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

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David McCullough wrote:
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.

Agreed.


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.

Agreed.


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.

Agreed.


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.

We already have the facilities to add entropy, as current use of hw_random+rngd shows.

	Jeff


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