JP4714842B2 - Information acquisition method in peer-to-peer communication network system - Google Patents

Description

  The present invention relates to a peer-to-peer communication network system for exchanging data with each other by peer-to-peer (P2P) and an information acquisition method in the system.

P2P communication network systems that exchange data with each other by peer-to-peer (hereinafter referred to as P2P) are becoming widespread. In such a system, each peer manages information, but when a certain peer becomes unable to connect, it becomes impossible to acquire information managed by the peer.
In order to solve this problem, an attempt to improve the availability of the P2P communication network system by redundantly storing information in other peers has also been studied. However, according to such a method, there is a drawback that information managed by the peer is leaked to other peers that originally do not need to acquire information.

On the other hand, an information sharing system that can share secret information among a plurality of users and that can prevent peeping or falsification of encrypted information without using complicated access control has been proposed (for example, , See Patent Document 1).
JP-A-11-143359

  As described above, when information is redundantly accumulated in other peers in order to improve the availability of the P2P communication network system, the peer also manages other peers that do not need to acquire information. Information is leaked, which is caused by using the same encryption key throughout the P2P communication network system. Further, the technique disclosed in Patent Document 1 does not support an application that stores a backup of information in another peer.

  The present invention has been made in view of the above circumstances, and information can be stored redundantly without leaking to other peers, and the user cannot connect to a peer that manages the necessary information. It is an object of the present invention to provide a peer-to-peer communication network system and an information acquisition method in the same system.

In order to solve the above-described problems, the present invention provides a method for acquiring information in a peer-to-peer communication network system that exchanges data with each other on a peer-to-peer basis. The content information is encrypted with the common key, and the common key is sequentially double-encrypted with the public keys of the second and third peer terminals, and the content information encrypted with the common key and the public key are used. The fourth peer terminal except the first peer terminal is requested to store the encrypted common key, and the fourth peer terminal encrypts the content information encrypted with the common key and the public key. The first step of storing the converted common key, the content information encrypted by the user terminal from the fourth peer terminal with the common key, and the common key double-encrypted with the public key Get the above 2 and the third peer terminal, sequentially request the second and third peer terminals for decryption, the second and third peer terminals sequentially decrypt the common key, and send to the user terminal A second step of transmitting, and a third step in which the user terminal acquires the decrypted common key and decrypts the content information using the acquired common key. And

According to the present invention, a common key obtained by encrypting content possessed by a certain peer is encrypted with a public key in each of a plurality of other peers and stored in any peer, and the user can use this multiple encrypted common key. And encrypting it with its own public key, requesting the other peers to sequentially decrypt the result, obtaining the result , decrypting the content with the common key, and browsing the other peer. the information is redundantly can accumulate without leakage, the user, Ru can also acquire the information when unconnectable to peers to manage information required.

FIG. 1 is a diagram showing a system configuration example of a P2P communication network system according to an embodiment of the present invention.
Here, peer A (1), peer B (2), peer C (3), peer D (4), and user terminal 5 are connected to the P2P network 6.
Each of the peers A to D (1 to 4) and the user terminal 5 connected to the P2P network 6 can exchange data with each other, and each of the peers 1 to 5 connected to the P2P network 6 receives the respective information. It takes the form of management. There are two types of P2P communication network systems: a server-mediated system and a non-server-based system, but the former has the advantage that information management is easier, and the latter has a part of the network that includes server down. There is also an advantage that the whole does not stop. Here, the latter system is assumed.

FIG. 2 is a block diagram showing the functions of the internal configurations of the peer A and the user terminal shown in FIG. 1, and here, only the blocks related to the present invention are extracted and shown.
In FIG. 2, peer A (1) functioning as the encryption information creation peer of the present invention includes a content DB 11, an encryption unit 12, and a content accumulation request unit 13.
Encrypting unit 1 2, a common key used to encrypt the content in the content DB 11, a plurality of other peers constituting the P2P network (in this case, peer B, peer C) have the ability to encrypt each with a public key of and, also, the content storage request unit 13, the information encrypted by the encrypting unit 1 2 (content), any of the peer (here is a peer D, if it is any other than peer a) accumulate in It has a function that requires that.

On the other hand, the user terminal 5 functioning as the encrypted information browsing peer of the present invention includes an accumulated peer identification unit 51, an encrypted content acquisition unit 52, decryption request units 53 and 55, and decrypted content acquisition units 54 and 56. And a content browsing unit 57.
When an index server (not shown) is connected to the P2P network 6, the stored peer identification unit 51 refers to the index server. On the other hand, when the index server is not connected, It has a function of specifying a content accumulation destination peer (in this case, peer D) by making an inquiry. The encrypted content acquisition unit 52 has a function of acquiring encrypted content from the peer specified by the accumulated peer specifying unit 51.

  In addition, the decryption requesting units 53 and 55 encrypt the content acquired by the encrypted content acquiring unit 52 with their own public key, and then encrypt the content to a plurality of other peers (peer B, peer C). It has a function for requesting sequential decryption of the common key. Furthermore, the content browsing unit 57 has a function of decrypting and browsing the decryption keys acquired from other peers (peer B, peer C) via the decryption key acquiring units 54 and 56 with their private keys. Have.

FIG. 3 is a sequence diagram cited for explaining a data acquisition method in the P2P communication system according to the embodiment of the present invention. Here, the flow of operations among the user terminal 5, the peer A (1), the peer B (2), the peer C (3), and the peer D (4) shown in FIG. 1 is shown.
A schematic sequence will be described below. Here, each of the peers 1 to 4 and the user 5 has a public key / private key pair, and each of the peers 1 to 4 and the user 5 does not perform collusion. The explanation is based on the above.

First, since the public keys y1 and y2 held by the peer A (1) are publicized from the peer B and the peer C (S31 and S32), a common key obtained by encrypting the content owned and managed by the peer A (1) is obtained. , Peer B (2), and peer C (3) respectively encrypt with public keys y1 and y2. Then, the peer D (4) is requested to store the encrypted content and the encrypted common key (S33). In this case, the peer D (4) is requested to store the content owned and managed by the peer D (4), but any peer other than the peer A may be used.
Next, the user terminal 5 refers to the index server or identifies the accumulated peer (peer D) by querying the peers A to D (1 to 4), and multiplexes from the identified peer D (4). The encrypted content and the encrypted common key are acquired (S34). Then, after encrypting with its own public key or random number, peer B (2) and peer C (3) are sequentially requested to decrypt (S35, S36). Then, the results can be obtained sequentially (S37, S38), and the private key or random number can be removed for decryption and browsing (S39).

Here, encryption and decryption follow an ElGammal encryption scheme. As is well known, the ElGammal cipher is a cipher that applies the discrete logarithm problem, and creates a ciphertext from a plaintext, a random number, and a public key, and decrypts it with a secret key. Here, a plurality of public keys are committed at the time of encryption, and encryption is performed as described below. Note that g and p shown below are disjoint public parameters.
The case of random numbers will be described. Now, if the secret key of peer B (2) is x1, the public key is y1 = g ^ x1, the secret key of peer C (3) is x2, and the public key is y2 = g ^ x2, then C1 = G ^ rmodp, C2 = m · y1 ^ r · modp. If this is masked by the user, C2 ′ = r ′ · C2modp. R represents a random number and m represents information to be encrypted.
When this is decrypted, the plaintext T becomes T = C2 / C1 ^ x. Where x is the private key of the entity to be decrypted. In order to remove the mask using the random number r ′, T = C / r ′ may be obtained.

The case of a public key will be described. Here, y3 is the user's private key. In encryption, C1 = g ^ rmodp and C2 = m · y1 ^ r · modp. If this is masked by the user, C1 ′ = g ^ rmodp, C2 ′ = r ′ · C2modp, where g ^ r ′ is stored.
When this is decrypted, the plaintext T becomes T = C2 / C1 ^ x. Where x is the private key of the entity to be decrypted. Further, in order to remove the mask, g ^ r'x3 is calculated from the user's private key x3 to C3, and T = C2 '/ C3 is obtained.

4 and 5 are flowcharts cited for explaining the operation according to the embodiment of the present invention, and show an encryption procedure and a decryption procedure, respectively.
Hereinafter, the procedure when the user uses the public key will be described in detail with reference to the flowcharts shown in FIGS.

  First, peer A encrypts data stored in another peer (peer D) with a common key sk (S41 in FIG. 4). Here, sk has a certain expiration date. Subsequently, the common key sk is sequentially and multiplex-encrypted using the public keys of two or more peers (here, peer B and peer C) and attached to the content (S42). Let this key be E ^ b + c (sk). Also, as the header information, which peer has been encrypted with the public key is attached. The peer A further requests the accumulation of the content to any peer (other than the peer A, here referred to as the peer D) (S43). Further, when an index server exists in the P2P network 6, the peer name is registered as to which peer has accumulated the content.

  On the other hand, the user searches for content in any of the following procedures. First, when the user terminal 5 does not have an index server in the P2P network 6, the user terminal 5 searches using the existing search technology in the P2P network 6. That is, by inquiring each of the peers A to D (1 to 4), the peer (peer D) in which the content is stored is specified. When the index server exists, the peer D (4) in which the content is stored is specified by making an inquiry to the index server (S51 in FIG. 5).

Subsequently, the user terminal 5 acquires the encrypted content and the encrypted key information E ^ b + c (sk) from the peer D (4) (S52). At that time, the peer D (4) performs authentication and disclosure control as necessary.
Then, the user terminal 5 encrypts the key information E ^ b + c (sk) with its own public key to obtain E ^ b + c + u (sk) (S53). Masking may be performed using random numbers instead of using public keys. Next, the user terminal 5 requests the peer B (2) and the peer C (3) to sequentially decrypt the key information E ^ b + c + u (sk) (S54). At that time, the peer B (2) and the peer C (3) perform user authentication as necessary.

  Finally, the user terminal 5 receives the decrypted result E ^ u (sk) (S55 “Yes”), decrypts it with its own secret key, and obtains the common key sk (S56). Note that when random numbers are used for masking, the random numbers are removed. Subsequently, the content can be decrypted and browsed using the acquired common key sk (S57).

  As described above, the present invention encrypts information possessed by a certain peer with the public keys of other peers and stores it in an arbitrary peer, and the user obtains this multiple encrypted information. After encrypting with your own public key or masking with a random number, ask the other peers to sequentially decrypt and obtain the result, decrypt with your own private key, or remove the random number mask, In this way, information can be stored redundantly without leaking to other peers, and even when the user is unable to connect to the peer that manages the required information. Can be obtained.

  In addition, according to the present invention, when an index server is connected to the P2P communication network, the index information storage destination peer is registered in the index server, and the user refers to the index server to store information. By specifying the destination peer, and when the index server is not connected, it is easy to create multiple encrypted contents by querying other peers and specifying the information storage destination peer. Can be acquired. Furthermore, by performing user authentication at a plurality of other peers requested to be decrypted by a certain peer, the access right can be controlled, and a further security effect can be obtained.

  As described above, according to the embodiment of the present invention, in a situation where each peer is monitoring each other (when there is no collusion), the common key sk cannot be obtained with the key information of one peer. The content is not leaked to other peers. In addition, since the user's public key is used for encryption and then decryption is requested, the common key sk is not leaked in the decryption process. Further, the security may be improved by including a reliable third-party server in place of peer B (2) or peer C (3) requested to decrypt.

It is a figure which shows the system configuration example of the P2P communication network system concerning embodiment of this invention. It is the block diagram which expanded and showed the internal structure of the peer A shown in FIG. 1, and a user terminal. It is the sequence diagram quoted in order to demonstrate the data acquisition method in the P2P communication system concerning embodiment of this invention. It is the flowchart quoted in order to demonstrate the operation | movement concerning this invention embodiment. It is the flowchart quoted in order to demonstrate the operation | movement concerning this invention embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Peer A (encryption information generation peer), 2 ... Peer B, 3 ... Peer C, 4 ... Peer D, 5 ... User terminal (encryption information browsing peer), 6 ... P2P network

Claims (1)

An information acquisition method in a peer-to-peer communication network system for exchanging data with each other on a peer-to-peer basis, comprising:
The first peer terminal encrypts the content information to be stored with the common key, and the common key is double-encrypted sequentially with the public keys of the second and third peer terminals, and encrypted with the common key. Request the fourth peer terminal excluding the first peer terminal to store the content information and the common key encrypted with the public key, and the fourth peer terminal is encrypted with the common key. A first step of storing the content information and the common key encrypted with the public key ;
The user terminal obtains the content information encrypted with the common key from the fourth peer terminal and the common key double-encrypted with the public key, and sends them to the second and third peer terminals. A second step of transmitting, requesting the second and third peer terminals to sequentially decrypt, the second and third peer terminals sequentially decrypting the common key, and transmitting to the user terminal ;
A third step in which the user terminal obtains the decrypted common key and decrypts the content information using the obtained common key ;
An information acquisition method in a peer-to-peer communication network system, comprising:

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