Air-Gap Decodermake a silent machine talk · listen across the gap
No wire, no network, no pairing. One machine plays sound; another, with only a microphone, reads the data back out of the air. Transmit from the laptop, listen on the phone — the gap between them was never really there.
idle — grant mic, then play from the other device
decoded text appears here
install ▸ Share → Add to Home Screen to run this full-screen like an app. Mic needs an https page. Keep the phone within a few feet, point it at the laptop speaker, and mute other audio.
turn the volume up. press broadcast — the bytes go out as tones.
how ▸ the text is framed (length · payload · checksum), split into 4-bit symbols, and each symbol is sent as one of 16 audible tones (900–3600 Hz) with a sync marker at the ends. ~6 bytes/sec.
what's real. this is a working acoustic modem — 16-tone MFSK with a Goertzel demodulator, the same DSP family used in real air-gap research (GSMem, Fansmitter, MOSQUITO). it genuinely moves bytes from a speaker to a microphone with nothing else between them.
honest frame. tones here are loud and audible so the channel is reliable in a noisy room. real exfiltration malware hides in near-ultrasonic bands or fan/coil whine you can't hear, trading speed and range for silence. the physics is identical; only the volume gives it away.
PAPER IV · AIR-GAP EXFILTRATION — make a silent machine talk◂ prev · III · ACOUSTIC SIDE CHANNELS