Securing systems with cryptographic authentication device on boot discussed in this app note from Microchip/Atmel. Link here (PDF)
Most systems that use programmable nonvolatile memory for their operating program whether it’s large or small can take advantage of a secure boot process. Secure boot is a method of ensuring that the operating program for a system is authorized, typically by the OEM that designed and built the system. By ensuring that the operating program is authentic, the OEM can prevent unpredictable system performance, safety or regulatory violations, excess warranty costs, lost revenue, and more.