JP7833355B2 - Secure search system, secure search method - Google Patents

Description

This invention relates to a secure search system and a secure search method.

With the expansion of computing power and advancements in information processing technology, data analysis—which involves aggregating and analyzing data owned by multiple companies and individuals to gain useful insights—has come to play a crucial role in the operation of society. However, because this data often contains sensitive information, many data owners and institutions are reluctant to disclose it. To balance data utilization with the confidentiality of individual information, confidential information processing technologies are being researched and developed. One example of confidential information processing technology is confidential search technology, which allows searching encrypted data without decryption. Confidential search technology is a technology specializing in basic search functions within information processing, and is envisioned as a system where data owners entrust data storage to data management devices such as cloud storage, and then extract and use the necessary data as needed.

For example, Patent Document 1 discloses a method for obtaining evidence of processing for secure computation based on secret sharing technology.

International Patent Application Publication No. 2021/014611

While there are several methods for implementing secure searches, using public-key cryptography significantly reduces processing speed and drastically increases data size due to encryption, making it difficult to apply to large datasets. On the other hand, in big data analysis, the data owner's device and the data user's device are often different. In systems based on symmetric-key cryptography, the data owner's device must disclose the private key necessary for searching and decrypting data to the data user's device. In this case, the data user's device faces the risk of using data beyond the scope authorized by the data owner's device.

Therefore, the present invention aims to provide a confidential search system and method that can determine whether data usage by data user devices is appropriate and contribute from a social perspective (i.e., from a security perspective).

According to a first aspect of the present invention, the following confidential search system is provided. This confidential search system comprises a data owner device, a data user device, a data administrator device, and a monitor device, and is a system that uses symmetric-key cryptography. The data administrator device has a first database and stores in the first database ciphertext data encrypted with a first secret key and the owner ID of the data owner device with respect to the data held by the data owner device. The data user device stores the first secret key and a search key used to search the ciphertext data associated with the first secret key. The data monitor device has a second database and stores in the second database the owner ID of the data owner device and information on who to report to the owner of the data owner device. Furthermore, when the data user device performs a data search, it sends a ciphertext search query encrypted with the search key to the data administrator device. Upon receiving the ciphertext search query, the data administrator device extracts the ciphertext data matching the query from the first database and sends the owner ID of the data owner device associated with the ciphertext data, along with the ciphertext search query, as a pair to the monitoring device. The second database contains entries for the owner ID of the data owner device, the reporting destination, and the ciphertext search query, which are recorded as search logs. Upon receiving data from the data administrator device, the monitoring device registers the ciphertext search query in the second database using the owner ID of the data owner device as the key. Then, after a period of time, the monitoring device extracts a list of ciphertext search queries associated with the owner ID of the data owner device from the search logs accumulated in the second database and sends it to the data owner device. The data owner device then obtains the list of ciphertext search queries sent from the monitoring device.

According to a second aspect of the present invention, the following confidential search method is provided. This confidential search method is performed using a data owner device, a data user device, a data administrator device having a first database, and a monitor device having a second database, and uses symmetric-key cryptography, and includes a registration phase, a search phase, and a reporting phase. The registration phase includes the steps of: a user of the data owner device encrypting the data they possess with a first secret key and entrusting it to the data administrator device along with the owner ID of the data owner device, and storing the entrusted data in the first database; a user of the data owner device entrusting the data user device with the first secret key and a search key for searching ciphertext data associated with the first secret key; and a user of the data owner device contacting the monitor device in advance with the owner ID of the data owner device and information to report to, and storing the contacted information in the second database, which includes the owner ID of the data owner device, contact information for the user of the data owner device, and queries as entries and records search logs. The search phase includes the steps of: the data user device sending a ciphertext search query, encrypted with the search key, to the data administrator device upon execution of the search; the data administrator device, upon receiving the ciphertext search query, extracting ciphertext data matching the ciphertext search query from the first database and sending the owner ID of the data owner device associated with the ciphertext data, along with the ciphertext search query, to the monitor device; and the monitor device, upon receiving data from the data administrator device, registering the ciphertext search query in the second database using the owner ID of the data owner device as the key. The reporting phase includes the steps of: the monitor device extracting a list of ciphertext search queries associated with the owner ID from the search logs accumulated in the second database over a period of time and sending it to the data owner device; and the data owner device obtaining the list of received ciphertext search queries.

According to the present invention, a confidential search system and method are provided that can determine whether data usage by data user devices is appropriate and contribute from a social perspective (i.e., from a security perspective). Other issues, configurations, and effects not mentioned above will be clarified by the following description of embodiments for carrying out the invention.

A diagram showing an example of the configuration of a confidential information processing system. A diagram showing an example of a typical computer configuration. A schematic diagram illustrating the roles of entities. A diagram illustrating the details of the data owner's device. A diagram illustrating the details of the data management device. A diagram illustrating the details of the data user device. A diagram illustrating the details of the monitoring device. A diagram illustrating an example of the processing performed by a confidential information processing system. A diagram illustrating an example of a report format.

Embodiments of the present invention will be described below with reference to the drawings. The embodiments are illustrative examples for explaining the present invention, and have been omitted and simplified as appropriate for clarity of explanation. The present invention can also be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.
The positions, sizes, shapes, and ranges of the components shown in the drawings may not represent their actual positions, sizes, shapes, and ranges in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the positions, sizes, shapes, and ranges disclosed in the drawings.
Examples of various types of information may be described using terms such as "table,""list," and "queue," but these types of information may also be represented by other data structures. For example, various types of information such as "XX table,""XXlist," and "XX queue" may be referred to as "XX information." When describing identification information, terms such as "identification information,""identifier,""name,""ID," and "number" are used, but these terms are interchangeable.
When there are multiple components with the same or similar function, they may be described using the same symbol but with different subscripts. Furthermore, if it is not necessary to distinguish between these multiple components, the subscripts may be omitted in the description.
In embodiments, processing performed by executing a program may be described. Here, the computer executes the program using a processor (e.g., CPU, GPU) and performs processing defined by the program using memory resources (e.g., memory) and interface devices (e.g., communication ports). Therefore, the main entity performing the processing by executing the program may be the processor. Similarly, the main entity performing the processing by executing the program may be a controller, device, system, computer, or node having a processor. The main entity performing the processing by executing the program may be an arithmetic unit, and may include a dedicated circuit that performs a specific processing. Here, a dedicated circuit is, for example, an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), a CPLD (Complex Programmable Logic Device), etc.
The program may be installed on the computer from the program source. The program source may be, for example, a program distribution server or a storage medium readable by the computer. If the program source is a program distribution server, the program distribution server includes a processor and storage resources for storing the program to be distributed, and the processor of the program distribution server may distribute the program to other computers. In addition, in some embodiments, two or more programs may be implemented as a single program, or one program may be implemented as two or more programs.

In this embodiment, a secure information processing system (secure search system) based on symmetric-key cryptography is assumed. A known technology (for example, the technology disclosed in Japanese Patent Application Publication No. 2012-123614) can be used to implement such a secure search.

First, an example of the system configuration will be described with reference to Figure 1. The confidential information processing system comprises one or more data owner devices (101), one or more data user devices (102), a data administrator device (103), and a monitor device (104). These entities are interconnected via a network (105).

Next, with reference to Figure 2, an example of the configuration of the computer used in the system will be described. The computer (201) is a general-purpose computer and comprises a CPU (211), memory (212), storage (220), and a communication interface (230). The CPU (211) is the main component that performs calculations and executes predetermined processes. The memory (212) temporarily stores the calculation results. The CPU (211) reads data into the memory (212) and executes processing. The storage (220) stores data long-term. The communication interface (230) is connected to the network (105) by wired or wireless connection and is used for communication via the network (105). In this embodiment, an example using a CPU (211) as the processor is described, but any semiconductor device other than the CPU may be used as long as it can perform predetermined processes.

In this embodiment, communication between the two parties is encrypted using a channel encryption function (240), preventing eavesdropping by other entities. This channel encryption can be achieved using a general-purpose TLS (Transport Layer Security) or similar.

Next, the role of each entity will be explained with reference to Figure 3. The data owner device (101) is the device of the owner of the data (301). The data owner device (101) may be an individual's device or a corporate device that holds customer data, etc. The data administrator device (103) stores the data (301) entrusted to it by the data owner device (101) in an encrypted state, performs searches in response to requests from the data user device (102), and returns the search results to the data user device (102). The data user device (102) is an entity that has received permission from the data owner device (101) to use the data (301) to a certain extent. When the data user device (102) uses the data (301), it sends a query to the data administrator device (103) to retrieve the necessary information as a search request, and decrypts and uses the ciphertext, which is the search response from the data administrator device (103). The monitoring device (104) monitors the search performed by the data user device (102) and reports the results to the data owner device (101).

Next, referring to Figure 4, we will explain the functional configuration of the data owner device and an example of the information it holds. Figure 4 is a diagram summarizing the functional configuration of the computer used by the data owner device (101) and the information held by the data owner device (101).

The computer used by the data owner device (101) is equipped with, in addition to the functions of a general computer 201, a key generation function (401) and a secure search data encryption function (402) that encrypts the data to be protected using a secure information processing system and outputs ciphertext data (451). Furthermore, the storage (220) stores the data to be protected (301) and the regulations (411) that define the scope of data use. Also stored are the private key 1 (421), private key 2 (422), private key 3 (423) generated using the key generation function 401, the search key 1 (431) associated with private key 1 (421), the owner ID (441), and the contact address (442).

Next, referring to Figure 5, we will explain the functional configuration of the data management device and an example of the information it holds. Figure 5 is a diagram summarizing the functional configuration of the computer used by the data management device (103) and the information held by the data management device (103).

The computer used by the data administrator device (103) is equipped with, in addition to the functions of a general-purpose computer (201), a secure search ciphertext matching function (501) that matches data encrypted with a secure search cipher with queries using the secure search cipher. Furthermore, the storage (220) contains a database 1 (510) containing ciphertext data (511) and encrypted IDs (512) entrusted by the data owner device (101), and also stores a secret key 3 (523) shared with the data owner device (101).

Next, referring to Figure 6, we will explain the functional configuration of the data user device and an example of the information it holds. Figure 6 is a diagram summarizing the functional configuration of the computer used by the data user device (102) and the information held by the data user device (102).

The computer used by the data user device (102) has, in addition to the functions of a general-purpose computer (201), a secure search query encryption function (601) that encrypts queries and outputs ciphertext queries (651) during secure searches, a secure search data decryption function (602) that decrypts received search results, and a data analysis function (603) that performs analysis using the decrypted data. Furthermore, the storage (220) stores the secret key 1 (621) and search key (631) received from the data owner device (101).

Next, referring to Figure 7, we will explain the functional configuration of the monitoring device and an example of the information it holds. Figure 7 is a diagram summarizing the functional configuration of the computer used by the monitoring device (104) and the information held by the monitoring device (104).

The computer used by the monitoring device (104) has, in addition to the functions of a general-purpose computer (201), an owner ID verification function (701) for verifying the owner ID. In the diagram, this is labeled as the user ID verification function. Furthermore, the storage (220) stores a database 2 (710) containing user contact information (712) and ciphertext queries (713) encrypted with the private key 3, all linked to the owner ID (711), as well as the private key 2 (722) received from the data owner device (101).

Next, an example of the processing of the confidential information processing system will be described with reference to Figure 8. Figure 8 is a message sequence chart representing the communication protocol between entities in this embodiment. This protocol consists of three phases: registration (801), retrieval (802), and reporting (803). Each of these will be described below.

First, let's explain the registration phase. The users of the data owner device (101) and the data user device (102) consult in advance regarding the use of the data (301), summarize the scope of use in an agreement (411), and store it in each other's storage (Registration Step 1).

The data owner device (101) generates a private key 1 (421) and its associated search key 1 (431) using its key generation function (401), transmits them to the data user device (102), and also stores them in its own storage (220). The data user device (102) stores the received private key 1 (621) and search key 1 (631) in its storage (220) (registration step 2).

The data owner device (101) generates a private key 2 (422) using the key generation function (401) and stores it in the storage (220). It also transmits the private key 2 (422), the owner ID (441) of the data owner device (101), and the reporting address (442) of the data owner device to the monitoring device (104). The monitoring device (104) stores the received private key 2 (722), the owner ID (441) of the data owner device (101), and the reporting address (442) of the data owner device in the storage (220) (registration step 3).

The data owner device (101) generates a private key 3 (423) using the key generation function (401) and transmits it to the data administrator device (103). The data administrator device (103) stores the received private key 3 (523) in the storage (220) (registration step 4).

The data owner device (101) encrypts the data (301) using the confidential search data encryption function (402) and secret key 1 (421), generating ciphertext data (451). It also encrypts the owner ID (441) using secret key 2 (422), generating ciphertext ID (452). The data owner device (101) sends the ciphertext data (451) and ciphertext ID (452) as a pair to the data administrator device (103). The data administrator device (103) links the received ciphertext data (451), ciphertext ID (452), and secret key 3 (523) received in registration step 4, and stores them in database 1 (510) (registration step 5).

Next, the search phase will be described. The data user device (102) generates an encrypted query (651) by encrypting the search query using the search key 1 (631) and sends it to the data administrator device (103) (search step 1).

The data administrator device (103) searches database 1 (510) where the ciphertext data (511) is stored using the received ciphertext query (651), and sends the pairs of ciphertext data (511) and ciphertext owner IDs (512) that match the search result to the monitoring device (104). It also sends the ciphertext query (651), encrypted with the secret key 3 (523), to the monitoring device (104) (search step 2).

The monitoring device (104) transmits the received ciphertext data (511) to the data user device (102) (search step 3).

The monitoring device (104) decrypts the received ciphertext ID (512) using the secret key 2 (722) and associates the corresponding owner ID (711) with the search query (651) encrypted with the secret key 3 (search step 4).

The data user device (102) decrypts the received ciphertext data (511) using the secret key 1 (621), and the user of the data user device (102) utilizes the data (search step 5).

Next, the reporting phase will be described. The monitoring device (104) extracts data associated with the owner ID (711) from the list of search queries (713) encrypted with the secret key 3 accumulated in search step 4, for each data owner device, and sends the list of encrypted queries (713) to the contact address (712) of the data owner device also associated with the owner ID (711) (reporting step 1).

The data owner device (101) decrypts the list of ciphertext queries (713) encrypted with the received secret key 3 using the secret key 3 (423), and checks whether there has been any use beyond the scope of use by comparing it with the agreement (411) (reporting step 2).

According to this embodiment, the data user device (102) can only access partial information about the data obtained as a search result. Furthermore, since the search content is known to the data owner device (101), it is considered possible to deter the data user device (102) from using the data (301) without restriction. The data administrator device (103) does not obtain any information beyond what it would know as a conventional secure search database based on symmetric-key cryptography. Additionally, the monitor device (104) receives encrypted search queries and owner IDs, but since the search queries themselves are encrypted, it cannot obtain any useful information.

Furthermore, the following may also be used. In this embodiment, in registration step 2, the data owner device (101) generates the secret key 1 (421) and the search key 1 (431), but these keys may also be generated by the data user device (102). In this case, the data user device (102) transmits the generated secret key 1 (421) to the data owner device (101). Also, in registration step 5, the data owner device (101) encrypts the data (301) with the received secret key 1 (421) and generates ciphertext data (451).

Furthermore, in this embodiment, in search step 1, the data user device (102) transmits the ciphertext query (651) to the data administrator device (103). However, the data user device (102) may transmit the ciphertext query (651) to the monitor device (104), and the monitor device (104) may forward the ciphertext query (651) to the data administrator device (103). Also, in search step 2, the data administrator device (103) may transmit the ciphertext data (511) to the data user device (102). In this case, the transmission of the ciphertext data (511) by the monitor device (104) to the data user device (102) in search step 103 may be omitted.

Furthermore, in this embodiment, since the data owner device (101) does not directly use the data (301), the plaintext data (301) may be deleted from the data owner device (101) once the registration phase is complete. Similarly, since the private key 1 (421) and private key 2 (422) are not used by the data owner device (101), they may also be deleted from the data owner device (101).

Furthermore, in this embodiment, if there are multiple data user devices, in search step 1 of this embodiment, the data user device (102) may transmit the ID information of the data user device along with the ciphertext query (651) to the data monitor device (104). The data administrator device (103) may encrypt the received ID information of the data user device with the secret key 3 (523) and transmit it to the monitor device (104). The monitor device (104) may then transmit the ID information of the data user device encrypted with the secret key 3 (523) along with a list of ciphertexts to the data owner device (101). This allows the data owner device (101) to identify the data user device that executed each query. In other words, it can verify whether data usage exceeded the scope of the license for each individual data user device.

Next, an example of the report format will be described with reference to Figure 9. Figure 9 shows an example of the display of the report received and decoded by the data owner device (101) in reporting step 2 of this embodiment. Here, the data owner device (101) described in Figure 4 further includes a display (910) for displaying information and a search query determination function (920) for determining whether the search query conforms to the rules.

The search query determination function (920) determines compliance with the rules (411) for each decrypted search log entry (940) and outputs the result to the display (910). Items displayed on the display (910) include, for example, the time the query was issued (941), the data user's ID (942), the search command (943), and one or more search keywords (944).

On the display, entries that do not comply with the rules, or whose compliance is unclear, can be highlighted with color or font, or an alert message (950) can be displayed to improve visibility for data owners. Alternatively, only entries that do not comply with the rules may be displayed by default. Statistical information, such as the percentage of entries that do not comply with the rules, may also be displayed.

If a data user does not wish to disclose their search keywords, this may be stipulated in the terms of service, and the data administrator device (103) may remove the keywords from the search query in search step 2.

In search step 1, the time information (941) may be added to the transmission information by the data user device (102) at the time of transmission. Alternatively, in search step 2, the data administrator device (103) may add the time of reception to the transmission information.

Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. For example, the embodiments described above are described in detail for the purpose of clearly explaining the present invention, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. Moreover, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

Various functions are implemented, for example, by the processor executing a program. Here, the program may be stored in storage, and the processor may read the data into memory and execute predetermined processing. Alternatively, the program may be acquired from an external storage device via a network, portable storage medium, etc.

105…Network, 211…CPU, 212…Memory, 220…Storage, 230…Communication Interface, 240…Channel Encryption Function, 401…Key Generation Function, 402…Secure Search Data Encryption Function

Claims (15)

A secure search system comprising a data owner device, a data user device, a data administrator device, and a monitor device, using symmetric-key cryptography,
The aforementioned data administrator device is
Equipped with the first database,
With respect to the data held by the data owner device, the ciphertext data encrypted with the first secret key and the owner ID of the data owner device are stored in the first database.
The aforementioned data user device is
The system stores the first private key and a search key used to search for the ciphertext data associated with the first private key.
The monitoring device is,
Equipped with a second database,
The owner ID of the data owner device and the information of the recipient of the report to the owner of the data owner device are stored in the second database.
The aforementioned data user device is
When performing a data search, the ciphertext search query encrypted with the search key is sent to the data administrator device.
The aforementioned data administrator device is
Upon receiving the aforementioned ciphertext search query, the system extracts the ciphertext data matching the ciphertext search query from the first database, and transmits the owner ID of the data owner device associated with the ciphertext data and the ciphertext search query as a pair to the monitoring device.
The second database includes, as a search log, the owner ID of the data owner device, the reporting destination, and entries for the ciphertext search query.
The monitoring device is,
When data is received from the data management device, the ciphertext search query is registered in the second database using the owner ID of the data owner device as the key.
The monitoring device is,
After a period of time, a list of the ciphertext search queries associated with the owner ID of the data owner device is extracted from the search logs accumulated in the second database and sent to the data owner device.
The aforementioned data owner device is
Obtain a list of the ciphertext search queries transmitted from the monitoring device.
A secure search system characterized by the following features. A secure search system according to claim 1,
The aforementioned data administrator device is
The ciphertext data that matches the ciphertext search query transmitted from the data user device is transmitted to the data user device.
The aforementioned data user device is
The received ciphertext data is decrypted using the first secret key.
A secure search system characterized by the following features. A secure search system according to claim 1,
The aforementioned data administrator device is
The ciphertext data that matches the ciphertext search query transmitted from the data user device is transmitted to the monitor device.
The monitoring device is,
The ciphertext data is transferred to the data user device.
The aforementioned data user device is
The received ciphertext data is decrypted using the first secret key.
A secure search system characterized by the following features. A secure search system according to claim 1,
The owner ID of the data owner device stored in the first database is encrypted with a second secret key.
The monitoring device is,
Store the aforementioned second private key,
The owner ID of the data owner device received is decrypted with the second secret key, and then the search log is registered in the second database.
A secure search system characterized by the following features. The confidential search system according to claim 2,
The owner ID of the data owner device stored in the first database is encrypted with a second secret key.
The monitoring device is,
Store the aforementioned second private key,
The owner ID of the data owner device received is decrypted with the second secret key, and then the search log is registered in the second database.
A secure search system characterized by the following features. The confidential search system according to claim 3,
The owner ID of the data owner device stored in the first database is encrypted with a second secret key.
The monitoring device is,
Store the aforementioned second private key,
The owner ID of the data owner device received is decrypted with the second secret key, and then the search log is registered in the second database.
A secure search system characterized by the following features. A secure search system according to claim 1,
The data owner device and the data administrator device are
Store the third private key,
The aforementioned data administrator device is
The aforementioned ciphertext search query is encrypted with the third secret key and then sent.
The aforementioned data owner device is
The acquired ciphertext search query is decrypted with the third secret key.
A secure search system characterized by the following features. The confidential search system according to claim 2,
The data owner device and the data administrator device are
Store the third private key,
The aforementioned data administrator device is
The aforementioned ciphertext search query is encrypted with the third secret key and then sent.
The aforementioned data owner device is
The acquired ciphertext search query is decrypted with the third secret key.
A secure search system characterized by the following features. The confidential search system according to claim 3,
The data owner device and the data administrator device are
Store the third private key,
The aforementioned data administrator device is
The aforementioned ciphertext search query is encrypted with the third secret key and then sent.
The aforementioned data owner device is
The acquired ciphertext search query is decrypted with the third secret key.
A secure search system characterized by the following features. The confidential search system according to claim 4,
The data owner device and the data administrator device are
Store the third private key,
The aforementioned data administrator device is
The aforementioned ciphertext search query is encrypted with the third secret key and then sent.
The aforementioned data owner device is
The acquired ciphertext search query is decrypted with the third secret key.
A secure search system characterized by the following features. The confidential search system according to claim 5,
The data owner device and the data administrator device are
Store the third private key,
The aforementioned data administrator device is
The aforementioned ciphertext search query is encrypted with the third secret key and then sent.
The aforementioned data owner device is
The acquired ciphertext search query is decrypted with the third secret key.
A secure search system characterized by the following features. The confidential search system according to claim 6,
The data owner device and the data administrator device are
Store the third private key,
The aforementioned data administrator device is
The aforementioned ciphertext search query is encrypted with the third secret key and then sent.
The aforementioned data owner device is
The acquired ciphertext search query is decrypted with the third secret key.
A secure search system characterized by the following features. A secure search system according to claim 1,
The aforementioned data owner device is
Equipped with a display,
Based on the list of ciphertext search queries obtained, the content related to the data search execution by the data user device is displayed on the display.
A secure search system characterized by the following features. A confidential search system according to claim 13,
The aforementioned data owner device is
We will keep a record of the terms and conditions that define the scope of data use.
Regarding the content of data retrieval execution by the data user device that does not comply with the aforementioned regulations, or whose compliance is not clear, an alert message will be displayed on the display.
A secure search system characterized by the following features. A confidential search method using a data owner device, a data user device, a data administrator device equipped with a first database, and a monitor device equipped with a second database,
The aforementioned confidential search method is:
This method uses symmetric-key cryptography and includes a registration phase, a search phase, and a reporting phase.
The aforementioned registration phase is
The user of the data owner device encrypts the data they possess with a first secret key, entrusts it to the data administrator device along with the owner ID of the data owner device, and stores the entrusted data in the first database.
The user of the data owner device entrusts the data user device with the first private key and a search key for searching for ciphertext data associated with the first private key,
The steps include: the user of the data owner device in advance contacts the monitoring device with the owner ID of the data owner device and information of the reporting destination; and stores the contacted information in the second database which records a search log and includes the owner ID of the data owner device, contact information for the user of the data owner device, and queries as entries;
The aforementioned search phase is,
The data user device sends a ciphertext search query, which is the search query encrypted with the search key, to the data administrator device when performing a search.
When the data administrator device receives the ciphertext search query, it extracts ciphertext data matching the ciphertext search query from the first database, and sends the owner ID of the data owner device associated with the ciphertext data and the ciphertext search query as a set to the monitor device.
The monitoring device, upon receiving data from the data administrator device, includes the step of registering the ciphertext search query in the second database using the owner ID of the data owner device as the key.
The aforementioned reporting phase is,
The monitoring device extracts a list of ciphertext search queries associated with the owner ID from the search logs accumulated in the second database after a period of time, and sends it to the data owner device.
The data owner device includes the step of obtaining a list of received ciphertext search queries,
A confidential search method characterized by the following features.