cvs commit: src/sys/modules/random Makefile src/sys/dev/random harvest.c hash.c hash.h nehemiah.c nehemiah.h probe.c randomdev.c randomdev.h randomdev_soft.c randomdev_soft.h yar

Sam Leffler sam at
Sat Apr 10 13:58:34 PDT 2004

On Apr 10, 2004, at 1:54 AM, Mark Murray wrote:

> Bruce M Simpson writes:
>>> Actually, I have. I read it again, now, to be sure. Nothing it says
>>> suggests that what I did here is a "huge mistake". Nearest I get is
>>> the suggestion that the output from the on-chip RNG is used as a
>>> source for a hash function (like Yarrow). I feel that is overkill,
>>> and that the output of the on-chip RNG is sufficient.
>> I'm inclined to trust your judgement here on this, Mark, but Nate does
>> have a valid point; we need to be sure that the entropy sources are of
>> sufficiently high quality or we risk compromising the system.
>> If you could cite some independent tests for the VIA C3 on-chip RNG
>> that would be very helpful to all.
> How about Nate's paper? It gives the VIA C3 a very high assessment WRT
> the quality of the entropy delivered.
> If it is felt that further whitening of the VIA C3 RNG is needed,
> then I believe that Yarrow would be overkill, and that a much smaller
> hash function will be sufficient.

Unless I misread the paper it seemed very clear in stating that you 
need to post-process the h/w RNG.  I run all my h/w entropy sources 
through the rndtest module (FIPS-140 testing) and frequently see that 
h/w entropy sources are not to be trusted (note that rndtest samples 
the entropy and that the FIPS test suite is far less stringent than the 
testing done in the papers).

I have not had time to review Marks changes but I agree with Nate that 
h/w entropy sources should not be trusted and some form of 
post-processing must be done.  Whether this is Yarrow or something else 
is unclear but the papers cited did a thorough analysis while all I've 
seen from Mark are statements that he believes these sources are good.  
When it comes to stuff like this I believe strongly in taking a 
conservative approach.


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