WO2016197769A1

WO2016197769A1 - Cloud storage ciphertext access control system based on table attributes

Info

Publication number: WO2016197769A1
Application number: PCT/CN2016/081386
Authority: WO
Inventors: 张鹏; 喻建平; 刘宏伟; 孙志伟
Original assignee: 深圳大学
Priority date: 2015-06-12
Filing date: 2016-05-09
Publication date: 2016-12-15
Also published as: CN105141574B; CN105141574A

Abstract

The present invention pertains to the technical field of cloud storage services, and provides a cloud storage ciphertext access control system based on table attributes and an access control method thereof. According to the system and the method, during the process of encryption, a data owner classifies leaf nodes on an access structure tree according to whether the threshold of a parent node corresponding to each leaf node is 1; the data owner further classifies a set of leaf nodes of which the thresholds of the parent nodes are 1 according to different types of parent nodes; then the data owner encrypts data according to the result of the classification and uploads the data to the cloud. In this way, the length of ciphertext obtained by the data owner, the amount of encryption calculation, and the amount of decryption calculation for subsequent sharing users are only related to an attribute set in which thresholds of parent nodes are not 1. In the access structure tree, if the threshold is 1, the parent node corresponds to an OR gate; otherwise, the parent node corresponds to an AND gate. Therefore, the system overheads are only related to an attribute set in which parent nodes are AND gates. When the number of OR gates in the access structure tree increases, the computational cost and communication overheads of the system are greatly reduced.

Description

Cloud storage ciphertext access control system based on table attribute

Technical field

The invention belongs to the technical field of cloud storage services, and in particular relates to a cloud storage ciphertext access control system based on table attributes.

Background technique

In the cloud storage service platform, because of the data remote hosting technology, the cloud storage service provider is the physical owner of the data, but not in the same trust domain as the data owner. A cloud storage service provider manages multiple users and their resources. When users access other user resources across borders, they need to adopt certain access control policies to control access to data and services. However, in practice, because the cloud storage service platform adopts the virtualized storage technology, the cloud storage service is loosely coupled with the underlying hardware environment, and the data of different users lacks a fixed security boundary, thereby increasing the cloud storage. The difficulty of the service platform to implement access control on data.

In the prior art, an Attribute-based Encryption (ABE) scheme describes a user identity by an attribute, and a user private key and a ciphertext are respectively associated with a set of attributes, and when the user private key attribute and the ciphertext attribute match each other When the threshold is set, the user can successfully decrypt the ciphertext.

However, the ABE scheme can only support the threshold access control policy. In order to express a more flexible access control policy, a Cipher Policy Attribute-based Encryption (CP-ABE) scheme is proposed. In the CP-ABE scheme, the ciphertext is related to the access policy, and the user private key is related to the attribute set. The user can successfully decrypt the ciphertext only if the attribute of the user's private key satisfies the ciphertext access policy. The CP-ABE solution greatly reduces the network bandwidth and node computing overhead caused by fine-grained access control of data sharing, and is one of the most suitable ciphertext access control technologies for cloud storage platforms.

For the cloud storage platform adopting the CP-ABE solution, consider the enterprise application scenario, and the attributes and access policies need to be deployed through the table. However, due to the large set of attributes, the access structure is very complicated, CP-ABE The implementation of the solution in the cloud storage platform is very inefficient.

Summary of the invention

The object of the present invention is to provide a cloud storage ciphertext access control system based on a table attribute, which aims to solve the problem that a cloud storage platform adopting the CP-ABE solution deploys attributes and access policies through a table, because the attribute set is large and the access structure is complicated. , making the CP-ABE scheme implementation inefficient.

The present invention is implemented as a cloud storage ciphertext access control system based on a table attribute, the system comprising:

a management end running by the authentication center, configured to generate and distribute a user private key to each legal user, where the user private key is associated with an attribute of the corresponding user;

The client running by the user is used to select a session key and encrypt the data to be uploaded when uploading data to the cloud, and then according to whether the threshold of the parent node corresponding to each leaf node on the access tree is 1. Classifying each leaf node, and further classifying the set of leaf nodes whose parent node has a threshold of 1 according to the type of the parent node, and then encrypting the session key according to the classification result to obtain the session key ciphertext. The session key ciphertext and the encrypted data are uploaded to the cloud, and are used to download the session key ciphertext and the corresponding shared data from the cloud when the data is downloaded from the cloud, and is related to the private key of the user. When the linked attribute satisfies the access tree, the session key is decrypted to obtain the session key, and then the corresponding shared data is decrypted by using the decrypted session key.

Another object of the present invention is to provide an access control method for a cloud storage ciphertext access control system based on a table attribute as described above, the method comprising:

The certification center runs the management terminal, generates a system public key and a master private key, and uploads the system public key to the cloud;

The authentication center runs the management terminal to authenticate the user as a legitimate user according to the system join request sent by the user. When the user is a legitimate user, the user's private key is calculated and distributed to the user.

The data belongs to the main running client, and the session key is selected and encrypted for the data to be uploaded, and then the leaf nodes are determined according to whether the threshold of the parent node corresponding to each leaf node in the access tree is 1. Performing classification, and further classifying the set of leaf nodes whose parent node has a threshold of 1 according to the type of the parent node, and then encrypting the session key according to the classification result to obtain the session key ciphertext, and then the The session key ciphertext and the encrypted data are uploaded to the cloud;

The shared user runs the client, downloads the session key ciphertext and the corresponding shared data from the cloud, and when the attribute associated with the private key of the user meets the access structure tree, the session key is decrypted to obtain the session key, and then the session key is decrypted. The corresponding shared data is decrypted using the decrypted session key.

According to the table attribute-based cloud storage ciphertext access control system and the access control method thereof, the data owner belongs to the encryption process, and according to whether the threshold of the parent node corresponding to each leaf node on the access structure tree is 1, The leaf nodes are classified, and the collection of leaf nodes whose parent node has a threshold of 1 is further classified according to the type of the parent node, and then the data is encrypted according to the classification result and then uploaded to the cloud. In this way, the ciphertext length obtained by the data owner, the cryptographic calculation amount, and the decryption calculation amount of the subsequent shared user are only related to the attribute set whose parent node threshold is not 1, and in the access structure tree, the threshold value is 1 corresponding to the gate. Otherwise, it corresponds to the AND gate. Therefore, it can be said that the system overhead is only related to the parent node's attribute set of the AND gate. When the OR gate in the access structure tree increases, the calculation cost and communication of the system relative to the existing CP-ABE scheme. The overhead will be greatly reduced, enabling users to provide privacy protection, data sharing and access control services more efficiently.

DRAWINGS

1 is a structural diagram of a cloud storage ciphertext access control system based on a table attribute provided by the present invention;

2 is a flowchart of an access control method of a cloud storage ciphertext access control system based on a table attribute provided by the present invention;

3 is a diagram showing an example of an access tree of the present invention.

detailed description

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

In view of the problems existing in the prior art, it is considered that the table attribute has the following two characteristics: First, the attribute is classified, as shown in Table 1 below is a roster of an enterprise:

Table 1

序号Serial number	姓名Name	性别gender	职位position	部门department
001001	AlanAlan	女Female	首席执行官Chief executive	总部Headquarters
002002	JohnJohn	男male	总经理General manager	总部Headquarters
003003	AlexAlex	男male	经理manager	人力资源部Human Resources Department
004004	StevenSteven	男male	经理manager	财务部Finance department
…...	…...	…...	…...	…...

In the above table, all attributes are divided into five types. Second, the same attribute type or gate (OR gate) in the access structure tree is more than the AND gate (AND gate). As shown in the above table, the probability of occurrence of the serial number 001OR 002OR 003 is higher. Large, the serial number 001AND 002AND 003 has a very low probability of occurrence. Therefore, in the present invention, in the encryption process, the data owner classifies each leaf node according to whether the threshold of the parent node corresponding to each leaf node on the access tree is 1, and further according to the type of the parent node, The collection of the leaf nodes whose threshold is 1 on the parent node is classified, and then the data is encrypted according to the classification result and uploaded to the cloud.

FIG. 1 shows the structure of a table attribute-based cloud storage ciphertext access control system provided by the present invention. For the convenience of description, only parts related to the present invention are shown.

Specifically, the system of the present invention includes: a management terminal 11 operated by an authentication center for generating and distributing a user private key to each legal user, the user private key being associated with the attribute of the corresponding user; and the client running by the user 12, when the data is uploaded to the cloud, the session key is selected and encrypted according to the data to be uploaded, and then the leaf nodes are performed according to whether the threshold of the parent node corresponding to each leaf node on the access tree is 1. Classification, and further classifying the set of leaf nodes whose parent node has a threshold of 1 according to the type of the parent node, and then encrypting the session key according to the classification result to obtain the session key ciphertext, and then the session key ciphertext And encrypted data is uploaded to the cloud and also used in the cloud When the data is downloaded, the session key ciphertext and the corresponding shared data are downloaded from the cloud, and when the attribute associated with the private key of the user meets the access tree, the session key is decrypted to obtain the session key, and then the session key is used. The decrypted session key decrypts the corresponding shared data.

In the present invention, the legal user of the system can be divided into the data owner and the shared user, the data owner and the shared user are the running entities of the client 12, and the authentication center is the running body of the management terminal 11. The data owner refers to the provider of the shared data in the cloud, the data owner formulates the access policy, and encrypts the data to be uploaded based on the access policy, and then the encrypted data is hosted to the cloud; the shared user (ie, the visitor) ) is to download the shared data from the cloud and share the ciphertext data that the user accesses the cloud. The shared user can successfully decrypt the ciphertext only if the attributes in the private key of the shared user meet the access policy defined in the cipher text. Refers to a trusted third party that interacts with the cloud in addition to the data owner and shared users. The certificate authority establishes a system and accepts user registration, and is responsible for generating a user private key associated with its respective attributes for each user. It should be understood that the purpose of defining the data owner and the shared user is to distinguish that the function of the main body running the client 12 during the running of the system is to upload data or download data, so that the data owner in a certain running process of the system can It is another shared user in the running process. Similarly, the shared user in a certain running process of the system can be the data owner in another running process.

The working principle of the cloud storage ciphertext access control system based on the table attribute of the present invention is: after the system is established, the authentication center runs the management terminal 11, generates the system public key and the main private key, and uploads the system public key to the cloud.

If the user wants to join the system, the client 12 is run to issue a system join request to the authentication center. The authentication center runs the management terminal 11, and according to the system join request, the user is authenticated as a legitimate user, and the user's private key is calculated. And distributed to the user.

When the data owner uploads the data, the data belongs to the main running client 12, and the session key is selected and encrypted according to the data to be uploaded, and then according to whether the threshold of the parent node corresponding to each leaf node in the access tree is 1. Classify each leaf node, and further classify the set of leaf nodes whose parent node has a threshold of 1 according to the type of the parent node, and then add the session key according to the classification result. Obtain the session key ciphertext, and then upload the session key ciphertext and the encrypted data to the cloud.

When the shared user downloads data from the cloud, the shared user runs the client 12, downloads the session key ciphertext and the corresponding shared data from the cloud, and when the attribute associated with the private key of the user meets the access tree, the session is dense. The key ciphertext decrypts the session key, and then decrypts the corresponding shared data by using the decrypted session key.

In the cloud attribute ciphertext access control system based on the table attribute provided by the present invention, in the encryption process, the data owner performs the leaf node according to whether the threshold of the parent node corresponding to each leaf node on the access tree is 1. Classification, and further classifying the set of leaf nodes whose parent node has a threshold of 1 according to the type of the parent node, and then encrypting the data according to the classification result and uploading it to the cloud. In this way, the ciphertext length obtained by the data owner, the cryptographic calculation amount, and the decryption calculation amount of the subsequent shared user are only related to the attribute set whose parent node threshold is not 1, and in the access structure tree, the threshold value is 1 corresponding to the gate. Otherwise, it corresponds to the AND gate. Therefore, it can be said that the system overhead is only related to the parent node's attribute set of the AND gate. When the OR gate in the access structure tree increases, the calculation cost and communication of the system relative to the existing CP-ABE scheme. The overhead will be greatly reduced, enabling users to provide privacy protection, data sharing and access control services more efficiently.

2 shows a flow of an access control method for a cloud storage ciphertext access control system based on a table attribute provided by the present invention, comprising the following steps:

S1: The authentication center runs the management terminal 11, generates a system public key and a master private key, and uploads the system public key to the cloud.

Further, the step of generating the system public key and the master private key may further comprise the following steps:

S11: Definition

Is a bilinear group of primes p, g is

The generator. Defining bilinear mapping

Is a hash function. Define the attribute space U={U ₁ ,...,U _m } of the system, for

With attribute set S, attribute set

Defining the Lagrangian coefficient

S12: Input security parameter λ, select random number

And calculate h=g ^β , u=g ^α and v=e(g,g) ^α , and then according to the formula

The system public key PK is obtained, and the master private key MK is obtained according to the formula MK=(β, u).

S2: The authentication center runs the management terminal 11, and according to the system joining request sent by the user, the user is authenticated as a legitimate user, and when the user is a legitimate user, the user's private key is calculated and distributed to the user.

Further, the step of calculating the user's private key of the user further includes the following steps:

S21: The authentication center uses the attribute space U to allocate a corresponding attribute set S, a set of attributes, according to the role or identity of the user.

S22: input the primary private key MK and the attribute set S of the user, and select a random number for the user.

And selecting a random number for each attribute j∈S in the attribute set S

Calculate the user private key SK according to the following formula:

Where type(j) is the table class in which attribute j is located, and D is a bilinear group

The upper element, D _j is a bilinear group

Element on,

Bilinear group

On the element, D' _j is a bilinear group

The element on it.

S3: The data belongs to the main running client 12, and the session key is selected and encrypted according to the data to be uploaded, and then the leaf nodes are classified according to whether the threshold of the parent node corresponding to each leaf node in the access tree is 1. And further classifying the set of leaf nodes whose parent node has a threshold of 1 according to the type of the parent node, and then encrypting the session key according to the classification result to obtain the session key ciphertext, and then the session key ciphertext and The encrypted data is uploaded to the cloud.

Further, step S3 further includes the following steps:

S31: The data belongs to the main running client 12, selects the session key ck, and encrypts the data M to be uploaded by using a symmetric encryption algorithm to obtain the encrypted data E _ck (M).

S32: input system public key PK, session key ck, and access tree

For accessing the structure tree

Each node x in it sets its child node number to num _x , sets its threshold value to t _x , and has 0<t _{x ≤} num _x , defines the degree of polynomial q _x as d _x , and d _x =t _x - 1, the child node of node x is sequentially labeled with the sequence number 1, ..., num _x , index (x) is the sequence number of the return node x, and att(x) is the attribute associated with the node x, type(att(x)) To return the table class in which the attribute att(x) is located, and then to access the structure tree

Root node, select random number

And set q _R (0)=s, further randomly select d _R sub-nodes to completely define the polynomial q _R , for the access tree

The node x other than the root node sets q _x (0)=q _parent (index(x)), and further randomly selects d _x child nodes to completely define the polynomial q _x . The public key PK of the system is obtained by the data owner downloading from the cloud.

S33: For accessing the structure tree

Leaf node x, if the threshold t _parent(x) of the parent node parent(x) of leaf node x is =1, then q _x (0)=q _parent(x) (0), let Y ₁ be the access tree

The set of leaf nodes in this class, Y ₂ is the access tree

The remaining set of leaf nodes, and further depending on the types of the respective parent node of the leaf node Y _1, Y ₁ is divided into the Y _11, Y _12, ....

S34: Encrypt the session key according to the following formula, and calculate the session key ciphertext CT:

among them,

For the calculation of the session key, C is the calculation of the root node, C _y is the calculation of the attribute value corresponding to the attribute y, and C' _y is the calculation of the table class of the attribute y. In particular, all leaf nodes in Y _1i have the same C _y , and if the attributes of different leaf nodes belong to the same type, they have the same C' _y .

S35: Upload the _session key ciphertext CT and the encrypted data E _ck (M) to the cloud.

S4: The shared user runs the client 12, downloads the session key ciphertext and the corresponding shared data from the cloud, and decrypts the session key ciphertext to obtain the session secret when the attribute associated with the private key of the user meets the access tree. The key is then decrypted by the decrypted session key to decrypt the corresponding shared data.

Further, step S4 may further comprise the following steps:

S41: The shared user runs the client 12, downloads the session key ciphertext CT and the corresponding shared data E _ck (M) from the cloud, and inputs the system public key PK, the private key SK _S corresponding to the attribute set S owned by the user, And the key ciphertext CT.

S42: The shared user invokes a predefined recursive function

If the shared user's attribute set S satisfies the access tree

Then calculate the decryption information A as:

In the present invention, the recursive function DecryptNode(CT, SK, x) is defined as follows:

a. If node x is a leaf node and its parent node has a threshold k _x >1, then define:

b. If node x is a leaf node and its parent node has a threshold k _x =1, then define:

c, such that a non-leaf node of node x, z for all child nodes of node x, the recursive call DecryptNode (CT, SK, z) and the output F _z. Define S _x as a set of arbitrary t _x nodes z, and F _z ≠⊥, calculate F _x according to the following formula, if no S _x set satisfying the condition is found, F _x =⊥:

S43: Decrypt the session key ciphertext CT according to the following formula to obtain the session key ck:

S44: Decrypt the data M according to the decrypted session key ck and the shared data E _ck (M).

The following is an analysis of the efficiency of the access control method based on the table attribute-based cloud storage ciphertext access control system:

definition

with

Indicates the point multiplication operation on the group, and C _e represents the bilinear pair operation. make

versus

The lengths of the elements are respectively

versus

Finite field

The length of the upper element. Definition A _C is the attribute set contained in ciphertext c, A _C1 is the attribute set whose parent node threshold is 1 and N is the number of parent nodes satisfying the condition, and A _C2 is the attribute set whose parent node threshold is greater than 1, so there is | A _C |=|A _C1 |+|A _C2 |. Definition A _u is a set of user attributes, and S represents a minimum set of attributes that satisfy the access structure. The efficiency comparison between the present invention and the classic BSW07 scheme is shown in Table 2 below:

Table 2

According to the above Table 2, the private key length of the present invention is slightly longer than the BSW07 scheme and the present invention. However, the ciphertext length and the encryption calculation amount in the BSW07 scheme are all related to |A _C |, and the ciphertext length, encryption calculation amount, and decryption calculation amount of the proposed method are related to |A _C2 |, due to |A _C |>|A _C2 |, the present invention significantly improves the communication and computational efficiency of the ciphertext access control method.

If the data owner performs the encryption process using the access tree as shown in FIG. 3, the ciphertext length of the BSW07 scheme is

The amount of encryption calculation is

The ciphertext length of the method of the present invention is

The amount of encryption calculation is

At the same time, the more efficiency improvements in the access tree in the access tree, the more significant the improvement.

In summary, in the cloud attribute ciphertext access control system and the access control method thereof based on the table attribute provided by the present invention, the data owner belongs to each leaf node in the access structure tree in the encryption process. Whether the threshold of the parent node is 1, to classify each leaf node, and further classify the set of leaf nodes whose parent node has a threshold of 1 according to the type of the parent node, and then encrypt and upload the data according to the classification result. To the cloud. In this way, the ciphertext length obtained by the data owner, the cryptographic calculation amount, and the decryption calculation amount of the subsequent shared user are only related to the attribute set whose parent node threshold is not 1, and in the access structure tree, the threshold value is 1 corresponding to the gate. Otherwise, it corresponds to the AND gate. Therefore, it can be said that the system overhead is only related to the parent node's attribute set of the AND gate. When the OR gate in the access structure tree increases, the calculation cost and communication of the system relative to the existing CP-ABE scheme. The overhead will be greatly reduced, enabling users to provide privacy protection, data sharing and access control services more efficiently.

A person of ordinary skill in the art can understand that all or part of the steps in implementing the above embodiments may be controlled by a program to control related hardware, and the program may be stored in a computer readable storage medium, the storage. Media, such as ROM/RAM, disk, CD, etc.

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

Claims

A cloud storage ciphertext access control system based on a table attribute, wherein the system comprises:

a management end running by the authentication center, configured to generate and distribute a user private key to each legal user, where the user private key is associated with an attribute of the corresponding user;

The client running by the user is used to select a session key and encrypt the data to be uploaded when uploading data to the cloud, and then according to whether the threshold of the parent node corresponding to each leaf node on the access tree is 1. Classifying each leaf node, and further classifying the set of leaf nodes whose parent node has a threshold of 1 according to the type of the parent node, and then encrypting the session key according to the classification result to obtain the session key ciphertext. The session key ciphertext and the encrypted data are uploaded to the cloud, and are used to download the session key ciphertext and the corresponding shared data from the cloud when the data is downloaded from the cloud, and is related to the private key of the user. When the linked attribute satisfies the access tree, the session key is decrypted to obtain the session key, and then the corresponding shared data is decrypted by using the decrypted session key.
An access control method for a cloud storage ciphertext access control system based on a table attribute according to claim 1, wherein the method comprises:

The certification center runs the management terminal, generates a system public key and a master private key, and uploads the system public key to the cloud;

The authentication center runs the management terminal to authenticate the user as a legitimate user according to the system join request sent by the user. When the user is a legitimate user, the user's private key is calculated and distributed to the user.

The data belongs to the main running client, and the session key is selected and encrypted according to the data to be uploaded, and then the leaf nodes are classified according to whether the threshold of the parent node corresponding to each leaf node in the access tree is 1, and further Sorting the set of leaf nodes whose threshold value is 1 of the parent node according to the type of the parent node, and then encrypting the session key according to the classification result to obtain the session key ciphertext, and then the session key ciphertext And the encrypted data is uploaded to the cloud;

The shared user runs the client, downloads the session key ciphertext and the corresponding shared data from the cloud, and decrypts the session key ciphertext when the attribute associated with the private key of the user meets the access tree. The voice key is then decrypted by the decrypted session key to decrypt the corresponding shared data.
The access control method for a cloud storage ciphertext access control system based on a table attribute according to claim 2, wherein the step of generating a system public key and a master private key comprises the following steps:

definition
Is a bilinear group of primes p, g is
The generator, defining the bilinear map e: H:
Is a hash function that defines the system's attribute space U={U 1 ,...,U m }, for
With the attribute set S, the attribute set
Defining the Lagrangian coefficient

Enter the security parameter λ and select the random number
And calculate h=g β , u=g α and v=e(g,g) α , and then according to the formula
The system public key PK is obtained, and the master private key MK is obtained according to the formula MK=(β, u).
The access control method for a cloud storage ciphertext access control system based on a table attribute according to claim 3, wherein the step of calculating a user private key of the user comprises the following steps:

The authentication center uses the attribute space U to assign a corresponding attribute set S to the user according to the role or identity of the user, and the attribute set

Enter the primary private key MK and the user's attribute set S to select a random number for the user.
And selecting a random number for each attribute j∈S' in the attribute set S
Calculate the user private key SK according to the following formula:

Where type(j) is the table class in which attribute j is located, and D is a bilinear group
The upper element, D j is a bilinear group
Element on,
Bilinear group
On the element, D' j is a bilinear group
The element on it.
The access control method for a cloud storage ciphertext access control system based on a table attribute according to claim 4, wherein the data belongs to a main running client, and a session key is selected and encrypted for data to be uploaded, and then Classify each leaf node according to whether the threshold of the parent node corresponding to each leaf node in the access tree is 1, and further classify the set of leaf nodes whose parent node has a threshold of 1 according to different parent node types. And then adding the session key according to the classification result. The step of obtaining the session key ciphertext and then uploading the session key ciphertext and the encrypted data to the cloud includes the following steps:

The data belongs to the main running client, selects the session key ck, and encrypts the data M to be uploaded by using a symmetric encryption algorithm to obtain the encrypted data E ck (M);

Enter the system public key PK, session key ck, and access tree
For accessing the structure tree
Each node x in it sets its child node number to num x , sets its threshold value to t x , and has 0<t x ≤ num x , defines the degree of polynomial q x as d x , and d x =t x - 1, the child node of node x is sequentially labeled with the sequence number 1, ..., num x , index (x) is the sequence number of the return node x, and att(x) is the attribute associated with the node x, type(att(x)) To return the table class in which the attribute att(x) is located, and then to access the structure tree
Root node, select random number
And set q R (0)=s, further randomly select d R sub-nodes to completely define the polynomial q R , for the access tree
For other nodes x other than the root node, set q x (0) = q parent (index(x)), and further randomly select d x child nodes to completely define the polynomial q x ;

For accessing the structure tree
Leaf node x, if the threshold t parent(x) of the parent node parent(x) of leaf node x is =1, then q x (0)=q parent(x) (0), let Y 1 be the access tree
The set of leaf nodes in this class, Y 2 is the access tree
The remaining set of leaf nodes, and further depending on the type of the parent node Y 1 each leaf node of the Y 1 is divided into Y 11, Y 12, ...;

The session key is encrypted according to the following formula, and the session key ciphertext CT is calculated:

among them,
For the calculation of the session key, C is the calculation of the root node, C y is the calculation of the attribute value corresponding to the attribute y, and C' y is the calculation of the table category of the attribute y;

Upload the session key ciphertext CT and the encrypted data E ck (M) to the cloud.
The access control method for a cloud storage ciphertext access control system based on a table attribute according to claim 5, wherein the shared user runs a client, and downloads a session key ciphertext from the cloud. Corresponding shared data, and when the attribute associated with the private key of the user meets the access tree, the session key is decrypted to obtain the session key, and then the session key obtained by decrypting is used to decrypt the corresponding share. The steps of the data include the following steps:

The shared user runs the client, downloads the session key ciphertext CT and the corresponding shared data E ck (M) from the cloud, and inputs the system public key PK, the private key SK S corresponding to the attribute set S owned by the user, and the key. Ciphertext CT;

Shared user calls a predefined recursive function
If the shared user's attribute set S satisfies the access tree
Then calculate the decryption information A as:

The session key ciphertext CT is decrypted according to the following formula to obtain the session key ck:

The data M is decrypted based on the decrypted session key ck and the shared data E ck (M).