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SubjectRe: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver
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Am Samstag, 25. März 2017, 17:26:52 CEST schrieb Krzysztof Kozlowski:

Hi Krzysztof,

> +static int exynos_rng_set_seed(struct exynos_rng_dev *rng,
> + const u8 *seed, unsigned int slen)
> +{
> + u32 val;
> + int i;
> +
> + dev_dbg(rng->dev, "Seeding with %u bytes\n", slen);
> +
> + if (slen < EXYNOS_RNG_SEED_SIZE) {
> + dev_warn(rng->dev, "Seed too short (only %u bytes)\n", slen);
> + return -EINVAL;
> + }
> +
> + for (i = 0 ; i < EXYNOS_RNG_SEED_REGS ; i++) {
> + val = seed[i * 4] << 24;
> + val |= seed[i * 4 + 1] << 16;
> + val |= seed[i * 4 + 2] << 8;
> + val |= seed[i * 4 + 3] << 0;
> +
> + exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(i));
> + }

Would it make sense to add another outer loop here to allow all of slen to be
injected into the DRNG? Note, in some cases, a user wants to add more seed
into the DRNG than the actual seed size. In this case, the DRNG acts as a
compression operation of entropy. This is used when the entropy-to-data ratio
is not 1:1. In a lot of cases, users have a seed which has less entropy in
bits per data bit.

Ciao
Stephan

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