3 ms·

Seems like a suitable countermeasure would be a localized source of randomized ENF (say a Zener diode in cascade overload in a low-freq oscillator), but the cou

Seems like a suitable countermeasure would be a localized source of randomized ENF (say a Zener diode in cascade overload in a low-freq oscillator), but the coupling would be sufficiently different as to highlight the deliberate attempt at ENF obfuscation. As the U.S. has essentially 5 power grids, they would need a more detailed database too. Still, fascinating stuff.

ars 16y ago
Random ENF would not work, since you could filter it out and look only at the 60 hz +- a few ppm signal. You need a random source that is very very close to 60 hz, but just slightly different. But that might not be enough - the original signal is still there, and it's much stronger than your noise. The frequency is still powering your power supply, and still causing a 60 hz variation in the voltage. You would need to isolate the power supply completely, or run it entirely through your noise adder. It would work best if you could add the noise to the DC output of the power supply.
- bonsaitree 16y ago
  "You need a random source close to 60hz" Correct. I specified a Zener diode source coupled to an oscillator. This would provide the signal noise filtering and phase-locked-loop (e.g. the necessary +- ppm signal power spectral distribution control). Given propagation losses, my ENF signal doesn't have to be nearly as powerful--merely more closely coupled to the device(s) being "shielded". Also, I think a so-called fast-switching DC-to-DC converter would provide the necessary isolation. Plenty are being manufactured now that isolate down to 40Hz, but outside of the audiophile realm, that quality of filtering isn't typically used for low-power applications.
bitwize 16y ago
Seems like a suitable countermeasure would be a localized source of randomized ENF (say a Zener diode in cascade overload in a low-freq oscillator), I think we have our new line of CSI dialogue right here. Followed closely by "I think this case just had -- [puts on sunglasses] a shocking new development."

ars 16y ago

Random ENF would not work, since you could filter it out and look only at the 60 hz +- a few ppm signal. You need a random source that is very very close to 60 hz, but just slightly different. But that might not be enough - the original signal is still there, and it's much stronger than your noise. The frequency is still powering your power supply, and still causing a 60 hz variation in the voltage. You would need to isolate the power supply completely, or run it entirely through your noise adder. It would work best if you could add the noise to the DC output of the power supply.

bonsaitree 16y ago
"You need a random source close to 60hz" Correct. I specified a Zener diode source coupled to an oscillator. This would provide the signal noise filtering and phase-locked-loop (e.g. the necessary +- ppm signal power spectral distribution control). Given propagation losses, my ENF signal doesn't have to be nearly as powerful--merely more closely coupled to the device(s) being "shielded". Also, I think a so-called fast-switching DC-to-DC converter would provide the necessary isolation. Plenty are being manufactured now that isolate down to 40Hz, but outside of the audiophile realm, that quality of filtering isn't typically used for low-power applications.

bitwize 16y ago

Seems like a suitable countermeasure would be a localized source of randomized ENF (say a Zener diode in cascade overload in a low-freq oscillator), I think we have our new line of CSI dialogue right here. Followed closely by "I think this case just had -- [puts on sunglasses] a shocking new development."