Lightweight Information Security Methods for Indoor Wireless Body Area Networks: from Channel Modeling to Secret Key Extraction

A group of wirelessly communicating sensors that are placed inside, on or around a human body constitute a Wireless Body Area Network (WBAN). Continuous monitoring of vital signs through WBANs have a potential to revolutionize current health care services by reducing the cost, improving accessibility, and facilitating medical diagnosis. However, sensitive nature of personal health data requires WBANs to integrate appropriate security methods and practices. As limited hardware resources make conventional security measures inadequate in a WBAN context, this work is focused on alternative techniques based on Wireless Physical Layer Security (WPLS). More specifically, we introduce a symbiosis of WPLS and Compressed Sensing to achieve security at the time of sampling. We successfully show how the proposed framework can be applied to electrocardiography data saving significant computational and memory resources. In the scenario when a WBAN Access Point can make use of diversity methods in the form of Switch-and-Stay Combining, we demonstrate that output Signal-to-Noise Ratio (SNR) and WPLS key extraction rate are optimized at different switching thresholds. Thus, the highest key rate may result in significant loss of output SNR. In addition, we also show that the past WBAN off-body channel models are insufficient when the user exhibits dynamic behavior. We propose a novel Rician based off-body channel model that can naturally reflect body motion by randomizing Rician factor K and considering small and large scale fading to be related. Another part of our investigation provides implications of user\u27s dynamic behavior on shared secret generation. In particular, we reveal that body shadowing causes negative correlation of the channel exposing legitimate participants to a security threat. This threat is analyzed from a qualitative and quantitative perspective of a practical secret key extraction algorithm