CN102916954B - Attribute-based encryption cloud computing safety access control method - Google Patents

Abstract

The invention provides a cloud computing security access control method based on attribute encryption, which is mainly used to solve the security and privacy protection problems of the cloud computing access control structure. The purpose of this invention is to propose a method based on CP-ABE A brand-new framework MAH-ABE (Multiple and Hierarchical attribute based encryption) access control model is a ABE security framework with hierarchical domain-based multi-trust institutions-MAH-ABE. The framework not only distinguishes attributes according to private domains and public domains , and the attributes in the public domain are divided according to the level of trust institutions, so that trust institutions with different permissions are in charge of different attribute key distribution mechanisms, which greatly reduces the workload of a single trust institution and improves the user's data privacy protection. It provides features to achieve high efficiency, flexibility, and fine-grainedness.

Description

A security access control method for cloud computing based on attribute encryption

technical field

The invention is a security solution for cloud computing environment. It is mainly used to solve the security and privacy protection problems of the cloud computing access control structure, and belongs to the field of cloud computing security technology.

Background technique

Cloud computing is a new computing architecture based on virtualization and parallel distributed computing. In recent years, cloud computing has been upgraded to one of the most effective and influential industries in the IT industry, and many enterprises have transplanted a large amount of business to cloud service centers. On the one hand, users no longer need to invest in a large amount of software and hardware facilities and hire software talents to maintain these facilities, thus saving infrastructure construction costs and labor costs. On the other hand, cloud computing pays according to the user's service needs at a lower price, which has high flexibility and convenience.

The outsourced storage service model of cloud storage leads to the existence of privileged users, who have the ability to access user data without authorization, which can easily lead to internal attacks such as data information and privacy disclosure. Security is one of the important factors restricting the widespread use of cloud computing technology, so it is of great significance to study security issues in cloud computing environment. The research of access control model is a hot spot in solving security problems.

The three main problems of the access control model are: (1) The division of trust mechanism. (2) Establishment of access control tree. (3) Fine-grained division of access users. The past methods have certain defects and deficiencies in the realization of these three problems. At present, most researchers only have a lot of research on the second problem, such as the key policy attribute encryption scheme KP-ABE (key-policy attribute-based encryption) and the ciphertext policy attribute encryption scheme CP-ABE (ciphertext-policy attribute-based encryption). based encryption), the research on the (1) and (3) questions is still in the preliminary stage. A complete and practical access control system is far from enough to rely on a single trust organization and a single user group, which will bring various security and privacy issues. The existence of these problems has brought certain difficulties to the promotion of cloud computing.

Contents of the invention

Technical problem: The purpose of this invention is to propose a new framework MAH-ABE (Multiple and Hierarchical attribute based encryption) access control model on the basis of CP-ABE to solve the security and For privacy issues, the present invention provides a cloud computing security access control method based on attribute encryption, which achieves the characteristics of high efficiency, flexibility and fine-grained granularity.

Technical solution: The present invention proposes an ABE security framework with hierarchical multi-trust institutions in domains - MAH-ABE. The framework not only distinguishes attributes according to private domains and public domains, but also divides attributes in the public domain according to the levels of trust organizations , so that trust agencies with different permissions are in charge of different attribute key distribution mechanisms, which greatly reduces the workload of a single trust agency, and at the same time improves the user's data privacy protection.

Bilinear pairing is one of the key tools when designing an ABE encryption scheme. Firstly, the theorem of bilinear pairing is given: select two groups G ₁ and G ₂ whose order is a large prime number p, and define an efficient computable bilinear map e: G ₁ ×G ₁ →G ₂ , the map Must meet:

(a) Bilinear: A mapping e:G ₁ ×G ₁ →G ₂ is bilinear, when e(g ^a ,h ^b )=e(g,h) ^ab , for all g, h∈G ₁ and all a, b ∈ Z _p .

(b) Non-degenerate: there exists g, h∈G ₁ such that e(g, h)≠1. That is, all elements of G ₁ ×G ₁ cannot be mapped to the same element in G ₂ .

1. Architecture

Figure 1 shows the system model diagram of MAH-ABE, which is mainly composed of the following main bodies, a cloud service provider (a cloud service provider) referred to as CSP, a first-level trusted institution, multiple regional trusted institutions, data Subjects and Data Users. CSP provides cloud storage services, and data subjects store encrypted data in the cloud for data users to share. In order to obtain cloud data, data users download the encrypted files they need from the cloud for decryption. Compared with the traditional access control structure, this structure mainly modifies five parts: (1) the division of hierarchical trusted institutions (2) the hierarchy of attribute structure (3) the classification of user groups in public and private domains (4) ) Establishment of multi-domain access control tree (5) Setting of conversion nodes in access control tree. After modifying these parts, the increase of the overhead of the attribute-based encryption model is small, but the efficiency and fine-grained improvement of the entire access control structure are great, and the security and privacy of the system are not compromised.

Below we give a description of several specific parts:

Public domain and private domain: In this invention, two domains are divided, public domain (PUD) and private domain (PRD). PRD is mainly for some users with special rights, such as the family members of the data subject, personal assistants, etc. When the subject agrees to authorize, such groups can not only have the right to read, but also have the right to manage and modify files. This field is characterized by few users, small attribute sets, and easy management. PUD is mainly for users in large environments, such as employees of group companies and customers of medical insurance companies. Due to the large number of users and the large number of attributes, fine-grained attributes are required. distribution mechanism. The data owner does not need to know which users are in the PUD environment.

Key distribution method: In the PRD environment, due to the small number of users and small attribute scale, the CP ABE access control method is sufficient. The user principal can entrust a trusted organization to distribute and manage keys, or participate in the distribution and management of keys himself. The attribute obtained by the user in PRD is called data attribute (data attribute), which is the classification attribute of the file. Each file is pasted with data attributes, such as blog_file, photo_file, etc. Therefore, the size of the user key is linearly related to the number of data attributes obtained. In the PUD environment, due to the large number of users and the large number of attributes, we use a hierarchical regional trusted authority (domain authority, DA) to manage user attributes. Different DAs have different permissions, and each DA has Authorized by his parent trusted authority to form a hierarchical authority. Users in PUD have role attributes (role attribute, RA), and each DA is responsible for distributing and managing the private keys of users under its jurisdiction. In the PUD field, users do not need to know which users have access rights when encrypting and uploading files. They only need to specify that users with designated RAs can access the files, which greatly reduces the workload of the main user.

Hierarchical key structure: In PUD, this scheme adopts a hierarchical key structure, as shown in Figure 2. Assuming that the key level is 2, the first level is attribute individual or attribute set, and the second level can only be attribute individual. Such as: {Dept: Hospital A, Addr: West, {Position: physician, level: 3}, {Position: nurse, level: 4}}, the first layer is {Dept: Hospital A, Addr: West} and recorded as A ₀ , the second layer is {{Position:physician,level:3}, {Position:nurse,level:4}}, denoted as A ₁ and A ₂ . To sum up, the user key structure is A={A ₀ ,A ₁ ,...,A _m }, A ₀ represents the first layer key, A _i represents the i-th attribute of the second layer key Set (1≤i≤m). In this way, we can simply express this key structure as A ₀ = {0, Dept: HospitalA}, A ₁ = {1, Position: physician}, A ₂ = {2, Position: nurse}.

Access Control Trees and Transformation Nodes: In both domains, we use access control trees, where leaf nodes are attribute values and non-leaf nodes are threshold values. Assume that num _x is the number of children of the node, and k _x is the threshold value of node x, such as the values of k _x of AND and OR are 2 and 1 respectively. At the same time, we define the function parent(x) to return the parent node of x, index(x) to return the serial number of node x, and att(x) to return the attribute value represented by the leaf node. If an attribute structure satisfies an access control tree, then at least one attribute set of the attribute structure satisfies all attributes of the access control tree. In general, the combination of attributes between different attribute sets to satisfy the access control tree is not allowed. However, due to the large number of attribute sets in the PUD domain, we define a node called a translating node. The attribute values of the child nodes of the translating node can come from different attribute sets, that is, joint attributes are allowed.

The steps included in the cloud computing security access control method based on attribute encryption of the present invention are:

Step 1). Divide two user environments, public domain PUD and private domain PRD;

Step 2). The trusted organization first randomly selects generators to generate bilinear groups and bilinear maps, and then selects the key level of the PUD field to generate the master key and public key of the PUD. The master key is retained, and the public key public;

Step 3). The trusted organization uses the bilinear group and bilinear map generated in step 2 to generate the master key and public key of the PRD, the master key is kept, and the public key is made public;

Step 4). The trusted organization creates the next layer of trusted sub-organizations, assigns the first layer of attribute individuals or attribute sets, and generates master keys, and the next layer of trusted organizations can create smaller sub-organizations and assign the second layer of attributes Individuals or attribute sets, the second-level attribute individuals or attribute sets are subsets of the first-level attribute individuals or attribute sets, and keys are assigned, and so on;

Step 5). The user provides relevant information to the trusted organization and applies for legal user authority in the relevant field. If applying for the authority of the PUD field, perform step 6, and apply for the authority of the PRD field to perform step 7;

Step 6). According to the information submitted by the user, the trusted organization judges whether the user can apply for the authority of the PUD field. If not, it returns empty; The letter organization assigns the corresponding attribute individual or attribute set, generates a key component, and sends it to the user; jump to step 8;

Step 7). According to the information submitted by the user, the trusted organization judges whether the user can apply for the authority of the PRD field. If not, it will return empty. Key component, sent to the user;

Step 8). The data owner selects a unique identifier for the file uploaded to the cloud, encrypts the file symmetrically, reserves the key, and selects a public domain attribute set to form a public access control tree, and selects a private domain attribute set to form a private access control tree. Plant a tree to encrypt the file key to generate ciphertext and send it to the cloud;

Step 9). The user initiates access to the file to the cloud, and the cloud returns the ciphertext of the corresponding file. The user inputs the private key generated in step 6 or 7, and matches it with the access control tree T in the ciphertext. If it matches, the corresponding file encryption key is obtained. Key, get the file after decryption, if not match, return empty;

Step 10). The data owner sends a notice to the trusted organization, revokes the relevant user attributes, submits the relevant attribute sequence and expiration time, and entrusts the trusted organization to update the relevant user permissions;

Step 11). The trusted organization sends a notification to the relevant trusted sub-organization, and the trusted sub-organization updates the expiration time of the relevant attributes, generates a new private key assembly, and sends it to the relevant user;

Step 12). The data owner sends a notification to the cloud, updates the access control tree, submits the relevant attribute sequence and expiration time, and entrusts the cloud to update the access control structure tree;

Step 13). After receiving the update information, the cloud generates relevant components, and finally updates to the relevant access control tree, and outputs new ciphertext to replace the original ciphertext;

Step 14). The owner of the user revokes the file, and sends the file ID and his own signature to the cloud;

Step 15). The cloud deletes the file after confirming the signature, and returns the message that the owner deleted it successfully.

The key structure of the PUD is a hierarchical key structure, and the trusted institution is a hierarchical trusted institution.

There are two types of access control tree: public access control tree and private access control tree. The nodes in the public access control tree have joint nodes, which support joint attribute set access.

Beneficial effects: the method of the present invention aims at the security and privacy issues in the cloud computing environment, and on the basis of CP-ABE, proposes a new access control model of MAH-ABE, which divides the public domain and the private domain, and the private domain adopts CP-ABE ABE ciphertext access control, the public domain uses hierarchical multi-trust institutions to manage attributes and keys, reducing management complexity. At the same time, the model introduces the attribute of failure time to perform attribute update operations. The model is efficient, flexible, fine-grained and secure. Below we give specific instructions.

[Different areas are divided] Based on the different characteristics of the user groups, the present invention divides the public area and the private area. In the past model, all users are in one domain, subject to the same access control model, and have the same key management and distribution method. Inconvenience to users with special privileges. For example, in the personal health record cloud computing system, the private domain is the relatives and friends of the data owner, who enjoy special permissions, and the data owner can authorize such users to manage their own file system. The public domain is doctors, nurses, insurance company staff, etc. in various hospitals. They have permission to view the user's own data etc. The properties of these two realms should have different qualities and should enjoy different ways of key management and distribution. The invention divides two different types of user groups, making data access more flexible and user management more fine-grained.

[Division of Hierarchical Trusted Organizations] The present invention divides multi-trusted trusted organizations with levels, breaking through the traditional method of managing all users by a single trusted organization. With a single trust mechanism, the frequent interaction between users and trust institutions not only brings bottlenecks to the system load capacity, but also increases potential security risks. Once a trusted organization is stolen by an unauthorized user, he may use illegal means to steal all user data, causing huge losses to group users. Moreover, it is not feasible to hand over all the key distribution work to one TA in practice. Different organizations should have different responsibilities and each govern their own sub-organizations. Each sub-organization should define and specify various attribute sets within its own authority, and distribute them to users under the jurisdiction of the department. In the present invention, users are in different trusted institutions, even if a certain trusted institution is threatened, it will not affect the security of other trusted institutions, and the user's privacy is protected.

[Establishment of access control tree] The present invention establishes different access control trees for users in different fields. In the public field, due to the large number of attributes, an access control tree supporting the union between different attribute sets is established. In a large number of CP-ABE-based models, there is only one attribute set used in the access control structure, that is, the data owner can only be in one attribute set, and various combinations of attributes are selected to meet the access policy. The attribute sets are completely isolated, and the connection between the attribute sets cannot be established. This greatly reduces the flexibility of access control. Because users need to span multiple attribute sets when necessary, select attributes to satisfy a certain access control structure. There are two types of nodes in the access control tree of the present invention: ordinary nodes and joint nodes. Ordinary nodes only support the association of attributes within a single collection, while joint nodes support joint access to multiple attribute collections spanning a single collection, which greatly improves the flexibility of the access control structure.

Description of drawings

Fig. 1 is a system model diagram of the present invention.

Fig. 2 is a schematic diagram of a hierarchical key structure of a user in a PUD environment.

Detailed ways

Method flow

1. System parameter generation

In PUD, Setup(d=2)→(PK.MK).d is the level of the key, which is assumed to be 2. The trusted institution first randomly selects the bilinear group G ₀ with generator g and order p and the bilinear map e:G ₀ ×G ₀ =G _T , randomly selects random numbers α,β _i ∈ Z _p , Generate public and master keys as:

${\mathrm{<span\; class="notranslate">\; PK</span>}}_{\mathrm{<span\; class="notranslate">\; PUDs</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}<span\; class="notranslate">\; )</span>$

MK _PUD =(β ₁ ,β ₂ ,g ^α )

In PRD, randomly select parameters α ₃ , β ₃ ∈ Z _p to generate public key and master key as

${\mathrm{<span\; class="notranslate">\; PK</span>}}_{\mathrm{<span\; class="notranslate">\; PRD</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; \}</span>$

${\mathrm{<span\; class="notranslate">\; MK</span>}}_{\mathrm{<span\; class="notranslate">\; PRD</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; )</span>$

2. Generate user private key

Assign PRD user private key. In PRD, the attribute set obtained by user u is Randomly select r∈Z _p , and select a random value r _j ∈ Z _p for each attribute a _j , call keyGen to generate the private key of user u as ${\mathrm{SK}}_u=\{\widehat{\mathrm{D.}}=g^{\frac{{\mathrm{\&alpha;}}_3+r}{{\mathrm{\&beta;}}_3}},{\&ForAll;a}_j\&Element;\hat{A}:{\widehat{\mathrm{D.}}}_j=g^r\&CenterDot;h{\left(j\right)}^{r_j},{\widehat{\mathrm{D.}}}_j^{\&prime;}=g^{r_j}\}$

The first-level regional trusted agency authorization. In PUD, each first-level DA consists of two parts: ID and the attribute set A={A ₀ ,A ₁ ,...A _m } where A _i = {a _{i, 1} , a _{i, 2} ,...a _{i, n} }, a _{i, j} represents the jth attribute in the attribute set of A _i . The first-level DA is the one with the most authority, such as the various branches of the company. If a new first-level DA (set as DA _i ) joins, the trusted institution creates a master key for DA _i by calling the CreateDA(PK, MK, A) method. After obtaining the authority, DA _i will have the authority to assign authority to the DA of the next level, such as various departments of the subsidiary. The results of the master key situation obtained by DA _i are as follows:

${\mathrm{<span\; class="notranslate">\; MK</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{\frac{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}}{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}}<span\; class="notranslate">\; ,</span>$

${\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{\text{<span class="notranslate"> \&prime;</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ,</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}}{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>$

Among them, A is the attribute structure, r ^{u} is the unique ID of the DA, and it is also the ID of A ₀ , is the ID of each attribute set A _i , and E _i is used for conversion between different A _i , which will be described in detail in the decryption section below.

Lower-level DA/user private key structure. (1) DA _i is the private key authorized by the lower-level DA, denoted as DA _i+1 , call (2) DAi authorizes the private key for the user in the _DAi , call It is the attribute structure of the next-level user/DA, which must be a subset of the attribute structure of the upper-level DA, such as A={A ₀ ,A ₁ ,A ₂ }, The structure of the next-level user/DA private key is

${\mathrm{<span\; class="notranslate">\; SK</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; MK</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; ,</span>\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{\frac{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}}{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}<span\; class="notranslate">\; ,</span>$

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; D.</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}}<span\; class="notranslate">\; ,</span>$

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; D.</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ,</span>$

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{\text{<span class="notranslate"> g</span>}}^{\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>$

3. File Creation

The user subject selects a unique ID for the file uploaded to the cloud, randomly selects the key FEK, and encrypts the file symmetrically, that is, E _DEK (F)←FEK. Then the user subject invokes the Encrypt method to encrypt the key FEK to generate ciphertext CT, and generate an access control tree T composed of attribute resources, T=(T _PUD )OR(T _PRD ), T _PUD is the access control tree in the PUD, T _PRD is the access control tree in PRD. The final ciphertext stored in the cloud is in the form of E(F)=<CT, E _FEK (F)>.

The process of establishing an access control tree T _PUD is as follows:

i. Select a polynomial q _x for each node in the access control tree, and the order of the polynomial is d _x , then d _x =k _x -1.

ii. Randomly select s∈Z _p for the root node R, satisfying q _R (0)=s, use polynomial interpolation method to randomly select q _R values to define the polynomial q _R .

iii. For the node x on the tree except the root node, set q _x (0)=q _parent(x) (index(x)) and then randomly select d _x points to define all polynomials completely.

Follow the above three steps to create an access control tree T _PRD for the PRD environment.

Let Y be the set of leaf nodes, and X be the set of conversion nodes (X is only used in T _PUD ), then the plaintext M is encrypted according to the following formula:

$\mathrm{<span\; class="notranslate">\; CT</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; PUDs</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; PRD</span>}}<span\; class="notranslate">\; ,</span>$

$\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ,</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ,</span>\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ,</span>$

$<span\; class="notranslate">\; \&ForAll;</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; \&SubsetEqual;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; PUDs</span>}}<span\; class="notranslate">\; :</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{{\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; h</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; att</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}^{{{\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; ,</span>$

$<span\; class="notranslate">\; \&ForAll;</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; \&SubsetEqual;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; PRD</span>}}<span\; class="notranslate">\; :</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}^{{{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; q</span>}}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; ,</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; h</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; att</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}^{{{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; q</span>}}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; ,</span>$

$<span\; class="notranslate">\; \&ForAll;</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \&SubsetEqual;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; PUDs</span>}}{\stackrel{<span\; class="notranslate">\; ^</span>}{<span\; class="notranslate">\; :</span>\mathrm{<span\; class="notranslate">\; C</span>}}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{{\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span>$

Define a helper data W to help users in PRD to obtain plaintext:

$\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; \&gamma;s</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; \&alpha;s</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ,</span>$

That is, α ₃ =γ-α

CT and W are stored together in the cloud.

4. File Access

User u sends a request to the cloud to apply for accessing files, and the cloud sends the corresponding ciphertext to the user. The user invokes the Decrypt(CT, SK _u ) algorithm to decrypt:

(1) If u is a user in PUD, call T(A) to confirm whether the attributes in SK _u satisfy the access control tree T _PUD . T(A) is the recursive way from the leaf node to the root node.

i t is a leaf node, if A _i ∈ A then DecryptDode(CT, SK _u , t, i) = null, if att(t) = a _{i, j} ∈ A _i , A _i ∈ A, then

$\mathrm{<span\; class="notranslate">\; DecryptDode</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; CT</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; SK</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>$

ii t is a non-leaf node, define the child node of t as z, B _t is the set of k _t z nodes that meet the threshold, S _z is the label set of k _x z nodes, define F _z =DecryptDode(CT, SK _u , t, i) is the judgment result of any node in T and the attribute in A, if there is no such set S _z , then F _z =⊥. If yes, and (1) label i∈S _z , (2) label i′∈S _z and there exists i′≠i, then z is a transition node, let DecryptDode(CT,SK _u ,z,i′)= F′ _Z , if i≠0 (not in A ₀ ) convert F′ _Z to F _z :

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; (</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\stackrel{<span\; class="notranslate">\; `</span>}{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}$

otherwise $f_z=\frac{e({\hat{C}}_z,{\mathrm{E.}}_{\stackrel{\&prime;}{i}})}{f_z^{\&prime;}}=e{(g,g)}^{r^{\left\{u\right\}}\&CenterDot;q_z\left(0\right)}.$

iii According to the lagrange property, when calculating the parent node t,

$f_t={\mathrm{\&Pi;}}_{z\&Element;B_t}{f}_Z^{{\mathrm{\&Delta;}}_k,B_z^{\&prime;}\left(0\right)}=\left\{\begin{array}{cc}e{(g,g)}^{r_i^{\left\{u\right\}}\&Center\; Dot;q_t\left(0\right)},& i\&NotEqual;0\\ e{(g,g)}^{r^{\left\{u\right\}}},& i=0\end{array}\right\},$ in

k=index(z),B′ _z ={index(z):z∈B _t }

iv R is the root node,

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}}$

Then the decryption process is as follows:

$\frac{\tilde{C}\&CenterDot;f_r}{e(C,\mathrm{D.})}=\frac{m\&Center\; Dot;e{(g,g)}^{\mathrm{\&alpha;}\&Center\; Dot;\mathrm{the\; s}}\&Center\; Dot;e{(g,g)}^{r^{\left\{u\right\}}\&Center\; Dot;\mathrm{the\; s}}}{e(g^{\mathrm{the\; s}\&CenterDot;{\mathrm{\&beta;}}_1},g^{\frac{(r^{\left\{u\right\}}+\mathrm{\&alpha;})}{{\mathrm{\&beta;}}_1}})}=m$ get plaintext.

(2) If u is a user in PRD, call T(A) to confirm whether the attributes in SK _u satisfy the access control tree T _PRD , the decryption process is similar to the CP-ABE process,

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; DecrptNode</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; CT</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; SK</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; r</span>}{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; q</span>}}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; rs</span>}}<span\; class="notranslate">\; ,</span>$

Use W to get the plaintext

$\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\frac{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; ,</span>}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; \&alpha;s</span>}}\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; rs</span>}}\mathrm{<span\; class="notranslate">\; e</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}}}$

5. File revocation

To revoke a file, the user only needs to send the file ID and his own signature to the cloud. After the cloud confirms that it is the request sent by the user subject, the file is deleted.

6. Attribute revocation

MAH-ABE has an efficient attribute revocation mechanism. When DA assigns attributes to users, an expiration time (expiration_time) X is added to each attribute set. The attributes in the access control tree contain the time attribute Y, if X≥Y, and the attributes match, the file can be accessed. The user can control the user's access rights by changing the value of the time attribute.

User attribute revocation. This task is mainly completed by the DA to which the user belongs.

(1) DA calculates the minimum attribute set MinimalSet(A)→A _min that can revoke the user's access right, A _new =AA _min , so that T(A _new ) returns empty.

(2) Assign a new failure time to each attribute set in A _min , And generate the corresponding new private key component, $\mathrm{keyUpdate}(S{k}_u,t_i^{\mathrm{new}})\&Right\; Arrow;{{\mathrm{Sk}}_u}^{\mathrm{new}}=\{A_{\min },\{{\mathrm{D.}}_{i\&Center\; Dot;j}^{\mathrm{new}},{{\mathrm{D.}}_{i,j}^{\&prime;}}^{\mathrm{new}}{\}}_{\&Element;A\min }\}$

(3) send back to the user. send(Sk _u ) here adopts lazy re-encryption, that is, the user's private key will be automatically updated when the user logs in to the system next time, and does not need to be updated in time to avoid burdening the system.

File attribute revocation. If the user wants to update the access rights of the file, he only needs to change the expiration time of the leaf node, and then send the corresponding update information to the cloud, which is encrypted by the cloud proxy. Because the cloud only obtains part of the node attribute information, it is impossible to deduce the entire plaintext from this, and the security and privacy of the data are protected. (1) Set the attribute set of the leaf node to be updated as Ymin.

(2) Update the failure time of leaf nodes and generate new components

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; updateAttFile</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Right\; Arrow;</span><span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; new</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}^{\mathrm{<span\; class="notranslate">\; new</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}^{<span\; class="notranslate">\; \&prime;</span>\mathrm{<span\; class="notranslate">\; new</span>}}<span\; class="notranslate">\; \}</span>$

(3) Update the content of the access control leaf node ${\mathrm{the\; y}}_i\&Element;Y\min ,\mathrm{update}(C_{{\mathrm{the\; y}}_i},C_{{\mathrm{the\; y}}_i}^{\&prime;})\&Right\; Arrow;C_{{\mathrm{the\; y}}_i}^{\mathrm{new}},C_{{\mathrm{the\; y}}_i}^{\&prime;\mathrm{new}},$ Delete obsolete nodes y _i ∈ {Y-Ymin}, delete

(4) Output new ciphertext ${\mathrm{CT}}^{\mathrm{new}}=(T^{\mathrm{new}},\tilde{C},C,\stackrel{\&OverBar;}{C},\&ForAll;\mathrm{the\; y}\&Element;Y:C_{{\mathrm{the\; y}}^{\mathrm{new}}}^{\&prime;},\&ForAll;x\&Element;x:{\hat{C}}_x).$

For the convenience of description, we assume the following application examples:

A data owner O stores a file F in the cloud, and the user U applies to a trusted organization for a private key, and then initiates access to the file F to the cloud. The data owner performs three operations on the file: 1. Revokes the attribute of the relevant user. 2. Update the access control structure tree. 3. Delete the file. Then its specific implementation method is:

(1) The trusted organization first randomly selects generators to generate bilinear groups and bilinear maps, and then selects the key hierarchy in the PUD field to generate the master key and public key of the PUD. The master key is kept and the public key is made public.

(2) The trusted authority then generates the master key and public key of the PRD. The master key is kept and the public key is made public.

(3) The trusted organization distributes the master key of the next level trusted sub-organization (distributed when there are sub-organizations).

(4) The data owner selects a unique ID for the file F uploaded to the cloud, encrypts the file symmetrically, and retains the key K.

(5) The data owner selects the PUD domain attribute set to form the access control tree T _PUD , selects the PRD domain attribute set to form the access control tree T _PRD , encrypts the key K with the two trees to generate the ciphertext CT, and sends it to the cloud.

(6) The user provides relevant information to the trusted organization and applies for legal user authority in the relevant field. If applying for the authority of the PUD field, execute (7), and apply for the authority of the PRD field to execute (8).

(7) The trusted organization judges whether the user can apply for permission in the PUD field based on the information submitted by the user. If not, return empty. If yes, send the information provided by the user to the corresponding trusted sub-organization (there may be more than one qualified sub-organization). Different sub-organizations assign different sets of role attributes to the user. Finally, the relevant key component SK is generated and sent to the user.

(8) Based on the information submitted by the user, PRD judges whether the user can apply for permission in the PRD field. If not, return empty. If yes, the corresponding data attribute will be assigned according to the information provided by the user, and the key component SK will be generated and sent to the user.

(9) The user U initiates access to the file F to the cloud, the cloud returns the ciphertext CT, the user enters the private key SK, and matches it with the access control tree T of the relevant field. If it matches, execute (10), if it does not match, then Execute (11).

(10) Return the key K of the file F to the user, and obtain the file F after decryption.

(11) returns empty.

(12) The data owner sends a notification to the trusted organization, submits the relevant attribute sequence S and expiration time, and entrusts the trusted organization to update the relevant users corresponding to S.

(13) The trusted organization sends a notification to the relevant trusted sub-organization, and the trusted sub-organization updates the expiration time of the relevant attributes, generates a new private key component, and sends it to the relevant user.

(14) The data owner sends a notification to the cloud, submits the relevant attribute sequence S and expiration time, and entrusts the cloud to update the access control structure tree T.

(15) After the cloud receives the update information, it generates relevant components and finally updates them to the relevant access control tree.

(16) The cloud outputs new ciphertext CT to replace the original ciphertext.

(17) User owner revocation file: Send the file ID and your own signature to the cloud.

(18) The cloud deletes the file after confirming the signature, and returns the information that the owner deleted it successfully.

(19) The whole process is over.

Claims (3)

1., based on a cloud computing safety access control method for encryption attribute, it is characterized in that the step that the method comprises is:

Step 1). divide two kinds of user environments, public sphere PUD and private domain PRD;

Step 2). trust authority is Stochastic choice generator first, generates Bilinear Groups and bilinear map, then selects the key hierarchy in PUD field, and generate master key and the PKI of PUD, master key retains, and PKI is open;

Step 3). trust authority utilizes step 2) Bilinear Groups that generates and bilinear map, generate master key and the PKI of PRD, master key retains, and PKI is open;

Step 4). trust authority creates the lower credible clamp mechanism of one deck, distribute ground floor attribute individuality or community set, and generate master key, lower one deck trust authority can create less clamp mechanism, distribute second layer attribute individuality or community set, second layer attribute individuality or community set are the subset of ground floor attribute individuality or community set, and distribute key, the like;

Step 5). user provides relevant information to trust authority, the validated user authority of application association area, if the authority in application PUD field, performs step 6), the authority in application PRD field performs step 7);

Step 6). the information that trust authority is submitted to according to user, judges that can this user apply for the authority in PUD field, if can not, then return sky; If can, will send to corresponding credible clamp mechanism according to this user profile, corresponding credible clamp mechanism distributes corresponding attribute individuality or community set, generates a key module, sends to user; Redirect performs step 8);

Step 7). the information that trust authority is submitted to according to user, judges that can this user apply for the authority in PRD field, if can not, then return sky, if can, by data attribute corresponding for the information distribution that provides according to this user, generate key module, send to user;

Step 8). data owner is that the file uploading to high in the clouds chooses unique identification to file symmetric cryptography, retain key, and choose public sphere property set composition public visit control tree, choose the private visit of private domain's property set composition and control tree, with two kinds of trees to file key encryption generating ciphertext, and be sent to high in the clouds;

Step 9). user initiates the access to file to high in the clouds, high in the clouds returns the ciphertext of respective file, user's input step 6) or 7) private key in key module, mate with the access control tree T in ciphertext, if coupling obtains respective file key, obtain file after deciphering, if do not mate, return sky;

Step 10). data owner give notice to trust authority, cancels associated user's attribute, submits association attributes sequence and out-of-service time, entrusts trust authority to upgrade associated user's authority;

Step 11). trust authority is given notice to relevant credible clamp mechanism, and credible clamp mechanism upgrades the out-of-service time of association attributes, generates new private key assembly, sends to associated user;

Step 12). data owner give notice to high in the clouds, upgrades access control tree, submit association attributes sequence and out-of-service time, entrusts high in the clouds to upgrade access control structure tree;

Step 13). after high in the clouds receives lastest imformation, generate associated component, final updating in relevant access control tree, and exports new ciphertext, replaces original ciphertext;

Step 14). user owner cancels file, and file identification and the signature of oneself are sent to high in the clouds;

Step 15). by this file erase after high in the clouds confirmation signature, return owner and delete successful information.

2. the cloud computing safety access control method based on encryption attribute according to claim 1, is characterized in that, described public sphere PUD, and its key structure is hierarchical encryption structure, and described trust authority is the gradational trust authority of tool.

3. the cloud computing safety access control method based on encryption attribute according to claim 1, it is characterized in that, access control tree controls tree for public visit and private visit controls two kinds, tree, and the node that public visit controls in tree exists association node, supports the access of federation properties collection.