A Privacy-Preserving Thin-Client Scheme in Blockchain-Based PKI

Traditional centralized PKIs are vulnerable due to the single point of failure. A feasible solution is to build a decentralized PKI without certificate authority (CA). Web of Trust is the first step toward realizing a decentralized PKI, but it still has some limitations such as missing incentive and leaking user's privacy. Blockchain's numerous desirable properties, such as cryptographical security, decentralized nature and unalterable transaction record, make it a suitable tool to implement a decentralized PKI. However, the latest research findings about blockchain-based PKI are still incompatible with the thin-clients which have limited storage ability to download the entire blockchain. To combat that, we firstly present a Privacy-preserving Thin-client Scheme (PTS) utilizing the idea of k-anonymity, which enables thin-clients to run normally as full node users and protect user's privacy simultaneously. After that, in order to reduce cost, we further propose an Efficient Privacy preserving Thin-client Scheme (EPTS) employing the method of PIR (private information retrieval). Then security analysis and functional comparison are performed to demonstrate the high security and comprehensive functionality of EPTS compared with existing schemes. Finally, extensive experiments are undertaken to confirm that EPTS can reduce computational cost and communication cost impressively.