Data marketplaces are online platforms where sellers look for buyers motivated by the promise of payment for their potentially private information. However, both sellers and buyers have security concerns. The former worry about losing control over their data and not collecting their payments while the latter worry about the correctness of the purchased data. Previous works address these security concerns by relying on trusted entities. In this thesis, we propose Agora, the first secure blockchain-based data marketplace that does not rely on trusted third parties. Agora achieves data privacy, output verifiability, and atomicity of payments by leveraging cryptographic techniques, and is designed as a decentralized application via smart contracts. Particularly, sellers provide enc...[ Read more ]

Data marketplaces are online platforms where sellers look for buyers motivated by the promise of payment for their potentially private information. However, both sellers and buyers have security concerns. The former worry about losing control over their data and not collecting their payments while the latter worry about the correctness of the purchased data. Previous works address these security concerns by relying on trusted entities. In this thesis, we propose Agora, the first secure blockchain-based data marketplace that does not rely on trusted third parties. Agora achieves data privacy, output verifiability, and atomicity of payments by leveraging cryptographic techniques, and is designed as a decentralized application via smart contracts. Particularly, sellers provide encrypted information to brokers who use a functional secret key to learn solely the output of a specific, agreed upon, function over the raw data. Buyers purchase decrypted results from brokers either in singles or in batches, verifiably, by receiving corresponding zero-knowledge proofs of validity. We implement a working prototype on Ethereum and demonstrate, via extensive experimentation, Agora’s scalability, feasibility, and efficiency. We prove Agora secure against active and passive attacks, and report its performance and monetary costs.