Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1609375

Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver

Show all headers | View raw

On Sun, Mar 26, 2017 at 07:11:28PM +0200, Stephan Müller wrote:
> Am Samstag, 25. März 2017, 17:26:52 CEST schrieb Krzysztof Kozlowski:
> > +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.

Hi,

I do not know whether this would have any benefit on hardware. The
datasheet is not describing too much here. It is actually saying only:
1. Write SEED to each register (five in total).
2. Confirm that STATUS register says seeding done.
3. Start RNG engine.
4. Wait for engine finish (another bit in STATUS - clear it then).
5. Read the randoms.

I would guess that the hardware will ignore all previously written seeds
and use the last one. Maybe the hardware will use all of the seeds
written as you imply. It is just a guessing.

Best regards,
Krzysztof

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH v3 0/3] crypto: hw_random - Add new Exynos RNG driver Krzysztof Kozlowski <krzk@kernel.org> - 2017-03-25 17:30 +0100
  [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver Krzysztof Kozlowski <krzk@kernel.org> - 2017-03-25 17:30 +0100
    Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com> - 2017-03-26 17:40 +0200
      Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver Krzysztof Kozlowski <krzk@kernel.org> - 2017-03-26 18:10 +0200
        Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver Stephan Müller <smueller@chronox.de> - 2017-03-26 18:20 +0200
        Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com> - 2017-03-26 18:50 +0200
          Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver Stephan Müller <smueller@chronox.de> - 2017-03-26 19:10 +0200
            Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver Krzysztof Kozlowski <krzk@kernel.org> - 2017-03-26 20:20 +0200
    Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver Stephan Müller <smueller@chronox.de> - 2017-03-26 19:20 +0200
      Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver Krzysztof Kozlowski <krzk@kernel.org> - 2017-03-26 20:10 +0200
        Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver Stephan Müller <smueller@chronox.de> - 2017-03-26 23:30 +0200
          Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com> - 2017-03-27 06:30 +0200
            Re: [PATCH v3 1/3] crypto: hw_random - Add new Exynos RNG driver Stephan Müller <smueller@chronox.de> - 2017-03-27 16:00 +0200
  Re: [PATCH v3 0/3] crypto: hw_random - Add new Exynos RNG driver Stephan Müller <smueller@chronox.de> - 2017-03-25 17:40 +0100

csiph-web