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Hardware random number generators do have some security issues though. Linux devs were opposed to solely relying on them, because they can be compromised by the

by iib 5y ago

Hardware random number generators do have some security issues though. Linux devs were opposed to solely relying on them, because they can be compromised by the vendor [1]. So they are at best used in algorithms that they can not compromise (still in [1], but lower, in the comments). [1] https://web.archive.org/web/20180611180213/https://plus.google.com/117091380454742934025/posts/SDcoemc9V3J https://web.archive.org/web/20180611180213/https://plus.goog...

adrian_b 5y ago
The security issues are not with hardware random number generators in general, but with those that are included inside complex devices like monolithic CPUs or TPMs, so that the owners of those devices cannot verify that the RNG's really do what they are claimed to do. Discrete hardware RNG's, like that of the Ferranti Mark I, are perfectly secure. For a modern device, the best way to implement a hardware RNG is to just include an ADC (analog-digital converter) input. Then you may connect externally on the PCB some noisy analog amplifier, e.g. one which has a noisy resistor or diode at its input. Digitizing the noise with the ADC will provide the random numbers and the ADC input can be isolated and tested separately at any time, so the user can verify that there is no hidden functionality. Most microcontrollers have ADC inputs, so it is easy to add a secure hardware RNG for them. The same could be done for a personal computer by making a noisy amplifier that can be plugged in the microphone input, or by making a USB device with a microcontroller.
- iib 5y ago
  I remembered something, and I want to say as an aside, for anybody reading that at one point has to design a toy RNG from an ADC, as I had to some years ago, you should not take the last bits as they are--as was my first thought--, you should pass them through something like the von Neumann corrector [1]. [1] https://everything2.com/title/von+Neumann+corrector https://everything2.com/title/von+Neumann+corrector
ncmncm 5y ago
Indeed, AMD has more than once shipped CPUs in which the random-number instruction would always yield the same value, that had to be monkey-patched to yield apparently random numbers. A valuable hint.

by iib 5y ago

adrian_b 5y ago

The security issues are not with hardware random number generators in general, but with those that are included inside complex devices like monolithic CPUs or TPMs, so that the owners of those devices cannot verify that the RNG's really do what they are claimed to do. Discrete hardware RNG's, like that of the Ferranti Mark I, are perfectly secure. For a modern device, the best way to implement a hardware RNG is to just include an ADC (analog-digital converter) input. Then you may connect externally on the PCB some noisy analog amplifier, e.g. one which has a noisy resistor or diode at its input. Digitizing the noise with the ADC will provide the random numbers and the ADC input can be isolated and tested separately at any time, so the user can verify that there is no hidden functionality. Most microcontrollers have ADC inputs, so it is easy to add a secure hardware RNG for them. The same could be done for a personal computer by making a noisy amplifier that can be plugged in the microphone input, or by making a USB device with a microcontroller.

iib 5y ago
I remembered something, and I want to say as an aside, for anybody reading that at one point has to design a toy RNG from an ADC, as I had to some years ago, you should not take the last bits as they are--as was my first thought--, you should pass them through something like the von Neumann corrector [1]. [1] https://everything2.com/title/von+Neumann+corrector https://everything2.com/title/von+Neumann+corrector

ncmncm 5y ago

Indeed, AMD has more than once shipped CPUs in which the random-number instruction would always yield the same value, that had to be monkey-patched to yield apparently random numbers. A valuable hint.