Strobedual-channel · light and sound carry the same byte
One byte, two channels. The audio path encodes each bit as an FSK tone. The optical path encodes each bit as a screen strobe — slow flash for 0, fast flash for 1. Both transmit simultaneously. Both are decoded independently. If either channel is blocked, the other still recovers the message. Two physics, one secret.
⚠ photosensitivity warning — the transmit button strobes the screen at 6–14 Hz. if you are sensitive to flashing light, use the audio-only decode (the optical channel can be verified in the results without watching the strobe).
set the byte
the beacon
idle
acoustic channel
—
optical channel
—
set 8 bits — transmit sends light and sound together; decode reads them apart
the acoustic channel uses 600 Hz / 950 Hz FSK (as in Paper V's baseband). the optical channel uses 6 Hz / 14 Hz screen strobe. a real optical covert channel would use an LED or a screen pixel — Guri's lab demonstrated air-gap exfiltration via HDD LEDs, keyboard LEDs, and screen brightness modulation.
what's authentic. the audio FSK modem uses the same Goertzel spectral analysis as the cipher papers — verified. the optical channel genuinely records the strobe pattern (timestamps of each flash) and classifies the flash frequency per segment to recover each bit — not a label lookup, a real frequency measurement.
honest frame. the "photodetector" is reading back a pattern this page generated — in a real optical side channel, a camera or photodiode across the room would capture the light. the screen strobe is visible to the naked eye (6–14 Hz is well within human flicker perception), so this is not covert in the way a sub-pixel modulation or IR LED would be. the dual-channel principle is real; the covertness is not.