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To: Robert Huff <roberthuff@rcn.com>
References: <18648.30321.369520.631459@jerusalem.litteratus.org>
From: Lowell Gilbert <freebsd-questions-local@be-well.ilk.org>
Date: Tue, 23 Sep 2008 10:29:15 -0400
In-Reply-To: <18648.30321.369520.631459@jerusalem.litteratus.org> (Robert
	Huff's message of "Tue\, 23 Sep 2008 00\:54\:09 -0400")
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Cc: questions@freebsd.org
Subject: Re: using /dev/random
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Robert Huff <roberthuff@rcn.com> writes:

> 	What is the canonical way to get data from /dev/random?
> Specifically: having opened the file, how do I read the stream?
> I'm currently using
>
>
>   union {
>     float f;
>     char c[4];
>   } foo;
>
>   foo.f = 0.0;
>
>   fscanf(rand_fp,"%4c",foo.c);
>
>
> 	which doesn't seem to produce anywhere near "random bytes" as
> promised by the man page.

Have you turned off the "seeded" variable?  You'll fall back to a
software pseudorandom sequence if you don't.

Most computers don't have all that much real random data ("entropy") to
work with, and if you need a lot of random data, you're more or less
forced to use a good pseudorandom generator.  "Good" can vary a bit
depending on application, but random(3) is generally more than good
enough for monte carlo style simulation purposes.

Cryptography is another story.  I have a hardware random number
generator on my server, which helps with performance in some cases...


-- 
Lowell Gilbert, embedded/networking software engineer, Boston area
		http://be-well.ilk.org/~lowell/