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

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

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