JP2009135721A - Content distribution system, and content distribution method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system corresponding to P2P content distribution which does not need a storage for performing content management, or the like. <P>SOLUTION: A client terminal receives a content file comprising a user key encrypted by a master key, a content key encrypted by the user key and a content encrypted by the content key, and transmits the encrypted user key and content key to a management server. The management server decrypts the user key by a master key that management server holds, uses the user key to decrypt a content key from the encrypted content key, and encrypts the master key to generate a new user key. Furthermore, the management server encrypts the decrypted content key with the new user key and returns the new user key and the content key to the client terminal, and the client terminal decrypts the content key with the new user key, and decrypts the content with the content key. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to DRM (Digital Rights Management) technology, and in particular, to a content distribution system, a content distribution method, and a program corresponding to P2P content distribution.

  In recent years, with the development of networks such as the Internet and mobile phone networks, network distribution of multimedia contents such as music and moving images has been actively performed. In the music field, the transition from CD distribution to network distribution is gradually progressing due to the cooperation between portable music players and PCs and mobile phones, and streaming services on the network are also increasing.

  For this reason, there is a method of encrypting content in order to prevent unauthorized use, unauthorized distribution, and unauthorized copying of the content. An individual encryption key is created for the user (this is used as a user key). A double key method that encrypts the content encryption key (this is the content key), a triple key method that encrypts the content key with another key, and encrypts the key with the user key. There has been proposed a method for efficiently performing content control for each user.

In addition, the encrypted content key corresponding to the terminal that issued the viewing request for the first time is retrieved and obtained from the encrypted content key main database in which the information of all the terminals is registered. A technique for reducing search time (for example, refer to Patent Document 1) and data reproduction by searching and acquiring from an encrypted content key sub-database in which only valid terminals connected to a distribution server are registered and created from the history The device requests the decryption key necessary for decrypting the encrypted content from the encryption key storage server, and the encryption key storage server compares the decryption key expiration date with the real time, and the decryption key is only within the expiration date. Is sent to the data reproducing device, the cipher data usable time is managed on the information provider side and cannot be arbitrarily reproduced on the user side. (E.g., see Patent Document 1) has been proposed.
JP 2005-117380 A JP 2003-174439 A

By the way, at present, the server distribution type is the mainstream in commercial services in terms of content management and the like, and iTS (iTunes Store), Youtube, and the like are typical examples. On the other hand, based on content distribution load distribution and word-of-mouth distribution effects, P2P (Peer
to Peer) technology has attracted attention, and in recent years, trends such as Winny have been seen, and in some cases, a system using P2P technology for commercial services has begun to be tested. It is estimated that this type of content distribution will be performed.

  However, in the conventional method, it is necessary to manage the content key encrypted with the user key, and it is necessary to know all the user keys in order to distribute the content key to all users. In this case, even in a model in which content is distributed without going through a server as in P2P, a storage for performing content management and user management is necessary, which causes a problem in content distribution by P2P.

  Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a content distribution system, a content distribution method, and a program corresponding to P2P content distribution that do not require a storage for performing content management and user management. And

  The present invention proposes the following items in order to solve the above-described problems.

  (1) The present invention encrypts with a master key by P2P between client terminals (for example, equivalent to the client terminal 1 in FIG. 1) via a management server (for example, equivalent to the management server 2 in FIG. 1). A content distribution system that distributes a content file composed of a user key that has been encrypted, a content key encrypted with the user key, and a content encrypted with the content key, wherein a master key held by the management server is A new user key is generated by encryption, and the content key is encrypted with the generated new user key and transmitted to the client terminal. The client terminal uses the received content key as the new user key. The content distribution system is characterized in that the content is decrypted using the decrypted content key and decrypted using the decrypted content key. It is.

  According to the present invention, the master key held by the management server is encrypted to generate a new user key, and the content key is encrypted with the generated new user key and transmitted to the client terminal. The received content key is decrypted using the new user key, and the content is decrypted using the decrypted content key. Therefore, since the content file format is a user key encrypted with the master key, a content key encrypted with the user key, and a content encrypted with the content key, the management server only manages the master key. Therefore, there is no need for a storage for managing user keys for each client and managing content keys for each content.

  (2) The present invention is a content distribution system that distributes encrypted content by P2P between client terminals via a management server, wherein the client terminal is a user encrypted with a master key. Receiving means (for example, equivalent to the receiving unit 11 in FIG. 2) for receiving a content file comprising a key, a content key encrypted with the user key, and a content encrypted with the content key; Transmission means for transmitting a user key encrypted with a master key and a content key encrypted with the user key to the management server (for example, corresponding to the transmission unit 12 in FIG. 2), and the management server Using the holding means for holding the master key (for example, corresponding to the master key holding unit 23 in FIG. 3) and the received master key using the master key. Key decrypting means for decrypting the content key from the content key encrypted with the user key using the decrypted user key and decrypting the user key from the encrypted user key (for example, the key decrypting unit in FIG. 3) 22), user key generation means for encrypting the master key to generate a new user key (for example, corresponding to the user key generation unit 24 in FIG. 3), and the decryption with the generated new user key. An encryption means for encrypting the content key (for example, corresponding to the encryption unit 25 in FIG. 3), the new user key, and the content key encrypted with the new user key are returned to the client terminal. Return means (for example, corresponding to the transmission unit 26 in FIG. 3), wherein the client terminal decrypts the returned content key using the new user key, and further decrypts the decrypted content key. And a content decrypting means for decrypting the content (for example, corresponding to the decrypting unit 13 in FIG. 2).

  According to this invention, the receiving means of the client terminal receives a content file composed of a user key encrypted with a master key, a content key encrypted with the user key, and content encrypted with the content key, The transmission means transmits the user key encrypted with the received master key and the content key encrypted with the user key to the management server. The management server possession means retains the master key, and the key decryption means decrypts the user key from the user key encrypted with the received master key using the master key and uses the decrypted user key. The content key is decrypted from the content key encrypted with the user key. The user key generation unit encrypts the master key to generate a new user key, the encryption unit encrypts the content key decrypted with the generated new user key, and the return unit generates a new user key and a new user key. The content key encrypted with a simple user key is returned to the client terminal. Then, the content decrypting means of the client terminal decrypts the returned content key using the new user key, and further decrypts the content with the decrypted content key. Therefore, since the content file format is a user key encrypted with the master key, a content key encrypted with the user key, and a content encrypted with the content key, the management server only manages the master key. Therefore, there is no need for a storage for managing user keys for each client and managing content keys for each content.

  (3) The present invention proposes a content distribution system that can include a plurality of the management servers in the content distribution system of (2).

  According to this invention, a plurality of management servers can be provided. Therefore, the system can be easily expanded by adding management servers.

  (4) The present invention is a content distribution method in a content distribution system that distributes encrypted content between client terminals by P2P via a management server, wherein the client terminal is encrypted with a master key. A first step (for example, corresponding to step S101 in FIG. 5) of receiving a content file comprising an encrypted user key, a content key encrypted with the user key, and content encrypted with the content key; The client terminal transmits a second user key encrypted with the received master key and a content key encrypted with the user key to the management server (for example, step S102 in FIG. 5). The management server holds the master key and uses the master key to receive the received master key. A third step of decrypting the user key from the user key encrypted with the star key and decrypting the content key from the content key encrypted with the user key using the decrypted user key (for example, FIG. 5). The management server encrypts the master key to generate a new user key (e.g., corresponds to step S104 in FIG. 5), and the management server A fifth step (for example, corresponding to step S105 in FIG. 5) for encrypting the decrypted content key with the generated new user key, and the management server using the new user key and the new user key A sixth step of returning the encrypted content key to the client terminal (for example, corresponding to step S106 in FIG. 5), and the client terminal And a seventh step (for example, corresponding to step S107 of FIG. 5) of decrypting the content key using the new user key and decrypting the content with the decrypted content key. A content distribution method is proposed.

  According to this invention, a client terminal receives a content file composed of a user key encrypted with a master key, a content key encrypted with the user key, and a content encrypted with the content key, and receives the received master file. The user key encrypted with the key and the content key encrypted with the user key are transmitted to the management server. The management server has a master key, uses the master key to decrypt the user key from the user key encrypted with the received master key, and encrypts the user key using the decrypted user key The content key is decrypted from the content key, the master key is encrypted to generate a new user key, the decrypted content key is encrypted with the generated new user key, and the new user key and the new user key are used. The encrypted content key is returned to the client terminal. Then, the client terminal decrypts the returned content key using the new user key, and further decrypts the content with the decrypted content key. Therefore, since the content file format is a user key encrypted with the master key, a content key encrypted with the user key, and a content encrypted with the content key, the management server only manages the master key. Therefore, there is no need for a storage for managing user keys for each client and managing content keys for each content.

  (5) The present invention is a program for causing a computer to execute a content distribution method in a content distribution system that distributes encrypted content by P2P between client terminals via a management server, A first step in which the client terminal receives a content file composed of a user key encrypted with a master key, a content key encrypted with the user key, and content encrypted with the content key (for example, FIG. 5), and the client terminal transmits the received user key encrypted with the master key and the content key encrypted with the user key to the management server. (For example, corresponding to step S102 in FIG. 5), the management server holds the master key. The user key is decrypted from the user key encrypted with the received master key by using the master key, and the content key is decrypted from the content key encrypted by the user key by using the decrypted user key. And a fourth step in which the management server encrypts the master key to generate a new user key (for example, the step in FIG. 5). A fifth step (equivalent to step S105 in FIG. 5) in which the management server encrypts the decrypted content key with the generated new user key, and the management server A sixth step of returning the new user key and the content key encrypted with the new user key to the client terminal (for example, step S10 in FIG. 5). 6), the client terminal decrypts the returned content key using the new user key, and further decrypts the content with the decrypted content key (for example, the step of FIG. 5). (Corresponding to S107) is proposed.

  According to this invention, a client terminal receives a content file composed of a user key encrypted with a master key, a content key encrypted with the user key, and a content encrypted with the content key, and receives the received master file. The user key encrypted with the key and the content key encrypted with the user key are transmitted to the management server. The management server holds the master key, decrypts the user key from the user key encrypted with the received master key using the master key, and encrypts with the user key using the decrypted user key The content key is decrypted from the content key, the master key is encrypted to generate a new user key, the decrypted content key is encrypted with the generated new user key, and the new user key and the new user key are used. The encrypted content key is returned to the client terminal. Then, the client terminal decrypts the returned content key using the new user key, and further decrypts the content with the decrypted content key. Therefore, since the content file format is a user key encrypted with the master key, a content key encrypted with the user key, and a content encrypted with the content key, the management server only manages the master key. Therefore, there is no need for a storage for managing user keys for each client and managing content keys for each content.

  According to the present invention, since the content file format is configured as a user key encrypted with a master key, a content key encrypted with a user key, and a content encrypted with a content key, the management server only has a master key. Therefore, there is an effect that a storage for managing a user key for each client and a content key for each content is not necessary. As a result, content distribution that prevents unauthorized distribution / use without requiring special storage can be realized, and copyright protection can be realized for content on P2P.

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 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.

  The embodiment of the present invention will be described with reference to FIGS.

<System configuration>
As shown in FIG. 1, the content distribution system according to the present embodiment includes a client terminal 1 that performs P2P communication and a management server 2 that manages a master key. The client terminal 1 and the management server 2 are connected to a network 3. Connected through. The management server 2 can be expanded according to the scale of the system.

<Configuration of client terminal>
As illustrated in FIG. 2, the client terminal 1 includes a reception unit 11, a transmission unit 12, a decryption unit 13, and a client information storage unit 14.

  As shown in FIG. 4, the receiving unit 11 includes a user key encrypted with a master key from another client terminal 1, a content key encrypted with the user key, and content encrypted with the content key. In addition to receiving a new content file, the management server 2 receives a new user key and a content key encrypted with the new user key.

  The transmission unit 12 transmits the user key encrypted with the master key received by the reception unit 11 and the content key encrypted with the user key to the management server. In addition, client information necessary for issuing a new user key is transmitted.

  The decryption unit 13 decrypts the content key received from the management server 2 using the new user key, and further decrypts the content using the decrypted content key. The client information storage unit 14 stores client information necessary for issuing a new user key (user information when bound to a user, terminal-specific information when bound to a client terminal and cannot be used by other clients, etc. ).

<Configuration of management server>
As shown in FIG. 3, the management server 2 includes a reception unit 21, a key decryption unit 22, a master key holding unit 23, a user key generation unit 24, an encryption unit 25, and a transmission unit 26. ing.

  The receiving unit 21 receives the user key encrypted with the master key received from the client terminal 1 and the content key encrypted with the user key. In addition, client information necessary for issuing a new user key is transmitted.

  The key decryption unit 22 decrypts the user key from the user key encrypted with the master key received by the reception unit 21 using the master key, and encrypts the user key with the decrypted user key. Decrypt the content key from the content key.

  The master key holding unit 23 stores and manages the master key. The user key generation unit 24 generates a new user key by encrypting the master key using client information necessary for issuing a new user key received by the reception unit 21.

  The encryption unit 25 encrypts the content key decrypted with the new user key generated by the user key generation unit 24. The transmission unit 26 transmits a new user key and a content key encrypted with the new user key to the client terminal 1.

<Processing of content distribution system>
Next, processing of the content distribution system will be described with reference to FIG.

  First, the reception unit 11 of a client terminal includes a user key encrypted with a master key from another client terminal 1, a content key encrypted with the user key, and content encrypted with the content key A file is received (step S101).

  Then, the transmission unit 12 of the client terminal transmits the user key encrypted with the master key received by the reception unit 11 and the content key encrypted with the user key to the management server 2 (step S102).

  The management server 2 has a master key, and uses the master key to decrypt the user key from the user key encrypted with the master key received by the receiving unit 21 and uses the decrypted user key to The content key is decrypted from the content key encrypted with the key (step S103).

  Next, the management server 2 generates a new user key by encrypting the master key in the user key generation unit 24 (step S104). Further, the encryption unit 25 of the management server 2 encrypts the content key decrypted with the new user key generated by the user key generation unit 24 (step S105).

  Further, the transmission unit of the management server 2 transmits the new user key generated by the user key generation unit 24 and the content key encrypted with the new user key to the client terminal (step S106). Then, the reception unit 11 of the client terminal 1 decrypts the received content key using the new user key in the decryption unit 13, and further decrypts the content with the decrypted content key (step S107).

  Therefore, according to this embodiment, since the content file format is configured as a user key encrypted with a master key, a content key encrypted with a user key, and a content encrypted with a content key, the management server Since only the master key needs to be managed, a storage for managing the user key for each client and the content key for each content is not necessary.

<Example>
Next, a more specific embodiment will be described with reference to FIGS.

In this embodiment, it is assumed that the following usage environment and conditions are satisfied.
1) Content search technology in P2P is in place.
2) PKC (Public Key Certificate) and certificate authority are in place when necessary, and public keys / private keys, signature keys / verification keys are properly issued and used in procedures such as authentication. .
3) Apart from the content key owned by the client terminal, there is a master key owned only by the license management server.
4) It is assumed that processing (billing etc.) related to copyright information accompanying the content and license terms accompanying the user is separately prepared.
5) The client terminal has a tamper-resistant module in which user license information is incorporated. Assume that it is impossible for a user to tamper with and eavesdrop on internal information and processing.

In the present embodiment, the symbols used are as follows.
1) r _n :
Random number 2) SENC (m, k): Data obtained by encrypting message (m) with common key encryption system using shared key (k) 3) Ka, Kb: User key (Ka for client A, Kb for client B)
4) g _x , p _x , s, t, u, v [where x = {0, 1}]:
DH key sharing numerical values (primary element g _x , prime number p _x ), secret information s of client A (content supply source and content key encryption change request source) for temporary keys used in communication during content distribution, and v, secret information t of client B (content receiving destination), secret information u of distribution management server (content key update request destination)
5) TK: Shared key for temporary communication between clients A and B 6) c, Meta, CID, CK: Content (c), associated information (Meta), content ID (CID), and content encryption Content key (CK)
7) g ₂ , p ₂ , u: User key (= key for communication) shared between the content distribution management server and the client B requesting content use ( _primary element g ₁ , prime number p ₁ , distribution management server secret) Information u)
8) IDb: Terminal unique information of client terminal used by client B 9) f (•): Conversion function of terminal unique information 10) Km: Master key possessed by content distribution management server 11) ||: Concatenation of previous and subsequent values

<Example 1>
Hereinafter, Example 1 will be described with reference to FIGS.

<Content distribution processing>
First, as shown in FIG.
1) When a content transmission request is signaled from the client B, the client A generates a random number r ₀ and numerical values g ₀ , p ₀ , s ₀ for generating a DH key and transmits them to the client B.
2) Client B generates t and g ₀ ^t mod
to calculate the p _0. Also, temporary key TK = g ₀ ^st mod
p ₀ is calculated, and SENC (r ₀ , TK) obtained by encrypting the received random number r ₀ is calculated. Furthermore, another random number r ₁ is generated, and r ₁ , g ₀ ^t mod
p ₀ and SENC (r ₀ , TK) are transmitted to the client A.
3) The client A obtains the TK, decodes the received SENC (r ₀ , TK), and checks whether it matches the r ₀ transmitted by itself. When the confirmation is completed, SENC (r ₁ , TK) is calculated and transmitted to the client B.
4) Client B decrypts SENC (r ₁ , TK) and checks whether it matches r ₁ transmitted by itself. When the confirmation is completed, SENC (CID, TK) is calculated from the CID that is the ID of the received content, and transmitted to the client A.
5) The client A confirms the CID, and if there is a corresponding content, the content key obtained by encrypting the content with the user key is encrypted with the content key meta information Meta and the master key. SENC (Meta || Ka, Km) || SENC (CK, Ka) is transmitted to the management server and encrypted with a temporary key for content distribution. SENC (Meta || DK, Km) || SENC (CK, DK) is received. SENC (SENC (Meta || DK, Km) || SENC (CK, DK) || SENC (c, CK), TK), which is encrypted with TK and the encrypted content, is used as a transmission packet. , To client B.

The procedure for changing the encryption of the content key in 5) will be described with reference to FIG.
1) When the content delivery request is signaled from the client A, the management server generates a random number r ₂ and numerical values g ₁ , p ₁ , u for generating the DH key and transmits them to the client A.
2) Client A generates v and g ₁ ^v mod
to calculate the p _1. Also, the temporary key TK ′ = g ₁ ^uv mod
p ₁ is calculated, and SENC (r ₂ , TK ′) obtained by encrypting the received random number r ₂ is calculated. Furthermore, another random number r ₃ is generated, and r ₃ , g ₁ ^v mod
p ₁ and SENC (r ₂ , TK ′) are transmitted to the management server.
3) The management server obtains TK ′, decrypts the received SENC (r ₂ , TK ′), and checks whether it matches r ₂ transmitted by itself. When the confirmation is completed, SENC (r ₃ , TK ′) is calculated and transmitted to the client A.
4) Client A decrypts SENC (r ₃ , TK ′) and checks whether it matches r ₃ transmitted by itself. After confirmation, a temporary encryption key DK for content distribution is generated. SENC (Meta || Ka, Km) || SENC (CK, which is obtained by encrypting the content key obtained by encrypting the content key with the user key, and encrypting the user key together with Meta. , Ka) together with SENC (DK || SENC (Meta || Ka, Km) || SENC (CK, Ka), TK '), which is encrypted with TK'.
6) The management server generates SENC (Meta || DK, Km) || SENC (CK, DK), which is re-encrypted with DK after decrypting all information, and encrypts it with TK ' Send to client A.
7) The client A decrypts the received information and obtains SENC (Meta || DK, Km) || SENC (CK, DK).
In the case where the request is made not by P2P but by the content distribution server (the person who receives content distribution for the first time or the person who has not found the content in the P2P search), the client A is determined by the same procedure as the content distribution server. However, in the procedure 4), SENC (CID || DK || CK, TK ') is transmitted instead. The procedure of 5) is the same.

<Processing of content use request>
The content use request process will be described with reference to FIG.

1) When a request for use of content is received from the client B, the management server generates a random number r ₄ and numerical values g ₂ , p ₃ , w for generating a DH key and transmits them to the client B.
2) Client B generates f (IDb) from IDb, which is the hardware ID of its own terminal, and calculates g ₂ ^{f (IDb)} mod p ₂ . Also, the encryption key Kb = g ₂ ^{wf (id)} mod
The p ₂ was calculated, the random number _{r 4} received for calculating a SENC encrypted _{(r 4,} Kb). Further, another random number r ₅ is generated, and r ₅ , g ₂ ^{f (IDb)} mod
p ₅ and SENC (r ₄ , Kb) are transmitted to the management server.
3) The management server obtains Kb, decrypts the received SENC (r ₄ , Kb), and checks whether it matches r ₄ transmitted by itself. When the confirmation is completed, SENC (r ₅ , Kb) is calculated and transmitted to the client B.
4) Client B decrypts SENC (r ₅ , Kb) and checks whether it matches r ₅ transmitted by itself. After confirmation, SENC (SENC (Meta || DK, Km) || SENC (CK, DK) ||, Kb) is calculated from the one received from the client A and transmitted to the management server.
5) The management server derives and decrypts DK, performs re-encryption processing with Kb, and calculates SENC (SENC (Meta || Kb, Km) || SENC (CK, Kb) ||, Kb) Send to client B. Client B receives the received g ₂ ^w mod
To save the p _2.

<Example 2>
A second embodiment will be described with reference to FIGS.
In the first embodiment, the communication at the time of content acquisition and the use at the time of use is shown separately. However, in this embodiment, at the time of content acquisition, the content is bound to a distribution destination terminal and communication at the time of use is not required. I will explain things. In other words, the first embodiment is intended to protect privacy information such as cooperation between users by applying the method when a method capable of generating a key in a method in which the user cannot be traced in the future is proposed. However, the present embodiment is intended to reduce the burden on the user by terminating all the processes at the time of content acquisition.

<User key issuance process>
The user key issuance processing in this embodiment will be described with reference to FIG.
1) When there is a user key request signal from the client B, the management server generates a random number r ₀ and numerical values g ₂ , p ₃ , w for generating a DH key and transmits them to the client B.
2) Client B generates f (IDb) from IDb, which is the hardware ID of its own terminal, and calculates g ₂ ^{f (IDb)} mod p ₂ . Also, the encryption key Kb = g ₂ ^{wf (id)} mod
p ₂ is calculated, and SENC (r ₀ , Kb), which is an encrypted version of the received random number r ₀ , is calculated. Further, another random number r ₁ is generated, and r ₁ , g ₂ ^{f (IDb)} mod
p ₅ and SENC (r ₀ , Kb) are transmitted to the management server.
3) The management server obtains Kb, decrypts the received SENC (r ₀ , Kb), and checks whether it matches r ₀ transmitted by itself. When the confirmation is completed, SENC (r ₁ , Kb) is calculated and transmitted to the client B.
4) Client B decrypts SENC (r ₁ , Kb) and checks whether it matches r ₁ transmitted by itself. Once confirmed, Client B will g ₂ ^w mod
To save the p _2.

<Content distribution processing>
The content distribution processing in this embodiment will be described with reference to FIGS. 10 and 11.
1) When there is a content transmission request signal from the client B, the client A generates a random number r ₂ and numerical values g ₀ , p ₀ , s ₀ for DH key generation and transmits them to the client B.
2) Client B generates t and g ₀ ^t mod
to calculate the p _0. Also, temporary key TK = g ₀ ^st mod
p ₀ is calculated, and SENC (r ₂ , TK) obtained by encrypting the received random number r ₂ is calculated. Furthermore, another random number r ₃ is generated, and r ₃ , g ₀ ^t mod
p ₀ and SENC (r ₂ , TK) are transmitted to the client A.
3) The client A obtains the TK, decrypts the received SENC (r ₂ , TK), and checks whether it matches the r ₂ transmitted by itself. When the confirmation is completed, SENC (r ₃ , TK) is calculated, and client B is transmitted.
4) Client B decrypts SENC (r ₃ , TK) and checks whether it matches r ₃ transmitted by itself. After confirmation, SENC (CID || g ₂ ^{f (IDb)} mod p ₂ , TK) is calculated from the CID that is the ID of the received content and the user key generation seed, and is transmitted to the client A.
5) The client A confirms the CID, and if there is a corresponding content, the content key obtained by encrypting the content is encrypted with the user key, and the user key is combined with the content meta information Meta with the master key. The encrypted SENC (Meta || Ka, Km) || SENC (CK, Ka) is connected to the user key generation seed received from the client B and transmitted to the management server. SENC (Meta || Kb, Km) || SENC (CK, Kb), which has been re-encrypted, is received. SENC (SENC (Meta || Kb, Km) || SENC (CK, Kb) || SENC (c, CK), TK) is used as a transmission packet, which is encrypted with TK by combining this and the encrypted content. Send to B.
6) Client B decrypts and stores the received data.

A procedure for changing the encryption of the content key in the above 5) will be described.
1) When there is a content delivery request signal from the client A, the management server generates a random number r ₄ and numerical values g ₁ , p ₁ , u for generating a DH key and transmits them to the client A.
2) Client A generates v and g ₁ ^v mod
to calculate the p _1. Also, the temporary key TK ′ = g ₁ ^uv mod
p ₁ is calculated, and SENC (r ₄ , TK ′) obtained by encrypting the received random number r ₄ is calculated. Further, another random number r ₅ is generated, and r ₅ , g ₁ ^v mod
p ₁ and SENC (r ₄ , TK ′) are transmitted to the management server.
3) The management server obtains TK ′, decrypts the received SENC (r ₄ , TK ′), and checks whether it matches r ₄ transmitted by itself. When the confirmation is completed, SENC (r ₅ , TK ′) is calculated and transmitted to the client A.
4) Client A decrypts SENC (r ₅ , TK ′) and checks whether it matches r ₅ transmitted by itself. After confirmation, the client B user key generation seed and the content key obtained by encrypting the content are encrypted with the user key, and the user key is encrypted with the master key SENC ( Meta || Ka, Km) || SENC (g ₂ ^{f (IDb)} mod p ₂ || SENC (Meta || Ka, Km) | encrypted with TK ′ together with SENC (CK, Ka) | SENC (CK, Ka), TK ′) is transmitted to the management server.
5) The management server decrypts all the information, generates Kb from the user key generation seed of the client B, and re-encrypts with this key SENC (Meta || Kb, Km) || SENC (CK, Kb) is generated, encrypted with TK ′, and transmitted to the client A.
6) The client A decrypts the received information and obtains SENC (Meta || Kb, Km) || SENC (CK, Kb).

  These programs are recorded on a computer-readable recording medium, and the programs recorded on the recording medium are read into the client terminal 1 and the management server 2 (both are computer systems) and executed, thereby executing the present invention. A content distribution system can be realized. 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. For example,

1 is a configuration diagram of a system according to an embodiment of the present invention. It is a block diagram of the client terminal which concerns on embodiment of this invention. It is a block diagram of the management server which concerns on embodiment of this invention. It is the figure which illustrated the composition of the contents file concerning the embodiment of the present invention. It is a processing flow concerning the embodiment of the present invention. It is a processing flow of the content delivery which concerns on Example 1 of this invention. It is a processing flow of the content key encryption change which concerns on Example 1 of this invention. It is a processing flow of the content use request which concerns on Example 1 of this invention. It is a processing flow of the user key issue which concerns on Example 2 of this invention. It is a processing flow of the content delivery which concerns on Example 2 of this invention. It is a processing flow of the content key encryption change which concerns on Example 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Client terminal, 2 ... Management server, 3 ... Network, 11 ... Reception part, 12 ... Transmission part, 13 ... Decoding part, 14 ... Client information storage part, DESCRIPTION OF SYMBOLS 21 ... Reception part, 22 ... Key decryption part, 23 ... Master key holding part, 24 ... User key generation part, 25 ... Encryption part, 26 ... Transmission part

Claims (5)

A content file consisting of a user key encrypted with a master key, a content key encrypted with the user key, and a content encrypted with the content key by P2P between client terminals via the management server A content distribution system that performs distribution,
The master key held by the management server is encrypted to generate a new user key, and the content key is encrypted with the generated new user key and transmitted to the client terminal. A content distribution system, wherein a content key is decrypted using the new user key, and the content is decrypted with the decrypted content key. A content distribution system that distributes encrypted content by P2P between client terminals via a management server,
The client terminal is
Receiving means for receiving a content file composed of a user key encrypted with a master key, a content key encrypted with the user key, and content encrypted with the content key;
Transmitting means for transmitting the received user key encrypted with the master key and the content key encrypted with the user key to the management server;
With
The management server is
Holding means for holding the master key;
The master key is used to decrypt the user key from the received user key encrypted with the master key, and the decrypted user key is used to decrypt the content key from the content key encrypted with the user key. Key decryption means for decryption;
User key generation means for generating a new user key by encrypting the master key;
An encryption means for encrypting the decrypted content key with the generated new user key;
Return means for returning the new user key and the content key encrypted with the new user key to the client terminal;
With
The client terminal is
Content decrypting means for decrypting the returned content key using the new user key, and decrypting the content with the decrypted content key;
A content distribution system comprising:   The content distribution system according to claim 2, wherein a plurality of the management servers can be provided. A content distribution method in a content distribution system that distributes encrypted content by P2P between client terminals via a management server,
A first step in which the client terminal receives a content file consisting of a user key encrypted with a master key, a content key encrypted with the user key, and content encrypted with the content key;
A second step in which the client terminal transmits a user key encrypted with the received master key and a content key encrypted with the user key to the management server;
The management server holds the master key, uses the master key to decrypt the user key from the user key encrypted with the received master key, and uses the decrypted user key to A third step of decrypting the content key from the content key encrypted with the key;
A fourth step in which the management server encrypts the master key to generate a new user key;
A fifth step in which the management server encrypts the decrypted content key with the generated new user key;
A sixth step in which the management server returns the new user key and a content key encrypted with the new user key to the client terminal;
A seventh step in which the client terminal decrypts the returned content key using the new user key and further decrypts the content with the decrypted content key;
A content distribution method comprising: A program for causing a computer to execute a content distribution method in a content distribution system that distributes encrypted content by P2P between client terminals via a management server,
A first step in which the client terminal receives a content file consisting of a user key encrypted with a master key, a content key encrypted with the user key, and content encrypted with the content key;
A second step in which the client terminal transmits a user key encrypted with the received master key and a content key encrypted with the user key to the management server;
The management server holds the master key, uses the master key to decrypt the user key from the user key encrypted with the received master key, and uses the decrypted user key to A third step of decrypting the content key from the content key encrypted with the key;
A fourth step in which the management server encrypts the master key to generate a new user key;
A fifth step in which the management server encrypts the decrypted content key with the generated new user key;
A sixth step in which the management server returns the new user key and a content key encrypted with the new user key to the client terminal;
A seventh step in which the client terminal decrypts the returned content key using the new user key and further decrypts the content with the decrypted content key;
A program that causes a computer to execute.

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