Re: Collecting entropy from device_attach() times.

On Thursday, 20 September 2012 at 10:20, Dag-Erling Sm=C3=B8rgrav wrote:

> Please understand that the timers used here have a resolution of around=

> 1e-8 to 1e-10 seconds. You may be able to predict the first six digits
> with reasonable accuracy - in fact, the first four or five will almost
> always be 0, except for devices with moving parts - but anything beyond=

> that is a crapshoot, even in a virtual machine.

And this conclusion seems to be borne out by Pawel's data, at least on on=
e machine on one architecture. RW's point is still valid, though: if we'r=
e going to start asserting that =22we have gathered entropy from source X=
=22, we owe it to the consumers of that entropy to really check that we'v=
e done what we claim.

=46or instance: on an embedded board with few devices, that uses =46DT ra=
ther than bus enumeration whatsits, perhaps the time is more deterministi=
c and therefore yields less entropy. I don't know, maybe it doesn't, but =
we must have data.


Jon
-- =20
Jonathan Anderson
jonathan=40=46reeBSD.org

_______________________________________________
[e-mail] mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-security
To unsubscribe, send any mail to "[e-mail]"