Re: [PATCH] random: add blocking facility to urandom

Steve Grubb
2011-09-09T13:04:30Z

On Thursday, September 08, 2011 10:21:13 PM Sandy Harris wrote:
> > The system being low on entropy is another problem that should be
> > addressed. For our purposes, we cannot say take it from TPM or RDRND or
> > any plugin board. We have to have the mathematical analysis that goes
> > with it, we need to know where the entropy comes from, and a worst case
> > entropy estimation.
>
> Much of that is in the driver code's comments or previous email
> threads. For example,
> this thread cover many of the issues:
> http://yarchive.net/comp/linux/dev_random.html
> There are plenty of others as well.
>
> > It has to be documented in detail.
>
> Yes. But apart from code comments, what documentation
> are we talking about? Googling for /dev/random on tldp.org
> turns up nothing that treats this in any detail.

Thanks for the reply. I see that you are trying to be helpful. But I think you
misunderstand what I was trying to say or maybe I was not entirely clear. We have the
correct analysis for the kernel and it does indeed pass FIPS-140, unaided. We know the
entropy comes from what the minimum entropy estimation is, and quality. (The only
issue is guaranteeing that any seed source must also include entropy.)

But what I was trying to say is that we can't depend on these supplemental hardware
devices like TPM because we don't have access to the proprietary technical details
that would be necessary to supplement the analysis. And when it comes to TPM chips, I
bet each chip has different details and entropy sources and entropy estimations and
rates. Those details we can't get at, so we can't solve the problem by including that
hardware. That is the point I was trying to make. :)

Thanks,
-Steve