  Advancements in distributed ledger technologies are rapidly driving the rise
of decentralized crowdsourcing systems on top of open smart contract platforms
like Ethereum. While decentralized blockchain-based crowdsourcing provides
numerous benefits compared to centralized solutions, current implementations of
decentralized crowdsourcing suffer from fundamental scalability limitations by
requiring all participants to pay a small transaction fee every time they
interact with the blockchain. This increases the cost of using decentralized
crowdsourcing solutions, resulting in a total payment that could be even higher
than the price charged by centralized crowdsourcing platforms. This paper
proposes a novel suite of protocols called NF-Crowd that resolves the
scalability issue by reducing the lower bound of the total cost of a
decentralized crowdsourcing project to O(1). NF-Crowd is a highly reliable
solution for scaling decentralized crowdsourcing. We prove that as long as
participants of a project powered by NF-Crowd are rational, the O(1) lower
bound of cost could be reached regardless of the scale of the crowd. We also
demonstrate that as long as at least one participant of a project powered by
NF-Crowd is honest, the project cannot be aborted and the results are
guaranteed to be correct. We design NF-Crowd protocols for a representative
type of project named crowdsourcing contest with open community review
(CC-OCR). We implement the protocols over the Ethereum official test network.
Our results demonstrate that NF-Crowd protocols can reduce the cost of running
a CC-OCR project to less than $2 regardless of the scale of the crowd,
providing a significant cost benefit in adopting decentralized crowdsourcing
solutions.
