Searching for available parking spaces is a major problem for drivers in big cities, causing traffic congestion and air pollution, and wasting drivers' time. Smart parking systems enable drivers to solicit real-time parking information and book parking slots. However, current smart parking systems require drivers to disclose their sensitive information, such as their desired destinations. Moreover, existing schemes are centralized which makes them vulnerable to bottlenecks and single point of failure problems and privacy breaches by service providers. In this paper, we propose a privacy-preserving smart parking system using blockchain and private information retrieval. First, a consortium blockchain is created by different parking lot owners to ensure security, transparency, and availability of the parking offers. Then, to preserve the drivers' location privacy, we adopt private information retrieval technique to privately retrieve parking offers from blockchain nodes. In addition, a short randomizable signature is used to allow drivers to authenticate for reserving available parking slots from parking owners anonymously. Our evaluations demonstrate that our proposed scheme preserves drivers' privacy with low communication and computation overheads.Index Terms-Smart parking, blockchain, security and privacy preservation, and private information retrieval.

Most of the existing smart parking systems threaten the drivers' privacy by revealing information about their visited locations. Moreover, they are centralized making them vulnerable to a single point of failure and attack, which threatens the availability of the parking service. They also suffer from a lack of transparency, where the centralized service organizer may favor some parking lots by booking their parking slots first. To tackle these concerns, we propose a blockchain-based smart parking system with privacy preservation and reputation management. In our system, a consortium blockchain is created by different parking lots to run the parking system securely and transparently, where the parking offers are recorded on a shared and immutable ledger. We use a commitment technique during the submission of the offers to ensure fair parking rates. Then, we use a private information retrieval technique during the offers retrieval to preserve the drivers' location privacy. Furthermore, to anonymously and efficiently authenticate drivers during the reservation process, we use a short randomizable signature. We also use a time-locked anonymous payment technique to discourage drivers from not committing to their parking reservations and provide a secure and privacy-preserving payment method for parking service. Finally, we integrate a blockchain-based anonymous reputation management scheme into our system, where drivers can anonymously rate the parking service to ensure high quality of service. Our evaluations demonstrate that our smart parking system is secure and capable of preserving drivers' privacy with low communication, computation, and storage overheads.

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