linux-kernel - Re: [PATCH v6 7/7] crypto: caam - limit single JD RNG output to maximum of 16 bytes

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Date:   Mon, 13 Jan 2020 14:10:51 +0000
From:   Horia Geanta <horia.geanta@....com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>
CC:     Chris Healy <cphealy@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Iuliana Prodan <iuliana.prodan@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH v6 7/7] crypto: caam - limit single JD RNG output to
 maximum of 16 bytes

On 1/8/2020 5:42 PM, Andrey Smirnov wrote:
> In order to follow recommendation in SP800-90C (section "9.4 The
> Oversampling-NRBG Construction") limit the output of "generate" JD
> submitted to CAAM. See
> https://lore.kernel.org/linux-crypto/VI1PR0402MB3485EF10976A4A69F90E5B0F98580@VI1PR0402MB3485.eurprd04.prod.outlook.com/
> for more details.
> 
> This change should make CAAM's hwrng driver good enough to have 999
> quality rating.
> 
[...]
> @@ -241,6 +241,7 @@ int caam_rng_init(struct device *ctrldev)
>  	ctx->rng.init    = caam_init;
>  	ctx->rng.cleanup = caam_cleanup;
>  	ctx->rng.read    = caam_read;
> +	ctx->rng.quality = 999;
>  
AFAICS the maximum value of hwrng.quality is 1024.

Any reason why it's configured to be lower, now that CAAM RNG-based DRBG
is configured to reseed as requested by FIPS spec to behave as a TRNG?

Horia