[PLUG] rngd

wes plug at the-wes.com
Mon Sep 28 20:59:20 UTC 2009


>
> I don't know if I buy the claim that /dev/urandom will never run dry.
> It might not block if it does.  But there is only one entropy pool,
> which is shared by /dev/urandom and /dev/random.  /dev/random will
> block.  This means that using /dev/urandom to excess can cause
> blocking indirectly via /dev/random.
>

>From my friend that is knowledgeable on such matters:

Linux collects randomness from interrupt timings, etc.  It
keeps an estimate of how much entropy it has in its pool of randomness,
and when it doesn't feel that it has enough randomness it won't emit
data from /dev/random.  It waits for more interrupts, etc.  Or it pokes
the hardware RNG if you have one.

/dev/urandom acts like /dev/random until the entropy pool
is exhausted, then it reverts to a Mersenne twister or some classical
pseudo-random number generator, which will theoretically 'start over'
in a few thousand years.  Except that more entropy will be available
before then, which would make the period even longer.

-wes



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