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

[Andy Lutomirski]

> On Nov 16, 2019, at 1:40 AM, Stephan MÃller <smueller@xxxxxxxxxx> wrote:
> 
> ïThe 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 donât 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.