linux-kernel - Re: [PATCH 0/7] Rework random blocking

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Date:   Mon, 9 Sep 2019 11:42:31 +0200
From:   Pavel Machek <pavel@....cz>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Theodore Tso <tytso@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: Re: [PATCH 0/7] Rework random blocking

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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