Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 11 Sep 2020 16:57:38 +1000
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     Marco Felsch <m.felsch@pengutronix.de>
Cc:     martin@kaiser.cx, prasannatsmkumar@gmail.com, linux-imx@nxp.com,
        festevam@gmail.com, mpm@selenic.com, Anson.Huang@nxp.com,
        horia.geanta@nxp.com, arnd@arndb.de, ceggers@arri.de,
        linux-crypto@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kernel@pengutronix.de
Subject: Re: [PATCH] hwrng: imx-rngc - add quality to use it as kernel
 entropy pool
Message-ID: <20200911065738.GE32150@gondor.apana.org.au>
References: <20200831140042.2049-1-m.felsch@pengutronix.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200831140042.2049-1-m.felsch@pengutronix.de>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-crypto-owner@vger.kernel.org
Precedence: bulk

On Mon, Aug 31, 2020 at 04:00:42PM +0200, Marco Felsch wrote:
> The RM describes the RNGB as follow:
> 8<----------------------------------------------------------------
> The RNGB uses the True Random Number Generator (TRNG) and a
> Pseudo-Random Number Generator (PRNG) to achieve a true randomness and
> cryptographic strength.
> 8<----------------------------------------------------------------
> 
> The RNGB has 3 operation modes: self-test, seed-generation and the final
> 'random number generation' mode. Before we can retrieve random numbers
> from the RNGB we need to generate the seed pool:
> 8<----------------------------------------------------------------
> During the seed generation, the RNGB adds the entropy generated in the
> TRNG to the 256-bit XKEY register. The PRNG algorithm executes 20.000
> entropy samples from the TRNG to create an initial seed for the random
> number generation.
> 8<----------------------------------------------------------------
> 
> The RNGB can generate 2^20 words (1 word == 4 byte) of 'random' data
> after the seed pool was initialized. The pool needs to be reseeded if
> more words are required. The reseeding is done automatically since
> commit 3acd9ea9331c ("hwrng: imx-rngc - use automatic seeding").
> 
> We can't retrieve the TRNG values directly so we need a other way to get
> the quality level. We know that the PRNG uses 20.000 entropy samples
> from the TRNG to generate 2^20 words (1MiB) and the quality level is
> defined as (in bits of entropy per 1024 bits of input). So the quality
> level can be calculated by:
> 
>    20.000 * 1024
>    ------------- = ~ 19.5
>         2^20
> 
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> ---
>  drivers/char/hw_random/imx-rngc.c | 1 +
>  1 file changed, 1 insertion(+)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt