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Re: FYI/RFC: early-rng-init-tools




On Sun, 2019-03-03 at 18:59 +0100, Kurt Roeckx wrote:
[...]
> Most people will actually have at least 2 hardware RNGs: One in
> the CPU and one in the TPM. We can make the kernel trust those as
> entropy source without using something in userspace to feed it.
> I'm not sure in the kernel has the option to use the TPM directly
> as source, but it makes it available as /dev/hwrng.
[...]

If there is at least one hardware RNG with a non-zero "quality" then
the kernel will start a thread (khwrngd) that reads from the hardware
RNG and adds those bits to the core RNG, crediting each bit with
quality/1024 bits of entropy.

Most hardware RNG drivers don't specify quality and it defaults to
zero, but this can be overridden by setting the module parameter
rng-core.default_quality.  Perhaps we should set a low but non-zero
default value?

There are potential problems with doing this: some of these hardware
RNGs are probably quite weak, so we have to be very conservative, but
then the less entropy we credit the more CPU time will be spent in the
hardware RNG reader thread.

Ben.

-- 
Ben Hutchings
No political challenge can be met by shopping. - George Monbiot


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