Blockchain-Enabled Searchable Encryption in Clouds: A Review

Nowadays, the demand of storage and computational resources is increasing. As a result, the number of organisations and individuals that outsource their data to cloud is also increasing. Since data privacy and security are the main concerns, the users always encrypt their data before uploading the data to the cloud server. However, it obstructs the search operation which is one of the basic data utilisation. Search operation can be seen as one of the most important function in daily life as people frequently search for data they wanted. When the uploaded data is encrypted, the capability of a server to search for certain keyword is limited as it is not able to carry out a plaintext keyword search on encrypted data. In order to realise the privacy needs, a cryptographic primitive called searchable encryption that allows the search of keyword over the uploaded data that is encrypted is introduced. The concept of searchable encryption has been presented to enable data users to search for certain keyword over the encrypted data without leaking any information to the cloud server. However, most of the conventional searchable encryption schemes do not offer features that satisfy the real-world application such as fair payment, verifiability of search result, etc. While blockchain is well-known with its features such as decentralised, integrity, and immutability, thus blockchain-enabled searchable encryption schemes will be discussed on how it can be used to overcome or complement the downsides of conventional searchable encryption. In this paper, the state-of-the-art of blockchain-enabled searchable encryption schemes will be reviewed and compared.