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.
Authenticated encryption (AE) is a cryptographic construction that simultaneously protects confidentiality and integrity. A considerable amount of research has been devoted to the area since its formal inception in 2000. Different lines of research have been proposed to enhance the available schemes in terms of security, efficiency, and design and to implement new ideas. However, a comprehensive systematic literature review (SLR) of the topic has not been provided to the best of the authors' knowledge. This study fills this gap in the literature by proposing a framework for classifying AE schemes and highlighting past contributions to help researchers familiarize themselves with the current state and directions for future research in the area. This SLR covered AE schemes proposed from 2000 to 2020. A total of 217 articles, selected from eight sources, were categorized into independent schemes, CAESAR competition schemes, and NIST lightweight competition schemes. These schemes were then classified according to their design approaches, security-related properties, and functional features. Our analysis reveals that a significant outstanding challenge in AE is to balance security, efficiency, and the provision of desirable features.
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