4 ms·
A properly designed crypto subsystem that cared about security would detect the voltage drop and either refuse to operate or would have its own local power regu
by bradfa 5y ago
A properly designed crypto subsystem that cared about security would detect the voltage drop and either refuse to operate or would have its own local power regulation circuits such that a system level voltage reduction wouldn't impact it.
I presume the CPU here was VERY cost conscious and so trade-offs were made.
I have no background in gaming but have worked with flawed "security" solutions. Often the business does not care that the engineers explain how flawed some security thing is before release, if there's more money to be made by not fixing it then it won't get fixed. Often doing all of the right things is MUCH too expensive, either in dollars, size, or power.
- baybal2 5y ago> would have its own local power regulation circuits such that a system level voltage reduction wouldn't impact it. How do you know if external voltage is low if you check it against... a voltage derived from it?
- thebruce87m 5y agoIsn’t that what bandgap voltages are for? https://en.m.wikipedia.org/wiki/Bandgap_voltage_reference https://en.m.wikipedia.org/wiki/Bandgap_voltage_reference
- joshvm 5y agoAlmost all micros have brown out detection so you can tell if the device undervolts, and typically you can force the device to auto shut down/reset if that condition trips using an onboard programmable fuse. I don't know how much of an attack surface your typical BOD circuit is though. https://microchipdeveloper.com/8avr:bod https://microchipdeveloper.com/8avr:bod
- pjc50 5y agoThis is called brownout detection, and it's a common feature even on low-end microcontrollers. As the other commenter says, it's derivable from a bandgap reference. In re "properly secured system": it's a cost-sensitive games console for children, while there's a big incentive against piracy ultimately there's a limit to how much you can defend. And this is the second line of defense, the bootloader having been breached earlier.
- baybal2 5y agoBandgap reference can't tell anything about body bias voltage, unless it itself built on top of insulator
- pjc50 5y agoCould you elaborate? Isn't the substrate usually tied to ground so we can ignore it in modelling? Or are you saying that it could be floated separately to ground in order to attack the chip?
- baybal2 5y agoYes, and normally it is. I think on every moderately modern CMOS IC, body bias is controlled. > What is body bias? > Body bias is used to dynamically adjust the threshold voltage (Vt) of a CMOS transistor. While CMOS transistors are usually thought of as having three terminal devices, with terminals for the source, gate, and drain, it’s increasingly common to have a fourth terminal connected to the body (substrate). Because the voltage difference between the source voltage (Vs) and body voltage (Vb) affects the Vt, the body can be thought of as a second gate that helps determine how a transistor turns on and off. https://semiengineering.com/body-bias-what-it-is-and-why-you-should-care/ https://semiengineering.com/body-bias-what-it-is-and-why-you...
- floatboth 5y agoThe whole "games console" context also comes waaaay after the chip was made — it's not a custom for-Nintendo chip! tegra210 was previously used in the Nvidia Shield 2015, then the Google Pixel C (also from 2015) and the Jetson TX1 dev board.
- Mindwipe 5y ago> I presume the CPU here was VERY cost conscious and so trade-offs were made. It was also more intended as a media chipset and they managed to flog it to Nintendo, and was an early effort by the team involved.