An outer bound of the capacity region of biometric systems under keys, secrets, and privacy requirements

This paper establishes an outer bound of the capacity region of general biometric systems. The goals of biometric systems considered include person identification and secret binding, while template protection, privacy, and secrecy leakage are security issues addressed. A general model of biometric systems is proposed, in which the use of private keys are also incorporated. The system model captures main aspects of major biometric system designs including biometric cryptosystems, cancelable biometrics, and salt biometric systems. In addition to attacks on the database, information leakage from data links between the sensor module and the database is also considered. A general information theoretic rate outer bound is derived for characterizing and comparing the fundamental capacity, and security risks and benefits of different system designs.