🚀 go-pugleaf

"Duke Arber" <duke_arber@yahoo.com> wrote in message
news:b4ihfk$4oh$1@slb0.atl.mindspring.net...
> >
> > How accurately can you measure time?
> >
> > Read the time and date.  Reschedule so the operating system
> > runs and read the time when you are reactivated.  The
> > entropy comes from the run time of the other programs and
> > the date.  You may be able to play games with the disks and
> > operator reply times.
> >
> > Andrew Swallow
> >
>
> The hardware clock resolution depends on the actual hardware model.  The
> Time-Of-Day (TOD) API returns a microsecond resolution.  I think it's
"safe
> to say" that most of the models produced in the last 5 years have <=20
> microsecond resolution.  Others in the IBM-MAIN newsgroup may be able to
> fill in the details.
>
> Basically, use the current O/S activity rate as a basis for entropy.  Hand
> off control back to the O/S and depending on its activity, it will hand
> control back in some period of time.  During an IPL, there is a lot of
> activity.  During other periods of the day, there may be very little.
Would
> this hold up during periods of low activity?
>
If the crypto program is the only one running the time delays
will be very similar making the values guessable.  This gives
low entropy.  Where there is a complicated mixture of programs
running the delay on a low priority program becomes
unpredictable producing lots of entropy.

Disk reads and writes, when the program waits until the
peripheral has completely finished, gains entropy from
several places.  First the random speed variations that all
motors have, second the variable distance between the
current location of the head and the required sector (assuming
that the disk is already run up) and third disk activity due to
other programs.

On PCs other measures such as amount of disk and
ram being used are also used as a source of entropy
by some web browsers.

Fitting a proper random number generator to the
computer would be a better source for random data.
If one is not made for your mainframe, buying a
PC random number generator module and fitting it
into a dedicated PC is a cheap way of making one.

Andrew Swallow