Not obviously security related. But worth thinking about. By looking at the electromagnetic emanations of the human brain recorded by an EEG, researchers were able to identify what words or sentences the subject was hearing with 90% accuracy.
Fortunately the frequencies at issue (less than 20Hz) tend not to radiate very well given the “antenna”. You’d have to have an obscenely good receiver to pick up a 10Hz signal from neurons that are capable of putting out picowatts at best.
However, given a) earlier mentioned attacks that used on-chip mixing of external signals (e.g cell phones) to read out crypto keys and b) the apparent ability of the nervous system to act as a very crude mixer (discovered independently by WWII radar techs, who found they could hear radar pulses when standing in front of antennas, and Flanagan in the first-generation neurophone), I could see a potential route for a nasty attack.
(Documented already are attacks using radar to measure vibrations due to speech of e.g filing cabinets in rooms…)
Call it another reason to turn off your cell phone when you’re not using it.
“Electrical and magnetic brain waves of two subjects were recorded for the purpose of recognizing which one of 12 sentences or seven words auditorily presented was processed. The analysis consisted of averaging over trials to create prototypes and test samples, to each of which a Fourier transform was applied, followed by filtering and an inverse transformation to the time domain. The filters used were optimal predictive filters, selected for each subject. A still further improvement was obtained by taking differences between recordings of two electrodes to obtain bipolar pairs that then were used for the same analysis. Recognition rates, based on a least-squares criterion, varied, but the best were above 90%.”