Re: Continuing /dev/random problems with 2.4

Peter Monta
2002-02-01T20:56:24Z

> > > Anything that is meant to be a server really pretty much needs an
> > > enthropy generator these days.
> >
> > Many motherboards have on-board sound. Why not turn the mic
> > gain all the way up and use the noise---surely there will be
> > a few bits' worth?
>
> Even if you think you have a good true source of random noise, you need
> to run good fitness tests on the data to ensure it's truly random.

Well, yes and no. What you really need is a conservative estimate
of how much entropy is contained in n bits of input; a cryptographic
hash, such as MD5, will distill out the "truly random". The comments
in drivers/char/random.c claim that the input hash is cryptographically
noncritical, but to be pedantic, maybe MD5 the audio noise before
writing to /dev/random.

Assuming the sound-card output looks like reasonable noise of
a few LSBs amplitude, a conservative estimate might be 0.1 bit
of entropy per sample. This is 9600 bits of entropy per second
from a stereo card, more than enough.

A small daemon would wake up every so often, check if /dev/random
needs topped up, read some audio samples, MD5(), write(),
ioctl(# of claimed entropy bits). I haven't seen the i810 RNG tools,
but I guess they do something similar.