On Tue, Jun 06, 2000 at 08:30:02AM -0400, William Allen Simpson wrote:
> I've been putting a cheap sound card in every machine, not connected to
> any external wires, cp'ing from it on reboot. Seems to generate a nice
> chunk of randomness, but I've never measured it.
About 5 years ago when I was working with the author of Sun's cryptorand
I got the same idea (to read from an unconnected soundcard, in this
case from the sound "card" on the motherboard of a Sun workstation).
While looking at the output, we noticed that while most of the bytes
were in a small range, sometimes the range would shift (i.e. it would be
producing mostly 0x90, 0x91, 0x92s, then shift to 0xa5, 0xa6, 0xa7s).
Bill later figured out that the CPU load was the cause- raise the load
and the sound "card" output changed dramatically. We dropped the
white noise idea at that point and Bill wrote cryptorand instead.
I don't know if the typical PC chassis sound card has the same problem
but it's possible since it's next to the sources of electrical noise
in the chassis.
Depending on your security model and how you gather the entropy, that
could be a problem since there are many ways for an attacker to change
the CPU load on a host.
--
Eric Murray www.lne.com/~ericm ericm at the site lne.com PGP keyid:E03F65E5
