A system and method is provided for a cryptographic primitive and authentication protocol comprised of micro-cavity resonators at optical wavelengths. A micro-cavity resonator is illuminated with an optical challenge signal and the cavity returns an output response that is dependent on the input signal. Digital signal processing is performed on the output signal to generate a corresponding digital representation. This process is repeated for variations of the input signal with its digital output being stored in a database. A user or object claiming an identity presents a token to the system. The system selects a subset of the available challenge-response pairs and presents the challenges to the token. The system compares the digitized responses with the original responses expected for that token. The system will approve or deny the claimed identity corresponding to the presented token.