Re: [Qemu-devel] [PATCH v3 1/1] virtio-rng: hardware random number generator device

[Stefan Berger]

On 06/22/2012 07:06 AM, Amit Shah wrote:
> On (Wed) 20 Jun 2012 [16:29:22], Anthony Liguori wrote:
> > On 06/20/2012 01:59 AM, Amit Shah wrote:
> > > The Linux kernel already has a virtio-rng driver, this is the device
> > > implementation.
> > >
> > > When the guest asks for entropy from the virtio hwrng, it puts a buffer
> > > in the vq.  We then put entropy into that buffer, and push it back to
> > > the guest.
> > >
> > > The chardev connected to this device is fed the data to be sent to the
> > > guest.
> > >
> > > Invocation is simple:
> > >
> > >    $ qemu ... -device virtio-rng-pci,chardev=foo
> > >
> > > In the guest, we see
> > >
> > >    $ cat /sys/devices/virtual/misc/hw_random/rng_available
> > >    virtio
> > >
> > >    $ cat /sys/devices/virtual/misc/hw_random/rng_current
> > >    virtio
> > >
> > >    # cat /dev/hwrng
> > >
> > > Simply feeding /dev/urandom from the host to the chardev is sufficient:
> > >
> > >    $ qemu ... -chardev socket,path=/tmp/foo,server,nowait,id=foo \
> > >               -device virtio-rng,chardev=foo
> > >
> > >    $ nc -U /tmp/foo<   /dev/urandom
> > >
> > > A QMP event is sent for interested apps to monitor activity and send the
> > > appropriate number of bytes that get asked by the guest:
> > >
> > >    {"timestamp": {"seconds": 1337966878, "microseconds": 517009}, \
> > >     "event": "ENTROPY_NEEDED", "data": {"bytes": 64}}
> > Nack.
> >
> > Use a protocol.
> How does one write a program on Linux to get random numbers?
>
> He uses /dev/random, of course.
You could also use the nss freebl crypto library that provides a random 
number generator that for example seeds itself from /dev/urandom and 
then uses hash operations on the seed before it goes back to getting 
random numbers from /dev/urandom again. So, another idea:  call 
RNG_GenerateGlobalRandomBytes() to get the entropy.

   Stefan