Blockchain-enabled multi-authorization and multi-cloud attribute-based keyword search over encrypted data in the cloud

With the arrival of the 5G era, fast and secure data sharing is attracting increased attention. Among of the presented solutions, keyword search plays an important role since it can identify users and search ciphertext without decryption. However, the existing searchable algorithms have many limitations, such as powerful central authority, match processes being only carried out on the cloud server, and center corruption and single point of failure being easy to cause. Presently, the fairness of the keyword search is still a challenge. To solve these problems, we present a multi-authority and multi-cloud keyword search scheme based on the consortium blockchain and attribute-based encryption. Under this framework, multi-cloud block storage technique is used to address the unreliability of cloud servers, where at least two ciphertext files are stored in blocks on multiple cloud servers. It can resist malicious leaks, ciphertext tampering, and deletion of ciphertext by cloud servers. Blockchain allows the proposed scheme to achieve the integrity and correctness of the encrypted data, which also solves the fairness of search results. Furthermore, the scheme realizes privacy protection by hiding the keyword and the access policy in the trapdoor matching process. Finally, the security analyses and performance comparisons show the advantages of the proposed scheme over the existing work.