Physical characteristics of information, systems, components,
or infrastructure is analyzed to detect deviations from expectations.
Examples include the use of time domain reflectometers to detect wiring
changes and listening devices, the use of pressure and gas sensors in pipes
containing critical wiring to detect breaches of the enclosure, and the
analysis of dollar bills to detect forgeries.
Complexity: No fundamental complexity limitations are inherent in the use of
physical techniques, however, they may be quite difficult to use in
networked environments over which physical processes can not easily be