Due to recent advances in various technologies such as integrated circuit, embedded systems and wireless communications, the wireless body area network (WBAN) becomes a propitious networking paradigm. WBANs play a very important role in modern medical systems as the real-time biomedical data through intelligent medical sensors in or around the patients' body can be collected and sent the data to remote medical personnel for clinical diagnostics. However, wireless nature of communication makes an adversary to intercept or modify the private and secret data collected by the sensors in WBANs. In critical applications of WBANs, there is a great requirement to access directly the sensing information collected by the body sensors by an external user (e.g., a doctor) in order to monitor the health condition of a patient. In order to do so, the user needs to first authenticate with the accessed body sensors, and only after mutual authentication between that user and the body sensors the real-time data can be directly accessed securely by the user.

In this paper, we propose a new user authentication and key management scheme for this purpose. The proposed scheme allows mutual authentication between a user and personal server connected to WBAN via the healthcare server situated at the cloud, and once the mutual authentication is successful, both user and personal server are able to establish a secret session key for their future communication. In addition, key management process is provided for establishment of secret keys among the sensors and personal server for their secure communication. The formal security based on broadly-accepted Real-Or-Random (ROR) model and informal security give confidence that the proposed scheme can withstand several known attacks needed for WBAN security. A detailed comparative analysis among the proposed scheme and other schemes shows that the proposed scheme provides better security & functionality features, low computation and comparable communication costs as compared to recently proposed related schemes. Finally, the practical demonstration using the NS2 based simulation is shown for the proposed scheme and also for other schemes.