BASPED: Blockchain assisted searchable public key encryption over outsourced data

Outsourcing data to the cloud is now a common practice in many organizations to reduce data storage and maintenance costs. Outsourced data is stored in encrypted form over the cloud. Therefore, efficient search techniques are required to perform operations over the encrypted data. The existing solutions provide secure search operations, considering cloud servers as honest-but-curious. However, cloud servers may act malicious and produce inaccurate outcomes to the data users. Thus, a secure and verifiable search technique is required. This work proposes a Blockchain-Assisted Searchable Public key Encryption over outsourced Data (BASPED), using an inverted index. We exploit the potential of blockchain technology for equitable and trusted computing, by deploying a smart contract for secure and verifiable search operations to prevent the cloud server from cheating (intentionally or unintentionally). The most appealing feature of BASPED is that it is non-interactive and achieves both forward and backward privacy. It also resists keyword guessing attacks, chosen keyword attacks, search pattern leakage, and access pattern leakage. We prove the security of our proposed scheme assuming the difficulty of bilinear Diffie-Hellman problem. The proposed scheme is implemented and deployed on the Ethereum test network. Comprehensive evaluation of theory and practice demonstrates the practicability of our decentralized search scheme.