SEPAR: A Privacy-Preserving Blockchain-based System for Regulating Multi-Platform Crowdworking Environments

Despite recent intensive research, existing crowdworking systems do not adequately address all the requirements of a real-world crowdworking environment. First, crowdworking platforms need to integrate within society and in particular to interface with legal and social institutions. Global regulations must be enforced, such as minimal and maximal work hours that participants can spend on crowdworking platforms. Second, crowdworking platforms are naturally distributed and need to collaborate with each other to process complex tasks, resulting in the rise of multi-platform crowdworking systems. Moreover, while collaborating to enforce global regulations or while processing complex tasks that require the transparent sharing of information about the tasks, the system needs to preserve the privacy of all participants. In this paper, we present SEPAR, a multi-platform crowdworking system that enforces global constraints on distributed independent entities. In SEPAR, Privacy is ensured using lightweight and anonymous tokens, while transparency is achieved using a permissioned blockchain shared across multiple platforms. To support fault tolerance and support collaboration among platforms, SEPAR provides a suite of distributed consensus protocols. The privacy guarantees of SEPAR against covert adversaries are formalized and thoroughly demonstrated, and the experiments reveal the efficiency of SEPAR in terms of performance and scalability.