Abstract: While smart healthcare enhances the convenience of people’s lives,it also poses significant challenges for the secure transmission of massive medical data in open wireless network communication environments.These data are susceptible to various internal and external attacks during transmission.To ensure timely and effective medical data transmission,the cloud-fog architecture,widely adopted in smart healthcare for network communication,significantly shortens the communication distance between the cloud and terminal devices through the effective extension of cloud computing by fog computing,thereby effectively mitigating network latency and jitter issues caused by excessive distance.However,most existing authentication and communication schemes based on the cloud-fog architecture adopt a centralized architecture of single-cloud,multiple-fogs and multiple-devices,which is prone to the risk of single-point failure.More seriously,these schemes often assume that the cloud is completely trustworthy,whereas in reality,cloud servers also face the risk of internal attacks,enabling attackers to compute session keys during the identity authentication and key agreement phase,leading to the leakage of communication data privacy and severely impacting communication security.In response to these communication security challenges,this paper proposes a secure authentication and key agreement protocol for smart healthcare that is resistant to cloud-fog compromise attacks.Leveraging blockchain technology to ensure the security of protocol data,this protocol can withstand various known attacks while also resisting cloud-fog leakage attacks.The semantic security of the proposed protocol is demonstrated using the extended Random Oracle Model.A heuristic security analysis method is employed to show that the proposed protocol satisfies all eight security properties.Additionally,the security of the proposed protocol is verified using the AVISPA security analysis tool.Performance analysis indicates that,compared with existing related protocols,the proposed protocol has lower communication overhead,lower computational cost,lower energy consumption,and stronger resistance to security attacks.

Key words: Smart healthcare, Cloud and fog compromise attack, Fog computing, Authentication, Blockchain