t a single security abstraction layer, but rather is a roblem spanning multiple abstraction levels. We use an embedded biometric authentication device to demonstratethenecessityofaddressingalllevelsofthesecuritypyramidtoensureafullyrobustandsecureembedded system. (See the "Related Work and Design Alternatives" sidebar for a discussion of some other solutions to the embedded systems security problem.) Embedded design challenges Embedded systems are essentially processor-based devices operating under resource-constrained conditions. Embedded devices include systems as diverse as automobile microcontrollers, cellular phones, smart cards, embedded network sensors, and digital cable boxes.Thesedevicesareoftenportable,communicatevia wireless channels, and are battery-powered or otherwise energy-limited. Because these systems are often considered small computers, it's tempting to port workstationbased security techniques directly onto the devices to make them secure. However, e...