linux-kernel - Re: [PATCH 5/7] random: replace non-blocking pool with a Chacha20-based CRNG

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Date:	Mon, 20 Jun 2016 11:52:10 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Stephan Mueller <smueller@...onox.de>,
	"Theodore Ts'o" <tytso@....edu>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	linux-crypto@...r.kernel.org, andi@...stfloor.org,
	sandyinchina@...il.com, jsd@...n.com
Subject: Re: [PATCH 5/7] random: replace non-blocking pool with a
 Chacha20-based CRNG

On 06/20/16 08:49, Stephan Mueller wrote:
> Am Montag, 20. Juni 2016, 11:01:47 schrieb Theodore Ts'o:
> 
> Hi Theodore,
> 
>>
>> So simply doing chacha20 encryption in a tight loop in the kernel
>> might not be a good proxy for what would actually happen in real life
>> when someone calls getrandom(2).  (Another good question to ask is
>> when someone might be needing to generate millions of 256-bit session
>> keys per second, when the D-H setup, even if you were using ECCDH,
>> would be largely dominating the time for the connection setup anyway.)
> 
> Is speed everything we should care about? What about:
> 
> - offloading of crypto operation from the CPU
> 

This sounds like a speed operation (and very unlikely to be a win given
the usage).

> - potentially additional security features a hardware cipher may provide like 
> cache coloring attack resistance?

How about burning that bridge when and if we get to it?  It sounds very
hypothetical.

I guess I could add in some comments here about how a lot of these
problems can be eliminated by offloading an entire DRNG into hardware,
but I don't think it is productive.

	-hpa