Collecting entropy in headless systems

[Peter Gutmann]

Ralf-Philipp Weinmann <ralf at fimaluka.org> writes:

>Have a look at Havege [1,2]:
>
>[1] HAVEGE [ HArdware Volatile Entropy Gathering and Expansion
>     http://www.irisa.fr/caps/projects/hipsor/index.php

I've had a quick look, it just reads something like the Pentium TSC in
a loop and, if the delta is more than a certain value, decides that an
interrupt has occurred and takes the result as a new entropy value.
There's a lot of handwaving, and some more stuff involving (hopefully)
the nondeterminism resulting from a CPU cache-thrashing algorithm.  It's
just another in a long series of cool-but-unverifiable ideas for
gathering info from a CPU, the first being the clock-skew mechanism from
the early 1990s (time a fast clock using a slow clock, this predates
the Pentium so the original version used a fast loop sampled from the
18.2 Hz PC clock).  If you really want do go down this path, use Matt
Blaze's TrueRand, circa 1995 (and unpatented).

Peter.