Privacy-Preserving Decentralized Crowdsensing: a Smart Contract-based approach

Mobile crowdsensing enables the collection of distributed geographic data by aggregating contributions from a large number of participants, each with a sensing device. Existing solutions rely on a centralised server to coordinate the campaign, introducing a single point of trust that can compromise data confidentiality and participant privacy. This thesis presents a privacy-preserving decentralised crowdsensing protocol in which coordination is delegated to an Ethereum smart contract, replacing the trusted server with a publicly verifiable and tamper-resistant intermediary. Data confidentiality is achieved through hybrid encryption: each sender encrypts their payload with a symmetric key that is in turn wrapped under an asymmetric key distributed by the campaign initiator, and stores the ciphertext on IPFS, publishing only the encrypted content identifier on-chain. Participation is incentivised through a custom ERC-20 token and a bond mechanism, while the campaign area is partitioned into a spatial grid of chunks so the contract records each submission's chunk on-chain and caps per-chunk submissions, preventing over-representation of densely populated areas. A second contract extends the base protocol by addressing three open issues: verifier access to submitted data at any time through a shared decryption key and on-chain visibility, lack of geographic reward incentives, and absence of penalties for incorrect votes beyond bond loss. An empirical evaluation covers gas consumption across multiple networks, block capacity contention under concurrent campaigns, and spatial coverage on a real-world taxi trajectory dataset from the city of Porto. The results show that the optimised contract reduces verifier gas costs by approximately 98% relative to the FIFO baseline, and that the reward decay mechanism successfully redirects sender contributions towards underrepresented areas. On some Layer 2 networks, the cost of participation becomes negligible for all roles.