Secure On-skin Biometric Signal Transmission using Galvanic Coupling

Increasing threats of malicious eavesdropping raise concerns in confidential data reporting by body-worn sensors. We propose a secure, body-guided transmission channel through the use of galvanic coupling (GC). This method involves injecting weak electrical current into the body, which propagates primarily through the skin. The proposed approach makes the transmission of biometric data impervious to sniffing attacks, enabling the body to serve as a waveguide. This paper makes the following contributions: (i) An analytical channel model using a tissue equivalent circuit of the human arm-wrist-palm GC-propagation path is formulated and empirically verified. (ii) A simulation study is conducted for a comparative analysis of various modulation schemes, leveraging the validated GC-channel behavior. (iii) A GC-transceiver with optimized communication parameters (modulation, frequency, power) is designed and implemented using a dielectrically equivalent tissue phantom, and (iv) through experimental trials, resilience to over-the-air susceptibility (i.e., likelihood of adversarial eavesdropping) of the GC-signal and similar body communication techniques are demonstrated. Performance results of the GC-transceiver prototype yield a bit error rate of $10^{-6}$ with a transmit power of -2dBm, in addition to over 7x reduction of signal radiation outside the body compared to capacitive coupling.