Implementation of Speaker-to-Speaker Side-Channel Attack in an Air-Gapped Environment

This paper investigates the feasibility of speaker-to-speaker near ultrasonic data transmission without microphones, the motivation and simple performance results of which had been disclosed in some past works. Using Binary Frequency Shift Keying (BFSK) modulation, binary data are encoded into near ultrasonic frequency pairs, and the induced voltage from the receiving speaker is analyzed with the Goertzel algorithm. Besides the implementation, we also conduct additional experiments that have not been reported yet in the previous works. Concretely, we vary transmission distance (15–700 cm) and carrier frequency combination to evaluate propagation and detection stability. Results show reliable performance at short range but degradation at longer distances or higher frequencies, highlighting practical limits and factors affecting system robustness.