CN108111540A - The hierarchical access control system and method for data sharing are supported in a kind of cloud storage - Google Patents

Abstract

The invention belongs to the technical field of protecting data access through a platform, and discloses a layered access control system and method supporting data sharing in cloud storage, including: a trusted authorization center generates system secret information and public information, and sends Users disclose public information of the system; the trusted authorization center generates the key of each user group based on the key aggregation method according to the hierarchical structure of the user group and distributes it to all corresponding users; the user utilizes the system public information of any target user group to The data to be shared is encrypted and uploaded to the cloud server; legitimate users obtain the ciphertext data stored in the cloud server and use the user group key to decrypt the data; The system update and re-encryption process are carried out by the letter authorization center and the cloud server. The invention realizes layered access control that supports flexible data security sharing and does not require a key derivation process under a public key cryptosystem for a cloud storage environment.

Description

Hierarchical access control system and method supporting data sharing in cloud storage

technical field

The invention belongs to the technical field of protecting data access through a platform, and in particular relates to a layered access control system and method supporting data sharing in cloud storage.

Background technique

At present, the existing technologies commonly used in the industry are as follows: cloud computing is a new computing model, which is based on dynamically scalable virtualization technology, uses computing as a resource, and provides on-demand services to users with limited resources through the Internet. computing services. With the explosive growth of data volume in cyberspace, the problem of data storage becomes more and more difficult. As an extension of cloud computing technology, cloud storage service provides outsourced storage solutions for data. Cloud service providers use cloud storage servers to provide users with data storage resources and related management services. Users purchase storage services by paying a certain fee, and outsource and store related data on cloud servers. Compared with organizations or individual users who deploy storage devices and management software by themselves, this outsourced storage model has the advantages of lower cost, on-demand selection, convenient management, and access anywhere. However, users' outsourced storage data may contain sensitive information, such as government confidential documents, corporate business data, and personal medical information. data poses a security threat. Once the user uploads the data to the cloud server, it can only access and process the outsourced storage data through remote operation. In this way, users are likely to lose autonomous control over outsourced storage data. In addition, in addition to malicious attackers, cloud service providers may also be driven by interests to work in a semi-trusted mode, that is, cloud service providers strictly enforce the provisions of the agreement, but maximize user interaction through interaction with users. privacy information. Therefore, the user should encrypt the data and store it on the cloud server in the form of cipher text to ensure that the data information is not leaked to unauthorized users. How to ensure the safe sharing and access of data by multiple users in the cloud storage mode Control became a burning problem. Existing cloud storage data security sharing and access control schemes are generally based on attribute-based encryption (ABE) technology, that is, assign a set of specific attributes to users according to their identities, and formulate different access rights for file data with different access authority requirements. Control policy, only users whose attributes meet the requirements of the file access control policy can decrypt files. However, in some common cloud storage application scenarios, such as enterprise cloud, government cloud, etc., users are organized in a hierarchical structure, that is, different users belong to different user groups, and there is a hierarchical relationship between user groups. , high-level users have the authority to access the data of their subordinate users, while low-level users cannot access the data of high-level users. Aiming at the problem of data access control in hierarchical scenarios, a cryptography-based solution is firstly proposed. The hierarchical structure between user sets is described as a partially ordered set relationship between security classes. Several theorems in number theory are used to The cryptographic system provides a hierarchical key management scheme to prevent collusion, but this scheme has the problem that the key size increases rapidly with the increase of the breadth and depth of the user hierarchy, and is not suitable for extending to large-scale complex structures. middle. Based on the idea of one-way function, a hierarchical access control implementation scheme under tree structure is proposed, in which different users have a single key with a fixed size. Later, a multi-user security access control scheme for outsourced data was proposed. The user hierarchical structure type of this scheme is tree type, and the key derivation method based on one-way function is adopted. The disadvantage is that each user needs to store multiple a symmetric encryption key. A dynamic hierarchical key management scheme expresses the partial order relationship between security classes in the form of a directed graph. By assigning specific public information to the nodes and edges in the graph, a hash function is used to implement any high-level class to The key derivation process for its descendant lower-level classes. Most of the current hierarchical access control methods are based on symmetric cryptosystems, and users usually only have the symmetric keys of themselves and subordinate users, so they cannot use the keys of other users to encrypt the data to be shared and store them in the cloud. Share the ciphertext data that can be decrypted by the other party to these users.

To sum up, the problem existing in the existing technology is: in the hierarchical access control method based on the symmetric cryptosystem, the user usually cannot share the ciphertext data that the other party can decrypt with any other user, which is not suitable for cloud storage data security. Share the scene.

The difficulty and significance of solving the above technical problems: How to use and improve the cryptographic methods under the public key cryptography system to realize the hierarchical key management in user hierarchical application scenarios is the difficulty in solving the above technical problems, which can be realized in cloud storage environment. Flexible data sharing for users at any level and hierarchical access control without key derivation process.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a layered access control system and method supporting data sharing in cloud storage.

The present invention is achieved in this way, a layered access control method supporting data sharing in cloud storage, the layered access control method supporting data sharing in cloud storage includes: a trusted authorization center generates system secret information and public information, And disclose the system public information to users; the trusted authorization center generates the key of each user group based on the key aggregation method according to the hierarchical structure of the user group and distributes it to all corresponding users; the user uses the system public information of any target user group The information encrypts the data to be shared, and uploads and stores it in the cloud server; legitimate users obtain the ciphertext data stored in the cloud server, and use the user group key to decrypt the data; when it is necessary to revoke the access authority of a user , trusted authorization center and cloud server for system update and re-encryption process.

Further, the layered access control method supporting data sharing in the cloud storage includes the following steps:

(1) The operating system of the trusted authorization center establishes the algorithm Setup(1 ^λ ,G), inputs the security parameter 1 ^λ and the user group hierarchical structure G, and generates a non-public random number α, which represents n user groups Group system parameters {γ _i }, identities {id _i } of n user groups, public matrix M and system public parameter param, and public user group identity {id _i }, public matrix M and system public parameter param;

(2) The trusted authorization center generates and distributes keys for each user group in the system, runs the key generation algorithm KeyGen(G,param,i,γ _i ), inputs the user group hierarchical structure G, and the system public parameter param , the serial number i of the user group to which the key is to be distributed and its corresponding system parameter γ _i , generate the key K _i of the user group i, and distribute it to all users in the user group i;

(3) When any user intends to share the file DataFile with the target user group k, a hybrid encryption method is used to randomly generate a symmetric encryption key DEK, and the file is encrypted into {DataFile} _DEK with a symmetric encryption algorithm, and the encryption algorithm Encrypt is run (param,DEK,k,id _k ), input the system public parameter param, the symmetric encryption key DEK of the file to be shared, the serial number k of the target user group and its identity id _k , obtain the ciphertext C _DEK , and put the ciphertext header The part (k, C _DEK ) and the ciphertext body {DataFile} _DEK are uploaded and stored in the cloud server;

(4) User u in user group i obtains the ciphertext header (k, C _DEK ) and ciphertext body {DataFile} _DEK of the target user group k from the cloud server, and runs the decryption algorithm Decrypt(G, M ,param,i,K _i ,(k,C _DEK )), input user group hierarchical structure G, public matrix M, system public parameter param, serial number i of the group where user u belongs to and its corresponding key K _i And the ciphertext header (k, C _DEK ), if the user group k is the user group i and its subordinate groups, it can be decrypted to obtain the symmetric key DEK, and then the symmetric encryption algorithm is used to decrypt to obtain the DataFile, otherwise it cannot be decrypted;

(5) When a certain user v in the user group l needs to be removed from the group, that is, the user no longer has the level access rights of the group l and its subordinate user groups, the trusted authorization center runs the update algorithm Update (α,{γ _i },param,l) Update and revoke the key of the user group l and all its subordinate user groups, input the non-public random number α, and represent the non-public parameters {γ of n user groups _i }, the system public parameter param and the group number l of the user v to be revoked, generate a new public matrix M' and user group l and all its subordinate user groups New system parameters {γ _q ′} are not disclosed to anyone, new identities {id _q ′}, new keys {K _q ′} and re-encrypted tokens {TK _q } for each user group, are public New M′ and {id _q ′}, distribute new {K _q ′} to users in user group l and all its subordinate user groups, and send the re-encryption token (q, TK _q ) to the cloud server;

Each user group involved in the cloud server is user group l and all its subordinate user groups Run the re-encryption algorithm ReEncrypt((q,C _DEK ), TK _q ) for each ciphertext data in respectively, input the ciphertext header (q,C _DEK ) and its corresponding re-encryption token TK _q , and generate a new The ciphertext header (q, C _DEK ′) is updated in the cloud server.

Further, the specific process of the system establishment algorithm in (1) is as follows:

Setup(1 ^λ ,G)→(α,{γ _i },{id _i },M,param): G=(V,E) is a directed acyclic graph representing the hierarchical structure of user groups, where V= {SC _i } _1≤i≤n is a vertex set representing n user groups in the system, and E is a directed edge set representing a partial order relationship between user groups;

Randomly Selected Bilinear Cyclic Groups of Prime Order p where 2 ^λ ≤ p ≤ 2 ^λ+1 , in the group Select the generator g in the p-order prime field The selected random number α is not disclosed to the public. For i=1,...,n,n+2,...,2n, calculate Set the system public parameters as param=(g,g ₁ ,...,g _n ,g _n+2 ,...,g _2n );

in the p-order prime field Select n random numbers {γ _i } _1≤i≤n for n user groups in the system, and keep them open to no one. Set the identity of each user group i as Set the public matrix as:

Among them, if order but Otherwise, let t _i,k =0.

Further, the specific process of the key generation algorithm in (2) is as follows:

KeyGen(G,param,i,γ _i )→K _i : For the set of user groups in graph G that contains SC _i and all its descendant nodes, all j such that make calculate is the private key of user group i.

Further, the specific process of the encryption algorithm in (3) is as follows:

Encrypt(param,m,k,id _k )→(k,C _m ): for any message whose target user group is k in the p-order prime field Choose a random number t in , and calculate the ciphertext as

Further, the specific process of the decryption algorithm in (4) is as follows:

Decrypt(G,M,param,i,K _i ,(k,C _m ))→m _d : If in graph G Then the users in the user group i cannot use the key K _i to decrypt the ciphertext C _m , and return ⊥;

If in figure G Then the users in the user group i can use the key K _i to decrypt the plaintext:

in It can be obtained from the public matrix M and returns m _d .

Further, the specific process of the update algorithm in (5) is as follows:

in the p-order prime field Select new random numbers for the user group l to be updated and all its subordinate user groups It is not disclosed to anyone, and the identities of user group l and its subordinate user groups are updated as Update the public matrix M with The relevant elements generate a new public matrix M′, and recalculate the private keys of user group l and its subordinate user groups in Generate re-encryption token

Further, the specific process of the re-encryption algorithm in (5) is as follows:

ReEncrypt((q,C _m ),TK _q )→(q,C _m ′): use the re-encryption token Will update all ciphertexts of user group q middle update to get new ciphertext

Another object of the present invention is to provide a layered access control system supporting data sharing in the cloud storage according to the layered access control method supporting data sharing in the cloud storage, and the layered access supporting data sharing in the cloud storage The control system includes:

The trusted authorization center module is connected with the layered user group module and the cloud server module, and is used to generate system information and keys of all user groups in the layered user group module, and can generate a re-encryption token for The cloud server module performs data re-encryption;

The layered user group module is connected with the trusted authorization center module and the cloud server module, and is used to encrypt and store the local data to be shared on the cloud, and obtain the ciphertext data stored in the cloud server module, and manage the data The task is submitted to the cloud server module;

The cloud server module is connected with the trusted authorization center module and the layered user group module, and is used to provide data outsourcing storage and ciphertext data re-encryption services, instead of user storage and management of data.

Another object of the present invention is to provide a cloud storage service system applying the layered access control method supporting data sharing in the cloud storage.

In summary, the advantages and positive effects of the present invention are: the present invention realizes hierarchical access control under the public key cryptosystem based on the key aggregation method, and only needs to distribute a single key with a fixed length to the user to realize self-protection. Decryption of the user group and subordinate user group data. At the same time, users can share ciphertext data that can be decrypted by the other party to user groups of any level, without using the other party's key to encrypt the data to be shared, which is suitable for cloud storage data security sharing scenarios. In addition, the decryption process of the present invention does not require a key derivation step, and the user can directly use the key of the user group to decrypt the ciphertext data of the subordinate user group. In addition, the present invention also supports local key update and cloud server entrusted re-encryption, that is, in the process of user revocation, it is only necessary to update the keys of the revoked user's group and its subordinate groups and entrust the cloud server to Group's data is re-encrypted without affecting other user groups.

The comparison between the technical effect realized by the present invention and the prior art is shown in Table 1.

Table 1

Description of drawings

Fig. 1 is a flowchart of a hierarchical access control method supporting data sharing in cloud storage provided by an embodiment of the present invention.

2 is a schematic structural diagram of a hierarchical access control system supporting data sharing in cloud storage provided by an embodiment of the present invention;

In the figure: 1. Trusted authorization center module; 2. Hierarchical user group module; 3. Cloud server module.

Fig. 3 is a structural block diagram of a hierarchical access control system supporting data sharing in cloud storage provided by an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The present invention realizes hierarchical access control under the public key cryptosystem based on the key aggregation method, and only needs to distribute a single key with a fixed length to the user to realize the decryption of the data of the user group in which the user belongs and subordinate user groups.

As shown in Figure 1, the layered access control method supporting data sharing in the cloud storage provided by the embodiment of the present invention includes the following steps:

S101: System initialization: the trusted authorization center generates system secret information and public information, and discloses system public information to users;

S102: Hierarchical key distribution: the trusted authorization center generates the key of each user group based on the key aggregation method according to the hierarchical structure of the user group and distributes it to all corresponding users;

S103: Ciphertext data sharing: the user encrypts the data to be shared by using the system public information of any target user group, and uploads and stores it to the cloud server;

S104: Data decryption: the legal user obtains the ciphertext data stored in the cloud server, and uses the user group key to decrypt the data;

S105: User revocation: when the access right of a certain user needs to be revoked, the trusted authorization center and the cloud server perform a system update and re-encryption process.

As shown in FIG. 2 , the hierarchical access control system supporting data sharing in cloud storage provided by the embodiment of the present invention includes: a trusted authorization center module 1 , a hierarchical user group module 2 and a cloud server module 3 .

The trusted authorization center module 1 is connected with the layered user group module 2 and the cloud server module 3, and is used to generate system information and keys of all user groups in the layered user group module 2, and can generate a re-encryption order card, used for cloud server module 3 to re-encrypt data;

The layered user group module 2 is connected with the trusted authorization center module 1 and the cloud server module 3, and is used to encrypt and store the local data to be shared on the cloud, and obtain the ciphertext data stored in the cloud server module 3 , the data management task is submitted to the cloud server module 3;

The cloud server module 3 is connected with the trusted authorization center module 1 and the layered user group module 2, and is used to provide data outsourcing storage and ciphertext data re-encryption services, instead of user storage and management of data.

The present invention assumes that the cloud server is honest but curious. That is to say, the cloud server will honestly perform operations such as data storage and re-encryption specified by the protocol, but may try to analyze and obtain relevant plaintext information from the ciphertext data stored in the cloud server.

The layered access control method supporting data sharing in the cloud storage of the present invention mainly achieves the following goals:

Flexible data sharing. All users can choose any user group in the hierarchical user group as the target group, encrypt the data to be shared, and generate and share ciphertext data that can be decrypted by the other party.

safety. For the ciphertext data stored in the cloud server, only users in the corresponding target user group and its subordinate user groups can decrypt the ciphertext data, and the cloud server and other users cannot obtain the plaintext information of the data.

Support dynamic update. When a user in a user group exits the user group, the trusted authorization center can update the information related to the user group and its subordinate user groups in the system, and entrust the cloud server to update the information of the user group involved. The group's ciphertext data is re-encrypted for forward and backward security.

In the system of the embodiment of the present invention, the cryptographic primitives used are bilinear pairings, which are specifically described as follows:

make and is a cyclic group of two order prime numbers p, is a mapping relationship with the following properties:

1) Bilinear: for any and have established;

2) Non-degenerate: exists Satisfy e(g,g)≠1;

3) Computability: There are efficient algorithms such that for any Both e(g ₁ , g ₂ ) can be calculated.

in, is called a bilinear group. Many types of elliptic curves satisfy the properties of the bilinear group.

Hierarchical access control method of the present invention

(1) System initialization

Trusted authorization center operation system establishes algorithm Setup(1 ^λ , G), inputs security parameter 1 ^λ and user group hierarchical structure G, generates non-public random number α, non-public system representing n user groups Parameters {γ _i }, identities {id _i } of n user groups, public matrix M and system public parameter param, and public user group identity {id _i }, public matrix M and system public parameter param;

(2) Level key distribution

The trusted authorization center generates and distributes keys for each user group in the system, runs the key generation algorithm KeyGen(G,param,i,γ _i ), and inputs the user group hierarchical structure G, the system public parameter param, the proposed distribution The user group number i of the key and its corresponding system parameter γ _i , generate the key K _i of user group i, and distribute it to all users in user group i;

(3) Ciphertext data sharing

When any user intends to share the file DataFile with the target user group k, a hybrid encryption method is adopted. First, a symmetric encryption key DEK is randomly generated, and the file is encrypted into {DataFile} _DEK with a symmetric encryption algorithm, and then the encryption algorithm Encrypt( param, DEK, k, id _k ), input the system public parameter param, the symmetric encryption key DEK of the file to be shared, the serial number k of the target user group and its identity id _k to obtain the ciphertext C _DEK , and add the ciphertext header (k, C _DEK ) and the ciphertext body {DataFile} _DEK are uploaded and stored in the cloud server;

(4) Data decryption

User u in user group i obtains the ciphertext header (k,C _DEK ) and ciphertext body {DataFile} _DEK of the target user group k from the cloud server, and runs the decryption algorithm Decrypt(G,M,param, i,K _i ,(k,C _DEK )), input user group hierarchical structure G, public matrix M, system public parameter param, serial number i of the group where user u belongs to and its corresponding key K _i and ciphertext Header (k, C _DEK ), if the user group k is user group i and its subordinate groups, it can be decrypted to obtain the symmetric key DEK, and then the symmetric encryption algorithm is used to decrypt to obtain the DataFile, otherwise it cannot be decrypted;

(5) User cancellation

Since in real application scenarios, the frequency of changes involving the hierarchical structure of user groups is low, such as adding user groups, deleting user groups, adding hierarchical relationships, and deleting hierarchical relationships, etc., in the first case, consider re-initializing the system and As for the follow-up steps, in the last three cases, consider updating the hierarchical structure G of user groups and performing processes such as key update and re-encryption of relevant user groups. The invention mainly considers the more frequently occurring update case of revoking a user's access rights in a user group.

When a certain user v in user group l needs to be removed from the group, that is, the user no longer has the level access authority of group l and its subordinate user groups, the trusted authorization center runs the update algorithm Update(α, {γ _i },param,l) Update and revoke the keys of the group l the user belongs to and all its subordinate user groups, input the non-public random number α, the non-public parameters {γ _i } representing n user groups, The system public parameter param and the group number l of the user v to be revoked generate a new public matrix M' and user group l and all its subordinate user groups New system parameters {γ _q ′} are not disclosed to anyone, new identities {id _q ′}, new keys {K _q ′} and re-encrypted tokens {TK _q } for each user group, are public New M′ and {id _q ′}, distribute new {K _q ′} to users in user group l and all its subordinate user groups, and send the re-encryption token (q, TK _q ) to the cloud server;

Each user group involved in the cloud server is user group l and all its subordinate user groups Run the re-encryption algorithm ReEncrypt((q,C _DEK ), TK _q ) for each ciphertext data in respectively, input the ciphertext header (q,C _DEK ) and its corresponding re-encryption token TK _q , and generate a new The ciphertext header (q, C _DEK ′) is updated in the cloud server.

The algorithm contained in the present invention is described in detail

The hierarchical structure of user groups in the present invention can be composed of a partially ordered set express. Here, V={SC ₁ ,...,SC _n } is a set of user groups. The element SC _i represents an individual user or an access group composed of multiple users with equal access rights. binary relationship Represents the hierarchical relationship of elements in the set V. symbol It means that the users in the user group SC _j can access the data corresponding to the user group SC _i . That is to say, user group SC _j has a higher access level than user group SC _i . if And there is no SC _k ∈ V such that established, it is recorded as

From the point of view of graph theory, any poset Both can be expressed as a directed graph G=(V,E). If SC _i , SC _j ∈ V and satisfy Then there exists an edge from SC _j to SC _i in G. In the hierarchical access control method of the present invention, a directed acyclic graph is used as a parameter describing the hierarchical structure of user groups.

1) System establishment algorithm Setup(1 ^λ ,G)→(α,{γ _i },{id _i },M,param):

G=(V,E) is a directed acyclic graph representing the hierarchical structure of user groups, where V={SC _i } _1≤i≤n represents the vertex set of n user groups in the system, and E represents the user group Directed edge set of partial order relationship between groups;

Randomly Selected Bilinear Cyclic Groups of Prime Order p where 2 ^λ ≤ p ≤ 2 ^λ+1 , in the group Select the generator g in the p-order prime field The selected random number α is not disclosed to the public. For i=1,...,n,n+2,...,2n, calculate Set the system public parameters as param=(g,g ₁ ,...,g _n ,g _n+2 ,...,g _2n );

in the p-order prime field Select n random numbers {γ _i } _1≤i≤n for n user groups in the system, and keep them open to no one. Set the identity of each user group i as Set the public matrix as:

Among them, if order but Otherwise, let t _i,k = 0;

2) Key generation algorithm KeyGen(G,param,i,γ _i )→K _i :

For the set of user groups in graph G that contains SC _i and all its descendant nodes, that is, all j such that make calculate is the private key of user group i.

3) Encryption algorithm Encrypt(param,m,k,id _k )→(k,C _m ):

For any message with target user group k in the p-order prime field Choose a random number t in , and calculate the ciphertext as

4) Decryption algorithm Decrypt(G,M,param,i,K _i ,(k,C _m ))→m _d :

If in figure G Then the users in the user group i cannot use the key K _i to decrypt the ciphertext C _m , and return ⊥;

If in figure G Then the users in the user group i can use the key K _i to decrypt the plaintext:

in It can be obtained from the public matrix M and returns m _d .

5) Update algorithm

in the p-order prime field Select new random numbers for the user group l to be updated and all its subordinate user groups It is not disclosed to anyone, and the identities of user group l and its subordinate user groups are updated as Update the public matrix M with The relevant elements generate a new public matrix M′, and recalculate the private keys of user group l and its subordinate user groups in Generate re-encryption token

6) Re-encryption algorithm ReEncrypt((q,C _m ),TK _q )→(q,C _m ′):

Use re-encryption token Will update all ciphertexts of user group q middle update to get new ciphertext

correctness analysis

The correctness of the data decryption process in the present invention can be drawn by the following detailed derivation process:

For the ciphertext with target user group k like Then the users in the user group i can use the and the group key Decrypt the plaintext:

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. A layered access control method supporting data sharing in cloud storage, characterized in that, the layered access control method supporting data sharing in the cloud storage comprises: a trusted authorization center generates system secret information and public information, and Public information of the system is disclosed to users; the trusted authorization center generates the key of each user group based on the key aggregation method according to the hierarchical structure of the user group and distributes it to all corresponding users; the user utilizes the system public information of any target user group Encrypt the data to be shared and upload it to the cloud server; legitimate users obtain the ciphertext data stored in the cloud server and use the user group key to decrypt the data; when it is necessary to revoke the access authority of a user, Trusted Authorization Center and cloud server for system update and re-encryption process. 2. the layered access control method supporting data sharing in cloud storage as claimed in claim 1, is characterized in that, the layered access control method supporting data sharing in described cloud storage comprises the following steps: (1) The operating system of the trusted authorization center establishes the algorithm Setup(1 ^λ ,G), inputs the security parameter 1 ^λ and the user group hierarchical structure G, and generates a non-public random number α, which represents n user groups Group system parameters {γ _i }, identities {id _i } of n user groups, public matrix M and system public parameter param, and public user group identity {id _i }, public matrix M and system public parameter param; (2) The trusted authorization center generates and distributes keys for each user group in the system, runs the key generation algorithm KeyGen(G,param,i,γ _i ), inputs the user group hierarchical structure G, and the system public parameter param , the serial number i of the user group to which the key is to be distributed and its corresponding system parameter γ _i , generate the key K _i of the user group i, and distribute it to all users in the user group i; (3) When any user intends to share the file DataFile with the target user group k, a hybrid encryption method is used to randomly generate a symmetric encryption key DEK, and the file is encrypted into {DataFile} _DEK with a symmetric encryption algorithm, and the encryption algorithm Encrypt is run (param,DEK,k,id _k ), input the system public parameter param, the symmetric encryption key DEK of the file to be shared, the serial number k of the target user group and its identity id _k , obtain the ciphertext C _DEK , and put the ciphertext header The part (k, C _DEK ) and the ciphertext body {DataFile} _DEK are uploaded and stored in the cloud server; (4) User u in user group i obtains the ciphertext header (k, C _DEK ) and ciphertext body {DataFile} _DEK of the target user group k from the cloud server, and runs the decryption algorithm Decrypt(G, M ,param,i,K _i ,(k,C _DEK )), input user group hierarchical structure G, public matrix M, system public parameter param, serial number i of the group where user u belongs to and its corresponding key K _i And the ciphertext header (k, C _DEK ), if the user group k is the user group i and its subordinate groups, it can be decrypted to obtain the symmetric key DEK, and then the symmetric encryption algorithm is used to decrypt to obtain the DataFile, otherwise it cannot be decrypted; (5) When a certain user v in the user group l needs to be removed from the group, that is, the user no longer has the level access rights of the group l and its subordinate user groups, the trusted authorization center runs the update algorithm Update (α,{γ _i },param,l) Update and revoke the key of the user group l and all its subordinate user groups, input the non-public random number α, and represent the non-public parameters {γ of n user groups _i }, the system public parameter param and the group number l of the user v to be revoked, generate a new public matrix M' and user group l and all its subordinate user groups New system parameters {γ _q ′} are not disclosed to anyone, new identities {id _q ′}, new keys {K _q ′} and re-encrypted tokens {TK _q } for each user group, are public New M′ and {id _q ′}, distribute new {K _q ′} to users in user group l and all its subordinate user groups, and send the re-encryption token (q, TK _q ) to the cloud server; Each user group involved in the cloud server is user group l and all its subordinate user groups Run the re-encryption algorithm ReEncrypt((q,C _DEK ), TK _q ) for each ciphertext data in respectively, input the ciphertext header (q,C _DEK ) and its corresponding re-encryption token TK _q , and generate a new The ciphertext header (q, C _DEK ′) is updated in the cloud server. 3. the layered access control method that supports data sharing in cloud storage as claimed in claim 2, is characterized in that, the specific process of system establishment algorithm in described (1) is as follows: Setup(1 ^λ ,G)→(α,{γ _i },{id _i },M,param): G=(V,E) is a directed acyclic graph representing the hierarchical structure of user groups, where V= {SC _i } _1≤i≤n is a vertex set representing n user groups in the system, and E is a directed edge set representing a partial order relationship between user groups; Randomly Selected Bilinear Cyclic Groups of Prime Order p where 2 ^λ ≤ p ≤ 2 ^λ+1 , in the group Select the generator g in the p-order prime field The selected random number α is not disclosed to the public. For i=1,...,n,n+2,...,2n, calculate Set the system public parameters as param=(g,g ₁ ,...,g _n ,g _n+2 ,...,g _2n ); in the p-order prime field Select n random numbers {γ _i } _1≤i≤n for n user groups in the system, and keep them open to no one. Set the identity of each user group i as Set the public matrix as: Among them, if order but Otherwise, let t _i,k =0. 4. the layered access control method that supports data sharing in cloud storage as claimed in claim 2, is characterized in that, the specific process of key generation algorithm in described (2) is as follows: KeyGen(G,param,i,γ _i )→K _i : For the set of user groups in graph G that contains SC _i and all its descendant nodes, all j such that make calculate is the private key of user group i. 5. the layered access control method that supports data sharing in cloud storage as claimed in claim 2, is characterized in that, the specific process of encryption algorithm in the described (3) is as follows: Encrypt(param,m,k,id _k )→(k,C _m ): for any message whose target user group is k in the p-order prime field Choose a random number t in , and calculate the ciphertext as 6. the layered access control method that supports data sharing in cloud storage as claimed in claim 2, is characterized in that, the specific process of decryption algorithm in the described (4) is as follows: Decrypt(G,M,param,i,K _i ,(k,C _m ))→m _d : If in graph G Then the users in the user group i cannot use the key K _i to decrypt the ciphertext C _m , and return ⊥; If in figure G Then the users in the user group i can use the key K _i to decrypt the plaintext: in It can be obtained from the public matrix M and returns m _d . 7. the layered access control method that supports data sharing in cloud storage as claimed in claim 2, is characterized in that, the specific process of update algorithm in the described (5) is as follows: in the p-order prime field Select new random numbers for the user group l to be updated and all its subordinate user groups It is not disclosed to anyone, and the identities of user group l and its subordinate user groups are updated as Update the public matrix M with The relevant elements generate a new public matrix M′, and recalculate the private keys of user group l and its subordinate user groups in Generate re-encryption token 8. the layered access control method that supports data sharing in cloud storage as claimed in claim 2, is characterized in that, the specific process of re-encryption algorithm in the described (5) is as follows: ReEncrypt((q,C _m ),TK _q )→(q,C _m ′): use the re-encryption token Will update all ciphertexts of user group q middle update to get new ciphertext 9. A layered access control system supporting data sharing in cloud storage according to a layered access control method supporting data sharing in cloud storage according to claim 1, characterized in that, the layered access control system supporting data sharing in the cloud storage Layer access control systems include: The trusted authorization center module is connected with the layered user group module and the cloud server module, and is used to generate system information and keys of all user groups in the layered user group module, and can generate a re-encryption token for The cloud server module performs data re-encryption; The layered user group module is connected with the trusted authorization center module and the cloud server module, and is used to encrypt and store the local data to be shared on the cloud, and obtain the ciphertext data stored in the cloud server module, and manage the data The task is submitted to the cloud server module; The cloud server module is connected with the trusted authorization center module and the layered user group module, and is used to provide data outsourcing storage and ciphertext data re-encryption services, instead of user storage and management of data. 10. A cloud storage service system applying the layered access control method supporting data sharing in cloud storage according to any one of claims 1 to 8.