JP2010193343A - Content distribution system and method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To change time-release cryptography and decrypt a content using a public key of a content distribution server. <P>SOLUTION: The content distribution server previously distributes an encrypted content to which a time index is added and an encryption key to a plurality of user terminals. A time authentication server broadcasts a time signal packet to the plurality of user terminals at a specified time. The plurality of user terminals receive the time signal packet from the time authentication server, and based on the received time signal packet, searches stored encrypted contents for a corresponding encrypted content. A decryption key for decrypting an encrypted content is generated from the received time signal packet, the stored encrypted contents, and the public key of the content distribution server. The generated decryption key is used to decrypt the retrieved encrypted content. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a content distribution system, a content distribution method, and a program for broadcasting content using a server that broadcasts time information.

  Conventionally, a Time Release cipher that can decrypt a ciphertext using a time signal packet received from a time certificate authority at a specific time has been proposed (see Non-Patent Document 1, for example).

Global Time-Release Encryption, Yoshida, Fujiwara (Osaka Univ.), Proc. Of 26th IEEE Int'l Conf. On Consumer Electronics (ICCE 2008).

  However, the Time Release encryption is a method in which only a designated recipient can decrypt the content using a secret key. For this reason, it is difficult to apply this technique as it is to a service that assumes a plurality of recipients.

  Accordingly, the present invention has been made in view of the above-described problems, and provides a content distribution system, a content distribution method, and a program that can change the time release encryption and decrypt the content with the public key of the content distribution server. Objective.

  The present invention proposes the following matters in order to solve the above problems.

  (1) The present invention includes a content distribution server, a time authentication server, and a plurality of user terminals, and the content distribution server receives the encrypted content with the time index added and the encryption key. Content distribution means for distributing in advance to user terminals, and the time authentication server includes time signal packet distribution means for broadcasting time signal packets to the plurality of user terminals at a specified time, wherein the plurality of user terminals are Storage means for storing the encrypted content to which the time index is added and an encryption key, receiving means for receiving a time signal packet from the time authentication server, and the storage based on the received time signal packet Search means for searching for the corresponding encrypted content from the means, and the received time signal packet, storage The decryption key generation means for generating a decryption key for decrypting the encrypted content from the encrypted content and the public key of the content distribution server, and a search using the generated decryption key Proposed is a content distribution system comprising a decrypting means for decrypting encrypted content.

  According to this invention, the content distribution means of the content distribution server distributes the encrypted content with the time index added and the encryption key to a plurality of user terminals in advance. A time signal packet distribution means of the time authentication server broadcasts a time signal packet to a plurality of user terminals at a specified time. The storage means of the plurality of user terminals stores the encrypted content to which the time index is added and the encryption key, and the receiving means receives the time signal packet from the time authentication server. Then, the retrieval means retrieves the corresponding encrypted content from the storage means based on the received time signal packet, and the decryption key generation means includes the received time signal packet, the encrypted content to be stored, and A decryption key for decrypting the encrypted content is generated from the public key of the content distribution server, and the decrypting means decrypts the retrieved encrypted content using the generated decryption key. Therefore, any user terminal can decrypt the encrypted content distributed in advance using the public key of the content distribution server after the specified time.

  (2) The present invention proposes a content distribution system in which the content distribution server distributes the encrypted content in advance using a P2P network in the content distribution system of (1). .

  According to the present invention, the content distribution server distributes the encrypted content in advance using the P2P network. Here, the P2P network refers to a network formed by a set of nodes that do not have a defined client or server and that act as both a client and a server with respect to other computers (nodes) on the network. Therefore, concentration of access to the distribution server can be suppressed by sharing the content via the P2P network among the plurality of distribution servers and the recipient terminals.

  (3) The present invention proposes a content distribution system in which the content distribution server publishes an association between its own identification number and a public key for the content distribution system of (1).

  According to this invention, the content distribution server discloses the association between its own identification number and public key. Therefore, a broadcast service with a registered name can be realized.

  (4) The present invention proposes a content distribution system in which the content distribution server makes the association between its own identification number and public key private in the content distribution system of (1). .

  According to this invention, the content distribution server makes the association between its own identification number and the public key private. Therefore, this makes it possible to realize an anonymous broadcast service.

  (5) The present invention proposes a content distribution system according to (1), wherein the content distribution server includes user authentication means for authenticating a user participating in the network. .

  According to the present invention, the content distribution server authenticates users who participate in the network. Accordingly, it is possible to realize a limited broadcast that can be viewed only by a specific user.

  (6) The present invention includes a content distribution server, a time authentication server, and a plurality of user terminals, and a time index is added to the download time registered by the content distribution server with respect to the user terminals. Content distribution means for distributing encrypted content and an encryption key in advance, and a time signal packet distribution means for the time authentication server to broadcast a time signal packet to the plurality of user terminals at a specified time Registration means for registering a time at which the plurality of user terminals download the specific encrypted content to the content distribution server, an encrypted content to which the time index is added, and an encryption key; Storing means for storing, receiving means for receiving a time signal packet from the time authentication server, Based on the received time signal packet, the search means for searching for the corresponding encrypted content from the storage means, the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server And a decryption key generating means for generating a decryption key for decrypting the encrypted content, and a decryption means for decrypting the retrieved encrypted content using the generated decryption key. We have proposed a content distribution system characterized by

  According to this invention, the content distribution means of the content distribution server distributes the encrypted content and the encryption key with the time index added to the user terminal in advance at the registered download time. The time signal packet distribution means of the time authentication server broadcasts the time signal packet to a plurality of user terminals at a designated time. The registration means of the plurality of user terminals registers the time at which specific encrypted content is downloaded to the content distribution server. The storage means stores the encrypted content to which the time index is added and the encryption key. The receiving means receives a time signal packet from the time authentication server. The retrieval means retrieves the corresponding encrypted content from the storage means based on the received time signal packet. The decryption key generating means generates a decryption key for decrypting the encrypted content from the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server. Then, the decryption means decrypts the retrieved encrypted content using the generated decryption key. Accordingly, since the registration function (reservation function) is provided in the user terminal, the download start time of the content from the content distribution server becomes random, so that access to the content distribution server by the user terminal can be reduced.

(7) The present invention includes a content distribution server, a time authentication server, a plurality of user terminals, and an index server that holds index information of the encrypted content stored in the plurality of user terminals. Distribution server
Content distribution means for distributing in advance the encrypted content with the time index added and the encryption key to the plurality of user terminals, and the time authentication server sends the time signal packet to the specified time A time signal packet distribution means for broadcasting to a plurality of user terminals, wherein the plurality of user terminals search the index server, and the encrypted content and the encryption key to which a desired time index is added are transmitted over a network; Download means for downloading from a nearby user terminal, storage means for storing the encrypted content with the time index added and an encryption key, and reception means for receiving a time signal packet from the time authentication server; Based on the received time signal packet, the corresponding encryption from the storage means A decryption key for decrypting the encrypted content is generated from search means for retrieving the received content, the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server A content distribution system comprising a decryption key generation means and a decryption means for decrypting the retrieved encrypted content using the generated decryption key is proposed.

  According to this invention, the content distribution means of the content distribution server distributes the encrypted content with the time index added and the encryption key to a plurality of user terminals in advance. A time signal packet distribution means of the time authentication server broadcasts a time signal packet to a plurality of user terminals at a specified time. The downloading means of the plurality of user terminals searches the index server and downloads the encrypted content and the encryption key to which the desired time index is added from the neighboring user terminals on the network. The storage means stores the encrypted content to which the time index is added and the encryption key. The receiving means receives a time signal packet from the time authentication server. The retrieval means retrieves the corresponding encrypted content from the storage means based on the received time signal packet. The decryption key generating means generates a decryption key for decrypting the encrypted content from the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server. Then, the decryption means decrypts the retrieved encrypted content using the generated decryption key. Therefore, the network load can be reduced by providing an index server, registering index information of encrypted content owned by each user terminal, and downloading the content from a nearby user terminal.

  (8) The present invention is a content distribution method in a content distribution system comprising a content distribution server, a time authentication server, and a plurality of user terminals, wherein the content distribution server is encrypted with a time index added A first step of distributing content and an encryption key to the plurality of user terminals in advance; and a second step in which the time authentication server broadcasts a time signal packet to the plurality of user terminals at a specified time. A third step in which the plurality of user terminals receive a time signal packet from the time authentication server, and the plurality of user terminals store the encrypted message stored on the basis of the received time signal packet. A fourth step of searching for the corresponding encrypted content from among the stored content; and A fifth step in which the user terminal generates a decryption key for decrypting the encrypted content from the received time signal packet, the stored encrypted content, and the public key of the content distribution server; And a sixth step in which the plurality of user terminals decrypts the retrieved encrypted content using the generated decryption key, and proposes a content distribution method.

  According to the present invention, the content distribution server distributes the encrypted content with the time index added thereto and the encryption key to a plurality of user terminals in advance. The time authentication server broadcasts a time signal packet to a plurality of user terminals at a designated time. The plurality of user terminals receive the time signal packet from the time authentication server, and search for the corresponding encrypted content from the stored encrypted content based on the received time signal packet. Then, a decryption key for decrypting the encrypted content is generated from the received time signal packet, the encrypted content to be stored and the public key of the content distribution server, and a search is performed using the generated decryption key. Decrypt the encrypted content. Therefore, any user terminal can decrypt the encrypted content distributed in advance using the public key of the content distribution server after the specified time.

  (9) The present invention is a content distribution method in a content distribution system including a content distribution server, a time authentication server, and a plurality of user terminals, wherein the content distribution server is registered by the plurality of user terminals. A first step of distributing in advance the encrypted content with the time index added and the encryption key to the plurality of user terminals, and the time authentication server at the specified time, A second step of broadcasting a time signal packet to the plurality of user terminals; a third step of receiving a time signal packet from the time authentication server by the plurality of user terminals; and the plurality of user terminals receiving the time signal packet. Based on the time signal packet, the encrypted content corresponding to the encrypted content stored is stored. A fourth step of retrieving the encrypted content, and the plurality of user terminals from the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server, the encrypted content And a sixth step in which the plurality of user terminals decrypts the retrieved encrypted content using the generated decryption key. A content distribution method characterized by this is proposed.

  According to the present invention, the content distribution server distributes the encrypted content and the encryption key with the time index added to the plurality of user terminals in advance at the download time registered by the plurality of user terminals. To do. The time authentication server broadcasts a time signal packet to a plurality of user terminals at a designated time. The plurality of user terminals receive the time signal packet from the time authentication server, and search for the corresponding encrypted content from the stored encrypted content based on the received time signal packet. Then, a decryption key for decrypting the encrypted content is generated from the received time signal packet, the encrypted content to be stored and the public key of the content distribution server, and a search is performed using the generated decryption key. Decrypt the encrypted content. Accordingly, since the registration function (reservation function) is provided in the user terminal, the download start time of the content from the content distribution server becomes random, so that access to the content distribution server by the user terminal can be reduced.

  (10) The present invention is a content distribution system comprising a content distribution server, a time authentication server, a plurality of user terminals, and an index server that holds index information of the encrypted content stored in the plurality of user terminals. The content distribution method according to claim 1, wherein the content distribution server distributes the encrypted content with the time index added thereto and the encryption key to the plurality of user terminals in advance, and the time A second step in which the authentication server broadcasts a time signal packet to the plurality of user terminals at a specified time; and the plurality of user terminals search the index server and the desired time index is added. Neighboring users on the network with encrypted content and encryption key A third step of downloading from the end, a fourth step in which the plurality of user terminals store the encrypted content and the encryption key to which the time index is added, and the plurality of user terminals, A fifth step of receiving a time signal packet from the time authentication server; and a sixth step in which the plurality of user terminals retrieves the corresponding encrypted content from the storage unit based on the received time signal packet. And a plurality of user terminals generate a decryption key for decrypting the encrypted content from the received time signal packet, the stored encrypted content, and the public key of the content distribution server A seventh step, wherein the plurality of user terminals use the generated decryption key to retrieve the retrieved encrypted content An eighth step of Gosuru proposes a content distribution method characterized by comprising.

  According to the present invention, the content distribution server distributes the encrypted content with the time index added thereto and the encryption key to a plurality of user terminals in advance. The time authentication server broadcasts a time signal packet to a plurality of user terminals at a designated time. Multiple user terminals search an index server, download encrypted content and encryption key with a desired time index added from a neighboring user terminal on the network, and encryption with a time index added Stored content and encryption key are stored. In addition, a time signal packet is received from the time authentication server, the corresponding encrypted content is retrieved from the storage means based on the received time signal packet, and the received time signal packet, the encrypted content to be stored and the content are stored. A decryption key for decrypting the encrypted content is generated from the public key of the distribution server, and the retrieved encrypted content is decrypted using the generated decryption key. Therefore, the network load can be reduced by providing an index server, registering index information of encrypted content owned by each user terminal, and downloading the content from a nearby user terminal.

  (11) The present invention is a program for causing a computer to execute a content distribution method in a content distribution system including a content distribution server, a time authentication server, and a plurality of user terminals. A first step of distributing the encrypted content and the encryption key added to the plurality of user terminals in advance, and the time authentication server sends the time signal packet to the plurality of times at a specified time. Based on the second step of broadcasting to the user terminal, the third step of the plurality of user terminals receiving a time signal packet from the time authentication server, and the plurality of user terminals based on the received time signal packet, The corresponding encrypted content is stored in the stored encrypted content. A fourth step of searching for content, and the plurality of user terminals decrypt the encrypted content from the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server And a fifth step of causing the plurality of user terminals to decrypt the retrieved encrypted content using the generated decryption key. A program for this is proposed.

  According to the present invention, the content distribution server distributes the encrypted content with the time index added thereto and the encryption key to a plurality of user terminals in advance. The time authentication server broadcasts a time signal packet to a plurality of user terminals at a designated time. The plurality of user terminals receive the time signal packet from the time authentication server, and search for the corresponding encrypted content from the stored encrypted content based on the received time signal packet. Then, a decryption key for decrypting the encrypted content is generated from the received time signal packet, the encrypted content to be stored and the public key of the content distribution server, and a search is performed using the generated decryption key. Decrypt the encrypted content. Therefore, any user terminal can decrypt the encrypted content distributed in advance using the public key of the content distribution server after the specified time.

  (12) The present invention is a program for causing a computer to execute a content distribution method in a content distribution system including a content distribution server, a time authentication server, and a plurality of user terminals. A first step of distributing, in advance to the plurality of user terminals, encrypted content and an encryption key to which a time index is added at a download time registered by the user terminal; and the time authentication server A second step of broadcasting a time signal packet to the plurality of user terminals at a designated time, a third step of receiving a time signal packet from the time authentication server by the plurality of user terminals, and the plurality of The user terminal of the user terminal is stored based on the received time signal packet. A fourth step of searching for the corresponding encrypted content among the encoded content, and the plurality of user terminals, the received time signal packet, the encrypted content to be stored, and the content distribution A fifth step of generating a decryption key for decrypting the encrypted content from the public key of the server, and the plurality of user terminals searched using the generated decryption key A program for causing a computer to execute a sixth step of decrypting content is proposed.

  According to the present invention, the content distribution server distributes the encrypted content and the encryption key with the time index added to the plurality of user terminals in advance at the download time registered by the plurality of user terminals. To do. The time authentication server broadcasts a time signal packet to a plurality of user terminals at a designated time. The plurality of user terminals receive the time signal packet from the time authentication server, and search for the corresponding encrypted content from the stored encrypted content based on the received time signal packet. Then, a decryption key for decrypting the encrypted content is generated from the received time signal packet, the encrypted content to be stored and the public key of the content distribution server, and a search is performed using the generated decryption key. Decrypt the encrypted content. Accordingly, since the registration function (reservation function) is provided in the user terminal, the download start time of the content from the content distribution server becomes random, so that access to the content distribution server by the user terminal can be reduced.

  (13) The present invention is a content distribution system comprising a content distribution server, a time authentication server, a plurality of user terminals, and an index server that holds index information of the encrypted content stored in the plurality of user terminals. A program for causing a computer to execute the content distribution method according to claim 1, wherein the content distribution server distributes, in advance, the encrypted content to which the time index is added and the encryption key to the plurality of user terminals. A first step; a second step in which the time authentication server broadcasts a time signal packet to the plurality of user terminals at a specified time; and the plurality of user terminals search the index server to obtain a desired The encrypted content with the time index of A third step of downloading an encryption key from a neighboring user terminal on the network; and a fourth step in which the plurality of user terminals store the encrypted content to which the time index is added and the encryption key. A fifth step in which the plurality of user terminals receive a time signal packet from the time authentication server, and the plurality of user terminals correspond to the storage means based on the received time signal packet. A sixth step of searching for encrypted content, and the plurality of user terminals, from the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server, A seventh step of generating a decryption key for decrypting the content, and the plurality of user terminals generating the decryption key Used proposes a program for executing an eighth step of decoding the retrieved encrypted content and the computer.

  According to the present invention, the content distribution server distributes the encrypted content with the time index added thereto and the encryption key to a plurality of user terminals in advance. The time authentication server broadcasts a time signal packet to a plurality of user terminals at a designated time. Multiple user terminals search an index server, download encrypted content and encryption key with a desired time index added from a neighboring user terminal on the network, and encryption with a time index added Stored content and encryption key are stored. In addition, a time signal packet is received from the time authentication server, the corresponding encrypted content is retrieved from the storage means based on the received time signal packet, and the received time signal packet, the encrypted content to be stored and the content are stored. A decryption key for decrypting the encrypted content is generated from the public key of the distribution server, and the retrieved encrypted content is decrypted using the generated decryption key. Therefore, the network load can be reduced by providing an index server, registering index information of encrypted content owned by each user terminal, and downloading the content from a nearby user terminal.

  According to the present invention, there is an effect that a broadcast service can be performed without preparing a large-scale facility. Further, instead of placing the encrypted content on the server, it is possible to avoid concentration of access to the server when the content is released by distributing in advance by P2P.

  If user authentication is introduced when participating in a P2P network, there is an effect that a limited broadcast that can be viewed only by a specific user can be realized. Furthermore, an anonymous broadcast service can also be executed by concealing the association between the distribution server and its public key. This anonymous broadcast has an effect of enabling fair content popularity voting and the like.

1 is a configuration diagram of a system according to a first embodiment. It is a block diagram of the content delivery server which concerns on 1st Embodiment. It is the figure which showed an example of the data format which a content delivery server delivers beforehand. It is a block diagram of the time authentication server which concerns on 1st Embodiment. It is a block diagram of the user terminal which concerns on 1st Embodiment. It is a processing flow of the system concerning a 1st embodiment. It is a block diagram of the content delivery server which concerns on 2nd Embodiment. It is a block diagram of the user terminal which concerns on 2nd Embodiment. It is a processing flow of the system concerning a 2nd embodiment. It is a block diagram of the system which concerns on 3rd Embodiment. It is a block diagram of the user terminal which concerns on 3rd Embodiment. It is a processing flow of the system concerning a 3rd embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Note that the constituent elements in the present embodiment can be appropriately replaced with existing constituent elements and the like, and various variations including combinations with other existing constituent elements are possible. Therefore, the description of the present embodiment does not limit the contents of the invention described in the claims.

<First Embodiment>
The first embodiment of the present invention will be described in detail with reference to FIGS.

<System configuration>
As shown in FIG. 1, the content distribution system according to the present embodiment includes a content distribution server 1, a time authentication server 2, and a plurality of user terminals 3a, 3b, 3c, and 3d. The content distribution server 1 and the plurality of user terminals 3a, 3b, 3c, and 3d are connected via the P2P network 4. Here, the P2P network refers to a network formed by a set of nodes that do not have a fixed client or server and that act as both a client and a server for other computers (nodes) on the network. If user authentication is introduced when participating in the P2P network, it is possible to realize limited broadcasting that can be viewed only by a specific user.

  The content distribution server 1 distributes encrypted content to the plurality of user terminals 3a, 3b, 3c, and 3d in advance in response to access requests from the plurality of user terminals 3a, 3b, 3c, and 3d. The time authentication server 2 broadcasts a plurality of user terminals 3a, 3b, 3c, and 3d time packets for decrypting the encrypted content at the designated time. The plurality of user terminals 3a, 3b, 3c, and 3d are terminals owned by a user who views content, and a mode in which the user operates the content distribution server 1 can also be assumed.

<Configuration of content distribution server>
As shown in FIG. 2, the content distribution server 1 includes a time index generation unit 11, a content information generation unit 12, a content encryption unit 13, an encryption key generation unit 14, a distribution data generation unit 15, and a distribution unit. 16.

  The time index generation unit 11 generates a time index unique to each content and outputs it to the transmission content generation unit 12. The content information generation unit 12 is based on the time index received from the time index generation unit 11, the search index shown in FIG. 3, the content information, the decryption time associated with this content information, and the data string of the public key of the content distribution server 1 Is generated. In addition, this public key may disclose the association with the identification number of the content distribution server 1 or may be private. A broadcast service with a registered name can be realized in the case of publishing, and an anonymous broadcast service can be realized in the case of non-disclosure.

  The content encryption unit 13 encrypts the content with the encryption key generated by the encryption key generation unit 14. The encryption key generation unit 14 generates an encryption key for encrypting the content. The distribution data generation unit 15 generates a data string as shown in FIG. 3 based on the information received from the content information generation unit 12, the content encryption unit 13, and the encryption key generation unit 14. In addition, you may perform a signature as needed.

<Configuration of time authentication server>
As shown in FIG. 4, the time authentication server 2 includes a time measuring unit 21, a time signal packet generating unit 22, and a time signal packet transmitting unit 23.

  The timekeeping unit 21 has a timekeeping function and transmits time information to the time signal packet generation unit 22. The hourly packet generation unit 22 generates a hourly packet and outputs it to the hourly packet transmission unit 23 at a predetermined time. When the hourly packet transmitting unit 23 receives the hourly packet from the hourly packet generating unit 22, the hourly packet transmitting unit 23 broadcasts the hourly packet to a plurality of user terminals 3a, 3b, 3c, and 3d.

<Configuration of user terminal>
As shown in FIG. 5, the user terminal includes a content receiving unit 31, a storage unit 32, a time signal packet receiving unit 33, a content search unit 34, a decryption key generation unit 35, and a decryption unit 36. Yes.

  The content receiving unit 31 receives the encrypted content from the content distribution server 1 via the P2P network. The storage unit 32 stores the encrypted content received by the content receiving unit 31.

  The time signal packet receiving unit 33 receives a time signal packet from the time authentication server 2. When the hourly packet receiving unit 33 receives the hourly packet, the content search unit 34 searches the storage unit 32 for encrypted content whose decryption time matches the hourly packet.

  The decryption key generation unit 35 generates a decryption key for decrypting the encrypted content from the time signal packet, the encryption key, and the public key of the content distribution server 1. The decryption unit 36 decrypts the encrypted content using the decryption key generated by the decryption key generation unit 35.

<System processing>
Processing of the system according to the present embodiment will be described with reference to FIG.

In the following description, the following symbols are used.
K: Security parameter (key length of the key for encrypting the content).
Zq *: a set obtained by removing 0 from a finite field of order q.
G1: Cyclic additive group of order q.
G2: Cyclic multiplicative group of order q.
H1: Mapping from a bit string of arbitrary length to the element of G1.
H2: It is necessary to select a mapping from the source of G2 to a bit string of length n bits, where n ≧ k.
e: A mapping (pairing function) from an element pair of G1 to an element of G2, which satisfies the following four equations.
1) e (aP, Q) = e (P, Q) ^ a = e (P, aQ) (^ represents a power)
2) e (aP, bQ) = e (P, Q) ^ (ab)
3) e ((a, b) P, Q) = e (aP, Q) e (bP, Q)
4) e (P, (a + b) Q) = e (P, aQ) e (P, bQ)

  First, as pre-processing, the content distribution server 1 and the time authentication server 2 perform the following processing.

  The time authentication server 2 selects an arbitrary element G from G1 and an arbitrary element s from Zq *. s is stored as a secret key, and (G, sG) is disclosed as a public key. The validity of the time signal packet sH1 (T) that the time authentication server 2 broadcasts to the plurality of user terminals 3a, 3b, 3c, and 3d at time T is G, sG, and H1 (T) that are public information. This can be confirmed by using e (G, sH1 (T)) = H (sG, H1 (T)).

  The content distribution server 1 (identification number i) selects an arbitrary source bi from Zq *. Next, biG is calculated using G disclosed by the time authentication server 2, and this value is disclosed as a public key. When there are a plurality of content distribution servers using the P2P network, all the content distribution servers perform this process. If the association between the identification number i and the public key biG is disclosed, broadcast with a registered name can be realized, and if the association is not disclosed, anonymous broadcast can be realized.

In addition, the content distribution server 1 performs the following encryption processing on the content M and the publication time T.
First, the content distribution server 1 arbitrarily selects a k-bit key K and encrypts the content M with the key K. Further, the time T is added as an index to the encrypted content. Further, an arbitrary element r is selected from Zq *, and ρ = e (rsG, H1 (T)) e (bis sG, H1 (T)) is calculated. Next, (rG, σ = K xor H2 (ρ)) is calculated as an encryption key.

  When the above processing ends, the content distribution server 1 distributes in advance the encrypted content EM to which the time index T is added and the encryption key EK to the plurality of user terminals 3a, 3b, 3c, and 3d. (Step S101). An example of the data format to be distributed is shown in FIG.

  The time authentication server 2 broadcasts the time signal packet sH1 (T) to the plurality of user terminals 3a, 3b, 3c, and 3d at the designated time T (step S102).

  The plurality of user terminals 3a, 3b, 3c, and 3d receive the time signal packet sH1 (T) from the time authentication server 2 (step S103), and the stored encryption is based on the received time signal packet sH1 (T). A corresponding encrypted content EM is searched from the converted content EM (step S104).

  The plurality of user terminals 3a, 3b, 3c, and 3d receive the encrypted content EM from the received time signal packet sH1 (T), the encrypted content EM to be stored, and the public key biG of the content distribution server 1. A decryption key for decrypting is generated (step S105), and the retrieved encrypted content EM is decrypted using the generated decryption key (step S106).

  Specifically, the plurality of user terminals 3a, 3b, 3c, and 3d receive the received time signal packet sH1 (T), the rG included in the encryption key EK, and the public key biG of the broadcast server, ρ = e (rsG, H1 (T)) e (bis sG, H1 (T)) is calculated. The public key to be used is specified by content information included in data distributed in advance. Next, k = σ xor H2 (ρ) is calculated from σ included in the encryption key EK. Finally, the encrypted content EM is decrypted with the key K to obtain the content M.

  Therefore, according to the present embodiment, a broadcast service can be performed without preparing a large-scale facility. Also, instead of placing the encrypted content on the server, it is possible to avoid concentration of access to the server when the content is released by distributing it in advance by P2P. If user authentication is introduced when participating in a P2P network, a limited broadcast that can be viewed only by a specific user can also be realized. Furthermore, by concealing the association between the distribution server and its public key, an anonymous broadcast service can also be executed. By this anonymous broadcast, fair content popularity voting and the like can be realized.

<Second Embodiment>
A second embodiment according to the present invention will be described with reference to FIGS. The overall configuration of the system is the same as that of the first embodiment, and a detailed description thereof is omitted.

<Configuration of content distribution server>
As shown in FIG. 7, the content distribution server according to this embodiment includes a download time DB (database) 17 as compared to the content distribution server according to the first embodiment. The download time DB (database) 17 is a storage device that receives, for each of the plurality of user terminals 3a, 3b, 3c, and 3d, download times for predetermined contents in the form of a reservation function, and stores them in association with each other. Specifically, the distribution unit 16 searches the information in the download time DB (database) 17 at predetermined time intervals, and if there is something corresponding to a specific time, in response to an access request from the user terminal, The corresponding encrypted content is distributed to the user terminal via the P2P network.

<Configuration of user terminal>
As illustrated in FIG. 8, the user terminal according to the present embodiment further includes a download time registration unit 37 and a download time transmission unit 38 with respect to the user terminal according to the first embodiment. Here, the download time registration unit 37 functions as a download reservation function, and can arbitrarily register the time when the user downloads specific content. The download time transmission unit 38 transmits the download time for the specific content registered in the download time registration unit 37 to the content distribution server.

<System processing>
The processing of the system according to the present embodiment will be described using FIG. Since the main processing is the same as that of the first embodiment, detailed description thereof is omitted.
The content distribution server 1 uses the plurality of user terminals 3a, 3b to transmit the encrypted content and the encryption key to which the time index is added at the download time registered by the plurality of user terminals 3a, 3b, 3c, 3d. 3c and 3d are distributed in advance (step S201).

  The time authentication server 2 broadcasts a time signal packet to the plurality of user terminals 3a, 3b, 3c, and 3d at the designated time (step S202).

  The plurality of user terminals 3a, 3b, 3c, and 3d receive the time signal packet from the time authentication server 2 (step S203), and respond from the stored encrypted content based on the received time signal packet. The encrypted content to be searched is searched (step S204).

  Then, a decryption key for decrypting the encrypted content is generated from the received time signal packet, the encrypted content to be stored and the public key of the content distribution server (step S205), and the generated decryption key is In step S206, the retrieved encrypted content is decrypted.

  Therefore, according to this embodiment, since the registration function (reservation function) is provided in the user terminal, the download start time of the content from the content distribution server becomes random, so that the user terminal can access the content distribution server. Can be reduced.

<Third Embodiment>
A third embodiment according to the present invention will be described with reference to FIGS.

<System configuration>
As shown in FIG. 10, the system according to the present embodiment is provided with an index server 5 in the P2P network as compared with the system according to the first embodiment. The index server 5 stores index information of encrypted contents held by the plurality of user terminals 3a, 3b, 3c, and 3d.

<Configuration of user terminal>
As shown in FIG. 11, the user terminal according to the present embodiment further includes an index information transmission unit 39, an index information search unit 40, and an access unit 41 with respect to the user terminal according to the first embodiment. ing. Here, the index information transmission unit 39 transmits the index information of the content stored in the storage unit 32 to the index server 5.

  The index information search unit 40 searches the index server 5 to extract a user terminal that stores desired content. Based on the search result of the index information search unit 40, the access unit 41 accesses a predetermined user terminal for downloading desired content.

<System processing>
Processing of the system according to the present embodiment will be described with reference to FIG. Since the main processing is the same as that of the first embodiment, detailed description thereof is omitted.
The content distribution server 1 distributes the encrypted content to which the time index is added and the encryption key to the plurality of user terminals 3a, 3b, 3c, and 3d in advance (step S301). The time authentication server 2 broadcasts a time signal packet to the plurality of user terminals 3a, 3b, 3c, and 3d at the designated time (step S302).

  The plurality of user terminals 3a, 3b, 3c, and 3d search the index server 5, and download the encrypted content and the encryption key with the desired time index added from the neighboring user terminals on the network ( In step S303, the encrypted content to which the downloaded time index is added and the encryption key are stored (step S304).

  Next, when a time signal packet is received from the time authentication server 2 (step S305), the corresponding encrypted content is searched from the storage means based on the received time signal packet (step S306).

  Then, a decryption key for decrypting the encrypted content is generated from the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server (step S307). In step S308, the retrieved encrypted content is decrypted.

  Therefore, according to the present embodiment, the network load can be reduced by providing the index server, registering the index information of the encrypted content owned by each user terminal, and downloading the content from the nearby user terminal.

  The processing of the content distribution system is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a content distribution server, a time authentication server, a plurality of user terminals, or an index server forming the content distribution system. The content distribution system of the present invention can be realized by executing. The computer system here includes an OS and hardware such as peripheral devices.

  Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW (World Wide Web) system is used. The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line.

  The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

  The embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to the embodiments, and includes designs and the like that do not depart from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Content delivery server 2 ... Time authentication server 3a, 3b, 3c, 3d ... Multiple user terminals 4 ... P2P network 5 ... Index server 11 ... Time index production | generation part 12. .. Content information generation unit 13 ... Content encryption unit 14 ... Encryption key generation unit 15 ... Distribution data generation unit 16 ... Distribution unit 17 ... Download time DB (database)
DESCRIPTION OF SYMBOLS 21 ... Timekeeping part 22 ... Time signal packet generation part 23 ... Time signal packet transmission part 31 ... Content reception part 32 ... Storage part 33 ... Time signal packet reception part 34 ... Content search part 35 ... Decryption key generation unit 36 ... Decryption unit 37 ... Download time registration unit 38 ... Download time transmission unit 39 ... Index information transmission unit 40 ... Index information search unit 41 ... Access section

Claims (13)

It consists of a content distribution server, a time authentication server, and multiple user terminals.
The content distribution server is
Content distribution means for distributing the encrypted content and the encryption key with the time index added to the plurality of user terminals in advance;
The time authentication server is
A time signal packet distribution means for broadcasting a time signal packet to the plurality of user terminals at a designated time;
The plurality of user terminals are
Storage means for storing the encrypted content to which the time index is added and an encryption key;
Receiving means for receiving a time signal packet from the time authentication server;
Search means for searching for the corresponding encrypted content from the storage means based on the received time signal packet;
Decryption key generation means for generating a decryption key for decrypting the encrypted content from the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server;
Decryption means for decrypting the retrieved encrypted content using the generated decryption key;
A content distribution system comprising:   The content distribution system according to claim 1, wherein the content distribution server distributes the encrypted content in advance using a P2P network.   The content distribution system according to claim 1, wherein the content distribution server publishes an association between its own identification number and a public key.   The content distribution system according to claim 1, wherein the content distribution server makes the association between its own identification number and a public key private.   The content distribution system according to claim 1, wherein the content distribution server includes user authentication means for authenticating a user who participates in the network. It consists of a content distribution server, a time authentication server, and multiple user terminals.
The content distribution server is
Content distribution means for distributing in advance the encrypted content with the time index added and the encryption key at the registered download time to the user terminal,
The time authentication server is
A time signal packet distribution means for broadcasting a time signal packet to the plurality of user terminals at a designated time;
The plurality of user terminals are
Registration means for registering a time for downloading the specific encrypted content in the content distribution server;
Storage means for storing the encrypted content to which the time index is added and an encryption key;
Receiving means for receiving a time signal packet from the time authentication server;
Search means for searching for the corresponding encrypted content from the storage means based on the received time signal packet;
Decryption key generation means for generating a decryption key for decrypting the encrypted content from the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server;
Decryption means for decrypting the retrieved encrypted content using the generated decryption key;
A content distribution system comprising: A content distribution server, a time authentication server, a plurality of user terminals, and an index server that holds index information of the encrypted content stored in the plurality of user terminals,
The content distribution server is
Content distribution means for distributing the encrypted content and the encryption key with the time index added to the plurality of user terminals in advance;
The time authentication server is
A time signal packet distribution means for broadcasting a time signal packet to the plurality of user terminals at a designated time;
The plurality of user terminals are
Downloading means for searching the index server and downloading the encrypted content and encryption key to which a desired time index is added from a neighboring user terminal on the network;
Storage means for storing the encrypted content to which the time index is added and an encryption key;
Receiving means for receiving a time signal packet from the time authentication server;
Search means for searching for the corresponding encrypted content from the storage means based on the received time signal packet;
Decryption key generation means for generating a decryption key for decrypting the encrypted content from the received time signal packet, the encrypted content to be stored, and the public key of the content distribution server;
Decryption means for decrypting the retrieved encrypted content using the generated decryption key;
A content distribution system comprising: A content distribution method in a content distribution system comprising a content distribution server, a time authentication server and a plurality of user terminals,
A first step in which the content distribution server distributes the encrypted content with the time index and the encryption key to the plurality of user terminals in advance;
A second step in which the time authentication server broadcasts a time signal packet to the plurality of user terminals at a specified time;
A third step in which the plurality of user terminals receive a time signal packet from the time authentication server;
A fourth step in which the plurality of user terminals retrieves the corresponding encrypted content from the stored encrypted content based on the received time signal packet;
The plurality of user terminals generate a decryption key for decrypting the encrypted content from the received time signal packet, the stored encrypted content, and the public key of the content distribution server. Steps,
A sixth step in which the plurality of user terminals decrypts the retrieved encrypted content using the generated decryption key;
A content distribution method comprising: A content distribution method in a content distribution system comprising a content distribution server, a time authentication server and a plurality of user terminals,
The content distribution server first distributes the encrypted content with the time index added thereto and the encryption key to the plurality of user terminals in advance at the download time registered by the plurality of user terminals. And the steps
A second step in which the time authentication server broadcasts a time signal packet to the plurality of user terminals at a specified time;
A third step in which the plurality of user terminals receive a time signal packet from the time authentication server;
A fourth step in which the plurality of user terminals retrieves the corresponding encrypted content from the stored encrypted content based on the received time signal packet;
The plurality of user terminals generate a decryption key for decrypting the encrypted content from the received time signal packet, the stored encrypted content, and the public key of the content distribution server. Steps,
A sixth step in which the plurality of user terminals decrypts the retrieved encrypted content using the generated decryption key;
A content distribution method comprising: A content distribution method in a content distribution system, comprising: a content distribution server; a time authentication server; a plurality of user terminals; and an index server that holds index information of the encrypted content stored in the plurality of user terminals. ,
A first step in which the content distribution server distributes the encrypted content with the time index and the encryption key to the plurality of user terminals in advance;
A second step in which the time authentication server broadcasts a time signal packet to the plurality of user terminals at a specified time;
A third step in which the plurality of user terminals search the index server and download the encrypted content and the encryption key to which a desired time index is added from neighboring user terminals on the network;
A fourth step in which the plurality of user terminals store the encrypted content to which the time index is added and an encryption key;
A fifth step in which the plurality of user terminals receive a time signal packet from the time authentication server;
A sixth step in which the plurality of user terminals retrieve the corresponding encrypted content from the storage means based on the received time signal packet;
A plurality of user terminals generating a decryption key for decrypting the encrypted content from the received time signal packet, the stored encrypted content, and the public key of the content distribution server; Steps,
An eighth step in which the plurality of user terminals decrypts the retrieved encrypted content using the generated decryption key;
A content distribution method comprising: A program for causing a computer to execute a content distribution method in a content distribution system including a content distribution server, a time authentication server, and a plurality of user terminals,
A first step in which the content distribution server distributes the encrypted content with the time index and the encryption key to the plurality of user terminals in advance;
A second step in which the time authentication server broadcasts a time signal packet to the plurality of user terminals at a specified time;
A third step in which the plurality of user terminals receive a time signal packet from the time authentication server;
A fourth step in which the plurality of user terminals retrieves the corresponding encrypted content from the stored encrypted content based on the received time signal packet;
The plurality of user terminals generate a decryption key for decrypting the encrypted content from the received time signal packet, the stored encrypted content, and the public key of the content distribution server. Steps,
A sixth step in which the plurality of user terminals decrypts the retrieved encrypted content using the generated decryption key;
A program that causes a computer to execute. A program for causing a computer to execute a content distribution method in a content distribution system including a content distribution server, a time authentication server, and a plurality of user terminals,
The content distribution server first distributes the encrypted content with the time index added thereto and the encryption key to the plurality of user terminals in advance at the download time registered by the plurality of user terminals. And the steps
A second step in which the time authentication server broadcasts a time signal packet to the plurality of user terminals at a specified time;
A third step in which the plurality of user terminals receive a time signal packet from the time authentication server;
A fourth step in which the plurality of user terminals retrieves the corresponding encrypted content from the stored encrypted content based on the received time signal packet;
The plurality of user terminals generate a decryption key for decrypting the encrypted content from the received time signal packet, the stored encrypted content, and the public key of the content distribution server. Steps,
A sixth step in which the plurality of user terminals decrypts the retrieved encrypted content using the generated decryption key;
A program that causes a computer to execute. A content distribution method in a content distribution system comprising: a content distribution server; a time authentication server; a plurality of user terminals; and an index server that holds index information of the encrypted content stored in the plurality of user terminals. A program for executing the program,
A first step in which the content distribution server distributes the encrypted content with the time index and the encryption key to the plurality of user terminals in advance;
A second step in which the time authentication server broadcasts a time signal packet to the plurality of user terminals at a specified time;
A third step in which the plurality of user terminals search the index server and download the encrypted content and the encryption key to which a desired time index is added from neighboring user terminals on the network;
A fourth step in which the plurality of user terminals store the encrypted content to which the time index is added and an encryption key;
A fifth step in which the plurality of user terminals receive a time signal packet from the time authentication server;
A sixth step in which the plurality of user terminals retrieve the corresponding encrypted content from the storage means based on the received time signal packet;
A plurality of user terminals generating a decryption key for decrypting the encrypted content from the received time signal packet, the stored encrypted content, and the public key of the content distribution server; Steps,
An eighth step in which the plurality of user terminals decrypts the retrieved encrypted content using the generated decryption key;
A program that causes a computer to execute.

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