Secure search system, secure search method

Abstract

To grasp whether data is appropriately used on a data user device to provide a contribution from a social viewpoint.SOLUTION: In a secret information processing system, a secret retrieval data administrator device stores both cipher text data obtained by encryption using a first secret key and an owner ID of a data owner device in a first database. A data user device stores a first secret key and a retrieval key that is associated with the first secret key and used for retrieval of cipher text data. A data monitor device stores both the owner ID and information on a report destination, in a second database. The data user device transmits a cipher text retrieval query obtained by encryption by the retrieval key, to the data administrator device. The data administrator device transmits, when receiving the cipher text retrieval query, both the owner ID associated with the cipher text data and the cipher text retrieval query to the monitor device. The monitor device registers the cipher text retrieval query and transmits a list of cipher text retrieval queries; and the data owner device obtains the list of cipher text retrieval queries.SELECTED DRAWING: Figure 8

Description

Technical Field

[0005]

[0001] The present invention relates to a confidential search system and a confidential search method.

Background Art

[0002] With the expansion of computer capabilities and the progress of information processing technology, data analysis, which obtains useful insights by aggregating and analyzing data owned by multiple companies and individuals, has come to play an important role in social operations. On the other hand, since a large number of these data contain sensitive information, there are many data owner devices that are negative about disclosure. As a technology that balances data utilization and the confidentiality of individual information, confidential information processing technology has been researched and developed. As one aspect of confidential information processing technology, there is a confidential search technology that searches encrypted data without decrypting it. Confidential search technology is a technology specialized in the basic search function in information processing, and it is assumed that a data owner device entrusts the storage of data to a data management device such as cloud storage and appropriately extracts and uses necessary data.

[0003] For example, Patent Document 1 discloses a method of taking a trace of processing for confidential calculation based on secret sharing technology.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] 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 risks using the data beyond the scope authorized by the data owner's device.

[0006] Therefore, the present invention aims to provide a confidential search system and a confidential search method that can determine whether the data usage of a data user device is appropriate and contribute from a social perspective (i.e., from a security perspective). [Means for solving the problem]

[0007] 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. When the data administrator device receives the ciphertext search query, it extracts the ciphertext data that matches the ciphertext search 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 monitor device. The second database includes entries for the owner ID of the data owner device, the reporting destination, and the ciphertext search query, which are recorded as search logs. When the monitor device receives data from the data administrator device, it 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 monitor 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 monitor device.

[0008] 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 a query as entries and records a search log. The search phase includes the steps of: the data user device sending a ciphertext search query, which is the search query encrypted with the search key when the search is executed, to the data administrator device; 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 pair to the monitor device; and when the monitor device receives data from the data administrator device, it registers 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. [Effects of the Invention]

[0009] According to the present invention, a confidential search system and a confidential search method are provided that can determine whether the data usage of a data user device 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. [Brief explanation of the drawing]

[0010] [Figure 1] A diagram showing an example of the configuration of a confidential information processing system. [Figure 2] A diagram showing an example of a typical computer configuration. [Figure 3] A schematic diagram illustrating the roles of entities. [Figure 4] A diagram illustrating the details of the data owner's device. [Figure 5] A diagram illustrating the details of the data management device. [Figure 6] A diagram illustrating the details of the data user device. [Figure 7] A diagram illustrating the details of the monitoring device. [Figure 8] A diagram illustrating an example of the processing performed by a confidential information processing system. [Figure 9] A diagram illustrating an example of a report format. [Modes for carrying out the invention]

[0011] 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," "XX list," 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, and 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, when 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 dedicated circuits that perform specific processing. Here, dedicated circuits include, for example, FPGAs (Field Programmable Gate Arrays), ASICs (Application Specific Integrated Circuits), CPLDs (Complex Programmable Logic Devices), 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.

[0012] In this embodiment, a confidential information processing system (confidential 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 realize such a confidential search.

[0013] 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).

[0014] Next, an example of the configuration of the computer used in the system will be described while referring to FIG. 2. The computer (201) is a general computer and includes a CPU (211), a memory (212), a storage (220), and a communication interface (230). The CPU (211) executes operations and is the main body for executing predetermined processing. The memory (212) temporarily stores the operation results. The CPU (211) reads data from the memory (212) and executes processing. The storage (220) stores data in the long term. The communication interface (230) is connected to the network (105) by wire or wirelessly and is used for communication via the network (105). In this embodiment, an example in which the CPU (211) is used as the processor is described, but as long as predetermined processing can be executed, a semiconductor device different from the CPU may be used.

[0015] In this embodiment, the communication between the two parties is encrypted by the communication path encryption function (240) so that other entities cannot eavesdrop. This communication path encryption may use general TLS (Transport Layer Security) or the like.

[0016] Next, while referring to FIG. 3, the roles of each entity will be described. The data owner device (101) is the device of the owner of the data (301). The data owner device (101) may be an individual device or a corporate device having customer data or the like. The data manager device (103) stores the data (301) entrusted by the data owner device (101) in an encrypted state, executes a search in response to a request from the data user device (102), and answers the data user device (102) with the search result. The data user device (102) is an entity that has received permission from the data owner device (101) within a certain range regarding the use of the data (301). When using the data (301), the data user device (102) transmits a query that extracts the information necessary as a search request to the data manager device (103), and decrypts and uses the ciphertext that is the search response from the data manager device (103). The monitor device (104) monitors the search of the data user device (102) and reports the result to the data owner device (101).

[0017] Next, while referring to FIG. 4, the functional configuration of the data owner device and an example of the information held by the data owner device will be described. FIG. 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).

[0018] The computer used by the data owner device (101) includes, in addition to the functions of a general computer 201, a key generation function (401) and a confidential search data encryption function (402) that encrypts the data to be protected by a confidential information processing system and outputs ciphertext data (451). Also, in the storage (220), the data (301) to be protected and the convention (411) that defines the scope of use of the data are stored. Also, the secret key 1 (421), secret key 2 (422), secret key 3 (423) generated using the key generation function 401, the search key 1 (431) associated with the secret key 1 (4, the owner ID (441), and the contact address (442) are stored.

[0019] Next, with reference 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).

[0020] 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. The storage (220) contains a database 1 (510) which includes 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).

[0021] Next, with reference to Figure 6, we will explain the functional configuration of the data user device and an example of the information held by the data user device. 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).

[0022] The computer used by the data user device (102) is equipped with, in addition to the functions of a general computer (201), a secure search query encryption function (601) that encrypts queries in secure searches and outputs ciphertext queries (651), 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 the search key (631) received from the data owner device (101).

[0023] Next, with reference 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).

[0024] The computer used by the monitoring device (104) has, in addition to the functions of a general computer (201), an owner ID verification function (701) for verifying the owner ID. In the diagram, this is referred to as the user ID verification function. The storage (220) also stores a database 2 (710) containing user contact information (712) and ciphertext queries (713) encrypted with secret key 3, which are linked to the owner ID (711), as well as the secret key 2 (722) received from the data owner device (101).

[0025] 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.

[0026] 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).

[0027] The data owner device (101) generates a private key 1 (421) and its associated search key 1 (431) using its key generation function (401), sends 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).

[0028] The data owner device (101) generates a secret key 2 (422) using the key generation function (401) and stores it in the storage (220). It also sends the secret key 2 (422), the owner ID (441) of the data owner device (101), and the reporting address (442) of the data owner device (442) to the monitoring device (104). The monitoring device (104) stores the received secret key 2 (722), the owner ID (441) of the data owner device (101), and the reporting address (442) of the data owner device (442) in the storage (220) (registration step 3).

[0029] The data owner device (101) generates a private key 3 (423) using the key generation function (401) and sends 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).

[0030] The data owner device (101) encrypts the data (301) using the confidential search data encryption function (402) and secret key 1 (421) to generate ciphertext data (451). It also encrypts the owner ID (441) using secret key 2 (422) to generate 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) associates the received ciphertext data (451) and ciphertext ID (452) with the secret key 3 (523) received in registration step 4 and stores them in database 1 (510) (registration step 5).

[0031] 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).

[0032] 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 ID (512) that match the search 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).

[0033] The monitoring device (104) transmits the received ciphertext data (511) to the data user device (102) (search step 3).

[0034] 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).

[0035] The data user device (102) decrypts the received ciphertext data (511) with the secret key 1 (621), and the user of the data user device (102) uses the data (search step 5).

[0036] Next, the reporting phase will be explained. For each data owner device, 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, 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).

[0037] 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).

[0038] According to this embodiment, the only information the data user device (102) can access is partial information of the data obtained as a search result. Furthermore, since the search content is known to the data owner device (101), it is considered that the unlimited use of the data (301) by the data user device (102) can be deterred. 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 encryption. In addition, the monitor device (104) receives encrypted search queries and owner IDs, but since the search queries themselves are encrypted, it is not possible to obtain any useful information.

[0039] The following may also be done. 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) sends the generated secret key 1 (421) to the data owner device (101). Furthermore, 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).

[0040] Furthermore, in this embodiment, in search step 1, the data user device (102) sends the ciphertext query (651) to the data administrator device (103). However, the data user device (102) may also send 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 send the ciphertext data (511) to the data user device (102). In this case, the sending of the ciphertext data (511) by the monitor device (104) to the data user device (102) in search step 103 may be omitted.

[0041] 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).

[0042] Furthermore, in this embodiment, if there are multiple data user devices, in search step 1 of this embodiment, the data user device (102) may send 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 send it to the monitor device (104), and the monitor device (104) may send the ID information of the data user device encrypted with the secret key 3 (523) along with the 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 check whether there has been data usage beyond the scope of the license for each data user device.

[0043] Next, an example of the report format will be described with reference to Figure 9. Figure 9 shows an example of the display of a 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 is further equipped with a display (910) for displaying information and a search query determination function (920) for determining whether the search query conforms to the rules.

[0044] 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).

[0045] 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.

[0046] 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.

[0047] 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. In search step 2, the data administrator device (103) may also add to the transmission information at the time of reception.

[0048] 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 in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment 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.

[0049] 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 obtained from a storage medium of an external device via a network, portable storage medium, etc. [Explanation of Symbols]

[0050] 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

1. 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 entries for the owner ID of the data owner device, the reporting destination, and the ciphertext search query, which are recorded as a search log. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

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