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

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Date:   Fri, 15 May 2020 11:06:46 +0200
From:   Lukasz Stelmach <l.stelmach@...sung.com>
To:     Stephan Mueller <smueller@...onox.de>
Cc:     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>,
        Krzysztof Kozlowski <krzk@...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-samsung-soc@...r.kernel.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH 1/2] hwrng: iproc-rng200 - Set the quality value

It was <2020-05-15 pią 10:32>, when Stephan Mueller wrote:
> Am Freitag, 15. Mai 2020, 00:18:41 CEST schrieb Lukasz Stelmach:
>
>> I am running tests using SP800-90B tools and the first issue I can see
>> is the warning that samples contain less than 1e6 bytes of data. I know
>> little about maths behind random number generators, but I have noticed
>> that the bigger chunk of data from an RNG I feed into either ent or ea_iid
>> the higher entropy they report. That is why I divided the data into 1024
>> bit chunks in the first place. To get worse results. With ea_iid they
>> get even worse (128 bytes of random data)
>
> I read that you seem to just take the output data from the RNG. If this is 
> correct, I think we can stop right here. The output of an RNG is usually after 
> post-processing commonly provided by a cryptographic function.
>
> Thus, when processing the output of the RNG all what we measure here is the 
> quality of the cryptographic post-processing and not the entropy that may be 
> present in the data.
>
> What we need is to access the noise source and analyze this with the given 
> tool set. And yes, the analysis may require adjusting the data to a format 
> that can be consumed and analyzed by the statistical tests.

I took data from /dev/hwrng which is directly connected to the
hardware. See rng_dev_read() in drivers/char/hw_random/core.c.

-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

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