Internet of Things data sharing method supporting user hierarchical management and dynamic updating

Abstract

The invention discloses an Internet of Things data sharing method supporting hierarchical management and dynamic updating of users, which comprises the following steps: in an initial stage of an Internet of Things data sharing system, a trusted center initializes a public key and a master key of the Internet of Things data sharing system; in a key generation stage of the Internet of Things sharing system, the trusted center generates a domain authority center master key for the domain authority center, the domain authority center generates a domain key for the data center, and the data center generates a user master key for a user and distributes a user group key for a group where each user is located; in the uploading stage of the Internet of Things data, the trusted center encrypts the Internet of Things data uploaded by the Internet of Things data owner, and the data center re-encrypts the encrypted Internet of Things data through the user group key; in the access stage of the data of the Internet of Things, the group manager of the user group where the user is located sends a data access request to the domain authority department, the group manager forwards the access data to the corresponding user after receiving the access data, and the user decrypts the access data according to the key of the user group.

Description

Technical Field

[0001] The present invention belongs to the technical field of big data sharing, and in particular, relates to an Internet of Things data sharing method that supports user hierarchical management and dynamic updating. Background Art

[0002] With the rapid development of Internet of Things technology, we have entered the era of big data. The information involved in the Internet of Things comes from various fields, including various information, such as location, schedule, personal preferences or important company business information. Data sharing plays a key role in the application of the Internet of Things. Through data sharing, the data center transmits data to users. In order to promote the development of the Internet of Things, it is of great significance to ensure the security and privacy of data sharers.

[0003] Researchers have proposed many methods to protect the security and privacy in IoT data sharing, such as clustering-based methods and differential privacy, but they all face the problem of balancing privacy and data practicality: on the one hand, if the privacy protection parameters are too strict, that is, the privacy protection level is high, the practicality of the data may be too low; on the other hand, in order to ensure the availability of the data, if the privacy protection parameters are relatively loose, the privacy protection level will be insufficient and the user's private information may be leaked.

[0004] Attribute-based encryption is one of the effective methods for security and privacy protection. It encrypts related models according to different attributes owned by users. Although data security and privacy protection schemes based on attribute encryption have been widely studied, most of them are aimed at cloud computing environments: Cui et al. introduced a data sharing scheme for cloud storage environments that can delete duplicate data; Wan et al. designed a hierarchical attribute-based encryption scheme HASBE based on ciphertext policy attribute encryption by hierarchically managing users in the system; inspired by tree-based signatures, Shen et al. improved the HASBE scheme and proposed a security authentication method based on hierarchical attribute access control structure. Although attribute encryption methods are relatively mature in cloud computing environments, their computational complexity, energy consumption, real-time performance, key management, and other issues make them face great challenges when applied in the Internet of Things environment.

[0005] In addition, in the IoT data sharing mechanism, the user scale is very large, and the existing IoT data sharing solutions do not consider the issue of user management, resulting in lax authority control, data abuse, privacy leakage, data compliance risks, etc.; at the same time, the lack of user update mechanism in the IoT data sharing solution will lead to lagging authority management, increased risk of data leakage, and insufficient adaptability to dynamic environments. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides an Internet of Things data sharing method that supports user hierarchical management and dynamic updating, effectively manages and dynamically updates users in Internet of Things data sharing, and improves the privacy protection and security of Internet of Things data sharing.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solutions: an IoT data sharing method supporting hierarchical management and dynamic update of users, realizing IoT data sharing on an IoT data sharing system, wherein the IoT data sharing system includes: a trusted center, a domain authority center, a data center, a domain authority department and users;

[0008] In the initial stage of the IoT data sharing system, the trusted center initializes the public key and master key of the IoT data sharing system;

[0009] In the key generation phase of the IoT sharing system, based on the public key and master key of the IoT data sharing system, the trusted center generates a domain authority center master key for the domain authority center, the domain authority center generates a domain key for the data center, the data center generates a user master key for the user, and the data center distributes a user group key to each user's group;

[0010] During the IoT data upload phase, the trusted center encrypts the IoT data uploaded by the IoT data owner based on the public key of the IoT data sharing system, and the data center re-encrypts the encrypted IoT data using the user group key;

[0011] During the IoT data access phase, the group manager of the user group sends a data access request to the domain authority department. After the access request is approved, the group manager receives the access data and forwards it to the corresponding user, who decrypts the access data based on the user group key.

[0012] Furthermore, the public key of the trusted center to initialize the IoT data sharing system is: The master key of the Internet of Things data sharing system initialized by the trusted center is MK=(β, B=g α ), where e:G 0 ×G 1 →G 1 represents a bilinear map, G 0 and G 1 Both represent two bilinear groups of prime order p, and g represents G 0 The generators of , α and β both represent elements of the finite field modulo prime number p, h and f both represent components of the public key, and B is a component of the master key of the IoT data sharing system.

[0013] Furthermore, the specific process of the trusted center generating the domain authority center master key for the domain authority center is as follows: the domain authority center has an attribute set Θ = (w 0 ,w 1 ,…w κ ,…w m ), where w κ is the k-th attribute of Θ, m is the total number of attributes in Θ, and for each attribute w in the domain authority center κ ∈Θ, select the domain authority center attribute code Combined with the public key of the IoT sharing system, the master key elements of the domain authority center are calculated separately: Generate the master key of the domain authority center as MK ca =(Θ,D,D κ ,D' κ ), where r ca A unique number is selected for the domain authority center, and H() is the hash function.

[0014] Furthermore, the specific process of the domain authority center generating a domain key for a data center is as follows: when a data center wants to join the domain authority center, it sends an access request to the domain authority center, and the domain authority center selects a unique number r for the data center. da , and assign attributes to data centers Domain Authority Center for each property Select Data Center Attribute Code Combined with the public key of the IoT sharing system and the master key of the domain authority center, the domain key elements of the data center are calculated respectively: Generate the domain key for the data center as Among them, w γ represents the γth attribute in θ, D γ Indicates that w γ Substitute the master key element D of the domain authority center κ The calculated value of D' γ Indicates that w γ Substitute the master key element D' of the domain authority center k The calculated value of .

[0015] Furthermore, the specific process of the data center generating a user master key for a user is as follows: when user u wants to join the data center, he sends a request to the data center, and the data center selects a unique number r for user u u , and the data center collects the valid attribute set of user u For each valid attribute w i ∈θ u Select User Attribute Code Combined with the public key and domain key of the IoT shared system, the user master key elements are calculated separately: Generate a user master key in, Indicates that w i Substitute the domain key element of the data center The calculated value of Indicates that w i Substitute the domain key element of the data center The calculated value of .

[0016] Furthermore, the specific process of the data center distributing the user group key to each user's group is as follows:

[0017] i. Each attribute w in the trusted central domain authority center k Create a user group, and the trusted center is each user u in the user group δ Choose a unique number And transmit it to the corresponding user, and the trusted center calculates the update parameters of the user group key respectively Where l represents the number of users in the user group, and δ represents the index of l;

[0018] ii. Trusted Center Based on Select element μ δ , and calculate the intermediate parameters y δ =μ δ × δ ,η= For each user group, the trusted center randomly generates parameters As the user group key, and calculate the user group public parameters Among them, y i Represents one of all the selected user attributes, Z p represents a finite field modulo a prime number p;

[0019] iii. Add users with corresponding attributes to a unified user group, and the data center broadcasts messages to all users in a user group. y , users in the user group receive β y Then, through the modulus operation Get the attribute group key

[0020] Furthermore, when a user in the user group is revoked, the trusted center calculates the intermediate parameter η'=η-y i , and regenerate the parameters As the new user group key of the corresponding user group, update the user group public parameters Trusted Center will update the beta yBroadcast to users in the user group. When users in the user group receive the updated β y When the modulus operation is Get updated user group key

[0021] Furthermore, when a new user joins a user group, the new user sends a joining request to the trusted center, and the trusted center calculates the intermediate parameter η'=η+y l , and regenerate the parameters As the new user group key of the corresponding user group, update the user group public parameters Trusted Center will update the beta y Broadcast to users in the user group. When users in the user group receive the updated β y When the modulus operation is Get updated user group key Among them, q represents the attributes of the newly added user.

[0022] Furthermore, the specific process of the domain authority center re-encrypting the encrypted IoT data using the user group key is as follows:

[0023]

[0024] Among them, τ represents the access tree, s represents the element of the selected finite field modulo prime number p, and M represents the IoT data to be encrypted. represents encrypted IoT data, Y represents the set of leaf nodes in the access tree, and y represents the elements in Y. att(y) represents the attribute corresponding to the leaf node y, C, q y (0) are all intermediate parameters for re-encryption calculation.

[0025] Furthermore, the process of decrypting access data according to the user group key is:

[0026]

[0027] Where M represents the decrypted access data, r represents the sum of the selected numbered parameters, Indicates that the data center selects a unique number for users to access data.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The IoT data sharing method of the present invention supports hierarchical user management and dynamic update, distributes and manages user keys in a hierarchical management manner, and solves the problem of difficulty in large-scale user management in the IoT environment; during data access and revocation, users are grouped and managed to achieve dynamic revocation of users and attribute-level user updates, thereby preventing unauthorized access and ensuring data security.

[0030] (2) The encryption process of the uploaded data of the present invention is completed jointly by the trusted center and the data center to prevent the data center from illegally using the data.

[0031] (3) The IoT data sharing method of the present invention supports user hierarchical management and dynamic update, which can realize security, privacy protection and efficient data sharing between data centers and users in the IoT environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The figure is a schematic diagram of the IoT data sharing method supporting user hierarchical management and dynamic updating according to the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further explained below in conjunction with the accompanying drawings.

[0034] The present invention discloses an Internet of Things data sharing system, including: the Internet of Things data sharing system includes: a trusted center, a domain authority center, a data center and a user, and the Internet of Things data sharing is realized on the Internet of Things data sharing system, such as Figure 1 , the specific process is as follows:

[0035] In the initial stage of the IoT data sharing system, the trusted center initializes the public key and master key of the IoT data sharing system; the public key initialized by the trusted center for the IoT data sharing system is: The master key of the IoT data sharing system initialized by the trusted center is MK = (γ, B = g α ), where e:G 0 ×G 1 →G 1 represents a bilinear map, G 0 and G 1 Both represent two bilinear groups of prime order p, and g represents G 0 The generators of , α and β both represent elements of the finite field modulo prime number p, h and f both represent components of the public key, and B is a component of the master key of the IoT data sharing system.

[0036] During the key generation phase of the IoT sharing system, based on the public key and master key of the IoT data sharing system, the trusted center generates a domain authority center master key for the domain authority center, the domain authority center generates a domain key for the data center, the data center generates a user master key for the user, and the data center distributes user group keys to each user's group.

[0037] The specific process of the trusted center generating the master key of the domain authority center for the domain authority center is as follows: the domain authority center has an attribute set Θ = (w 0 ,w 1 ,…w κ ,…w m ), where w κ is the kth attribute of Θ, m is the total number of attributes in Θ, and for each attribute w in the domain authority center κ ∈Θ, select the domain authority center attribute code Combined with the public key of the IoT sharing system, the master key elements of the domain authority center are calculated separately: Generate the master key of the domain authority center as MK ca =(Θ,D,D κ ,D' κ ), where r ca A unique number is selected for the domain authority center, and H() is the hash function.

[0038] The specific process of the domain authority center generating a domain key for a data center is as follows: when a data center wants to join the domain authority center, it sends an access request to the domain authority center, and the domain authority center selects a unique number r for the data center. da , and assign attributes to data centers Domain Authority Center for each property Select Data Center Attribute Code Combined with the public key of the IoT sharing system and the master key of the domain authority center, the domain key elements of the data center are calculated respectively: Generate the domain key for the data center as Among them, w γ represents the γth attribute in θ, D γ Indicates that w γ Substitute the master key element D of the domain authority center κ The calculated value of D' γ Indicates that w γ Substitute the master key element D' of the domain authority center k The calculated value of

[0039] The specific process of the data center generating a user master key for a user is as follows: when user u wants to join the data center, he sends a request to the data center, and the data center selects a unique number r for user u u , and the data center collects the valid attribute set of user u For each valid attribute w i ∈θ u Select User Attribute Code Combined with the public key and domain key of the IoT shared system, the user master key elements are calculated separately: Generate a user master key in, Indicates that w i Substitute the domain key element of the data center The calculated value of Indicates that w i Substitute the domain key element of the data center The calculated value of

[0040] In order to accommodate more users and manage them effectively, the solution supports domain expansion, that is, the data center can generate and manage user master keys for users, and can also continue to authorize the next layer of data centers. Specifically, the DA of the next layer of data center φ When joining a data center, send a joining request to the data center, and the data center will become the DA of the next layer of data centers φ Choose a unique number And for the next layer of data center DA φ Assigning properties Domain Authority Center for each property θ φ Select the next data center attribute code Combined with the public key and domain key of the IoT shared system, the next layer of data center master key elements are calculated separately: Generate the next layer of data center master key in, Indicates that w θ Substitute the domain key element of the data center The calculated value of Indicates that Substitute the domain key element of the data center The calculated value of .

[0041] Users are divided into different groups according to their attributes, and user group keys are used to manage users. When a user joins or revokes, the user group key is updated to protect the data from being used by the revoked user, thereby ensuring the security of data access. Specifically,

[0042] The specific process of the data center distributing the user group key to each user group is as follows:

[0043] i. Each attribute w in the trusted central domain authority center κ Create a user group, and the trusted center is each user u in the user group δ Choose a unique number And transmit it to the corresponding user, and the trusted center calculates the update parameters of the user group key respectively Where l represents the number of users in the user group, and δ represents the index of l;

[0044] ii. Trusted Center Based on Select element μ δ , and calculate the intermediate parameters respectively For each user group, the trusted center randomly generates parameters As the user group key, and calculate the user group public parameters Among them, y i Represents one of all the selected user attributes, Z p represents a finite field modulo a prime number p;

[0045] iii. Add users with corresponding attributes to a unified user group, and the data center broadcasts messages to all users in a user group. y , users in the user group receive β y Then, through the modulus operation Get the attribute group key

[0046] When a user in a user group is revoked, the IoT data sharing system must ensure that the revoked user can no longer access the associated data. One way to solve this problem is to re-encrypt all associated data that the revoked user has accessed, and it must be ensured that users in other groups still have access to these data files. In the IoT data sharing system of the present invention, the user revocation mechanism is fine-grained, down to the revocation of a certain attribute of the user. In order to ensure that the revoked user can no longer access the data, the present invention designs an attribute-level user update mechanism to ensure the proper use of data. When a certain attribute of a user is revoked, the access rights to the data related to the attribute can be revoked in a timely manner. Specifically, the trusted center calculates the intermediate parameter η'=η-y i , and regenerate the parameters As the new user group key of the corresponding user group, update the user group public parameters Trusted Center will update the beta y Broadcast to users in the user group. When users in the user group receive the updated β yWhen the modulus operation is Get updated user group key Therefore, even if the revoked user receives the broadcast message β y After that, since η' is unknown, the updated user group key cannot be obtained. This scheme can achieve attribute-level access control for data publishing.

[0047] Similarly, when a new user joins a user group, the new user sends a joining request to the trusted center, and the trusted center calculates the intermediate parameter η'=η+y l , and regenerate the parameters As the new user group key of the corresponding user group, update the user group public parameters Trusted Center will update the beta y Broadcast to users in the user group. When users in the user group receive the updated β y When the modulus operation is Get updated user group key Among them, y l Indicates the attributes of the newly added user.

[0048] In the IoT data uploading stage, the trusted center encrypts the IoT data uploaded by the IoT data owner according to the public key of the IoT data sharing system to ensure the privacy of the data sharer. Specifically, each node x in the access tree τ is associated with the order d x The polynomial q x Associated, threshold k x Represented as d x =k x -1, if x is a leaf node, set d x =0, for each leaf node, define q x (0) = q p(x) (index(x)), and randomly select q x Other polynomial terms of; for the root node R, choose s∈Z p And set q R (0) = s, and randomly select q R Let Y be the set of leaf nodes of τ, and the ciphertext CT is expressed as:

[0049]

[0050] Among them, τ represents the access tree, s represents the element of the selected finite field modulo prime number p, and M represents the IoT data to be encrypted. represents encrypted IoT data, Y represents the set of leaf nodes in the access tree, y represents the elements in Y, att(y) represents the attribute corresponding to the leaf node y, q y(0) and C are intermediate parameters of the re-encryption calculation.

[0051] In order to achieve effective attribute control of users, the data center re-encrypts the encrypted IoT data using the user group key:

[0052]

[0053] In the present invention, data encryption and re-encryption are performed in the trusted center and the data center respectively, which not only reduces the encryption calculation burden of both parties, but also effectively prevents the data center from modifying and abusing the encrypted data.

[0054] In the IoT data access phase, in order to ensure the user's personal privacy, the user group is used to protect the identity of the user accessing the data. When a user wants to access the data, the access requirement is transmitted to the group manager, and the group manager of the user group to which the user belongs sends a data access request to the domain authority department. After the access request is approved, the group manager receives the access data and forwards it to the corresponding user. The user decrypts the access data according to the user group key. It is specifically divided into the AGK decryption process and the data decryption process:

[0055] The AGK decryption process is as follows: If user u t With legal attribute w y , then u t ∈G y ,u t Can be done by one modulus Calculate the user group key Then calculate the user u t Master Key

[0056]

[0057] The data decryption process is: Input the re-encrypted ciphertext CT', user u t The master key of user u t Master Key The attribute set Λ is associated with the node x in the access tree τ, and the plaintext of the data is obtained through a recursive method, as follows:

[0058] When x is a leaf node, if or Decryption failed; otherwise, you can get

[0059]

[0060] When x is a non-leaf node, for all child nodes v of node x, call And store the output as F vLet θ x is any k in the set v x The size subsets are such that F v ≠⊥, calculate:

[0061]

[0062] If θ satisfies the access tree τ and the user's attributes have not been revoked, set

[0063] Get the decrypted access data:

[0064]

[0065] in, Indicates that the data center selects a unique number for the user accessing the data. x (0) represents the value of the polynomial related to x at point 0.

[0066] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for sharing Internet of Things data that supports user hierarchical management and dynamic updating, characterized in that: Implementing IoT data sharing on an IoT data sharing system, wherein the IoT data sharing system includes: a trusted center, a domain authority center, a data center, a domain authority department, and a user; In the initial stage of the IoT data sharing system, the trusted center initializes the public key and master key of the IoT data sharing system; In the key generation phase of the IoT sharing system, based on the public key and master key of the IoT data sharing system, the trusted center generates a domain authority center master key for the domain authority center, the domain authority center generates a domain key for the data center, the data center generates a user master key for the user, and the data center distributes a user group key to each user's group; During the IoT data upload phase, the trusted center encrypts the IoT data uploaded by the IoT data owner based on the public key of the IoT data sharing system, and the data center re-encrypts the encrypted IoT data using the user group key; During the IoT data access phase, the group manager of the user group sends a data access request to the domain authority department. After the access request is approved, the group manager receives the access data and forwards it to the corresponding user, who decrypts the access data based on the user group key.

2. According to claim 1, a method for sharing Internet of Things data supporting hierarchical management and dynamic updating of users, characterized in that: The public key of the trusted center to initialize the IoT data sharing system is: The master key of the Internet of Things data sharing system initialized by the trusted center is MK=(β, B=g α ), where e:G0×G1→G1 represents a bilinear mapping, G0 and G1 both represent two bilinear groups of order p, g represents the generator of G0, α and β both represent elements of the finite field modulo prime number p, h and f both represent components of the public key, and B is a component of the master key of the IoT data sharing system.

3. The method for sharing Internet of Things data supporting hierarchical management and dynamic updating of users according to claim 2, characterized in that: The specific process of the trusted center generating the master key of the domain authority center for the domain authority center is as follows: the domain authority center has an attribute set Θ = (w0, w1, ... w κ ,…w m ), where w κ is the k-th attribute of Θ, m is the total number of attributes in Θ, and for each attribute w in the domain authority center κ ∈Θ, select the domain authority center attribute code Combined with the public key of the IoT sharing system, the master key elements of the domain authority center are calculated separately: Generate the master key of the domain authority center as MK ca =(Θ,D,D κ ,D' k ), where r ca A unique number is selected for the domain authority center, and H( ) is a hash function.

4. The method for sharing Internet of Things data supporting hierarchical management and dynamic updating of users according to claim 3, characterized in that: The specific process of the domain authority center generating a domain key for a data center is as follows: when a data center wants to join the domain authority center, it sends an access request to the domain authority center, and the domain authority center selects a unique number r for the data center. da , and assign attributes to data centers Domain Authority Center for each property Select Data Center Attribute Code Combined with the public key of the IoT sharing system and the master key of the domain authority center, the domain key elements of the data center are calculated respectively: Generate the domain key for the data center as Among them, w γ represents the γth attribute in θ, D γ Indicates that w γ Substitute the master key element D of the domain authority center κ The calculated value of D' γ Indicates that w γ Substitute the master key element D' of the domain authority center k The calculated value of .

5. The method for sharing Internet of Things data supporting hierarchical management and dynamic updating of users according to claim 4, characterized in that: The specific process of the data center generating a user master key for a user is as follows: when user u wants to join the data center, he sends a request to the data center, and the data center selects a unique number r for user u u , and the data center collects the valid attribute set of user u For each valid attribute w i ∈θ u Select User Attribute Code Combined with the public key and domain key of the IoT shared system, the user master key elements are calculated separately: Generate a user master key in, Indicates that w i Substitute the domain key element of the data center The calculated value of Indicates that w i Substitute the domain key element of the data center The calculated value of .

6. The method for sharing Internet of Things data supporting hierarchical management and dynamic updating of users according to claim 5, characterized in that: The specific process of the data center distributing the user group key to each user group is as follows: i. Each attribute w in the trusted central domain authority center κ Create a user group, and the trusted center is each user u in the user group δ Choose a unique number And transmit it to the corresponding user, and the trusted center calculates the update parameters of the user group key respectively Among them, l represents the number of users in the user group, δ represents The index of ii. Trusted Center Based on Select element μ δ , and calculate the intermediate parameters y δ =μ δ × δ , For each user group, the trusted center randomly generates parameters As the user group key, and calculate the user group public parameters Among them, y i Represents one of all the selected user attributes, Z p represents a finite field modulo a prime number p; iii. Add users with corresponding attributes to a unified user group, and the data center broadcasts messages to all users in a user group. y , users in the user group receive β y Then, through the modulus operation Get the attribute group key 7. The method for sharing Internet of Things data supporting hierarchical management and dynamic updating of users according to claim 6, characterized in that: When a user in the user group is revoked, the trusted center calculates the intermediate parameter η'=η-y i , and regenerate the parameters As the new user group key of the corresponding user group, update the user group public parameters Trusted Center will update the beta y Broadcast to users in the user group. When users in the user group receive the updated β y When the modulus operation is Get updated user group key 8. The method for sharing Internet of Things data supporting hierarchical management and dynamic updating of users according to claim 6, characterized in that: When a new user joins a user group, the new user sends a joining request to the trusted center, and the trusted center calculates the intermediate parameter η'=η+y l , and regenerate the parameters As the new user group key of the corresponding user group, update the user group public parameters Trusted Center will update the beta y Broadcast to users in the user group. When users in the user group receive the updated β y When the modulus operation is Get updated user group key Among them, y l Indicates the attributes of the newly added user.

9. The method for sharing Internet of Things data supporting hierarchical management and dynamic update of users according to any one of claims 6 to 8, characterized in that: The specific process of the domain authority center re-encrypting the encrypted IoT data using the user group key is as follows: Among them, τ represents the access tree, s represents the element of the selected finite field modulo prime number p, and M represents the IoT data to be encrypted. represents encrypted IoT data, Y represents the set of leaf nodes in the access tree, and y represents the elements in Y. att(y) represents the attribute corresponding to the leaf node y, C, q y (0) are all intermediate parameters for re-encryption calculation.

10. The method for sharing Internet of Things data supporting hierarchical management and dynamic updating of users according to claim 9, characterized in that: The process of decrypting access data based on the user group key is: Where M represents the decrypted access data, r represents the sum of the selected numbered parameters, Indicates that the data center selects a unique number for users to access data.

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