Securing Wireless Neurostimulators

Implantable medical devices (IMDs) typically rely on proprietary protocols to wirelessly communicate with external device programmers. In this paper, we fully reverse engineer the proprietary protocol between a device programmer and a widely used commercial neurostimulator from one of the leading IMD manufacturers. For the reverse engineering, we follow a black-box approach and use inexpensive hardware equipment. We document the message format and the protocol state-machine, and show that the transmissions sent over the air are neither encrypted nor authenticated. Furthermore, we conduct several software radio-based attacks that could compromise the safety and privacy of patients, and investigate the feasibility of performing these attacks in real scenarios. Motivated by our findings, we propose a security architecture that allows for secure data exchange between the device programmer and the neurostimulator. It relies on using a patient>>s physiological signal for generating a symmetric key in the neurostimulator, and transporting this key from the neurostimulator to the device programmer through a secret out-of-band (OOB) channel. Our solution allows the device programmer and the neurostimulator to agree on a symmetric session key without these devices needing to share any prior secrets; offers an effective and practical balance between security and permissive access in emergencies; requires only minor hardware changes in the devices; adds minimal computation and communication overhead; and provides forward and backward security. Finally, we implement a proof-of-concept of our solution.