Re: x86 MSRs - example program

Joerg Pommnitz (
Fri, 07 Mar 1997 12:42:55 -0500

Matthias Urlichs wrote:
> In, article <m0w1e9H-000AA6C@cerebro>,
> (Marc Lehmann) writes:
> > >> ON the other hand... security hole????? how????????
> > >>
> > >Cryptography. If you know exactly how long a given algorithm takes for
> > >different inputs, you can sometimes infer clues about the secret key.
> >
> > gettimeofyday is always available, and in that scenario is just
> > as good as rdtsc.
> >
> gettimeofday isn't nearly as accurate. While that's not an absolute
> barrier, it raises the number of iterations required to get accurate data.

A few random length busy loops are enough to protect against a Kocher
attack. This is certainly not a reason to prevent ordinary users from
access to high resolution timers.

Best regards

Joerg Pommnitz   || Never attribute to malloc 
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