Re: [PATCH] (0/4) Entropy accounting fixes

From: Oliver Xymoron (
Date: Sat Aug 17 2002 - 23:42:42 EST

On Sat, Aug 17, 2002 at 08:25:55PM -0700, Linus Torvalds wrote:
> Hmm.. After more reading, it looks like (if I understood correctly), that
> since network activity isn't considered trusted -at-all-, your average
> router / firewall / xxx box will not _ever_ get any output from
> /dev/random what-so-ever. Quite regardless of the context switch issue,
> since that only triggers for trusted sources. So it was even more
> draconian than I expected.

But it will get data of _equal quality_ to the current approach from
> Are you seriously trying to say that a TSC running at a gigahertz cannot
> be considered to contain any random information just because you think you
> can time the network activity so well from the outside?

Yes. The clock of interest is the PCI bus clock, which is not terribly
fast next to a gigabit network analyzer.

> Oliver, I really think this patch (which otherwise looks perfectly fine)
> is just unrealistic. There are _real_ reasons why a firewall box (ie one
> that probably comes with a flash memory disk, and runs a small web-server
> for configuration) would want to have strong random numbers (exactly for
> things like generating host keys when asked to by the sysadmin), yet you
> seem to say that such a user would have to use /dev/urandom.
> If I read the patch correctly, you give such a box _zero_ "trusted"
> sources of randomness, and thus zero bits of information in /dev/random.
> It obviously won't have a keyboard or anything like that.

Anyone who'd have that problem has it today. Current kernels only add
entropy for a small number of rare cards. Grep for SA_SAMPLE_RANDOM:


In reality, most apps are using /dev/urandom for routine entropy as
they should be.

 "Love the dolphins," she advised him. "Write by W.A.S.T.E.." 
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