KR100839220B1 - Method for searching encrypted database and System thereof - Google Patents

Abstract

An encrypted database retrieval method and system are disclosed.

According to the present invention, when an authenticated user inputs a document and a representative keyword for the document, the document is encrypted with a document encryption key, the representative keyword is encrypted with a search key, and an index is generated. Transmitting to the server, when a user authenticated by an arbitrary client inputs a keyword for a document to be searched, generating a trap door using the input keyword and the user's search key and querying the server; and Retrieving an encrypted document using the trapdoor and an index stored in the server, and transmitting the retrieved document to the client.

According to the present invention, it is possible to apply an encryption technique to a database and at the same time enable efficient retrieval, prevent leakage of information to prevent misuse of information, and provide hierarchical access rights.

Description

Method for searching encrypted database and system

1 is a block diagram of an encrypted database search system in accordance with the present invention.

2 is a flowchart of an encrypted database search method according to an embodiment of the present invention.

3 is a flowchart of an encrypted database search method according to another embodiment of the present invention.

4 is a flowchart of an encrypted database search method according to another embodiment of the present invention.

TECHNICAL FIELD The present invention relates to server and client systems, and more particularly, to a method and system for searching encrypted databases.

In an information society, the management of the database, the repository of the information, is of paramount importance. The most practical way to protect sensitive and private information is the encryption of the database that stores it. The encryption method provided by commercial modules up to now is mostly a form of searching a keyword after reading and decrypting an encrypted document, and information leakage by an internal administrator is pointed out as another problem in this decryption process. In addition, the biggest reason why the encryption method was not practical until now was that the efficient data retrieval was not guaranteed on the encrypted database, and the study for this was limited to the safety-oriented theoretical study for individual users, which was somewhat far from realistic. will be. That is, the research so far started with Song et al.'S research on the system for retrieving the entire document based on the symmetric key in 2000. After that, the system searched using the index created by encrypting the keyword of the document. As research has become mainstream, its main purpose has been to prove its safety.

However, efficient retrieval of encrypted documents is the most necessary technique for protecting sensitive information as well as personal information. Therefore, what is urgently needed is to build a searchable system without decrypting encrypted documents, which must be not only secure but also commercially available, and suitable for documents for organizational group management as well as private secret documents. . Since mass storage media such as USB are commonplace today, it is not necessary to encrypt and store individual secret documents in a database, but it is possible to encrypt and store secret information shared by members in an organization and store it on a server, which can be retrieved and updated from time to time. Because this is more realistic.

However, the design of an encrypted search system in such a group environment is not so simple. Because the group is a dynamic environment in which subscribers can freely enter or leave the subscriber, the group key used for encryption has a property that must be updated for its security whenever membership changes. In addition, an encrypted search system in a group environment requires the following security requirements. First, the withdrawing member must be inaccessible to all documents related to the group, and newly joined members must be able to search both the current document and the previous document for that group. A solution to this would first be to decrypt all the documents in the group and re-encrypt them with the updated key. However, this process requires a great deal of computation.

Therefore, an efficient retrieval system in a group environment should allow new subscribers to search for previous documents without re-encryption of existing documents in the situation of membership change, and those who withdraw should not be able to access subsequent documents.

Park et al. First proposed a retrieval scheme for this group environment using the unidirectional hash function keychain inversely. However, this scheme does not satisfy forward secrecy. In other words, if one of the opt-outs tells the server the group key he knew, the server can decrypt both the document as well as the previous one, which means a complete system crash.

Goll et al. Proposed a conjunctive search, but the entire document must be updated with each search. Their scheme provides the security for 'query isolation' (the server does not know any information about the plain text other than the search results from the accumulated results) that the previous research did not provide, and implements the perfect security that the crypto search system should have. It was. However, in order to achieve this, there is an inefficient aspect of updating every document every search.

In addition, Ballad et al. The search scheme using the pairing function of takes 720 seconds (720000 ms) to search 10,000 indexes. This is a performance that is never commercially available. This performance is not only due to the amount of computation of the pairing function, but also due to problems with the server's database storage structure and the retrieval process itself.

Therefore, the conventional method of retrieving encrypted documents cannot prevent information leakage of internal administrators, is not suitable for documents for group management of an organization, all documents must be updated every time the documents are retrieved, and problems in data storage structure are required. There is an inefficient problem due to the impossibility of applying DB schema due to problems of search procedure due to encryption and encryption.

Accordingly, the first technical problem to be achieved by the present invention is to minimize the inefficiency in retrieving encrypted documents, to enable efficient retrieval while applying encryption techniques to the database, and to prevent information leakage and misuse of information by preventing information leakage. In addition, it provides an encrypted database search method that enables hierarchical access to systematically manage information and enable efficient data retrieval.

The second technical problem to be achieved by the present invention is to provide an encrypted database search system to which the encrypted database search method is applied.

In order to achieve the first technical problem, when the authenticated user inputs a document and a representative keyword for the document, the present invention encrypts the document with a document encryption key and encrypts the representative keyword with a search key to generate an index. Transmitting the encrypted document and the index to the server, when a user authenticated by an arbitrary client inputs a keyword for a document to be searched, generates a trap door using the input keyword and the search key of the user. And querying the server and retrieving the encrypted document using the trapdoor and the index stored in the server, and transmitting the retrieved document to the client.

In addition, in order to achieve the first technical problem, the present invention comprises the steps of an authenticated user inputs a document and a plurality of keywords for the document, encrypting the document with a key for document encryption, any keyword from the plurality of keywords Constructing a merged search term for a simultaneous search and encrypting the plurality of keywords and the merged search term with a search key to generate an index, transmitting the encrypted document and the index to the server, When a user authenticated in the client inputs a keyword for a document to be searched, a trap door is generated by encrypting the plurality of keywords and the merged keyword with the user's search key and a randomly generated random number. Querying the server and at the server the trapdoor and the server A method of searching an encrypted database, the method comprising: searching for an encrypted document using an index stored in and transmitting the retrieved document to the client.

In addition, in order to achieve the first technical problem, the present invention comprises the steps of an authenticated user inputs a document and a plurality of keywords for the document, encrypting the document with a document encryption key, and encrypting the plurality of keywords with a search key Generating an index, transmitting an identifier for the encrypted document, the encrypted document, and the index to the server, generating a first list of matching the index and the identifier at the server; Generating a second list of matching encrypted documents; when an authenticated user inputs a keyword for a document to be searched by an arbitrary client, a trap door is generated by encrypting the input keyword with the search key of the user; Querying a server and using the first list and the second list at the server W provides an encrypted database, the search method comprising the trap retrieve encrypted document door points and transmits the retrieved document to the client.

In order to achieve the second technical problem, the present invention provides a database retrieval system including a plurality of clients and servers, wherein the database retrieval system sets a security policy to be used, user ID, password, key for document password and retrieval key. Generate and store in a key matching table, the group manager periodically transmitting the key matching table to a client of each user, wherein the client is authorized by the key matching table to represent the document and the document. If a keyword is inputted, the document is encrypted with a key for document encryption, the representative keyword is encrypted with a search key to generate an index, and is authenticated by an uploading unit for transmitting the encrypted document and the index to the server and the key matching table. To the document you want to retrieve. When a keyword is input, a search unit is generated to query the server by generating a trap door using the input keyword and the search key of the user, and the server is a protocol contracted using the trap door and the index stored in the server. It provides an encrypted database retrieval system, characterized in that for retrieving the document encrypted by the transmission and transmitting the retrieved document to the client.

As mentioned above, the present invention aims to design a fully encrypted retrieval system. A system that encrypts a database that stores sensitive information and makes it possible to query and search by encrypted search terms without decrypting it. This is unreliable because the server administrator does not know what search terms the user is searching for. The server administrator can prevent the user's information from leaking out arbitrarily.

Next, the present invention aims to design a multipurpose search system in a group environment. The existing one-to-one relationship between users and servers has been extended to many-to-one to solve the problem of the search system in the group environment due to the membership change described above. In addition, by designing a multipurpose retrieval system that enables the retrieval of both private and private documents and group members' secret documents, it also grants access by configuring retrieval systems using different encryption keys.

Finally, the present invention aims to provide a variety of functions and compatible efficiencies. According to the organization's policy, it is possible to select an ideal security system for managing top secrets such as top secrets and an efficient search system that is commercially suitable in a somewhat less secure but realistic environment. An efficient search system that can be used commercially must overcome the inefficiency of the search system due to encryption. For this purpose, an efficient search system must be applicable to the DB schema. And it should be a search system capable of efficient simultaneous search.

The present invention relates to a method and system for searching for a desired document using an encrypted keyword without decrypting the encrypted document.

Scenario of the present invention to store the encrypted p _j is a member of the group shared secret document D ₁ in the g _i sub-group of huge hierarchical organization of the group to a server and retrieve the D ₁ using the keyword w _1. At this time, the following four processes.

First is the setup process. The group manager (GM) determines the function and variable size, key size, etc. to be used in the retrieval system. In addition, the group manager performs registration of users. Each group member and individual user generates an ID, a password, a document password key, and a retrieval key and stores them in a key matching table. The group manager sends a keymatching table to the client program of each user.

Second is the authentication process. The user login may be performed by inputting an ID and password in an input window and scanning whether a value matching it is in a key matching table in the client program. In the case of successful authentication, the document encryption key and the search key of the user encrypted with the client secret key are decrypted.

Third is the uploading process. The user enters the document and a representative keyword of the document. The client program encrypts the document input by the user with the decrypted user's document encryption key and search key, encrypts the keyword with the search key, and generates an index and transmits the index to the server.

Fourth, the search process. When user authentication is completed and the authenticated user inputs a keyword to search, the client generates a query word (trap door) using the keyword and the user's search key and queries the server. The server performs the test process using the query and sends the document to the client. The client decrypts the received document and outputs it to the user's monitor.

Hereinafter, with reference to the drawings will be described a preferred embodiment of the present invention. However, embodiments of the present invention illustrated below may be modified in many different forms, and the scope of the present invention is not limited to the embodiments described below.

1 is a block diagram of an encrypted database search system in accordance with the present invention.

The encrypted database search system according to the present invention includes a group manager 100, a plurality of clients 110-180, and a server 190.

The group manager 100 sets a security policy to be used in the system, generates user IDs, passwords, document encryption keys, and search keys and stores them in the key matching table, and stores the key matching table in real time or periodically for each client of the user. Send it to (110-180).

The client 110 includes a client program, which includes an authenticator 111, an uploader 112, and a searcher 113.

The authenticator 111 authenticates a user accessing the client 110. For example, the authentication unit 111 may authenticate a user by inputting an ID and a password into an input window and scanning whether a value matching the input ID and password exists in a key matching table in the client program. The authentication unit 111 authenticates individual user and group membership using the ID and password of the key matching table.

When the user authenticated by the key matching table inputs a representative keyword for a document and a document to be uploaded, the uploading unit 112 encrypts the document with a key for document encryption and generates an index by encrypting the representative keyword with a search key. In addition, the uploader 112 transmits the encrypted document and the index to the server 190.

When the user authenticated by the key matching table inputs a keyword for a document to be searched, the search unit 113 generates a trap door using the input keyword and the user's search key and queries the server 190.

The server 190 retrieves the encrypted document using the trapdoor and the index stored in the server and transmits the retrieved document to the client 110. For example, the server 190 retrieves the encrypted document from the database 191 using a database 191, a trapdoor and an index for storing the encrypted document and the index, and retrieves the retrieved document from the client 110. It may include a server search unit 192 for transmitting to. In this case, the database 191 may use a VLDB.

2 is a flowchart of an encrypted database search method according to an embodiment of the present invention.

First, when an authenticated user inputs a representative keyword for a document and a document, the input document is encrypted with a document encryption key, the representative keyword is encrypted with a search key, an index is generated, and the encrypted document and index are transmitted to the server ( 210 courses).

Next, it is determined whether an authenticated user inputs a keyword for a document to be searched by an arbitrary client (operation 220).

If a keyword is input, a trapdoor using the input keyword and the user's search key is generated and inquired to the server (step 225). On the other hand, if a keyword is not entered, the authenticated user waits until the user inputs the keyword or completes another task (step 220).

Finally, the server retrieves the encrypted document using the trapdoor and the index and transmits the retrieved document to the client (step 230).

Preferably, the encrypted database search method according to an embodiment of the present invention may further include a process of the client decrypting the document received from the server with a key for the document encryption of the user. In this case, the method may further include outputting the decrypted document to the user's monitor.

In the present invention, an encrypted document retrieval system is designed in a group environment in consideration of a more realistic environment. Overcoming the aforementioned problems of Goll et al, we propose an SSIS designed scheme in a group environment in which safety is maintained as best as their scheme. We propose ESIS, an encrypted DB retrieval system optimized to be commercially viable by breaking away from the conventional scheme. Both of these schemes consist of four steps (setup, authentication, uploading, and search) in the above figure.

는 그룹 i의 s번째 세션의 그룹키,

는 그룹 i의 검색키(인덱스 생성키)이다.

는 그룹 i의 문서 암호용 키이다. 즉, 문서의 암호와 인덱스 생성에 쓰이는 키를 달리한다.

는 개인 사용자

의 개인키,

는 사용자

의 검색키,

는 개인 사용자

의 문서 암호용 키,

는 사용자 j의 아이디,

는 n번째 문서,

는 문서

의 식별자,

는 n번째 문서

의 t번째 키워드,

는 n번째 문서

의 t번째 인덱스,

는 클라이언트 프로그램의 비밀키,

는 q번째 쿼리에 생성된 난수이다.The symbols used below are defined as follows.

Is the group key of the sth session of group i,

Is the search key (index generation key) of group i.

Is the key for document encryption in group i. In other words, the key used to create the document's password and index is different.

An individual user

'S private key,

Is a user

'S search key,

An individual user

Keys for document encryption,

Is the id of user j,

Is the nth document,

Document

Identifier of,

Is the nth document

T keyword of,

Is the nth document

T index of,

Is the secret key of the client program,

Is a random number generated in the qth query.

An encrypted database search method according to another embodiment of the present invention, that is, Secure Searchable Index Schemes (SSIS) is configured as follows.

First, the setup process. The group manager determines the security policy, including the functions, variables, and key sizes to be used in the retrieval system, and the registration process of the users is made. The keys generated in this process are stored in the form of a key matching table, which is then sent back to the client program of each user.

Table 1 shows an example of a key matching table.

ID PW Search key Document encryption key ID ₁ , ID ₂ , ID ₃ ...... h (PW ₁ ) E _kc (K ₁ ) E _kc (R ₁ ) ID ₃₅ , ID ₃₆ , ID ₃₉ ..... h (PW ₂ ) E _kc (K ₂ ) E _kc (R ₂ ) ............ .... ..... ....... ID ₂₅₁ , ID ₂₅₃ , ID ₂₇₄ ..... h (PW ₁₁ ) E _kc (K ₁₁ ) E _kc (R ₁₁ ) ............. .... ..... ...... ID ₂ , h (pw ₂ ) E _kc (k ₂ ) E _kc (r ₂ ) ID ₅ , h (pw ₅ ) E _kc (k ₅ ) E _kc (r ₅ ) ...... .... ........ .......

Next is the authentication process. This is a process of authenticating whether a login user is a valid user registered in advance.

Next, an uploading process. The user who successfully authenticates enters the documents to upload and keywords for the documents, and the client program encrypts them, creates an index, and sends them to the server.

SSIS constructs an index using t keywords for each document, and forms meta-keywords by extracting r of t for conjunctive search. For example, if the number of keywords t is 7 and r is 3, there are 7 single keywords, 21 two keywords ( ₇ C ₂ ), and 35 three keywords ( ₇ C ₃ ). It will form an index string. The index string construction method is shown in Equation 1 below;

Next, the search process includes a trapdoor generation stage and a test and search stage.

First, the trapdoor generation step will be described. The trapdoor is a query word that requests a search by encrypting a keyword with a user's search key (secret key). The algorithm Trapdoor outputs T _w = (T ₁ , T ₂ ).

An example of trapdoor generation in SSIS is shown in Equation 2 below.

는 매 쿼리시 마다 새롭게 랜덤하게 생성되어지는 값이고, 트랩도어는 모듈 연산으로 연산되어진다. 때문에 서버는 다음과 같은 사실을 알 수 없다 ; 1)쿼리된 키워드가 이전에 쿼리되어졌던 키워드와 같은 것인지, 2)쿼리에 사용된 검색키 K_i가 이전 질의자의 키와 같은 것인지, 비록 같은 그룹의 멤버가 같은 키 워드를 검색했을지라도 서버는 그 사실을 알 수 없다. 이것으로 인해, 서버는 축적된 결과들로부터 어떤 새로운 사실을 알아낼 수 없어 암화화된 검색 시스템 상에서 완벽한 안전성을 제공할 수 있다. here

Is a new randomly generated value at every query, and trapdoor is calculated by module operation. Because of this, the server cannot know the following facts; 1) whether the queryed keyword is the same as the one that was queried previously, 2) the search key K _i used in the query is the same as the key of the previous query, even if members of the same group searched for the same keyword. It is not known. Because of this, the server cannot learn any new facts from the accumulated results and can provide complete security on the encrypted search system.

Next, the test and search stage will be described. For every n = {1,2, ..., n}, the server uses the following equation (3) using the trapdoors received and the identifiers (id ₀ and id ₁ ) in the index string of each document: The operation will retrieve the document.

을 클라이언트에게 리턴한다.The server checks if there is something in the index string that equals this result computed for each document, and if so, the ciphertext.

To the client.

가 연산후 결과값에는 존재하지 않는다)에 의해서 Golle의 스킴처럼 검색시마다 문서 전체를 업데이트하는 과정 없이도 'query isolation'을 제공할 수 있다.In this way, an efficient test configuration ( randomly generated in the trapdoor

Is not present in the result after the operation), as in Golle's scheme, we can provide 'query isolation' without the need to update the entire document on every search.

을 문서암호용키 R_i를 사용하여 복호화하고, 그 결과를 사용자의 컴퓨터에 출력한다.Finally, the output stage is as follows. Client received cipher text

Is decrypted using the document encryption key R _i and the result is output to the user's computer.

3 is a flowchart of an encrypted database search method according to another embodiment of the present invention.

First, an authenticated user inputs a document and a plurality of keywords for the document (step 310). Next, the input document is encrypted with a document encryption key, an arbitrary keyword is extracted from the plurality of keywords to form a merged search term for simultaneous search, and the index is generated by encrypting the plurality of keywords and the merged search term with the search key ( 315 courses).

Next, the encrypted document and the index are transmitted to the server and uploaded (step 317).

When the upload is completed, it is determined whether an authenticated user inputs a keyword for a document to be searched by an arbitrary client (step 320). When the keyword is input, the input keyword is encrypted with the user's search key to generate a trap door for the plurality of keywords and the merged search word, and the server is queried with the trap door (step 325).

Finally, the server retrieves the encrypted document using the trapdoor and the index and transmits the retrieved document to the client (step 330).

An encrypted database search method according to another embodiment of the present invention, that is, ESIS (Efficient Searchable Index Schemes) is configured as follows. The scheme progression also describes the uploading and retrieval steps as the preparation and authentication steps are the same as for SSIS.

First, the uploading process will be described as follows. Unlike SSIS, ESIS does not create indexes for merge keywords (meta-keywords) and instead uses the intersection algorithm for simultaneous searches. The cipher text and the index generation method may use Equation 4 below.

When the client program sends the document to be uploaded by the user to the server as above, the server creates the index list as follows. In other words, ESIS consists of two databases, where d _n serves not only as a document identifier but also as an address.

In this way, because the structure of the index list is created, an efficient DB schema using primary and foreign keys can be applied.

An example of the structure of the generated index list is shown in Table 2.

index Document identifier Document identifier Encrypted document

..... .... ..... .....

... .... ..... .....

..... .... .... .....

...... .... ..... ......

...... ....

Hereinafter, the index list shown on the left side of Table 2 is defined as the first list, and the encrypted document shown on the right side is defined as the second list.

Next, a search process, which includes a trapdoor generation stage, a test and search stage.

First, the trap door generation step generates a trap door as shown in Equation 5 below.

Next, the test and search phase scans the server for a value equal to that in the index list when the server receives the trapdoor. If it does, find the corresponding document identifier in the table on the right and return the corresponding encrypted document. If there are two or more conjunctive searches, the first keyword is searched, then the second keyword is searched only for the index corresponding to the result, and only the common result is stored, and the next keyword is used only for this common result. Search for. After doing this for the keywords that were queried, only the final result is returned to the user. In other words, a simultaneous search is performed through an intersection operation.

Finally, in the output stage, the client program decrypts the cipher text received from the server with the user's document encryption key and outputs the result to the user.

4 is a flowchart of an encrypted database search method according to another embodiment of the present invention.

First, a user inputs a plurality of keywords for documents and documents to be uploaded (step 410). Next, the input document is encrypted with a document encryption key, a plurality of keywords are encrypted with a search key to generate an index, and an identifier, an encrypted document, and an index for the encrypted document are transmitted to the server (step 415).

When the upload is completed, the server generates a first list that matches the index and the identifier, and generates a second list that matches the identifier and the encrypted document (step 417). In this case, the relational DB is constructed by declaring the index and identifier of the first list as a 'primary key' and declaring the identifier of the second list as a 'foreign key' to apply a DB schema.

Next, it is determined whether an authenticated user inputs a keyword for a document to be searched by an arbitrary client (operation 420). If a keyword is input, a trapdoor in which the input keyword is encrypted using the user's search key is generated and the server is queried (step 425).

Finally, the server searches for the encrypted document indicated by the trapdoor using the first list and the second list, and transmits the retrieved document to the client (step 430).

The present invention relates to a system that enables retrieval without decrypting a document encrypted using an encryption key.

The present invention relates to an index search system using keywords. Treat server administrators as untrusted internal attackers In order to build a secure system from such an internal attacker and an external grid, each document is encrypted, and key documents representing each document are extracted and encrypted to create an index corresponding to the document. When searching, the query is encrypted by query, and the server tests whether the index corresponding to the query belongs to the document and returns the document to the user.

The present invention relates to a commercially suitable algorithm considering security and functionality at the same time. The present invention uses an encryption technique using an encryption key for secure information management. In addition, access is granted through authentication process as a login group member and individual user. The server administrator can not know the contents of the document because it can be searched without decryption at the server side. SSIS is an algorithm that improves the highest security and efficient aspect of a password retrieval system.

The present invention can be linked to a commercial DB. ESIS speeds up the search by designing the DB schema used for general commercial databases to be used in an encrypted search system. Concurrent search (document search that includes two or more search terms) is possible without using the pairing function.

The present invention relates to a multipurpose system. It extends from a one-to-one search system where the relationship between a user and a server is 1: 1. That is, consider a large organization as a hierarchical group, and build a searchable system not only as a member of the entire group and its subgroups, but also as an individual user.

The present invention is management efficient. The group manager is responsible for key management and registration procedures for members of various subgroups of the hierarchical group. Determine key size, variables, and number of keywords in consideration of safety and functionality. It acts as a security policy maker. The client program is a type of access program in the search system. Perform a search with the server on your behalf. For this purpose, it holds a key matching table, which periodically downloads updated information from the group manager and synchronizes it. The key matching table performs an authentication function upon user login, thereby allowing access restriction. In addition, updates are easy. If there is a document that you want to encrypt and store on the server, you can update it without any limitation because you can do it in the same way as the uploading step.

The P-SSIS and P-ESIS, which are plain text versions of the schemes SSIS and ESIS, were tested together. According to Table 3, the performance of ESIS is much better than SSIS, and it is almost no difference from the plain text version. However, the first experiment without DB schema did not show such results. In the first experiments, ESIS was also very poor. So, we tried to experiment with DB schema, but SSIS had structure and search method that DB schema could not be applied. Therefore, we experimented by applying DB schema using primary key and foreign key only to ESIS. Since SSIS is a scheme that improves efficiency while maintaining the structure and search method of the previous studies, the conventional scheme was also experimented under the assumption that the conventional scheme would also perform poorly. As expected, as shown in Table 4, ESIS was about 480 times faster than Golle et al. And SSIS and about 10 times faster than Song et al.

The unit of Table 3 and Table 4 is ms.

P- SSIS SSIS P- ESIS ESIS Upload time (1 document) 54 154 28 49 Search 1-keyword 2-keyword 1-keyword 2-keyword 1-keyword 2-keyword 1-keyword 2-keyword 2500 documents 94 102 6171 14148 30 33 35 41 5000 documents 172 203 12359 28250 41 45 47 52 7500 documents 203 250 18516 42554 51 55 61 74 10000 documents 281 320 37828 57578 65 71 79 92

Number of documents Song Golle SSIS ESIS 2,500 262 8,328 6171 35 5,000 345 16,422 12359 47 7,500 608 24,453 18516 61 10,000 825 32,454 37828 79

In the above, we designed SSIS, a safety-oriented scheme, and ESIS, an efficiency-oriented scheme, and implemented both experiments and analyzed them. In this process, it can be seen how important the proper use of the schema provided by the DB in the DB search system plays an important role in the efficiency of the search system. Experiments show that the conventional schemes are not suitable for commercialization because the DB schema is not applicable. . Therefore, it can be seen that not only the efficiency of the calculation and communication of the functions used, but also the efficiency when interworking with its application layer is an important factor to consider.

Along with the implementation of NEIS and e-government, privacy has become a very important hot issue. The most reliable protection against misuse of databases used by NEIS and e-government is encryption of databases responsible for privacy and confidential information protection. The present invention can improve the competitiveness of the company, the public trust of the government, and the security reliability of service providers and financial institutions by applying encryption techniques to the database and at the same time enabling efficient search. The fact that large-scale leaks in job candidates of large Korean companies in recent years have been leaked to the Internet shows the importance of database encryption.

On the economic side, we can expect the DB industry to respond. Already in the development stage abroad, inefficiency of encryption technique is prejudice and lack of awareness of security problem, so there is no attempt to research in Korea. It seems to be able to inspire the importance of and to induce product development. In addition, such product development is expected to be used by all organizations that have databases that deal with personal and sensitive information, such as companies, hospitals, government offices, financial institutions, and service providers, and thus have a broad market. Public institutions such as corporations, public offices and hospitals deal with a lot of confidential information that should not be exposed to the outside. The present invention not only prevents information leakage by applying encryption techniques to their databases, but also provides hierarchical access rights to enable systematic management of information and efficient data retrieval, and realize an efficient retrieval system of such databases. By implementing a secure information management system, it will be the driving force of national policy development as well as economic growth in the information society.

Preferably, a program for executing the encrypted database retrieval method of the present invention on a computer may be recorded and provided on a computer-readable recording medium.

The invention can be implemented via software. When implemented in software, the constituent means of the present invention are code segments that perform the necessary work. The program or code segments may be stored on a processor readable medium or transmitted by a computer data signal coupled with a carrier on a transmission medium or network.

The computer-readable recording medium includes all kinds of recording devices in which data is stored which can be read by a computer system. Examples of computer-readable recording devices include ROM, RAM, CD-ROM, DVD ± ROM, DVD-RAM, magnetic tape, floppy disks, hard disks, optical data storage devices, and the like. The computer readable recording medium can also be distributed over network coupled computer devices so that the computer readable code is stored and executed in a distributed fashion.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary and will be understood by those of ordinary skill in the art that various modifications and variations can be made therefrom. However, such modifications should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, according to the present invention, it is possible to apply an encryption scheme to a database and at the same time enable efficient retrieval, prevent leakage of information to prevent misuse of information, and provide hierarchical access rights to systematically manage and manage information. It has the effect of enabling data retrieval.

Claims (11)

When an authenticated user inputs a document and a representative keyword for the document, the document is encrypted with a document encryption key, the representative keyword is encrypted with a search key to generate an index, and the encrypted document and the index are transmitted to the server. Making; When a user authenticated in an arbitrary client inputs a keyword for a document to be searched, generating a trap door using the input keyword and the user's search key and querying the server; And And retrieving the encrypted document using the trapdoor and the index stored in the server, and transmitting the retrieved document to the client. The method of claim 1, And decrypting, at the client, the retrieved document using the document encryption key of the user. The method of claim 2, And outputting the decrypted document to the monitor of the client. The method of claim 1, Entering the document and a representative keyword for the document Determining a security policy including a function, a variable, and a key size to be used in the retrieval system in the group manager, generating a user ID, a password, a key for a document password, and a retrieval key and storing the key in a key matching table; And Periodically transmitting the keymatching table to a client of each user. The method of claim 4, wherein Entering the document and a representative keyword for the document Authenticating a user who inputs the ID and password if the ID and password input by the user in any client exist in the key matching table; And And decrypting a document encryption key and a retrieval key encrypted with a secret key at a client of the authenticated user. Inputting a document and a plurality of keywords for the document by an authenticated user; Encrypting the document with a key for document encryption; Extracting an arbitrary keyword from the plurality of keywords to construct a merged search term for simultaneous search, and generating an index by encrypting the plurality of keywords and the merged search term with a search key; Sending the encrypted document and the index to the server; When a user authenticated in an arbitrary client inputs a keyword for a document to be searched, a trapdoor which encrypts the input keyword for the plurality of keywords and the merged search word with the user's search key and a randomly generated random number is generated. Generating and querying the server; And And retrieving the encrypted document using the trapdoor and the index stored in the server, and transmitting the retrieved document to the client. The method of claim 6, The step of transmitting the retrieved document to the client For every n = {1,2, ..., n}, the trapdoor received from the server

And the identifiers id ₀ and id ₁ in the index of each document

And if the same as the result value calculated for each document exists in the index, transmitting the corresponding encrypted document to the client. Inputting a document and a plurality of keywords for the document by an authenticated user; Encrypting the document with a key for document encryption, encrypting the plurality of keywords with a search key to generate an index, and transmitting an identifier, the encrypted document, and the index for the encrypted document to the server; Generating a first list in which the index matches the identifier and a second list in which the identifier matches the encrypted document; When a user authenticated in an arbitrary client inputs a keyword for a document to be searched, generating a trap door encrypted with the input keyword using the search key of the user and querying the server; And Searching for the encrypted document indicated by the trapdoor using the first list and the second list at the server and transmitting the retrieved document to the client. The method of claim 8, Retrieving the encrypted document and transmitting the retrieved document to the client When the trapdoor indicates a simultaneous search that includes two or more keywords, a simultaneous search is performed using an intersection operation that searches for the next keyword and extracts a common result only for an index corresponding to one keyword search result. And encrypting the database. The method of claim 8, Generating the second list Declaring an index and an identifier of the first list as a primary key, Declaring the identifier of the second list as a foreign key to apply a DB schema to configure a relational DB in an encrypted database Search method. In a database search system including a plurality of clients and servers, The database search system Setting a security policy to be used, generating a user ID, password, document encryption key and search key, and storing the key matching table, and including a group manager to periodically transmit the key matching table to clients of each user, The client is When a user authenticated by the key matching table inputs a document and a representative keyword for the document, the document is encrypted with a document encryption key and the representative keyword is encrypted with a search key to generate an index. The encrypted document and the Upload unit for transmitting the index to the server; And When a user authenticated by the key matching table inputs a keyword for a document to be searched, the search unit generates a trap door using the input keyword and the search key of the user and queries the server. And the server retrieves the document encrypted by the contract protocol using the trapdoor and the index stored in the server, and transmits the retrieved document to the client.

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