Re: [PATCH v25 10/12] LRNG - add TRNG support

Stephan Müller
2019-11-17T11:12:20Z

Am Samstag, 16. November 2019, 17:09:09 CET schrieb Andy Lutomirski:

Hi Andy,

> > On Nov 16, 2019, at 1:40 AM, Stephan Müller <smueller@chronox.de> wrote:
> >
> > ﻿The True Random Number Generator (TRNG) provides a random number
> > generator with prediction resistance (SP800-90A terminology) or an NTG.1
> > (AIS 31 terminology).
>
> ...
>
> > The secondary DRNGs seed from the TRNG if it is present. In addition,
> > the /dev/random device accesses the TRNG.
> >
> > If the TRNG is disabled, the secondary DRNGs seed from the entropy pool
> > and /dev/random behaves like getrandom(2).
>
> As mentioned before, I don’t like this API. An application that, for some
> reason, needs a TRNG, should have an API by which it either gets a TRNG or
> an error. Similarly, an application that wants cryptographically secure
> random numbers efficiently should have an API that does that. With your
> design, /dev/random tries to cater to both use cases, but one of the use
> cases fails depending on kernel config.
>
> I think /dev/random should wait for enough entropy to initialize the system
> but should not block after that. A TRNG should have an entirely new API
> that is better than /dev/random.

I apologize for the misunderstanding. I assumed we would introduce such /dev/
true_random at a later stage.

If you agree, I can certainly add /dev/true_random right now that links with
the TRNG and make /dev/random behave as discussed, i.e. behave exactly like
getrandom(..., 0);

As this would introduce a new device file now, is there a special process that
I need to follow or do I need to copy? Which major/minor number should I use?

Looking into static const struct memdev devlist[] I see

[8] = { "random", 0666, &random_fops, 0 },
[9] = { "urandom", 0666, &urandom_fops, 0 },

Shall a true_random be added here with [10]?

Ciao
Stephan