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RSA Keys Can Be Harvested With Microphones (theregister.co.uk)
Researchers have now demonstrated that even with modern laptop, desktop, and server computers, an inexpensive attack can harvest 4,096-bit encryption keys using a parabolic microphone within 33 feet -- or even from 12 inches away, using a cellphone microphone.
An anonymous reader quotes this article from The Register:
In both cases it took an hour of listening to get the 4,096-bit RSA key... As a computer's processor churns through the encryption calculations, the machine emits a high-frequency "coil whine" from the changing electrical current flowing through its components... The team recommends encryption software writers build in "blinding" routines that insert dummy calculations into cryptographic operations. After discussions with the team, GNU Privacy Guard now does this.
Play an MP3 at the same time so they get a audio download then send them a DCMA takedown notice :)
33 feet which is 10 meters, easy to spot, hardly "low key" (ehm) eves dropping. I would imagine the eves dropper would get a bloody nose before getting to the door...
I'll remember you said that when you discover that "innocent" cell phone charger sitting in the corner of your office is actually a microphone with a 64GB microSD card and SIM card inside, dumping a day's worth of key listening across a covert channel, to include your voice conversations.
Or perhaps the device listening will be your cell phone itself. After all, those never get hacked.
Perhaps you should start considering the fact that it's hardly a human sitting in the room listening to high-frequency whine, nor does it need to be. Good luck with your bloody nose defense.