The vehicular social networks (VSNs) provide passengers, drivers and vehicles with multiple services, such as safe driving, data sharing, and traffic management. However, transmitting data in VSNs can expose information, such as the user’s identity and location. Malicious users who tamper with shared data can even cause serious traffic accidents. Considering the privacy protection and secure transmission of shared data in VSNs, we propose a blockchain-based and fog computing-assisted data access control (BFDAC) scheme. We combine the multi-authority ciphertext-policy attribute-based encryption algorithm with the consortium blockchain to avoid the security and trust issues in the form of centralized key management, and outsource part of the decryption calculations to roadside units (RSUs) as fog nodes to realize lightweight calculation for users. Our BFDAC scheme also supports user tracking and revocation, while users can also revoke shared data saved in the cloud. Security analysis shows that the BFDAC scheme can effectively protect the shared data. Experiments show that our BFDAC scheme reduces 32.8% in storage cost, 9.5% in encryption cost, and 57.1% in outsourced decryption cost compared to previous ones.

Nowadays, data between hospitals are usually not interoperable, which brings great inconvenience to medical data sharing and patients’ medical treatment. In addition, patients do not want their medical data to be leaked during the sharing process. Researchers have employed blockchain to build data-sharing systems to address these issues. However, current systems do not restrict the power of participants, nor do they prevent visitors from sharing the obtained data to unauthorized parties. To address these issues, we propose a private data-sharing system with symmetric encryption for the medical industry that implements power restriction and access control, and prevents the leakage of private data. To be specific, firstly, symmetric encryption algorithm is utilized to encrypt medical data to protect the privacy of data owner. Secondly, our proposed system is built on a new blockchain framework, in which only visitors with permission can access the medical data. Thirdly, we employ chameleon signature to prevent visitors from sharing data with other parties without permission. Finally, we make the power of participants in the system revocable to prevent them from abusing their power. Our proposed system has been proven to be secure through security analysis and can protect the privacy of patients. In addition, the experimental results show that our system has excellent performance in terms of time overhead compared to other systems.