linux-kernel - Re: [PATCH 07/10] random: add new get_random_bytes

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Date:	Wed, 25 Jul 2012 20:16:19 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Theodore Ts'o" <tytso@....edu>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	torvalds@...ux-foundation.org, w@....eu, ewust@...ch.edu,
	zakir@...ch.edu, greg@...ah.com, mpm@...enic.com,
	nadiah@...ucsd.edu, jhalderm@...ch.edu, tglx@...utronix.de,
	davem@...emloft.net, stable@...nel.org,
	DJ Johnson <dj.johnson@...el.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 07/10] random: add new get_random_bytes_arch() function

On 07/25/2012 08:10 AM, Theodore Ts'o wrote:
> Aside from whether it's better to do this step in
> xfer_secondary_pool() or extract_entropy() ...

By the way, I looked at doing this in xfer_secondary_pool()... the 
problem there is that xfer_secondary_pool() is called exactly once per 
invocation of extract_entropy() and so there is no way to make it inject 
the same amount of material as it consumes.

One could put it in extract_entropy[_user]() and if you prefer I'll 
rewrite the patch to do that, however that code would look very similar 
to the one in extract_buf() -- pretty much the same code in the caller 
rather than the callee -- but would have the same downside with being 
processed on 10-byte chunks because the final buffer might be misaligned 
and/or partial.  It would mean just running it once rather than twice 
per output datum, but I actually expected you would prefer the 
additional mashing and security margin.

	-hpa

P.S. Anyone who have any insider info on when we can expect the SHA-3 
selection?  Switching to SHA-2 at this time with SHA-3 around the corner 
(and based on numbers I have seen, likely to be faster) seems a bit silly...

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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