PriRPT: Practical blockchain-based privacy-preserving reporting system with rewards

In order to obtain evidence of a crime timely, most authorities encourage whistleblowers to provide valuable reports by rewarding them with prizes. However, criminals will try their best to delete or tamper with the reports and even threaten and revenge the whistleblowers to escape punishment. Hence, to make the reporting system work, it is essential to ensure the integrity of reported messages and the anonymity of the reporting and rewarding procedures in the reporting system. Most existing schemes for this problem are generally based on ring signatures, which incur high computational overhead and imperfect anonymity. In this paper, we introduce a novel practical blockchain-based privacy-preserving reporting system with rewards dubbed as PriRPT. Specifically, the proposed scheme integrates the permissioned blockchain system, keyed-verification anonymous credential (KVAC), and structure-preserving signatures on equivalence classes (SPS-EQ) to provide reliable auditing of reports, and support anonymous reporting and anonymous rewarding simultaneously. In addition, we achieve higher efficiency in the reporting and rewarding protocol by replacing costly zero-knowledge proofs with KVAC and SPS-EQ. We also formalize the scheme along with security proof and provide rigorous evaluations on an open blockchain platform (JUICE) and a personal laptop to demonstrate its practicability.