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From: Pavel Machek <>
To: Andy Lutomirski <>
Cc: Theodore Tso <>,
	LKML <>,
	Linux API <>,
	Kees Cook <>,
	"Jason A. Donenfeld" <>
Subject: Re: [PATCH 0/7] Rework random blocking
Date: Mon, 9 Sep 2019 11:42:31 +0200
Message-ID: <20190909094230.GB27626@amd> (raw)
In-Reply-To: <>

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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...


> 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?

(cesky, pictures)

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  parent reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-30  1:11 Andy Lutomirski
2019-08-30  1:11 ` [PATCH 1/7] random: Don't wake crng_init_wait when crng_init == 1 Andy Lutomirski
2019-08-30  1:11 ` [PATCH 2/7] random: Add GRND_INSECURE to return best-effort non-cryptographic bytes Andy Lutomirski
2019-08-30  1:11 ` [PATCH 3/7] random: Ignore GRND_RANDOM in getentropy(2) Andy Lutomirski
2019-08-30  1:11 ` [PATCH 4/7] random: Make /dev/random be almost like /dev/urandom Andy Lutomirski
2019-08-30  1:11 ` [PATCH 5/7] random: Remove the blocking pool Andy Lutomirski
2019-08-30  1:11 ` [PATCH 6/7] random: Delete code to pull data into pools Andy Lutomirski
2019-08-30  1:11 ` [PATCH 7/7] random: Remove kernel.random.read_wakeup_threshold Andy Lutomirski
2019-08-30  1:49 ` [PATCH 0/7] Rework random blocking Theodore Y. Ts'o
2019-08-30  2:01   ` Andy Lutomirski
2019-09-09  9:42 ` Pavel Machek [this message]
2019-09-09 22:57   ` Andy Lutomirski

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