CN112100649A - Multi-keyword searchable encryption method and system supporting Boolean access control strategy - Google Patents

Multi-keyword searchable encryption method and system supporting Boolean access control strategy Download PDF

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CN112100649A
CN112100649A CN202010781185.XA CN202010781185A CN112100649A CN 112100649 A CN112100649 A CN 112100649A CN 202010781185 A CN202010781185 A CN 202010781185A CN 112100649 A CN112100649 A CN 112100649A
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ciphertext
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token
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徐玲玲
陈建彰
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South China University of Technology SCUT
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Abstract

The invention discloses a multi-keyword searchable encryption method and a multi-keyword searchable encryption system supporting Boolean access control strategies, wherein the method comprises the steps that a trusted authority generates a system public key, a main key and an ElGamal private key, the system public key is cloud-opened, and the private key is sent to a data user; then the data owner generates an index ciphertext and a data ciphertext for the document and uploads the index ciphertext and the data ciphertext in the cloud; when a data user is searched, the attribute set and the query keyword predicate of the data user are uploaded to a credible authority to verify whether the user identity is legal or not, and when the user identity is legal, a search token is generated and sent to the data user; after receiving the retrieval token, the data user uploads the retrieval token in the cloud; after the cloud server receives the data, the system public key is used for checking whether each index ciphertext is matched with the retrieval token or not, and the matched data ciphertext is sent to the data user; and the data user recovers the data ciphertext into plaintext content by using the private key. The invention can realize fine-grained Boolean access control, Boolean multiple key word search and constant system key length.

Description

Multi-keyword searchable encryption method and system supporting Boolean access control strategy
Technical Field
The invention relates to the technical field of information retrieval and cryptography, in particular to a multi-keyword searchable encryption method and a multi-keyword searchable encryption system supporting Boolean access control strategies.
Background
With the rapid development of internet technology and the popularity of cloud computing technology, more and more enterprise users and individuals store their data in the cloud instead of the past practice of storing the data in their own data centers. The user can retrieve data in the cloud anytime and anywhere and can easily share the data to the licensee. However, cloud computing offers us convenience and also presents a serious security risk. When data is outsourced to a cloud server in clear text, it may be subject to illegal access by a cloud service provider or hacker. The conventional solution is to encrypt data and store the encrypted data in a cloud server in a form of ciphertext, but the conventional plaintext retrieval technology cannot be applied to the ciphertext.
In order to enable a user to perform keyword search on ciphertext data, a Searchable Encryption (SE) technique has been proposed as a solution. According to different Encryption methods, Searchable Encryption can be divided into Searchable Symmetric Encryption (SSE) and Public Key Searchable Encryption (PEKS). In public key based searchable encryption, data owners encrypt data using a public key of a given user before uploading the data to a cloud server, after which these users can search and decrypt the data using their private keys. The basic PEKS scheme cannot be effectively applied in some practical application scenarios. For example, in a healthcare system, a patient may desire that his personal health record be retrievable only by authorized physicians in some designated roles. Under such circumstances, in order to achieve both keyword query and fine-grained access control on encrypted data, researchers have proposed a searchable encryption method based on attributes, and many of the existing works have made corresponding studies on this method. In these works, each data is encrypted using a mandatory access control policy, and the ciphertext can only be decrypted if and only if the set of attributes of the data user satisfies the access policy.
Although the existing work provides solutions for attribute-based keyword search, none of the solutions can simultaneously solve four problems of flexible expressiveness of access policy, concealment of access policy, flexible expressiveness of keyword search, and fixed system key length. The flexible expressiveness of the Access policy can help data owners manage data flexibly, and most of the existing work adopts the Access policy expressed by a Linear Secret Sharing Scheme (LSSS) or an Access Tree (Access Tree). Hiding of the access policy plays a very important role in ensuring user privacy and data security, some existing methods do not support this feature, and some methods support hiding of part of the policy, that is, only the attribute name of the access policy is exposed, while all attribute values are hidden in the cloud server. The flexibility of keyword search can bring flexible choice for the search of data users, and the existing scheme mainly supports one of the following three search modes: match search, join key search, and boolean key search, with match search being the least flexible and boolean key search being the most flexible. A constant level of key length is an ideal feature for attribute-based keyword searching, and in some existing schemes, the key length depends on the size of an attribute field or the size of a keyword field, the size of the attribute field must be bounded by a polynomial, and some schemes have a constant level of key length, which may allow the attribute field to grow exponentially.
In summary, even though some work has proposed excellent solutions to some of the above four problems, it is inevitable to make compromises in other aspects, and the four problems cannot be solved at the same time. Therefore, how to design a complete attribute-based keyword search method aiming at the above four problems in the context of big data and cloud storage becomes a key problem to be solved urgently.
Disclosure of Invention
The first purpose of the present invention is to overcome the drawbacks and disadvantages of the prior art, and to provide a multi-key searchable encryption method supporting boolean access control policy, which can be used to solve the technical problems of fine-grained boolean access control, boolean multi-key search, security of ciphertext data, and the like, in the context of big data and cloud storage.
It is a second object of the present invention to provide a multi-key searchable encryption system that supports boolean access control policies, which can support both boolean key search and boolean access control, as well as constant-level system key lengths.
The first purpose of the invention is realized by the following technical scheme: a multi-keyword searchable encryption method supporting Boolean access control strategies comprises the following steps:
s1, generating a system public key pk, a master key mk and an ElGamal private key a 'by the trusted authority TA, distributing the system public key pk to a cloud server in a public way, storing the master key mk in the trusted authority TA, and sending the ElGamal private key a' to a data user;
s2, encryption: the data owner uses the system public key pk and the keyword set O ═ O1，...，om) And an access policy P for generating an index ciphertext C for the documentIAnd data ciphertext CDAnd combines the ciphertext CI、CDUploading to a cloud server;
s3, generating a token: when a data user performs a search operation, it is first necessary to set the attribute set S to (a)1，...，an) And query keyword predicates
Figure BDA0002620273030000031
Uploading the data to a trusted authority TA, verifying whether the identity of the data user is legal or not by the trusted authority TA, and if the identity of the data user is legal, generating a retrieval token for the data user by using a system public key pk and a master key mk
Figure BDA0002620273030000032
And store the token
Figure BDA0002620273030000033
Sending the data to the data user;
s4, searching ciphertext: the data user receives the search token sent by the credible authority TA
Figure BDA0002620273030000034
Then, sending the retrieval token to a cloud server; after the cloud server receives the index ciphertext C, aiming at each index ciphertext CIChecking whether the index ciphertext and the retrieval token are matched by using the system public key pk, and transmitting the data ciphertext C meeting the matching conditionDSending the data to a data user;
s5, decryption: data user receives data cipher text CDThereafter, the data ciphertext C is encrypted using the ElGamal private key aDRestored to the corresponding plaintext content.
Preferably, in step S1, the trusted authority TA generates the system public key pk, the master key mk, and the ElGamal private key a' as follows:
s11 group generator using complex order bilinear group by trusted authority TA
Figure BDA0002620273030000035
Execute
Figure BDA0002620273030000036
Generating tuples (p)1，p2，p3，p4，G，GTAnd e), wherein,
Figure BDA0002620273030000037
for inputting safety parameters of the group generator, p1，p2，p3，p4Is four different prime numbers, G and GTIs a cyclic group of order N, and N ═ p1p2p3p4And satisfying bilinear mapping relation e: g → GTThe relational expression maps two elements in the group G to the group GTOne element of (1);
Figure BDA00026202730300000313
each represents p of G1，p2，p3，p4A subgroup of orders;
s12, the trusted authority TA randomly selects the element a, a', alpha ∈ group ZNRandomly extracting elements g, h belonging to a group
Figure BDA0002620273030000038
Element X3E group
Figure BDA0002620273030000039
Elements Z, X4E group
Figure BDA00026202730300000310
And calculated to obtain H-hZ, Y-e (g, g)αH and Y represent members of the system public key, respectively;
s13, the trusted authority TA selects a collision-resistant hash function f, where the hash function f satisfies the following mapping:
Figure BDA00026202730300000311
s14, the trusted authority TA obtains the system public key pk according to the above variables<N，g，ga，ga′，f，Y，H，X4>The master key mk ═<α，h，X3>And the ElGamal private key a';
the ElGamal private key a' is specifically sent to the data user through an encrypted channel.
Further, the encryption process of step S2 is as follows:
s21, the data owner maps the keyword predicate P into a linear secret sharing scheme expression
Figure BDA00026202730300000312
Wherein A is lsShared matrix of x n, lsRepresenting the number of rows and n representing the number of columns; ρ is a function that maps each row of matrix a to an attribute field; t is represented by
Figure BDA0002620273030000041
Form (a) tρ(i)Is an attribute of the attribute field rho (i), i is greater than or equal to 1 and less than or equal to ls；
The data owner randomly generates a vector v ═ (s, v)2,., vn) belonging to group
Figure BDA0002620273030000042
And slave group
Figure BDA0002620273030000043
In the random selection of an element Z1；s，v2，vnAs components in vector v;
for each row A of the matrix AiFrom group ZNIn the random selection of element riAnd slave group
Figure BDA0002620273030000044
In the random selection of two elements Zc，i，Zd，i；
For each keyword oxFrom the group
Figure BDA0002620273030000045
In the random selection of an element Ze，xWherein x is more than or equal to 1 and less than or equal to m;
s22, the data owner calculates the index ciphertext C according to the variablesI：
Figure BDA00026202730300000422
Wherein, C0＝Ys，C1＝gsZ1，
Figure BDA0002620273030000046
Figure BDA0002620273030000047
S23, randomly generating a multi-bit symmetric key psi by the data owner, encrypting the document content by using an AES algorithm to obtain a ciphertext CD，1；
S24, the data owner uses ElGamal algorithm to encrypt the symmetric key psi to obtain the ciphertext CD，2The specific process comprises the following steps: obtaining g and g from system public key pka′Randomly selecting element y from group G, and calculating to obtain1＝gy，＝(ga′)y(ii) a Then, the symmetric key ψ is mapped to an element ψ' on G and calculated2Psi' and finally generating the ciphertext CD，2＝(1，2)；
S25, the data owner obtains the variables according to the steps S23 and S24Data cipher text CD＝<CD，1，CD，2>。
Further, in step S3, the process of generating the token by the trusted authority TA is as follows:
s31, the credible authority TA predicates the query key words
Figure BDA0002620273030000048
Mapping to a linear secret sharing scheme representation
Figure BDA0002620273030000049
Figure BDA00026202730300000410
Wherein the content of the first and second substances,
Figure BDA00026202730300000411
is aOShared matrix of x m, lORepresenting the number of rows, m representing the number of columns;
Figure BDA00026202730300000412
is a general matrix
Figure BDA00026202730300000413
Each line of (a) maps to a function of a key field;
Figure BDA00026202730300000414
is shown as
Figure BDA00026202730300000415
In the form of (a) a (b),
Figure BDA00026202730300000416
is a keyword field
Figure BDA00026202730300000417
The key word of 1 is less than or equal to x' and less than or equal to lO；
S32, trusted authority TA Slave group ZNIn the random selection of two elements c1，c2Generating a vector
Figure BDA00026202730300000418
Wherein the content of the first and second substances,
Figure BDA00026202730300000419
as random numbers, from the group
Figure BDA00026202730300000420
In the random selection of two elements R0，R1；
S33, for attribute set S ═ (a)1，...，an) Each attribute a ini′From the group
Figure BDA00026202730300000421
In the random selection of element Ri′，1≤i′≤n；
S34, for
Figure BDA0002620273030000051
Each row of
Figure BDA0002620273030000052
From group ZNIn the random selection of an element sx′From the group
Figure BDA0002620273030000053
In the random selection of two elements
Figure BDA0002620273030000054
S35, the trusted authority TA calculates and obtains the retrieval token according to the variables
Figure BDA0002620273030000055
Figure BDA0002620273030000056
Wherein the content of the first and second substances,
Figure BDA0002620273030000057
Figure BDA0002620273030000058
further, the ciphertext search process of step S4 is as follows:
s41, the cloud server searches the token
Figure BDA0002620273030000059
Is resolved into
Figure BDA00026202730300000510
Index ciphertext CIIs resolved into
Figure BDA00026202730300000511
S42, the cloud server calculates I from (A, rho)A，ρHere IA，ρRepresents {1,.. multidot.lsAll minimum subsets of (A, rho) are satisfied; wherein, if present
Figure BDA00026202730300000512
And the existence of a set of constants wi″}i″∈ISo that ∑i″∈Iwi″Ai″When (1, 0,. 0), I is said to satisfy (a, ρ);
likewise, cloud server slave
Figure BDA00026202730300000513
Middle calculation
Figure BDA00026202730300000514
Here, the
Figure BDA00026202730300000515
Represents {1,.. multidot.lOAll of them satisfy
Figure BDA00026202730300000516
A set formed by the smallest subset of (c); whereinIf present, if present
Figure BDA00026202730300000517
And existence of a set of constants
Figure BDA00026202730300000518
So that
Figure BDA00026202730300000519
Figure BDA00026202730300000520
Then call
Figure BDA00026202730300000521
Satisfy the requirement of
Figure BDA00026202730300000522
S43, if there is I ∈ IA，ρAnd
Figure BDA00026202730300000523
wherein ∑i″∈Iwi″Ai″Given (1, 0.., 0) for some constants { w }i″}i″∈IIs formed,
Figure BDA00026202730300000524
For some constant
Figure BDA00026202730300000525
If it holds, so that the following equation holds, the algorithm outputs 1, indicating the search token
Figure BDA00026202730300000526
Index ciphertext CIMatch and cipher the corresponding dataDSending the data to a data user; otherwise, the algorithm outputs 0, which indicates that the two are not matched;
the equation is:
Figure BDA00026202730300000527
further, the decrypted data ciphertext C of step S5D＝<CD，1，CD，2>The process of (2) is as follows:
s51, the data user uses ElGamal algorithm to encrypt the ciphertext
Figure BDA00026202730300000528
Decryption to obtain a symmetric key psi:
using the ElGamal private key a', calculated as ═1 a′And then calculating psi ═2 -1Finally mapping psi' back to the symmetric key psi;
s52, decrypting ciphertext by using the symmetric key psi
Figure BDA0002620273030000061
And obtaining the plaintext content of the document.
Preferably, the trusted authority TA is a fully trusted third party security authority, and is responsible for generating a system public key pk and a master key mk, and an ElGamal private key a 'for file decryption, where the system public key pk, the master key mk, and the ElGamal private key a' are binary codes with a certain length.
The second purpose of the invention is realized by the following technical scheme: a multi-key searchable encryption system that supports boolean access control policies, comprising: an initialization and token generation subsystem operating in a trusted authority TA, an encryption subsystem operating in a data owner side, a cloud storage subsystem operating on a cloud server, a user retrieval and decryption subsystem operating in a data user side, wherein,
the initialization and token generation subsystem operating in the trusted authority TA comprises an initialization module, a master key storage module and a token generation module:
the initialization module is used for generating a system public key pk, a master key mk and an ElGamal private key a ', distributing the public development of the system public key pk to a cloud server, storing the master key mk to the master key storage module and sending the ElGamal private key a' to a data user;
the master key storage module is used for storing a master key mk and only allowing the access of a trusted authority TA;
the token generation module is used for responding to a retrieval token generation request of the data user, checking the validity of the identity of the data user, and generating a retrieval token for the data user by using the system public key pk and the master key mk under the condition that the identity of the data user is legal
Figure BDA0002620273030000062
And to token the search
Figure BDA0002620273030000063
Sending the data to a data user;
the encryption subsystem running at the data owner end comprises a data encryption module and an index encryption module:
the data encryption module is used for acquiring a system public key pk from the cloud server, encrypting the document by using the system public key pk to obtain a data ciphertext, and then sending the data ciphertext to the cloud server;
the index encryption module is used for encrypting the keyword set of each document and the implemented access strategy by using the system public key pk to obtain a corresponding index ciphertext and sending the index ciphertext to the cloud server;
the cloud storage subsystem running on the cloud server comprises a system public key public module, a storage module and a retrieval module:
the system public key public module is used for publicly releasing the system public key generated by the trusted authority TA;
the storage module is used for storing the data ciphertext and the index ciphertext encrypted by the data owner;
the retrieval module is used for aiming at each index ciphertext CIChecking whether the index ciphertext is matched with the search token by using the system public key pk, and obtaining a data ciphertext C meeting the matching condition from the storage moduleDAnd sends it to the data user;
the user retrieval and decryption subsystem running at the data user side comprises a user retrieval module and a data decryption module:
the user search module is used for sending a token generation request to the trusted authority TA and simultaneously setting the attribute set S of the data user to be (a)1，...，an) And query keyword predicates
Figure BDA0002620273030000071
Uploading the search token to a trusted authority TA to finish the generation operation of the search token, and when receiving the search token of the trusted authority TA
Figure BDA0002620273030000072
Then, the user retrieval module is further used for sending the token to the cloud server to continue to complete retrieval operation;
the data decryption module is used for using an ElGamal private key a' to obtain a data ciphertext CDAnd decrypting and restoring the data ciphertext into corresponding plaintext content.
Preferably, the data owner terminal and the data user terminal are terminal devices with operation processing capability, including a smart phone, a tablet, and a computer.
Compared with the prior art, the invention has the following advantages and effects:
(1) in the multi-keyword searchable encryption method AND system, the data owner is allowed to implement the access strategy on the data, AND the access strategy supports Boolean expression forms of logic word nesting such as AND, OR AND the like, so that the data owner can be helped to flexibly control AND authorize the data, AND fine-grained Boolean access control is realized.
(2) The invention also supports Boolean keyword search represented by a Linear Secret Sharing Scheme (LSSS), AND the existing two schemes based on ABE (attribute-based encryption) or PEKS (public-key encryption with keyword search) can realize fine-grained access control, but the search strategy still focuses on equivalent search or AND connection search of multiple keywords, etc., but NOT the Boolean keyword search of logic word nesting such as AND, OR, etc., while the invention supports fine-grained access control, the invention also can support the search strategy of logic word nesting such as AND, OR, NOT, etc., therefore, the method brings greater flexibility to the data user in searching the encrypted data, helps the user to find out the required data accurately, reduces the transmission cost and the calculation cost, and realizes the Boolean keyword search and fine-grained access control.
(3) The method and the system are constructed by adopting a composite order group, bilinear mapping and a Linear Secret Sharing Scheme (LSSS), have the characteristics of strategy hiding and leakage resistance, and have stronger safety; and the problems of flexible expressiveness of the access strategy, concealment of the access strategy, flexible expressiveness of keyword search, key length and the like are balanced, and the method has better practicability.
(4) The invention adopts the access strategy expressed by a Linear Secret Sharing Scheme (LSSS), only the structure with the attribute field is contained in the ciphertext, the attribute value is not exposed to the cloud in a plaintext mode, and the data concealment and the safety are good.
(5) The key used by the invention can adopt the system key length of a constant level, and is mainly based on the use of a hash function f, and does not depend on the number of the attribute field and the key field, nor the scale of the attribute field.
Drawings
FIG. 1 is a flow chart of a multi-key searchable encryption method of the present invention that supports Boolean access control policies.
Fig. 2 is a block diagram of the architecture of a multi-key searchable encryption system supporting boolean access control policies of the present invention.
Fig. 3 is a schematic diagram of an application environment of the multi-key searchable encryption system supporting boolean access control policies of the present invention.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.
Example 1
The embodiment discloses a multi-keyword searchable encryption method supporting Boolean access control strategies, and in the background of cloud storage, the embodiment is based on searchable encryption technology and attribute encryption technology, uses LSSS to express access strategies and search strategies, can support Boolean keyword search, and can effectively locate data in which a user is interested; meanwhile, flexibility and hiding of an access strategy are realized, and fine-grained Boolean access control is supported; and supports a constant level of system key length. As shown in fig. 1, the method is applied to an application system including a trusted authority, a data user side, a data owner side, and a cloud server, such as a healthcare system, a school educational administration system, and the method includes the following steps:
s1, generating a system public key pk, a master key mk and an ElGamal private key a' by a trusted authority TA, distributing the system public key pk to a cloud server in a public way, and allowing all data users of the system to have the right of accessing the system public key pk; the trusted authority TA stores the master key mk in the trusted authority TA, and only the trusted authority TA has the authority of accessing the master key mk; the trusted authority TA sends the ElGamal private key a' to the data users through the encryption channel, and each data user has a private key specific to itself.
The trusted authority TA is a fully trusted third-party security authority, and is responsible for generating a system public key pk and a master key mk, and an ElGamal private key a 'for file decryption, where the system public key pk, the master key mk, and the ElGamal private key a' all represent (or are encoded) into a binary code with a certain length under a computer.
The system public key pk, the master key mk, and the ElGamal private key a' are generated as follows:
s11 group generator using complex order bilinear group by trusted authority TA
Figure BDA0002620273030000081
Execute
Figure BDA0002620273030000082
Generating tuples (p)1，p2，p3，p4，G，GTAnd e), wherein,
Figure BDA0002620273030000083
for inputting safety parameters of the group generator, p1，p2，p3，p4Is four different prime numbers, G and GTIs a cyclic group of order N, and N ═ p1p2p3p4And satisfying bilinear mapping relation e: g → GTThe relational expression maps two elements in the group G to the group GTOne element of (1);
Figure BDA0002620273030000084
each represents p of G1，p2，p3，p4A subgroup of orders;
s12, the trusted authority TA randomly selects the element a, a', alpha ∈ group ZNRandomly extracting elements g, h belonging to a group
Figure BDA0002620273030000091
Element X3E group
Figure BDA0002620273030000092
Elements Z, X4E group
Figure BDA0002620273030000093
And calculated to obtain H-hZ, Y-e (g, g)αH and Y represent members of the system public key, respectively;
s13, the trusted authority TA selects a collision-resistant hash function f, where the hash function f satisfies the following mapping:
Figure BDA0002620273030000094
s14, the trusted authority TA obtains the system public key pk according to the above variables<N，g，ga，ga′，f，Y，H，X4>The master key mk ═<α，h，X3>And the ElGamal private key a'.
S2, encryption: the data owner uses the system public key pk and the keyword set O ═ O1，...，om) And an access policy P for generating an index ciphertext C for the documentIAnd data cipher textCDAnd combines the ciphertext CI、CDAnd uploading to a cloud server.
Wherein the access policy
Figure BDA00026202730300000915
The access policy may be referred to as a keyword predicate, AND may be regarded as an attribute set formed by connecting logical words such as AND OR, AND used to represent attribute conditions that must be satisfied by a data user who can read the file. For example, assume that there is a document with an access policy of
Figure BDA0002620273030000095
OR (institution AND department) with the number, institution AND department as attribute fields AND 01234, hospital a AND department as attribute values, the access policy
Figure BDA0002620273030000096
Representing that the document can only be accessed by data users meeting the code 01234, or institutions hospital a and department cardiology.
Index ciphertext CIThe data owner encrypts the key words and the access strategy to obtain the data. Data cipher text CDThe method refers to ciphertext data obtained by encrypting the content of the document. Index ciphertext CIAnd data ciphertext CDThe encryption process of (1) is as follows:
s2l, predicating the keywords by the data owner
Figure BDA0002620273030000097
Mapping to a Linear Secret Sharing Scheme (LSSS) representation
Figure BDA0002620273030000098
Wherein A is lsShared matrix of x n, lsRepresenting the number of rows and n representing the number of columns; ρ is a function that maps each row of matrix a to an attribute field; t is represented by
Figure BDA0002620273030000099
Form (a) tρ(i)Is an attribute of the attribute field rho (i), i is greater than or equal to 1 and less than or equal to ls；
The data owner randomly generates a vector v ═ (s, v)2，...，vn) E group
Figure BDA00026202730300000910
And slave group
Figure BDA00026202730300000911
In the random selection of an element Z1(ii) a Here, all components in the vector are randomly selected, wherein S is continuously used in step S22;
for each row A of the matrix AiCorresponding to the slave group ZNIn the random selection of element riAnd slave group
Figure BDA00026202730300000912
In the random selection of two elements Zc，i，Zd，i；
For each keyword oxCorresponding to the slave group
Figure BDA00026202730300000913
In the random selection of an element Ze，xWherein x is more than or equal to 1 and less than or equal to m;
s22, the data owner calculates the index ciphertext C according to the variablesI：
Figure BDA00026202730300000914
Wherein, C0＝Ys，C1＝gsZ1，
Figure BDA0002620273030000101
Figure BDA0002620273030000102
S23, data owner randomly generates multibit symmetric key psi using AESThe algorithm encrypts the document content to obtain a ciphertext CD，1(ii) a The embodiment specifically generates a symmetric key ψ of 256 bits;
s24, the data owner uses ElGamal algorithm to encrypt the symmetric key psi to obtain the ciphertext CD，2The specific process comprises the following steps: obtaining g and g from system public key pka′，g、ga′Is an element in the system public key pk, and since the data owner can access the system public key, he can also extract the corresponding element from the system public key; randomly selecting element y from group G, and calculating to obtain1＝gy，＝(ga′) y; then, the symmetric key ψ is mapped to an element ψ' on G and calculated2Psi' and finally generating the ciphertext CD，2＝(1，2)；
S25, the data owner obtains the data ciphertext C according to the variables of the steps S23 and S24D＝<CD，1，CD，2>。
S3, generating a token: when a data user performs a search operation, it is first necessary to set the attribute set S to (a)1，...，an) And query keyword predicates
Figure BDA0002620273030000103
Uploading the data to a trusted authority TA, verifying whether the identity of the data user is legal or not by the trusted authority TA, and if the identity of the data user is legal, generating a retrieval token for the data user by using a system public key pk and a master key mk
Figure BDA0002620273030000104
And store the token
Figure BDA0002620273030000105
And sending the data to the data user. The retrieval token may also be referred to as a query token.
Wherein the query key predicates
Figure BDA0002620273030000106
Can be regarded as a keyword set formed by connecting logical words such as AND, OR, etcIndicating what data the user wants to query. For example, assume that there is a query keyword predicate of
Figure BDA0002620273030000107
Figure BDA0002620273030000108
OR name ═ plum ", where provider, disease, name are keyword fields, hospital a, heart disease, plum are keywords, the query keyword predicates
Figure BDA0002620273030000109
The representative user wants to search all documents whose provider is hospital a and whose disease is heart disease, or whose name is plum.
The procedure for the trusted authority TA to generate tokens is as follows:
s31, the credible authority TA predicates the query key words
Figure BDA00026202730300001010
Mapping to a linear secret sharing scheme representation
Figure BDA00026202730300001011
Wherein the content of the first and second substances,
Figure BDA00026202730300001012
is aOShared matrix of x m, lORepresenting the number of rows, m representing the number of columns;
Figure BDA00026202730300001013
is a general matrix
Figure BDA00026202730300001014
Each line of (a) maps to a function of a key field;
Figure BDA00026202730300001015
is shown as
Figure BDA00026202730300001016
In the form of (a) a (b),
Figure BDA00026202730300001017
is a keyword field
Figure BDA00026202730300001018
The key word of 1 is less than or equal to x' and less than or equal to lO；
S32, trusted authority TA Slave group ZNIn the random selection of two elements c1，c2Generating a vector
Figure BDA00026202730300001019
Wherein the content of the first and second substances,
Figure BDA00026202730300001020
as random numbers, from the group
Figure BDA00026202730300001021
In the random selection of two elements R0，R1；
S33, for attribute set S ═ (a)1，...，an) Each attribute a ini′From the group
Figure BDA0002620273030000111
In the random selection of element Ri′，1≤i′≤n；
S34, for
Figure BDA0002620273030000112
Each row of
Figure BDA0002620273030000113
From group ZNIn the random selection of an element sx′From the group
Figure BDA0002620273030000114
In the random selection of two elements
Figure BDA0002620273030000115
1≤x′≤lO；
S35, canThe credit authority TA calculates and obtains a retrieval token according to the variables
Figure BDA0002620273030000116
Figure BDA0002620273030000117
Wherein the content of the first and second substances,
Figure BDA0002620273030000118
Figure BDA0002620273030000119
s4, searching ciphertext: the data user receives the search token sent by the credible authority TA
Figure BDA00026202730300001110
Then, sending the retrieval token to a cloud server; after the cloud server receives the index ciphertext C, aiming at each index ciphertext CIChecking whether the index ciphertext and the retrieval token are matched by using the system public key pk, and transmitting the data ciphertext C meeting the matching conditionDAnd sending the data to a data user.
The ciphertext search process is as follows:
s41, the cloud server searches the token
Figure BDA00026202730300001111
Is resolved into
Figure BDA00026202730300001112
Index ciphertext CIIs resolved into
Figure BDA00026202730300001113
S42, the cloud server calculates I from (A, rho)A，ρHere IA，ρRepresents {1,.. multidot.lsAll minimum subsets of (A, rho) are satisfied; it is composed ofIn, if present
Figure BDA00026202730300001114
And the existence of a set of constants wi″}i″∈ISo that ∑i″∈I wi″Ai″When (1, 0,. 0), I is said to satisfy (a, ρ);
likewise, cloud server slave
Figure BDA00026202730300001115
Middle calculation
Figure BDA00026202730300001116
Here, the
Figure BDA00026202730300001117
Represents {1,.. multidot.lOAll of them satisfy
Figure BDA00026202730300001118
A set formed by the smallest subset of (c); wherein, if present
Figure BDA00026202730300001119
And existence of a set of constants
Figure BDA00026202730300001120
So that
Figure BDA00026202730300001121
Figure BDA00026202730300001122
Then call
Figure BDA00026202730300001123
Satisfy the requirement of
Figure BDA00026202730300001124
S43, if there is I ∈ IA，ρAnd
Figure BDA00026202730300001125
wherein ∑i″∈I wi″Ai″Given (1, 0.., 0) for some constants { w }i″}i″∈IIs formed,
Figure BDA00026202730300001126
For some constant
Figure BDA00026202730300001127
If it holds, so that the following equation holds, the algorithm outputs 1, indicating the search token
Figure BDA00026202730300001128
And index ciphertext CIMatch and cipher the corresponding dataDSending the data to a data user; otherwise, the algorithm outputs 0, which indicates that the two are not matched;
the outputs "1" and "0" are generally expressed by using boolean variables (bool) under a computer, where "1" corresponds to "true" of the boolean variable, i.e., "the two match". While a "0" corresponds to a "false" of the boolean variable, denoted "false", i.e., "the two do not match".
The equation is:
Figure BDA0002620273030000121
s5, decryption: data user receives data cipher text CDThereafter, the data ciphertext C is encrypted using the ElGamal private key aDRecovering to corresponding plaintext content, as follows:
s51, the data user uses ElGamal algorithm to encrypt the ciphertext
Figure BDA0002620273030000122
Decryption to obtain a symmetric key psi:
using the ElGamal private key a', calculated as ═1 a′And then calculating psi ═2 -1Finally mapping psi' back to the symmetric key psi;
s52, LiDecrypting ciphertext with the symmetric key psi
Figure BDA0002620273030000123
And obtaining the plaintext content of the document.
Example 2
The embodiment discloses a multi-key searchable encryption system supporting a boolean access control policy, as shown in fig. 2, including: the system comprises an initialization and token generation subsystem running in a trusted authority TA, an encryption subsystem running in a data owner end, a cloud storage subsystem running in a cloud server, and a user retrieval and decryption subsystem running in a data user end.
The trusted authority TA is a completely trusted third-party security organization, and the data owner side and the data user side are terminal devices with operation processing capability, including smart phones, tablets, and computers. The system may perform the multi-key searchable encryption method described in embodiment 1 that supports boolean access control policies.
The initialization and token generation subsystem operating in the trusted authority TA comprises an initialization module, a master key storage module and a token generation module:
the initialization module is used for generating a system public key pk, a master key mk and an ElGamal private key a ', distributing the public development of the system public key pk to a cloud server, storing the master key mk to the master key storage module and sending the ElGamal private key a' to a data user;
the master key storage module is used for storing a master key mk and only allowing the access of a trusted authority TA;
the token generation module is used for responding to a retrieval token generation request of the data user, checking the validity of the identity of the data user, and generating a retrieval token for the data user by using the system public key pk and the master key mk under the condition that the identity of the data user is legal
Figure BDA0002620273030000124
And to token the search
Figure BDA0002620273030000125
And sending the data to a data user.
The encryption subsystem running at the data owner end comprises a data encryption module and an index encryption module:
the data encryption module is used for acquiring a system public key pk from the cloud server, encrypting the document by using the system public key pk to obtain a data ciphertext, and then sending the data ciphertext to the cloud server;
the index encryption module is used for encrypting the keyword set of each document and the implemented access strategy by using the system public key pk to obtain a corresponding index ciphertext and sending the index ciphertext to the cloud server.
As shown in fig. 2, since each document has its own data ciphertext and index ciphertext, which are associated with each other, the data ciphertext is usually packed with the index ciphertext and sent to the storage module.
The cloud storage subsystem running on the cloud server comprises a system public key public module, a storage module and a retrieval module:
the system public key public module is used for publicly releasing the system public key generated by the trusted authority TA;
the storage module is used for storing the data ciphertext and the index ciphertext encrypted by the data owner;
the retrieval module is used for aiming at each index ciphertext CIChecking whether the index ciphertext is matched with the search token by using the system public key pk, and obtaining a data ciphertext C meeting the matching condition from the storage moduleDAnd sends it to the data user.
The user retrieval and decryption subsystem running at the data user side comprises a user retrieval module and a data decryption module:
the user search module is used for sending a token generation request to the trusted authority TA and simultaneously setting the attribute set S of the data user to be (a)1，...，an) And query keyword predicates
Figure BDA0002620273030000131
Upload to trusted authorityThe authority TA completes the generation operation of the search token, and when receiving the search token of the credible authority TA
Figure BDA0002620273030000132
Then, the user retrieval module is further used for sending the token to the cloud server to continue to complete retrieval operation;
the data decryption module is used for using an ElGamal private key a' to obtain a data ciphertext CDAnd decrypting and restoring the data ciphertext into corresponding plaintext content.
As shown in fig. 3, the system of the present embodiment is applied to a medical scene, and the system may specifically be a healthcare system. The system has multiple-bit data users (data user 1, data user 2, … …, data user m) that can store documents of multiple-bit data owners (data owner 1, data owner 2, … …, data owner n). Here, the number m' of keyword fields of the document is set to 5, and each keyword field is name, age, sex, disease, provider; the number n' of attribute fields of the data user is 4, and each attribute field is name, number, organization, and department.
The working process of the system is as follows:
firstly, the trusted authority runs an initialization module of an initialization and token generation subsystem: according to security parameters
Figure BDA0002620273030000133
Generating a system public key pk, a master key mk and an ElGamal private key a ', distributing the system public key pk to a cloud server, storing the master key mk to a master key storage module, and sending the ElGamal private key a' to a data user.
The data owner 1 is set to own three documents 1, 2, 3. Wherein:
the keywords corresponding to each keyword field of the document 1 are as follows: "wu li", 23 ", men", heart disease "and hospital a" implement the access policy: the number is "01234" OR (institution "hospital a" AND department "cardiology");
the keywords corresponding to each keyword field of the document 2 are as follows: "plum", "27", "male", "myocarditis", "hospital a", the access policy implemented was: the numbering is "01234" OR institution "hospital a";
the keywords corresponding to each keyword field of the document 3 are as follows in sequence: "liu hua", "20", "man", "heart disease" and "hospital a", the access policies implemented are: the number is "12345" OR (institution "hospital a" AND department "cardiology");
in order to encrypt the documents, the data owner 1 firstly operates an encryption subsystem, obtains a system public key pk from a cloud storage subsystem on a cloud server, and then sequentially encrypts the three documents by using the system public key pk to generate an index ciphertext
Figure BDA0002620273030000141
And data cipher text
Figure BDA0002620273030000142
And cipher the data
Figure BDA0002620273030000143
And uploading to a cloud server.
And after receiving the data ciphertext of the data owner 1, the cloud server stores the data ciphertext in a storage module of the cloud storage subsystem. For simplicity of explanation, it is assumed here that the current storage module stores only the above three ciphertexts of data owner 1
Figure BDA0002620273030000144
The attributes corresponding to each attribute field of the data user 1 are as follows in sequence: "royal jelly", "01234", "Hospital A" and "department of cardiology". If the data user wants to inquire about the document with the provider being hospital A and the disease being heart disease, the user searching module of the user searching and decrypting subsystem is operated, and the user attribute set S is (royal frost, 01234, hospital A and cardiology), and predicates of the query keywords are set by the user searching and decrypting module
Figure BDA0002620273030000145
AND (heart disease) to the trusted authority TA so that the trusted authority TA verifies the user identity AND generates a search token.
The trusted authority TA receives the user attribute set S and the query keyword predicate of the data user 1
Figure BDA0002620273030000146
Thereafter, a token generation module is run which, after verifying that the identity of the data user 1 is legitimate, uses the system public key pk and the master key mk to generate a retrieval token for it
Figure BDA0002620273030000147
And to token the search
Figure BDA0002620273030000148
To the data user 1.
Data user 1 receives search token of credible authority TA
Figure BDA0002620273030000149
And then, operating the user retrieval module to send the retrieval token to the cloud server so as to perform the next retrieval operation.
After the cloud server receives a query request of a data user 1 (the data user operates a user retrieval module of a user retrieval and decryption subsystem and inputs a user attribute set and a query keyword predicate), the cloud server operates a retrieval module which uses a system public key pk to retrieve a token
Figure BDA0002620273030000151
And index ciphertext in storage module
Figure BDA0002620273030000152
And carrying out matching operation in sequence. Assume here that the data cipher text
Figure BDA0002620273030000153
Match, when matching operationAfter the completion, the cloud server encrypts the data ciphertext meeting the conditions
Figure BDA0002620273030000154
And returns to data user 1.
The data user 1 receives the returned data ciphertext
Figure BDA0002620273030000155
Then, a decryption module of the user retrieval and decryption subsystem is operated, and the decryption module decrypts the data ciphertext by using the ElGamal private key a
Figure BDA0002620273030000156
The plaintext content of the document 1 is recovered.
It should be noted that, the system of the present embodiment is only illustrated by the division of the functional modules, and in practical applications, the functions may be distributed by different functional modules as needed, that is, the internal structure may be divided into different functional modules to complete all or part of the functions described above.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (9)

1. A multi-keyword searchable encryption method supporting Boolean access control policies is characterized by comprising the following steps:
s1, generating a system public key pk, a master key mk and an ElGamal private key a 'by the trusted authority TA, distributing the system public key pk to a cloud server in a public way, storing the master key mk in the trusted authority TA, and sending the ElGamal private key a' to a data user;
s2, encryption: the data owner uses the system public key pk and the keyword set O ═ O1，...，om) And access policy
Figure FDA00026202730200000114
Generating index ciphertext C for a documentIAnd data ciphertext CDAnd combines the ciphertext CI、CDUploading to a cloud server;
s3, generating a token: when a data user performs a search operation, it is first necessary to set the attribute set S to (a)1，...，an) And query keyword predicates
Figure FDA0002620273020000012
Uploading the data to a trusted authority TA, verifying whether the identity of the data user is legal or not by the trusted authority TA, and if the identity of the data user is legal, generating a retrieval token for the data user by using a system public key pk and a master key mk
Figure FDA0002620273020000013
And store the token
Figure FDA0002620273020000014
Sending the data to the data user;
s4, searching ciphertext: the data user receives the search token sent by the credible authority TA
Figure FDA0002620273020000015
Then, sending the retrieval token to a cloud server; after the cloud server receives the index ciphertext C, aiming at each index ciphertext CIChecking whether the index ciphertext and the retrieval token are matched by using the system public key pk, and transmitting the data ciphertext C meeting the matching conditionDSending the data to a data user;
s5, decryption: data user receives data cipher text CDThereafter, the data ciphertext C is encrypted using the ElGamal private key aDRestored to the corresponding plaintext content.
2. The multi-key searchable encryption method supporting boolean access control policy according to claim 1, characterized in that in step S1, the procedure for the trusted authority TA to generate the system public key pk, the master key mk, and the ElGamal private key a' is as follows:
s11 group generator using complex order bilinear group by trusted authority TA
Figure FDA0002620273020000016
Execute
Figure FDA0002620273020000017
Generating tuples (p)1，p2，p3，p4，G，GTAnd e), wherein,
Figure FDA0002620273020000018
for inputting safety parameters of the group generator, p1，p2，p3，p4Is four different prime numbers, G and GTIs a cyclic group of order N, and N ═ p1p2p3p4And satisfying bilinear mapping relation e: g → GTThe relational expression maps two elements in the group G to the group GTOne element of (1);
Figure FDA0002620273020000019
Figure FDA00026202730200000110
each represents p of G1，p2，p3，p4A subgroup of orders;
s12, the trusted authority TA randomly selects the element a, a', alpha ∈ group ZNRandomly extracting elements g, h belonging to a group
Figure FDA00026202730200000111
Element X3E group
Figure FDA00026202730200000112
Elements Z, X4E group
Figure FDA00026202730200000113
And calculated to obtain H-hZ, Y-e (g, g)αH and Y represent members of the system public key, respectively;
s13, the trusted authority TA selects a collision-resistant hash function f, where the hash function f satisfies the following mapping:
Figure FDA0002620273020000021
s14, the trusted authority TA obtains the system public key pk according to the above variables<N，g，ga，ga′，f，Y，H，X4>The master key mk ═<α，h，X3>And the ElGamal private key a';
the ElGamal private key a' is specifically sent to the data user through an encrypted channel.
3. The multi-key searchable encryption method supporting a boolean access control policy according to claim 2, characterized in that the encryption process of step S2 is as follows:
s21, predicating the keywords by the data owner
Figure FDA0002620273020000022
Mapping to a linear secret sharing scheme representation
Figure FDA0002620273020000023
Wherein A is lsShared matrix of x n, lsRepresenting the number of rows and n representing the number of columns; ρ is a function that maps each row of matrix a to an attribute field; t is represented by (T)ρ(1)，...，tρ(ls)) Form (a) tρ(i)Is an attribute of the attribute field rho (i), i is greater than or equal to 1 and less than or equal to ls；
The data owner randomly generates a vector v ═ (s, v)2，...，vn) E group
Figure FDA0002620273020000024
And slave group
Figure FDA0002620273020000025
In the random selection of an element Z1；s，v2，vnAs components in vector v;
for each row A of the matrix AiFrom group ZNIn the random selection of element riAnd slave group
Figure FDA0002620273020000026
In the random selection of two elements Zc，i，Zd，i；
For each keyword oxFrom the group
Figure FDA0002620273020000027
In the random selection of an element Ze，xWherein x is more than or equal to 1 and less than or equal to m;
s22, the data owner calculates the index ciphertext C according to the variablesI：
Figure FDA0002620273020000028
Wherein, C0＝Ys，C1＝gsZ1，
Figure FDA0002620273020000029
Figure FDA00026202730200000210
Figure FDA00026202730200000211
S23, randomly generating a multi-bit symmetric key psi by the data owner, encrypting the document content by using an AES algorithm to obtain a ciphertext CD，1；
S24, the data owner uses ElGamal algorithm to encrypt the symmetric key psi to obtain the ciphertext CD，2Which isThe specific process is as follows: obtaining g and g from system public key pka′Randomly selecting element y from group G, and calculating to obtain1＝gy，＝(ga′)y(ii) a Then, the symmetric key ψ is mapped to an element ψ' on G and calculated2Psi' and finally generating the ciphertext CD，2＝(1，2)；
S25, the data owner obtains the data ciphertext C according to the variables of the steps S23 and S24D＝<CD，1，CD，2>。
4. The multi-key searchable encryption method according to claim 2, wherein in step S3, the procedure for the trusted authority TA to generate the token is as follows:
s31, the credible authority TA predicates the query key words
Figure FDA0002620273020000031
Mapping to a linear secret sharing scheme representation
Figure FDA0002620273020000032
Wherein the content of the first and second substances,
Figure FDA0002620273020000033
is aOShared matrix of x m, lORepresenting the number of rows, m representing the number of columns;
Figure FDA0002620273020000034
is a general matrix
Figure FDA00026202730200000333
Each line of (a) maps to a function of a key field;
Figure FDA0002620273020000036
is shown as
Figure FDA0002620273020000037
In the form of (a) a (b),
Figure FDA0002620273020000038
is a keyword field
Figure FDA0002620273020000039
The key word of 1 is less than or equal to x' and less than or equal to lO；
S32, trusted authority TA Slave group ZNIn the random selection of two elements c1，c2Generating a vector
Figure FDA00026202730200000310
Wherein the content of the first and second substances,
Figure FDA00026202730200000311
as random numbers, from the group
Figure FDA00026202730200000312
In the random selection of two elements R0，R1；
S33, for attribute set S ═ (a)1，...，an) Each attribute a ini′From the group
Figure FDA00026202730200000313
In the random selection of element Ri′，1≤i′≤n；
S34, for
Figure FDA00026202730200000314
Each row of
Figure FDA00026202730200000315
From group ZNIn the random selection of an element sx′From the group
Figure FDA00026202730200000316
In the random selection of two elements
Figure FDA00026202730200000317
S35, the trusted authority TA calculates and obtains the retrieval token according to the variables
Figure FDA00026202730200000318
Figure FDA00026202730200000319
Wherein the content of the first and second substances,
Figure FDA00026202730200000320
Figure FDA00026202730200000321
5. the multi-key searchable encryption method supporting a boolean access control policy according to claim 4, wherein the search ciphertext process of step S4 is as follows:
s41, the cloud server searches the token
Figure FDA00026202730200000322
Is resolved into
Figure FDA00026202730200000323
Index ciphertext CIIs resolved into
Figure FDA00026202730200000324
S42, the cloud server calculates I from (A, rho)A，ρHere IA，ρRepresents {1,.. multidot.lsAll minimum subsets of (A, rho) are satisfied; wherein, if present
Figure FDA00026202730200000325
And the existence of a set of constants wi″}i″∈ISo that ∑i″∈Iwi″Ai″When (1, 0,. 0), I is said to satisfy (a, ρ);
likewise, cloud server slave
Figure FDA00026202730200000326
Middle calculation
Figure FDA00026202730200000327
Here, the
Figure FDA00026202730200000328
Represents {1,.. multidot.lOAll of them satisfy
Figure FDA00026202730200000334
A set formed by the smallest subset of (c); wherein, if present
Figure FDA00026202730200000330
And existence of a set of constants
Figure FDA00026202730200000331
So that
Figure FDA00026202730200000332
Figure FDA0002620273020000041
Then call
Figure FDA0002620273020000042
Satisfy the requirement of
Figure FDA0002620273020000043
S43, if there is I ∈ IA，ρAnd
Figure FDA0002620273020000044
wherein ∑i″∈Iwi″Ai″Given (1, 0.., 0) for some constants { w }i″}i″∈IIs formed,
Figure FDA0002620273020000045
For some constant
Figure FDA0002620273020000046
If it holds, so that the following equation holds, the algorithm outputs 1, indicating the search token
Figure FDA0002620273020000047
And index ciphertext CIMatch and cipher the corresponding dataDSending the data to a data user; otherwise, the algorithm outputs 0, which indicates that the two are not matched;
the equation is:
Figure FDA0002620273020000048
6. the multi-key searchable encryption method supporting a Boolean access control policy according to claim 3, wherein the decrypted data ciphertext C of step S5D＝<CD，1，CD，2>The process of (2) is as follows:
s51, using ElGamal algorithm by data user, and aiming at ciphertext CD，2Decryption to obtain a symmetric key psi:
using the ElGamal private key a', calculated as ═1 a′And then calculating psi ═2 -1Finally mapping psi' back to the symmetric key psi;
s52, decrypting ciphertext C by using symmetric key psiD，1And obtaining the plaintext content of the document.
7. The multi-key searchable encryption method supporting a boolean access control policy according to claim 1, wherein the trusted authority TA is a fully trusted third party security authority responsible for generating a system public key pk and a master key mk, and an ElGamal private key a 'for file decryption, wherein the system public key pk, the master key mk, and the ElGamal private key a' are all binary codes with a certain length.
8. A multi-key searchable encryption system that supports boolean access control policies, comprising: an initialization and token generation subsystem operating in a trusted authority TA, an encryption subsystem operating in a data owner side, a cloud storage subsystem operating on a cloud server, a user retrieval and decryption subsystem operating in a data user side, wherein,
the initialization and token generation subsystem operating in the trusted authority TA comprises an initialization module, a master key storage module and a token generation module:
the initialization module is used for generating a system public key pk, a master key mk and an ElGamal private key a ', distributing the public development of the system public key pk to a cloud server, storing the master key mk to the master key storage module and sending the ElGamal private key a' to a data user;
the master key storage module is used for storing a master key mk and only allowing the access of a trusted authority TA;
the token generation module is used for responding to a retrieval token generation request of the data user, checking the validity of the identity of the data user, and generating a retrieval token for the data user by using the system public key pk and the master key mk under the condition that the identity of the data user is legal
Figure FDA0002620273020000051
And to token the search
Figure FDA0002620273020000052
Sending the data to a data user;
the encryption subsystem running at the data owner end comprises a data encryption module and an index encryption module:
the data encryption module is used for acquiring a system public key pk from the cloud server, encrypting the document by using the system public key pk to obtain a data ciphertext, and then sending the data ciphertext to the cloud server;
the index encryption module is used for encrypting the keyword set of each document and the implemented access strategy by using the system public key pk to obtain a corresponding index ciphertext and sending the index ciphertext to the cloud server;
the cloud storage subsystem running on the cloud server comprises a system public key public module, a storage module and a retrieval module:
the system public key public module is used for publicly releasing the system public key generated by the trusted authority TA;
the storage module is used for storing the data ciphertext and the index ciphertext encrypted by the data owner;
the retrieval module is used for aiming at each index ciphertext CIChecking whether the index ciphertext is matched with the search token by using the system public key pk, and obtaining a data ciphertext C meeting the matching condition from the storage moduleDAnd sends it to the data user;
the user retrieval and decryption subsystem running at the data user side comprises a user retrieval module and a data decryption module:
the user search module is used for sending a token generation request to the trusted authority TA and simultaneously setting the attribute set S of the data user to be (a)1，...，an) And query keyword predicates
Figure FDA0002620273020000053
Uploading the search token to a trusted authority TA to finish the generation operation of the search token, and when receiving the search token of the trusted authority TA
Figure FDA0002620273020000054
Then, the user retrieval module is further used for sending the token to the cloud server to continue to complete retrieval operation;
the data decryption module is used for encrypting the retrieved data by using an ElGamal private key aCharacter CDAnd decrypting and restoring the data ciphertext into corresponding plaintext content.
9. The multi-key searchable encryption system supporting boolean access control policies according to claim 8, characterized in that the data owner side and the data user side are terminal devices with arithmetic processing capabilities, including smart phones, tablets, computers.
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