linux-kernel - Re: [PATCH v3 3/4] crypto: exynos - Reseed PRNG after generating 2^16 random bytes

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Date:   Wed, 13 Dec 2017 09:12:35 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Łukasz Stelmach <l.stelmach@...sung.com>
Cc:     robh+dt@...nel.org, Stephan Mueller <smueller@...onox.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Kukjin Kim <kgene@...nel.org>, linux-crypto@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v3 3/4] crypto: exynos - Reseed PRNG after generating 2^16
 random bytes

On Tue, Dec 12, 2017 at 5:36 PM, Łukasz Stelmach <l.stelmach@...sung.com> wrote:
> Reseed PRNG after reading 65 kB of randomness. Although this may reduce
> performance, in most cases the loss is not noticeable. Also the time
> based threshold for reseeding is changed to one second. Reseeding is
> performed whenever either limit is exceeded.
>
> Reseeding of a PRNG does not increase entropy, but it helps preventing
> backtracking the internal state of the device from its output sequence,
> and hence, prevents potential attacker from predicting numbers to be
> generated.
>
> Signed-off-by: Łukasz Stelmach <l.stelmach@...sung.com>
> Reviewed-by: Stephan Mueller <smueller@...onox.de>
> ---
>  drivers/crypto/exynos-rng.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>

Reviewed-by: Krzysztof Kozlowski <krzk@...nel.org>

Best regards,
Krzysztof