Question - seeding the hw pseudo random number generator

[Harald Freudenberger]

On 03/20/2017 02:39 PM, Stephan Müller wrote:
> Am Montag, 20. März 2017, 14:28:58 CET schrieb Herbert Xu:
>
> Hi Herbert,
>
>> On Mon, Mar 20, 2017 at 12:19:32PM +0530, PrasannaKumar Muralidharan wrote:
>>> AF_ALG interface for rng does have seeding support. I think hw_random
>>> does not provide seeding support intentionally as I understand that
>>> True RNG need not require seeding (please correct me if I am wrong).
>> Yes.  We should be converting PRNGs in hwrng over to algif_rng.
> IMHO this not only applies to the PRNGs in drivers/crypto (which should simply 
> register with crypto_register_rngs) but also to ~/hacking/sources/linux/arch/
> s390/crypto/prng.c which exports a /dev/prandom file.
>
> For the seeding, it may make sense to follow the example given with crypto/
> drbg.c using the add_random_ready_callback function.
>
> Ciao
> Stephan
>

I'll have a look on it. Currently the s390/crypto/prng seeds itself with
an algorithm based on the jitter of the very fine granular hardware
clock of a s390 machine. There were some thoughts and measurements
by an mathematician which let to this algorithm. However, long-term
the s390 platform will provide some kind of true hardware random number
generator and the idea is to use this for seeding the prng.

regards
Harald Freudenberger