks the frequency of use of the cache index database 19, and transmits a request to delete the content 12 with a low frequency of use. This process is executed at a cycle determined by the administrator of the cache index server 17.
[0078]
First, the cache index server 17 searches its own cache index database 19 and determines whether there is any content 12 whose usage frequency is equal to or less than a certain number or an updated content 12.
[0079]
The content 12 whose usage frequency is equal to or less than a certain number includes the elapsed time tx from the date and time of first registration to the present, the total number of usages n of the content 12, the usage frequency threshold ft, and the non-deletion period te [registration] The period in which the content 12 that has just been created is not subject to deletion]]
Condition: If tx> te and n / tx <ft, delete target
It becomes.
[0080]
In addition, the determination condition of the updated content 12 is to search for the same content name having a different hash value 13 and to delete the one having the oldest registration date and time.
[0081]
When there is the content 12 to be deleted, the cache index server 17 deletes the cache index data from its own cache index database 19.
[0082]
Next, the cache index server 17 transmits a content deletion request to all the client devices 20 storing the content 12 to be deleted, and each client device 20 deletes the content 12 from its own cache storage device 21. . For example, the cache index server 17 transmits the content deletion request again after a certain period of time to the client device 20 that has failed to receive the content deletion request due to the power-off of the client device 20 or the like. In addition, when the number of registered data exceeds a certain number, the data that is used less frequently is deleted.
[0083]
Next, the flowchart will be described.
Step S31: The cache index server 17 determines whether there is any content whose usage frequency is equal to or less than a certain number or the updated content 12. If there is the content 12 whose usage frequency is equal to or less than the certain number or the updated content 12, the process proceeds to step S32. If there is no content 12 whose usage frequency is equal to or less than the certain number or the updated content 12, the process ends.
Step S32: The cache index server 17 deletes the registered contents from the cache index database 19.
Step S33: The cache index server 17 transmits a content deletion request to the client device 20.
Step S34: Each client device 20 deletes the content 12 from the cache storage device 21.
Step S35: The client device 20 transmits a deletion end to the cache index server 17.
Step S36: The cache index server 17 determines whether or not a content deletion request has been transmitted to all the client devices 20 having the content 12 to be deleted. When the content deletion request has been transmitted to all the client devices 20, the process is terminated, and when the content deletion request has not been transmitted to all the client devices 20, the process returns to step S33.
[0084]
As described above, in the present embodiment, the frequently used content 12 can be obtained directly from many client devices 20. Therefore, the load on the content distribution server 11 to which access has been concentrated is reduced, and the time required for acquiring the content 12 can be reduced.
[0085]
Further, even in an environment where the content of the content 12 changes irregularly, the content of the content 12 can be confirmed by the hash value 13, so that the communication processing with each content distribution server 11 can be shortened.
[0086]
Furthermore, since a means for confirming whether or not the content 12 obtained from another client device 20 is correct is provided, it is possible to prevent the display of the unauthorized content 12.
[0087]
Next, by adding a function of more strictly verifying the content distribution server 11 itself and the hash value 13, the number of processes is larger than in the first embodiment, but the reliability of the content body can be increased. A second embodiment of the present invention will be described. In addition, about what has the same structure as 1st Embodiment, the description is abbreviate | omitted by attaching the same code | symbol.
[0088]
FIG. 7 is a diagram showing a configuration of a distributed cooperative content distribution system according to the second embodiment of the present invention.
[0089]
As shown in the figure, the content distribution server 11a and the content distribution server 11b in the present embodiment store the content 12a and the content 12b, the content signature value 33a and the content signature value obtained by the public key encryption method in the storage unit, respectively. 33b, data such as a public key certificate 34a and a public key certificate 34b that certify the public key of the content distribution server 11a and the content distribution server 11b by a third party (CA) are stored. The content signature value 33a and the content signature value 33b are based on a hash value (MD5, SHA1, or the like) of the raw data of the content 12a or the content 12b based on a public key encryption method (for example, RSA or DSA). Created with its own private key. Note that the content signature value 33a and the content signature value 33b can be obtained in advance. Further, in the present embodiment, as a specific example of the public key certificate 34a and the public key certificate 34b, the most general X.264 certificate is used. 509 public key certificate will be described as an example. When the content signature value 33a and the content signature value 33b and the public key certificate 34a and the public key certificate 34b are described in an integrated manner, the content signature value 33 and the public key certificate 34 will be described.
[0090]
The client device 20a and the client device 20b have a cache storage device 21a and a cache storage device 21b, respectively, and have a public key certificate store 22a storing the public key certificate 34a and the public key certificate 34b. Each has a book store 22b. The public key certificate store 22a and the public key certificate store 22b are provided so that the public key certificate 34a and the public key certificate 34b do not have to be obtained from the content distribution server 11a and the content distribution server 11b each time. Provided. When the public key certificate store 22a and the public key certificate store 22b are described in an integrated manner, the public key certificate store 22 will be described.
Further, a public key certificate verification server 37 for verifying the validity of the public key certificate 34 is connected to the intranet 16. The public key certificate verification server 37 performs verification on behalf of whether the public key certificate 34 is valid. Verification means the expiration date of the public key certificate 34, determination of whether or not the public key certificate 34 is listed on a revocation list (CRL) published by the source (CA), This is verification of items such as a determination as to whether the signature of the transmission source (CA) attached to 34 is correct (this may be performed only when newly acquired from the content distribution server 11). Known public examples of the public key certificate verification server 37 include XKMS (http://www.w3.org/TR/xkms/), OCSP (Online Certificate Status Protocol: RFC2560), and SCVP (Simple Certificate). Validation Protocol).
[0091]
Next, the operation of the distributed cooperative content distribution system having the above configuration will be described.
[0092]
First, an operation until the client device 20a acquires the content 12 will be described.
[0093]
FIG. 8 is a flowchart showing an operation until a client device of the distributed cooperative content distribution system according to the second embodiment of the present invention acquires content.
[0094]
First, the client device 20a determines whether or not the public key certificate 34a of the content distribution server 11a to be accessed is stored in its own public key certificate store 22a, and the client device 20a stores the public key certificate 34a in the public key certificate store 22a. If not, a distribution request for the public key certificate 34a is transmitted to the content distribution server 11a. When receiving the distribution request for the public key certificate 34a from the client device 20a, the content distribution server 11a transmits its own public key certificate 34a to the client device 20a.
[0095]
When the public key certificate 34a of the content distribution server 11a is stored in its own public key certificate store 22a, the client device 20a sends a request for verification of the public key certificate 34a of the target content distribution server 11a. It is transmitted to the public key certificate verification server 37.
[0096]
Next, the public key certificate verification server 37 verifies the public key certificate 34a, and returns the verification result to the client device 20a. Subsequently, the client device 20a that has received the verification result of the public key certificate 34a determines whether the public key certificate 34a is valid based on the verification result. If the public key certificate 34a is not valid, the client device 20a deletes the public key certificate 34a from the public key certificate store 22a and acquires a new public key certificate 34a again from the content distribution server 11a. . If the public key certificate 34a is valid, the client device 20a adds the public key certificate 34a to its own public key certificate store 22a. The client device 20a acquires a public key from the public key certificate 34a.
[0097]
Subsequently, the client device 20a transmits a distribution request for the content signature value 33a to the content distribution server 11a. Upon receiving the distribution request, the content distribution server 11a transmits the content signature value 33a to the client device 20a.
[0098]
Next, the client device 20a obtains the hash value of the content 12a from the content signature value 33a based on the public key obtained from the public key certificate 34a.
Note that the subsequent operation is the same as in the first embodiment, and a description thereof will be omitted.
[0099]
Next, the flowchart will be described.
Step S41: The client device 20a determines whether or not the public key certificate 34a of the content distribution server 11a is stored. If possessed, the process proceeds to step S44; otherwise, the process proceeds to step S42.
Step S42: The client device 20a transmits a distribution request for the public key certificate 34a of the content distribution server 11a to the content distribution server 11a.
Step S43: The content distribution server 11a transmits the public key certificate 34a of the content distribution server 11a to the client device 20a.
Step S44: The client device 20a requests the public key certificate verification server 37 to verify the public key certificate 34a.
Step S45: The public key certificate verification server 37 verifies the public key certificate 34a.
Step S46: The public key certificate verification server 37 transmits the verification result of the public key certificate 34a to the client device 20a.
Step S47: The client device 20a determines whether or not the public key certificate 34a is valid based on the verification result of the public key certificate 34a. When the public key certificate 34a is valid, the process proceeds to step S49, and when the public key certificate 34a is not valid, the process proceeds to step S48.
Step S48: The client device 20a deletes the public key certificate 34a stored therein, and returns to step S41.
Step S49: The client device 20a adds the public key certificate 34a to the public key certificate store 22a.
Step S50: The client device 20a requests the content signature value 33a from the content distribution server 11a.
Step S51: The content distribution server 11a transmits the content signature value 33a to the client device 20a.
Step S52: The client device 20a acquires a hash value from the content signature value 33a.
[0100]
Thus, in the present embodiment, the content distribution server 11 itself and the hash value can be more strictly verified. However, the processing amount of the content distribution server 11 increases compared to the first embodiment.
[0101]
Also, only the secret key stored in the correct content distribution server 11 can create the correct content signature value 33a. Therefore, even if another device is impersonating the server that distributes the fake content, the hash value obtained with the public key of the public key certificate 34a from the content signature value 33a created by the device that distributed the fake content is , Because it does not match the hash value of the fake content.
[0102]
By the way, in the second embodiment, the public key certificate 34 of the content distribution server 11 is obtained and stored by the client device 20, but as another embodiment, the public key certificate management verification server A third embodiment of the present invention in which a public key certificate of a distribution server is obtained and stored will be described. In addition, about what has the same structure as 1st and 2nd embodiment, the description is abbreviate | omitted by attaching | subjecting the same code | symbol.
[0103]
FIG. 9 is a diagram showing a configuration of a distributed cooperative content distribution system according to the third embodiment of the present invention.
[0104]
In the present embodiment, a public key certificate management verification server 47 is connected to the intranet 16 instead of the public key certificate verification server 37 in the second embodiment. As shown in the figure, the public key certificate management verification server 47 includes a public key certificate store 48 for storing the public key certificate 34 of the content distribution server 11. When the public key certificate management verification server 47 receives a public key request from the content distribution server 11 specified by the client device 20a, the public key certificate management verification server 47 obtains and stores the corresponding public key certificate 34, and Verification of whether the certificate 34 is valid is performed instead. If the public key certificate 34 is valid, the public key is transmitted to the client device 20a. As a publicly known specific example of the public key certificate management verification server 47, there is XKMS (http://www.w3.org/TR/xkms/).
[0105]
Next, the operation of the distributed cooperative content distribution system having the above configuration will be described.
[0106]
First, an operation until the client device 20a acquires the content 12 will be described.
[0107]
FIG. 10 is a flowchart showing an operation until a client device of the distributed cooperative content distribution system according to the third embodiment of the present invention acquires content.
[0108]
First, the client device 20a requests the public key certificate management verification server 47 to acquire the public key of the content distribution server 41 owning the content 12a to be acquired. Then, the public key certificate management verification server 47 determines whether or not the requested public key certificate 34a of the content distribution server 41 is in its own public key certificate store 48. If not, it requests the public key certificate 34a from the content distribution server 41 and sends the public key certificate 34a.
[0109]
Next, the public key certificate management verification server 47 verifies the received public key certificate 34a. If it is determined from the verification result of the public key certificate 34a that the public key certificate 34a is invalid, the public key certificate management verification server 47 converts the public key certificate 34a into a public key certificate. Then, the public key certificate 34a is deleted from the content store 48, and a new public key certificate 34a is obtained from the content distribution server 41 again.
[0110]
If it is determined that the public key certificate 34a is valid, the public key certificate management verification server 47 adds the public key certificate 34a to its own public key certificate store 48, and verifies the verified public key certificate. The public key in the certificate 34a is transmitted to the client device 20a.
[0111]
Next, the client device 20a transmits a request for the content signature value 33a to the content distribution server 41. Upon receiving the request for the content signature value 33a, the content distribution server 41 transmits the content signature value 33a to the client device 20a. Then, the client device 20a obtains a hash value of the content from the content signature value 33a based on the received public key. Note that the subsequent operation is the same as in the first embodiment, and a description thereof will be omitted.
[0112]
Next, the flowchart will be described.
Step S61: The client device 20a requests the public key certificate management verification server 47 for the public key of the content distribution server 41.
Step S62: The public key certificate management verification server 47 determines whether or not the public key certificate 34a of the content distribution server 41 is owned. If so, the process proceeds to step S65, and if not, the process proceeds to step S63.
Step S63: The public key certificate management verification server 47 requests the content distribution server 41 for the public key certificate 34a of the content distribution server 41.
Step S64: The content distribution server 41 transmits the public key certificate 34a of the content distribution server 41 to the public key certificate management verification server 47.
Step S65: The public key certificate management verification server 47 verifies the public key certificate 34a.
Step S66: The public key certificate management verification server 47 determines whether the public key certificate 34a is valid based on the verification result of the public key certificate 34a. When the public key certificate 34a is valid, the process proceeds to step S68, and when the public key certificate 34a is not valid, the process proceeds to step S67.
Step S67: The public key certificate management verification server 47 deletes the public key certificate 34a stored therein, and returns to step S62.
Step S68: The public key certificate management verification server 47 adds the public key certificate 34a to the public key certificate store 48.
Step S69: The public key certificate management verification server 47 transmits the public key to the client device 20a.
Step S70: The client device 20a requests the content distribution server 41 for the content signature value 33a.
Step S71: The content distribution server 41 transmits the content signature value 33a to the client device 20a.
Step S72: The client device 20a acquires a hash value from the content signature value 33a.
[0113]
As described above, in the present embodiment, the client device 20 can delegate the acquisition and verification of the public key to another device, so that the processing load on the client device 20 is reduced as compared with the second embodiment. Can be reduced.
[0114]
Next, when the content 12 is not stored in the storage means of the client device 20 of the intranet 16 under the management of the cache index server 17, an inquiry is made to the cache index server 17 of another network 14. An embodiment will be described. In addition, about what has the same structure as 1st Embodiment, the description is abbreviate | omitted by attaching the same code | symbol.
[0115]
FIG. 11 is a diagram showing a configuration of a distributed cooperative content distribution system according to the fourth embodiment of the present invention.
[0116]
As shown in the figure, in the present embodiment, two intranets 16a and 16b are connected to the Internet 14. Here, the intranet 16a and the intranet 16b have the same configuration as the intranet 16 in the first embodiment, and the same devices are connected. That is, a cache index server 17a, a client device 20a, and a client device 20b are connected to the intranet 16a, and a cache index server 17b, a client device 20c, and a client device 20d are connected to the intranet 16b. The intranet 16a and the intranet 16b are connected to the Internet 14 via the router 15a and the router 15b, respectively. In addition, the thing with the same number in the provided code | symbol has the same structure.
[0117]
Next, the operation of the distributed cooperative content distribution system having the above configuration will be described.
[0118]
First, an operation until the client device 20a acquires the content will be described.
[0119]
FIG. 12 is a flowchart showing an operation until the client device of the distributed cooperative content distribution system according to the fourth embodiment of the present invention acquires content.
[0120]
Here, the operation until the client device 20a transmits the existence confirmation request to the cache index server 17a is the same as that of the first embodiment, and the description is omitted. The client device 20a transmits a presence confirmation request to the cache index server 17a on the same intranet 16a.
[0121]
Then, the cache index server 17a searches its own cache index database 19a, and if a client device 20 that stores the corresponding content 12 in the cache storage device 21 is registered, transmits the client device name to the client device 20a. I do. Then, the client device 20a performs the operation after step S9 in the first embodiment.
[0122]
If the client device 20 is not registered, the cache index server 17a transmits an inquiry to the cache index server 17b connected to another intranet 16b. Then, the cache index server 17b searches its own cache index database 19b, and if a client device 20 that stores the corresponding content 12 in the cache storage device 21 is registered, the client device name is stored in the cache index server 17a. Send. When the client device is not registered, the cache index server 17b transmits a notification to that effect to the cache index server 17a.
[0123]
Next, the cache index server 17a receives the result of the inquiry from the cache index server 17b. When the client device 20 connected to the intranet 16b stores the corresponding content 12, the client device 20 transmits the client device name to the client device 20a. If the client device has not been registered, the result of no registration is transmitted to the cache index server 17a. Note that the subsequent operation is the same as in the first embodiment, and a description thereof will be omitted.
[0124]
Next, the flowchart will be described.
Step S81: The client device 20a transmits an existence confirmation request of the corresponding content to the cache index server 17a.
Step S82: The cache index server 17a determines whether or not the client device 20 owning the corresponding content exists in the cache index database 19a. If it exists, the process proceeds to step S83. If it does not exist, the process proceeds to step S84.
Step S83: The cache index server 17a transmits the name of the client device storing the corresponding content 12 in the cache storage device 21 to the client device 20a.
Step S84: The cache index server 17a transmits an inquiry to another cache index server 17b.
Step S85: The cache index server 17b determines whether or not the client device 20 owning the corresponding content 12 exists in the cache index database 19b. If it exists, the process proceeds to step S86; otherwise, the process proceeds to step S87.
Step S86: The cache index server 17b transmits the name of the client device storing the relevant content 12 in the cache storage device 21 to the cache index server 17a.
Step S87: The cache index server 17b transmits to the cache index server 17a that there is no client device name storing the corresponding content in the cache storage device 21.
Step S88: The cache index server 17a receives a query result from another cache index server.
Step S89: The cache index server 17a determines whether or not the client device owning the corresponding content is registered in another cache index server 17. If it has been registered, the process returns to step S83, and if it has not been registered, the process proceeds to step S90.
Step S90: The cache index server 17a transmits “no registration” to the client device 20a.
[0125]
As described above, in the present embodiment, the range of the client devices 20 registered in the cache index database 19 is expanded, so that the number of times of content transmission from the content distribution server 11 can be further reduced. Load can be reduced.
[0126]
In the first to fourth embodiments, the target content 12 is, for example, a web page, character data, audio data such as music, video data, image data such as a photograph, software, and the like. It may be of any type. In addition, communication between the devices may be performed by encrypted communication such as SSL or IPsec. Further, the cache index server 17 may be composed of a plurality of servers for backup of the cache index database 19 and load distribution.
[0127]
In the second embodiment, the case where the public key certificate verification server 37 performs the verification of the public key certificate has been described. In the case where the client device 20 possesses the information, each client device 20 may perform the operation independently.
[0128]
In the second and third embodiments, the verification result can be used not every time if the policy of the source of the public key certificate verification permits, but within a period determined by the source. . For example, the previous verification result may be used until the next transmission date of the revocation list (CRL).
[0129]
FIG. 13 is a diagram showing another configuration of the distributed cooperative content distribution system according to the fourth embodiment of the present invention.
[0130]
Furthermore, in the fourth embodiment, only two cache index servers 17 are linked, but three or more cache index servers may be linked. Further, as shown in FIG. 13 as a connection form, intranets may be directly connected to each other.
[0131]
It should be noted that the present invention is not limited to the above-described embodiment, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.
[0132]
【The invention's effect】
As described above in detail, according to the present invention, in a distributed cooperative content distribution system, the load on the content distribution server can be reduced even in an environment where contents change irregularly, and the client device It is possible to confirm whether or not the contents stored in the cache of the client device have been illegally changed, and other client devices can access only the cache device of the client device.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a distributed cooperative content distribution system according to a first embodiment of the present invention.
FIG. 2 is a diagram showing contents of a cache index database according to the first embodiment of the present invention.
FIG. 3 is a first flowchart illustrating an operation until a client device of the distributed cooperative content distribution system according to the first embodiment of the present invention acquires content.
FIG. 4 is a second flowchart illustrating an operation of the client device of the distributed cooperative content distribution system according to the first embodiment of the present invention until the client device acquires the content.
FIG. 5 is a flowchart illustrating an operation of deleting content stored in a cache storage device according to an instruction of a client device according to the first embodiment of the present invention.
FIG. 6 is a flowchart illustrating an operation of deleting a content stored in a cache storage device according to an instruction of a cache index server in the first embodiment of the present invention.
FIG. 7 is a diagram illustrating a configuration of a distributed cooperative content distribution system according to a second embodiment of the present invention.
FIG. 8 is a flowchart showing an operation until a client device of the distributed cooperative content distribution system acquires content in the second embodiment of the present invention.
FIG. 9 is a diagram showing a configuration of a distributed cooperative content distribution system according to a third embodiment of the present invention.
FIG. 10 is a flowchart showing an operation until a client device of the distributed cooperative content distribution system according to the third embodiment of the present invention acquires content.
FIG. 11 is a diagram illustrating a configuration of a distributed cooperative content distribution system according to a fourth embodiment of the present invention.
FIG. 12 is a flowchart illustrating an operation until a client device of a distributed cooperative content distribution system obtains content according to a fourth embodiment of the present invention.
FIG. 13 is a diagram showing another configuration of the distributed cooperative content distribution system according to the fourth embodiment of the present invention.
[Explanation of symbols]
10 Distributed cooperative content distribution system
11, 11a, 11b, 41 Content distribution server
12, 12a, 12b content
13, 13a, 13b Hash value
17, 17a, 17b Cache index server
19, 19a, 19b Cache index database
20, 20a, 20b, 20c, 20d Client device
21, 21a, 21b, 21c, 21d Cache storage device
22, 22a, 22b, 48 Public key certificate store
33, 33a, 33b Content signature value
34, 34a, 34b Open Key Certificate
37 Public Key Certificate Verification Server
47 Public key certificate management verification server

Claims (17)

(A) a content distribution server that distributes content and unique information that specifies the content;
(B) a client device including a cache storage device that stores the acquired content;
(C) a distributed cooperative content distribution system, comprising: a cache index server having a cache index database that stores unique information corresponding to each of the contents and data relating to a client device. One client device acquires unique information corresponding to predetermined content from the content distribution server, and inquires of the cache index server whether there is another client device that stores the content corresponding to the unique information. Transmitting, when there is the other client device, acquiring the content from the other client device, calculating unique information corresponding to the content, and combining the unique information with the unique information acquired from the content distribution server. The distributed cooperative content distribution system according to claim 1, wherein the content is compared to determine whether the content is true, and when the content is true, the content is output and stored in a cache storage device. (A) a content distribution server that distributes a content, unique information for identifying the content, a content signature value obtained by a public key encryption method, and a public key certificate in which a public key is guaranteed by a third party;
(B) a client device including a cache storage device for storing the obtained content and a public key certificate store for storing the obtained public key certificate;
(C) a cache index server including a cache index database for storing unique information corresponding to each of the contents and data relating to the client device;
(D) A distributed cooperative content distribution system, comprising: a public key certificate verification server that verifies the validity of the public key certificate. (A) When the client device does not store the public key certificate of the predetermined content distribution server, the client device acquires the public key certificate from the content distribution server and checks the validity of the public key certificate. Sending a request to the public key certificate server,
(B) the public key certificate server transmits a verification result of the public key certificate to the one client device;
(C) if the public key certificate is valid, the one client device stores the public key certificate, acquires a public key from the public key certificate, and obtains a predetermined content from the content distribution server. And obtains unique information of the predetermined content from the content signature value based on the public key, and inquires whether there is another client device that stores the content corresponding to the unique information. To the cache index server, if there is the other client device, obtain the content from the other client device, calculate the unique information corresponding to the content, from the unique information and the content distribution server The authenticity of the content is determined by comparing the acquired unique information with the acquired unique information. Distributed Cooperative content distribution system according to claim 3, stored in the cache memory outputs the tool. (A) a content distribution server that distributes a content, unique information for identifying the content, a content signature value obtained by a public key encryption method, and a public key certificate in which a public key is guaranteed by a third party;
(B) a client device including a cache storage device for storing the obtained content and a public key certificate store for storing the obtained public key certificate;
(C) a cache index server including a cache index database for storing unique information corresponding to each of the contents and data relating to the client device;
(D) a public key certificate store for storing the obtained public key certificate, and a public key certificate verification server for obtaining, storing and validating the public key certificate. Distributed cooperative content distribution system. (A) one client device transmits the public key distribution request to a public key certificate management verification server,
(B) the public key certificate server acquires and verifies the public key, transmits a valid public key to the one client device,
(C) the one client device obtains a content signature value of predetermined content from the content distribution server, obtains unique information of the predetermined content from the content signature value based on the public key, and obtains the unique information. Sends to the cache index server an inquiry as to whether there is another client device that stores the content corresponding to the content, and if there is the other client device, obtains the content from the other client device; Is calculated, and the authenticity of the content is determined by comparing the unique information with the unique information acquired from the content distribution server. If the content is true, the content is output. 6. The distributed cooperative content distribution system according to claim 5, wherein the content distribution system stores the contents in a cache storage device. Temu. The distributed cooperative content distribution system according to claim 1, wherein the client device stores the content in the cache storage device after determining that the acquired content is true. The distributed cooperative content distribution system according to claim 1, wherein the client device stores the content in the cache storage device according to a name, a type, and the like of the content. The cache index server, when there are a plurality of other client devices that store predetermined content requested by one client device, sorts the list of the other client devices according to a predetermined algorithm into the one client device. The distributed cooperative content distribution system according to any one of claims 1 to 6, wherein the content is transmitted to a device, and the one client device tries to acquire the content in the order of the sorted list. The distributed cooperative content distribution system according to any one of claims 1 to 6, wherein the cache index server deletes predetermined information from a cache index database according to a request from the client device. The distributed cooperative content according to claim 10, wherein the client device transmits a request to the cache index server when a storage amount of the content stored in the cache storage device exceeds a condition determined by an administrator of the client device. Delivery system. The distributed cooperative content distribution system according to claim 1, wherein the client device deletes the content from the cache storage device according to a request from the cache index server. 13. The distributed cooperative content distribution system according to claim 12, wherein the cache index server periodically checks the use frequency of the cache index database and transmits a request to delete the content whose use frequency is low. 13. The distributed cooperative content distribution system according to claim 12, wherein the cache index server transmits a request to delete a content whose usage frequency is low when the amount of cached data exceeds a predetermined condition. 13. The distributed cooperative content distribution system according to claim 12, wherein the cache index server transmits a request for deleting content having older unique information from registered content having the same name, type, and the like. 7. The cache index server according to claim 1, wherein when another client device that stores the predetermined content requested by one client device is not included in the cache index database, the cache index server queries another cache index server. 8. A distributed cooperative content distribution system according to the section. The distributed cooperative content distribution system according to any one of claims 1 to 16, wherein the unique information is a hash value.

Images