  The security of many cryptographic constructions depends on random number
generators for providing unpredictable keys, nonces, initialization vectors and
other parameters. Modern operating systems implement cryptographic
pseudo-random number generators (PRNGs) to fulfill this need. Performance
counters and other system parameters are often used as a low-entropy source to
initialize (seed) the generators. We perform an experiment to analyze all
performance counters in standard installation of Microsoft Windows 7 operating
system, and assess their suitability as entropy sources. Besides selecting top
19 counters, we analyze their mutual information (independence) as well as
robustness in the virtual environment. Final selection contains 14 counters
with sufficient overall entropy for practical applications.
