WO2019178792A1

WO2019178792A1 - Ciphertext search method and system supporting access control

Info

Publication number: WO2019178792A1
Application number: PCT/CN2018/079918
Authority: WO
Inventors: 张鹏; 吴楚欣; 刘宏伟; 喻建平
Original assignee: 深圳大学
Priority date: 2018-03-22
Filing date: 2018-03-22
Publication date: 2019-09-26

Abstract

A search method supporting access control, comprising: a client encrypting files of a database to obtain encrypted ciphertexts, constructing indices according to file identifiers and encrypting same, so as to obtain a ciphertext database; the client receiving a key ciphertext, a private key and a retrieval keyword set to generate a trap door; a cloud server retrieving a corresponding indexed ciphertext according the trap door; the client using the key to decrypt the indexed ciphertext, uploading the decrypted file identifier onto the cloud server to obtain an encrypted ciphertext, so as to decrypt the encrypted ciphertext, to obtain a search result; the client presenting the search result according to a preset presentation mode. The present invention uses attribute-based encryption to control the ability of a searching user to access data, while setting access control to the overall database instead of indices, thereby enabling calculation overheads taken to encrypt the database by a data owner to be greatly reduced whilst enabling a user to acquire a search trap door without the participation of the data owner.

Description

Ciphertext search method and system supporting access control

Technical field

The invention belongs to the technical field of data processing, and in particular relates to a ciphertext search method and system supporting access control.

Background technique

The emergence of cloud computing enables users to enjoy ubiquitous, convenient and on-demand network access to share configurable computing resource pools with high efficiency and minimal economic overhead. Despite the advantages of cloud services, outsourcing sensitive information (such as email, personal health records, corporate financial data, government documents, etc.) to remote servers presents privacy concerns. Once the user uploads the data to the cloud server, the user loses control of the data. The cloud service provider CSP (Cloud Service Provider) that stores the user data can access the user's sensitive information without authorization. Therefore, cloud security has become a challenge and a prerequisite for determining whether cloud storage can be more widely used. How to enjoy the cloud service brings us convenience, while maintaining the privacy of data has become an urgent issue.

In order to ensure the privacy of user data and prevent data from being stolen by unauthorized users or attackers, the most common way is to encrypt the user data and then store it in the cloud server. However, the encrypted data has already destroyed the search function of the plaintext. In the face of a large amount of encrypted data in the cloud server, how to effectively search the data required by the user has become a hot issue in current research. The searchable encryption mechanism performs the search operation of the encrypted data through the keyword query trapdoor, and the cloud server returns the encrypted file set that satisfies the query condition, and the user uses the decrypted file after the client decrypts, thereby ensuring the data confidentiality and the search function simultaneously, and realizing the secure storage. Organic unity with efficient search.

Currently, searchable encryption is mainly divided into symmetric searchable encryption and public key searchable encryption. The construction of symmetric searchable encryption is usually based on pseudo-random functions, and has the characteristics of small computational cost, simple algorithm and fast speed. Sun et al. introduced attribute-based encryption to construct a symmetric searchable encryption scheme that implements access control. The scheme first performs a fast search on ciphertext data and then controls the ability of the search user to access data, but the scheme has certain defects. On the one hand, the process of obtaining the search trapdoor requires the data owner to participate, which requires the data owner to be online at all times; on the other hand, each index corresponding to each keyword adopts an access policy, which requires a large amount of implementation. The operation can be guaranteed, which makes the data owner expensive to generate an encrypted database.

Summary of the invention

The technical problem to be solved by the present invention is to provide a ciphertext search method and system for supporting access control, which aims to solve the problem that the prior art requires the data owner to be online in real time when searching, and requires a large number of operations to ensure access control. .

The present invention is implemented in this way, a ciphertext search method supporting access control, the ciphertext search system includes a client and a cloud server, and the ciphertext search method includes:

Step A: The client encrypts the file of the database by using a preset symmetric encryption algorithm to obtain an encrypted ciphertext, and builds an index on the encrypted ciphertext according to the file identifier of the file of the database, and encrypts the index to obtain a ciphertext database including an index ciphertext, and sending the encrypted ciphertext and the ciphertext data to a cloud server;

Step B: The client receives a key ciphertext, a private key, and a search key set input when the user searches, and generates a trapdoor according to the key ciphertext, the private key, and the search keyword set, and the The trapdoor is sent to the cloud server;

Step C: The cloud server searches, according to the trapdoor, an index ciphertext corresponding to the trapdoor in a ciphertext database;

Step D: The client decrypts the index ciphertext by using a key, and uploads the decrypted file identifier to the cloud server, so that the cloud server returns the encryption key corresponding to the file identifier. And decrypting the encrypted ciphertext by using a preset symmetric encryption algorithm to obtain a search result;

In step E, the client displays the search result according to a preset display manner.

Further, the step A includes:

The client receives the database and encrypts the file in the database using a pseudo-random function to obtain the encrypted ciphertext.

Further, the pseudo-random function is PRF F: {0, 1} ^λ × {0, 1} ^λ → {0, 1} ^λ , PRP P: {0, 1} ^λ × {0, 1} ^λ → {0,1} ^λ indicates that the ciphertext database is represented by EDB, and the database is represented by DB.

Id _i ∈{0,1} ^λ represents the file identifier,

Represents the set of keywords contained in id _i , the set of keywords

The file set Doc={f ₁ ,f ₂ ,...,f _d }, the key set of the encrypted file is represented as R={r ₁ , r ₂ ,..., r _d }, defining a symmetric encryption algorithm SE=(Enc,Dec The step A specifically includes:

Encrypting f _i with r _i before constructing the index, to obtain encrypted ciphertext ct _i ←SE.Enc(r _i ,f _i )(i=1,2,...,d);

The ciphertext access control authority is set, and the encrypted ciphertext is uploaded to the cloud server, and the ciphertext access control permission scheme is an attribute-based encryption scheme ABE=(Setup, Encrypt, KeyGen, Decrypt);

Enter the system security parameter λ and the global attribute set N, the authority PKG runs (PK, MSK) ← ABE.Setup(1 ^λ , N);

Selecting the key k randomly for the PRF F;

Defining an empty array T of the keyword set W index;

Define XSet as an empty set;

For each w∈W, define t as an empty list and calculate the keyword ciphertext stag←F(k,w);

Initialization key k ₁ ←F(k,1||w);

For all id _i in the DB, the counter c←0 is initialized in a random order, and the index cipher rind←P(k, id _i ||r _i ) is calculated, and the encryption k _{1 is} obtained by z←P(k ₁ ,c), And define y←rind·z ^-1 , add (rind, y) to t, define xtag as the element of XSet, calculate

And add xtag to XSet, c←c+1, T[stag]←t;

Calculate the ciphertext C←ABE.Encrypt(PK,k,Γ) and get EDB=(XSet,T,C), where Γ is the access policy.

Further,

Representing the search keyword set,

The key ciphertext is represented by C, the private key is represented by SK, and the trapdoor is represented by stag, xtoken[1], xtoken[2], ..., in step B, the user pair of the attribute set is S Keyword collection

To perform the search, step B specifically includes:

The client generates a private key SK←ABE.KeyGen(MSK,S) according to the attribute S of the user;

Calculating a key k according to the key ciphertext and the private key;

Determining that the attribute S of the user satisfies the access policy of the ciphertext database. If yes, the decryption succeeds k←ABE.Decrypt(C,SK), and the key k is obtained. If not, the decryption fails;

Generating a keyword ciphertext stag←F(k, w ₁ ), and generating a key k ₁ ←F(k,1||w ₁ );

When i=2,...,n, calculate the trapdoor element

The trapdoor is obtained, namely: xtoken[c]←(xtoken[c,2], xtoken[c,3],...,xtoken[c,n]).

Further, a set of the index ciphertext is represented by l, and step C includes:

Define l, t is an empty set;

Determine whether the equation T[stag]=stag is true, if it is established, then t=T[stag]; if not, return an empty set;

For c=1, 2,...,|t|, retrieve from the c-th tuple in t (rind, y), if

Then l←l∪rind.

Further, the step D includes:

The client decrypts the set l of the index ciphertext using the key k, obtains the file identifier id _i and the corresponding key r _i ; for the rind ∈ l, calculates (id _i ||r _i )←P ^-1 (k , rind), get the search results (id _i , r _i );

Id _i sends to the server cloud, the cloud server returns the obtained _{_{ct i = SE.Enc (r i,}} f i), f _i = SE.Dec extract the files with the corresponding symmetric key r _{_i} (r _i , ct _i ).

The embodiment of the invention further provides a ciphertext search system supporting access control, comprising:

The client encrypts the file of the database using a preset symmetric encryption algorithm to obtain an encrypted ciphertext, and builds an index on the encrypted ciphertext according to the file identifier of the file of the database, and encrypts the index to obtain the inclusion. Indexing the ciphertext database of the ciphertext, sending the encrypted ciphertext and the ciphertext data to the cloud server for inclusion; and receiving the key ciphertext, the private key, and the search keyword set input by the user during the search, according to The key ciphertext, the private key, and the search key set generate a trapdoor, and send the trapdoor to the cloud server;

The cloud server is configured to save the encrypted ciphertext and the ciphertext database; and is further configured to retrieve, according to the trapdoor, an index ciphertext corresponding to the trapdoor in a ciphertext database; The identifier looks up the corresponding encrypted ciphertext;

The client is further configured to decrypt the index ciphertext by using a key, and upload the decrypted file identifier to the cloud server, so that the cloud server returns an encryption corresponding to the file identifier. The ciphertext decrypts the encrypted ciphertext using a preset symmetric encryption algorithm to obtain a search result, and displays the search result according to a preset display manner.

Further, the client is specifically configured to:

Receiving a database, using a pseudo-random function to encrypt a file in the database to obtain the encrypted ciphertext;

The pseudo-random function is PRF F: {0, 1} ^λ × {0, 1} ^λ → {0, 1} ^λ , PRP P: {0, 1} ^λ × {0, 1} ^λ → {0, 1} ^λ indicates that the ciphertext database is represented by EDB, and the database is represented by DB.

Id _i ∈{0,1} ^λ represents the file identifier,

Represents the set of keywords contained in id _i , the set of keywords

The file set Doc={f ₁ ,f ₂ ,...,f _d }, the key set of the encrypted file is expressed as R={r ₁ , r ₂ ,..., r _d }, and the symmetric encryption algorithm SE=(Enc, Dec);

Encrypting f _i with r _i before constructing the index, and obtaining a file ciphertext ct _i ←SE.Enc(r _i ,f _i )(i=1,2,...,d);

Setting the ciphertext control permission to upload the encrypted ciphertext to the cloud server, and the ciphertext access control permission scheme is an attribute-based encryption scheme ABE=(Setup, Encrypt, KeyGen, Decrypt);

Enter the system security parameter λ and the global attribute set N, the authority PKG runs (PK, MSK) ← ABE.Setup(1 ^λ , N):

Selecting the key k randomly for the PRF F;

Defining an empty array T of the keyword set W index;

Define XSet as an empty set;

Initialization key k ₁ ←F(k,1||w);

And add xtag to XSet, c←c+1, T[stag]←t;

Calculate the ciphertext C←ABE.Encrypt(PK,k,Γ) and get EDB=(XSet,T,C), where Γ is the access strategy.

Further,

Representing the search keyword set,

The key ciphertext is represented by C, and the private key is represented by SK, and the trapdoor is represented by stag, xtoken[1], xtoken[2], . . .

Generate a private key SK←ABE.KeyGen(MSK,S) according to the attribute S of the user;

Calculating a key k according to the key ciphertext and the private key; determining that the attribute S of the user satisfies an access policy of the ciphertext database, and if yes, decrypting succeeds k←ABE.Decrypt(C,SK ), get the key k, if not, the decryption fails;

When i=2,...,n, calculate the trapdoor element

Further, a set of the index ciphertext is represented by l, and the cloud server is specifically configured to:

Define l, t is an empty set;

For c=1, 2,...,|t|, retrieve from the c-th tuple in t (rind, y), if

Then l←l∪rind;

The client is also used to:

Decrypting the set l of the index ciphertext using the key k, obtaining the file identifier id _i and the corresponding key r _i ; for rind∈l, calculating (id _i ||r _i )←P ^-1 (k,rind), Get the search result (id _i , r _i );

Compared with the prior art, the present invention has the beneficial effects that: when detecting the key ciphertext, the private key, and the search key set input when the user searches, the trapdoor is generated according to the trapdoor in the ciphertext. Searching the index ciphertext corresponding to the trapdoor in the database, decrypting the index ciphertext by using a key, obtaining a file identifier, and searching for the corresponding encrypted ciphertext according to the file identifier, and decrypting the encrypted ciphertext to obtain a search result. In the implementation process, the attribute base encryption is used to control the ability of the search user to access the data, but the access control is set to the entire database instead of the index, which can greatly reduce the calculation overhead when the data owner encrypts the database, and the user The process of obtaining a search trap does not require data owner participation. The embodiment of the invention solves the data security problem, the efficient ciphertext search and the data access control problem existing in the existing cloud storage service.

DRAWINGS

1 is a flowchart of a ciphertext search method for supporting access control provided by the prior art;

2 is a schematic diagram of total running time of different methods provided by an embodiment of the present invention;

3 is a schematic diagram of a running time of a ciphertext database initialization according to an embodiment of the present invention;

4 is a schematic diagram of a running time of a trapdoor generation process and an extraction process according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a running time of performing a search method according to an embodiment of the present invention; FIG.

FIG. 6 is a schematic structural diagram of a ciphertext search system supporting access control provided by the prior art.

detailed description

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

FIG. 1 shows a ciphertext search for supporting access control according to an embodiment of the present invention, including:

S101. The client encrypts the file of the database by using a preset symmetric encryption algorithm to obtain an encrypted ciphertext, and builds an index on the encrypted ciphertext according to the file identifier of the file of the database, and encrypts the index to obtain the inclusion. Indexing the ciphertext database of the ciphertext, and sending the encrypted ciphertext and the ciphertext data to the cloud server;

S102. The client receives a key ciphertext, a private key, and a search key set input when the user searches, and generates a trapdoor according to the key ciphertext, the private key, and the search keyword set, and the trapdoor Sending the gate to the cloud server;

S103. The cloud server searches, according to the trapdoor, an index ciphertext corresponding to the trapdoor in a ciphertext database;

S104. The client decrypts the index ciphertext by using a key, and uploads the decrypted file identifier to the cloud server, so that the cloud server returns the encrypted ciphertext corresponding to the file identifier. Decrypting the encrypted ciphertext using a preset symmetric encryption algorithm to obtain a search result;

S105. The client displays the search result according to a preset display manner.

It is assumed that the ciphertext search system provided by the embodiment of the present invention has n attributes, which are represented by N={a ₁ , a ₂ , . . . , a _n }. {0,1} ^d consists of 0,1 sequences of length d, {0,1} ^* consists of 0,1 sequences of indefinite length, with λ indicating the safety parameter, G ₀ means that the prime order is p, and the generator is Bilinear group of g. Definition database

among them

As a file identifier,

The collection of keywords included. Define all keyword collections

The file set Doc={f ₁ , f ₂ , . . . , f _d }, and the key set of the encrypted file is R={r ₁ , r ₂ , . . . , r _d }.

In the embodiment of the present invention, step S101 specifically includes: in order to ensure the confidentiality of the outsourced file, define a symmetric encryption algorithm SE=(Enc, Dec), and the data owner encrypts f _i by using r _i to obtain encryption before constructing the index. Ciphertext ct _i ←SE.Enc(r _i ,f _i )(i=1,2,...,d), and upload the encrypted ciphertext to the cloud server. In order to implement access control, the data owner needs to set access control rights before uploading data, and define the ciphertext access control scheme used as the attribute-based encryption scheme ABE=(Setup, Encrypt, KeyGen, Decrypt). Enter the security parameter λ of the search system and the global attribute set N, and the authority PKG runs (PK, MSK) ← ABE.Setup(1 ^λ , N). Define the pseudo-random function PRF F: {0,1} ^λ ×{0,1} ^λ →{0,1} ^λ , PRP P:{0,1} ^λ ×{0,1} ^λ →{0,1} ^λ .

In the embodiment of the present invention, before the search is performed according to the search keyword set input by the user, the data needs to be encrypted. The encryption process specifically includes:

Enter the database DB, output the ciphertext database EDB, and the ciphertext database initialization algorithm EDBSetup (DB) is described as follows:

1. Select the key k randomly for PRF F and denote DB as

2. Define T as an empty array of key set W indexes;

3. Define XSet as an empty set;

4. For each w∈W:

a), define t as an empty list, and calculate the keyword ciphertext stag←F(k,w);

b), initialization key k ₁ ←F(k,1||w);

c), for all id _i in the DB, initialize the counter c←0 in random order, then:

i. Calculate the index cipher rind←P(k, id _i ||r _i ), encrypt k ₁ to get z←P(k ₁ ,c), and define y←rind·z ^-1 ;

Ii, add (rind, y) to t;

Iii. Define xtag as XSet is an element, calculate

And add xtag to XSet;

Iv, c←c+1;

d), T[stag]←t;

5. Calculate the ciphertext C←ABE.Encrypt(PK,k,Γ), where Γ is the access strategy;

6. Output EDB=(XSet, T, C).

In the above step S101, a set of search keywords for a legitimate user whose attribute set is S is assumed

To perform a search, assume that w ₁ is the least frequent keyword in the search keyword set. Generate a private key SK←ABE.KeyGen(MSK,S) through PKG according to the key ciphertext C requested by the user;

Step S102 specifically includes:

Receive user input C, SK,

Output trapdoor stag, xtoken[1], xtoken[2],...;

Trapdoor generation step TokenGeneration

Specifically include:

1. Calculate k←ABE.Decrypt(C,SK). If the attribute S of the user satisfies the access policy of the ciphertext database, the user successfully decrypts and obtains the key k; otherwise, returns null;

2. The steps for generating messages (stag, xtoken[1], xtoken[2],...) include:

a), generate a keyword ciphertext stag←F(k, w ₁ );

b), generate a key k ₁ ←F(k,1||w ₁ );

c), the counter c = 1, 2, ... until the cloud server stops;

i. Calculate the trapdoor element for i=2,...,n

Ii. There is xtoken[c]←(xtoken[c,2],xtoken[c,3],...,xtoken[c,n]);

In step S103, the search of the encrypted ciphertext is performed by the cloud server. After the trapdoor (stag, xtoken[1], xtoken[2], ...) is generated in step S102, the cloud server searches in the previously generated ciphertext database EDB. , to obtain the search result, that is, the set of index ciphertext l, the search step Search (stag, (xtoken[1], xtoken[2], ...), EDB) includes:

1. Define l, t is an empty set;

2. Verify that the equation T[stag]=stag is true. If it is true, then t=T[stag]; otherwise, return null;

3. For c=1, 2,...,|t|;

a) retrieved from the c-th tuple in t (rind, y);

b) If for

Let l←l∪rind.

In step S104, the search result 1 is decrypted by using the key k to obtain a search result. The decryption process Retrieve (l, k) specifically includes:

1. The user decrypts the search result l with the key k, and obtains the file identifier id _i and the corresponding key r _i ;

2. For rind∈l:

a), calculate (id _i ||r _i )←P ^-1 (k,rind);

b), return (id _i , r _i ).

3. Send id _i to the cloud server, obtain ct _i =SE.Enc(r _i ,f _i ), and extract the file f _i =SE.Dec(r _i , ct _i ) with the corresponding symmetric key r _i .

In a specific application, the embodiment of the present invention implements the foregoing functions through a client and a cloud server, and the client includes a handheld terminal or a personal computer. In step S101, the user inputs data to the database through the client, and the client can perform the step of encrypting the database to obtain the ciphertext database. After the client obtains the ciphertext database, the ciphertext database is sent to the client, or The database is transmitted to the cloud service, and the database is encrypted by the cloud server to obtain a ciphertext database. In step S102, it is assumed that a legitimate user whose attribute set is S performs a search keyword set through the client.

The search assumes that w ₁ is the least frequent keyword in the search keyword set. The user requests the key ciphertext C from the cloud server through the client, and generates a private key SK←ABE.KeyGen(MSK,S) through the PKG, and the client according to the key ciphertext C, the private key SK, and the search keyword set

Generating a trapdoor and sending the trapdoor to the cloud server. In step S103, the cloud server performs a retrieval step. After the cloud server receives the trapdoor, the cloud server searches the ciphertext data according to the trapdoor to obtain an index key. Text. After the cloud service obtains the encrypted ciphertext, the index ciphertext is sent to the client, and the client performs step S104. In step S105, after completing the search step of step S101 to step S104, the client will display the search result according to a preset display manner.

In practical applications, the efficiency of the Sun scheme and the embodiment of the present invention are compared by experimental simulation. The computer used in the simulation is 3.60GHz Inter(R)Core(TM)i7-4790CPU and 8.00GB RAM. The operating system used is Windows 7. The programming language is Java, which uses cpabe toolkit and Java. Pairing-Based Cryptography library (JPBC). Specifically, in this experiment, the Enron mail database was used to evaluate the performance of the program, and the experimental parameters shown in Table 1 were used to perform six sets of experiments.

Table 1 experimental parameters

分组Grouping	数据库大小Database size	关键字数量Number of keywords	含每个关键字文件数量Number of files per keyword
11	200200	1010	2020
22	800800	2020	4040
33	15001500	3030	5050
44	30003000	5050	6060
55	80008000	100100	8080
66	2000020000	200200	100100

Figure 2 shows the total computation time for the Sun scheme and the embodiment of the invention. As can be seen from FIG. 2, the total time cost in Sun's solution is much higher than the embodiment of the present invention, and increases exponentially with the increase of the database, and the time cost increases in the process of increasing the database in the embodiment of the present invention. The magnitude is small.

The total time cost in FIG. 2 mainly includes a ciphertext database initialization algorithm executed by the data owner, a trapdoor generation step executed by the user's client, and a search step performed by the cloud server, as shown in FIG. 3 and FIG. 4. Figure 5 shows. The time cost of the initialization algorithm of the Sun scheme in FIG. 3 is significantly higher than that of the embodiment of the present invention, and increases almost exponentially with the increase of the database, and the time cost increase of the embodiment of the present invention in the process of increasing the database. Smaller.

In FIG. 4 and FIG. 5, the time cost of the trapdoor generation step and the search step of the Sun scheme and the embodiment of the present invention are almost the same, and both increase linearly with the increase of the database.

In summary, the experimental results show that the embodiment of the present invention is more efficient than the Sun scheme.

FIG. 6 shows a search system for supporting access control according to an embodiment of the present invention, including:

The client 601, the user encrypts the file of the database by using a preset symmetric encryption algorithm, obtains the encrypted ciphertext, builds an index on the encrypted ciphertext according to the file identifier of the file of the database, and encrypts the index to obtain a ciphertext database including an index ciphertext, the encrypted ciphertext and the ciphertext data are sent to the cloud server 602; and is further configured to receive a key ciphertext, a private key, and a search keyword set input by the user, according to the The key ciphertext, the private key, and the search key set generate a trapdoor, and send the trapdoor to the cloud server 602;

The cloud server 602 is configured to save the encrypted ciphertext and the ciphertext database, and is further configured to: retrieve, according to the trapdoor, an index ciphertext corresponding to the trapdoor in a ciphertext database; Find the corresponding encrypted ciphertext;

The client 601 is further configured to decrypt the index ciphertext by using a key, and upload the decrypted file identifier to the cloud server, so that the cloud server returns the encryption key corresponding to the file identifier. And decrypting the encrypted ciphertext by using a preset symmetric encryption algorithm to obtain a search result, and displaying the search result according to a preset display manner.

Further, the client 601 is specifically configured to:

Id _i ∈{0,1} ^λ represents the file identifier,

Represents the set of keywords contained in id _i , the set of keywords

Selecting the key k randomly for the PRF F;

Defining an empty array T of the keyword set W index;

Define XSet as an empty set;

Initialization key k ₁ ←F(k,1||w);

And add xtag to XSet, c←c+1, T[stag]←t;

Further,

Representing the search keyword set,

The key ciphertext is represented by C, and the private key is represented by SK. The trapdoor is represented by stag, xtoken[1], xtoken[2], ..., and the client 601 is used to:

When i=2,...,n, calculate the trapdoor element

Further, the set of the index ciphertext is represented by l, and the cloud server 602 is specifically configured to:

Define l, t is an empty set;

For c=1, 2,...,|t|, retrieve from the c-th tuple in t (rind, y), if

Then l←l∪rind;

Client 601 is also used to:

The embodiment of the present invention further provides a terminal, including a memory, a processor, and a computer program stored on the memory and running on the processor, wherein when the processor executes the computer program, the support shown in FIG. 1 is implemented. Access to each step in the controlled ciphertext search method.

The embodiment of the present invention further provides a readable storage medium, wherein the computer program is stored thereon, wherein when the computer program is executed by the processor, the ciphertext search method supporting the access control as shown in FIG. 1 is implemented. Each step in the process.

In addition, each functional module in each embodiment of the present invention may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module. The above integrated modules can be implemented in the form of hardware or in the form of software functional modules.

The integrated modules, if implemented in the form of software functional modules and sold or used as separate products, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention, which is essential or contributes to the prior art, or all or part of the technical solution, may be embodied in the form of a software product stored in a storage medium. A number of instructions are included to cause a computer device (which may be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, and the like. .

The above is only the preferred embodiment of the present invention, and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. Within the scope.

Claims

A ciphertext search method for supporting access control, characterized in that the ciphertext search system comprises a client and a cloud server, and the ciphertext search method comprises:

Step A: The client encrypts the file of the database by using a preset symmetric encryption algorithm to obtain an encrypted ciphertext, and builds an index on the encrypted ciphertext according to the file identifier of the file of the database, and encrypts the index to obtain a ciphertext database including an index ciphertext, and sending the encrypted ciphertext and the ciphertext data to a cloud server;

Step B: The client receives a key ciphertext, a private key, and a search key set input when the user searches, and generates a trapdoor according to the key ciphertext, the private key, and the search keyword set, and the The trapdoor is sent to the cloud server;

Step C: The cloud server searches, according to the trapdoor, an index ciphertext corresponding to the trapdoor in a ciphertext database;

Step D: The client decrypts the index ciphertext by using a key, and uploads the decrypted file identifier to the cloud server, so that the cloud server returns the encryption key corresponding to the file identifier. And decrypting the encrypted ciphertext by using a preset symmetric encryption algorithm to obtain a search result;

In step E, the client displays the search result according to a preset display manner.
The ciphertext search method according to claim 1, wherein said step A comprises:

The client receives the database and encrypts the file in the database using a pseudo-random function to obtain the encrypted ciphertext.
A ciphertext search method according to claim 2, wherein said pseudo-random function is PRF F: {0, 1} λ × {0, 1} λ → {0, 1} λ , PRP P: { 0,1} λ ×{0,1} λ →{0,1} λ indicates that the ciphertext database is represented by EDB, and the database is represented by DB.
Id i ∈{0,1} λ represents the file identifier,
Represents the set of keywords contained in id i , the set of keywords
The file set Doc={f 1 ,f 2 ,...,f d }, the key set of the encrypted file is represented as R={r 1 , r 2 ,..., r d }, defining a symmetric encryption algorithm SE=(Enc,Dec The step A specifically includes:

Encrypting f i with r i before constructing the index, to obtain encrypted ciphertext ct i ←SE.Enc(r i ,f i )(i=1,2,...,d);

The ciphertext access control authority is set, and the encrypted ciphertext is uploaded to the cloud server, and the ciphertext access control permission scheme is an attribute-based encryption scheme ABE=(Setup, Encrypt, KeyGen, Decrypt);

Enter the system security parameter λ and the global attribute set N, the authority PKG runs (PK, MSK) ← ABE.Setup(1 λ , N);

Selecting the key k randomly for the PRF F;

Defining an empty array T of the keyword set W index;

Define XSet as an empty set;

For each w∈W, define t as an empty list and calculate the keyword ciphertext stag←F(k,w);

Initialization key k 1 ←F(k,1||w);

For all id i in the DB, the counter c←0 is initialized in a random order, and the index cipher rind←P(k, id i ||r i ) is calculated, and the encryption k 1 is obtained by z←P(k 1 ,c), And define y←rind·z -1 , add (rind, y) to t, define xtag as the element of XSet, calculate
And add xtag to XSet, c←c+1, T[stag]←t;

Calculate the ciphertext C←ABE.Encrypt(PK,k,Γ) and get EDB=(XSet,T,C), where Γ is the access strategy.
A ciphertext search method according to claim 3, wherein
Representing the search keyword set,
The key ciphertext is represented by C, the private key is represented by SK, and the trapdoor is represented by stag, xtoken[1], xtoken[2], ..., in step B, the user pair of the attribute set is S Keyword collection
To perform the search, step B specifically includes:

The client generates a private key SK←ABE.KeyGen(MSK,S) according to the attribute S of the user;

Calculating a key k according to the key ciphertext and the private key;

Determining that the attribute S of the user satisfies the access policy of the ciphertext database. If yes, the decryption succeeds k←ABE.Decrypt(C,SK), and the key k is obtained. If not, the decryption fails;

Generating a keyword ciphertext stag←F(k, w 1 ), and generating a key k 1 ←F(k,1||w 1 );

When i=2,...,n, calculate the trapdoor element
The trapdoor is obtained, namely: xtoken[c]←(xtoken[c,2], xtoken[c,3],...,xtoken[c,n]).
The ciphertext search method according to claim 4, wherein the set of the index ciphertext is represented by 1, and the step C comprises:

Define l, t is an empty set;

Determine whether the equation T[stag]=stag is true, if it is established, then t=T[stag]; if not, return an empty set;

For c=1, 2,...,|t|, retrieve from the c-th tuple in t (rind, y), if
Then l←l∪rind.
The ciphertext search method according to claim 5, wherein the step D comprises:

The client decrypts the set l of the index ciphertext using the key k, obtains the file identifier id i and the corresponding key r i ; for the rind ∈ l, calculates (id i ||r i )←P -1 (k , rind), get the search results (id i , r i );

Id i sends to the server cloud, the cloud server returns the obtained ct i = SE.Enc (r i, f i), f i = SE.Dec extract the files with the corresponding symmetric key r i (r i , ct i ).
A ciphertext search system supporting access control, comprising:

The client encrypts the file of the database using a preset symmetric encryption algorithm to obtain an encrypted ciphertext, and builds an index on the encrypted ciphertext according to the file identifier of the file of the database, and encrypts the index to obtain the inclusion. Indexing the ciphertext database of the ciphertext, sending the encrypted ciphertext and the ciphertext data to the cloud server; and receiving the key ciphertext, the private key, and the search key set input by the user during the search, according to the Generating a ciphertext, a private key, and the set of search keywords to generate a trapdoor, and sending the trapdoor to the cloud server;

The cloud server is configured to save the encrypted ciphertext and the ciphertext database; and is further configured to retrieve, according to the trapdoor, an index ciphertext corresponding to the trapdoor in a ciphertext database; The identifier looks up the corresponding encrypted ciphertext;

The client is further configured to decrypt the index ciphertext by using a key, and upload the decrypted file identifier to the cloud server, so that the cloud server returns an encryption corresponding to the file identifier. The ciphertext decrypts the encrypted ciphertext using a preset symmetric encryption algorithm to obtain a search result, and displays the search result according to a preset display manner.
The ciphertext search system according to claim 7, wherein the client is specifically configured to:

Receiving a database, using a pseudo-random function to encrypt a file in the database to obtain the encrypted ciphertext;

The pseudo-random function is PRF F: {0, 1} λ × {0, 1} λ → {0, 1} λ , PRP P: {0, 1} λ × {0, 1} λ → {0, 1} λ indicates that the ciphertext database is represented by EDB, and the database is represented by DB.
Id i ∈{0,1} λ represents the file identifier,
Represents the set of keywords contained in id i , the set of keywords
The file set Doc={f 1 ,f 2 ,...,f d }, the key set of the encrypted file is expressed as R={r 1 , r 2 ,..., r d }, and the symmetric encryption algorithm SE=(Enc, Dec);

Encrypting f i with r i before constructing the index, and obtaining a file ciphertext ct i ←SE.Enc(r i ,f i )(i=1,2,...,d);

Setting the ciphertext control permission to upload the encrypted ciphertext to the cloud server, and the ciphertext access control permission scheme is an attribute-based encryption scheme ABE=(Setup, Encrypt, KeyGen, Decrypt);

Enter the system security parameter λ and the global attribute set N, the authority PKG runs (PK, MSK) ← ABE.Setup(1 λ , N):

Selecting the key k randomly for the PRF F;

Defining an empty array T of the keyword set W index;

Define XSet as an empty set;

For each w∈W, define t as an empty list and calculate the keyword ciphertext stag←F(k,w);

Initialization key k 1 ←F(k,1||w);

For all id i in the DB, the counter c←0 is initialized in a random order, and the index cipher rind←P(k, id i ||r i ) is calculated, and the encryption k 1 is obtained by z←P(k 1 ,c), And define y←rind·z -1 , add (rind, y) to t, define xtag as the element of XSet, calculate
And add xtag to XSet, c←c+1, T[stag]←t;

Calculate the ciphertext C←ABE.Encrypt(PK,k,Γ) and get EDB=(XSet,T,C), where Γ is the access strategy.
A ciphertext search system according to claim 8 wherein
Representing the search keyword set,
The key ciphertext is represented by C, and the private key is represented by SK, and the trapdoor is represented by stag, xtoken[1], xtoken[2], . . .

Generate a private key SK←ABE.KeyGen(MSK,S) according to the attribute S of the user;

Calculating a key k according to the key ciphertext and the private key; determining that the attribute S of the user satisfies an access policy of the ciphertext database, and if yes, decrypting succeeds k←ABE.Decrypt(C,SK ), get the key k, if not, the decryption fails;

Generating a keyword ciphertext stag←F(k, w 1 ), and generating a key k 1 ←F(k,1||w 1 );

When i=2,...,n, calculate the trapdoor element
The trapdoor is obtained, namely: xtoken[c]←(xtoken[c,2], xtoken[c,3],...,xtoken[c,n]).
The ciphertext search system of claim 9, wherein the set of the index ciphertext is represented by l, and the cloud server is specifically configured to:

Define l, t is an empty set;

Determine whether the equation T[stag]=stag is true, if it is established, then t=T[stag]; if not, return an empty set;

For c=1, 2,...,|t|, retrieve from the c-th tuple in t (rind, y), if
Then l←l∪rind;

The client is also used to:

Decrypting the set l of the index ciphertext using the key k, obtaining the file identifier id i and the corresponding key r i ; for rind∈l, calculating (id i ||r i )←P -1 (k,rind), Get the search result (id i , r i );

Id i sends to the server cloud, the cloud server returns the obtained ct i = SE.Enc (r i, f i), f i = SE.Dec extract the files with the corresponding symmetric key r i (r i , ct i ).