JP2004032307A - Method and server for delivering content, computer-readable storage medium recording content delivery processing program and content delivery processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for delivering contents in which utilization of the contents can be prompted to users by correcting the sense of unfairness among users in the utilization of contents. <P>SOLUTION: In the method for delivering a content where contents encrypted by a content key, the content key encrypted by a delivery key, and a secure package storing content information are delivered to terminals via a network, a decrypt key (=decrypt delivery key) of a previously encrypted content is distributed by a secret distributing method to L distribute decrypt delivery keys. A hash value, being obtained from contents utilized by a user, is employed as an arbitrary distributed decrypt delivery key among those distributed by the secret distributing method. Remaining distributed decrypt delivery keys are obtained, using the arbitrary distribute decrypt delivery key and employed as a distribute decrypt delivery key for a content different from that utilized by the user. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to content distribution using a network, and more particularly, to a content distribution method, a content distribution server, and a content distribution server for associating a plurality of contents with each other and realizing billing based on a use history of the contents. The present invention relates to a computer-readable storage medium storing a processing program and a content distribution processing program.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, various contents (referred to as digital contents having a structure as a set of bit strings that can be recorded on a single recording medium) such as audio data, image data, and a game program have been used for networks on the Internet, CDs, DVDs and the like. It is distributed via a storage medium, and can be reproduced on a device such as a personal computer owned by a user or stored in an attached storage device. When distributing the above content via an Internet network, user information such as a credit number is acquired at the time of distribution, and a usage fee for providing the content is acquired. On the other hand, if the content is distributed by a storage medium such as a CD or a DVD, the price is collected when the content is provided.
[0003]
In the distribution of contents, a system that considers security is constructed in order to prevent unauthorized duplication and the like, and a method of providing contents only to authorized users is generally adopted. For example, as a method of providing content only to authorized users, a concept called “super distribution” has been proposed. In this “super distribution”, the content to be protected is encrypted with an encryption key corresponding to the content, and is freely distributed through various channels such as a mobile phone, the Internet, a CD-ROM, and a KIOSK terminal. The user can obtain the copyrighted content and copy it without restriction, but without the license including the key information for decrypting the encrypted content, the user cannot reproduce the encrypted content. As described above, in the "super distribution", a legal peer-to-peer distribution is realized.
[0004]
[Problems to be solved by the invention]
By the way, in the "super distribution" described above, each content is handled independently. Therefore, at the time of video distribution on TV, even if an advertisement is broadcast, the TV program does not become free, even if the user purchases a magazine, the product in the magazine cannot be purchased, or the user is inconvenient. Had become something.
[0005]
In the content distribution service for mobile terminals such as mobile phones, since mobile phones are always carried around by users, it is possible to use short-capacity content such as digest video or frame-by-frame video with immediacy. Since the communication speed and the size of the screen are limited, it is generally difficult to use large-capacity content such as high-quality video. However, after using small-capacity content (movie trailer) on a mobile phone or the like, and then using large-capacity content (movie main part) related to the used content on a personal computer or the like, the small-capacity content is used. It is disadvantageous for a user who has already used the small-capacity content to charge a fee in the same way as a user who does not have a fee. As described above, conventionally, content is independently distributed, and the billing method is based on the unit of use of the content. Therefore, unfairness occurs between users.
[0006]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to solve the problem of unfairness among users at the time of using content and to promote content usage to users. A distribution method, a content distribution server, a computer-readable storage medium recording a content distribution processing program, and a content distribution processing program are provided.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a secure package storing content encrypted with a content key, a content key encrypted with a distribution key, and content information. In a content distribution method for distributing to a terminal via a network, a decryption key (= decryption distribution key) of the encrypted content is distributed to L distributed decryption distribution keys by a secret sharing method, and the obtained user uses the decryption key. A hash value obtained from the content is set as an arbitrary distributed decryption distribution key among the distributed decryption distribution keys distributed by the secret sharing method, and the remaining distributed decryption of the decryption key is performed using the arbitrary distributed decryption distribution key. A distribution key is obtained, and the obtained distributed decryption distribution key is used as a distributed decryption distribution key for content different from the content used by the user. It is characterized in Rukoto.
[0008]
According to a second aspect of the present invention, in the content distribution method, the secret sharing scheme is any one of a (l, L) threshold secret sharing scheme and an (L, L) threshold secret sharing scheme. And
[0009]
According to a third aspect of the present invention, in the content distribution method, in the content distribution method, a plurality of hash values obtained from a plurality of contents used by the user are included in a distributed decryption distribution key distributed by the secret sharing method. And using the arbitrary distributed decryption distribution key as the arbitrary distributed decryption distribution key, obtaining the remaining distributed decryption distribution key of the decryption key, and using the obtained remaining distributed decryption distribution key as a plurality of contents used by the user. It is characterized in that it is used as a distributed decryption distribution key for contents different from the above.
[0010]
A fourth aspect of the present invention is characterized in that in the content distribution method, charging is performed for use of the distributed decryption distribution key.
[0011]
According to a fifth aspect of the present invention, in the content distribution method, a history of the content used by the user is obtained, and usage of the content is controlled according to the usage history of the content.
[0012]
According to a sixth aspect of the present invention, in the content distribution method, an ID of the content already used by the user is input from a predetermined input unit, and the distributed decryption distribution key associated with the input ID of the content is used by the user. It is characterized in that whether or not the content to be used is related to the already used content is determined, and a distributed decryption distribution key to be used is obtained according to the determination result and notified to a predetermined destination.
[0013]
According to a seventh aspect of the present invention, in the content distribution method, the ID of the content already used by the user is input from a predetermined input unit, and the user wants to use the content by using the decryption distribution key of the content already used by the user. It is characterized in that a secure package including content related to the content is searched, content desired by the user is selected from the search result, and a distributed decryption distribution key of the selected content is notified to a predetermined destination.
[0014]
According to these configurations, the remaining distributed decryption distribution key of the decryption key is obtained by using the hash value obtained from the content already used by the user, and the obtained residual distributed decryption distribution key is already used by the user. Since the distributed decryption distribution key of the content related to the set content is used, the content can be associated with each other, and by this association, charging can be performed according to the usage history of the content. Accordingly, when a user who uses the advertising content uses a certain content, it is possible to provide advantages such as a discount on the usage fee as compared with a user who does not benefit from the advertising content. Similarly, it is possible to provide the user with an advantage such as discounting the usage fee even when a certain content is purchased regularly or when a related large-capacity content is purchased after purchasing a small-capacity content. As a result, it is possible to reduce the feeling of unfairness between users to some extent, and it is possible to improve user convenience when using the content distribution service.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 is a schematic configuration diagram of a content distribution system to which the content distribution method of the present invention is applied. 1, this system includes a content distribution server 10, a key management server 20, a billing server 30, a network 40, and a mobile terminal 50. The content distribution server 10 secure-packages the content provided by the content provider and distributes the content to the mobile terminal 50 via the network 40 (mobile communication network). The key management server 20 manages keys that can be used by the user, and notifies the content distribution server 10 of predetermined key information in response to a key information request from the content distribution server 10. The billing server has functions such as issuing a bill to the user based on the billing information output from the content distribution server 10.
[0016]
Super-distribution, which is digital information distribution, is a method in which copying and secondary distribution of content are permitted, and usage is charged for use of the content. FIG. 2 is a diagram showing an example of a format of a secure package distributed from the content distribution server 10 in super distribution, and the following information is packaged.
[0017]
(1) Content information (Information)
{Circle around (2)} Content encrypted with a content key based on common key encryption (Enc (K, content))
{Circle around (3)} A content key (enc (k, K)) encrypted with a distribution key k based on public key encryption or common key encryption
The content information (1) includes an ID for identifying the content, price information for using the content, and the like. In this embodiment, the decryption key of the content key encrypted by the distribution key k is defined as “decryption distribution key”.
[0018]
The content distribution server 10 has a tamper-resistant function for preparing for unauthorized access (tamper-resistant function: a function of leaving a trace of intrusion or deleting data for unauthorized access), and uses this tamper-resistant function. However, in the present invention, a hash value (a number unique to the content) of the used content is stored, and the hash value is stored in the distributed decryption distribution key of the secure package associated with the used content. The greatest feature is that the contents are associated with each other and billed based on the association.
[0019]
Here, the distributed decryption distribution key will be described.
[0020]
First, the above-mentioned decryption distribution key is considered as a source of a set. For example, ElGamal encryption (a public key type encryption method which applies a mathematical problem called a discrete logarithm problem, and is obtained by encrypting a plaintext, a random number, and a public key. Is a cryptographic method that creates a sentence and decrypts it with a secret key)
p: prime, Zp ^*: multiplicative group, g: Zp ^k of origin, k∈Zp-1: secret ^{key, y = g ∧ k (modp} ): a public key. The encryption of the content key K, choose a random number ^{r∈Zp-1, c1 = g ∧} r (modp), c2 = K [y ^∧ r] was (modp) (c1, c2) is the ciphertext. Decryption key ciphertext is k is the private key, it can be decrypted by ^{K = c2 / (c1 ∧ k} ). In the present embodiment, this decryption key is defined as a “decryption distribution key”. Here, a secret sharing method (secret sharing method), which is a kind of secret sharing method (Secret Sharing method), is such that when a certain secret s is distributed into n pieces and k or more of them are collected, s can be completely restored. Therefore, the secret s is secure even if k-1 information is leaked, and s can be restored even if nk information is lost. It is possible to distribute the decryption distribution key by using the above method. As a secret sharing scheme, there is a threshold secret sharing scheme called an (l, L) threshold scheme. In this threshold secret sharing method, original data (secret information) is restored from one of the L data, but in the present embodiment, a method in which a threshold is not determined, that is, l = L (l , L) Disperse the decryption distribution key into L pieces using a threshold method (a method that requires all data to be collected).
[0021]
For example, when the decryption distribution key of the ElGamal encryption shown above is distributed into three, k1, k2, and k3 satisfying k = k1 + k2 + k3 (modp−1) are distributed decryption keys, that is, “distributed decryption distribution keys”. It becomes.
[0022]
Next, an operation of selecting a decryption distribution key to be used based on the usage history of the content will be described with reference to the flowchart of FIG.
[0023]
In FIG. 3, k1 represents a hash value (k1 = hash (content1)) obtained from content1, and this k1 is set as a distribution key of the distribution key k. Similarly, k2 represents a hash value (k2 = hash (content2)) obtained from content2, and is set as a distribution key of the distribution key k. The content distribution server 10 determines a distribution key k of the content (content to be used). In addition, since k1 is determined from content1 and k2 is determined from content2 as described above, k, k1, and k2 are determined. From this, k3 that satisfies k = k1 + k2 + k3 (modp-1) is determined. Therefore, the keys managed by the key management server 20 are k, k3, k'2 = k2 + k3, k'1 = k1 + k3, and k, k3, k'2, and k'1 are keys that can be used by the user. It becomes.
[0024]
Now, assume that the content that the user wants to use is “content”. When the content distribution server 10 acquires the secure package including the content ID to be used, the content distribution server 10 inquires of the key management server 20 to obtain key information (distribution key k) to be used. Here, when the user's mobile terminal 50 is notified of the use history of only the content already used, for example, content1 (= content ID), the mobile terminal 50 of the user is the owner of the hash value k1 of content1. (YES in S1 → NO in S2), the content distribution server 10 queries the key management server 20 for k−k1 = k2 + k3 = k′2 (the remaining distributed decryption distribution key) and obtains it. Therefore, a user who has a usage history of only the content1 may use the decryption distribution key of k′2, and the association of the decryption key distribution key is associated with the contents, that is, the content (content1) related to the content (content) to be used. Is associated.
[0025]
Similarly, when the use history of only the content2 is notified as the content already used by the user's mobile terminal 50, the user's mobile terminal 50 is the owner of the hash value k2 of the content2 (NO in S1 and NO in S2). (YES), the content distribution server 10 inquires of the key management server 20 and obtains k−k2 = k1 + k3 = k′1 (the remaining distributed decryption distribution key). Therefore, the mobile terminal 50 of the user having the usage history of only the content2 only needs to use the decryption distribution key of k′1, and this decryption key distribution key is associated with the contents, that is, the association between the content and the content2.
[0026]
Furthermore, when the use history of content1 and content2 is notified as the already used content by the mobile terminal 50 of the user, the mobile terminal 50 of the user is the owner of the hash value k1 of content1 and the hash value k2 of content2. (YES in S1 → YES in S2), the content distribution server 10 inquires the key management server 20 of k−k1−k2 = k3 (remaining distributed decryption distribution key) and acquires it. Therefore, a user who has a usage history of content1 and content2 only needs to use the decryption distribution key of k3, and the association of the decryption key distribution key is the association of content with content1 and content2.
[0027]
When the user's mobile terminal 50 notifies that there is no content already used (NO in S1 → NO in S2), the content distribution server 10 queries the key management server 20 for k as a decryption key distribution key. To get.
[0028]
As described above, according to the present embodiment, the content such as the digest video and the advertisement is associated with the other content by using the hash value of the content already used by the user as the distributed decryption distribution key of the related content. be able to. Further, the association between the contents can be any one-to-one, one-to-many, many-to-one, many-to-many association. Further, by associating the contents with each other, it is possible to perform charging according to the usage history of the contents. In this case, charging information is generated by the content distribution server 10 for the distributed decryption distribution key used as described above, and the charging information is processed by the charging server 30 to realize charging according to the usage history of the content. It is possible to do.
[0029]
FIG. 4 is a flowchart showing a process for searching for and using a secure package including related content based on the usage history of the content.
[0030]
When the content distribution server 10 acquires a certain content, for example, the package 1 including the content 1 information from the content provider (S11), the decryption distribution key for using the content 1 is inquired to the key management server 20 to acquire ( S12), and the hash value obtained by hashing the content 1 is stored in a memory or the like (S13).
[0031]
Subsequently, when trying to use another content and acquiring a package including the other content, the use history of the used content is input by operating the mobile terminal 50 on the user side (S14). When the usage history is input to the mobile terminal 50 in this manner, information indicating the usage history is sent to the content distribution server 10 via the network 40. The content distribution server 10 searches for content related to the content indicated by the usage history based on the received usage history information (S15). For example, referring to FIG. 3 as an example, if the content used by the user is content1, the usage history is content1, and the content related to content1 is searched.
[0032]
When the search for the related content is completed in this way, the related content (not necessarily one content, here, content 2) corresponding to the search result is obtained from the content provider (S16), and the content is retrieved. (2) The key management server 20 is queried for key information necessary for use. When the content related to the content 1 is the content 2 as in this example, the key management server 20 uses the distributed decryption distribution key instead of the decryption distribution key for the use of the content 2 as the key information. It returns to the distribution server 10 (S17). The content distribution server 10 transmits the distributed decryption distribution key for using the content 2 received from the key management server 20 to the user's mobile terminal 50 (S18).
[0033]
As described above, according to the present embodiment, when the user inputs the usage history of the content already used, the content related to the content having the usage history is searched for, and the related content is used. The distributed decryption distribution key is used as the decryption key of the. For example, it is possible to search for a related large-capacity content from the use history such as the ID of the small-capacity content, and to associate the contents with each other. Flexible and flexible billing can be realized. For example, it is possible to set a charging system in consideration of the user's viewpoint, such as a sponsor advertiser paying a fee for the difference obtained by discounting. In this case, the advertiser can specify the related content, and any one-to-one, one-to-many, many-to-one, many-to-many association is possible. As a result, efficient marketing can be performed for the advertiser and profits can be returned to the user, so that promotion of use of the content can be expected.
[0034]
FIG. 5 is a schematic diagram showing that the key used differs according to the usage history of the user, and shows a response of the key management server 20 to the key usage request of the user (= mobile terminal 50 owned by the user). .
[0035]
In FIG. 5, for example, in order for the user to use the content, it is necessary to use the distribution key k. The user sends a use request for the k to the key management server 20 to obtain the key information. Furthermore, even when attempting to use content, it is necessary to inquire the key management server 20 of a use request for k and obtain key information for k. However, according to the present invention, if the user tries to use the content after using the content ′ associated with the content, the user owns k1 as the hash value of the content ′, so that k−k1 = k2 instead of k. Is available to the key management server 20, k can be used. When permitting use of k in response to a use request of k from the user, the key management server 20 sends a message for billing processing to the mobile terminal 50 of the user.
[0036]
As described above, according to the present embodiment, the remaining distributed decryption distribution key of the decryption key is obtained by using the hash value obtained from the content already used by the user, and the obtained remaining distributed decryption key is obtained. Since the decryption distribution key is used as the distributed decryption distribution key of the content related to the content already used by the user, it is possible to associate the contents with each other, and by this association, it becomes possible to charge according to the usage history of the content.
[0037]
Further, since the key management server 20 prepares only the shared key, only the user who uses the related small-capacity content can use the large-capacity content, and can control the use of the content.
[0038]
Furthermore, by using the hash value of the content used in advance as a distributed decryption key for newly used content for the regular purchase of a certain content, the use of the related content can be reduced compared to the use of the decryption distribution key. Then, by giving the user an advantage such as making the use of the distributed decryption key cheaper, an effect of promoting further use and continuous use is exerted.
[0039]
Further, even if there is a design change or the like within a range not departing from the gist of the present invention, it is included in the present invention. For example, in the above-described embodiment, a content distribution processing program for realizing the function of the content distribution server 10 is recorded on a computer-readable recording medium, and the content distribution processing program recorded on the recording medium is stored in a computer. The content distribution processing may be performed by reading and executing. Note that the recording medium includes a portable recording medium such as an optical disk, a floppy (registered trademark) disk, and a hard disk.
[0040]
In the above example, the key calculation function of the content distribution server 10 is the distributed decryption distribution key calculation unit, the key information acquisition function required for using the desired content is the distributed decryption distribution key acquisition unit, and the charging information generation / output function is the charging unit. Corresponding. Further, the content use control function corresponds to the content use control means, the content relevance judgment function corresponds to the judgment means, and the key information notification function corresponds to the first distributed decryption distribution key notification means and the second distributed decryption distribution key notification means. . Further, the related content search function corresponds to a related package search means.
[0041]
【The invention's effect】
As described above, according to the present invention, the remaining distributed decryption distribution key of the decryption key is obtained by using the hash value obtained from the content already used by the user, and the obtained distributed decryption distribution key is obtained. Since the key is used as the distributed decryption distribution key of the content related to the content already used by the user, it is possible to associate the contents with each other, and by this association, it becomes possible to charge according to the usage history of the content. As a result, unfairness between users during use of the content is corrected, and use of the content to the user can be promoted.
[0042]
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a content distribution system to which a content distribution method of the present invention is applied.
FIG. 2 is a diagram illustrating an example of a format of a secure package distributed from a content distribution server.
FIG. 3 is a flowchart showing an operation of selecting a decryption distribution key to be used based on a use history of contents.
FIG. 4 is a flowchart illustrating a process for searching for and using related content based on a usage history of the content.
FIG. 5 is a diagram showing that a key to be used is different according to a use history of a user.
[Explanation of symbols]
10 Content Distribution Server 20 Key Management Server 30 Billing Server 40 Network 50 Mobile Terminal

Claims (20)

In a content distribution method of distributing a content encrypted with a content key, a content key encrypted with a distribution key, and a secure package storing content information to a terminal via a network,
The decryption key (= decryption distribution key) of the encrypted content is distributed to L distributed decryption distribution keys by a secret sharing method,
A hash value obtained from the content used by the user, as an arbitrary distributed decryption distribution key among the distributed decryption distribution keys distributed by the secret sharing method,
Using the arbitrary distributed decryption distribution key, obtain the remaining distributed decryption distribution key of the decryption key, and use the obtained distributed decryption distribution key as a distributed decryption distribution key for content different from the content used by the user. A content distribution method, characterized in that: The content distribution method according to claim 1,
The content distribution method, wherein the secret sharing method is any one of a (l, L) threshold secret sharing method and an (L, L) threshold secret sharing method. The content distribution method according to claim 1 or 2,
Using a plurality of hash values obtained from a plurality of contents used by the user as an arbitrary distributed decryption distribution key among the distributed decryption distribution keys distributed by the secret sharing method, using the arbitrary distributed decryption distribution key Content obtained by obtaining the remaining distributed decryption distribution key of the decryption key, and using the obtained remaining distributed decryption distribution key as a distributed decryption distribution key for content different from a plurality of contents used by the user. Delivery method. The content distribution method according to claim 1 or 3,
A content distribution method, wherein charging is performed for use of the distributed decryption distribution key. The content distribution method according to claim 1 or 3,
A content distribution method characterized by taking a history of contents used by a user and controlling use of the contents according to the use history of the contents. The content distribution method according to claim 1 or 3,
Input the ID of the content already used by the user from a predetermined input means,
By the distributed decryption distribution key associated with the input content ID,
Determine whether the content the user wants to use is related to the content already used,
A content distribution method comprising: obtaining a distributed decryption distribution key to be used according to a determination result; and notifying a terminal of a predetermined user. The content distribution method according to claim 1 or 3,
Input the ID of the content already used by the user from a predetermined input means,
Using the decryption distribution key of the content already used by the user, search for a secure package including the content related to the content desired by the user,
Select the content that the user wants to use from the search results,
A content distribution method, wherein a distributed decryption distribution key required for using the selected content is notified to a terminal of a predetermined user. In a content distribution server that distributes a content encrypted with a content key, a content key encrypted with a distribution key, and a secure package storing content information to a terminal via a network,
The decryption key (= decryption distribution key) of the encrypted content is distributed to L distributed decryption distribution keys by a secret sharing method,
A hash value obtained from the content used by the user, as an arbitrary distributed decryption distribution key among the distributed decryption distribution keys distributed by the secret sharing method,
Using the arbitrary distributed decryption distribution key, obtain the remaining distributed decryption distribution key of the decryption key from the key management server connected to the own server, and obtain the obtained remaining distributed decryption distribution key with the content used by the user. Is a first distributed decryption distribution key calculation unit that is a distributed decryption distribution key for different contents;
A content distribution server, comprising: a distributed decryption distribution key obtaining unit that obtains the distributed decryption distribution key obtained by the first distributed decryption distribution key calculation unit by inquiring of the key management server. The content distribution server according to claim 8,
Content distribution characterized in that the secret sharing method used in the distributed decryption distribution key generation means is either (l, L) threshold secret sharing method or (L, L) threshold secret sharing method. server. The content distribution server according to claim 8, wherein:
Using a plurality of hash values obtained from a plurality of contents used by the user as an arbitrary distributed decryption distribution key among the distributed decryption distribution keys distributed by the secret sharing method, using the arbitrary distributed decryption distribution key Obtain the remaining distributed decryption distribution key of the decryption key from the key management server, and use the obtained remaining distributed decryption distribution key as a distributed decryption distribution key for a content different from the plurality of contents used by the user. Second distributed decryption distribution key calculation means,
A content distribution server, comprising: a distributed decryption distribution key obtaining unit that obtains the distributed decryption distribution key obtained by the second distributed decryption distribution key calculation unit by inquiring of the key management server. The content distribution server according to claim 8, wherein:
A content distribution server comprising a charging unit for charging for use of the distributed decryption distribution key. The content distribution server according to claim 8, wherein
What is claimed is: 1. A content distribution server, comprising: a content usage control unit that obtains a history of content used by a user and controls usage of the content in accordance with the usage history of the content. The content distribution server according to claim 8, wherein
Input the ID of the content already used by the user from a predetermined input means,
By the distributed decryption distribution key associated with the input content ID,
Determining means for determining whether the content desired by the user is related to the already used content,
A first distributed decryption distribution key notification for transmitting a determination result obtained by the determination means to the key management server and notifying a terminal of a predetermined user of a distributed decryption distribution key to be used which is responded from the key management server; And a means for distributing content. The content distribution server according to claim 8, wherein
Input the ID of the content already used by the user from a predetermined input means,
A related package search unit that searches for a secure package including content related to the content desired by the user by using a decryption distribution key of the content already used by the user;
A second distributed decryption distribution for selecting a content desired by the user from the search result obtained by the related package searching means, and notifying a terminal of a predetermined user of a distributed decryption distribution key required for using the selected content; A content distribution server comprising: a key notification unit. A computer recording a content distribution processing program for distributing a content encrypted by a content key, a content key encrypted by a distribution key, and a secure package storing the content information to a terminal via a network by a content distribution server. In a readable storage medium,
The decryption key (= decryption distribution key) of the encrypted content is distributed to L distributed decryption distribution keys by a secret sharing method,
A hash value obtained from the content used by the user, as an arbitrary distributed decryption distribution key among the distributed decryption distribution keys distributed by the secret sharing method,
The remaining distributed decryption distribution key of the decryption key is obtained from the key management server connected to the content distribution server using the arbitrary distributed decryption distribution key, and the obtained remaining distributed decryption distribution key is used by the user. A first distributed decryption distribution key calculation step to be a distributed decryption distribution key for a content different from the content;
Computer-readable recording of a distribution processing program for causing a computer to execute a distributed decryption distribution key obtained in the first distributed decryption distribution key calculation step by inquiring of the key management server; Possible storage medium. A computer-readable storage medium recording the content distribution processing program according to claim 15,
The secret sharing method used in the distributed decryption distribution key generation step is any one of a (l, L) threshold secret sharing method and an (L, L) threshold secret sharing method. Possible storage medium. A computer-readable storage medium recording the content distribution processing program according to claim 15 or 16,
Using a plurality of hash values obtained from a plurality of contents used by the user as an arbitrary distributed decryption distribution key among the distributed decryption distribution keys distributed by the secret sharing method, using the arbitrary distributed decryption distribution key Obtain the remaining distributed decryption distribution key of the decryption key from the key management server, and use the obtained remaining distributed decryption distribution key as a distributed decryption distribution key for a content different from the plurality of contents used by the user. A second distributed decryption distribution key calculation step;
Computer-readable recording of a distribution processing program for causing a computer to execute a distributed decryption distribution key obtained in the second distributed decryption distribution key calculation step by inquiring of the key management server to obtain the distributed decryption distribution key; Possible storage medium. Computer
The decryption key (= decryption distribution key) of the encrypted content is distributed to L distributed decryption distribution keys by a secret sharing scheme,
A hash value obtained from the content used by the user, as an arbitrary distributed decryption distribution key among the distributed decryption distribution keys distributed by the secret sharing method,
Using the arbitrary distributed decryption distribution key, obtain the remaining distributed decryption distribution key of the decryption key from the key management server connected to the content distribution server that is the distribution source of the content, and obtain the obtained remaining distributed decryption distribution key A first distributed decryption distribution key calculating means, which is a distributed decryption distribution key for a content different from the content used by the user,
Distributed decryption distribution key acquisition means for inquiring the key management server to acquire the distributed decryption distribution key obtained by the first distributed decryption distribution key calculation means,
Content distribution processing program to function as The content distribution processing program according to claim 18, wherein
Content distribution characterized in that the secret sharing method used in the distributed decryption distribution key generation means is either (l, L) threshold secret sharing method or (L, L) threshold secret sharing method. Processing program. The content distribution processing program according to claim 18, wherein:
Using a plurality of hash values obtained from a plurality of contents used by the user as an arbitrary distributed decryption distribution key among the distributed decryption distribution keys distributed by the secret sharing method, using the arbitrary distributed decryption distribution key Obtain the remaining distributed decryption distribution key of the decryption key from the key management server, and use the obtained remaining distributed decryption distribution key as a distributed decryption distribution key for a content different from the plurality of contents used by the user. Second distributed decryption distribution key calculation means,
Distributed decryption distribution key acquisition means for inquiring the key management server to acquire the distributed decryption distribution key obtained by the second distributed decryption distribution key calculation means,
Content distribution processing program to function as

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