Electromagnetic Information Leakage of Audio Signals Induced by RF Illumination

Due to the wide use of voice communication across diverse IT equipment, the reception of audio compromising emanations (CE), introduces a vulnerability in terms of electromagnetic emission security (EMSEC). This paper demonstrates a method for the feasibility of electromagnetic (EM) leakage reception of audio signals by measurement of electrical changes in the information transmission process by RF illumination (irradiating EM waves) that cause information leakage. The effectiveness of the approach is evaluated through measurements conducted in an anechoic chamber. The method demonstrates that transmitted audio information, which cannot be detected by conventional TEMPEST test methods, can be obtained. In particular, when evaluating a voice communication device with headphones, we demonstrate that the output impedance of the integrated circuit (IC) undergoes changes corresponding to the output of the audio processing circuit, leading to amplitude modulation of the reflected waves. As a result, electromagnetic information leakage of audio signals induced by RF illumination could pose threats to a broader range of IT devices that use audio signals, necessitating the implementation of countermeasures.