4 ms·

This is solved by extending the constant time calculation principle to the CPU instruction level. Easier said than done, but probably only really necessary on H

• lloydatkinson 3y ago
  I’m fairly sure it is also solved by having a decoupling capacitor for the LED too…
  • yonatan8070 3y ago
    I'm guessing a capacitor would help negate this issue but it won't be possible to entirely eliminate the issue
    • rolandog 3y ago
      // TODO remove ductape; temp fix of https://ia.cr/2023/923 Edit: Joking aside, capacitors and black tape are actual countermeasures: Fig. 15. A circuit that leaks information via its power LED (a). Counter- measures using a capacitor (b), an additional OPAMP (c), and an existing OPAMP (d). And: Consumer Side Methods. The attack can also be prevented by placing black tape over a device’s power LED.
      • jacquesm 3y ago
        or just snipping it.
        • TedDoesntTalk 3y ago
          Or simply manufacturers not using LEDs to indicate activity.
          • sokoloff 3y ago
            This is not an intentional indication of activity, but rather just of power.
          • jacquesm 3y ago
            They don't. The LEDs fluctuations are a by-product of power rail fluctuation and this in turn can be detected to discover some elements of the computations involved. 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.
        • qingcharles 3y ago
          I'd at least solder another diode across the terminals if I did that. An LED is a diode at the end of the day and breaking the circuit might break the device.
          • jacquesm 3y ago
            Not if it is just a power LED. No circuit that I'm aware of would break if the power LED wasn't drawing power. You'd have to go out of your way to make it that way.
            • qingcharles 3y ago
              Thank you for the clarification. I've not soldered anything for a couple of decades so my knowledge is poor.
              • jacquesm 3y ago
                I did think that your approach is very thorough, 'change nothing' is a good principle.
    • properparity 3y ago
      A capacitor is a few extra cents on the bom which is a no go for profit maximizing companies.
      • mikelovenotwar 3y ago
        Dyson batteries are a good example: 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. https://github.com/tinfever/FU-Dyson-BMS https://github.com/tinfever/FU-Dyson-BMS
        • tjoff 3y ago
          That is not about saving cents tough.
    • H8crilA 3y ago
      No, it will completely eliminate it, if the capacitor is large enough. If you're super paranoid you can do the maths and compute how much does it cut off at such frequency ranges. It's likely to be a ridiculous value. And one does not have an infinite amplitude resolution in any measurement device. 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.)
      • dvwobuq 3y ago
        It's a harder EE problem than you think. For example the Samsung Galaxy S8 was attacked by analyzing video footage of the power LED of Logitech Z120 USB speakers. Those were most certainly on a different power supply and the two were connected by a long wire. 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…
  • husam212 3y ago
    Best solutions are the simplest ones, and this is the right one! It's an electrical coupling issue so I think it should be fixed electrically.