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Access Control and Data Updation in Cloud Computing

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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 encrypted before outsourcing. The data owner is responsible for determining the access structure for each data, and distributing secret keys to each user. When a user wishes to access data, he will first request appropriate keys from the data owner, and then request the CSP to download the ciphertext. If his access right is effective when he requests the data, he can successfully execute decryption. The data owner is the only one allowed to give read/write permission to users. Data users with write permission can perform the updations and even delete the data within their effective time period. A typical cloud environment is shown in Fig 1. Fig 1 A typical cloud environment 3.2 Design Goals The main objective of our scheme is to achieve, 1) Data confidentiality: The data is encrypted

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