linux-kernel - Re: random(4) changes

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Message-ID: <20160426194155.GB11111@amd>
Date:	Tue, 26 Apr 2016 21:41:55 +0200
From:	Pavel Machek <pavel@....cz>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	Theodore Ts'o <tytso@....edu>,
	Sandy Harris <sandyinchina@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-crypto@...r.kernel.org, Jason Cooper <jason@...edaemon.net>,
	John Denker <jsd@...n.com>, "H. Peter Anvin" <hpa@...or.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: random(4) changes

Hi!

> > > > When dropping the add_disk_randomness function in the legacy
> > > > /dev/random, I
> > > > would assume that without changes to add_input_randomness and
> > > > add_interrupt_randomness, we become even more entropy-starved.
> > > 
> > > Sure, but your system isn't doing anything magical here.  The main
> > > difference is that you assume you can get almost a full bit of entropy
> > > out of each interrupt timing, where I'm much more conservative and
> > > assume we can only get 1/64th of a bit out of each interrupt timing.
> > 
> > Maybe 1/64th of a bit is a bit too conservative? I guess we really
> > have more than one bit of entropy on any system with timestamp
> > counter....
> > 
> > Making it 1/2 of bit (or something) should be very easy way to improve
> > entropy early during boot...
> 
> I can easily settle on 1/2 bit here. The LRNG currently uses 0.9 bits which 
> are based on measurements plus a safety margin. But I see no issue to even 
> lower it further to, say, 1/2.

No, you don't need to change anything. But maybe mainline rng should
change.

									Pavel
									
-- 
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