Experimental Phantom-Based Security Analysis for Next-Generation Leadless Cardiac Pacemakers

Abstract

With technological advancement, implanted medical devices can treat a wide range of chronic diseases such as cardiac arrhythmia, deafness, diabetes, etc. Cardiac pacemakers are used to maintain normal heart rhythms. The next generation of these pacemakers is expected to be completely wireless, providing new security threats. Thus, it is critical to secure pacemaker transmissions between legitimate nodes from a third party or an eavesdropper. This work estimates the eavesdropping risk and explores the potential of securing transmissions between leadless capsules inside the heart and the subcutaneous implant under the skin against external eavesdroppers by using physical-layer security methods. In this work, we perform phantom experiments to replicate the dielectric properties of the human heart, blood, and fat for channel modeling between in-body-to-in-body devices and from in-body-to-off-body scenario. These scenarios reflect the channel between legitimate nodes and that between a legitimate node and an eavesdropper. In our case, a legitimate node is a leadless cardiac pacemaker implanted in the right ventricle of a human heart transmitting to a legitimate receiver, which is a subcutaneous implant beneath the collar bone under the skin. In addition, a third party outside the body is trying to eavesdrop the communication. The measurements are performed for ultrawide band (UWB) and industrial, scientific, and medical (ISM) frequency bands. By using these channel models, we analyzed the risk of using the concept of outage probability and determine the eavesdropping range in the case of using UWB and ISM frequency bands. Furthermore, the probability of positive secrecy capacity is also determined, along with outage probability of a secrecy rate, which are the fundamental parameters in depicting the physical-layer security methods. Here, we show that path loss follows a log-normal distribution. In addition, for the ISM frequency band, the probability of successful eavesdropping for a data rate of 600 kbps (Electromyogram (EMG)) is about 97.68% at an eavesdropper distance of 1.3 m and approaches 28.13% at an eavesdropper distance of 4.2 m, whereas for UWB frequency band the eavesdropping risk approaches 0.2847% at an eavesdropper distance of 0.22 m. Furthermore, the probability of positive secrecy capacity is about 44.88% at eavesdropper distance of 0.12 m and approaches approximately 97% at an eavesdropper distance of 0.4 m for ISM frequency band, whereas for UWB, the same statistics are 96.84% at 0.12 m and 100% at 0.4 m. Moreover, the outage probability of secrecy capacity is also determined by using a fixed secrecy rate.

Evaluating Secrecy Capacity for In-Body Wireless Channels

“…After simplification (as provided in detail in Appendix A and adapted from [ 29 ]), can be represented in the form of Q-function for log-normal channels [ 19 , 29 ] as whereas the outage probability ( ) can be expressed as where and represents the mean SNR of respective links (legitimate and Eve Link, as expressed in Equation ( 5 )). In addition, and , where a and b is the standard deviation of the Gaussian distribution which corresponds to a log-normal distribution (if is the standard deviation of , then ).…”

“…Information theoretic measures or security via PLS depend on wireless channel characteristics for securing the communication between legitimate nodes. These characteristics may involve received signal strength, angle of arrival, phase or the inherent noise in the wireless channels that degrades the signal-to-noise ratio [ 17 , 18 , 19 , 20 ]. Therefore, channel modeling is the key aspect to evaluating the possibilities of using the PLS methods for securing the information content between legitimate nodes.…”

Evaluation of Secrecy Capacity for Next-Generation Leadless Cardiac Pacemakers

“…Furthermore, for experiments, a small battery powered antenna with transmitter is utilized instead of using conventional coaxial cables and vector network analyzer (VNA) for generation of sounding signal. This is because, in case of small dimensions of antenna, the adjoined coaxial cables also radiate which is being ignored by authors in the literature [37]. Another aspect of this work is that it evaluates the in-body to off-body link (Eve link) directly from deep implant (inside the right ventricle) and computes the channel attenuation of entire space around the body.…”

RSS-Based Secret Key Generation in Wireless In-body Networks

“…The setup used for the channel measurements is shown in Fig. 3 [13], [14]. Our experimentation setup includes, phantom containers to hold the liquid phantoms, Anechoic chamber to avoid surrounding contributions, Vector Network Analyzer (VNA) to generate sounding signal in UWB frequency band, a magnetic tracker to track the distance between transmitter and receiver antenna at different spatial measurement positions, and the positioner, to move the antenna to different positions.…”