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Comment by silent90 | Hacker News Reader

Capturing the CPU instructions by a side-channel is indeed possible but the "real-life, working" use of the method described here is questionable for me. CPU in modern phones runs above 1GHz. USB sound card they're using provides max 192kHz which allows max 96kHz signal. 4 orders of magnitude less. There's also a lot of noise from different circuitry (GPU, display, wireless comm.) and laptop's noise as well which will obfuscate the signal.

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It still strikes me as plausible. Sub-harmonics are a thing; it is entirely possible to leak data about what the CPU is or isn't doing down into the ultrasonic or audible bands.

As an example, one of my computers leaks a ton of noise into the onboard audio that quickly becomes audible with a moderate amount of gain. So much so, that I've learned to recognize changes in the noise pattern from various activities (shuffling windows around the gui, launching a program, compiling a program, etc).

How practical a real-life, working use of the method described here will depend in no small part how much noise the device being attacked casts off. There's some pretty bad devices out there.

You misunderstand the attack. You don't need to sample at 1GHz. Each 0 and each 1 in private key material leads to calculations taking thousands of tens of thousands of clock cycles. So you only need to sample EM radiations at around 100 kHz or 1 MHz.

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