By configurable hardware we mean a class of integrated circuits most commonly known as FPGAs field-programmable gate arrays,8 although there are also other devices like programmable logic devices (PLDs) that could approach the same definition but not the capabilities) that can be bought off the shelf and reconfigured by the designer. Each configuration can be redone within a fraction of a second and along with it, the FPGA integrated circuit can be made to perform a completely different function. One thinks therefore about unlimited reprogrammability. The subject is highly elaborate as different vendors offer different architectures, different configuration loading techniques, based on different fusing technologies. Therefore, only a cursory view of the utility FPGAs play in the development of secure wireless communications systems will be given here. Large amounts of information in the form of white papers is readily available.9 ^,10 ^,11 ^,12

FPGA devices can be reconfigured to change logical functions while resident in the target system.13 This capability gives the systems designer an extraordinary degree of freedom not available with any other type of logic. Hardware can be changed as easily as software. Design updates or modifications are easy and can even be made in the field, directly to products already shipped. An FPGA can even be reconfigured dynamically to perform different functions at different times. Reconfigurable logic can be used in numerous types of systems to implement system self-diagnostics, create systems capable of being reconfigured for different environments or...