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

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Message-ID: <4493123.C11H8YMYNy@tauon.chronox.de>
Date:   Thu, 14 May 2020 22:20:26 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Łukasz 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 Donnerstag, 14. Mai 2020, 21:07:33 CEST schrieb Łukasz Stelmach:

Hi Łukasz,

> The value has been estimaded by obtainig 1024 chunks of data 128 bytes
> (1024 bits) each from the generator and finding chunk with minimal
> entropy using the ent(1) tool. The value was 6.327820 bits of entropy
> in each 8 bits of data.

I am not sure we should use the ent tool to define the entropy level. Ent 
seems to use a very coarse entropy estimation.

I would feel more comfortable when using other measures like SP800-90B which 
even provides a tool for the analysis.

I understand that entropy estimates, well, are estimates. But the ent data is 
commonly not very conservative.

[1] https://github.com/usnistgov/SP800-90B_EntropyAssessment

Ciao
Stephan