Video: Power LED Attack [video]
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Most chips have a capacitor across the power pins. That would tend to "integrate" the signal.
Recent chips operate at sub-volt values but the LED is in the 2+ volt range so they likely are on different rails of the power supply or have buck/boost circuits.
Even trivial designs don't use full in-order processing so multiple ADDs might overlap a MULT. This ain't your father's first processor.
The traces on the board, if not carefully designed, likely have reflection and ringing effects, especially at via points making the signal rather noisy.
Processors are running in the nano/pico range but the led/camera likely can't reach that resolution.
At these speeds the resistor-to-ground circuit on the LED would have capactive and inductive effects that would be hard to model and need to be pre-measured.
If it is a near-field (touch card) key then there are a lot of other noise sources including other chips and circuit trace induced voltages.
Cryptographic coprocessors in Verilog/VHDL are available as open source or vendor IP. They won't leak.
I could construct a "bench level test" that MIGHT be able to detect the computation but I'd need a really good oscilloscope on a well engineered circuit board knowing the exact specs of the processor and knowledge of the algorithm used.
Oh, and as mentioned, nobody who knows anything about crypto already knows and protects against timing/power attacks.
You don't need a lot of precision to get enough hints of a key to be able to brute-force the rest.
> Oh, and as mentioned, nobody who knows anything about crypto already knows and protects against timing/power attacks.
Sounds like this could never be a problem then! But it is.
No need. The author of the original paper already did that for you. https://eprint.iacr.org/2023/923
"We demonstrate the application of video-based cryptanalysis by performing two side-channel cryptanalytic timing attacks and recover: (1) a 256- bit ECDSA key from a smart card by analyzing video footage of the power LED of a smart card reader via a hijacked Internet-connected security camera located 16 meters away from the smart card reader, and (2) a 378-bit SIKE key from a Samsung Galaxy S8 by analyzing video footage of the power LED of Logitech Z120 USB speakers that were connected to the same USB hub (that was used to charge the Galaxy S8) via an iPhone 13 Pro Max."
To all the EEs out there. PSRR and power supply cross talk is a thing...
Damn, i have to cover my hdd led on the computer case so the neighbours do not see the pornos that i watch. /s
On a side note, the Computerphile[0] YouTube channel has an endlessly fascinating variety of computer science, theory, and history videos. A related channel that is equally worth following is Numberphile[1].
// TODO remove ductape; temp fix of https://ia.cr/2023/923
Fig. 15. A circuit that leaks information via its power LED (a). Counter-
measures using a capacitor (b), an additional OPAMP (c), and an existingAnd:
Consumer Side Methods. The attack can also be prevented
by placing black tape over a device’s power LED.It's pretty subtle. This isn't like a flashing harddrive LED, it is an LED that to all intents and purposes is burning steadily. Until you look at it in more detail and you realize that it isn't quite as steady as it should be.
Dyson vacuum batteries are designed to fail
* Series battery cells in a battery pack inevitably become imbalanced. This is extremely common and why cell balancing was invented.
* Dyson uses a very nice ISL94208 battery management IC that includes cell balancing. It only requires 6 resistors that cost $0.00371 each, or 2.2 cents in total for six.
* Dyson did not install these resistors. (They even designed the V6 board, PCB 61462, to support them. They just left them out.)
* Rather than letting an unbalanced pack naturally result in lower usable capacity, when the cells go moderately (300mV) out of balance (by design, see step 3) Dyson programmed the battery to stop working...permanently. It will give you the 32 red blinks of death and will not charge or discharge again. It could not be fixed. Until now.
Also, you can just power the LED from a separate voltage regulator. Which is somewhat likely anyways, as the IC will probably want a lower voltage.
(Don't get me wrong, it's cool stuff, but there's also a very easy solution.)
There are circuit level solutions but the solution is not a $0.01 MLCC.
And once you solve the LED problem remember: The S8 was attacked by plugging in a peripheral to it’s 5V USB supply. Imagine if the peripheral was instead a high speed ADC that just measured 5V USB directly…
That's amazing. The paper is called "Video-Based Cryptanalysis: Extracting Cryptographic Keys from Video Footage of a Device’s Power LED" [0].
Edit: Also, worth viewing the video [1] on the author's post [2].
[0] https://eprint.iacr.org/2023/923
For example to extract sound from just a camera [1].
Additionally, while not directly related to the rolling shutter effect [2] uses a technique to increase the framerate of the Raspi Camera by 10x or more, but reducing image resolution.
Of course one could still use LEDs of which they have gained control for exfiltrating information, whether LEDs have a capacitor in parallel or not. If there is a capacitor and the LED can't be turned on and off effectively at say more than 5Hz, one could just use 1Hz pulses and, given enough time, transmit the information anyway.
I actually highly recommend the rest of computerphile YT channel - basically, it would seem that most of these guys actually teach computer stuff for a living.