Re: Gathering entropy for PRNGs on MVS

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From: Glenn Baddeley
Date: Tue, 11 Mar 2003 03:37

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Duke,

The gettimeofday() function or a direct equivalent doesn't seem
to exist on OS/390 C like it does on Unix.

I have used an exclusive-or combination of time(), getpid() and the .tms_utime,
.tms_cutime, and .tms_cstime values returned by the times() function
as a source of entropy on OS/390.  Its hardly perfect, but it was good enough
for what I wanted.

Glenn.

Duke Arber wrote:

> >
> > 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?

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From: Glenn Baddeley <Glenn.Baddeley.snip123@team.telstra.com>
Newsgroups: sci.crypt.random-numbers,bit.listserv.ibm-main,sci.crypt
Subject: Re: Gathering entropy for PRNGs on MVS
Date: Tue, 11 Mar 2003 14:37:11 +1100
Organization: IBM GSA (delete .snip123 to reply)
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