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Access Control And Data Updation With At Pre: Attribute Time Based Proxy Re Encryption For Shared Data In Cloud

2111 words - 9 pages

We consider a cloud computing environment consisting of a cloud service provider (CSP), a data owner, and many users [few with read and few with both read/write permission]. The CSP maintains cloud infrastructures, which pool the bandwidth, storage space, and CPU power of many cloud servers to provide 24/7 services. The CSP mainly provides two services: data storage and re-encryption. After obtaining the encrypted data from the data owner, the CSP will store the data. On receiving a data access request from a user, the CSP will re-encrypt the ciphertext based on attributes, and return the re-encrypted ciphertext.
The data owner outsources a set of data to the cloud. Each piece of data is ...view middle of the document...

User’s access right is terminated automatically after a predetermined period of time.

4) Fine-grained access control: The data owner specifies expressive access structure for each data and give read/write access to authorized users.

5) Cost efficiency: The re-encryption cost on the CSP is relatively low and the cost of data updation by data owner and data users are relatively same.
3.3 Main Idea

The main idea is to combine CPABE and attribute based PRE and also to incorporate the concept of time. Intuitively, each user is identified by a set of attributes and a set of effective time periods that denotes how long the user is eligible for these attributes, i.e., the period of validity of the user’s access right. The data accessed by the users is associated with an attribute-based access structure and an access time. The access structure is specified by the data owner, but the access time is updated by the CSP with the time of receiving an access request. The data can be recovered by only the users whose attributes satisfies the access structure and whose access rights are effective in the access time.
After specifying the access structure, data owner encrypts and uploads the data to cloud. Before sending this Ciphertext to the users the CSP re-encrypt it by using re-encryption algorithm which is attribute based. If the user needs to access the data means they need to decrypt the data twice.
Data owner issues the encryption key to users with write permission. They can perform updation or deletion of data if their attributes satisfy the access structure and their access time is within effective time period.

Fig 2 Example demonstrating AT-PRE scheme
Fig 2 illustrates an example of our proposed scheme. An access structure is defined for data. According to which only users with attributes {Faculty, CS} or {Faculty, IS} can access the data. As the concept of time is incorporated, even though attributes are satisfies, if access time is not within eligible time period then user cannot access the data.

3.4 Algorithms

The AT-PRE scheme could be described by a tuple of five algorithms: (KeyGen , Enc , Dec , ReKeyGen ,ReEnc)

 KeyGen: Returns a pair of keys (Pk , Sk) where Pk is a public key and Sk is a private key.
 Enc: Is used to encrypt a message M given a public key Pk . The output is a ciphertext message CPk =Enc (M , Pk).
 ReKeyGen: Generates a re-encryption key Rk.
 ReEnc: Given a ciphertext message CPk and re-encryption key Rk, it outputs a ciphertext message CRk = ReEncRk(CPk).
 Dec: Given the re-encrypted ciphertext CRk , it is first decrypted using Rk to obtain CPk. Then given the ciphertext message CPk and corresponding private key Sk , it outputs the original message M.
In brief, M =DecSk(DecRk (ReEncRk (EncPk(M))))

3.5 Architecture of Proposed Scheme

The architecture of AT-PRE scheme is represented in Fig 3.There are 3 main entities as shown in figure.

Data Owner: stores their data on the cloud and depends on the Cloud...

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