  Current blockchain-based reputation solutions for crowdsourcing fail to
tackle the challenge of ensuring both efficiency and privacy without
compromising the scalability of the blockchain. Developing an effective,
transparent, and privacy-preserving reputation model necessitates on-chain
implementation using smart contracts. However, managing task evaluation and
reputation updates alongside crowdsourcing transactions on-chain substantially
strains system scalability and performance. This paper introduces
RollupTheCrowd, a novel blockchain-powered crowdsourcing framework that
leverages zkRollups to enhance system scalability while protecting user
privacy. Our framework includes an effective and privacy-preserving reputation
model that gauges workers' trustworthiness by assessing their crowdsourcing
interactions. To alleviate the load on our blockchain, we employ an off-chain
storage scheme, optimizing RollupTheCrowd's performance. Utilizing smart
contracts and zero-knowledge proofs, our Rollup layer achieves a significant
20x reduction in gas consumption. To prove the feasibility of the proposed
framework, we developed a proof-of-concept implementation using cutting-edge
tools. The experimental results presented in this paper demonstrate the
effectiveness and scalability of RollupTheCrowd, validating its potential for
real-world application scenarios.
