linux-kernel - Re: [PATCH v2 1/2] hwrng: iproc-rng200

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Date:   Wed, 20 May 2020 14:00:01 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Stephan Mueller <smueller@...onox.de>
Cc:     Lukasz Stelmach <l.stelmach@...sung.com>,
        Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Kukjin Kim <kgene@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Markus Elfring <elfring@...rs.sourceforge.net>,
        Matthias Brugger <mbrugger@...e.com>,
        Stefan Wahren <wahrenst@....net>, linux-crypto@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v2 1/2] hwrng: iproc-rng200 - Set the quality value

On Wed, 20 May 2020 at 13:53, Stephan Mueller <smueller@...onox.de> wrote:
> > > That said, the illustrated example is typical for hardware RNGs. Yet
> > > it is never guaranteed to work that way. Thus, if you can point to
> > > architecture documentation of your specific hardware RNGs showing that
> > > the data read from the hardware is pure unconditioned noise data, then
> > > I have no objections to the patch.
> >
> > I can tell for sure that this is the case for exynos-trng[1].
>
> So you are saying that the output for the exynos-trng is straight from a ring
> oscillator without any post-processing of any kind?

Hi,

I think we will never be able to state this because the manual is
quite limited in sharing internals. What the driver does and probably
Lukasz wanted to say is that there is "post processing" block and
feature which can be disabled. The manual is saying the TRNG block
generates random data from thermal noise but not how much in a direct
way. There could be some simple post-processing or not (except the one
able to on/off). Also manual says this post processing block is there
to remove statistical weakness from the TRNG block. To me it does not
prove enough that raw data is really raw...

Best regards,
Krzysztof