You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: A Survey on Data Confidentiality and Privacy in Cloud Computing 
Chapter Title:  INTRODUCTION 
1. Abstract of Cited Paper (BIB001):  Cloud computing has emerged as one of the most influential paradigms in the IT industry in recent years. Since this new computing technology requires users to entrust their valuable data to cloud providers, there have been increasing security and privacy concerns on outsourced data. Several schemes employing attribute-based encryption (ABE) have been proposed for access control of outsourced data in cloud computing; however, most of them suffer from inflexibility in implementing complex access control policies. In order to realize scalable, flexible, and fine-grained access control of outsourced data in cloud computing, in this paper, we propose hierarchical attribute-set-based encryption (HASBE) by extending ciphertext-policy attribute-set-based encryption (ASBE) with a hierarchical structure of users. The proposed scheme not only achieves scalability due to its hierarchical structure, but also inherits flexibility and fine-grained access control in supporting compound attributes of ASBE. In addition, HASBE employs multiple value assignments for access expiration time to deal with user revocation more efficiently than existing schemes. We formally prove the security of HASBE based on security of the ciphertext-policy attribute-based encryption (CP-ABE) scheme by Bethencourt and analyze its performance and computational complexity. We implement our scheme and show that it is both efficient and flexible in dealing with access control for outsourced data in cloud computing with comprehensive experiments. 
2. Abstract of Cited Paper (BIB002):  Healthcare data has stringent security requirements for confidentiality, availability to authorized users, and traceability of access. The focus of this study is to investigate on these requirements and propose a solution for healthcare cloud providers that will help in protecting patient' data they host, which is of high importance. The focus will be on specific cloud computing healthcare security concerns and how cloud homomorphic encryption with splitting key and key delegation can help in meeting healthcare regulatory requirements. The suggested technique is based on FHE algorithm with key delegation to ensure data confidentiality, authentication, integrity, and availability in a multi-level hierarchical order. This will enable the healthcare provider to apply/omit any access rule in any order, especially in medical research environment.

Literature Review:
In recent years, the world has witnessed a rapid evolution in technology. The boom in wireless and mobile communication technologies has led to a significant increase in the number of Internet users. With the advent of new wireless applications and technologies, the amount of electronic data is growing exponentially day by day. The large volumes of data is one of the key drivers for the demand and the popularity of Cloud computing. Cloud computing is defined by the National Institution of Standards and Technology as "a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g. networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction" BIB003 . The essential characteristics of Cloud computing are on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service. Cloud computing has been noticed by end users as a low-cost technology trend that offers many efficient on-demand services, such as storage, hardware, and software. However, the availability of these services is dependent on the reliability of an Internet connection. The advantages of Cloud computing are numerous, such as offering more scalable, elastic, and flexible access to virtual computing resources such as processing, storage, and applications. Of all the benefits provided by the Cloud, data storage represents one of the most interesting and attractive prospects, particularly for small organisations due to the low rental cost and the possibility to store and retrieve a volume of data at anytime and anywhere. It is also appealing to large enterprises as it helps to reduce the cost and maintenance overheads of computing services. Cloud computing also attracts individual users, because they can access all data irrespective of the communication medium or access device, such as mobile, laptop, and smart devices. Today, Cloud computing remains a robust technology that offers high data availability. According to Han et al BIB003 and Wan et al BIB002 , Cloud computing is now considered to be a utility-along with gas, electricity, water, and phone services. The security of Cloud systems poses a challenge to both the provider and customers at the same time. Security is a common concern for any technology; however, in the Cloud, security leaks are the main issue that prohibits people from fully adopting Cloud systems. Storing sensitive and private data on Cloud servers is a major concern for clients. Currently, Cloud providers compete to enhance their servers, specifically, in terms of data security and user privacy. However, it is evident that users are increasingly concerned and aware of protecting their data and privacy from attackers. Many incidents affecting users stem from the frequent Cloud failures and successful attacks. For instance, Google Docs was found to be unintentionally sharing users' documents in 2009 BIB001 . This survey paper outlines the key challenges of data security in Cloud computing and then presents some methods and potential solutions related to enhancing and achieving data confidentiality. The paper is organised into four sections. Following on from the introduction, Section 2 gives an overview of the major challenges facing data security in the Cloud, with a focus on data confidentially. Section 3 presents a survey of recent security solutions to overcome data confidentialityrelated security challenges. Finally, Section 4 summarises the main findings of the survey and outlines future research avenues.