A powerful new technology solution for anti-counterfeiting, Physical Unclonable Functions (PUFs) are innovative circuit primitives that extract secrets from physical characteristics of integrated circuits (ICs). PUF-based systems exploit inherent delay characteristics of wires and transistors that differ from chip to chip, can enable low-cost authentication of individual ICs, and generate volatile secret keys for cryptographic operations.

From a paper on PUFs by Srinivas Devadas and G. Edward Suh