Practical and Secure Keyword Search Services on Blockchain

This thesis investigates the challenges and solutions in developing blockchain-based searchable encryption systems, with a focus on key aspects such as security, scalability, and incentives. First, this thesis introduces a novel off-chain verification method for SSE systems, addressing both dishonest server nodes and users, ensuring security and on-chain scalability. Second, it proposes a non-verification-based approach to enhance the scalability of blockchain databases, introducing a VRF-based load-balancing algorithm that improves throughput while preserving the security guarantees of blockchain technology. Third, it presents SEARCHAIN, a proof-of-useful-work blockchain system for SSE queries, which incorporates a novel committee selection algorithm to incentivise honest verification by auditors, ensuring service fairness. Through both theoretical analysis and empirical evaluation, this thesis demonstrates how these approaches enhance the security and practicality of blockchain-based SSE systems.