Searchable Symmetric Encryption (SSE) when deployed in the cloud allows one to query encrypted data without the risk of data leakage. Despite the widespread interest, existing surveys do not examine in detail how SSE’s underlying structures are designed and how these result in the many properties of a SSE scheme. This is the gap we seek to address, as well as presenting recent state-of-the-art advances on SSE. Specifically, we present a general framework and believe the discussions may lead to insights for potential new designs. We draw a few observations. First, most schemes use index table, where optimal index size and sublinear search can be achieved using an inverted index. Straightforward updating can only be achieved using direct index, but search time would be linear. A recent trend is the combinations of index table, and tree, deployed for efficient updating and storage. Secondly, mechanisms from related fields such as Oblivious RAM (ORAM) have been integrated to reduce leakages. However, using these mechanisms to minimise leakages in schemes with richer functionalities (e.g., ranked, range) is relatively unexplored. Thirdly, a new approach (e.g., multiple servers) is required to mitigate new and emerging attacks on leakage. Lastly, we observe that a proposed index may not be practically efficient when implemented, where I/O access must be taken into consideration.

BackgroundWith the rapid development of cloud computing and mobile networking technologies, users tend to access their stored data from the remote cloud storage with mobile devices. The main advantage of cloud storage is its ubiquitous user accessibility and also its virtually unlimited data storage capabilities. Despite such benefits provided by the cloud, the major challenge that remains is the concern over the confidentiality and privacy of data while adopting the cloud storage services [1]. For instance, unencrypted user data stored at the remote cloud server can be vulnerable to external attacks initiated by unauthorized outsiders and internal attacks initiated by the untrustworthy cloud service providers (CSPs) [2]. There are several reports that confirm data breaches related to cloud servers, due to malicious attack, theft or internal errors [3]. This raises concern for many users/ AbstractEnsuring the cloud data security is a major concern for corporate cloud subscribers and in some cases for the private cloud users. Confidentiality of the stored data can be managed by encrypting the data at the client side before outsourcing it to the remote cloud storage server. However, once the data is encrypted, it will limit server's capability for keyword search since the data is encrypted and server simply cannot make a plaintext keyword search on encrypted data. But again we need the keyword search functionality for efficient retrieval of data. To maintain user's data confidentiality, the keyword search functionality should be able to perform over encrypted cloud data and additionally it should not leak any information about the searched keyword or the retrieved document. This is known as privacy preserving keyword search. This paper aims to study privacy preserving keyword search over encrypted cloud data. Also, we present our implementation of a privacy preserving data storage and retrieval system in cloud computing. For our implementation, we have chosen one of the symmetric key primitives due to its efficiency in mobile environments. The implemented scheme enables a user to store data securely in the cloud by encrypting it before outsourcing and also provides user capability to search over the encrypted data without revealing any information about the data or the query. Salam et al. Hum. Cent. Comput. Inf. Sci. (2015) et al. Hum. Cent. Comput. Inf. Sci. (2015) 5:19 organizations as the outsourced data might contain very sensitive personal organization/ information. RESEARCHPage 2 of 16 SalamSeveral researches have addressed the issue of ensuring confidentiality and privacy of cloud data without compromising the user functionality. Here, confidentiality refers to the secrecy of the stored data so that only the client can read the contents of the stored data. To solve the problem of confidentiality, data encryption schemes can come in handy to provide the users with some control over the secrecy of their stored data. This has been adopted by many recent researches which allow users to encrypt their data...

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A vast number of e-voting schemes including mix-net-based e-voting, homomorphic e-voting, blind signature-based e-voting, blockchain-based e-voting, post-quantum e-voting, and hybrid e-voting have been proposed in the literature for better security and practical implementation. In this paper, we review various e-voting approaches to date. We first compare the structures, advantages, and disadvantages of the different e-voting approaches. We then summarise the security properties of the e-voting approaches in terms of their functional requirements and security requirements. In addition, we provide a comprehensive review of various types of e-voting approaches in terms of their security properties, underlying tools, distinctive features, and weaknesses. We also discuss some practical considerations in the design of e-voting systems. Subsequently, some potential research directions are suggested based on our observations.

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