###### Abstract  
Managing and controlling access to the tremendous data in Cloud storage is very challenging. Due to various entities engaged in the Cloud environment, there is a high possibility of data tampering. Cloud encryption is being employed to control data access while securing Cloud data. The encrypted data are sent to Cloud storage with an access policy defined by the data owner. Only authorized users can decrypt the encrypted data. However, the access policy of the encrypted data is in readable form, which results in privacy leakage. To address this issue, we proposed a reinforcement hiding in access policy over Cloud storage by enhancing the Ciphertext Policy Attribute-based Encryption (CP-ABE) algorithm. Besides the encryption process, the reinforced CP-ABE used logical connective operations to hide the attribute value of data in the access policy. These attributes were converted into scrambled data along with a ciphertext form that provides a better unreadability feature. It means that a two-level concealed tactic is employed to secure data from any unauthorized access during a data transaction. Experimental results revealed that our reinforced CP-ABE had a low computational overhead and consumed low storage costs. Furthermore, a case study on security analysis shows that our approach is secure against a passive attack such as traffic analysis. CP-ABE; fine-grained access control; policy hiding; privacy-preserving +
Footnote †: journal: Future Internet  
that organizations particularly choose is using Cloud storage to afford them the ability to access their files (data and information) from any device and any place. Another reason is by making Cloud storage to be part of the backup solution. In addition, assessing and sharing data from the Cloud environment offers highly available services. That feature is crucial for organizations dealing with numerous clients besides diverse roles and demands. Once Cloud computing is established with its core services (i.e., IaaS, PaaS, SaaS), Cloud users begin to be concerned about security matters [5; 6; 7; 8]. From the Cloud storage perspective, data confidentiality and privacy have become debatable among Cloud users due to the skeptical location where the files reside. Furthermore, when they noticed that the CSPs operated in a multi-tenant environment, the organizations raised the demand for security features from the CPSs. It is mainly to ensure the users' data and information stored in the Cloud are not exposed or disclosed to any illegitimate access. Since early in the year of 2000, many types of research have been developed in tackling the Cloud security issue. Among security approaches, encryption has initially become the essence of the Cloud security call. The authors of [9; 10; 11] proposed the encryption algorithm for securing Cloud data that converts the data into unreadable forms. Therefore, any attempt to sniff data over cloud storage can be prevented. However, studies by the authors of [12; 13] stated that the encryption algorithm alone does not guarantee data safety in Cloud storage. In fact, in a multi-tenant environment, the probability of data exposure is high because different users share the same Cloud infrastructure and storage. It means that they stored the data in the same location, and more crucially, it was probably kept in the same stack of the server. This leads to unauthorized access by other users [14; 15], especially when those users have the intention of hacking and stealing the data. Thus, besides performing data encryption, access control over Cloud storage needs to be addressed. Therefore, other researchers began to bring together encryption with other solutions, such as privacy-preserving schemes and access control schemes [16], to enhance data privacy further. Attribute-based Encryption (ABE) is a promising solution that offers fine-grained access control and provides data confidentiality on Cloud storage [17].