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SubjectRe: Seeding /dev/random not working
On 5/29/07, Pavel Machek <pavel@ucw.cz> wrote:
> Hi!
>
> > > I have two embedded boards (one ARM, one PowerPC), running two
> > > different versions of 2.6. They have no hard drives, keyboards or
> > > mice. They each have a NIC, but I understand these make no
> > > contribution to the entropy pool.
> > >
> > > if [ -f $random_seed ]; then
> > > cat $random_seed >/dev/urandom # should seed the pool
> > > fi
> > > dd if=/dev/urandom of=$random_seed count=1 2>/dev/null # save some
> > > data from urandom for next boot
> > >
> > > I have rebooted my boards many times, and after each boot I read the
> > > contents of $random_seed. Whilst it does not happen every time, the
> > > contents of $random_seed are /often the same/. To give you a feel:
> > > rebooted 11 times, got a total of 3 different outputs.
> >
> > Ok, so this is telling me a couple of things. First of all, if you're
> > only getting three outputs, it means that you don't have any
> > peripherals feeding entropy into the system from the boot sequence.
> > Without any hard drives, keyboards or mice, and a NIC whose device
> > driver hasn't been configured to feed entropy, you're definitely
> > hosed.
>
> Can we get at least time-of-boot from rtc clock to the pool? We really
> should not be getting identical outputs...

Ah yes that is one thing I forgot to mention - when you turn these
boards off, you really do turn them off - no battery means no clock.
They wake up every time in 1970.

I am planning on providing my own entropy to this system by feeding
/dev/random (which leads to the problem of it not working...).
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