KR20240022203A - Communication system for private information retrieval using user preference based cache and its operation method - Google Patents

Abstract

A technology for achieving private retrieval using preference-based caching of a user terminal is disclosed. Stores caching data based on preferences in the user terminal for each file stored in a plurality of databases, and transmits query information for requesting a target file based on the caching data to the plurality of databases, The target file can be detected from the response string received from the plurality of databases.

Description

Communication system for private information retrieval using user preference based cache and its operation method for achieving private retrieval using preference-based caching of a user terminal

The explanation below is about a technique for achieving private retrieval that guarantees the privacy of data requested from multiple databases.

A database is an essential element of a network that stores data needed by individuals. However, in publicly accessible databases, there is a risk of exposing personal privacy because information about the requested data can be inferred backwards through the details of the data requested by the user. A technology called private information retrieval is a communication technique that prevents the database from inferring information about the data requested by an individual. It ensures the privacy of the data requested by the individual from the database and quickly receives the data. It is emerging as one of the technologies.

Research on communication techniques for achieving private retrieval basically proposes a technique in which an individual requests the desired data from a database together with other data other than the desired data, thereby hiding information about the desired data. To do this, the user requests the desired data and other data from the database through a query. In this process, as the amount of information in Query increases, the cost of downloading data received from the database may increase. Therefore, there is a need for a method that reduces download costs and allows users to obtain desired data without exposing the desired data.

Recent research is known about the minimum amount of information in Query to avoid exposing desired data when requesting data from a database in a situation where there is no caching in the terminal. Research [1] suggests a technique for generating a query through a greedy iterative algorithm, and research [2] suggests that if the length of a query is sufficiently long, a stochastic generation technique is used to quickly minimize the query. A technique is proposed to request data from the database without exposing the desired data due to the amount of information, and research [3] deals with a situation in which caching data is stored in the user terminal without considering preferences, and is stored in the user terminal. We propose a communication technique to achieve more efficient private retrieval by utilizing available caching data.

[1] H. Sun, S. Jafar, “The capacity of private information retrieval,” IEEE Trans. Inf. Theory, vo. 63, no. 7, pp. 4075-4088, Jul. 2017.

[2] H. Seo, W. Choi, “A Stochastic Approach in Private Information Retrieval”, IEEE WCNC pp.1-6, Apr. 2018.

[3] H. Seo, H. Lee, W. Choi “Fundamental Limits of Private Information Retrieval with Unknown Cache Prefetching”, IEEE Trans. Comm. vo. 69, no. 12, pp. 8132-8144, Dec. 2021

Provides a communication system technique for achieving efficient and private retrieval using cached data based on personal device preferences.

By storing caching data based on user preferences, communication resources can be used more efficiently to implement private retrieval technology.

In the method performed in a user terminal, the user terminal includes at least one processor configured to execute computer-readable instructions included in a memory, and the method includes, by the at least one processor, stored in a plurality of databases. storing caching data for each file based on preferences in the user terminal; transmitting, by the at least one processor, query information for requesting a target file based on the caching data to the plurality of databases; and detecting, by the at least one processor, the target file from a response string received from the plurality of databases.

According to one aspect, the storing step may store the caching data based on the preference according to the caching data capacity of the user terminal.

According to another aspect, the storing step includes storing the caching data starting from the file with the highest preference when the caching data capacity of the user terminal is greater than a certain size determined based on the number of the database and the number of files. can do.

According to another aspect, in the storing step, the caching data capacity (z) of the user terminal is (where N is the number of databases and K is the number of files), if it is more than a portion of the total data capacity (where M _f is the size of a single file), K files of the same size are Store as much as you need, and the remaining data capacity You can save data first, starting with files with the highest preference.

According to another aspect, the storing step may further include storing the caching data through linear combination when the caching data capacity of the user terminal is less than the predetermined size.

According to another aspect, in the transmitting step, different queries may be created and transmitted in the plurality of databases as query information for requesting the target file.

According to another aspect, the query information includes a query vector, which is a binary sequence of a predetermined length, and an index information vector, which is a tuple of the predetermined length, and the query vector is a linear combination in the database. The index information vector may represent information about a starting point participating in the linear combination.

According to another aspect, each of the databases may receive the query information from the user terminal and generate a response string composed of a function for a file stored in the database as a response bit to the query information.

A computer program stored on a computer-readable recording medium is provided to execute the method on a computer device.

A computer-implemented user terminal, comprising at least one processor configured to execute computer-readable instructions included in a memory, wherein the at least one processor The process of storing caching data based on preferences; transmitting query information for requesting a target file based on the caching data to the plurality of databases; and a user terminal that processes the process of detecting the target file from the response string received from the plurality of databases.

According to embodiments of the present invention, by storing cached data based on the user's preference and retrieving data desired by the user based on the cached data, communication resources can be used more efficiently to achieve a private retrieval technology. .

Figure 1 shows an example of a communication network configuration in one embodiment of the present invention.
Figure 2 shows a user's preferences for each file in one embodiment of the present invention.
Figure 3 shows database data and terminal caching data in one embodiment of the present invention.
Figure 4 shows the results of a normalized download cost experiment according to normalized caching capacity in one embodiment of the present invention.
Figure 5 shows an example of a preference-based data caching technique in one embodiment of the present invention.
Figure 6 shows an example of a caching data storage technique in one embodiment of the present invention.
Figure 7 is a flow chart illustrating a preference-based data retrieval method in one embodiment of the present invention.
Figure 8 is a block diagram showing an example of a computer system according to an embodiment of the present invention.

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

Embodiments of the present invention relate to technology that guarantees privacy for data requested by individuals from a database.

Embodiments including those specifically disclosed in this specification can provide a communication system technique for achieving efficient private retrieval using cached data based on the preferences of a personal terminal, thereby reducing costs, ensuring privacy, and Significant advantages can be achieved in terms of data processing speed and efficiency.

Telecommunications networks and data

Figure 1 shows an example of a communication network configuration in one embodiment of the present invention.

Referring to FIG. 1, the present invention assumes a network consisting of one user terminal 110 and N databases 120 that transmit data requested by the user. The databases 120 do not exchange information with each other (non-colluding), and each database 120 stores the same set of K different file data. All K files have the same length of M _f bits. The number of files is It is assumed that the bit strings that make up each file satisfy and do not overlap each other, and the bit strings of each file are expressed as Equation 1.

[Equation 1]

Figure 2 shows the user's preference for each file in one embodiment of the present invention, and Figure 3 shows database data and terminal caching data in one embodiment of the present invention.

In this embodiment, preference can be calculated based on the number of accesses to the file, access frequency, access cycle, etc.

For example, as shown in FIG. 2, users have different preferences for K files (F ₁ , F ₂ , ??, F _K ), and the user terminal 110 makes a request to the database according to the preferences. probability It appears differently. At this time, assume that the numbers of each file are sorted in descending order according to preference. .

Communication between the user terminal 110 and the database 120 is performed through a noise-free channel, and two-way communication is possible.

The user terminal 110 is capable of storing caching data, and the caching data capacity is It has bit size. z is the normalized caching capacity, the ratio of the cached data size to the single file size am. At this time, the caching data Z stored in the user terminal 110 is expressed as Equation 2, and the caching data once stored is fixed until receiving the response string from the database 120 is completed, and the database 120 is stored in the user terminal ( 110) The caching data stored in is unknown.

[Equation 2]

The user terminal 110 determines the data to be stored in the caching data capacity before determining the desired file, that is, the target file. At this time, the data stored is stored in Z in the form of random linearly combined data bits of random single bits from different files selected with a certain probability according to the z value, or as single bits of a certain ratio of single files.

Query Configuration

In the present invention, the user terminal 110 uses the stored caching data as additional information and retrieves the file desired by the user from the database 120. Handles situations where requests are made while ensuring privacy. here, is the probability mentioned above among all K files. This is the index of the file the user wants to request, determined by . The user terminal 110 is a file In order to obtain, different queries are created and transmitted to N databases 120. file The query transmitted to each database 120 to request is expressed as Equation 3.

[Equation 3]

Query sent to random database n silver Qary vector, which is a K-length binary sequence and an index information vector that is a K-length tuple. It includes. The query vector and index vector can be expressed as Equation 4.

[Equation 4]

Here, the role of the query vector is to inform the database 120 from which message information bits will be taken and linearly combined. For example, if there are two messages in the database, if a query vector of [1 0] is transmitted, an information bit is requested in the first message, and if a query vector of [0 1] is transmitted, an information bit is requested in the second message. When transmitting a query vector of [1 1], it is requested to create a response bit by linearly combining one information bit of the first message and one information bit of the second message. The query vector is created in consideration of cached data so that the user terminal 110 can request data from the database 120 without exposing the desired data. The detailed generation technique will be described again below.

The index information vector determines the starting point that participates in combining among the M _f bits of each file. To create a response bit, not only is information about which message's information bits to be linearly combined, but information is also needed to determine which bits are to be linearly combined. In order to minimize upload costs, this technique will be used to create response bits in the order in which the information bits of the message were originally arranged, so the user must transmit the initial message bit index information, which is the starting point of the sequence, to each database.

Configuration of the response string

in database n When you receive bit-long response string is generated and expressed in the same way as Equation 5. The response string is a function for files stored in the query and database.

[Equation 5]

The next function is a function that calls information bits sequentially starting from the initial file index data bit.

privacy security

crystalline sequence Let us assume that the tuple of sequences is expressed as Equation 6.

[Equation 6]

Additionally, there may be an empirical probability mass function definition such as Equation 7.

[Equation 7]

According to the above equation, if the generated query is in a sequence tuple as expressed in Equation 8, privacy can be expressed as safe.

[Equation 8]

The performance of this technique is limited to any file the user wants. The total amount of data in the response string that must be downloaded from the entire database to receive the data. It can be measured by the normalized download cost, which is the ratio of the data amount of a single file, M _f . At this time, the normalized download cost for the entire file is expressed as Equation 9.

[Equation 9]

The performance of this technique can be measured through the indicator in Equation 9.

When a query is created considering the caching data information, the normalized download cost has the same size as Equation 10 for the normalized caching capacity z, which is the ratio of the storage capacity to the single file size.

[Equation 10]

here, am.

The results of comparing the above results through simulation with existing techniques that do not take user preferences into account are shown in Figure 4. The simulation environment was conducted in the case where the number of databases is 2 and the number of files that can be requested is 4, and the number of databases is 3 and the number of files that can be requested is 7. Assume that the size of each file is 1Mbit. At this time, the normalized download cost according to the ratio z of the caching data capacity of the user terminal and the single file capacity is compared.

Unlike the proposed technique that caches data by reflecting the preference of each file, in the case of the existing technique, the user caches data under the assumption that the request probability of each file is the same without considering the user's preference. As a result of applying the technique, a section where data is stored in the form of a single bit, reflecting preference It can be seen that when using this technique, the normalized download cost can be reduced by up to 30% (0.5->0.35) and 27% (0.64->0.47).

In the present invention, a user stores caching data and creates a query in different ways depending on the capacity of the user's caching data. Capacity size is based on the relative ratio z of the caching data capacity to the size of a single file M ^f .

(i) Caching data capacity If

Of total data capacity As long as the total K pieces of data are the same size Save it as much as you need. The remaining capacity after that For , data is saved first, starting from the file with the highest preference.

Referring to Figure 5, if there are a total of K = 9 files, the total file size is M _f = 6Mb, and the number of databases is 2, this technique creates the same size of 6/3 = 2Mb for each of the 9 files. You can save it. Afterwards, if there is remaining caching capacity, data is saved first starting from the file with the highest preference (the file on the left). As a result, the fourth file stores a total of 4Mb, and for subsequent files, only the initially stored 2Mb of data is stored. This is a situation that can be cached.

After saving all caching data, the user can select the file he or she wants. Query to decide and request creates . If all the desired files determined by the user are already cached, the required download cost is zero. In other cases, follow the process below.

Query to send to random database n As explained previously, dog curry vector and index information vector It is created by tying it together, and each is created as follows.

curary vector is created according to the following rules.

dog curry vector All elements of each quarry vector are 1. In other words, we want to request data in the form of a linear combination of data from all data files. In this case, the same amount of data is requested for all data, so the curry vector generated in this way is It can be shown that the equation is satisfied, in other words, it becomes a safe query.

And, the index information vector is the file index that the user wants to request. Except for the first element, the index of the currently cached data is transmitted equally to all databases. If the first bit index that is not cached in the terminal of the first file is b, the index information vector transmitted to the first database is The th element is b, and the index information vector transmitted to the ith database is The second element is It becomes.

below The caching details for the area are as follows.

(ii) Caching data capacity If

As shown in Figure 6, the user's total Of the storage capacity of bits Bits are linearly combined to determine which bits to store. The bits to be stored through linear combination are determined in the following order.

First, select some of the K files. Choose with a probability of In FIG. 6, the files selected to be stored in the first storage space Z ₁ are the 1st file and the 4th file. Next, a uniform bit to be stored is selected for each selected file.

Once you have selected the bits to be stored, the storage space In each storage space, the selected bits are linearly combined and stored.

As shown in Figure 6, when the total number of files is K = 4 and M _c = 5 and M' = 3, the first bit to be stored Z ₁ is a file selected with a certain probability among K = 4 files ( Determine the bits to be stored uniformly at k=1, 4). The bit decided like that class Then, the linearly combined bits of the two are stored in Z ₁ . In addition to the M' bits stored in linear combination, one uniformly selected bit of one uniformly selected file is stored in the capacity. In the example, you can see that the random bits of the second file and the random bits of the third file are stored in Z ₄ and Z ₅ , respectively.

Query to send to random database n As explained previously, dog curry vector and index information vector It is created by tying it together, and each is created as follows.

curary vector is created according to the following rules.

User-desired file index for each curry vector In the case of the kth element, the file included in the user's kth cached data is set to 1, and the rest is set to 0.

not yet decided elements (of each curary vector) The first element) is the user's cached data. Select only the index that contains the information of the th file. The set of indices thus selected is It is said. Among that set Sequentially starting from the query vector of the th index of the curary vector of the th index Only the first element is set to 0, the rest are set to 1. This can be expressed as Equation 11.

[Equation 11]

The Qurey vector created in this way is It can be shown that the equation is satisfied, and in other words, if the file size is large enough, it becomes a safe query.

And the index information vector is generated by uniformly determining the file length M _f for the first database K times. After that The index information vector for the first database is each K elements of the index information vector for the first database. Created by adding .

(iii) caching data capacity If

Data is stored in the caching data storage capacity in the same way as in case (ii). This time, out of the total storage capacity M _c bits Only bits are generated and stored through linear combination. Other capacities are not considered.

Query to send to random database n As explained previously, dog curry vector and index information vector are created, and each is created as follows.

The total number of transmitted Quri vectors is when Sending four curary vectors, curary vector is created according to the following rules.

First, the query vector of the 1st to M''th index is determined in the following manner, as in case (i).

User-desired file index for each curry vector In the case of the kth element, the file included in the user's kth cached data is set to 1, and the rest is set to 0.

not yet decided elements (of each curary vector) The first element) is the user's cached data. Select only the index that contains the information of the th file. The set of indices thus selected is It is said. Among that set Sequentially starting from the query vector of the th index of the curary vector of the th index Only the first element is set to 0, the rest are set to 1. This can be expressed as Equation 12.

[Equation 12]

In addition, the query vector of the M'''th index from M''+1th to M'''th index is created in the same way as technique [2].

The Qurey vector created in this way is It can be shown that the equation is satisfied, and in other words, if the file size is large enough, it becomes a safe query.

And the index information vector is created through the same process as described in (ii).

That is, the algorithm of the entire communication technique proposed in the present invention, including the system configuration described above, can be expressed as shown in FIG. 7 on the user terminal 110 and the database 120, respectively.

Referring to FIG. 7, the user terminal 110 can store preference-based caching data (S11), and when desired data is generated from the database 120 according to a user request, the query vector and index information vector Generate (S12 to 14).

The user terminal 110 provides query information about the desired data (i.e., query vector and index information vector ) is transmitted to the database 120 (S15).

The database 120 provides query information (i.e., query vector) about data desired by the user terminal 110 from the user terminal 110. and index information vector ) is received (S21), a response string that is a function for files stored in the query and database is constructed and transmitted to the user terminal 110 (S22 to 23).

Accordingly, the user terminal 110 may receive a response string for the query information from the database 120 and detect desired data from the received response string (S16 to S17).

These embodiments can be used as a technology that can guarantee personal privacy in mobile communication or PC communication when a terminal device capable of storing data requests data from a server holding the data.

Figure 8 is a block diagram showing an example of a computer system according to an embodiment of the present invention.

Figure 8 is a block diagram showing an example of a computer system according to an embodiment of the present invention. The user terminal 110 and database 120 described above may be implemented by a computer system 800 configured as shown in FIG. 8.

As shown in FIG. 8, the computer system 800 is a component for executing the preference-based data retrieval method according to embodiments of the present invention, and includes a memory 810, a processor 820, a communication interface 830, and It may include an input/output interface 840.

The memory 810 is a computer-readable recording medium and may include a non-permanent mass storage device such as random access memory (RAM), read only memory (ROM), and a disk drive. Here, non-perishable large-capacity recording devices such as ROM and disk drives may be included in the computer system 800 as a separate permanent storage device that is distinct from the memory 810. Additionally, an operating system and at least one program code may be stored in the memory 810. These software components may be loaded into the memory 810 from a computer-readable recording medium separate from the memory 810. Such separate computer-readable recording media may include computer-readable recording media such as floppy drives, disks, tapes, DVD/CD-ROM drives, and memory cards. In another embodiment, software components may be loaded into the memory 810 through the communication interface 830 rather than a computer-readable recording medium. For example, software components may be loaded into memory 810 of computer system 800 based on computer programs being installed by files received over network 860.

The processor 820 may be configured to process instructions of a computer program by performing basic arithmetic, logic, and input/output operations. Commands may be provided to the processor 820 by the memory 810 or the communication interface 830. For example, the processor 820 may be configured to execute received instructions according to program codes stored in a recording device such as memory 810.

The communication interface 830 may provide a function for the computer system 800 to communicate with other devices through the network 860. For example, a request, command, data, file, etc. generated by the processor 820 of the computer system 800 according to a program code stored in a recording device such as a memory 810 is transmitted to the network ( 860) and can be transmitted to other devices. Conversely, signals, commands, data, files, etc. from other devices may be received by the computer system 800 through the communication interface 830 of the computer system 800 via the network 860. Signals, commands, data, etc. received through the communication interface 830 may be transmitted to the processor 820 or memory 810, and files, etc. may be stored in a storage medium (as described above) that the computer system 800 may further include. It can be stored as a permanent storage device).

The communication method is not limited, and may include not only a communication method utilizing communication networks that the network 860 may include (e.g., mobile communication network, wired Internet, wireless Internet, and broadcasting network), but also short-distance wired/wireless communication between devices. there is. For example, the network 860 may be a personal area network (PAN), a local area network (LAN), a campus area network (CAN), a metropolitan area network (MAN), a wide area network (WAN), or a broadband network (BBN). , may include one or more arbitrary networks such as the Internet. Additionally, the network 860 may include any one or more of network topologies including a bus network, star network, ring network, mesh network, star-bus network, tree or hierarchical network, etc. Not limited.

The input/output interface 840 may be a means for interfacing with the input/output device 850. For example, input devices may include devices such as a microphone, keyboard, camera, or mouse, and output devices may include devices such as displays and speakers. As another example, the input/output interface 840 may be a means for interfacing with a device that integrates input and output functions, such as a touch screen. The input/output device 850 may be configured as a single device with the computer system 800.

Additionally, in other embodiments, computer system 800 may include fewer or more components than those of FIG. 8 . However, there is no need to clearly show most prior art components. For example, the computer system 800 may be implemented to include at least some of the input/output devices 850 described above, or may further include other components such as a transceiver, various databases, etc.

In this way, according to embodiments of the present invention, it is possible to implement a technology for achieving private retrieval by using communication resources more efficiently by storing cached data based on user preferences and retrieving data desired by the user based on the cached data. there is.

The device described above may be implemented with hardware components, software components, and/or a combination of hardware components and software components. For example, the devices and components described in the embodiments include a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), and a programmable logic unit (PLU). It may be implemented using one or more general-purpose or special-purpose computers, such as a logic unit, microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. Additionally, a processing device may access, store, manipulate, process, and generate data in response to the execution of software. For ease of understanding, a single processing device may be described as being used; however, those skilled in the art will understand that a processing device includes multiple processing elements and/or multiple types of processing elements. It can be seen that it may include. For example, a processing device may include a plurality of processors or one processor and one controller. Additionally, other processing configurations, such as parallel processors, are possible.

Software may include a computer program, code, instructions, or a combination of one or more of these, which may configure a processing unit to operate as desired, or may be processed independently or collectively. You can command the device. The software and/or data may be embodied in any type of machine, component, physical device, computer storage medium or device for the purpose of being interpreted by or providing instructions or data to the processing device. there is. Software may be distributed over networked computer systems and stored or executed in a distributed manner. Software and data may be stored on one or more computer-readable recording media.

The method according to the embodiment may be implemented in the form of program instructions that can be executed through various computer means and recorded on a computer-readable medium. At this time, the medium may continuously store a computer-executable program, or temporarily store it for execution or download. In addition, the medium may be a variety of recording or storage means in the form of a single or several pieces of hardware combined. It is not limited to a medium directly connected to a computer system and may be distributed over a network. Examples of media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical recording media such as CD-ROMs and DVDs, magneto-optical media such as floptical disks, And there may be something configured to store program instructions, including ROM, RAM, flash memory, etc. Additionally, examples of other media include recording or storage media managed by app stores that distribute applications, sites that supply or distribute various other software, or servers.

As described above, although the embodiments have been described with limited examples and drawings, various modifications and variations can be made by those skilled in the art from the above description. For example, the described techniques are performed in a different order than the described method, and/or components of the described system, structure, device, circuit, etc. are combined or combined in a different form than the described method, or other components are used. Alternatively, appropriate results may be achieved even if substituted or substituted by an equivalent.

Therefore, other implementations, other embodiments, and equivalents of the claims also fall within the scope of the claims described below.

Claims (17)

In the method performed on the user terminal,
The user terminal includes at least one processor configured to execute computer-readable instructions contained in a memory,
The above method is,
storing, by the at least one processor, caching data based on preferences in the user terminal for each file stored in a plurality of databases;
transmitting, by the at least one processor, query information for requesting a target file based on the caching data to the plurality of databases; and
Detecting, by the at least one processor, the target file from a response string received from the plurality of databases.
How to include . According to paragraph 1,
The saving step is,
Storing the caching data based on the preference according to the caching data capacity of the user terminal.
A method characterized by . According to paragraph 1,
The saving step is,
If the caching data capacity of the user terminal is greater than a certain size determined based on the number of databases and the number of files, storing the caching data starting from the file with the highest preference.
How to include . According to paragraph 1,
The saving step is,
The caching data capacity (z) of the user terminal is (where N is the number of databases and K is the number of files),
A portion of the total data capacity (where M _f is the size of a single file), K files of the same size are Save it as much as you need,
remaining data capacity Saving data first, starting with files with the highest preference.
A method characterized by . According to paragraph 3,
The saving step is,
If the caching data capacity of the user terminal is less than the predetermined size, storing the caching data through linear combination.
How to further include . According to paragraph 1,
The transmitting step is,
Creating and transmitting different queries to the plurality of databases with query information for requesting the target file
A method characterized by . According to clause 6,
The query information includes a query vector, which is a binary sequence of a predetermined length, and an index information vector, which is a tuple of the predetermined length,
The query vector represents information about information bits for linear combination in the database,
The index information vector represents information about the starting point participating in the linear combination.
A method characterized by . According to clause 6,
In each of the databases, the query information is received from the user terminal, and a response string consisting of a function for the file stored in the database is generated as a response bit to the query information.
A method characterized by . A computer program stored in a computer-readable recording medium for executing the method of any one of claims 1 to 8 on a computer device. In a user terminal implemented by a computer,
At least one processor configured to execute computer readable instructions contained in memory
Including,
The at least one processor,
A process of storing caching data based on preferences in the user terminal for each file stored in a plurality of databases;
transmitting query information for requesting a target file based on the caching data to the plurality of databases; and
A process of detecting the target file from response strings received from the plurality of databases
A user terminal that processes . According to clause 10,
The at least one processor,
Storing the caching data based on the preference according to the caching data capacity of the user terminal.
A user terminal characterized by . According to clause 10,
The at least one processor,
If the caching data capacity of the user terminal is greater than a certain size determined based on the number of databases and the number of files, storing the caching data starting from the file with the highest preference.
A user terminal characterized by . According to clause 10,
The at least one processor,
The caching data capacity (z) of the user terminal is (where N is the number of databases and K is the number of files),
A portion of the total data capacity (where M _f is the size of a single file), K files of the same size are Save it as much as you need,
remaining data capacity Saving data first, starting with files with the highest preference.
A user terminal characterized by . According to clause 12,
The at least one processor,
If the caching data capacity of the user terminal is less than the certain size, storing the caching data through linear combination.
A user terminal characterized by . According to clause 10,
The at least one processor,
Creating and transmitting different queries to the plurality of databases with query information for requesting the target file
A user terminal characterized by . According to clause 15,
The query information includes a query vector, which is a binary sequence of a predetermined length, and an index information vector, which is a tuple of the predetermined length,
The query vector represents information about information bits for linear combination in the database,
The index information vector represents information about the starting point participating in the linear combination.
A user terminal characterized by . According to clause 15,
In each of the databases, the query information is received from the user terminal, and a response string consisting of a function for the file stored in the database is generated as a response bit to the query information.
A user terminal characterized by .

Images