From: Stephan Mueller <smueller@chronox.de>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>,
LKML <linux-kernel@vger.kernel.org>,
dave.taht@bufferbloat.net
Subject: Re: [PATCH] /dev/random: Insufficient of entropy on many architectures
Date: Thu, 12 Sep 2013 14:35:53 +0200 [thread overview]
Message-ID: <2140053.ysf7239sM3@tauon> (raw)
In-Reply-To: <CAMuHMdX5-kSWVJ_QFXY+L2L6iY0Zo7GAL5uF-uPGJAXM=wZxgw@mail.gmail.com>
Am Donnerstag, 12. September 2013, 14:15:35 schrieb Geert Uytterhoeven:
Hi Geert,
>On Thu, Sep 12, 2013 at 2:08 PM, Stephan Mueller <smueller@chronox.de>
wrote:
>>>BTW, I prefer a different name than "random_get_fast_cycles()", as
>>>it's better to have something that returns different and
>>>unpredictable numbers than an actual monotonic cycle counter.
>>>
>> A monotonic counter is fully ok. Note, for /dev/random, the
>> occurrence
>> of events delivers entropy. Thus, we have to be able to precisely
>> measure that occurrence. The timer itself does not need to deliver
>> any
>> entropy as long as it is fast.
>
>Well, in my specific case (m68k/Amiga) I can use:
> - a 24-bit counter running at only ca. 15 or 31 kHz (actual
>frequency may vary),
> - a 16-bit counter running at ca. 700 kHz.
>
>That is, if they have to be monotonic cycle counters.
>
>If not, I can mix the two (e.g. "a << 8 | (b & 0xff)") to get a 32-bit
>value. That result would be fine for /dev/random, I guess, but it's
>not really "get_cycles()".
Note, get_cycles should return an u64.
Not sure what a and b here is, but if a is the 24 bit value and b the
faster 16 bit value, wouldn't there be a gap?
I.e. wouldn't it be better to use the full 16 bit counter as low value
and OR the 24 bit on bits 48 to 17?
Yet, there is a break in that counter: the 16 low bits rotate several
times (around 10 times) before bit 17 is changed once.
>
>Gr{oetje,eeting}s,
>
> Geert
>
>--
>Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
>geert@linux-m68k.org
>
>In personal conversations with technical people, I call myself a
>hacker. But when I'm talking to journalists I just say "programmer" or
>something like that. -- Linus Torvalds
Ciao
Stephan
next prev parent reply other threads:[~2013-09-12 12:36 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-10 11:31 [PATCH] /dev/random: Insufficient of entropy on many architectures Stephan Mueller
2013-09-10 11:46 ` Geert Uytterhoeven
2013-09-10 15:04 ` Theodore Ts'o
2013-09-10 16:54 ` Stephan Mueller
2013-09-10 18:25 ` Theodore Ts'o
2013-09-10 19:15 ` Stephan Mueller
2013-10-10 6:50 ` Pavel Machek
2013-10-14 21:13 ` Theodore Ts'o
2013-09-10 20:48 ` Geert Uytterhoeven
2013-09-10 21:14 ` Theodore Ts'o
2013-09-11 6:49 ` Stephan Mueller
2013-09-12 11:59 ` Geert Uytterhoeven
2013-09-12 12:08 ` Stephan Mueller
2013-09-12 12:15 ` Geert Uytterhoeven
2013-09-12 12:35 ` Stephan Mueller [this message]
2013-09-12 12:47 ` Geert Uytterhoeven
2013-09-12 12:57 ` Stephan Mueller
2013-09-12 21:18 ` Jörn Engel
2013-09-13 11:33 ` Thorsten Glaser
2013-09-12 14:25 ` Theodore Ts'o
2013-09-10 19:38 ` John Stultz
2013-09-10 19:44 ` John Stultz
2013-09-10 19:47 ` Stephan Mueller
2013-09-10 20:35 ` John Stultz
2013-09-10 20:38 ` Theodore Ts'o
2013-09-10 20:46 ` John Stultz
2013-09-10 21:10 ` Theodore Ts'o
2013-09-10 22:08 ` John Stultz
2013-09-10 22:33 ` Theodore Ts'o
2013-09-11 0:31 ` John Stultz
2013-09-11 0:50 ` Theodore Ts'o
2013-09-11 1:14 ` John Stultz
2013-09-12 20:46 ` H. Peter Anvin
2013-09-12 21:07 ` Jörn Engel
2013-09-12 23:31 ` Theodore Ts'o
2013-09-12 23:35 ` Jörn Engel
2013-09-13 0:00 ` Jörn Engel
2013-09-16 15:40 ` [PATCH,RFC] random: make fast_mix() honor its name Jörn Engel
2013-09-21 21:25 ` Theodore Ts'o
2013-09-21 21:41 ` Theodore Ts'o
2013-09-22 3:05 ` Theodore Ts'o
2013-09-22 21:01 ` Jörg-Volker Peetz
2013-09-22 21:27 ` Theodore Ts'o
2013-09-22 20:53 ` Jörn Engel
2013-09-22 23:36 ` Theodore Ts'o
2013-09-23 0:16 ` Jörn Engel
2013-09-23 2:43 ` Theodore Ts'o
2013-09-23 15:02 ` Jörn Engel
2013-09-23 7:39 ` Jörg-Volker Peetz
2013-09-22 20:31 ` Jörn Engel
2013-09-22 20:14 ` Jörn Engel
2013-09-12 21:31 ` [PATCH] /dev/random: Insufficient of entropy on many architectures Jörn Engel
2013-09-13 5:36 ` Stephan Mueller
2013-09-13 11:54 ` Thorsten Glaser
2013-09-13 19:29 ` Theodore Ts'o
2013-09-13 15:26 ` Jörn Engel
2013-09-13 18:59 ` Theodore Ts'o
2013-09-15 11:12 ` Stephan Mueller
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