A Survey on Data Confidentiality and Privacy in Cloud Computing <s> DISCUSSION AND ANALYSIS <s> 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. <s> BIB001 </s> A Survey on Data Confidentiality and Privacy in Cloud Computing <s> DISCUSSION AND ANALYSIS <s> Cloud computing is an emerging technology which has become today's blistering research area due to the advancement of increased connectivity and it is most interesting and attractable technology which offers the on demand services to the users over the internet. Since Cloud Computing stores the user data and allows the user to work on the cloud system and so the security has become the main concern which creates threat and tries to deploy the Cloud environments. Even though the Cloud Computing is efficient, there are many challenges for data security, which may take away the users from using the cloud computing. To ensure the security of data, we proposed a method by implementing Cramer - Shoup cryptosystem. <s> BIB002 </s> A Survey on Data Confidentiality and Privacy in Cloud Computing <s> DISCUSSION AND ANALYSIS <s> Cloud computing is based on network and computer applications. In cloud data sharing is an important activity. Small, medium, and big organization are use cloud to store their data in minimum rental cost. In present cloud proof their importance in term of resource and network sharing, application sharing and data storage utility. Hence, most of customers want to use cloud facilities and services. So the security is most essential part of customer's point of view as well as vendors. There are several issues that need to be attention with respect to service of data, security or privacy of data and management of data. The security of stored data and information is one of the most crucial problem in cloud computing. Using good protection techniques of access control we can resolved many security problems. Accept that managing privacy and security of information in web highly challenging. This paper describes how to secure data and information in cloud environment in time of data sharing or storing by using our proposed cryptography and steganography technique. <s> BIB003 </s> A Survey on Data Confidentiality and Privacy in Cloud Computing <s> DISCUSSION AND ANALYSIS <s> Individual user and organizations benefit from cloud computing services, which allow permanent online storage of files. The problem occurs when companies store highly confidential documents in cloud servers. Therefore, this paper aims to introduce a backbone structure for a cloud storage system where the security and personal privacy is highly maximized. It is very obvious that cloud computing servers are highly protected against unauthorized access, but in some cases these files stored can be accessible by the maintenance staffs. Fully protection is needed to ensure that the files stored in the server are only accessible to owners. This paper proposes a system that will employ Rivest-Shamir-Adleman (RSA) and Advanced Encryption Standard (AES) combination encryption process using USB device. The files may be accessed in the cloud but all the files will remain encrypted till the USB device is plugged into the computer. The point of applying such method is to fully protect the files and avoid using one single password. The randomly generated passkeys are very complex combinations thus user will not be able to fully memorize them. The proposed system will detect the USB that contains the private-key used for the files to be downloaded from the cloud. <s> BIB004 </s> A Survey on Data Confidentiality and Privacy in Cloud Computing <s> DISCUSSION AND ANALYSIS <s> Cloud computing is a technology or distributed network where user can move their data and any application software on it. But there are some issues in cloud computing, the main one is security because every user store their useful data on the network so they want their data should be protected from any unauthorized access, any changes that is not done on user's behalf. There are different encryption techniques used for security purpose like FDE and FHE. To solve the problem of Key management, Key sharing various schemes have been proposed like third party auditing scheme but it will be failed, if the third party's security is compromised or if the third party is malicious. In this paper, we have used the symmetric key agreement algorithm named Diffie Hellman, it is key exchange algorithm which creates session key between two parties who want to communicate with each other and HMAC for the data integrity and OTP (One Time Password) is created which provides more security. <s> BIB005 </s> A Survey on Data Confidentiality and Privacy in Cloud Computing <s> DISCUSSION AND ANALYSIS <s> Cloud computing is very popular in organizations and institutions because it provides storage and computing services at very low cost. However, it also introduces new challenges for ensuring the confidentiality, integrity and access control of the data. Some approaches are given to ensure these security requirements but they are lacked in some ways such as violation of data confidentiality due to collusion attack and heavy computation (due to large no keys). To address these issues we propose a scheme that uses threshold cryptography in which data owner divides users in groups and gives single key to each user group for decryption of data and, each user in the group shares parts of the key. In this paper, we use capability list to control the access. This scheme not only provides the strong data confidentiality but also reduces the number of keys. <s> BIB006 </s> A Survey on Data Confidentiality and Privacy in Cloud Computing <s> DISCUSSION AND ANALYSIS <s> Cloud computing is a rising technology that is still unclear to many security issues. The most challenging issue today in cloud servers is to ensure data security and privacy of the users. The proposed schema presents HE-RSA or hybrid encryption RSA along with Advanced Encryption Standard or AES to ensure efficiency, consistency and trustworthiness in cloud servers. The goal of this paper is to use various cryptography concepts during communication along with its application in cloud computing and to enhance the security of ciphertext or encrypted data in cloud servers along with minimizing the consumption of time, cost and memory size during encryption and decryption. <s> BIB007
In the previous section, we presented a review of some of the prominent approaches to provide data confidentiality in the Cloud. Our study included numerous solutions and techniques based on different algorithms and methods. In this section, all the solutions are further analysed and compared. The strengths and weakness of all the solutions are discussed. The comparative analysis is summarised based on key attributes, such as key management, algorithm efficiency, encryption complexity and the ability to search for encrypted data. All the solutions are listed in Table 1 along with their key attributes. A check mark () shows that a particular attribute is supported and available in the corresponding solution, whilst a negatory mark () shows that a particular attribute is missing in the solution. The strengths and weaknesses of each solution are given in Table 1 .  The solution provided by Pant et al. BIB003 is based on cryptographic and steganographic techniques, which makes cryptanalysis more complex. Data is highly protected by this technique, both on the network and on the Cloud. However, by introducing multilevel protection, the robustness of the process is compromised. It is an effective solution for highly confidential documents where the DO or users are limited. One of the core limitations of this solution is that steganography software is required on the user system on which the data is downloaded. Consequently, the availability of data is bound to the availability of the software on the machine. The solution does not discuss the mechanism of the key management, which is another overhead cost. Raju and Sirajudeen BIB002 addressed the potential threat of data leakage by implementing the Cramer-Shoup cryptosystem. This is a simple solution compared to the abovementioned approach. The disadvantage of this solution is that key management is the sole responsibility of the user, and there is no way to restore data if the key is lost. This solution does not provide other essential features, such as searching for or outsourcing data. A hybrid solution was presented by Pitchay et al. BIB004 based on the RSA and the AES algorithms. In this system, intruders are unable to easily obtain the original data even if they can capture the encrypted messages. A removable device is used for key management. The advantage is that data cannot be decrypted without the device, which holds the private key. Compared to the Cramer-Shoup cryptosystem, this is a comprehensive and more effective solution. The limitation of this solution is that users must plug the USB device in whenever they need to upload or download data. This problem limits the availability of data to the availability of the removable device. Furthermore, no backup mechanisms of the keys or the USB device were defined. Therefore, if the USB is lost, the data cannot be recovered. By implementing a backup mechanism, this solution could be made more effective and useful. Another hybrid solution was proposed by Bhandari et al. BIB007 . The authors examined the strengths and security of the RSA and the AES algorithms and proposed an abstract model based on them. A comprehensive examination of the RSA algorithm was conducted, and the efficiency of the algorithm was improved in terms of the running time, cost and memory size. The authors analysed general attacks on RSA and proposed a solution to overcome its vulnerabilities, in order to make the solution more complex and established. Therefore, the major advantage of the algorithm is its improved security and overall efficiency of the Cloud system. The limitation of the solution is, again, key management, which is ignored in many solutions. Generally, the number of encryption keys is associated with users. A large number of keys introduces new challenges for data security, i.e., key management. For large organisations, solutions that do not address key management become irrelevant, irrespective of their efficiency or ability to secure data. Some approaches have been introduced by researchers to overcome key management challenges, while ensuring data security in Cloud systems. In this regard, a homomorphic scheme was presented by Kaur and Wasson BIB005 . A new model was established for key sharing and management. The strength of this algorithm is its use of dynamic OTPs to accomplish authentication. The solution is based on the symmetric key algorithm and the Diffie-Hellman algorithm. The session key is exchanged between two parties in the process of communication over a secure channel. The process is efficient and reduces key sharing and management time. However, this model requires enhancements to the Cloud system, as the second party in communication must be the Cloud system. Another limitation of the process is that it does not provide a mechanism for searching for or outsourcing documents. The solution presented by Saroj et al. BIB006 also focuses on the issue of key management. The solution utilises a modified Diffie-Hellman algorithm and public key cryptography to maintain secure communication between the CSP and the user. The data is transmitted in an encrypted form, so threats to the CSP are reduced. The authors introduced the concept of a group key, reduced the number of keys and directly related the keys to groups instead of individuals. Therefore, by applying one key corresponding to one group, this solution avoids the key management issue; thus, helping to protect outsource data from attackers. This work is the most comprehensive and established system among the reviewed solutions. The limitation of this system is that the efficiency of the process has not been measured. Furthermore, this solution shares a similar limitation with the solution provided by Kaur and Wasson BIB005 , which is that no search functionality is supported for encrypted data. Both solutions can be improved to facilitate a search functionality, and a complete solution for data security can be presented to appeal to large organisations. The only reviewed solution that focuses on searching for outsourced data was presented by Han et al. BIB001 . The solution is based on ABE and FHE. The benefit of the solution is that, along with data security, this scheme allows users to search for encrypted data without a private key. The proposed solution is efficient and supports searches for encrypted data. The limitation of the solution is that it does not provide any mechanism for key management. However, most of the solutions discussed in this paper do not support this functionality.