Shared vehicles provided by car-sharing systems can help address several issues in cities, such as reducing the use of personal cars. The popularity of the Internet of Things has made it easier for people to access shared cars through simple mobile operations. However, the car-sharing system has vulnerabilities in terms of security, such as sensitive user data transmitted through public channels, which could be accessed by attackers for illegal purposes. Therefore, it's crucial to establish a secure authentication protocol. In addition, the traditional centralized car-sharing system has a single point of failure, necessitating a decentralized car-sharing scheme, which was proposed in this study using blockchain technology. This model ensures data integrity and offers a decentralized vehicle-sharing service with anonymous authentication of participating entities. The proposed car-sharing system provides mutual authentication, protects against several attacks, and was analyzed for computation and communication costs. The proposed blockchain-based decentralized car-sharing scheme has several advantages over the traditional centralized model. For example, it eliminates the need for a trusted third party. the proposed blockchain-based decentralized car-sharing scheme offers a more secure and efficient approach to car-sharing, addressing several security issues associated with traditional centralized models. It ensures data integrity and provides mutual authentication while offering anonymity to participating entities, making it a promising solution for car-sharing systems in smart cities. to maintain the integrity of the system, as blockchain technology is based on a distributed ledger that allows participants to validate transactions. Additionally, the anonymity of the participating entities ensures privacy while providing security against unauthorized access to sensitive data. Moreover, the proposed scheme's security was analyzed using several methods, such as informal analysis, AVISPA simulation, and BAN logic evaluation, to ensure the system's resilience to various attacks.