# Separable Data-Hiding Scheme for Encrypted Image to Protect Privacy of User in Cloud
## 1 Introduction  
Cloud computing is an important pillar of the transformation of the new generation of information technology (IT) and its application mode. As such, it has changed and facilitated people's lives significantly because of its low energy consumption, fast storage, good expansibility, high reliability, and resource-sharing characteristics. It can provide users with limitless computing resources and limitless storage resources [1]. Users can have access to computer resources when it is needed without large capital costs for hardware and people to deploy and operate their service. Such elasticity of resources is unprecedented in the history of IT [2; 3]. Gartner, an international research and consulting firm, said that the size of the global market for public cloud services was $260.2 billion in 2017, up 18.5% from $219.6 billion in 2016 [4]. By 2020, the global cloud computing market has been projected to reach $411 billion [5]. Gartner also predicts that cloud computing will become a $300-billion business by 2021 as companies increasingly use cloud services to implement their digital business activities. Therefore, cloud computing, as an indispensable infrastructure of the Internet society, has become a market opportunity in the next few years. However, the services provided by third-party cloud service providers are subject to additional security threats [6]. In recent years, there has been significant concern about protecting the privacy of cloud computing. In May 2014, the network used by the American e-commerce giant, Yibei Company, was attacked, and 145 million pieces of customers' information were leaked worldwide. In October 2014, the computer system of JPMorgan Chase and Company, the largest bank in the United States based on its assets, was attacked, and information of 76 million households and 7 million small businesses was leaked. In 2016, Google's Project Zero found a serious vulnerability at Cloudflare, the web performance and security company, which resulted in the leakage of the data of millions of website customers served by the Cloudflare content delivery network. In July 2017, after Baidu Cloud, a comprehensive cloud service provider, was exposed to automatic sharing/disclosure of users' photos in 2016, the Baidu network disk once again identified that there were problems with product logic, and users' photos, documents and other private information were leaked. In August 2017, server storage files at Amazon Web Services (AWS) were leaked, exposing the information of 1.8 million voters. At this point, the security of the data in cloud computing has been pushed to the cusp of the storm, and protecting the privacy of users' data has become an extremely important and urgent task. Many research [7; 8] efforts also are being devoted to protecting users' private data in cloud computing. Data hiding [9; 10; 11; 12] is a kind of technology that embeds secret information into a carrier dataset, such as text, audios, images, and videos, in an imperceptible manner. It ensures that the human eye cannot perceive any modification of the carrier data in order to avoid attracting the attention of malicious attackers. Encryption technology [13; 14] coverts ordinary signals into unintelligible data, which is an effective and popular way to protect the confidentiality of private data. Therefore, the combination of data hiding and encryption [15; 16] can provide two layers of protection for private data during cloud computing. In 2008, [PERSON] et al. [17] proposed the concept of data hiding for encrypted images (DH-EI). Later, many schemes [18; 19; 20; 21] were developed to improve the performance of DH-EI. According to the smoothness of image blocks, [PERSON]'s scheme [18] embedded additional data by flipping the three least significant bits (LSBs) of the specific pixels in each block, but the additional data cannot be extracted before image decryption. [PERSON] et al.