KR20210009782A - Encryption system, apparatus and method for providing searchable having forward stability - Google Patents

Abstract

According to the present invention, a searchable encryption apparatus having forward stability comprises: an encryption unit to use the identity of a user to be given a right to search for a file to encrypt a file identifier; a re-encryption unit to re-encrypt the encrypted identifier after constructing the identity of the user, a related keyword, and a search count (SC) of the user in layers; a transceiving unit to transmit the encrypted identifier and the re-encrypted identifier to a server; a search acquisition unit to acquire a total search count value of the user and a search state (KS) of a keyword to be searched up to now; a secret key generation unit to use a user key, the identity of the user, the related keyword, the total search count value, and the search state to generate a lower secret key; an identifier request unit to transmit the generated lower secret key to the server to request a file identifier; and an information acquisition unit to use an upper secret key pre-distributed from a key manager terminal to decrypt the encrypted identifier provided from the server to acquire the file identifier.

Description

A searchable encryption system with forward stability and its device and method {ENCRYPTION SYSTEM, APPARATUS AND METHOD FOR PROVIDING SEARCHABLE HAVING FORWARD STABILITY}

The present invention relates to an encryption scheme having forward stability, and more particularly, a searchable encryption system having forward stability that can be utilized in a plurality of user environments by using a hierarchical identity-based encryption scheme, which is one of public key encryption schemes, and its It relates to an apparatus and method.

As is known, the existing searchable encryption method is an encryption method that enables an appropriate keyword search at the same time without exposing information on data after a user sends his or her data to a server.

These existing searchable encryption methods can increase the utilization of data while guaranteeing the confidentiality of user data, and use a symmetric key encryption technique or a public encryption technique.

Using a symmetric key encryption technique, you can efficiently construct a navigable encryption method for a single user, and also use a public key encryption technique, which is slow but can be used for secure data sharing for multiple users. You can configure the way.

On the other hand, methods to efficiently attack the safety of existing searchable encryption methods have been recently announced, which encrypt arbitrary data around keywords that are likely to be used by malicious attackers or the server itself and insert them into the victim's database. .

Then, by reusing the previously used search query of the user, we observe whether any data inserted by the attacker is returned.

If arbitrary data inserted by an attacker is returned, the keyword included in the victim's search query can be easily inferred. Such an attack is called a file injection attack.

In order to prevent such a file insertion attack, it is necessary to ensure forward security that the newly inserted data cannot be found by the user's search query used previously.

Recently, in order to guarantee the confidentiality of a user's query from a file injection attack, an encryption method capable of forward safe search has been proposed. However, the proposed encryption methods capable of forward safe search only consider a single user environment by using a symmetric key encryption technique.

Simply, if the existing one is used to expand to a plurality of user environments, there is a problem that an inefficient key distribution process and a large storage cost of the user are required.

And, at present, an encryption method capable of safe forward search using public key encryption techniques has not yet been proposed.

Korean Patent Publication No. 2017-0087120 (Publication date: 2017. 07. 28.)

An object of the present invention is to provide a searchable encryption system having forward stability that can be utilized in a plurality of user environments, and an apparatus and method thereof using a hierarchical identity-based encryption technique.

An object of the present invention is to provide a computer-readable recording medium storing a computer program that causes a processor to perform a searchable encryption method with forward stability.

An object of the present invention is to provide a computer program in which a computer program for causing a processor to perform a searchable encryption method having forward stability is stored in a computer-readable recording medium.

The problem to be solved by the present invention is not limited to the ones mentioned above, and another problem to be solved that is not mentioned can be clearly understood by those of ordinary skill in the art from the following descriptions. will be.

According to an aspect of the present invention, a key manager terminal for generating a higher private key using the user's identity and distributing the generated higher private key to a user terminal, and a file identifier using the user's identity are encrypted. And, after hierarchically configuring the encrypted identifier, the user's identity, the related keyword, and the number of searches (SC) of the user, and re-encrypting the file, the file identifier, the encrypted identifier and the re-encrypted identifier to the server Stores and manages the transmitting user terminal, the file, the file identifier, the encrypted identifier and the re-encrypted identifier, and when a request for a file identifier using a lower secret key is received from the user terminal, the lower secret And the server that decrypts the re-encrypted identifier using a key, compares the encrypted identifier of the same pair with the decrypted identifier, and provides the encrypted identifier to the user terminal if they match, and the user terminal comprises: Searchable encryption with forward stability in which a file identifier is obtained by decrypting the encrypted identifier provided from a server using the previously distributed upper secret key, and a corresponding file is obtained from the server through the obtained file identifier System can be provided.

The key manager terminal of the present invention may generate a public parameter using a hierarchical identity-based encryption technique, and generate a higher private key based on the generated public factor.

The user terminal of the present invention may re-encrypt the encrypted identifier using a hierarchical identity-based encryption technique.

The user terminal of the present invention acquires a search state (KS) of the keyword to be searched up to now and a total search count value of the user, and the user key, the identity of the user, the related keyword, the total search count value, and the search The lower private key can be generated using the state.

According to another aspect, the present invention includes an encryption unit for encrypting a file identifier using the identity of a user who wishes to grant permission to search a file, and the identity of the user, related keywords, and the number of searches by the user (SC). A re-encryption unit for re-encrypting the encrypted identifier after hierarchical configuration of, and a transmission/reception unit for transmitting the encrypted identifier and the re-encrypted identifier to the server, and the search status of the keyword to be searched up to the present (KS) And a search acquisition unit that obtains a total search count value of the user, and a secret key generation unit that generates a lower secret key using a user key, the user's identity, the related keyword, the total search count value, and the search state. , An identifier request unit that transmits the generated lower private key to a server to request a file identifier, and the encrypted identifier provided from the server is decrypted using a higher private key previously distributed from a key manager terminal, and the file It is possible to provide a searchable encryption device having forward stability including an information obtaining unit that obtains an identifier.

The re-encryption unit of the present invention may re-encrypt the encrypted identifier using a hierarchical identity-based encryption technique.

The server of the present invention decrypts the re-encrypted identifier using the lower secret key, compares the encrypted identifier of the same pair as the decrypted identifier, and if they match, provides the encrypted identifier to the user terminal. have.

According to another aspect of the present invention, the step of encrypting a file identifier using the identity of a user who wishes to grant permission to search a file, and the identity of the user, a related keyword, and the number of searches by the user (SC) Re-encrypting the encrypted identifier after hierarchically configuring, and obtaining a search state (KS) of the keyword to be searched up to now and a total search count value of the user, a user key, the identity of the user, Generating a lower private key using the related keyword, the total search count value, and the search status, and requesting a file identifier by transmitting the generated lower private key to the server, and provided from the server. It is possible to provide a searchable encryption method having forward stability including the step of obtaining an identifier of the file by decrypting the encrypted identifier using the upper secret key previously distributed from the key manager terminal.

In the re-encrypting step of the present invention, the encrypted identifier may be re-encrypted using a hierarchical identity-based encryption technique.

The server of the present invention decrypts the re-encrypted identifier using the lower private key, compares the encrypted identifier of the same pair with the decrypted identifier, and if they match, provides the encrypted identifier to the user terminal It may include.

According to another aspect, the present invention is a computer-readable recording medium storing a computer program, wherein the computer program, when executed by a processor, uses the identity of a user who wishes to grant permission to search a file. And encrypting the file identifier; re-encrypting the encrypted identifier after hierarchically configuring the user's identity, the related keyword, and the number of searches (SC) of the user; and the search status of the keyword to be searched up to the present time (KS) and acquiring a total search count value of the user, generating a lower secret key using a user key, the user's identity, the related keyword, the total search count value, and the search state, and the Transmitting the generated lower private key to the server to request a file identifier, and obtaining the file identifier by decrypting the encrypted identifier provided from the server using the upper private key previously distributed from the key manager terminal. It is possible to provide a computer-readable recording medium including instructions for causing the processor to perform a method including the step of.

The present invention, according to another aspect, is a computer program stored in a computer-readable recording medium, wherein the computer program, when executed by a processor, uses the identity of a user who wishes to grant permission to search files. And encrypting the file identifier; re-encrypting the encrypted identifier after hierarchically configuring the user's identity, the related keyword, and the number of searches (SC) of the user; and the search status of the keyword to be searched up to the present time (KS) and acquiring a total search count value of the user, generating a lower secret key using a user key, the user's identity, the related keyword, the total search count value, and the search state, and the Transmitting the generated lower private key to the server to request a file identifier, and obtaining the file identifier by decrypting the encrypted identifier provided from the server using the upper private key previously distributed from the key manager terminal. A computer program including instructions for causing the processor to perform a method including the step of performing may be provided.

According to an embodiment of the present invention, it is possible to implement encryption capable of forward safe search that can be used in a plurality of user environments by using a hierarchical identity-based encryption technique.

According to an embodiment of the present invention, it is possible to apply a searchable encryption method to multiple user environments while ensuring safe data search from a cloud and a remote server.

According to an embodiment of the present invention, it is possible to obtain an effect of further enhancing performance when searching for a keyword that is safe from file insertion attacks and is frequently used.

1 is a schematic diagram of a searchable encryption system having forward stability according to an embodiment of the present invention.
2 is a block diagram of a searchable encryption device having forward stability according to an embodiment of the present invention.
3 is a flow chart showing a main process of generating data in a file, a file identifier, an encrypted identifier, and a re-encrypted identifier by a user terminal and transmitting the data to the server according to an embodiment of the present invention.
4 is a flowchart illustrating a main process of obtaining a file identifier and a file by a user terminal based on an encrypted identifier provided from a server according to an embodiment of the present invention.
5 is an example of a search status table for each keyword stored and managed in a user terminal for realization of the present invention.

Advantages and features of the present invention, and a method of achieving them will become apparent with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only these embodiments make the disclosure of the present invention complete, and those skilled in the art to which the present invention pertains. It is provided to fully inform the person of the scope of the invention, and the scope of the invention is only defined by the claims.

In describing the embodiments of the present invention, detailed descriptions of known functions or configurations will be omitted except when actually necessary in describing the embodiments of the present invention. In addition, terms to be described later are terms defined in consideration of functions in an embodiment of the present invention, which may vary according to the intention or custom of users or operators. Therefore, the definition should be made based on the contents throughout this specification.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram of a searchable encryption system having forward stability according to an embodiment of the present invention.

Referring to FIG. 1, a searchable encryption system includes a key manager terminal 110, a user terminal group 120 consisting of a plurality of user terminals 120/1 to 120/n, a network 130, a server 140, and It may include a management DB (150) and the like.

First, the key manager terminal 110 may refer to a wired terminal such as a personal computer, a notebook, or a wireless terminal such as a smart phone, mobile phone, or a smart pad, and uses the user's identity through a key setting protocol. Functions such as generating a secret key and distributing the generated upper secret key (the upper layer secret key) to each user terminal (eg, 120/1 to 120/n) through the network 130 Can provide.

For example, the key manager terminal 110 generates a public parameter using a hierarchical identity-based encryption technique, which is one of public key encryption techniques, and generates a higher private key based on the generated public factor. Function can be performed.

In addition, each user terminal (120/1 to 120/n) in the user terminal group 120 may mean a wired terminal such as a personal computer, a laptop, or a wireless terminal such as a smart phone, a mobile phone, and a smart pad. , The file identifier is encrypted using the user's identity, and the encrypted identifier, the user's identity, the related keyword, and the user's search count (SC) are hierarchically configured, and a hierarchical identity-based encryption technique is used. It is re-encrypted by using, and a function such as transmitting a file, a file identifier, and data in an encrypted identifier and a re-encrypted identifier to the remote server 140 through the network 130 may be provided.

In addition, each user terminal uses an encrypted identifier provided from the server 140 through the network 130 at the request of the terminal user using the lower private key, and the upper private key previously distributed by the key manager terminal 110 is used. Thus, it is possible to provide functions such as obtaining a file identifier by decrypting and obtaining a corresponding file from the server 140 through the obtained file identifier.

Here, the lower secret key acquires the search state (Keyword State: KS) of the keyword to be searched and the total search count value of the user, and the user key, the identity of the user, related keywords, the total search count value and search It can be created using states. In this case, the lower secret key may be defined as, for example, a token, and for this purpose, each user terminal may be equipped with a token generation algorithm.

Specific functions performed in each user terminal will be described in detail later with reference to FIGS. 2 to 4.

Here, the network 130 is a wired communication network including a wired Internet, and one or two of a second generation (2G), a third generation (3G), a fourth generation (4G), a fifth generation (5G), and a next generation mobile communication network. It may refer to a complex communication network that comprehensively includes a wireless communication network including the above.

On the other hand, the server 140 manages data including files, file identifiers, encrypted identifiers and re-encrypted identifiers, etc. provided through the network 130 from each user terminal 120/1 to 120/n. ), and when a request for a file identifier using a lower private key (token) is received from an arbitrary user terminal, the re-encrypted identifier is decrypted using the received lower private key, and the same pair as the decrypted identifier If the encrypted identifiers of are compared and matched, a function such as providing the encrypted identifier to the corresponding user terminal through the network 130 may be provided.

2 is a block diagram of a searchable encryption device having forward stability according to an embodiment of the present invention.

Referring to FIG. 2, a searchable encryption device, which can be installed in each user terminal, is a data transmission/reception unit 202, an encryption unit 204, a re-encryption unit 206, a search acquisition unit 208, and a secret. A key generation unit 210, an identifier request unit 212, an information acquisition unit 214, and a storage unit 216 may be included.

First, the data transmission/reception unit 202 receives data provided from the server 140 through the network 130 and provides it to a related component in the terminal, and provides various data provided from each component in the user terminal to the network 130 ) Through the server 140 may perform a function such as transmission.

The encryption unit 204 encrypts the file identifier using the identity of another user who intends to grant permission to browse the file, wherein the encryption of the file identifier is, for example, hierarchical identity-based encryption, which is one of public key encryption techniques. It can be done using a technique.

The re-encryption unit 206 hierarchically configures the encrypted identifier, the user's identity, the related keyword, and the number of searches (SC) of the user through the encryption unit 204, and then re-encrypts it using a hierarchical identity-based encryption technique. It can provide functions such as.

Here, data including a file, a file identifier, an encrypted identifier, and a re-encrypted identifier may be transmitted to the server 140 through a transmission path through the data transmission/reception unit 202 and the network 130. That is, the server 140 may store and manage data including files, file identifiers, encrypted identifiers, and re-encrypted identifiers provided by each user terminal in the management DB 150.

The search acquisition unit 208 may provide a function of acquiring a search state (KS) of a keyword to be searched by the terminal user and a total search count value of the terminal user. Here, FIG. 5 is an example of a search status table for each keyword stored and managed in a user terminal for realization of the present invention.

The secret key generation unit 210 can provide a function such as generating a plurality of lower secret keys (ie, tokens) using a user key, a user's identity, a keyword to be searched, a total search count value, and a search state. have. Here, the lower private key may be generated with several lower private keys in the same manner until the search state value is reached while reducing the total search count value.

The identifier request unit 212 transmits the lower secret keys (tokens) generated through the secret key generation unit 210 to the server 140 through a transmission path through the data transmission/reception unit 202 and the network 130 Thus, a function such as requesting a file identifier can be provided.

Here, when a request for a file identifier is received from the user terminal, the server 140 decrypts the re-encrypted identifier using valid secret keys, compares the encrypted identifier of the same pair with the decrypted identifier, and encrypts if they match. It can perform functions such as returning (providing) the generated identifier to the user terminal. In this case, the encrypted identifier returned to the user terminal may be stored in the storage unit 216.

In the storage unit 216, data such as a user key, a user's identity, various keywords, a total search count value, and a search status may be stored together with an encrypted identifier.

The information acquisition unit 216 decrypts the encrypted identifier returned from the server 140 at the request of the terminal user and received through the network 130 and the data transmission/reception unit 202 using a previously distributed upper secret key. , It is possible to provide a function of acquiring a file identifier of a file to be searched for, and acquiring a corresponding file from the server 140 using the obtained file identifier.

3 is a flow chart showing a main process of generating data in a file, a file identifier, an encrypted identifier, and a re-encrypted identifier by a user terminal and transmitting the data to the server according to an embodiment of the present invention.

First, the key manager terminal 110 generates a higher secret key using the user's identity through a key setting protocol, and transmits the generated upper secret key (the upper layer secret key) through the network 130. It is distributed to each user terminal (eg, 120/1 to 120/n) (step 302).

Next, the encryption unit 204 in an arbitrary user terminal encrypts the file identifier using the identity of another user who intends to grant permission to search the file (step 304). Here, the encryption of the file identifier may be performed using, for example, a hierarchical identity-based encryption technique, which is one of public key encryption techniques.

Then, the re-encryption unit 206 hierarchically configures the encrypted identifier, the user's identity, the relevant keyword, and the number of searches SC of the user, and then re-encrypts it using a hierarchical identity-based encryption technique (step 306).

Thereafter, the data transmission/reception unit 202 transmits data including a file, a file identifier, an encrypted identifier and a re-encrypted identifier to the server 140 through a transmission path via the network 130 (step 308).

Accordingly, the server 140 may store and manage data including a file, a file identifier, an encrypted identifier, and a re-encrypted identifier provided by the user terminal in the management DB 150 (step 310).

4 is a flowchart illustrating a main process of obtaining a file identifier and a file by a user terminal based on an encrypted identifier provided from a server according to an embodiment of the present invention.

Referring to FIG. 4, the search acquisition unit 208 acquires a search state (KS) of a keyword to be searched by the terminal user and a total search count value of the terminal user (step 402).

In addition, the secret key generation unit 210 generates a plurality of lower secret keys (ie, tokens) using the user key, the user's identity, the keyword to be searched, the total search count value, and the search state (step 404). In this case, the lower private key may be generated as several lower private keys in the same manner until the search state value is reached while reducing the total search count value.

Next, the identifier request unit 212 transmits the lower private keys (tokens) to the server 140 through the transmission path through the data transmission/reception unit 202 and the network 130 to request a file identifier (step 406).

In addition, when a request for a file identifier is received from an arbitrary user terminal, the server 140 decrypts the re-encrypted identifier using valid secret keys, and compares the encrypted identifier of the same pair with the decrypted identifier to determine whether they match. Whether or not it is checked (step 408).

If the result of the comparison in step 408 coincide with each other, the server 140 provides the encrypted identifier to the user terminal (step 410).

Thereafter, in the information acquisition unit 216 in the user terminal, the encrypted identifier returned from the server 140 at the request of the terminal user and received through the network 130 and the data transmission/reception unit 202 is a previously distributed upper secret key. By decrypting using, a file identifier of a file to be searched is obtained (step 412), and a corresponding file is obtained from the server 140 by using the obtained file identifier (step 414).

Meanwhile, combinations of each block of the attached block diagram and each step of the flowchart may be performed by computer program instructions. Since these computer program instructions can be mounted on a processor of a general purpose computer, special purpose computer, or other programmable data processing equipment, the instructions executed by the processor of the computer or other programmable data processing equipment are shown in each block or flow chart of the block diagram. Each step creates a means to perform the functions described.

These computer program instructions can also be stored in a computer-usable or computer-readable memory, etc., which can be directed to a computer or other programmable data processing equipment to implement a function in a specific manner, so that the computer-usable or computer-readable memory It is also possible to produce an article of manufacture in which the instructions stored in the block diagram contain instruction means for performing the functions described in each block or flow chart.

In addition, since computer program instructions can be mounted on a computer or other programmable data processing equipment, a series of operation steps are performed on a computer or other programmable data processing equipment to create a process that is executed by a computer, It is also possible for the instructions to perform possible data processing equipment to provide steps for executing the functions described in each block of the block diagram and each step of the flowchart.

In addition, each block or each step may represent a module, segment, or part of code including at least one or more executable instructions for executing the specified logical function(s). It should also be noted that in some alternative embodiments, functions mentioned in blocks or steps may occur out of order. For example, two blocks or steps shown in succession may in fact be performed substantially simultaneously, or the blocks or steps may sometimes be performed in the reverse order depending on the corresponding function.

The above description is merely illustrative of the technical idea of the present invention, and those of ordinary skill in the art to which the present invention pertains, various substitutions, modifications, and changes, etc., within the scope not departing from the essential characteristics of the present invention. It will be easy to see that this is possible. That is, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain the technical idea, and the scope of the technical idea of the present invention is not limited by these embodiments.

Accordingly, the scope of protection of the present invention should be interpreted by the claims to be described later, and all technical thoughts within the scope equivalent thereto should be interpreted as being included in the scope of the present invention.

110: key manager terminal
120: user terminal group
120/1 ~ 120/n: User terminal
140: server
150: management DB
202: data transmission/reception unit
204: encryption unit
206: re-encryption unit
208: search acquisition unit
210: secret key generation unit
212: identifier request unit
214: information acquisition unit
216: storage unit

Claims (12)

A key manager terminal for generating a higher private key using the user's identity and distributing the generated higher private key to a user terminal;
The file identifier is encrypted using the user's identity, the encrypted identifier, the user's identity, the related keyword, and the user's search count (SC) are hierarchically configured and re-encrypted, and the file, the file identifier, and the encryption The user terminal for transmitting the encrypted identifier and the re-encrypted identifier to the server,
Stores and manages the file, the file identifier, the encrypted identifier, and the re-encrypted identifier, and when a request for a file identifier using a lower private key is received from the user terminal, it is re-encrypted using the lower private key. Comprising the server for decrypting the identifier, comparing the encrypted identifier of the same pair as the decrypted identifier, and providing the encrypted identifier to the user terminal if they match,
The user terminal,
Obtaining a file identifier by decrypting the encrypted identifier provided from the server using the previously distributed upper secret key, and obtaining a corresponding file from the server through the obtained file identifier
A searchable encryption system with forward stability. The method of claim 1,
The key manager terminal,
Generates a public parameter using a hierarchical identity-based encryption technique, and generates a higher private key based on the generated public parameter.
A searchable encryption system with forward stability. The method of claim 1,
The user terminal,
Re-encrypting the encrypted identifier using a hierarchical identity-based encryption technique
A searchable encryption system with forward stability. The method of claim 1,
The user terminal,
Acquires the search status (KS) of the keyword to be searched up to the present time and the total search count value of the user, and uses the user key, the identity of the user, the related keyword, the total search count value, and the search status to the lower secret key To generate
A searchable encryption system with forward stability. An encryption unit that encrypts the file identifier using the identity of the user who wants to grant permission to browse the file,
A re-encryption unit that re-encrypts the encrypted identifier after hierarchically configuring the user's identity, the related keyword, and the number of searches (SC) of the user;
A transceiver for transmitting the encrypted identifier and the re-encrypted identifier to a server,
A search acquisition unit that obtains a search status (KS) of the keyword to be searched up to the present and a total search count value of the user;
A secret key generation unit that generates a lower secret key using a user key, the user's identity, the related keyword, the total search count value, and the search state,
An identifier requesting unit for requesting a file identifier by transmitting the generated lower private key to a server,
Including an information acquisition unit for obtaining the file identifier by decrypting the encrypted identifier provided from the server using a higher secret key previously distributed from a key manager terminal
A searchable encryption device with forward stability. The method of claim 5,
The re-encryption unit,
Re-encrypting the encrypted identifier using a hierarchical identity-based encryption technique
A searchable encryption device with forward stability. The method of claim 5,
The server,
Decrypting the re-encrypted identifier using the lower secret key, comparing the encrypted identifier of the same pair with the decrypted identifier, and providing the encrypted identifier to the user terminal if they match.
A searchable encryption device with forward stability. Encrypting the file identifier using the identity of the user who wishes to grant permission to browse the file,
Re-encrypting the encrypted identifier after hierarchically configuring the user's identity, the related keyword, and the number of searches (SC) of the user; and
Obtaining a search state (KS) of the keyword to be searched up to the present and a total search count value of the user; and
Generating a lower private key using a user key, the user's identity, the related keyword, the total search count value, and the search state; and
Transmitting the generated lower private key to the server to request a file identifier;
Comprising the step of decrypting the encrypted identifier provided from the server using the upper secret key previously distributed from the key manager terminal, thereby obtaining the identifier of the file
A searchable encryption method with forward stability. The method of claim 8,
The re-encrypting step,
Re-encrypting the encrypted identifier using a hierarchical identity-based encryption technique
A searchable encryption method with forward stability. The method of claim 8,
The server,
Decrypting the re-encrypted identifier using the lower secret key, comparing the encrypted identifier of the same pair with the decrypted identifier, and providing the encrypted identifier to the user terminal if they match.
A searchable encryption method with forward stability. As a computer-readable recording medium storing a computer program,
The computer program, when executed by a processor,
Encrypting the file identifier using the identity of the user who wishes to grant permission to browse the file,
Re-encrypting the encrypted identifier after hierarchically configuring the user's identity, the related keyword, and the number of searches (SC) of the user; and
Obtaining a search state (KS) of the keyword to be searched up to the present and a total search count value of the user; and
Generating a lower private key using a user key, the user's identity, the related keyword, the total search count value, and the search state; and
Transmitting the generated lower private key to the server to request a file identifier;
Including instructions for causing the processor to perform a method comprising the step of obtaining an identifier of the file by decrypting the encrypted identifier provided from the server using a higher secret key previously distributed from a key manager terminal,
Computer-readable recording medium. As a computer program stored in a computer-readable recording medium,
The computer program, when executed by a processor,
Encrypting the file identifier using the identity of the user who wishes to grant permission to browse the file,
Re-encrypting the encrypted identifier after hierarchically configuring the user's identity, the related keyword, and the number of searches (SC) of the user; and
Obtaining a search state (KS) of the keyword to be searched up to the present and a total search count value of the user; and
Generating a lower private key using a user key, the user's identity, the related keyword, the total search count value, and the search state; and
Transmitting the generated lower private key to the server to request a file identifier;
Including instructions for causing the processor to perform a method comprising the step of obtaining an identifier of the file by decrypting the encrypted identifier provided from the server using a higher secret key previously distributed from a key manager terminal,
Computer program.

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