Distrust between data providers and data consumers is one of the main obstacles hampering the take-off of digital-data commerce. Data providers want to get paid for what they offer, while data consumers want to know exactly what they are paying for before actually paying for it. In this article, we present a protocol that overcomes this obstacle by building trust based on two main ideas. First, a probabilistic verification protocol, where some random samples of the real dataset are shown to buyers in order to allow them to make an assessment before committing any payment; and second, a guaranteed, protected payment process enforced with smart contracts on a public blockchain that guarantees the payment of data if and only if the provided data meet the agreed terms, and that honest players are otherwise refunded.
Privacy-Preserving Crowd-Monitoring Using Bloom Filters and Homomorphic Encryption