yarrow random generator

[RW]

On Fri, 25 Dec 2009 13:38:10 -0800
Doug Barton <dougb at FreeBSD.org> wrote:

> Robert Watson wrote:
> > I'll point Mark Murray at this thread and see if we can get him to
> > opine some on the current design choices and any potential changes
> > to address them.  I was interested by your observation that the
> > boot-time dumping of bits into /dev/random may overflow the
> > buffering -- 
> 
> I was peripherally involved in the introduction of yarrow in the sense
> that I wrote most of the rc and periodic stuff for it so I am also
> interested in this issue. Rather than speculating about whether it's
> overflowing the buffer perhaps a patch can be produced to test this
> hypothesis? 

It's not really speculation, the data is broken into 16 byte chunks,
random_harvest_internal() is called to copy each chunk into a buffer
and queue it. If there are 256 or more buffers in the queue
random_harvest_internal() returns without doing anything.
The kernel thread that processes the queues calls 
pause("-", hz /10) each time it loops.


A fairly simple solution would be piping all that low-grade entropy
from sysctl and ps etc through sha256, reducing it to 64 bytes.