# An Improved Ciphertext-Policy Attribute-Based Encryption Scheme in Power Cloud Access Control
## 1 Introduction
Calculations of this scheme is simplified with the matrix operation. [PERSON] [13] proposed a privacy-preserving decentralized CP-ABE (PPDCP-ABE) to reduce the trust on the central authority and protect the users' privacy. Each authority can work independently without any collaboration to initial the system and issue secret keys to users. Users can obtain secret keys from multiple authorities without them knowing anything about himself/herself. Since CP-ABE uses a long-key and computational time for the encryption, and the decryption algorithm increases with the grow of attributes number, [PERSON] [14] made improvements in the encryption algorithm. The algorithm they designed is independent of the number of attributes and the minimum secret key length. It is shortened to 672 bits, which greatly reduced the time for decryption. [PERSON] [15] proposed a collaborative key management protocol in CP-ABE to realize the distributed generation, issue, and storage of private keys, without adding any extra infrastructure. Experiments prove that [PERSON]'s scheme has better performance in mobile devices. [PERSON] [16] proposed an auditable \(\sigma\)-time outsourced CP-ABE, which provides \(\sigma\)-time fine-grained access control and audits the correctness of the operation. [PERSON] [17] proposed a fine-grained two-factor authentication (2 FA) access control system for web-based cloud computing services. The cloud server has no idea on the exact identity of the user, to protect the user's privacy. [PERSON] [18] proposed a new scheme called outsourcing attribute-based encryption with keywords search function(KSF-OABE).Cloud service privader perform search encrypted keywords instead of the keywords embedded in trapdoor. However, the existing CP-ABE schemes have not considered the security issue of the data source and the generation of the access structure. On one hand, the data sources in power cloud are not only collectors but also sensors which cannot judge who has access to the data, so there should be an administrator to generate the access structure. If an agent is responsible for generating the access structure, it is difficult to adapt to the high-frequency data storage, and the administrator may make some mistakes. If an entity undertakes the task of a human administrator, some security issues may be discovered. On the other hand, there may be malicious users on both data source-side and user-side, who could make the power cloud create a wrong access structure, by forging or tampering identification. In order to meet the high-frequency data storage requirements of the power cloud and prevent possible attacks, the access control scheme must contain both the data collection stage and the data obtainment stage. This paper proposes a Power Cloud Access Control (PCAC) scheme. PCAC improves the traditional CP-ABE system model, including outsourcing the generation of access structures and the verification of attribute sets to a third party, to reduce the computational complexity. Considering the heavy computation overhead in an access tree, PCAC generates an access structure with the access tree, and shares a secret key with the LSSS. In addition, our scheme achieves the action auditing of users and data sources. In previous research studies, private keys did not work for the decryption process, therefore, authentication is a must to protect data saved in the power cloud. The user's and the data source's action is audited with zero-knowledge proofs, which prevents malicious users from attacking the system from both the source side and the user side. The contribution of this paper can be summarized as follows:  
1. A power cloud access control scheme based on a CP-ABE has been proposed. Considering the generation of the access structure and the heavy computation required for an access tree, PCAC achieves the automatic generation of access structures and effective sharing of the secret key. 2.