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

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Message-ID: <3640422.T8yoyu11Ch@tauon.chronox.de>
Date:   Fri, 15 May 2020 11:10:45 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Lukasz Stelmach <l.stelmach@...sung.com>
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

Am Freitag, 15. Mai 2020, 11:01:48 CEST schrieb Lukasz Stelmach:

Hi Lukasz,


As I mentioned, all that is or seems to be analyzed here is the quality of the 
cryptographic post-processing. Thus none of the data can be used for getting 
an idea of the entropy content.

That said, the ent value indeed looks too low which seems to be an issue in 
the tool itself.

Note, for an entropy assessment commonly at least 1 million traces from the 
raw noise source are needed.

See for examples on how such entropy assessments are conducted in the LRNG 
documentation [1] or the Linux /dev/random implementation in [2]

[1] appendix C of https://www.chronox.de/lrng/doc/lrng.pdf

[2] chapter 6 of https://www.bsi.bund.de/SharedDocs/Downloads/EN/BSI/
Publications/Studies/LinuxRNG/LinuxRNG_EN.pdf

Ciao
Stephan