Re: [PATCH 1/2] hwrng: iproc-rng200 - Set the quality value

From: Lukasz Stelmach <l.stelmach@samsung.com>
To: Stephan Mueller <smueller@chronox.de>
Cc: Matt Mackall <mpm@selenic.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Ray Jui <rjui@broadcom.com>,
	Scott Branden <sbranden@broadcom.com>,
	bcm-kernel-feedback-list@broadcom.com,
	Kukjin Kim <kgene@kernel.org>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Markus Elfring <elfring@users.sourceforge.net>,
	Matthias Brugger <mbrugger@suse.com>,
	Stefan Wahren <wahrenst@gmx.net>,
	linux-crypto@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH 1/2] hwrng: iproc-rng200 - Set the quality value
Date: Fri, 15 May 2020 11:06:46 +0200	[thread overview]
Message-ID: <dleftjblmp8t3t.fsf%l.stelmach@samsung.com> (raw)
In-Reply-To: <2080864.23lDWg4Bvs@tauon.chronox.de> (Stephan Mueller's message of "Fri, 15 May 2020 10:32:22 +0200")

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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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