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Fine grained key computation scheme for secure data sharing in cloud

Data sharing is an important aspect of cloud storage. It is very imperative to ensure security during this sharing process. The basic idea of data security lies on encryption of data as well as delegation of decryption key. A data owner has to share the encrypted data as well as the decryption key of the corresponding data with another user, so that the latter can view the original data while maintaining the security of the data. This paper proposes a method of secure data sharing which is space and time efficient. In this method, data is encrypted based on a file identifier (id, which is an integer that ranges from 1 to a maximum number of branches in the hierarchical data model) and access policies. Access policies are represented using access tree structure. The key to be shared with the recipient provides fine-grained access to the files based on attributes of the recipient. This key is computed based on id and attributes of the user.