Re: [PATCH 0/7] Rework random blocking

Pavel Machek
2019-09-09T09:42:35Z

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On Thu 2019-08-29 18:11:35, Andy Lutomirski wrote:
> This makes two major semantic changes to Linux's random APIs:
>
> It adds getentropy(..., GRND_INSECURE). This causes getentropy to
> always return *something*. There is no guarantee whatsoever that
> the result will be cryptographically random or even unique, but the
> kernel will give the best quality random output it can. The name is
> a big hint: the resulting output is INSECURE.
>
> The purpose of this is to allow programs that genuinely want
> best-effort entropy to get it without resorting to /dev/urandom.
> Plenty of programs do this because they need to do *something*
> during boot and they can't afford to wait. Calling it "INSECURE" is
> probably the best we can do to discourage using this API for things
> that need security.
>
> This series also removes the blocking pool and makes /dev/random
> work just like getentropy(..., 0) and makes GRND_RANDOM a no-op. I
> believe that Linux's blocking pool has outlived its usefulness.
> Linux's CRNG generates output that is good enough to use even for
> key generation. The blocking pool is not stronger in any material
> way, and keeping it around requires a lot of infrastructure of
> dubious value.

Could you give some more justification? If crng is good enough for
you, you can use /dev/urandom...

are

> This series should not break any existing programs. /dev/urandom is
> unchanged. /dev/random will still block just after booting, but it
> will block less than it used to. getentropy() with existing flags
> will return output that is, for practical purposes, just as strong
> as before.

So what is the exact semantic of /dev/random after your change?
Pavel

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