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With the growth of cloud computing technology, more and more Cloud Service Providers (CSPs) begin to provide cloud computing service to users and ask for users' permission of using their data to improve the quality of service (QoS). Since these data are stored in the form of plain text, they bring about users' worry for the risk of privacy leakage. However, the existing watermark embedding and encryption technology is not suitable for protecting the Right to Be Forgotten. Hence, we propose a new Cloud-User protocol as a solution for plain text outsourcing problem. We only allow users and CSPs to embed the ciphertext watermark, which is generated and embedded by Trusted Third Party (TTP), into the ciphertext data for transferring. Then, the receiver decrypts it and obtains the watermarked data in plain text. In the arbitration stage, feature extraction and the identity of user will be used to identify the data. The fixed Hamming distance code can help raise the system's capability for watermarks as much as possible. Extracted watermark can locate the unauthorized distributor and protect the right of honest CSP. The results of experiments demonstrate the security and validity of our protocol.

This article describes how cloud storage dramatically benefits people in freeing up their local storage space, while bringing the separation of the data ownership and private manipulation. Hence, it is difficult for the cloud user to make sure that the cloud storage provider (CSP) has obeyed the request of deletion to remove all corresponding data. To solve the issue technically, this article proposes an interactive cloud-user watermarking protocol (CUW) based on the homomorphic encryption. To meet security requirements, the encrypted watermark is embedded into encrypted data. Moreover, to enjoy the convenient cloud services, the uploaded data is eventually stored in the cloud server in the form of plain text. The performance of the CUW protocol is evaluated through a prototype implementation.

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