Ghost Talk

This week I read the Ghost Talk Paper (https://spqr.eecs.umich.edu/papers/fookune-emi-oakland13.pdf) and learned about Amplitude Modulation, the concept behind transmitting AM radio waves. What's interesting is that in terms of long-distance communication, AM was preceded by Morse code; AM radio meant that audio, with varied tones, could finally be transmitted.
As the first broadcasting method, AM waves are the simplest. The way that Amplitude Modulation works is by looking at two frequencies: the frequency a receiver can accept (the carrier wave) and the frequency the receiver should output to produce the wanted sound. For Ghost Talk, the carrier frequency is determined by the victim device's circuitry. The carrier frequency is the frequency of the attacker's wave sent to the device. To transmit the audio data, though, the amplitude of the wave is varied. If the carrier wave has the right frequency, and is modulated correctly, then the peaks of the carrier wave will follow the curve of the desired output wave. The peaks are sampled, which is how the wave is demodulated, and the output is not at the frequency of the carrier wave, but the wanted sound. And so, with a little bit of cleverness and some modulated RF waves, a voice can even be transmitted to a device -- ghost talk!

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