linux-kernel - Re: [PATCH] crypto: sun4i-ss: support the Security System PRNG

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Date:   Thu, 17 Nov 2016 09:18:46 +0100
From:   Stephan Mueller <smueller@...onox.de>
To:     Corentin Labbe <clabbe.montjoie@...il.com>
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        maxime.ripard@...e-electrons.com, wens@...e.org,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] crypto: sun4i-ss: support the Security System PRNG

Am Donnerstag, 17. November 2016, 09:07:48 CET schrieb Corentin Labbe:

Hi Corentin,
> 
> Seed again, or just do not seed (and so return -EAGAIN for read() function)
> until ready_callback ?

This is your choice. But for the start sequence, you should not simply rely on 
get_random_bytes.

For the DRBG in crypto/drbg.c we seed with get_random_bytes and the Jitter RNG 
in case the input_pool is not fully seeded. The reseed trigger is reduced to 
50 DRBG requests, i.e. after 50 requests, the DRBG again reseeds from 
get_random_bytes / Jitter RNG. This is continued until the input_pool has been 
sufficiently seeded (i.e. the registered callback is triggered). At that 
point, another get_random_bytes call is made, the Jitter RNG is deactivated 
and the reseed threshold is set to the common value.

Ciao
Stephan