  With the rapid development of health equipments, increasingly more patients
have installed the implantable medical devices (IMD) in their bodies for
diagnostic, monitoring, and therapeutic purposes. IMDs are extremely limited in
computation power and battery capacity. Meanwhile, IMDs have to communicate
with an external programmer device (i.e., IMD programmer) through the wireless
channel, which put them under the risk of unauthorized access and malicious
wireless attacks. In this paper, we propose a proxy-based fine-grained access
control scheme for IMDs, which can prolong the IMD's lifetime by delegating the
access control computations to the proxy device (e.g., smartphone). In our
scheme, the proxy communicates with the IMD programmer through an audio cable,
which is resistant to a number of wireless attacks. Additionally, we use the
ciphertext-policy attribute-based encryption (CP-ABE) to enforce fine-grained
access control. The proposed scheme is implemented on real emulator devices and
evaluated through experimental tests. The experiments show that the proposed
scheme is lightweight and effective.
