Re: [PATCH] API for true Random Number Generators to add entropy (2.6.11)

David McCullough
2005-03-24T12:53:46Z

Jivin Jeff Garzik lays it down ...
> David McCullough wrote:
> >Jivin Jeff Garzik lays it down ...
> >
> >>On Thu, Mar 24, 2005 at 02:27:08PM +1000, David McCullough wrote:
> >>
> >>>Hi all,
> >>>
> >>>Here is a small patch for 2.6.11 that adds a routine:
> >>>
> >>> add_true_randomness(__u32 *buf, int nwords);
> >>>
> >>>so that true random number generator device drivers can add a entropy
> >>>to the system. Drivers that use this can be found in the latest release
> >>>of ocf-linux, an asynchronous crypto implementation for linux based on
> >>>the *BSD Cryptographic Framework.
> >>>
> >>> http://ocf-linux.sourceforge.net/
> >>>
> >>>Adding this can dramatically improve the performance of /dev/random on
> >>>small embedded systems which do not generate much entropy.
> >>
> >>We've already had hardware RNG support for a while now.
> >>
> >>No kernel patching needed.
> >
> >
> >Are you talking about /dev/hw_random ? If not then sorry I didn't see it
> >:-(
> >
> >On a lot of the small systems I work on, /dev/random is completely
> >unresponsive, and all the apps use /dev/random, not /dev/hw_random.
> >
> >Would you suggest making /dev/random point to /dev/hw_random then ?
>
> All the apps are supposed to use /dev/random, so that's correct.

Ok

> For Hardware RNGs, userspace rngd daemon obtains entropy, checks it
> (mainly checking for hardware failures), and then stuffs entropy into
> the kernel random device. http://sf.net/projects/gkernel/
>
> On the "to do" list is making rngd directly generate entropy use
> 'xstore' on VIA CPUs, rather than going kernel -> userland -> kernel.
>
> Also, there are other entropy daemons floating about. I think there is
> one that obtains noise from an audio device.

I had looked at hw_random, but it seemed a little platform specific (x86),
and it doesn't currently have a way for RNG providers to register themselves.
Admittedly I did not know how it's output was being used in practice.

The drivers I am working with do crypto/public key and RNG. Not all of
them can easily have the RNG support taken from the driver and plugged
into hw_random.c, since it is (in most cases) a single PCI chip with
it's own registers, initialisation and configuration, that, IMO
belongs in the driver for the particular chip.

Not that it isn't possible, but hw_random would start supporting a
much larger number of HW variants and I think it would get ugly.

It would be possible to add a "register" interface to hw_random so that
you can register other RNG's easily. This would seem reasonable.

I work on fairly resource constrained embedded devices a lot of the
time, so when I can avoid adding applications and reduce kernel size,
I do. Thus my motivation to add a simple API for adding entropy to
/dev/random.

Cheers,
Davidm

--
David McCullough, davidm@snapgear.com Ph:+61 7 34352815 http://www.SnapGear.com
Custom Embedded Solutions + Security Fx:+61 7 38913630 http://www.uCdot.org